Minerals of California Bulletin No. 113

State of California | February 15th, 1938

Regional nitrate and pesticide trends in ground water in the eastern San Joaquin Valley, California

American Society of Agronomy (ASA) | September 18th, 2008

Protection of ground water for present and future use requires monitoring and understanding of the mechanisms controlling long-term quality of ground water. In this stu

Protection of ground water for present and future use requires monitoring and understanding of the mechanisms controlling long-term quality of ground water. In this study, spatial and temporal trends in concentrations of nitrate and pesticides in ground water in the eastern San Joaquin Valley, California, were evaluated to determine the long-term effects of agricultural and urban development on regional ground-water quality. Trends in concentrations of nitrate, the nematocide 1,2-dibromo-3-chloropropane, and the herbicide simazine during the last two decades are generally consistent with known nitrogen fertilizer and pesticide use and with the position of the well networks in the regional ground-water fl ow system. Concentrations of nitrate and pesticides are higher in the shallow part of the aquifer system where domestic wells are typically screened, whereas concentrations are lower in the deep part of the aquifer system where public-supply wells are typically screened. Attenuation processes do not seem to significantly affect concentrations. Historical data indicate that concentrations of nitrate have increased since the 1950s in the shallow and deep parts of the aquifer system. Concentrations of nitrate and detection of pesticides in the deep part of the aquifer system will likely increase as the proportion of highly affected water contributed to these wells increases with time. Because of the time of travel between the water table and the deep part of the aquifer system, current concentrations in public-supply wells likely reflect the effects of 40- to 50-year-old management practices.

The Green Visions Plan for 21st Century Southern California: 21. Hydrology and Water Quality Modeling of the Calleguas Creek Watershed

University of Southern California (USC) | November 2nd, 2009

The hydrology and water quality simulation presented in this report is a part of the Green Visions Plan for 21st Century Southern California project. The primary

The hydrology and water quality simulation presented in this report is a part of the Green Visions Plan for 21st Century Southern California project. The primary focus of the Calleguas Creek Watershed water quality modeling is to determine the pollutant concentration and loads entering the stream network and to what degree surface waters are subject to water quality impairments.

Widespread deoxygenation in warming rivers

Nature Portfolio (Springer Nature) | September 14th, 2023

Deoxygenation is commonly observed in oceans and lakes but less expected in shallower, flowing rivers. Here we reconstructed daily water temperature and dissolved oxygen

Deoxygenation is commonly observed in oceans and lakes but less expected in shallower, flowing rivers. Here we reconstructed daily water temperature and dissolved oxygen in 580 rivers across the United States and 216 rivers in Central Europe by training a deep learning model using temporal weather and water quality data and static watershed attributes (for example, hydro-climate, topography, land use, soil). Results revealed persistent warming in 87% and deoxygenation in 70% of the rivers. Urban rivers demonstrated the most rapid warming, whereas agricultural rivers experienced the slowest warming but fastest deoxygenation. Mean deoxygenation rates (−0.038 ± 0.026 mg l−1 decade−1) were higher than those in oceans but lower than those in temperate lakes. These rates, however, may be underestimated, as training data are from grab samples collected during the day when photosynthesis peaks. Projected future rates are between 1.6 and 2.5 times higher than historical rates, indicating significant ramifications for water quality and aquatic ecosystems.