Location: Pasture Systems & Watershed Management Research
Project Number: 8070-13000-015-018-I
Project Type: Interagency Reimbursable Agreement
Start Date: Sep 1, 2021
End Date: Jul 30, 2026
Objective:
The overall goal of this project is to understand the contribution and processes of legacy phosphorus to loads at edge-of-field and small watershed scales to develop conservation strategies for legacy phosphorus mitigation. Specific project objectives are to (1) develop common data base and use state-of-the-art analytical techniques to quantify the contribution of legacy phosphorus to runoff loads at field and small watershed scales; (2) characterize legacy phosphorus sources and mobilization processes within study watersheds; and (3) develop watershed-specific recommendations for the mitigation of legacy phosphorus associated with agriculture.
Approach:
ARS will conduct a spatial sampling of legacy P in soils to characterize critical source areas (CSAs) of legacy P loss in two watersheds: the WE-38 watershed, a small headwater tributary to Mahantango Creek, and in Conewago Creek. Sampling efforts will be guided by past studies of CSAs that have relied on topographically-derived metrics like the topographic wetness index (TWI) and its variants to locate hydrologically active areas of the landscape. In addition to spatial surveys of legacy P CSAs, we will also conduct a synoptic survey of stream sediments for legacy P characterization and metrics like the equilibrium P concentration at zero net sorption or desorption (EPC0), which provides insight into baseflow P dynamics in streams. The synoptic stream survey will leverage an existing network of stream sampling nodes used in past synoptic water quality sampling campaigns in WE-38. In addition to collecting stream sediments for P metrics, we will also characterize water quality conditions at each location. Sediment samples will be collected during low flow conditions. To estimate legacy P loads, we will select three watershed monitoring locations in WE-38 (Mattern, FD-36, and the outlet of WE-38) and two locations in Conewago Creek (USGS gauges at Bellaire and Falmouth) and compile hydrologic and water quality data in support of a multi-location study that seeks to estimate the proportion of watershed P losses from legacy P sources. Scientists and technicians from PSWMRU will work with the project leads to estimate watershed P loads using Weighted Regressions on Time, Discharge, and Seasons (WRTDS) and will leverage findings from the legacy P characterization efforts to inform WRTDS estimates of legacy P losses from the WE-38 and Conewago Creek watersheds. In addition to the aforementioned field campaigns, PSMWRU's analytical facilities will serve as the central laboratory that provides common analyses of P concentrations and related agronomic metrics in soils and sediments from all participating research locations. This portion of the project will focus on the development and use of various laboratory techniques intended to characterize different P pools in soil, water, and sediment samples. In addition, several common analyses will be performed to characterize soil nitrogen and carbon to aid in the characterization of legacy P hotspots.
