Dystrophication of lake Suchar IV (NE Poland): an alternative way of lake development

espanolSe estudiaron la dinamica a largo plazo del desarrollo del lago y el papel de la cuenca de captacion y el cambio climatico en el proceso de distrofia. Se realizo un analisis paleolimnologico de los sedimentos del lago Suchar IV, NE Polonia (core de 880 cm de largo). La reconstruccion paleoecologica se baso en el analisis del polen, los cladoceros subfosiles, las diatomeas, los macrofosiles y el analisis quimico. La cronologia de los sedimentos se baso en los resultados de la datacion de 14C y el analisis palinologico. Los datos obtenidos mostraron que la sedimentacion lacustre en el lago Suchar IV comenzo en el periodo Glacial tardio y continua hasta ahora. La sucesion de plantas indica que los procesos de sedimentacion comenzaron hace 15 000 cal anos AP en el periodo Dryas primitivo. Se observaron cambios importantes en el espectro del polen de las plantas acuaticas a partir del periodo Atlantico Medio. En ese momento, las comunidades de Nymphaea y la mayoria de las especies de algas verdes desaparecieron del lago, lo que indica una transformacion ecologica significativa en el medio acuatico. Esta transfor-macion tambien se manifiesta en las comunidades de cladoceros subfosiles y en las diatomeas. La comunidad de cladoceros en los sedimentos del lago Suchar IV estuvo representada por 37 especies, en su mayoria litorales. A partir del tiempo de transicion (7200-5600 anos cal BP), las comunidades de cladoceros estuvieron dominadas por taxones tolerantes a la acidifi-cacion como Alonella excisa, Acroperus harpae, Alona affinis y Alonella nana. Se identificaron un total de 193 taxones de diatomeas (especies y variedades) en el sedimento, incluyendo 172 pertenecientes a Pennales y 21 a Centrales. En general, la comunidad de diatomeas estaba dominada por especies alcalofilas, en promedio el 45 % de la composicion de las especies. En terminos de preferencias troficas, el grupo mas abundante de diatomeas estaba representado por taxones oligotrafenticos, meso-eutrafenticos y eutrafenticos. No se encontraron diatomeas durante 6000 anos cal BP desde la etapa de transicion. La geoquimica de los sedimentos y los macrofosiles tambien indican el desarrollo limnologico y las tendencias climaticas. Los resultados paleolimnologicos obtenidos indican que el lago Suchar IV ha sufrido una transformacion ecologica de un ecosis-tema armonico a uno disarmonico. Durante el Glaciar Tardio y el Holoceno temprano, el lago Suchar IV era un lago armonico tipico que se transformo en un estado distrofico al final del periodo Atlantico. Los sedimentos del lago Suchar IV tambien muestran una secuencia muy interesante de cambios troficos, desde condiciones oligotroficas a mesotroficas y distroficas. EnglishThe long-term dynamics of a lake development and the role of the catchment and climate change in the dystrophication process were studied. Lacustrine sediments from Lake Suchar IV, NE Poland (880 cm long core), were selected for paleolim-nological studies. The paleoecological reconstruction was based on pollen, subfossil cladocerans, diatoms, macrofossils and chemical analyses. Sediment chronology was based on the results of 14C dating and palynological analysis. The obtained data showed that the lacustrine sedimentation at Lake Suchar IV began in the Late Glacial and continues to this day. The plant succession indicates that sedimentation processes started as early as the Oldest Dryas ~ over 15 000 cal yr BP ago. Important changes in the pollen spectrum of aquatic plants were noted from the mid-Atlantic period. At that time, communities of Nymphaea and most species of green algae disappeared from the lake, which indicates a significant ecological transformation in the aquatic environment. This transformation is also manifested in the subfossil Cladocera and diatom communities. The Cladocera community in the sediments of Lake Suchar IV was represented by 37 species, mostly littoral ones. From the transi-tion time (7200–5600 cal yr BP), Cladocera communities were dominated by taxa tolerant of acidification such as Alonella excisa, Acroperus harpae, Alona affinis and Alonella nana. A total of 193 diatom taxa (species and varieties) were identified in the sediment, including 172 belonging to Pennales and 21 to Centrales. In general, the diatom community was dominated by alkaliphilous – on average 45 % of the species composition. In terms of trophic preferences, the largest group of diatoms was represented by oligotraphentic, meso-eutraphentic and eutraphentic taxa. No diatoms were present during about 6000 cal yr BP from the transition stage. Sediment geochemistry and macrofossils also indicate the limnological development and climate trends. The obtained paleolimnological results indicate that Lake Suchar IV has undergone an ecological transformation from a harmonic to disharmonious ecosystem. During the Late Glacial and the early Holocene, Lake Suchar IV was a typical harmonic lake that transformed into a dystrophic state at the end of the Atlantic period. Sediments of Lake Suchar IV also show a very interesting sequence of trophic changes, from oligotrophic to mesotrophic and to dystrophic conditions.