Lake eutrophication and brownification downgrade availability and transfer of essential fatty acids for human consumption

摘要

Fish are an important source of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for birds, mammalsand humans. In aquatic food webs, these highly unsaturated fatty acids (HUFA) are essential for many physiologicalprocesses and mainly synthetized by distinct phytoplankton taxa. Consumers at different trophic levelsobtain essential fatty acids from their diet because they cannot produce these sufficiently de novo. Here, we evaluatedhow the increase in phosphorus concentration (eutrophication) or terrestrial organic matter inputs(brownification) change EPA and DHA content in the phytoplankton. Then, we evaluated whether these changescan be seen in the EPA and DHA content of piscivorous European perch (Perca fluviatilis), which is a widely distributedspecies and commonly consumed by humans. Data from 713 lakes showed statistically significant differencesin the abundance of EPA- and DHA-synthesizing phytoplankton as well as in the concentrations andcontent of these essential fatty acids among oligo-mesotrophic, eutrophic and dystrophic lakes. The EPA andDHA content of phytoplankton biomass (mg HUFA g−1) was significantly lower in the eutrophic lakes than inthe oligo-mesotrophic or dystrophic lakes. We found a strong significant correlation between the DHA contentin the muscle of piscivorous perch and phytoplankton DHA content (r = 0.85) as well with the contribution ofDHA-synthesizing phytoplankton taxa (r = 0.83). Among all DHA-synthesizing phytoplankton this correlationwas the strongest with the dinoflagellates (r = 0.74) and chrysophytes (r = 0.70). Accordingly, theEPA + DHA content of perch muscle decreased with increasing total phosphorus (r2 = 0.80) and dissolved organiccarbon concentration (r2 = 0.83) in the lakes. Our results suggest that although eutrophication generallyincrease biomass production across different trophic levels, the high proportion of low-quality primary producersreduce EPA and DHA content in the food web up to predatory fish. Ultimately, it seems that lake eutrophicationand brownification decrease the nutritional quality of fish for human consumers.