Small Boreal Lake Ecosystem Evolution under the Influence of Natural and Anthropogenic Factors: Results of Multidisciplinary Long-Term Study

Liudmila Shirokova,Natalia Kokryatskaya,Taissia Vorobieva,Oleg Pokrovsky,Artem Chupakov,Sergey Klimov,Vladimir Gogolitsyn,Anna Ershova,Olga Moreva,Elena Sobko,Svetlana Zabelina,Natalia Makhnovich,Natalia Shorina

doi:10.3390/w8080316

Abstract

Small aquatic ecosystems of the boreal zone are known to be most sensitive indicators of on-going environmental change as well as local anthropogenic pressure, while being highly vulnerable to external impacts. Compared to rather detailed knowledge of the evolution of large and small lakes in Scandinavia and Canada, and large lakes in Eurasia, highly abundant small boreal lakes of northwest Russia have received very little attention, although they may become important centers of attraction of growing rural population in the near future. Here we present the results of a multidisciplinary, multi-annual study of a small boreal humic lake of NW Russia. A shallow (3 m) and a deep (16 m) site of this lake were regularly sampled for a range of chemical and biological parameters. Average multi-daily, summer-time values of the epilimnion (upper oxygenated) layer of the lake provided indications of possible trends in temperature, nutrients, and bacterio-plankton concentration that revealed the local pollution impact in the shallow zone and overall environmental trend in the deep sampling point of the lake. Organic phosphorus, nitrate, and lead were found to be most efficient tracers of local anthropogenic pollution, especially visible in the surface layer of the shallow site of the lake. Cycling of trace elements between the epilimnion and hypolimnion is tightly linked to dissolved organic matter speciation and size fractionation due to the dominance of organic and organo-ferric colloids. The capacity of lake self-purification depends on the ratio of primary productivity to mineralization of organic matter. This ratio remained >1 both during winter and summer periods, which suggests a high potential of lake recovery from the input of allochthonous dissolved organic matter and local anthropogenic pollution.

Highlights

A growing interest in the carbon cycle of subarctic and arctic regions is caused primarily by climate change, which is most pronounced in high latitudes, where it leads to increased emissions of greenhouse gases carbon dioxide (CO2 ) and methane (CH4 ) from the water surfaces, which potentially enhances the effect of global warming
We demonstrate the synchronous behavior of macro- and micro-nutrients in the deep and shallow zones of the lake and assess the degree of local anthropogenic pollution versus global climate trends, as well as catastrophic weather events
Assessment of the environmental status of Lake Svyatoe is relevant at present, because it can serve as a model of water bodies used by the local population for economic, household, and recreational purposes, while being isolated from intensive anthropogenic and industrial influence

Summary

Introduction

A growing interest in the carbon cycle of subarctic and arctic regions is caused primarily by climate change, which is most pronounced in high latitudes, where it leads to increased emissions of greenhouse gases carbon dioxide (CO2 ) and methane (CH4 ) from the water surfaces, which potentially enhances the effect of global warming. In this regard, over the past decades, a priority for basic research has led to a complex ecosystem study of the northern lakes. Annual trends in the physical, chemical, and biological parameters of boreal lakes became a topic of high interest within the context of climate warming and the response of biogeochemistry of carbon in high-latitude aquatic ecosystems, with increasing ground and water temperatures being among the key issues of the prediction of ecosystem evolution under on-going environmental changes [1,2,3,4].

Objectives

Results

Conclusion