Transitions in Dissolved Organic Phosphorus and Dissolved Organic Carbon Across a Freshwater Estuary Gradient

Abstract

AbstractDespite the significant role that dissolved organic phosphorus (DOP) plays in ecosystem productivity, efforts to characterize inputs of phosphorus (P) into lakes have largely ignored P fractions complexed to dissolved organic matter (DOM). To address this gap, we characterized DOP and DOM along a transect of a Lake Erie tributary (Kettle Creek) from the headwaters to the rivermouth and into the nearshore and offshore central basin. DOM and DOP characteristics impart a chemical fingerprint that is useful for determining source and production in aquatic ecosystems. We analyzed DOM composition and concentration (DOC; organic carbon) in addition to DOP as phosphomonoesters (MP; predominantly terrestrial in origin) and phosphodiesters (DP; microbially‐produced), along with other water quality parameters. DOM and DOC within the river were relatively invariant. While there were no consistent trends in riverine MP and DP, an impoundment on the river appeared to act as a sink for some soluble P forms and a potential source of DP. At the rivermouth, we observed a rapid decrease in DOC, DOP, and total P and a shift to more autochthonous‐like DOM, though the decrease in DP was weaker. Relative to in‐flowing river water, P pools in nearshore and offshore Lake Erie were enriched in DOP, especially DP. DOP accounted for up to 42% of total P in Kettle Creek and up to 92% in Lake Erie's central basin. Our work shows the importance of considering DOP in P management efforts as its dynamics differ from those of other, more commonly measured P forms.