California Water Science Center
Agricultural Chemicals: Sources, Transport, and Fate (ACT)
ACT is trying to answer the following question:
How do environmental processes and agricultural practices interact to affect the transport and fate of agricultural chemicals in the hydrologic system of nationally important agricultural settings, and what are the effects on water quality and implications for management of water resources?
How will ACT answer this question:
The key aspect of the study approach is to investigate the sources, transport, and fate of selected agricultural chemicals in a variety of agricultural settings across the Nation. Each study unit of the ACT study will select an indicator watershed that represents a nationally important agricultural setting. The indicator stream watershed will define the primary area of the ground-water system for these studies. A smaller subbasin will be paired with the indicator stream for the studies. The multiple scales are necessary to understand how the natural hydrologic setting and the superimposed agricultural system interact to affect the fate of agricultural chemicals in the watersheds.
Cycle I data will be used to develop a conceptual and semi-quantitative mass-balance model to describe the sources, transport and fate of selected, important agricultural chemicals used in the watersheds, usually nitrogen and an important pesticide. This model will describe the hydrologic compartments through which transport occurs, important transformations that occur within each compartment, factors that control transformation rates, estimated residence times within each compartment, and fluxes between compartments. Data will be collected from the nested watersheds. Based on these Cycle II data, the conceptual model will be tested, adjusted, and refined by using mass-balance and numerical modeling (process and statistical).
By contrasting and comparing results from a variety of scales and a variety of settings, the study will (1) assess the influence of differing agricultural practices on water quality and the ecosystem, and (2) assess the degree to which methods and results from this work can be successfully transferred to larger scales or to different settings.
Specific objectives of ACT for each agricultural setting:
The area of focus for the SANJ ACT is the Merced River watershed. The SANJ ACT is located within the regional ground-water flow model of the SANJ TANC and will benefit from the characterization of the regional ground-water flow system. More detailed surface-water modeling, using TOPMODEL and SWAT, will be carried out on the Mustang Creek subbasin. The study components for the SANJ ACT are broken out in three broad hydrologic compartments: atmosphere, surface water, and ground water.
Sampling activities for SANJ ACT
ACT project sampling activities are shown on the following video clips. Click on photo to view video
Results of the SANJ ACT Study