Citation:

Wang, R., R. Bingner, G. Herring, Y. Yuan, Y. Luo, M. Locke, AND M. Zhang. Simulating Rice Pesticide Runoff at Basin Level via an Integrated RICEWQ-AnnAGNPS Modeling System. 2019 AGU Fall Meeting, San Francisco, CA, December 09 - 13, 2019.

Impact/Purpose:

Tens of thousands of chemicals are currently in use, and hundreds more are introduced into the market every year; however, only a small fraction have been thoroughly evaluated for potential risks to human health, wildlife, and the environment. Multiple EPA programs and regional offices must make risk-based decisions for addressing chemicals with inadequate or non-existent hazard. Current toxicity testing methods are expensive and time consuming, and approaches for characterizing impacts across the chemical/product life cycle are data and resource intensive. Thus, ecological modeling needs to be studied to advance efficient methods for improving risk assessments with limited data availability. This study focused on integrating a field scale model (RICEWQ) with a watershed water quality model (AnnAGNPS) to assess impacts of pesticide use on endangered and threatened aquatic species to provide practical and technical recommendations to address the many challenges facing EPA's risk assessment practices.

Description:

Thiobencarb is a widely applied herbicide in Northern California rice fields. The offsite movement of thiobencarb residues from upstream rice fields has potential to threaten non-targeted aquatic species living in the downstream waterbodies. Ecohydrological models are often employed to evaluate the fate and transport of pesticide at watershed scale. However, it is difficult to correctly reflect pesticide fate in both water and paddy sediment phase, because of the relatively complicated hydrological and water quality conditions (ponded condition, irrigation/drainage management) of rice fields. Models designed specifically for rice pesticide simulation are often at a field scale, and pesticide transport to and in-stream channel system is lacking. Furthermore, for a complicated watershed including rice farming, an integrated modeling system is needed not only to take loadings from rice fields, but also from other land uses such as orchards. To fill these research gaps, we integrated the field level RICEWQ model with watershed level AnnAGNPS model, with RICEWQ simulating rice farming and AnnAGNPS simulating other land uses as well as stream processes. The objective of this study is to demonstrate the application of this newly integrated modeling system in the Colusa River basin, where rice is the dominant crop, but also has a lot of other land uses. Detailed irrigation information was collected for non-rice crops to better reflect the runoff volumes in summer season, when rainfall is usually not available in this typical Mediterranean-like climate region. We calibrated and validated the integrated modeling system using data collected at Colusa Basin Drain station 5 (CBD5). Furthermore, to increase the simulation efficiency for each iteration during model calibration, the newly developed AnnAGNPS Subsetting Tool for Independent Runs (ASTIR) was used to extract information from a large AnnAGNPS watershed dataset, and then invoke multiple instances of AnnAGNPS to run concurrently on the subsets.

Record Details: