Phosphorus dynamics in a subtropical coastal lake in Southern Brazil

Temporal and spatial variations of organic and inorganic forms of phosphorus in the sediments of a subtropical oligo-mesotrophic shallow lake were investigated in relation to water column parameters, sediment characteristics and benthic fauna. The main results found were: 1) Phosphorus (P) concentration varied seasonally, with organic P and total P increasing in the sediments in warmer periods; 2) Sediment spatial variation, in terms of grain size composition and organic matter content, influenced P concentrations; 3) quantities and qualities of P in the sediments were positively correlated with water parameters, especially DO and NO3, Chl-a, water temperature, pH, and total P. Negative correlations were observed between %OP and DO in sites 1, 3 and 4, and with NO3 in sites 2, 3 and 4; 4) benthic functional feeding groups showed significant relationships with temporal variation in sediment P concentration, including gathering-collectors, shredders, filterers and filtering-collectors. The results suggest a high importance of temperature mediated control of sediment-P release, both directly, through its direct effects on primary production and decomposition rates, and indirectly through its effects on other water and sediment parameters, especially dissolved oxygen concentration.