Water Quality Management in Irrigated Pastures Runoff.

Dissolved organic matter (DOM) is a reactant in the formation of trihalomethanes (THMs) during drinking water chlorination treatment. THMs are a health concern since they are potential sources for different types of cancer and pregnancy problems. Agricultural irrigation can be a significant source of DOM in streams, but DOM fluxes, especially pastures, are poorly quantified. Therefore, we monitored DOM - carbon (DOC) and - nitrogen (DON), and THM formation potential (THMFP) in runoff water originating from irrigated pastures in the Sierra Nevada foothills in California. 2m wide vegetative buffer strips were installed to filter out these water pollutants. This study also searched for accessible chromophoric DOM (CDOM) approaches as proxies to the high cost THMFP laboratory analysis. Although buffers effectively controlled loads of pasture derived THM in runoff these filters can also be a source of DOC and DON, depending on irrigation management strategies. Moreover, we identified significant correlation with CDOM optical spectrum slopes and THMFP (R²=0.42) yet this model needs further improvements. In conclusion, a trade-off exists with the use of buffers to mitigate different pollutants, i.e. buffers can reduce loads of some pollutants or increase loads at specific conditions. Furthermore, CDOM proxies that could identify potential THM reactants need more development before they can be effectively used as indicators in other agricultural systems.