D. E. Beaudette

Litter contributions to dissolved organic matter and disinfection byproduct precursors in California oak woodland watersheds.

Export of dissolved organic matter (DOM) from California oak woodland ecosystems is of a great concern because DOM is a precursor for carcinogenic disinfection byproducts (DBPs) formed during drinking water treatment. Fresh litter and decomposed duff materials for the four dominant vegetation components of California oak woodlands: blue oak (Quercus douglassi H. & A.), live oak (Quercus wislizenii A. DC.), foothill pine (Pinus sabiniana Dougl.), and annual grasses, were exposed in natural condition for an entire rainy season (December to May) to evaluate their contributions of particulate (POC) and dissolved (DOC) organic carbon, particulate (PON) and dissolved (DON) organic nitrogen, inorganic nitrogen (NH4+ and NO3-), and trihalomethane (THM) and haloacetonitrile (HAN) formation potentials, to surface waters. Litter and duff materials can be significant sources of DOC (litter=29-126 mg DOC g(-1) C; duff=6.5-37 mg DOC g(-1) C) and THMs and HANs (up to 4600 mg-THMs g-C(-1) and 137 microg-HANs g-C(-1)). Blue oak litter had the highest yield of DOC, THM, and HAN precursors. When scaled to the entire watershed, leachate production yielded 445 kg-DOC ha(-1), as compared to DOC export via streams of 5.25 kg-DOC ha(-1). DOC transport to surface waters is facilitated by subsurface lateral flow through A horizons during storm events. The majority of DOM and DBP precursors was leached from plant materials in the initial rainfall events and thus may explain the seasonal stream pattern of a DOC pulse early in the rainy season.

California Simulation of Evapotranspiration of Applied Water and Agricultural Energy Use in California

Abstract The California Simulation of Evapotranspiration of Applied Water (Cal-SIMETAW) model is a new tool developed by the California Department of Water Resources and the University of California, Davis to perform daily soil water balance and determine crop evapotranspiration (ET c ), evapotranspiration of applied water (ET aw ), and applied water (AW) for use in California water resources planning. ET aw is a seasonal estimate of the water needed to irrigate a crop assuming 100% irrigation efficiency. The model accounts for soils, crop coefficients, rooting depths, seepage, etc. that influence crop water balance. It provides spatial soil and climate information and it uses historical crop and land-use category information to provide seasonal water balance estimates by combinations of detailed analysis unit and county (DAU/County) over California. The result is a large data base of ET c and ET aw that will be used to update information in the new California Water Plan (CWP). The application uses the daily climate data, i.e., maximum (T x ) and minimum (T n ) temperature and precipitation (P cp ), which were derived from monthly USDA-NRCS PRISM data (PRISM Group 2011) and daily US National Climate Data Center (NCDC) climate station data to cover California on a 4 km×4 km change grid spacing. The application uses daily weather data to determine reference evapotranspiration (ET o ), using the Hargreaves-Samani (HS) equation (Hargreaves and Samani 1982, 1985). Because the HS equation is based on temperature only, ET o from the HS equation were compared with CIMIS ET o at the same locations using available CIMIS data to determine correction factors to estimate CIMIS ET o from the HS ET o to account for spatial climate differences. Cal-SIMETAW also employs near real-time reference evapotranspiration (ET o ) information from Spatial CIMIS, which is a model that combines weather station data and remote sensing to provide a grid of ET o information. A second database containing the available soil water holding capacity and soil depth information for all of California was also developed from the USDA-NRCS SSURGO database. The Cal-SIMETAW program also has the ability to generate daily weather data from monthly mean values for use in studying climate change scenarios and their possible impacts on water demand in the state. The key objective of this project is to improve the accuracy of water use estimates for the California Water Plan (CWP), which provides a comprehensive report on water supply, demand, and management in California. In this paper, we will discuss the model and how it determines ET aw for use in water resources planning.