Subfossil Cladocera and pollen as indicators of natural and anthropogenic trophic changes of Lake Jelonek (Tuchola Forest, N Poland) during the Holocene

Abstract

<p class="Tre">Lake Jelonek is a small lake located in central northern Poland, in the Tuchola Forest. The sediments of the lake represent a natural archive that offers insights into the natural history of the region from the Late Glacial to present. In winter 2002, a 1330 cm long sediment core was recovered from the deepest part of lake. Using a multiproxy approach (cladocerans, pollen and basic geochemistry), we reconstructed trophic status changes through the last ~15,000 years. Special attention was devoted to the evaluation of nutrient contributions to the lake from natural and anthropogenic sources. The Cladocera analyses yielded a total of 29 species belonging to five families (Bosminidae, Daphniidae, Leptodoridae, Chydoridae, Sididae), with planktonic species representing more than 60% of Cladocera relative abundance throughout the core. The pollen results suggested four periods of increased human activity, so-called settlement phases. The first traces of human activity in the basin of Lake Jelonek appeared in the Atlantic period and were related with Mesolithic and Neolithic settlements. The second (Bronze Age) and the third (Iron Age) settlement phases are well marked by the paleolimnological proxies studied. This time period clearly manifested on the lake waters as an increasing trophy level probably caused by human-associated discharges of nutrients to the lake. After the third settlement phase cladoceran data indicated a significant decrease in the lake trophic level and the pollen data showed a recovery of forest cover. The fourth period of human economic activity during the early Middle Age was characterized by deforestation associated with land reclamation for grazing and cultivation of cereals, and the subsequent nutrient enrichment of lake waters. According to our results, the biological development of Lake Jelonek was determined by climate changes from Late Glacial up to the Atlantic period. Contrastingly, the most important driver for the lake development though the middle and late Holocene has been human activity within the lake catchment. The recovery of the lake trophic level during the last century, which is primarily related to extensive afforestation of the lake catchment, highlighted the importance of land use in the conservation of healthy water bodies.</p>

Millennial‐to‐centennial scale lake system development in the mountains of tropical Mexico

“…; Zawisza et al . ). Contrastingly, dense forest cover indicated by high percentages of arboreal pollen would be associated with less erosion and thus lower lake productivity.…”

“…Given their ability to maintain position in the photic zone (Zawisza et al . ), these species are associated with open water (Hobbs et al . ; Wojewódka et al .…”

“…4). Deforestation would favour erosion and therefore high nutrient input into the lake, resulting in enhanced biological productivity and flourishing of a benthic cladoceran assemblage Zawisza et al 2016). Contrastingly, dense forest cover indicated by high percentages of arboreal pollen would be associated with less erosion and thus lower lake productivity.…”

Paleośrodowiskowe znaczenie zmian tempa i charakteru sedymentacji osadów jeziora Jelonek w Borach Tucholskich = Paleoenvironmental significance of changes in the rate and type of sedimentation in Lake Jelonek within Poland’s Tuchola Pine Forest (Bory Tucholskie)

“…We wcześniejszych opracowaniach osady jeziora Jelonek analizowane były pod kątem obecności pyłku (Filbrandt-Czaja, 2009), okrzemek (Skulmowska, 2007) i wioślarek (Zawisza, 2008(Zawisza, , 2016. Analiza okrzemkowa miała charakter jedynie ekspertyzowy i realizowana była w ramach pracy magisterskiej na Uniwersytecie Mikołaja Kopernika w Toruniu.…”

“…Również analiza diatomologiczna i wioślarkowa (Skulmowska, 2007;Zawisza, 2008Zawisza, , 2016 oraz zwiększona ilość pancerzyków orzęsek wskazują na wyraźny wzrost eutrofizacji w tym okresie. Wzrost ten mógł być efektem ługowania związków ze zlewni użytkowanej rolniczo i dostawania się ich do wód gruntowych i jeziora (Bajkiewicz-Grabowska, 2002).…”