Catchment and in-stream processing contributions to sediment and phosphorus fluxes from a Midwest USA watershed
Abstract
Many agricultural watersheds within the midwestern USA have water quality concerns regarding sediment and phosphorus. Export of both sediment and phosphorus rely on a cascade of catchment and in-stream processes including source, transport and storage., each with their own range of timescales. With this contribution, we show several lines of evidence that key processes differ from upstream to downstream within a 20 square mile agricultural watershed within the Lower Fox River, Wisconsin, USA. A series of observations, experiments, and modeling efforts from reach to catchment scale highlight the importance of spatial and temporal scale as well as connectivity between the landscape and stream network for the [assessment] of sediment and phosphorus legacy and its continuum between agricultural fields and the catchment outlet. In this flashy watershed, events account for the vast majority of sediment and phosphorus transport. In the upper watershed, hysteresis and flushing indicies under storm flow conditions throughout the growing season indicate distal or landscape sources, while the same indicies at the outlet gage show the importance of near-stream and in-stream sources. Baseflow transport velocities are slow enough that it would take years for field-eroded sediment upstream to travel to the outlet gage. Equilibrium phosphorus concentrations are highest in upstream adjacent fields and decrease moving into and down the stream network. Throughout the stream network, sediments act as a sink rather than a source for P under baseflow conditions. Agricultural fields with a grassed waterway show sediment eroding with a different age than those without the best management practice. We will also show estimates of suspended sediment age throughout the fluvial network. Taken together, these studies show the importance of upstream processes and timescales for understanding catchment export of sediment and phosphorus, particularly for estimating water quality responses to landscape management in light of a long tail of legacy phosphorus.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.H32U1198K