Acta Palaeobotanica 61(2), 195–217, 2021 https://doi.org/10.35535/acpa-2021-0012 Coexistence of Lobelia dortmanna and Cladium mariscus, an ecological and paleobotanical study KRYSTYNA MILECKA1*, GRZEGORZ KOWALEWSKI2, AGNIESZKA LEWANDOWSKA1, WITOLD SZCZUCIŃSKI 3 and TOMASZ GOSLAR 4 1 Department of Anthropocene Research, Faculty of Geographical and Geological Sciences, Adam Mickiewicz University, Poznań, Poland; e-mail: milecka@amu.edu.pl 2 Applied Geoinformatics Laboratory, Faculty of Geographical and Geological Sciences, Adam Mickiewicz University, Poznań, Poland; e-mail: ichtys@amu.edu.pl 3 Geohazards Research Unit, Institute of Geology, Faculty of Geographical and Geological Sciences, Adam Mickiewicz University, Poznań, Poland; e-mail: witold.szczucinski@amu.edu.pl 4 Poznań Radiocarbon Laboratory, Faculty of Geographical and Geological Sciences, Adam Mickiewicz University, Poznań, Poland; e-mail: tomasz.goslar@radiocarbon.pl Received 29 October 2021; accepted for publication 10 December 2021 ABSTRACT. Lobelia dortmanna L. (Lobeliaceae family) is an indicator species that is predominantly found in oligotrophic and acidic lakes. They are mainly distributed in northwestern Europe. Their occurrence in Poland is highly threatened by the increasing grade of human activity and environmental eutrophication; however, new sites of Lobelia were discovered in the last few decades, for example, in Lake Krzywce Wielkie situated in Bory Tucholskie National Park (BTNP), Poland. The existence of Lobelia in this lake was unexpected because Cla- dium mariscus was also found in the lake. Cladium has different ecological demands and is regarded as a species typical of calcareous habitats where calcium is found in abundance in the substrate. To explain the coexistence of both species in Krzywce Wielkie, pollen analysis of organic sediments was performed for four short cores col- lected from the littoral zone of the lake and for one long deep-water core. Additionally, macrofossil analysis was done for all the short cores. Pollen analysis revealed the existence of Cladium from the early Holocene period up to the present time. Pollen and seeds of Lobelia were found to be present since the beginning of the 20th century. Development of L. dortmanna and Myriophyllum alterniflorum populations and a decrease in the number of aquatic macrophytes in the eutrophic water indicate oligotrophication of water. This process started following the construction of drainage canal and the consequent water level decrease. This situation can be attributed to the abandonment of the agricultural areas adjoining the lake, which causes a decrease in the inflow of nutrients into the lake. Development of pine forest and establishment of BTNP enabled the protection and conservation of the surrounding catchment areas, thus restricting the potential eutrophication of the habitats. KEYWORDS: Lobelia dortmanna, Cladium mariscus, Late Holocene, land use, trophy changes, Tuchola Forest INTRODUCTION e-ISSN 2082-0259 ISSN 0001-6594 Ongoing climate and environmental changes result in the shift of the geographical distri- bution of numerous plant and animal species (Pecl et al., 2017). However, various environ- mental factors, such as temperature, nutrient availability and humidity, and interactions among them (e.g., feedback effects) affect the © 2021 W. Szafer Institute of Botany, Polish Academy of Sciences This is an Open Access article, distributed under the terms of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited. nature of habitat. Therefore, the resulting response of a species to an ecological habitat may be highly variable. For instance, it was found that in lake environments an increase in water temperature may favor the growth of an ecologically dominant invasive species (Dziuba et al., 2020), whereas in other conditions, local but so far endangered species may be predom- inant (Kowalewski et al., 2013; Brzozowski * Corresponding author mailto:milecka@amu.edu.pl mailto:ichtys@amu.edu.pl mailto:witold.szczucinski@amu.edu.pl mailto:tomasz.goslar@radiocarbon.pl 196 K. Milecka et al. / Acta Palaeobotanica 61(2), 195–217, 2021 et al., 2021). Several features of the habitat contribute to the type of species living in it. For instance, in a lake environment, factors like an increase in water temperature, a drop in water level (Kornijów et al., 2016), a reduction in the period of ice cover, or changes in catch- ment management (Poraj-Górska, 2017) may play a crucial role in determining the nature of the species living in the lake. To interpret the future response of a particular species to the ecological changes, it is beneficial to obtain the information provided in sedimentary pale- orecords (Davidson et al., 2013). Lake environments are in constant danger of undergoing rapid changes in the near future, and this situation is particularly expected to be observed in the case of lakes dominated by species that have reached the limits of their modern distribution range. A good example of such lakes is the so-called Lobelian lakes that are characterized by the presence of Lobelia dortmanna L. (Lobeliaceae family), which is an indicator species and predominantly found in oligotrophic and acidic lakes with low conduc- tivity (Szmeja, 1997). Other species that com- monly inhabit these lakes are Isoëtes lacustris, I. echinospora, Littorella uniflora and Myrio- phyllum alterniflorum, and these plants have similar environmental demands (Szmeja, 1992; Hannon and Gaillard, 1997; Heegaard et al., 2001). The geographical distribution of these lakes correlates with the spatial limits of the above-mentioned species. They are dis- tributed mainly in the boreal zone of north- western Europe (Sculthorpe, 1985; Szmeja, 2014a, b), extending further to the northern boreal zone (Moen, 1999) and eastern Lithu- ania (Gostyńska-Jakuszewska and Lekavičius, 1994). Thus, they occur in regions with cool and wet temperate climates, with catchments frequently dominated by pine forests (Szmeja, 2014a). In Poland, 155 Lobelian lakes were identified (Szmeja, 1997); however, only 131 of them were inhabited by populations of L. dort- manna, which grow in the northwestern part of the country (Szmeja et al., 1998). Extensive studies focusing on Lobelian lakes were conducted during the second half of the 20th century (Sand-Jensen, 1978; Sand- Jensen and Borum, 1984; Rørslett, 1991; Szmeja et al., 1998). Hence, the environmen- tal conditions that influence the development of isoetids (Lobelia, Isoëtes, and Littorella) are well known. In addition, the structure of these specific populations was analyzed (Szmeja, 1987; Chmara et al., 2014, 2015a; Ronowski et al., 2020). However, their responses to mod- ern land use and human activities are poorly understood, especially in the context of politi- cal changes in Central and Eastern Europe at the end of the 20th century and following the development of nature conservation meas- ures. It turns out, in spite of many threats related to anthropogenic pressure, that many of these lake ecosystems are in good condi- tion due to the protection provided by law and stable environmental conditions in the catch- ments dominated by pine forest, acidic beech forest, and peatlands (Kraska et al., 2013; Szmeja, 2014a). Lobelian lakes constitute the most precious resource of Bory Tucholskie National Park (BTNP), which is also inhabited by lichen-rich Scotts pine forests and mires. There are six Lobelian lakes in the park (Fig. 1): Gacno Wiel- kie, Gacno Małe, Nierybno, Głuche, Krzywce Wielkie and Krzywce Małe, but L. dortmanna was not noticed in the last lake in recent years (Królikowska et al., 2012). The Lobelian lakes are often surrounded by patches of mires along the shore, which provide additional protection against eutrophication, as they restrict the transfer of nutrients from the catchment area (Tobolski, 2003; Szmeja, 2014a). Krzywce Wielkie Lake has been recently included in the group of Lobelian lakes. Infor- mation regarding the development of L. dort- manna population in this lake was first pub- lished by Kochanowski and Tobolski (2010) and further confirmed by Kochanowska et al. (2013). This occurrence seems to be interesting because a few clusters of Cladium mariscus L. Pohl (Cyperaceae family) were also found in this lake (Herbichowa and Wołejko, 2004; Mróz, 2010). This species has quite different ecological demands and usually grows in fer- tile, calcareous habitats. Both L. dortmanna and C. mariscus are used as indicator species in Habitats Directive’s Natura 2000 network (Council Directive 92/43/EEC). However, they are characterized by different types of habi- tats: code 3110 includes Lobelia lakes with Littorelletalia uniflorae and code 7210 includes calcareous fens with Cladietum marisci, Cari- cetum buxbaumi and Schoenetum nigricantis. The phenomenon of the coexistence of L. dortmanna and C. mariscus in the same lake was studied by adopting a paleoecological K. Milecka et al. / Acta Palaeobotanica 61(2), 195–217, 2021 197 approach, which provided useful informa- tion in a preliminary investigation carried out by Milecka and Tobolski (2015). In this study, pollen and macrofossil analyses were performed for the upper 314 cm of the deep- water core of sediments rich in organic matter (KW/2014) accumulated since about 2300 cal yr BP. These analyses revealed the presence of pollen grains of Cladium but the absence of Cladium fruits and also the absence of pollen and seeds of Lobelia. Lobelia species produce small amounts of pollen that are poorly trans- ported through the lake bottom (Milecka and Obremska, 2002), which could be the likely reason for the lack of Lobelia fossils. The quan- tity of Cladium pollen increased at ~350 cal yr BP and was concurrent with the occurrence of high trophy indicators (e.g., Rumex acetosella, Plantago lanceolata, Pediastrum boryanum, P. duplex); however, at ~200 cal yr BP, water trophy decreased resulting in the development of Chara population in the lake (Milecka and Tobolski, 2015). All these findings help to draw clear conclusions regarding the emergence of the Lobelia population and the duration of the coexistence between Lobelia and Cladium. Moreover, some questions also arise: (1) From when did Lobelia and Cladium start to occur together in the lake? (2) What conditions influ- enced their presence and what was the reason for the recent spread of Lobelia? (3) How did land use, human pressure and protection by law influence this recent spread? (4) What are the general conditions for the modern exist- ence of Lobelian lakes and what may be their future? To trace the development of the recent pop- ulation of Lobelia in Lake Krzywce Wielkie, a detailed paleoecological analysis of the lake’s sediments was conducted. The evaluation was based mainly on high-resolution pollen records and macrofossil analyses of 14C-, 210Pb- and 137Cs-dated sediment cores, and was supple- mented with the analysis of old maps that show the hydrological and land-use changes during the last 200 years, prepared by Nienar- towicz (2012). To determine the initial exist- ence of Lobelia populations in Lake Krzywce Wielkie, four cores of sediments from the lit- toral zone of the lake were taken. To trace the development of Cladium and Lobelia popula- tions, the pollen analysis of the older part of the long core from the central part of the lake (KW/2014) was done. Krzywce Wielkie BłotkoKrzywce Małe Małe Gacno Wielkie Gacno Nierybno Jeleń Zielone Ostrowite Głuche BA KW20/1 KW20/2 KW20/3 KW20/4 KW/2014 1 5 5 10 15 0 1 km 0 250 500 m Fig. 1. Study area. A – location of lake Krzywce Wielkie in BTNP. Inset map shows location in Poland. Dot-dashed line – border of BTNP, black circle – fossil site of Cladium mariscus according to Gałka and Tobolski (2006), yellow lake – sites of Lobelia dortmanna and C. mariscus, red lakes – sites of L. dortmanna, green lakes – site of C. mariscus; B – locations of sediment cores in Lake Krzywce Wielkie. Isobaths after Błoniarz et al. (2016) in metres 198 K. Milecka et al. / Acta Palaeobotanica 61(2), 195–217, 2021 STUDY AREA Tuchola Forest is a large forest located on an outwash plain formed during the last glaciation (Dysarz, 1998; Kowalewski, 2002). Woś (1999) defined the modern climate of the region as temperate, cool and wet. The mean temperature in January is –3.2°C and in July it is 19°C, the annual average rainfall is 573 mm, and the vegetative period lasts of 180–200 days. BTNP (Fig. 1), established in 1996, is located adjacent to the previously established five land- scape parks covering the entire area of Tuchola Forest. The area of BTNP is about 5000 ha, which comprises only a small portion of the whole complex. The park is almost completely covered by dry and fresh pine forest communi- ties with many lakes (Tobolski, 1998; Matusz- kiewicz et al., 2012). Lake Krzywce Wielkie is located in the northern part of BTNP. Its sur- face area is 25 ha, has a maximum depth of 15.1 m and a mean depth of 9.0 m (Błoniarz et al.,2016). Direct catchment of this endorheic lake is 1624 km2 (Bajkiewicz-Grabowska, 2004). The poor sandy soils and prevailing pine forest cover of the catchment limit the supply of nutri- ents to the lake (Bajkiewicz-Grabowska, 2004). In BTNP, two water courses connect some lakes (Fig. 1): the stream Struga Siedmiu Jezior and an artificial canal called Krzywce- Błotko. C. mariscus is found in three lakes located along the upper course of Struga Sied- miu Jezior (Solon and Matuszkiewicz, 2012); however, fossil macroremains were found in recent sediments along the whole course of this stream (Gałka and Tobolski, 2006). The growth of Lobelia was detected in some endor- heic lakes of the central part of BTNP and in the Krzywce-Błotko canal. Both species co- occur only in Krzywce Wielkie, along the west- ern and eastern shores of the lake. The coex- istence of C. mariscus and L. dortmanna was also documented in three lakes of Tuchola For- est (outside of BTNP): Nawionek, Głuche and an unnamed one in West Pomerania (Milecka, 2005; Kochanowska et al., 2013). L. dortmanna, M. alterniflorum, and Juncus bulbosus were identified in Krzywce Wielkie dur- ing the botanical analysis of two cross-sections traversing the eastern part of the lake (Bociąg, 2011). Polygonum amphibium and Potamogeton natans were also recorded. That research was conducted to monitor the protection efficiency of the park in retaining the natural ecosystem. Lobelia occurred down to 1 m of water depth. The patches of M. alterniflorum were abundant and clear down to 4 m of water depth. C. mar- iscus, Typha angustifolia, and Carex species developed along the lake shores. METHODS FIELD WORK AND SAMPLING On May 18, 2020, four cores (KW20/1, KW20/2, KW20/3 and KW20/4) of sediments rich in organic matter were collected from the littoral zone of Lake Krzywce Wielkie using a gravity corer (UWITEC Co., Austria). The inner diameter of the corer liner was 86 mm. The cores were sampled in the laboratory of the Faculty of Geographical and Geological Sciences, Adam Mickiewicz University, Poznań. The upper- most layers of the sediments (1–10 cm), characterized by high water content, were sectioned in 2-cm-thick intervals in order to ensure that sufficient volume of the sediment is sampled for macrofossil analysis and dating. The deeper parts (10–35 cm) were sliced into 1-cm-thick samples. Each sediment sample was fur- ther subsampled for pollen analysis (1 cm3), macro- fossil analysis and radiometric dating. The long core (624 cm, KW/2014) was drilled in 2014 from a deeper central part of the lake for paleobotanical analysis (Fig. 1). The upper half (314 cm) of the sediment was analyzed and discussed by Milecka and Tobolski (2015), while the lower half (310 cm) was investigated in this work. The samples were taken at 4-cm-thick intervals. CHRONOLOGY 14C dating Fifteen organic samples, each taken at 20 cm intervals in 1 cm slices from the lower part of the core KW/2014, were transported to Poznań Radiocar- bon Laboratory for 14C dating using the AMS tech- nique (Goslar et al., 2004). Most of the samples were macrofossils of terrestrial plants (Pinus needles, bud scales and Betula fruits, bud scales), but sediments from the deepest part contained few terrestrial mac- rofossils, and hence bulk sediment sample was taken from this area. 210Pb and 137Cs dating The age models for the cores collected from the recently formed lake sediments (deposited during the past century) of the littoral zone were constructed using 210Pb and 137Cs radioisotopes. 210Pb is a natu- ral radioisotope formed in the course of the decay of 238U and has a half-life of 22.3 years. In sediments, total 210Pb is the sum of the so-called supported 210Pb (210Pbsup), which is continuously produced by the decay of parent isotopes, and excess 210Pb (210Pbex), deliv- ered to the sediment surface mainly by atmospheric K. Milecka et al. / Acta Palaeobotanica 61(2), 195–217, 2021 199 deposition. Along with the continuous accumula- tion of the deposits, the activity of 210Pbex decreases with depth due to its decay and provides a tool for the assessment of sediment age using models based on various assumptions (Appleby and Oldfield, 1992; Sanchez-Cabeza and Ruiz-Fernández, 2012). The arti- ficial 137Cs was first introduced into the environment in measurable amounts in the early 1950s. It showed maximum activity in 1963 in relation to numerous nuclear bomb tests and also in 1986 related to the Chernobyl event (Ritchie and McHenry, 1990). The 137Cs and 210Pb activities were measured using gamma spectrometry at the Institute of Geol- ogy, Adam Mickiewicz University, Poznań, Poland (Szczuciński et al., submitted). The 2-cm-thick sedi- ment core samples were dried and homogenized. The activities of 137Cs, 210Pb, 214Pb and 214Bi were measured for ~50–70 hours using a high-purity coaxial wide- energy germanium detector (Canberra BE3830) with a remote detector chamber option set for low-energy background reduction. The average of 214Pb and 214Bi activities, which are in radioactive equilibrium with 226Ra, was used as a measure to determine the concen- tration of 210Pbsup. The 210Pbex value was calculated as the difference between the measured total  210Pb and 210Pbsup. The obtained analytical results were used to develop an age model for the sediments deposited dur- ing the last century using the serac package (Bruel and Sabatier, 2020). Constant flux constant sedimen- tation rate (CFCS) and constant initial concentration models were established and verified based on 137Cs activity profiles. The results revealing very low 210Pbex activities, much smaller than the activity obtained using 2-sigma accuracy tests, were not taken into con- sideration for the age model computation. POLLEN ANALYSIS Pollen analysis was done for every sample collected from four short cores, that is, 30 samples per core, and for 78 samples obtained from the long core KW/2014. The procedure for laboratory preparation followed that described by Berglund and Ralska-Jasiewiczowa (1986). Mineral particles were removed by HF, and organic compounds by KOH. Acetolysis was performed for 3 minutes. Prior to the preparation of pollen slides, samples were stained with safranine. Samples taken from core KW/2014 were counted to at least 700 pol- len grains of trees and shrubs. The analysis of the sediments of the littoral cores revealed lower pollen frequencies than observed in more consolidated sedi- ments from the deeper part of the lake. Hence, the sum of the pollen grains was not very high, exceeding 400 pollen grains of trees and shrubs in almost all spectra. The sum of AP (trees and shrubs) and herbs (NAP) was the basis for percentage calculations (calculation sum). Aquatics, telmatophytes, and selected nonpol- len palynomorphs (NPPs) were also counted; however, they were not included in the calculation sum. The pollen diagrams were initially compiled using Tilia and Tilia Graph programs (Grimm, 1992) and later improved using CorelDraw X16 software. Particular attention was given to the identification of the pollen of Lobelia and Cladium, which is the main objective of our research. Every pollen slide was examined in detail, regardless of the pollen sum, to find their grains. The pollen types of both species were identified according to Beug (2004). Every pollen grain type of Lobelia species was carefully examined, because there are some similar types of pollen, for example, Linaria, Digitalis and Verbascum. The determination of Cladium pollen was not simple either because some of them do not have an elongated ending, which is a critical feature for reliable classification. However, regular presence of Cladium in the samples allowed for the detailed observation and recognition of some additional indicator features, which include regular conical shape, relatively big size, very gentle, circular perforations at 1/3 of the grain length, and very clear perforation at the base of the cone. Pollen grains “cf. Cladium” were not classified as “Cladium” if the ana- lyzed grains were partially destroyed or crushed and the perfect observation of all the indicator features was not possible. MACROFOSSIL ANALYSIS Macrofossil analysis was conducted for sediment slices with a volume of 60 cm3 and collected from a depth of 1–10 cm and also for slices with a volume of 30 cm3 taken from 11–35 cm. The samples were washed with water and sieved using a mesh size of 0.125 mm. The residue was examined under a stereomicroscope (Nikon, Japan) at 10×, 40×, and 100× magnifications. The results were presented in the diagrams of abso- lute frequency prepared in R (R Core Team, 2020) in “rioja” package (Juggins, 2020) and modified in Corel- Draw X16. RESULTS The results showed that the long core KW/2014, drilled at the water depth of 546 cm, is composed of gray and fine detritus gyttja (314–604 cm of sediment depth) with increased content of mineral particles in the bottom part (604–624 cm). The four short sediment cores collected from the littoral zone of Lake Krzywce Wiel- kie showed very similar lithological features at the depth of 40–50 cm from the water surface (Fig. 1, Table 1). The samples are composed of dark brown detritus gyttja with decreasing content of mineral particles toward the upper part. Table 1. The location of coring sites (Fig. 1) Name of core Longitude Latitude KW/2014 17°33′40.18″E 53°50′21.55″N KW20/1 17°33′35.86″E 53°50′37.36″N KW20/2 17°33′30.85″E 53°50′30.91″N KW20/3 17°33′26.22″E 53°50′24.29″N KW20/4 17°33′25.18″E 53°50′10.55″N 200 K. Milecka et al. / Acta Palaeobotanica 61(2), 195–217, 2021 14C DATING The 14C ages of samples taken from the core KW/2014 (Table 2) were calibrated against the curve INTCAL20 (Reimer et al., 2020), and were used to build an age–depth model using a free shape algorithm (Goslar et al., 2009). For the development of models, the set of calibrated 14C dates was supplemented with the calendar date that marked the beginning of Holocene (11,550 cal BP, according to the increase of birch and decrease of juniper trees (Milecka, 2005; Filbrandt-Czaja, 2009), which has been clearly indicated in the pollen profile at the depth of 610 cm. The age–depth model (Fig. 2) indicates a rather slow (and variable) accumulation rate in the lower part of the pro- file (until ~6000 BP) and a distinctly faster (and almost constant) accumulation rate in the upper part (until ~2500 BP). It has to be con- sidered, however, that the 14C age of the low- ermost sample (at 620 cm) might be influenced by the reservoir effect of unknown magnitude, therefore the uncertainty of dates at the lowest 30 cm of the profile may be greater than that calculated using the algorithm. 210PB AND 137CS DATING The vertical distribution of 210Pbex and 137Cs activities is presented in Fig. 3, while the com- plete dataset is available in the supplementary material (Supplementary file 11). The total 210Pb and 210Pbex content was generally charac- terized by a downward decrease, although with some irregularities. The latter was likely due to sediment mixing. The sediment accumulation rates for the last century according to the CFCS model (Fig. 3) were as follows: 1.64 ± 0.36 mm/ yr in core KW20/1, 1.05 ± 0.19 mm/yr in core KW20/2, 1.06 ± 0.09 mm/yr in core KW20/3, and 1.38 ± 0.30 mm/yr in core KW20/4. The 137Cs activity profiles (Fig. 3) showed maximum values in the near-surface sedi- ments, decreasing with the sediment depth and reaching very low activities in the lower parts of the investigated cores. Such 137Cs pro- files often result from postdepositional remobi- lization of the isotope, both upward and down- ward, as previously documented in the littoral zones of other lakes and lagoons (Foster et al., 2006; Woszczyk et al., 2017; Brzozowski et al., 2021). However, taking into account the 210Pb- based sediment accumulation rates, the cal- culated sediment depths, dated to the early 1950s AD (Fig. 3), correspond to a decrease in 137Cs activities to values below 20 mBq/g. As a consequence, generally, the presence of moderate-to-high 137Cs activities in the sedi- ments dated post-1950s AD suggests that the 1 Supplementary file radionuclides in KW20 cores. Results of the radionuclide analysis of sediment cores. The tables include the analytical data (lab no, sampling depth intervals, 137Cs, total 210Pb, supported 210Pb, excess 210Pb, 40K, 232Th, 238U activi- ties, and the respective 2-sigma measurement uncertainties) and metadata (coring year, geographical coordinates, labora- tory name, instrument type, measurement start and end dates) 12000 10000 8000 6000 4000 D e p th [ cm ] .2.5 cm 600 550 500 450 400 350 300 Table 2. 14C ages of samples from the core KW/2014 Depth [cm] Material Lab no. Poz- Age 14C (BP) Modeled date (68.2% conf. interval, cal BP) 314 Plant remains 126617 2415±35 2490–2375 334 Plant remains 126618 2570±40 2760–2705 354 Plant remains 126619 2875±35 3060–2960 374 Plant remains 126621 3055±30 3340–3230 394 Plant remains 126622 3385±35 3680–3575 414 Plant remains 126623 3565±35 3920–3835 434 Plant remains 126624 3770±35 4220–4090 456 Plant remains 126625 3925±30 4420–4310 476 Plant remains 126626 4165±35 4825–4650 494 Plant remains 126627 4520±40 5175–5055 514 Plant remains 126628 4610±35 5450–5315 538 Plant remains 126629 5570±40 6385–6310 562 Plant remains 126631 6480±35 7400–7335 586 Plant remains 126632 9090±50 10270–10200 620 Bulk sediment 126633 11110±60 13095–12935 Fig. 2. Age-depth model of the lower part of profile KW/2014. Gray silhouettes represent calibrated dates of the samples analyzed with 14C. Black silhouette represents the date of the beginning of Holocene https://acpa.botany.pl/SuppFile/144764/5504/1aa5954469caa29ec9e370293a835ae7/ https://acpa.botany.pl/SuppFile/144764/5504/1aa5954469caa29ec9e370293a835ae7/ https://acpa.botany.pl/SuppFile/144764/5504/1aa5954469caa29ec9e370293a835ae7/ https://acpa.botany.pl/SuppFile/144764/5504/1aa5954469caa29ec9e370293a835ae7/ https://acpa.botany.pl/SuppFile/144764/5504/1aa5954469caa29ec9e370293a835ae7/ https://acpa.botany.pl/SuppFile/144764/5504/1aa5954469caa29ec9e370293a835ae7/ https://acpa.botany.pl/SuppFile/144764/5504/1aa5954469caa29ec9e370293a835ae7/ K. Milecka et al. / Acta Palaeobotanica 61(2), 195–217, 2021 201 210Pb-based age model is generally accurate. The comparison of the CFCS and CIC models with 137Cs profiles is presented in supplemen- tary files (Supplementary file 22). Since the cores show the evidence of sediment mixing, the sediment accumulation rates and conse- quently the calculated ages indicate approxi- mate values only. 2 Supplementary file 2. Age scale to the CFCS and CIC mod- els KW20_1–KW20_4 POLLEN AND MACROFOSSIL ANALYSES Core KW/2014 The sediment core from the deepest part of the lake demonstrates the occurrence of vege- tation changes from the end of the Late Glacial period to ~2300 cal yr BP (Fig. 4). The upper part of this core (2300 BP to the present) was studied by Milecka and Tobolski (2015). As the main objective of this paper was to trace the history and development of Cladium and Lobe- lia populations, only selected results relevant D e p th ( cm ) || || || || || || || 1 10 100 r2 = 0.805 SAR = 1.64 mm/yr || || || || || || || || || || || || || 0 20 40 60 D e p th ( cm ) || || || || || || || 1 10 100 1000 || || || | || || || || || || || || 0 20 40 60 80 100 3 0 2 5 2 0 1 5 1 0 5 0 D e p th ( cm ) || || || || 1 10 100 || || || || || || || || || || 0 20 40 60 80 100 120 D e p th ( cm ) || || || || || || || 1 10 100 1000 || || || || | || || || || || || || || 0 50 100 150 KW20_1 KW20_4KW20_3 KW20_2 210Pbex (mBq/g) 137Cs (mBq/g) 210Pbex (mBq/g) 137Cs (mBq/g)210Pbex (mBq/g) 137Cs (mBq/g) 210Pbex (mBq/g) 137Cs (mBq/g) r2 = 0.858 SAR = 1.05 mm/yr r2 = 0.986 SAR = 1.06 mm/yr r2 = 0.811 SAR = 1.38 mm/yr ~1950 ~1950 ~1950 | ~1950 3 0 2 5 2 0 1 5 1 0 5 0 3 0 2 5 2 0 1 5 1 0 5 0 3 0 2 5 2 0 1 5 1 0 5 0 Fig. 3. Short-lived radionuclide (210Pbex nd 137Cs) measurements in cores KW20_1, KW20_2, KW20_3 and KW20_4. 210Pbex activities are presented as semilogarithmic plots, the trend line was used for sediment accumulation rate (SAR) calculation using constant flux constant sedimentation rate model. The sediment depth of 210Pb-based age of 1950 AD is marked on 137Cs activity profile. The vertical error bars refer to analyzed sediment sample thickness, while the horizontal bars depict 2-sigma uncertainty. The plots were obtained using serac (Bruel and Sabatier, 2020) https://acpa.botany.pl/SuppFile/144764/5505/62c7c45973ec2897d1747aff60375248/ https://acpa.botany.pl/SuppFile/144764/5505/62c7c45973ec2897d1747aff60375248/ 202 K. Milecka et al. / Acta Palaeobotanica 61(2), 195–217, 2021 for the reconstruction of the local environment are presented. The oldest part, deposited during the Late Glacial period, contains pollen typical for open tundra and steppe-like vegetation with clus- ters of Juniperus. The beginning of the Holo- cene (11,550 cal yrs BP, Fig. 4) was marked by the disappearance of cold-demanding tundra species (Juniperus) and an increase of Betula. The phase of birch-pine forest lasted to 11,000 cal yrs BP, and was subsequently overtaken by the pine-birch forest, until the spread of deciduous forest (Quercus, Ulmus, Tilia, Fraxinus) at ~9850 cal yrs BP. During the middle part of the Holocene, approximately between 8200 and 4150 cal yrs BP, deciduous forest prevailed, as suggested by the presence of numerous pollen grains of Quercus, Ulmus, and Corylus. The record of the older part of the late Holocene approximately between 4150 and 2380 cal yrs BP, showed the pres- ence of a forest cover, but the proportion of Ulmus, Tilia, and Fraxinus decreased, pav- ing the way for the development of Carpinus. Pine forests with juniper and heather contin- ued to be present. In the youngest layers of the sediments, the proportion of the pollen of light-demanding plants increased, which included members of the Poaceae family, Arte- misia sp., Rumex sp. and Carex sp. This could be the result of occasional human activity in the Tuchola Forest. The investigation of younger sediments of the late Holocene, as reported by Milecka and Tobolski (2015), revealed continued forest cover in the areas adjacent to Lake Krzywce Wielkie. Pine trees with a minor proportion of deciduous trees were found, and Carpinus played an important role from 1800 to 750 BP. Later, Pinus became dominant, and some human activity indicators appeared (Milecka and Tobolski, 2015). L. dortmanna and C. mariscus in the core KW/2014 The pollen of Lobelia was not found in this core. Pollen grains of C. mariscus were found regularly from the depth of 579 cm (~9560 cal yr BP) to the uppermost layers (2380 cal yr BP), except for the climatic optimum period (5740–5235 cal yr BP). The pollen was also regularly identified in the youngest part of this 320 330 340 350 360 370 380 390 400 410 420 430 440 450 460 470 480 490 500 510 520 530 540 550 560 570 580 590 600 610 620 d e p th [ cm ] 20 40 60 80 100 APP in u s B e tu la NAP 2380 3000 4000 5000 6000 10000 ca l y r B P H o lo c e n e e a rl y la te m id d le Y D 20 Q u e rc u s U lm u s T ili a F ra x in u s 20 C o ry lu s C a rp in u s F a g u s 20 A ln u s 20 40 J u n ip e ru s C a llu n a v u lg a ri s 20 P o a c e a e A rt e m is ia R u m e x a c e to s a R u m e x a c e to s e lla C a re x t . C la d iu m m a ri s c u s c f C la d iu m trees and shrubs 11550 8000 Fig. 4. Pollen diagram of core KW/2014, selected percentage curves (in black). Exaggerations ×10 are given for better observa- tion of rare types. Division of the Holocene after Walker et al. (2012) K. Milecka et al. / Acta Palaeobotanica 61(2), 195–217, 2021 203 core, analyzed earlier by Milecka and Tobol- ski (2015). Stable and consistent occurrence of the pollen of C. mariscus through the entire Holocene indicates that this plant was present continuously in the reed beds of Lake Krzywce Wielkie. Littoral cores (KW20/1–KW20/4) The cores KW20/1 – KW20/4 (Figs 5A, B and 6) show ~200 years of sediment accumula- tion and development of vegetation in the lake and in the catchment. This is confirmed by similar time and pattern of the accumulation of sediments indicated by isotope dates and the general picture of vegetation succession in Tuchola Forest during the last centuries. Regional plant communities were dominated by pine forest and a low proportion of decidu- ous species, such as Quercus, Carpinus, Cory- lus, Alnus and Populus. They likely occurred as mixtures in some patches of forest and reflect the complex mosaic of habitats at these sites. The dominance of Pinus decreased slowly with time (Fig. 5A, B). In contrast, the proportion of herbs, especially grasses, increased. During the last 100 years, higher proportion of Juni- perus was also documented, accompanied by a declining contribution of deciduous species like Quercus, Carpinus and Corylus. Percent- ages below 1% of the calculation sum for these species indicate their possible disappearance in the areas directly adjacent to the lake; pol- len grains were blown from distant places (Milecka et al., 2004; Miotk-Szpiganowicz et al., 2004; Ralska-Jasiewiczowa et al., 2004). KW20/1 Cladium pollen was present in almost all the spectra of the entire core. Moreover, sin- gle fruits were found in the middle part of the core, which indicate that Cladium was likely present in this part of the lake for over 200 years. It was a regular constituent of reed bed communities, along with Carex, Schoenoplec- tus, Typha latifolia and probably Phragmites australis (common species at present). The presence of Schoenoplectus and Typha is con- firmed by the presence of their fruits revealed by the macrofossil analysis (not identified to species level). The investigations also revealed the presence of another species that is pre- dominantly found in high reed bed, Eleocharis palustris. Frequent occurrence of pollen grains and fruits of Carex species suggests that they are common inhabitants of low reed bed com- munities. Pollen grains of Lobelia were found in sam- ples taken from the depth of 14 cm in the sedi- ment toward the upper layers. There were sin- gular grains in a few samples, despite the fact that the core was collected from the area right next to the location where the modern popu- lation of Lobelia was found. Seeds of Lobelia were found in the samples at the sediment depth of 8 and 10 cm. The presence of Lobelia pollen in the sample at the depth of 14 cm indi- cates that the population must have developed before 1935 AD. Myriophyllum alterniflorum is a common component of aquatic plants in the upper part of the core. Its pollen grains were found in all the samples taken from the depth of 11 cm upward, with the maximum content being 2%. Moreover, single pollen grains were found at the depth of 14 and 23 cm. Fruits of Myrio- phyllum sp. were found at the depths of 10, 12 and 14 cm in the sediment. Taking into account the exact identification of pollen and the modern presence of M. alterniflorum in the lake, the fruits very likely belong to this species. Fruits of Potamogeton (6–28 cm, up to 9 specimens) and Chara oospores (2–29 cm, up to 219 specimens) were the most abundant in the macrofossil group. The relatively high numbers of subfossil Potamogeton fruits and Chara oospores suggest their local occurrence. KW20/2 Pollen of Cladium were found in many samples throughout the core; however, they occurred mostly as single grains. Subfossil fruits of Cladium were found at the depths of 2, 6 and 12 cm. Few fruits of other reed bed plants were also identified, for example, Typha sp. (at the depth of 6–22 cm) and E. palustris (32 cm). Low reed bed plants were relatively abundant, which comprised Carex fruits, P. amphibium, Ranunculus sceleratus, and J. bulbosus. A single pollen grain of L. dortmanna was found at the depth of 14 cm. The seeds were found at 10–13 cm. Thus, according to the fos- sil record, Lobelia was present in this part from the turn of the 19th and 20th centuries. Among the aquatic macrophytes, Potamoge- ton (3–33 cm, 1–4 specimens) and Chara sp. (2–31 cm, 1–1090 specimens) were the most abundant. Pollen of M. alterniflorum occurred 204 K. Milecka et al. / Acta Palaeobotanica 61(2), 195–217, 2021 at the depths of 4 and 12 cm. The existence of Myriophyllum fruits (at 4, 6 and 17 cm), despite low fruit production by this plant, suggests the in situ presence of this species (M. alterniflorum). KW20/3 Pollen grains of Cladium and cf. Cladium were found in the lower part of the core, up to 18 cm, and in the uppermost layers of the sediments. Singular seeds of this species were identified at the depths of 10, 14 and 25 cm, and more numerous, up to 12 specimens per sample, were found at the depths of 2 and 4 cm. Thus, the fossil records suggest almost continuous presence of this species. They were accompanied by other species of high reed beds as indicated by the seeds and pollen of Schoenoplectus lacustris, and seeds of Typha sp. and Eloecharis. Low reed beds are rep- resented by pollen of the Cyperaceae family, Carex sp., Thelypteris palustris, Hottonia, Iris pseudoacorus, and seeds of J. bulbosus, P. amphibium and R. sceleratus. Pollen of Lobelia was not found in the core KW20/3. However, singular seeds of Lobelia occurred at sediment depths of 6, 8, 10, 12 and 22 cm. During the macrofossil analysis, numer- ous seeds of Potamogeton (3–33 cm, 1–12 speci- mens) and some seeds of Myriophyllum sp. (6, 8, 20 and 22 cm, singular specimen) and Najas marina were identified. Singular pollen of Potamogeton and M. alterniflorum were iden- tified at 12 cm. Utricularia (8 cm) and Rumex aquaticus (4 cm) were also found as single pol- len. At the depth interval of l–13 cm, Chara KW20/1 0 5 10 15 20 25 30 35 D e p th [ c m ] 20 40 60 80 100 AP P in u s B e tu la Q u e rc u s U lm u s T ili a F ra x in u s C o ry lu s C a rp in u s F a g u s 20 A ln u s A rt e m is ia U rt ic a C h e n o p o d ia c e a e R u m e x a ce to sa t . R u m e x a c e to s e lla t . P la n ta g o la n c e o la ta C e n ta u re a c y a n u s S c le ra n th u s a n n u s S p e rg u la ri a t . S e c a le C e re a lia u n d iff . P o ly p o d ia c e a e C a re x t . C y p e ra c e a e C la d iu m S c h o e n o p le c tu s S p h a g n u m T y p h a la tif o lia S p a rg a n iu m e m e rs u m t . E q u is e tu m M yr io ph yl lu m v er tic ila tu m M yr io p h yl lu m a lt er n ifl o ru m R u m e x a q u a tic u s L o b e li a d o rt m a n n a P e d ia s tr u m b o ry a n u m P e d ia s tr u m f o rc ip a tu m P e d . a n g u lo s u m 20 P e d ia s tr u m in te g ru m C o e la s tr u m s p . 100 200 300 400 S c e n e d e s m u s C h a rc o a l human activity indicators telmatophytes aquatics algaetrees and shrubs NAP KW20/2 0 5 10 15 20 25 30 35 D e p th [ c m ] 20 40 60 80 100 AP P in u s B e tu la Q u e rc u s U lm u s T ili a F ra xi n u s C o ry lu s C a rp in u s F a g u s 20 A ln u s A rt e m is ia U rt ic a C h e n o p o d ia c e a e R u m e x a c e to s a t . R u m e x a c e to s e lla t . P la n ta g o la n c e o la ta C e n ta u re a c y a n u s S p e rg u la ri a t . S e ca le C e re a lia u n d iff . 20 P o ly p o d ia c e a e C a re x t. C yp e ra ce a e C la d iu m S ch o e n o p le c tu s S ch o e n u s A co ru s S p h a g n u m S p a rg a n iu m e m e rs u m t . M yr io p h yl lu m a lt er n ifl o ru m R u m e x a q u a tic u s L o b e li a d o rt m a n n a cf . L o b e lia P e d ia st ru m b o ry a n u m P e d ia st ru m f o rc ip a tu m P e d . a n g u lo s u m P e d ia st ru m in te g ru m 20 C o e la st ru m s p . 50 100 150 200 S ce n e d e s m u s C h a rc o a l human activity indicators telmatophytes aquatics algaetrees and shrubs NAP 2000 1980 1960 1940 1920 1900 2000 1980 1960 1940 1920 1900 Fig. 5A. Pollen diagrams of cores KW20/1 – KW20/2. Selected percentage curves of trees and shrubs, human indicators and pollen of local plant communities. Curve units – 10% unless otherwise stated. Red dates – dates derived from the 210Pb-based age model, gray dates – linear approximation of the model assuming constant accumulation rate K. Milecka et al. / Acta Palaeobotanica 61(2), 195–217, 2021 205 oospores (1–35) were found in the sediments. The consistent presence of Potamogeton fruits in most of the samples suggests the stable exist- ence of a pondweed population in the western part of the lake. KW20/4 Few pollen grains of Cladium were noted in the lower and middle parts of the core, but their seeds were not found. Today, fen-sedge does not exist in the southern part of the lake. Singular grains could come from long-distance transportation or from temporarily devel- oped small plant communities. The flora of high reed bed was represented by pollen and seeds of T. latifolia, probably T. angustifolia (Sparganium emersum type, Typha sp.) and Schoenoplectus. Low reed bed included Carex (pollen and seeds), ferns (spores) and seeds of J. bulbosus, R. sceleratus and P. amphibium. Neither pollen nor seeds of L. dortmanna were found in this core. According to the infor- mation provided by the manager of BTNP, Mr. Wojciech Błoniarz, during the last few years, few specimens of flowering Lobelia were observed in this place, which prompted us to select this site for coring. However, this fact was not confirmed during the field observation conducted in July 2020. Pollen of M. alterniflorum occurred abun- dantly in the sediments above 6 cm, and fruits were also found in the samples taken at depths of 2 and 4 cm (up to 6 specimens). Pollen grains of numerous other aquatic mac- rophytes were present in this core: R. aquati- cus (30–10 cm), Utricularia (4 cm), Alisma KW20/3 0 5 10 15 20 25 30 35 D e p th [ c m ] 20 40 60 80 100 AP P in u s B e tu la Q u e rc u s U lm u s T ili a F ra x in u s C o ry lu s 20 C a rp in u s F a g u s 20 A ln u s A rt e m is ia U rt ic a C h e n o p o d ia c e a e R u m e x a c e to s a t . R u m e x a c e to s e lla t . P la n ta g o l a n c e o la ta S e c a le C e re a lia u n d iff . P o ly p o d ia c e a e C a re x t . C y p e ra c e a e C la d iu m C la d iu m c f. S p h a g n u m S p a rg a n iu m e m e rs u m t . P e d ia s tr u m b o ry a n u m P e d ia s tr u m f o rc ip a tu m P e d . a n g u lo s u m P e d ia s tr u m i n te g ru m C o e la s tr u m 50 100 150 S c e n e d e s m u s C h a rc o a l human activity indicators telamtophytes algaetrees and shrubs NAP KW20/4 0 5 10 15 20 25 30 35 D e p th [ c m ] 20 40 60 80 100 AP P in u s B e tu la Q u e rc u s U lm u s T ili a F ra x in u s C o ry lu s C a rp in u s F a g u s 20 A ln u s A rt e m is ia U rt ic a C h e n o p o d ia c e a e R u m e x a c e to s a t . R u m e x a c e to s e lla t . P la n ta g o l a n c e o la ta C e n ta u re a c y a n u s P o ly g o n u m a v ic u la re t . F a g o p y ru m S e c a le C e re a lia u n d iff . P o ly p o d ia c e a e C a re x t . C y p e ra c e a e C la d iu m C la d iu m c f. S p h a g n u m T y p h a l a ti fo lia S p a rg a n iu m e m e rs u m M yr io p h yl lu m a lt er n ifl o ru m R u m e x a q u a ti c u s A lis m a p la n ta g o -a q u a tic a P e d ia s tr u m b o ry a n u m 20 P e d ia s tr u m f o rc ip a tu m P e d ia s tr u m a n g u lo s u m 20 P e d ia s tr u m i n te g ru m 20 C o e la s tr u m 100 200 300 400 S c e n e d e s m u s 20 C h a rc o a l human activity indicators telmatophytes aquatics algaetrees and shrubs NAP 2000 1980 1960 1940 1920 1900 2000 1980 1960 1940 1920 1850 1900 Fig. 5B. Pollen diagrams of cores KW20/3 – KW20/4. Selected percentage curves of trees and shrubs, human indicators and pollen of local plant communities. Curve units – 10% unless otherwise stated. Red dates – dates derived from the 210Pb-based age model, gray dates – linear approximation of the model assuming constant accumulation rate 206 K. Milecka et al. / Acta Palaeobotanica 61(2), 195–217, 2021 3 5 3 0 2 5 2 0 1 5 1 0 5 0 Depth [cm] 0 2 0 0 Chara sp. – oospore 1 Najas marina 1 Myriophyllum sp. 0 8 Potamogeton sp. 0 3 Nymphaea sp. 0 3 Nuphar lutea 1 Lobelia dortmanna 1 Cladium mariscus 1 Schoenoplectus lacustris 1 Typha sp. 1 Eleocharis palustris 0 7 Carex sp. – fruits 0 2 Polygonum amphibium 1 Ranunculus sceleratus 1 Juncus bulbosus 1 Alnus glutinosa – fruits 0 7 Betula sec. Alba – fruits 0 1 0 Pinus sylvestris – needles 0 1 0 Pinus sylvestris – bud scales 1 charcoal > 1mm 0 4 wood 3 5 3 0 2 5 2 0 1 5 1 0 5 0 Depth [cm] 0 1 0 0 0 Chara sp. – oospore 1 Najas marina 0 3 Myriophyllum sp. 0 4 Potamogeton sp. 0 2 Nymphaea sp. 0 7 Nuphar lutea 1 Lobelia dortmanna 1 Cladium mariscus 0 2 Typha sp. 1 Eleocharis palustris 0 6 Carex sp. – fruits 1 Polygonum amphibium 1 Ranunculus sceleratus 1 Juncus bulbosus 1 Alnus glutinosa – fruits 0 5 Betula sec. Alba – fruits 0 6 Pinus sylvestris – needles 0 8 Pinus sylvestris – bud scales 0 2 charcoal > 1mm 1 Insect – scales 0 3 wood 1 2 1 5 5 4 1 2 6 1 9 K W 2 0 /1 K W 2 0 /2 2 0 0 0 1 9 8 0 1 9 6 0 1 9 4 0 1 9 2 0 1 9 0 0 2 0 0 0 1 9 8 0 1 9 6 0 1 9 4 0 1 9 2 0 1 9 0 0 Fig. 6A. Macrofossil diagrams of cores KW20/1–KW20/2. Red dates – 210Pb-based age dates derived from the model, gray dates – linear approximation of the model assuming constant accumulation rate. Scales represent numbers in sample volume. Out of scale values are given next to the bars. Gray bar indicates approximate age of water level drop K. Milecka et al. / Acta Palaeobotanica 61(2), 195–217, 2021 207 3 5 3 0 2 5 2 0 1 5 1 0 5 0 Depth [cm] 0 3 5 Chara sp. – oospore 0 2 Najas marina 1 Myriophyllum sp. 0 1 0 Potamogeton sp. 0 2 Nymphaea. sp. 0 3 Nuphar lutea 1 Lobelia dortmanna 0 1 2 Cladium mariscus 1 Schoenoplectus lacustris 1 Typha sp. 0 2 Eleocharis palustris 0 3 Carex sp.– fruits 0 2 Polygonum amphibium 1 Ranunculus sceleratus 1 Ranunculus repens 1 Ranunculus sp. 1 Juncus bulbosus 1 Alisma plantago-aquatica 1 Alnus glutinosa – fruits 0 1 0 Betula sec. Alba – fruits 0 2 0 Pinus sylvestris – needles 0 1 0 Pinus sylvestris – bud scales 0 6 charcoal > 1mm 1 Insect – scales 0 8 wood 3 5 3 0 2 5 2 0 1 5 1 0 5 0 Depth [cm] 0 3 0 Chara sp. – oospore 0 2 Najas marina 0 5 Myriophyllum sp. 0 2 5 Potamogeton sp. 1 Nymphaea sp. 1 Nuphar lutea 1 Schoenoplectus lacustris 1 Typha sp. 0 4 Carex sp. – fruits 1 Polygonum amphibium 1 Ranunculus sceleratus 0 3 Juncus bulbosus 0 3 Alnus glutinosa – fruits 0 1 0 Betula sec. Alba – fruits 0 4 Pinus sylvestris – needles 0 1 0 Pinus sylvestris – bud scales 0 4 charcaoal > 1mm 1 Insect – scales 1 wood 1 5 1 5 0 4 5 1 5 1 4 9 3 7 3 6 3 2 1 3 1 5 K W 2 0 /3 K W 2 0 /4 2 0 0 0 1 9 8 0 1 9 6 0 1 9 4 0 1 9 2 0 1 9 0 0 Fig. 6B. Macrofossil diagrams of cores KW20/3–KW20/4. Red dates – 210Pb-based age dates derived from the model, gray dates – linear approximation of the model assuming constant accumulation rate. Scales represent numbers in sample volume. Out of scale values are given next to the bars. Gray bar indicates approximate age of water level drop 208 K. Milecka et al. / Acta Palaeobotanica 61(2), 195–217, 2021 plantago-aquatica (4 cm), and Myriophyllum spicatum (2 cm). Fruits of N. marina (35 cm), Nymphaea (8–18 cm), and Nuphar lutea (8 cm) were found during macrofossil analysis. Pota- mogeton fossils were the most abundant (up to 28 fruits). DISCUSSION EVIDENCE AND TIMING OF LOBELIA AND CLADIUM CO-OCCURRENCE IN THE LAKE The investigations revealed a low repre- sentation of both pollen and seeds of L. dort- manna. The results are in agreement with the conclusions of earlier studies (Moeller, 1978; Milecka and Obremska, 2002; Milecka, 2005). Lobelia is an aquatic plant, but the flowering shoot grows above the water surface and is pol- linated by insects. Dąmbska (1965) and Moe- ller (1978) found that the deeper the depth of water is, the smaller the number of flowering plants will be. Plants growing below 1.7–2 m do not flower at all. It has also been proved that some specimens do not open their flowers and undergo self-pollination (Faegri and Van der Pijl, 1979). Spence (1982) reported that the pro- cess of seed production requires a large amount of light. The significance of adequate light con- ditions was also stressed by Szmeja and Bociąg (2004), Banaś et al. (2012) and Ronowski et al. (2020). Consequently, low frequency of micro- and macrofossils is observed in lacustrine sedi- ments rich in organic matter. This observation was confirmed in the present study. Although two cores (KW20/1 and KW20/2) were collected from the direct neighborhood of flowering Lobe- lia patches, the frequency of occurrence of micro- and macrofossils was low. This proves that this species occurs along with other mac- rophytic plants in the lake. The lack of Lobelia pollen in the long sections of cores, confirmed by the lack of fruits, suggest that Lobelia was absent in the studied periods. The complete lack of Lobelia fossils in the older parts of four cores of sediments rich in organic matter and also in the long deep-water core (Milecka and Tobolski, 2015, and this research) suggests that Lobelia is a very recent component of aquatic vegetation in Lake Krzywce Wielkie. It likely appeared by the end of the 19th century. Studies that aimed to determine the pres- ence of Lobelia in the temperate climate zone based on pollen analysis of organic sediments were previously carried out in Europe. Accord- ing to Hjelmroos-Ericsson (1981) and Milecka (2005), L. dortmanna developed in Tuchola For- est lakes in the late Holocene period, at ~3800 yrs BP in Gacno Wielkie and at~2000 yrs BP in Nierybno, Lake Linowskie and Moczadło. On Wolin Island (NW Poland), Lobelia was found since ~1700 yrs BP (Latałowa, 1992). Odgaard (1994) identified Lobelia pollen occurring from ~4000 yrs BP in northern West Jutland. In Lake Krzywce Wielkie, Lobelia was documented only in the youngest sediments and it consti- tutes very recent floral species of this lake. The spread of Lobelia to the temperate zone of Cen- tral Europe during the late Holocene (decline of interglacial cooling) can be explained by its cli- matic demands and ecological optimum related to the cold climate of the boreal zone (Odgaard, 1994; Birks, 2000). The middle Holocene cli- matic optimum did not favor the existence of this boreal species. According to Farmer (1989), the temperature of 17°C in the month of July is a limiting factor for its expansion. Therefore, the occurrence of Lobelia was documented in many works mainly during the late Holocene cooling. However, it is not the case of Krzywce Wielkie, where Lobelia presence was documented during warming after the Little Ice Age (20th and 21st centuries). Thus, it is likely that environmental conditions (e.g., land use) and human activity as well significantly influence the development of Lobelia populations. The pollen profile of Krzywce Wielkie dem- onstrated the consistent presence of C. maris- cus from the beginning of the Holocene period (core KW/2014; Milecka and Tobolski, 2015) and in all cores of the littoral zone. However, relatively high content of fruits was found only in core KW20/3. DISTRIBUTION AND CONSERVATION IN POLAND AND EUROPE The existence of both species in BTNP is con- sidered to be of environmental value because it is within the geographical limits of Poland and hence is under strict jurisdiction (Regulation of the Ministry of Environment of 9 October 2014). Lobelia reaches the southern border of occur- rence in Poland (Sculthorpe, 1985; Szmeja, 2014a). However, there are some sites in west- ern Europe that are situated farther south (e.g., in France). Many authors (Czubiński, 1950; Kucharczyk, 2000; Herbichowa and Wołejko, 2004) assumed that the eastern European K. Milecka et al. / Acta Palaeobotanica 61(2), 195–217, 2021 209 border of the range of C. mariscus is in Poland. Considering the fact that the species is found in scattered locations south and east of the study area, for example, in Latvia (Salmina, 2004) and Czechia (Pokorny et al., 2010), it would be better to assume that it shows a “scattered distribution” and avoid the determination of an accurate border. As these species predomi- nantly occur within the borders of their occur- rence in Poland, their IUCN status in Poland differs from their global and European status. According to Maiz-Tome (2016), L. dortmanna globally (or in Europe) is not likely to meet the threshold for being included in the “Vul- nerable” IUCN category and is assessed as “Least Concern.” But locally, in Poland, the status of this species was changed from vul- nerable (Zarzycki and Szeląg, 2006) to endan- gered (Kaźmierczakowa et al., 2016). Similar status has been given to C. mariscus in Europe and the world (Lansdown et al., 2017), but in Poland it is placed under the category “Near Threatened” (Kaźmierczakowa et al., 2016). The reasons for the disappearance of Lobe- lia sites were widely discussed, and considered to be related to eutrophication and changes in land use over time (Farmer, 1989; Szmeja, 1997, 1998; Kraska et al., 2013). The causes for the disappearance of Cladium sites can be attributed to both natural (vegetation succes- sion) and anthropogenic changes of habitats, such as changes in water level and trophy (Herbichowa and Wołejko, 2004; Karcz, 2008). Report under Article 17 of the Habitats Direc- tive Period 2007–2012 indicated the factors that pose a threat to their existing habitat, which include physical and chemical changes in water bodies (29%), vegetation succession/ biocenotic evolution (16%) and other changes related to human activities (55%). Despite many known threats, new modern locali- ties of both Lobelia (Chmara, 2007; Chmara et al., 2015b) and Cladium (Namura-Ochalska, 2004; Gałka, 2007; Karcz, 2008; Towpasz and Stachurska-Swakoń, 2009; Krajewski, 2011) are still being identified in Poland. DIFFERENCES IN CONTEMPORARY ECOLOGICAL REQUIREMENTS OF LOBELIA AND CLADIUM Lobelia dortmanna and Cladium mariscus differ in their spatial ranges. Contrary to the boreal range of Lobelia, C. mariscus is an ever- green reed bed plant widely spread across all the continents except Antarctica (Pawłowska, 1972) and is considered to be an indicator of temperate warm climate (Tobolski, 2006; Brande, 2008). Both species are found in the areas subjected to a strong oceanic influence (Czubiński, 1950; Szmeja, 2014a). In Poland, Cladium tend to spread toward the north (Kłosowski, 1986–87) and separate sites are found in calcareous mires of eastern Poland (Fijałkowski, 1959; Buczek, 2005), whereas the present occurrence of Lobelia species is limited to northwestern Poland. Both species differ in their ecological demands. Podbielkowski and Tomaszewicz (1994) reported that Cladium is an expan- sive plant inhabiting eutrophic or dystrophic lakes. On the contrary, Zarzycki et al. (2002) classified it as a species of oligotrophic habi- tat. Ellenberg et al. (1991) present medium requirements with regard to nitrogen content. Cladium species represent group 3 (“indicator of more or less infertile sites”), while Lobelia is included in group 1 (“indicator of extremely infertile sites”). The biggest difference in their demands relates, however, to pH. According to Ellenberg et al. (1991), C. mariscus is an indicator of basic conditions prevalent in cal- careous or other high-pH soils where the maxi- mum pH is found to be 9. In contrast, Lobe- lia is an indicator of acidic conditions, where pH decreases to 2, and it exceptionally occurs in sediments with nearly neutral pH. Her- bichowa and Wołłejko (2004) and Mróz (2010) regarded C. mariscus as a calciphilous plant. Rothmaler (1994) reported that it can grow on basic and lime-rich substrates. However, it is also known that saw-sedge is capable of growing on habitats poor in calcium carbon- ate (Grosse-Brauckmann, 1964; Marek, 1991; Sawilska and Dąbrowska, 1995; Brande, 2008; Tobolski and Gałka, 2008). According to Gałka (2007), appropriate climatic conditions, espe- cially temperature and air moisture, are the main factors that contribute to the develop- ment of a Cladium population instead of the abundance of calcium carbonate. Calcium plays a key role only at the sites located adjacent to the border of the range of the population. In these regions, calcium compensates for the heat shortage due to the exothermic reaction of calcium oxide and water. This means that the calcareous soil is important, but only in the case of the eastern and northern sites of the range. The lack of the necessity of calciphilous 210 K. Milecka et al. / Acta Palaeobotanica 61(2), 195–217, 2021 sediments was also reported by Pokorny et al. (2010) in relation to fens. Lobelia occurs in acidic to neutral water, that is, pH 4–7 (Zarzycki et al., 2002). Han- non and Gaillard (1997) reported its presence in waters with pH 5.0–6.7. There is a wide range of calcium content in Lobelian lakes and the lakes with Cladium (Table 3). The lakes of the Krzywce-Błotko canal (including Krzy- wce Wielkie) have Ca contents similar to that of Lobelian lakes, while the concentration of Ca is found to be much higher in other lakes with Cladium in BTNP (Fig. 1). Thus, from this point of view, the presence of Cladium in Lake Krzywce Wielkie is exceptional. On the other hand, it presents a wide ecological scale in terms of pH because Cladium occurs in both the calcium-rich Struga Siedmiu Jezior stream and the calcium-poor Krzywce-Błotko canal. LAND-USE, HYDROLOGICAL AND TROPHY CHANGES Presently, Krzywce Wielkie is considered to be an endorheic lake. However, a topographic map from 1874 AD shows a drainage canal connecting it with Lake Krzywce Małe. On the younger maps, the drainage canal is clearly marked, which indicates that it existed at least before 1900 AD. According to Mr. Błoniarz, manager of BTNP, this drainage canal has been dry for many years. The altitude of the drainage threshold is about 124.4 m a.s.l., and the water level of the lake as shown on topo- graphic maps (1965, 1992, 1:10,000, see Nie- nartowicz 2012) is 123.5 m a.s.l. In the years 2000–2004, the water level was found to be 123.44 m a.s.l., which slightly increased in the following years; however, it has not exceeded 123.8 m a.s.l. (Marszelewski et al., 2016). When the threshold was dug in the 19th century, the water level was the same as or higher than the altitude of the threshold (124.4 m a.s.l). Thus, the outflow through the drainage canal caused a decrease in the water level of the lake by at least 60–90 cm, and strongly influenced the lit- toral zone of the lake and the plant commu- nities living therein. The above is reflected in macrofossil diagrams, and the gray bar roughly separate the two periods of higher and lower lake water levels (Figs 6A, B and 7). Exposure of the littoral areas of the lake as a consequence of the decreasing water level cre- ated conditions favorable for the development of Lobelia populations. Most of their fruits were found in sediments deposited at the time of the digging of the drainage canal or later. Pollen of Lobelia in core KW20/1 appeared likely at the time of drainage construction, and in core KW20/2 a singular grain was found shortly before the decrease of the water level. One seed of Lobelia in core KW20/3 at the depth of 22 cm was found probably due to disturb- ing the sediments in the course of the drilling (reposition from the upper layers by the corer). Hence, a Lobelia succession at the end of the 19th century would be possibly supported by the decrease of the water level. New habitats in shallow waters enabled the potential devel- opment of new-coming species. The analyses of old maps provide additional supporting evidence explaining the develop- ment of conditions favorable for Lobelia. At the turn of the 18th and 19th centuries, Schröter’s map showed open spaces on the eastern and western sides of the lake (Nienartowicz, 2012). They were suitable for rye cultivation or pas- tures. Riemann’s map, prepared in 1860 AD, showed a similar distribution. There was no drainage canal during that time, but fields existed in the west and southeast of the lake. Thus, only the areas adjacent to the northeast- ern part of the lake (cores KW20/1 and KW20/2) were covered by forests. The presence of culti- vated fields or pastures undoubtedly influenced Table 3. Ranges of calcium content, acidity and conductivity of water documented in Lobelian lakes and other lakes in BTNP Locality and references Ca mg/l pH conductivity 7 Lobelian lakes in Pomerania, NW Poland, some of them are degraded (Kraska and Piotrowicz, 1994) 1.45–23.6 4.6–8.77 42–170 16 lakes with Isoëto-Lobelietum community from Pomerania (Kłosowski, 1994) 6–17.6 6.4–8 – 18 lakes with Myriophylletum alterniflori community from Łęczyńsko-Włodawskie Lakeland, E Poland (Kłosowski, 1994) 8.2–17.6 6.5–7.6 – 9 Lobelian lakes in Zaborski Landscape Park, Tuchola Forest (including lakes in BTNP) (Gonet et al., 1994) 4–13 4.2–6.9 38–81 Lakes of Krzywce-Błotko channel (Zdanowski, 2004) 6.4–10.4 6.9–7.7 39.8–69.3 Lakes of Struga Siedmiu Jezior (Zdanowski, 2004) 43.3–48.9 8–8.5 215–232 K. Milecka et al. / Acta Palaeobotanica 61(2), 195–217, 2021 211 the trophy of the lake by the surface discharge of nutrients. The occurrence of Rumex and P. lanceolata and only a few pollen grains of weeds indicates that the neighborhood areas around the lake shore were used as pastures rather than as cultivation sites in the 19th century. Agricultural activity was abandoned and forest communities developed at the end of the 19th century, which is confirmed by the presence of a unit of Prussian Forestry Acad- emy in 1894 AD. According to the map created in 1920 AD, the whole area of presently exist- ing BTNP is covered by forests (Nienartowicz, 2012). The development of forests restricted the supply of nutrients and resulted in a decrease of the trophy of the lake. Additionally, pine for- ests and boggy patches protected the lake and contributed to decreasing pH and oligotrophy (Kraska et al., 1998; Zdanowski, 2004). The decrease of trophy at the turn of the 19th and 20th centuries is manifested by an increase in the Lobelia population, as well as by the growth of M. alterniflorum, J. bulbosus and Chara sp. Three species of Myriophyllum are found in Europe, and all of them are pre- sent in BTNP (Wróbel and Hutorowicz, 2012). Among them, M. alterniflorum adapted to the low nutrient content and constitutes the typi- cal component and indicator of oligotrophic lakes (Rutkowski, 2004). According to Zarzy- cki et al. (2002), trophy of M. alterniflorum is classified as level 2–3 (oligotrophy to mesotro- phy), while the other species are classified as level 4 (eutrophy). Juncus bulbosus grows in oligotrophic habitats (Zarzycki et al., 2002) and appeared not earlier than the second half of the 20th century. Chara oospores were not identified to species level; however, species of Characeae exist in the clear waters of oligo- trophic or mesotrophic lakes (Pełechaty et al., 2007; Schubert et al., 2018), and may be asso- ciated with rare plants such as L. dortmanna, L. uniflora and Isoëtes (Bertrin et al., 2013). The decrease of trophy during the 20th century is also indicated by the lower content of macro- fossils of eutrophic species, such as P. amphib- ium, R. sceleratus, Nuphar and Nymphaea, in the younger parts of all the cores. A decreas- ing trend was observed with regard to the con- tamination and concentration of P, K and Ca in the selected lakes of BTNP (Wielkie Gacno, Zmarłe, Czarne i Ostrowite), as reported by Chmara (2006). This trend is favorable for the Lobelian lakes situated within the Park, and is considered to be the result of land-use changes and the establishment of BTNP. The near-surface layers of sediments were characterized by a lower diversity of herbs due 0 5 10 15 20 25 30 35 D e p th [ c m ] C la d iu m m a ri sc u s M y ri o p h y llu m a lte rn ifl o ru m L o b e lia d o rt m a n n a KW20/1 L o b e lia d o rt m a n n a C la d iu m m a ri s c u s 0 5 10 15 20 25 30 35 D e p th [ c m ] C la d iu m m a ri s c u s M y ri o p h y llu m a lte rn ifl o ru m L o b e lia d o rt m a n n a c f. L o b e lia KW20/2 L o b e lia d o rt m a n n a C la d iu m m a ri s c u s 0 5 10 15 20 25 30 35 D e p th [ cm ] C la d iu m m a ri s c u s C la d iu m c f. KW20/3 L o b e lia d o rt m a n n a C la d iu m m a ri s c u s 0 5 10 15 20 25 30 35 D e p th [ c m ] C la d iu m m a ri s c u s C la d iu m c f. M y ri o p h y llu m a lte rn ifl o ru m KW20/4 2000 1980 1960 1940 1920 1900 2000 1980 1960 1940 1920 1900 2000 1980 1960 1940 1920 1900 2000 1980 1960 1940 1920 1900 Fig. 7. Summary diagram of the content of pollen and macrofossils of the indicative species discussed in the article. For expla- nations of scale, dates and gray bar see Figs 4–6 212 K. Milecka et al. / Acta Palaeobotanica 61(2), 195–217, 2021 to the unification of the vegetation cover and the development of a pine forest around Lake Krzywce Wielkie. However, in cores KW20/1, KW20/2 and KW20/4 the increased presence of indicators related to human activities was noted (Fig. 5A, B), mainly Rumex and Secale, which are wind-pollinated plants and release large amounts of pollen (Meese and Morris, 1984; Subba-Reddi and Reddi, 1986; Sugita et al., 1999). Their presence in the upper part of the sediments in the study area is the result of the regional transport. Thus, the increased occurrence of Rumex and Secale is the conse- quence of a huge production of pollen and the common presence of these species in the 20th century under the strong human activity. CONCLUSION Paleobotanical analysis of the sediments revealed that a C. mariscus population devel- oped during the early Holocene and has almost continuously existed in Lake Krzywce Wielkie since then. While L. dortmanna is a new spe- cies that appeared in this lake at the end of the 19th century. In the younger part of the cores, higher fre- quencies of oligotrophic species, other than L. dortmanna, such as M. alterniflorum, J. bul- bosus and Charophytes, were noted. There was a concurrent decrease in the population of aquatic macrophytes typical for eutrophic water, namely P. amphibium, R. sceleratus, Nuphar and Nymphaea. The spread of L. dort- manna and other oligotrophic species was pos- sible due to the artificial lowering of the lake water level and the changes in the land use of adjacent areas, which mainly included the abandonment of agricultural activities, graz- ing and the development of a pine forest. The drainage canal dug by the end of the 19th cen- tury resulted in a decrease of water level, which caused changes in the littoral zone of the lake and enabled the rebuilding of the plant com- munities and the development of new species. The changes in the surroundings of the lake favored the filtering of water from the catch- ment areas and resulted in the smaller sup- ply of nutrients, which enabled the develop- ment of oligotrophic species communities. The establishment of BTNP at the end of the 20th century contributed to the complex protection and conservation of the catchment area, which further limited the potential eutrophication of habitats. The recent development of L. dortmanna population proves that the presence of this oli- gotrophic species is generally possible under the present environmental conditions in the temperate zone, despite a continuous supply of nutrients to the lakes in the industrial coun- tries as a result of agricultural activities and synanthropic changes of flora and vegetation. The necessary conditions are related to the catchment. Forest cover, especially pine forest, is an important factor because of the low pH of the soil and infertile habitat. It is essential for such lakes that the adjacent areas would be protected by law so that changing the landuse would be impossible. Potentially, a gradual and slow decline of Cladium could be expected due to the oligo- trophication of the water of a lake. However, the often contradictorily defined ecological demands of Cladium and its presence in vari- ous habitats prevent us from drawing such a conclusion. 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