An example of land-use relaxation and its effect on soil stabilization in the catchment of Lake Lavijärvi, Russian Karelia: insights from multi-proxy sediment analysis

Abstract

Accelerated soil erosion due to land use is a far-reaching problem for today’s society. Soil degradation leads to outwash and redistribution of soil organic matter, which not only impacts soils but also adjacent ecosystems by downstream eutrophication of freshwater bodies. Despite the severity of the problem and the ever-growing footprint of agriculture, little is known about the long-term effects of past soil degradation periods on catchment soils and lake systems. This study addresses this question by analyzing a sediment sequence retrieved from Lake Lavijärvi, located near the city of Sortavala, north of Lake Ladoga in the Republic of Karelia, Russia, which has witnessed a period of intensive farming at the beginning of the twentieth century, followed by abandonment of the land post-World War II. We applied a multi-proxy approach using geophysical properties, the geochemical and isotopic composition of the bulk sediment, as well as the distribution of sedimentary leaf waxes and their relative ages (compound-specific radiocarbon dating). With the beginning of industrialization (ca. 1900 CE ), we observed severe soil erosion, evident as maxima in magnetic susceptibility and Ti concentrations, as well as high sediment mass accumulation rates. Intensive farming led to a reduction of soil-carbon-residence times (mean transfer time, MTT), indicated by the washout and deposition of pre-aged soil organic carbon. During the same time, the lake became eutrophic and varves were deposited, due to a surplus of soil-derived nutrients. Decreasing MTT after World War II reflected depopulation and land abandonment that resulted in stabilization of catchment soils. Even though soil erosion declined and the trophic status of Lake Lavijärvi returned to more oligotrophic conditions during the post-war period, the lake still suffers from anoxia today. We show that land-use legacies exert a major influence on freshwater ecosystems decades after land-use relaxation.

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