Tracking the Limnoecological History of Lake Hiidenvesi (Southern Finland) Using the Paleolimnological Approach

Abstract

We examined a sediment record from Lake Hiidenvesi in southern Finland using paleolimnological methods to trace its limnoecological history. In our record, beginning from the 1940's, chironomid (Diptera) assemblages shifted from typical boreal taxa towards mesotrophic community assemblages at ~1960-1980 CE being finally replaced by eutrophic taxa from the 1990's onward. The diatom (Bacillariophyceae) assemblages reflected relatively nutrient rich conditions throughout the record showing a further increase in eutrophic taxa from the 1970's onward. A chironomidbased reconstruction of late-winter hypolimnetic dissolved oxygen (DO) conditions suggested anoxic conditions already in the 1950's, probably reflecting increased inlake production due to allochthonous nutrient inputs and related increase in biological oxygen consumption. However, the reconstruction also indicated large variability in long-term oxygen conditions that appear typical for the basin. With regard to nutrient status, chironomid-and diatom-based reconstructions of total phosphorus (TP) showed a similar trend throughout the record, although, chironomids indicated a more straightforward eutrophication process in the benthic habitat and seemed to reflect the intensified human activities in the catchment more strongly than diatoms. The DO and TP reconstructions were mostly similar in trends compared to the measured data available since the 1970's/1980's. However, the increase in TP during the most recent years in both reconstructions was not visible in the monitored data. The results of our multiproxy study emphasize the significance of including both epilimnetic and hypolimnetic systems in water quality assessments and provide important long-term limnoecological information that will be useful in the future when setting targets for restoration.

Reconstruction and Trends of Total Phosphorus in Shallow Lakes in Eastern China in The Past Century

“…Transfer function methods enable the reconstructing of historical environmental indicators such as lake pH, salinity, nutrients and water temperature according to current ecological characteristics of biological groups and historical stratigraphic fossil data [44,45]. The diatom-total phosphorus (DI-TP) and chironomid-total phosphorus (CI-TP) transfer functions [46,47] were provided to reveal phosphorus changes on the assumption that TP is a strong controlling variable in diatom and chironomid assemblage composition and abundance.…”

Waste water discharge from a large Ni-Zn open cast mine degrades benthic integrity of Lake Nuasjärvi (Finland)

“…In particular, diatom assemblages (primary producers) tend to reflect the epilimnetic water quality (pH and nutrients) (Weckström et al, 2003;Tammelin et al, 2017) and cladocerans (secondary producers) the general limnoecological status (trophic state, pollution) of the water column (Jeppesen et al, 2011;Leppänen, 2018). In turn, the bottom-dwelling aquatic larval stages of chironomids have direct species-specific metabolic responses to the bottom water (hypolimnetic) dissolved oxygen concentration (Quinlan et al, 1998;Luoto et al, 2017) with some particular species having hemoglobin (red larvae known as "bloodworms") to survive under periods of anoxia (Brodersen et al, 2008).…”