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Davis, CA, United States

Henneberry Y.K.,University of California at Davis | Kraus T.E.C.,U.S. Geological Survey | Fleck J.A.,U.S. Geological Survey | Krabbenhoft D.P.,U.S. Geological Survey | And 2 more authors.
Science of the Total Environment | Year: 2011

The presence of inorganic mercury (IHg) and methylmercury (MeHg) in surface waters is a health concern worldwide. This study assessed the removal potential use of metal-based coagulants as a means to remove both dissolved IHg and MeHg from natural waters and provides information regarding the importance of Hg associations with the dissolved organic matter (DOM) fraction and metal hydroxides. Previous research indicated coagulants were not effective at removing Hg from solution; however these studies used high concentrations of Hg and did not reflect naturally occurring concentrations of Hg. In this study, water collected from an agricultural drain in the Sacramento-San Joaquin Delta was filtered to isolate the dissolved organic matter (DOM) fraction. The DOM was then treated with a range of coagulant doses to determine the efficacy of removing all forms of Hg from solution. Three industrial-grade coagulants were tested: ferric chloride, ferric sulfate, and polyaluminum chloride. Coagulation removed up to 85% of DOM from solution. In the absence of DOM, all three coagulants released IHg into solution, however in the presence of DOM the coagulants removed up to 97% of IHg and 80% of MeHg. Results suggest that the removal of Hg is mediated by DOM-coagulant interactions. There was a preferential association of IHg with the more aromatic, higher molecular weight fraction of DOM but no such relationship was found for MeHg. This study offers new fundamental insights regarding large-scale removal of Hg at environmentally relevant regarding large-scale removal of Hg at environmentally relevant concentrations. © 2010 Elsevier B.V.

Geisseler D.,University of Kassel | Lazicki P.A.,University of California at Davis | Stuart Pettygrove G.,University of California at Davis | Ludwig B.,University of Kassel | And 2 more authors.
Agronomy Journal | Year: 2012

Optimal manure management that ensures adequate crop nutrition while avoiding pollution problems requires estimates of manure N availability. The present study was performed in the San Joaquin Valley (California) on three dairy forage production fields where liquid manure is applied together with flood irrigation water. The objective of this study was to determine the fate of manure N by combining field measurements with model simulations using the Root Zone Water Quality Model (RZWQM). The average annual N application to corn (Zea mays L.) and winter forage (oat [Avena sativa L.], triticale [×Triticosecale Wittmack], or Sudan grass [Sorghum bicolor (L.) Moench ssp. drummondii (Steud.) de Wetex Davidse]) was 840 kg N ha-1, while 490 kg N ha-1 was removed with the harvested crops. The irrigation water input to corn ranged from 45 to 128 cm. The RZWQM described crop yield and N uptake well and accurately simulated the seasonal trends in soil moisture and mineral N content in the top 90 cm of the profile; however, the short-term changes and mineral N estimates for different soil layers were not accurate. For soil nutrient and water dynamics, sitespecific calibration was an essential requirement. The model estimated that between 140 and 320 kg N ha-1 was leached in a 12-mo period and up to 80 kg N ha-1 was volatilized as NH3, while losses due to denitrification were insignificant in these sandy soils. Field data and model estimates highlight the potential for a more efficient water and N use in the forage systems studied. © 2012 by the American Society of Agronomy.

Hernes P.J.,University of California at Davis | Spencer R.G.M.,University of California at Davis | Spencer R.G.M.,Woods Hole Oceanographic Institution | Dyda R.Y.,University of California at Davis | And 3 more authors.
Geochimica et Cosmochimica Acta | Year: 2013

Willow Slough, a seasonally irrigated agricultural watershed in the Sacramento River valley, California, was sampled synoptically in order to investigate the extent to which dissolved organic carbon (DOC) concentrations and compositions from throughout the catchment are represented at the mouth. DOC concentrations ranged from 1.8 to 13.9mgL-1, with the lowest values in headwater 1st and 2nd order streams, and the highest values associated with flood irrigation. Carbon-normalized vanillyl phenols varied from 0.05 to 0.67mg 100mgOC-1 (0.37 mean), indicative of considerable contributions from vascular plants. DOC concentrations and compositions at the mouth appear to be primarily influenced by land use (agriculture) in the lower reaches, and therefore very little of the headwater chemistry (1st and 2nd order streams) can be discerned from the chemistry at or near the mouth (3rd and 4th order streams), indicating the need for synoptic sampling to capture the breadth of organic carbon cycling within a catchment. Field sampling during irrigation showed the large impact that flood irrigation can have on DOC concentrations and compositions, likely a primary cause of significantly elevated Willow Slough DOC concentrations during the summer irrigation season. Optical proxies exhibited varying degrees of correlation with chemical measurements, with strongest relationships to DOC and dissolved lignin (r2=0.95 and 0.73, respectively) and weaker relationships to carbon-normalized lignin yields and C:V (r2 from 0.31 to 0.42). Demonstrating the importance of matching scale to processes, we found no relationship between dissolved lignin concentrations and total suspended sediments (TSS) across all sites, in contrast to the strong relationship observed in weekly samples at the mouth. As DOC concentrations and compositions at the mouth of Willow Slough are closely tied to anthropogenic activities within the catchment, future changes in land-use driven by climate change, water availability, and economic pressures on crop types will also bring about changes in the overall biogeochemistry. © 2013 Elsevier Ltd.

Florsheim J.L.,University of California at Davis | Pellerin B.A.,U.S. Geological Survey | Oh N.H.,Seoul National University | Ohara N.,University of California at Davis | And 5 more authors.
Geomorphology | Year: 2011

The spatial and temporal variability of sediment sources, storage, and transport were investigated in a small agricultural watershed draining the Coast Ranges and Sacramento Valley in central California. Results of field, laboratory, and historical data analysis in the Willow Slough fluvial system document changes that transformed a transport-limited depositional system to an effective erosion and transport system, despite a large sediment supply. These changes were caused by a combination of factors: (i) an increase in transport capacity, and (ii) hydrologic alteration. Alteration of the riparian zone and drainage network pattern during the past ~150years included a twofold increase in straightened channel segments along with a baselevel change from excavation that increased slope, and increased sediment transport capacity by ~7%. Hydrologic alteration from irrigation water contributions also increased transport capacity, by extending the period with potential for sediment transport and erosion by ~6months/year. Field measurements document Quaternary Alluvium as a modern source of fine sediment with grain size distributions characterized by 5 to 40% fine material. About 60% of an upland and 30% of a lowland study reach incised into this deposit exhibit bank erosion. During this study, the wet 2006 and relatively dry 2007 water years exhibited a range of total annual suspended sediment load spanning two orders of magnitude: ~108,500kg/km2/year during 2006 and 5,950kg/km2/year during 2007, only 5% of that during the previous year. Regional implications of this work are illustrated by the potential for a small tributary such as Willow Slough to contribute sediment - whereas large dams limit sediment supply from larger tributaries - to the Sacramento River and San Francisco Bay Delta and Estuary. This work is relevant to lowland agricultural river-floodplain systems globally in efforts to restore aquatic and riparian functions and where water quality management includes reducing fine sediment contributions that can couple with other pollutants. © 2011 Elsevier B.V.

Oh N.-H.,Seoul National University | Pellerin B.A.,U.S. Geological Survey | Bachand P.A.M.,Bachand and Associates | Hernes P.J.,University of California at Davis | And 5 more authors.
Agriculture, Ecosystems and Environment | Year: 2013

We investigated the role of land use/land cover and agriculture practices on stream dissolved organic carbon (DOC) dynamics in the Willow Slough watershed (WSW) from 2006 to 2008. The 415km2 watershed in the northern Central Valley, California is covered by 31% of native vegetation and the remaining 69% of agricultural fields (primarily alfalfa, tomatoes, and rice). Stream discharge and weekly DOC concentrations were measured at eight nested subwatersheds to estimate the DOC loads and yields (loads/area) using the USGS developed stream load estimation model, LOADEST. Stream DOC concentrations peaked at 18.9mgL-1 during summer irrigation in the subwatershed with the highest percentage of agricultural land use, demonstrating the strong influence of agricultural activities on summer DOC dynamics. These high concentrations contributed to DOC yields increasing up to 1.29gm-2 during the 6 month period of intensive agricultural activity. The high DOC yields from the most agricultural subwatershed during the summer irrigation period was similar throughout the study, suggesting that summer DOC loads from irrigation runoff would not change significantly in the absence of major changes in crops or irrigation practices. In contrast, annual DOC yields varied from 0.89 to 1.68gm-2yr-1 for the most agricultural watershed due to differences in winter precipitation. This suggests that variability in the annual DOC yields will be largely determined by the winter precipitation, which can vary significantly from year to year. Changes in precipitation patterns and intensities as well as agricultural practices have potential to considerably alter the DOC dynamics. © 2013 Elsevier B.V.

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