Assessing the effects of transient and long term phosphorous storage on the total phosphorous yields in distributed hydrologic model
On average most phosphorus (P) entering streams from agricultural fields arrives in particulate form (PP), and so a key to understanding long-term dynamics of P delivery to downstream water bodies is to use distributed hydrologic and sediment transport models. Most such models are keyed off of digital elevation models, and these underpredict P dynamics with respect to its deposition within stream channels. We showed that reservoirs could be used as an appropriate proxy for in-stream pools and suitable for quantifying in-channel sediment and PP storage in Dorn Creek, within the Mendota Watershed in southern Wisconsin. Our data suggest that the PP gives up soluble P (SP) during inter-storm periods, while PP is delivered during storms, and so actual P delivery downstream can be significantly delayed or modified en route. This has potential impact on downstream algae and other P consumers, and consequently is important for connected agricultural activities to water quality. In the nearly 10 km length Dorn Creek, total 47 points were sampled and analyzed to represent all stream conditions. Simulated and measured sediment and P storage were compared by placing reservoirs along the main channel sub-basins in the Agricultural Policy Environmental eXtender (APEX) model. We used the spatially distributed PP storage dynamics from APEX to drive a second model to release SP from in-stream storage and explain observed inter-storm SP discharge and long-term PP retention within the streams. The results support a need for improved model logic that deals with these complex PP-SP delivery processes.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 1847 Modeling;
- 1862 Sediment transport (4558);
- 1871 Surface water quality