APEX simulation: Water quality of Sacramento Valley wetlands impacted by waterfowl droppings

Authors: KIM, SUMIN - Oak Ridge Institute For Science And Education (ORISE); JEONG, JAEHAK - Texas Agrilife Research; KAHARA, SHARON - Humboldt State University; KIM, SOJUNG - Texas A&M University; Kiniry, James

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2020
Publication Date: 10/6/2020
Citation: Kim, S., Jeong, J., Kahara, S.N., Kim, S., Kiniry, J.R. 2020. APEX simulation: Water quality of Sacramento Valley wetlands impacted by waterfowl droppings. Journal of Soil and Water Conservation. 75(6):713-726. https://doi.org/10.2489/jswc.2020.00117.
DOI: https://doi.org/10.2489/jswc.2020.00117

Interpretive Summary: The Sacramento Valley of California is the most important wintering site for migratory waterfowl on the Pacific Flyway. More than 90% of its wetlands have been lost or degraded due to agricultural and urban development. Most remaining wetlands are managed for wintering waterfowl. However, many remaining wetlands are threatened by increasing frequency of extreme weather events such as drought. Most remaining wetlands are dependent on pumping water. Thus, supplying this water is a great challenge to wetland managers, especially during drought. In order to assure the needed water is available for waterfowl habitat management and improvement of water quality, simulation models are needed. These simulate various processes in wetlands. The Agricultural Policy Environmental eXtender (APEX) model was used to simulate managed wetlands in the Sacramento Valley. The model simulated wetting and drying of wetland soils, wetland plant species, settling of sediment, and nitrogen (N) removal. The model simulated four wetlands and was validated using actual measured data from 2015-2018. Based on the results of the model, the wetland water quality is influenced by waterfowl populations and eventually governed by water availability in each wetland pool. The N removal by wetlands was negatively affected by the volume of irrigation water. According to the results, the developed model can be effectively used to quantify the effects of wetland management on water balance, water quality, and vegetation and to optimize wetland management, water use, and ecosystem service functions of managed wetlands.

Technical Abstract: The Sacramento Valley of California is the most important wintering site for migratory waterfowl on the Pacific Flyway. To date, 90-95 % of its historic wetlands are lost or degraded due to agricultural and urban development. Most remaining wetlands are intensively managed to maximize resources for wildlife, particularly wintering waterfowl. However, many remaining wetlands are threatened by increasing frequency of extreme weather events such as drought. Since most remaining wetlands are dependent on artificial water delivery, supplying water for wetland management is the greatest challenge to wetland managers, especially during drought years. Efforts are needed to improve the security of water supplies for optimal habitat management and water quality improvement. Eco-hydrologic modeling of wetland systems is an effective technique for assessing various biophysical processes occurring in wetlands. The Agricultural Policy Environmental eXtender (APEX) model was used to simulate managed wetlands in the Sacramento Valley. Key components evaluated in the wetland simulation included wetting and drying of wetland soils, competition and response of wetland species to wetland hydrology, settling of sediment, and nitrogen (N) removal. APEX models for four serially connected wetlands were validated using actual wetland plant morphological traits, water quantity and quality variables monitored for three years (2015-2018). Based on the results of the model, the wetland water quality is influenced by waterfowl populations and eventually governed by water availability in each wetland cell. The N removal by wetlands was negatively affected by the volume of irrigation water. According to the results, the developed model can be effectively used to quantify the effects of wetland management on water balance, water quality, and vegetation and to describe the nexus of wetland management, water use, and ecosystem service functions of managed wetlands.