DRIVERS OF PHOSPHORUS SORPTION IN STREAMS ACROSS AN AGRICULTURAL WATERSHED DURING LOW AND HIGH FLOW

Excess dissolved phosphorus (P) exports from agriculturally dominated watersheds can contribute to harmful algal bloom (HAB) growth in lakes. To improve HABs management, we need a better understanding of the in-stream processes that shape dissolved P exports. Stream sediment can, depending upon environmental and sediment characteristics, sorb or desorb P, altering the bioavailability of P loads by altering the concentration of dissolved P. We hypothesized that sorption and desorption rates would differ between low and high flow because runoff delivers new sediment and increases stream water dissolved P. We also expected sorption rates to decline with stream size because sediment in larger streams can be more P saturated. To test these hypotheses, we conducted two surveys focused on P exchange during spring high flow events and summer low flow periods in the Maumee watershed, which plays an important role in shaping Lake Erie HABs. For both surveys, we sampled streams across a size gradient and measured rates of P sorption and desorption in sediment as well as aspects of sediment composition that likely influence exchange rates. Our results indicate that sediment sorbed P under both low flow and high flow. Under low flow, P sorption rate declined with stream size and was related to sediment organic matter and iron content. Under high flow, P sorption rate was not related to stream size or aspects of sediment composition. Our results help clarify factors influencing P sorption rates and could be used to identify streams that play an important role in shaping P exports.

Primary Presenter: Devan Mathie, The Ohio State University (mathie.22@buckeyemail.osu.edu)

Authors:

Laura Johnson, National Center for Water Quality Research  (ljohnson@heidelberg.edu)

Rebecca Kreiling, USGS  (rkreiling@usgs.gov)

Audrey Sawyer, The Ohio State University  (sawyer.143@osu.edu)

Christopher Spiese, Ohio Northern University  (c-spiese.1@onu.edu)

Jim Hood, The Ohio State University  (hood.211@osu.edu)