Abstract
Organic carbon (Corg) and total nitrogen (N) concentrations in combination with stable organic carbon (δ13Corg) and nitrogen (δ15N) isotopic composition were used to investigate the organic matter sources and influence of anthropogenic activities on recent sediments of eutrophic Lake Pamvotis (Greece) and oligotrophic Lake Bohinj (Slovenia). Corg and N concentrations increase upcore showing a progressive nutrient enrichment in both lakes. The C/N ratios vary with depth and indicate that allochthonous and autochthonous sources contributed to sedimentary organic matter. Nevertheless, an excursion to relatively low surface sediment C/N ratios suggests that recently the latter predominates. Finally, δ13Corg and δ15N records showed changes in carbon and nitrogen cycles related predominantly to local anthropogenic activities in Lake Pamvotis and to anthropogenic activities (i.e. woodcutting) and global atmospheric changes in Lake Bohinj.
Highlights
Lakes represent very sensitive ecosystems and interesting sedimentation environments
It is well known that anthropogenic nutrient loading of aquatic ecosystems from both point and nonpoint sources typically results in rapid a increase in the rate of biological production and a significant reduction in water column transparency, and can create a wide range of undesirable water quality changes in freshwater ecosystems (SMITH et al, 2006 and references therein)
A relatively higher proportion of allochthonous, more refractory, organic matter could be delivered to the lake as inferred by higher surface sediment C/N ratios at B2, reflecting the higher surface sediment Corg content at B2
Summary
Lakes represent very sensitive ecosystems and interesting sedimentation environments. The biggest concern related to lakes is induced eutrophication caused by anthropogenic activities. Despite 20th century advances in understanding eutrophication, it remains one of the foremost problems in protecting freshwater ecosystems (SCHINDLER, 2006). It is well known that anthropogenic nutrient loading of aquatic ecosystems from both point and nonpoint sources typically results in rapid a increase in the rate of biological production and a significant reduction in water column transparency, and can create a wide range of undesirable water quality changes in freshwater ecosystems (SMITH et al, 2006 and references therein). Two of the most consistent eutrophication effects are an excursion in algal species composition and an increase in the frequency and intensity of nuisance algal blooms.
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