Guano inputs from wintering waterbirds increase the organic carbon instability in eutrophic Lake Chaohu, China

Wintering waterbirds are important components of many shallow lakeshore ecosystems; however, their regulation mechanism of organic carbon fractions and their stabilities in lakes remain unclear. Therefore, we analyzed the organic carbon fractions and dissolved organic matter (DOM) contents of the surface sediment and overlying water in western Lake Chaohu, China, during October (pre-wintering), January (wintering), and May (post-wintering) to examine the effects of guano inputs from wintering waterbird on the organic carbon stability. Mantel tests indicate that cyanobacterial growth (Chl-a) and climate were correlated with the stability of DOM in the overlying water, whereas Chl-a was strongly correlated with the stability of DOM in the sediment. Therefore, cyanobacterial growth contributed to a decrease in the stability of DOM during the post-wintering period. Partial least squares path modeling indicates that the guano inputs affected the labile organic carbon fraction I relative to total organic carbon (LOC1/TOC). At omnivorous waterbird habitat sites, the proportion of LOC1/TOC in the sediment during the wintering period was higher than those in non-wintering periods, indicating that waterbird guano inputs were linked to increased sediment organic carbon instability. Close correlations among climate, Chl-a, dissolved organic carbon, and mineral-associated organic carbon (MAOC) suggest that climate-related cyanobacterially derived organic matter deposition was linked to increased labile organic fractions and simultaneously promoted MAOC formation, thereby partially buffering the destabilization of sediment organic carbon. These results provide new insights into the regulation of organic carbon stability in shallow eutrophic lakes by guano inputs from wintering waterbirds and offer a broader understanding of the carbon dynamics, as well as a scientific basis for lakeshore ecological restoration and management.