Phosphorus flux by macrobenthic invertebrates in a shallow eutrophic lake Donghu: spatial change

We estimated phosphorus flux mediated by benthic invertebrates from the sediments to the water in a shallow eutrophic lake (lake Donghu, central China) and quantified spatial (littoral and central sites) and specific (among different benthic taxa) differences. The mass-specific excretion rates of phosphorus (soluble reactive phosphorus (SRP, ηmol·mg dry mass–1·h–1) by benthic invertebrates (abundant taxa) were estimated experimentally and calculated as a final minus of initial nutrient mass divided by dry mass of organisms. Results showed high importance of chironomid larvae as a contributor to the total P flux from sediments to water in shallow lake Donghu. Benthic biomass (from 0.002 to 32.8 g dry mass·m–2) distribution and species composition (31 taxa) were studied (October 2009) in three regions of lake Donghu (Guozhenghu, Miaohu, Yujiahu) using samples from three depths: the shallow littoral site (0.2–1 m depth), central site with 2 m depth, and central site with more than 3 m depth. The total estimated SRP excretion by benthic invertebrate reaches 36% of the direct SPR flux from sediments to water in this lake. The phosphorus regeneration by benthic animals is the most intensive in the shallow littoral sites (69.5 µmol P·m–2·day–1) and at least 20 times greater than in central sites (3.4 µmol P·m–2·day–1) of lake Donghu. The results support notable differences in the SRP excretion rates between taxa and sites. The spatial difference in the SRP flux might be considered as a general feature of lakes with periodical changing oxygen near bottom.