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Media Advisory: Highlights of USGS Science in the Sacramento-San Joaquin Delta presented at the 2007 American Geophysical Union Meeting
Released: 12/10/2007 1:01:17 PM

Contact Information:
U.S. Department of the Interior, U.S. Geological Survey
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Stephanie Hanna 1-click interview
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Phone: 650-454-7264

The Effect of Land-Surface Subsidence Processes on the Remaining Peat in the Sacramento-San Joaquin Delta (H11C-0654)

de Fontaine, C S and Drexler, J Z

The Sacramento-San Joaquin Delta was once a tidal wetland that was drained and reclaimed for agricultural production beginning in the mid-nineteenth century. Drainage of the organic peat soils has resulted in land-surface subsidence in the region to as much as 8 m below sea level. Although the factors causing land-surface subsidence are well known (principally oxidation of organic matter), little is known about the physical and chemical condition of the remaining peat. As part of a project called Rates and Evolution of Peat Accretion through Time in the Delta, the physical and chemical condition of the remaining peat layer was studied on four farmed islands and four relatively undisturbed marsh islands. Peat cores were collected from all sites using a modified Livingstone corer. Core samples were analyzed for bulk density, percent organic matter and carbon, and for radiocarbon. Join us to hear how more than a century of agricultural practices have altered the condition of the remaining peat layer.

Monday, December 10, 8:00 AM MS Exh Hall B

Explorating Coupled Production of Dissolved Organic Material and Methyl Mercury in a Tidal Wetland Using the Intrinsic Chemical Composition of the Organic Material (B11B-0399)
Bergamaschi, Brian, Fleck, Jacob, Downing, B, et al.

Elevated methyl mercury (MeHg) levels found in biota of the San Francisco Estuary have been attributed to methylation processes in the peat-rich tidal wetlands of the Estuary, where the concentration of dissolved organic matter (DOM) is tightly coupled to that of MeHg. We sought to understand the geochemical processes that contribute to MeHg production by examining the composition of the co-occurring DOM. Come see more about our study and the relationships we found between DOM and MeHg.

Monday, December 10, 8:00 AM MS Exh Hall B

Mercury Cycling in Agricultural and Non-agricultural Wetlands in the Yolo Bypass Wildlife Area, California: Water Column Processes (B11B-0394)
Fleck, Jacob, Alpers, Charlie, Downing, B D, et al.

Organic matter (OM) plays a significant role in mercury (Hg) cycling. For instance, aromatic dissolved OM can enhance Hg solubility leading to greater cycling in the water column whereas bioavailable forms of OM may enhance Hg methylation by increasing the microbial activity of Hg-methylating bacteria. Differences in wetland management (e.g. fertilization, plant residue, water depth and movement) can influence the character of OM within the wetland, thus affecting Hg cycling as well. This study is investigating the role of OM in Hg cycling over a wide range of time scales and wetland management practices within the Yolo Bypass Wildlife Area.

We are comparing Hg and methylmercury (MeHg) concentrations in the water columns of three agricultural field types (wild rice, white rice, and shallow-flooded fallow) with those in two non-agricultural field types (seasonal and permanent wetlands).

Monday, December 10, 8:00 AM MS Exh Hall B

Bioaccumulation of Mercury in Small Fish in the Yolo Wildlife Area (B11B-0415)
Ackerman, J T, Eagles-Smith, C A, et al.

We examined the bioaccumulation of mercury in small fish within white rice, wild rice, and permanent wetland habitats at the Yolo Wildlife Area during the 2007 rice growing season. We introduced 30 mosquito fish in each of four cages placed at the inlet, center, and outlet (two cages) of each wetland in June, immediately after the white rice fields were re-flooded after being seeded. All fish were removed from their cages 60-days after their introduction, with the exception that ten fish from each of the second cages at the outlets were removed 30-days after introduction to assess temporal trends in mercury exposure. Mercury concentrations will be compared between fish that were introduced into cages and reference fish that originated from the same fish stock (Sacramento County Vector Control). We also measured fish length and mass both when they were introduced and collected to 1) control for growth effects on mercury bioaccumulation and 2) examine whether wetland habitat influenced growth rates. Fish are currently being analyzed for mercury and results will be available by the conference.

Monday, December 10, 8:00 AM MS Exh Hall B

Diurnal Variability in Riverine Dissolved Organic Matter Composition Determined by in Situ Optical Measurement in the San Joaquin River (H13A-0961)
Downing, B D, Spencer, R G, Pellerin, B A, Bergamaschi, Brian, Kraus, Tamara, et al.

Rivers have been commonly perceived as homogeneous with respect to dissolved organic matter (DOM) concentration and composition, particularly under steady flow conditions over short time periods. Few studies have evaluated the impact of short-term variability (<1 day) on DOM dynamics. In this session we present results from a 2006 study in the San Joaquin River where we evaluated the efficacy of using in situ optical measurements of absorption and fluorescence to elucidate changes in DOM composition. The results of this study highlight that short-term variability in DOM composition may complicate trends for studies aiming to distinguish different DOM sources in riverine systems and emphasizes the importance of sampling specific study sites to be compared at the same time of day. The utilization of in situ optical technology allows short-term variability in DOM dynamics to be monitored and serves to increase our understanding of its processing and fundamental role in the aquatic environment.

Monday, December 10, 1:40 PM MS Exh Hall B

A Geochemical Approach to Assessing the Relative Contributions of Rivers, Wetlands and Island Drains to Dissolved Organic Matter in the Sacramento-San Joaquin River Delta (B13G-03)
Kraus, Tamara E., Bergamaschi, Brian, et al.

The Sacramento-San Joaquin River Delta (Delta) is a hydrologically complex system that, in addition to being used for crop production, development, and recreation, provides drinking water to over 23 million Californians. Understanding how existing Delta habitats currently affect dissolved organic matter (DOM) dynamics seasonally will help us predict how future changes in land use might influence water quality. This study assessed whether different sources (rivers, wetlands, open water, island drains) contribute DOM to the Delta, examined the composition of the added DOM, and then assessed the relative importance of DOM derived from these sources to the quality of water arriving at Clifton Court for export into the California State Water Project.

Monday, December 10, 2:10 PM MW 2008

Mercury Cycling in Agricultural and Non-agricultural Wetlands of the Yolo Bypass Wildlife Area, California: Sediment Biogeochemistry (B14B-03)
Marvin-DiPasquale, Mark, Windham-Myers, L.,et al.

The Yolo Bypass Wildlife Area (YBWA) is part of the larger Yolo Bypass floodwater protection zone associated with the Sacramento River and the Sacramento-San Joaquin Delta. Land use in the YBWA consists of white and wild rice fields, seasonally flooded fallow agricultural fields, and permanently and seasonally flooded non-agricultural wetlands used for resident and migratory waterfowl. A recent assessment of mercury (Hg) and methylmercury (MeHg) loads indicates that the Yolo Bypass is responsible for a high proportion of the aqueous MeHg entering the Delta, and that biota from the Yolo Bypass are considerably elevated in MeHg. The current study examines benthic MeHg production and biogeochemical controls on this process, as a function of YBWA land use, wetland management, and agricultural practices during the 2007 rice growing season (June to October).

Monday, December 10, 4:40 PM MW 2006

Constraints on the Rupture of the October 21, 1868, Hayward Earthquake Determined From the Distribution of Modified Mercalli Intensity (S23C-01)
Boatwright, J., Bundock, H.

The October 21, 1868, Hayward earthquake was the most damaging earthquake to occur in California in the half- century following the 1848 annexation. The earthquake shattered the city centers of Oakland and San Francisco, and cracked brick buildings as far away as Santa Rosa and Gilroy. We have re-evaluated MMI intensities at the 124 sites with damage or felt reports compiled by Toppozada et al. (1981), and added 26 sites where we obtained reports from newspapers and historical narratives. Come listen to more information that we collected and compile to create a ShakeMap showing the intensity of the earthquake through the greater Bay Area and the San Joaquin Delta.

Tuesday, December 11, 1:40 PM MW 3014

Dissolved Organic Carbon as a Drinking Water Constituent of Concern in California Agricultural Watersheds (H41C-0665)
Pellerin, B A., Bergamaschi, Brian, et al.

Dissolved organic carbon (DOC) from the breakdown of plant and animal material is a concern for drinking water quality in California due to the potential formation of carcinogenic byproducts during disinfection. Agricultural DOC loading to surface water is a significant concern, but the sources and reactivity in agricultural runoff remains poorly understood. In this session we present data on DOC dynamics in surface water from the Willow Slough watershed, a 425\- km2 agricultural catchment in the Sacramento Valley, California. Additional data from plant leachates and ground water will be discussed, as well as the implications of watershed management on DOC dynamics and reactivity in agriculturally-dominated landscapes.

Thursday, December 13, 8:00 AM MS Exh Hall B

Tracing Seasonal Nitrate Sources and Loads in the San Joaquin River using Nitrogen and Oxygen Stable Isotopes (H41C-0652)
Young, M B., Kendall, Carol, Silva, Steve, et al.

The San Joaquin River (SJR) is a heavily impacted river draining a major agricultural basin in central California. This river receives nitrate inputs from multiple point and non-point sources including agriculture, livestock, waste water treatment plants, septic systems, urban run-off, and natural soil leaching. Nitrate inputs to the SJR may play a significant role in driving algal blooms and reducing overall water quality. The San Joaquin River discharges into the San Francisco Bay-Delta ecosystem, and reduced water quality and large algal blooms in the SJR may play a significant role in driving critically low oxygen levels in the Stockton Deep Water Shipping Channel. Correct identification of the major nitrate sources to the SJR is important for coordinating mitigation efforts throughout the SJR-Delta-San Francisco Bay region.

Measurements of the nitrogen and oxygen isotopic composition of nitrate were made monthly to bimonthly from 2005 through 2007 within the Lower SJR, major tributaries, and various other water input sources in order to assess spatial and temporal variations in nitrate inputs and cycling in this heavily impacted watershed. The oxygen and hydrogen isotopic composition of water was also measured to better distinguish water sources and identify changes in water inputs.

Thursday, December 13, 8:00 AM MS Exh Hall B

Earthquake Study Assesses Risk to San Joaquin/Sacramento River Delta Levees (S53B-1270)
Fletcher, J and Boatwright, J

The Sacramento/San Joaquin River Delta lies on the western edge of the Great Valley and contains a system of levees that are thought to be prone to catastrophic failure from a major earthquake in the San Francisco Bay area or on faults along the western border of the Great Valley. The seismic site response, which is an important part of any estimate of seismic hazard, was assessed at three levee sites in the Delta using digital recorders and broadband sensors. The experiment ran for a nine-month period from late 2006 to middle of 2007. Recordings of seismic events show that many of the sites are subject to large resonances that may represent a substantial risk to the levees. Come listen to techniques used and results found from this study.

Friday, December 14, 1:40 PM MS Exh Hall B

Nitrate and Dissolved Organic Carbon Concentrations in Riparian-Zone Ground Water of the Lower San Joaquin River (H54D-04)
Kratzer, C R, Bergamaschi, Brian, et al.

Previous studies have estimated ground water inputs to the San Joaquin River (SJR) could contribute up to 15 percent of downstream flow during the summer. However, there is a paucity of information concerning the chemical composition of ground water accretions in the lower SJR. The objective of this study was to quantify the amount of ground water accretions to the lower SJR and its nitrate and dissolved organic compound (DOC) contributions to the river. Come listen to the results of this study to date and find out the future aspects of this study that will estimate the rates of ground water flow into the SJR and the amount and source of nitrate and organic carbon contributed as a result.

Friday, December 14, 4:45 PM MW 2016

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