Postglacial evolution of a small lake in the South Baltic coastal zone based on geochemical, pollen and subfossil Cladocera analysis
Article Category: Original research paper
Published Online: Dec 03, 2018
Page range: 384 - 397
Received: Feb 28, 2018
Accepted: Apr 25, 2018
DOI: https://doi.org/10.1515/ohs-2018-0036
© 2018 Faculty of Oceanography and Geography, University of Gdańsk, Poland
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
Numerous natural exposures of sediments occur in coastal cliffs of the Southern Baltic, in the region of Middle Pomerania. They were the subject of mainly geological, geomorphological and stratigraphic studies. The stratigraphy of the Late Glacial and Holocene deposits is available for the cliff section located to the east of Ustka (Tomczak 1993; Olszak et al. 2008; 2012; Wróblewski et al. 2013). The Late Glacial sediments accumulated in shallow water reservoirs located near Orzechowo were described by Marsz & Tobolski (1993), Olszak et al. (2012), Wojciechowski (2012), and Kruczkowska et al. (2017). As part of the work related to the dynamics of the seashore, palynological studies of marine sediment cores taken from the central coastal zone of the Southern Baltic were carried out (Zawadzka 2001; Miotk-Szpiganowicz 2005). Despite adequate knowledge of geological structure and geomorphologic processes as a good basis for interpretation, comprehensive multi-proxy studies covering the period of lake formation and its evolution in the Holocene, which would provide information on fossil aquatic and terrestrial ecosystems as well as changes in the biological, climatic, and hydrological environment, are relatively rarely carried out. One of the well-known sites in the Pomerania region is the cliff in Niechorze. Two fossil lakes were studied: Niechorze I – outcropped in the cliff, and Niechorze IV – a fossil bog depression. Niechorze has been studied for many years, mostly by K. Kopczynska-Lamparska who prepared a geological map of the area and described in detail organogenic deposits outcropping in the cliff (Kopczynska-Lamparska et al. 1983). In addition, 14C dating, pollen analysis (Brykczynska 1978), Cladocera analysis (Szeroczynska 1985), diatom analysis (Kopczynska-Lamparska et al. 1983) and others were performed for these sediments. These sites provide very valuable information on the development of the area from the Oldest Dryas to the Subboreal.
Fossil cliffs containing lake and bog organic deposits are natural archives. Such reservoirs occur on cliffs relatively rarely, which is an additional difficulty in research. Their lifetime on the cliff wall is also relatively short. Depending on the season and the rate of abrasion processes, such reservoirs exposed on cliffs after the stormy period last from several months to several years. The average rate of cliff abrasion was estimated at 0.2–2.7 m/year at the coast near the study area, excluding catastrophic storms, which can cause a loss of 7–8 m (Florek et al. 2010).
Geochemical, palynological and subfossil Cladocera surveys make it possible to supplement our knowledge about the development of the area during the Late Glacial and the Holocene, which is now a border zone of the land and sea, formed during the period of receding glaciation and progressive warming, and will create a much more complete picture of the past environments. Pollen analysis supported by the results of radiocarbon dating plays a key role in the reconstruction of vegetation associated with water reservoirs and makes it possible to establish the chronostratigraphy of sediments (Latałowa 1982; Latałowa & Tobolski 1989).
This paper presents the results of interdisciplinary research on a small natural paleolake located near the village of Debina. Our research aimed to reconstruct the main phases of the development of the lake and mire ecosystem and the environmental conditions, with emphasis on paleohydrological events based on multi-proxy (geochemical, pollen, and subfossil Cladocera) analysis of the Debina profile. We have the opportunity to discover the history of this paleolake from its origin in the Late Glacial, through its development, to its decline and transformation into a mire in the middle Holocene.
The investigated profile is located within the section of the coastal cliff between 221.3 and 221.4 km of the Polish Baltic coast, near the village of Debina (54°38.642’N, 17°00.701’E) in the central part of the Slovincian Coast mesoregion (Fig. 1). The base consists of glacial till and glaciolimnic sediments of the Middle and Upper stadials of the Vistula Glaciation. The age of glacial till and glaciolimnic sediments is assigned to the Swiecie Stadial (Olszak et al. 2008), the Pomeranian Phase and the Gardno Phase (Petelski 1985; 2006; Jasiewicz 2005). The contemporary landscape of this area was shaped in the Late Glacial during the Gardno Phase of the Vistula Glaciation, 14500–14300 yr 14C BP (Rotnicki & Borówka 1994), and by the Holocene litho-morphogenetic processes, including the eolian activity (Olszak et al. 2008) and coastal abrasion (Florek et al. 2010), whose intensity varied over time. Eolian sands are the major type of superficial deposits within the investigated site and its surroundings. They usually lie on stratified shallow covers of fluvioglacial sands, which in some layers are enriched with organic matter, or on lacustrine sediments (lacustrine mud and calcareous gyttja). Coastal dunes are covered with forests of spatially varied species composition, usually with a dominance of pine. At the investigated site, it is a mixed forest with beech as the main component.
Figure 1
Location of the site (a, b), morphology of the cliff (c, d), location and morphology of the paleolake profile and its calibrated radiocarbon age (e)
The climate of the studied area is strongly influenced by the sea. The average annual temperature is about 8.1°C, with the maximum in July (average 17°C) and the minimum in January (average 0.3°C). Mean annual precipitation amounts to about 641 mm (Baranowski 2008). There are 10–32 days with storms during the year.
Fieldwork was carried out in May 2015. A 250 cm profile was collected for the research, which included lake bottom sediments (200–250 cm – fluvioglacial sands) and lake-bog sediments: non-calcareous lacustrine mud, calcareous gyttja, sand with organic matter, peat (0–200 cm). The entire profile was subjected to geochemical analysis. Part of the profile containing lacustrine and peat deposits (8–200 cm) was used for palynological and Cladocera analysis.
Radiocarbon dates were obtained for three samples collected from the Debina profile. Dating was performed in the Laboratory of Absolute Dating in Cianowice. Conventional dates were calibrated using the OxCal 4.2.3 software (Bronk Ramsey 2013) and the IntCal13 calibration curve (Reimer et al. 2013). In this paper, dates are given in calibrated years BP. Detailed information on dating is included in Table 1.
Results of radiocarbon dating of the Debina profile
| Depth (cm) | Laboratory number | Dated material | Result of dating in 14C yr BP | Calibrated ages in 14C cal yr BP (95.4%) probability | Calibrated ages in 14C cal yr BP (Median) |
|---|---|---|---|---|---|
| 5–10 | MKL-2590 | bark | 2160 ± 60 | 2318–2001 | 2165 |
| 70–72 | MKL-2591 | organic remains | 8810 ± 90 | 10173–9596 | 9870 |
| 83–85 | MKL-2592 | organic remains | 9170 ± 110 | 10663–10160 | 10365 |
One disturbed and two volumetric (using 100 cm3 steel rings) samples were collected from each sedimentary layer. In the volumetric samples, the bulk density and total porosity were determined by the dry weight method. Disturbed samples were dried at 40°C and sieved through a 2.0 mm sieve to remove the skeleton fraction. The particle size distribution was analyzed by the mixed pipette and sieve method, pH was measured potentiometrically in suspension with water at the soil:water ratio of 1:2.5 (Elmetron CPC-401 pH-meter), the content of CaCO3 was determined according to Scheibler’s method, total organic carbon (TOC) – by the Tyurin method in mineral samples and by the Alten method in organic samples (Dziadowiec & Gonet 1999), and total nitrogen (TN) – by the Kjeldahl method (van Reeuvijk 2002). The content of phosphorus was analyzed by the molybdenum blue method (van Reeuvijk 2002) after sample digestion in a mixture of 40% HF and 60% HClO4. In the same solutions, the total content of iron, aluminum, potassium, calcium, magnesium and manganese was determined using the microwave plasma atomic emission spectrometry (Agilent 4100 MP-AES). Based on the results of particle size distribution analysis, we calculated logarithmic graphical measures after Folk & Ward (1957) using Gradistat 5.11 software (Blott & Pye 2001) (Fig. 2).
Figure 2
Lithology, age (in calibrated years BP) and selected physical and chemical properties of the Debina profile
We collected 24 samples of 1 cm3 at intervals of 8 cm from a depth of 200 cm to 8 cm to analyze pollen from the Debina profile. The samples were boiled in 10% KOH, treated with 10% HCl or soaked for several days in HF (depending on sediment composition), and subsequently acetolyzed (Faegri & Iversen 1989; Dybova-Jachowicz & Sadowska 2003). The total number of pollen grains counted in each sample up to a minimum of 200 grains of arboreal pollen (AP; low pollen frequency) was used to calculate the concentration of trees, shrubs, aquatic plants and non-pollen palynomorphs (NPPs) (Fig. 3). The identification of microremains of fungi and faunal organisms (NPPs) followed van Geel & Bohncke (1978; 1981) and Barthelmes et al. (2012). Zonation was carried out visually based on changes in the dominant pollen, spores, and NPP taxa. The diagram was constructed using the POLPAL software (Nalepka & Walanus 2003). For the purpose of determining the aquatic concentration of trees, shrubs, and pollen/NPPs (Stockmarr 1971), Lycopodium tablets produced by the Department of Quaternary Geology, University of Lund, were added.
Figure 3
Pollen concentration diagram, of non-pollen palynomorphs (NPPs), aquatic and marsh plants from the Debina profile
The Cladocera analysis was performed in 48 samples collected every 4 cm from a depth of 200 cm to 8 cm from the Debina profile. Samples of 1 cm3 were prepared using a standard procedure (Frey 1986; Korhola & Rautio 2001). After the removal of carbonates using 10% HCl, each sample was boiled in 10% KOH for 30 min, washed with distilled water, and sieved through a 40 μm mesh sieve. The fine material was transferred into a polycarbonate test tube. Prior to counting, the remains were colored with safranin T. The analysis was performed under a Nikon model Eclipse Ci-L microscope with magnifications of 10, 40, and 60×. A minimum of 200 remains of Cladocera (3–8 slides) were examined in each sample. First, all remains from each slide were counted (headshields, shells, postabdomens, postabdominal claws, and antennules) and then converted to one Cladocera specimen and all ephippia together.
Identification and ecological interpretation of the Cladocera remains were based on Goulden (1964), Szeroczynska (1985; 1998), Hofmann (1986; 2000), Korhola (1990), Duigan (1992), Flössner (2000), and Szeroczynska & Sarmaja-Korjonen (2007). The results are shown in Figure 4, including the percentage diagram, the total number of Cladocera individuals, the number of species and their biodiversity. The numerical analysis was performed using the POLPAL software (Nalepka & Walanus 2003). The Cladocera species were classified into four habitat-preference groups: bottom-dweller species, species associated with or restricted to vegetation, planktic (offshore) and littoral (meiobenthic) species (Flössner 1964; Whiteside 1970; Whiteside & Swindoll 1988; Korhola 1990).
Figure 4
Relative abundance diagram of subfossil cladoceran taxa, the total number of Cladocera specimens, and the number of species in the Debina profile
The radiocarbon age of organic materials collected from the investigated profile ranged from 10 365 to 2165 yr cal BP (Table 1). The calibration results are presented for each date with a median (Table 1). The youngest date (2165 yr cal BP) obtained for bark particles from the roof (5–10 cm) of the profile determines the period of burial of lacustrine deposits by eolian sands. The remaining two C14 dates, 10 365 and 9870 yr cal BP for depths of 85 and 70 cm, respectively, confirm the proglacial nature of the investigated paleolake. The sedimentation rate in the period of lake development was about 0.27 mm yr−1.
Based on lithological and chemical properties, we distinguished five litho-geochemical zones, which developed as a result of various geomorphological processes (Fig. 2).
Particle size distribution and logarithmic measures of the studied deposits
| Depth (cm) | % of | Logarithmic measures (ϕ) | ||||||
|---|---|---|---|---|---|---|---|---|
| gravel | sand | silt | clay | MG | σG | SkG | KG | |
| 0–10 | 0.0 | 90.7 | 5.1 | 4.3 | 2.83 | 1.49 | 0.22 | 1.42 |
| 10–56 | 0.8 | 91.4 | 6.1 | 2.5 | 2.46 | 1.29 | 0.30 | 1.13 |
| 56–70 | 0.0 | 93.8 | 4.6 | 1.6 | 2.24 | 1.15 | 0.21 | 1.16 |
| 70–87 | 1.4 | 90.3 | 6.0 | 3.7 | 2.55 | 1.74 | 0.22 | 1.54 |
| 87–115 | 0.0 | 93.8 | 4.5 | 1.7 | 3.00 | 0.98 | 0.14 | 1.13 |
| 115–125 | 4.6 | 93.0 | 4.1 | 2.8 | 2.57 | 1.50 | -0.07 | 1.47 |
| 125–135 | 0.0 | 100.0 | 0.0 | 0.0 | 1.34 | 0.81 | 0.00 | 1.38 |
| 135–150 | 0.0 | 91.3 | 7.1 | 1.6 | 2.53 | 1.42 | 0.23 | 1.30 |
| 150–166 | 1.2 | 93.9 | 4.5 | 1.6 | 2.44 | 1.26 | -0.03 | 1.26 |
| 166–186 | 0.0 | 27.3 | 71.4 | 1.3 | 5.31 | 1.67 | 0.02 | 0.96 |
| 186–190 | 0.0 | 100.0 | 0.0 | 0.0 | 2.36 | 0.76 | -0.11 | 0.91 |
| 190–200 | 0.0 | 67.9 | 25.7 | 6.4 | 4.21 | 2.18 | 0.35 | 1.29 |
| 200–250 | 0.0 | 97.8 | 1.5 | 0.7 | 2.26 | 0.88 | 0.04 | 0.90 |
Based on pollen analysis of trees, shrubs, herbaceous, aquatic and mire vegetation, as well as other macrofossil NPPs, we distinguished three zones illustrating the evolution of the studied aquatic-mire ecosystem (Fig. 3). The most important findings in specific zones are described below.
The subfossil cladoceran fauna of sediments in the Debina profile is represented by 15 species that belong to three families: Bosminidae, Chydoridae, and Daphniidae. Most of the remains belong to the family of Chydoridae (11). Cladocera remains were identified in only three sections of the core – at depths of 200–156 cm (Zone I), 128–120 cm (Zone III) and 24–8 cm (Zone V) (Fig. 4). In the first zone,
The investigated profile constitutes an archive of fragmentary environmental changes during the Late Glacial and the Early Holocene. Physical and chemical properties, radiocarbon dating, Cladocera, and pollen analysis were used to interpret this information and to reconstruct the major phases of the evolution and processes of the lake-peatbog ecosystem and factors influencing them. Based on the obtained data, we distinguished three main phases of the development of the Debina paleolake (Fig. 5). The first phase includes the formation of a lake basin in the Late Glacial, which is a typical lacustrine phase with lacustrine mud and gyttja accumulation. The second transition phase involves the further development of the basin during the Late Glacial (Younger Dryas) and the Early Holocene. The third and final phase covers the decline of the lake and its transformation into a peat bog at the end of the Preboreal period. The characteristics of each phases involve a description of environmental conditions prevailing in the Debina paleolake, in particular changes in vegetation, the Cladocera community, geochemical composition, the trophic state, water temperature, and water level.
Figure 5
Reconstruction of the hydroclimatic conditions in the Debina paleolake during the Late Glacial and the Early Holocene
During the Late Glacial, stratified fluvioglacial sand accumulated in the foreland of the disappearing ice sheet, in which a small paleolake – Debina developed (250–200 cm). These sediments were enriched with small amounts of weakly humified organic matter and were poor in nitrogen and phosphorus. The results of studies by Pienitz & Smol (1993) demonstrate that the degree of humification of sediments is strongly influenced by climatic conditions, especially temperature, showing a positive correlation.
At the beginning of this period, starting from a depth of 200 cm, a small oligotrophic reservoir developed in the cold and dry climate. This was likely followed by further cooling and moistening of the climate, as indicated by the increasing content of TOC, N and P. The high varying content of Mn in sediments suggests surface water runoff into the reservoir. The presence of open water species:
With time (from a depth of 168 to 156 cm), the lake evolved toward a mesotrophic state, which is evidenced by the occurrence of
The species composition of Cladocera is typical for lakes developed during the Late Glacial in northern Poland [Lake Biskupin (Szeroczynska 1995), Lake Niechorze and Lake Woryty (Szeroczynska 1985)]. During the warm episodes of the Late Glacial (Bølling/Allerød), species typical of warmer waters occurred (Szeroczynska 2003), whereas in cold periods (the Oldest Dryas and Older Dryas), the species composition of Cladocera was limited to 3–5 taxa and the frequency of individuals was low (Szeroczynska & Zawisza 2007).
This phase is associated with the destabilization of hydrological conditions in the lake. Stratified fluvioglacial sands enriched with amorphous organic matter have accumulated in the reservoir. This process probably occurred in cold climate and could be associated with scarce vegetation cover in the surrounding area, for example, the occurrence of tundra vegetation and, consequently, greater erosion of material from the catchment. It is likely that there was a slow decrease in the water level and water temperature, as indicated by the lower content of Fe in the sediments and low TOC values. The high variability in the types of accumulated material may indicate the instability of hydrological conditions, with periods of alternating lower and higher water levels. Rush vegetation (pollen grains of Cyperaceae and spores of
At the beginning of the Preboreal period, the sea level rose as a result of the ice sheet melting and the glaciotectonic lifting of Scandinavia. In the southern parts of the Baltic, the coastline moved southward, but it was still several kilometers north of today’s coast. In the paleolake, the change in hydrological conditions was recorded in sediments at a depth of 128 cm. High abundance of the HdV-729 type and spores from the genus
In the first part of the third stage (84–52 cm) in the Boreal period, there is evidence of a wet period at about 10300 cal BP, similarly to other sites of Northern Europe (Magny 2004), for example in the southern part of the Gulf of Riga (Grudzinska et al. 2017) and northern Poland (Pedziszewska et al. 2015). This phase probably corresponds to the climate cooling identified as IRD-7 in the Bond cycle. On the other hand, it is most likely that the Ancylus Lake transgression ca. 10300 cal BP (Saarse et al. 2003) induced a rise in the groundwater table in some areas, which in turn caused an increase in the reservoir’s water depth. This phase is characterized by unstable hydrological conditions. The presence of
In the second part of the third phase in the Atlantic period (44–8 cm), the Baltic Sea transformations became relatively stable. In the last 6000 years, the rate of changes in sea level and shoreline has decreased. Erosion processes on the cliffs and gradual peneplanation of the coastal zone, initiated in the Atlantic period, predominated (Uscinowicz 2003; 2006). Despite the intensive processes and evolution of the coast, there were periods of relative stabilization.
In the first part of the Atlantic period, water levels decreased. This was caused by increases in air temperature and evaporation and is reflected in the presence of fungal spores of
The expansion of Cladocera is observed anew from a depth of 22 cm, indicating an increase in the water level. In this period, species specific to shallow and eutrophic waters occurred in the lake, such as
The termination of the peat bog was connected with its burial by eolian sands. The burial of the peat bog probably took place in the Early Subatlantic period, which is confirmed by the radiocarbon age of bark pieces from the roof of the Debina profile: 2165 cal yr BP. The intensification of eolian processes in this period was also determined at other sites along the coastal cliffs of Middle Pomerania. On the other hand, it should be taken into account that the date 2165 is clearly “rejuvenated” and palynological data indicate that there is a hiatus in the top part of the profile.
The results of this research represent one of the most detailed studies of the reservoir discovered on the cliffs, thus complementing the knowledge on the development of the Central Pomerania region during the Late Glacial and the Early and Middle Holocene period. The results of our studies confirm the importance of paleolakes as an archive of environmental conditions and their importance in palaeoenvironmental reconstructions.
The Late Glacial origin of the lake was confirmed by the results of pollen and Cladocera analysis. Unstable ecological conditions occurred in the lake. The subsequent significant changes in water level and trophic status can be explained by temporal variability of climate conditions. At that time, a small cliff lake developed, at the bottom of which lacustrine mud and then calcareous gyttja accumulated. In the Late Glacial and the Early Holocene, the lake basin was almost completely filled with stratified sediments, enriched with organic matter, constituting the products of soil erosion in the catchment.
The results of the multi-proxy research enabled the identification of three main stages in the development of the reservoir: the first initial stage associated with the development of a cold oligotrophic lake covering the late Glacial period, and the second – the transition stage – associated with the destabilization of hydrological conditions when periods of erosion and filling of the reservoir with fluvioglacial sands alternated with periods of stabilization and deposition of organic matter and stages of stabilization of hydrological conditions, water-level lowering and transformation of the lake into a peat bog. The functioning of the peat bog ceased with its burial by eolian sands. The history of the development of the Debina paleolake also resembles the evolution of other cliff paleolakes (Niechorze, Trzebielino T28).
In general, the results of subfossil Cladocera reconstruction based on radiocarbon dating and pollen analysis as well as the analysis of the sequence of physical and chemical properties of litho-morpho-geological processes correlate well with the dynamics of geomorphological processes established by other authors. However, the multi-proxy approach provides more comprehensive information regarding the evolution of the studied area.