Clustered anthropogenic activity can create hot spots of disturbance with corresponding ecological responses. Sewage released from lakeside development is a globally pervasive and frequently high impact disturbance with strong effects on littoral biota. Lake Baikal, the world’s most voluminous and biodiverse lake, has been suspected of localized sewage contamination, and nearshore benthic communities appear to be responding. In order to examine the extent to which sewage may create hot spots and gradients of disturbance, we sampled 14 nearshore and 3 pelagic locations for signs of human impact along a 40 km stretch of the southwestern shore. Water samples from ~1 m depth were analyzed for nutrients, chlorophyll a, pharmaceutical and personal care products (PPCPs), as well as microplastic concentrations. We also examined the community composition and abundance of periphyton and benthic macroinvertebrates at each littoral site. As trophic interactions may also be altered by disturbance, we evaluated foodweb structure using stable isotopes and fatty acids of periphyton and benthic macroinvertebrates.
Results/Conclusions
Sewage pollution in the nearshore of Lake Baikal was associated with size of and distance from human settlements. PPCPs, including caffeine (up to 60 ng/L), acetaminophen/paracetamol (up to 40 ng/L), associated metabolites (up to 20 ng/L), as well as microplastics (up to 8 plastics/L) were detected in the nearshore water column. PPCPs, phosphorus, and macroinvertebrate N15 values were associated with size of and proximity from the nearest developed site. Nearshore biotic communities appear to be responding to sewage inputs; benthic communities at sites with stronger sewage signals tended to contain lower fractions of mollusks and caddisflies and higher filamentous algae presence. Amphipods remained prevalent throughout all littoral sampling locations. Despite the observed spatial variation in community composition, the fatty acid compositions of consumers did not change along the sewage disturbance gradient. Our combined results demonstrate that sewage pollution gradients and associated biological responses in Baikal are nuanced and complex. However, highly specific indicators of sewage pollution paired with co-located biological measurements have the power to delineate gradients of sewage disturbance and ecological responses. For Lake Baikal, these results are timely, especially considering the potential environmental consequences of growing tourism (>1.2 million tourists annually).