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A Bayesian approach to infer nitrogen loading rates from crop and land-use types surrounding private wells in the Central Valley, California

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A Bayesian approach to infer nitrogen loading rates from crop and land-use types surrounding private wells in the Central Valley, California
European Geosciences Union | May 7, 2018...
Summary
This study is focused on nitrogen loading from a wide variety of crop and land-use types in the Central Valley, California, USA, an intensively farmed...
This study is focused on nitrogen loading from a wide variety of crop and land-use types in the Central Valley, California, USA, an intensively farmed region with high agricultural crop diversity. Nitrogen loading rates for several crop types have been measured based on field-scale experiments, and recent research has calculated nitrogen loading rates for crops throughout the Central Valley based on a mass balance approach. However, research is lacking to infer nitrogen loading rates for the broad diversity of crop and land use types directly from groundwater nitrate measurements.

Relating groundwater nitrate measurements to specific crops must account for the uncertainty about and multiplicity in contributing crops (and other land uses) to individual well measurements, and for the variability of nitrogen loading within farms and from farm to farm for the same crop type. In this study, we developed a Bayesian regression model that allowed us to estimate land-use-specific groundwater nitrogen loading rate probability distributions for 15 crop and land-use groups based on a database of recent nitrate measurements from 2149 private wells in the Central Valley.

The water and natural, rice, and alfalfa and pasture groups had the lowest median estimated nitrogen loading rates, each with a median estimate below 5 kg N ha -1 yr -1. Confined animal feeding operations (dairies) and citrus and subtropical crops had the greatest median estimated nitrogen loading rates at approximately 269 and 65 kg N ha -1 yr-1, respectively. In general, our probability-based estimates compare favorably with previous direct measurements and with mass-balance-based estimates of nitrogen loading. Nitrogen mass-balance-based estimates are larger than our groundwater nitrate derived estimates for manured and non-manured forage, nuts, cotton, tree fruit, and rice crops. These discrepancies are thought to be due to groundwater age mixing, dilution from infiltrating river water, or denitrification between the time when nitrogen leaves the root zone (point of reference for mass-balance derived loading) and the time and location of groundwater measurement.

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A Field Guide to the Identification of the Ordinary High Water Mark (OHWM) in the Arid West Region of the Western United States: A Delineation Manual

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A Field Guide to the Identification of the Ordinary High Water Mark (OHWM) in the Arid West Region of the Western United States: A Delineation Manual
U.S. Army Corps of Engineers, Cold Regions Research and Engineering Laboratory | August 1, 2008...
Summary
The Ordinary High Water Mark (OHWM) is an approach for identifying the lateral limits of non-wetland waters. However, determining whether any non-wetland water...

The Ordinary High Water Mark (OHWM) is an approach for identifying the lateral limits of non-wetland waters. However, determining whether any non-wetland water is a jurisdictional “Water of the United States” (WoUS) involves further assessment in accordance with the regulations, case law, and clarifying guidance. In the Arid West region of the U.S., the most problematic Ordinary High Water (OHW) delineations are associated with the ephemeral/intermittent channel forms that dominate the Arid West landscape. This report presents a method for delineating the lateral extent of the non-wetland waters in the Arid West using stream geomorphology and vegetation response to the dominant stream discharge.

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A hybrid machine learning model to predict and visualize nitrate concentration throughout the Central Valley aquifer, California, USA
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A hybrid machine learning model to predict and visualize nitrate concentration throughout the Central Valley aquifer, California, USA
Science of the Total Environment | June 9, 2017...
Summary
Intense demand forwater in the Central Valley of California and related increases in groundwater nitrate concentration threaten the sustainability of the groundwater resource....
Intense demand forwater in the Central Valley of California and related increases in groundwater nitrate concentration threaten the sustainability of the groundwater resource. To assess contamination risk in the region, we developed a hybrid, non-linear, machine learning model within a statistical learning framework to predict nitrate contamination of groundwater to depths of approximately 500m below ground surface.

A database of 145 predictor variables representing well characteristics, historical and current field and landscape-scale nitrogen mass balances, historical and current land use, oxidation/reduction conditions, groundwater flow, climate, soil characteristics, depth to groundwater, and groundwater age were assigned to over 6000 private supply and public supply wells measured previously for nitrate and located throughout the study area. The boosted regression tree (BRT) method was used to screen and rank variables to predict nitrate concentration at the depths of domestic and public well supplies.

The novel approach included as predictor variables outputs from existing physically based models of the Central Valley. The top five most important predictor variables included two oxidation/reduction variables (probability of manganese concentration to exceed 50 ppb and probability of dissolved oxygen concentration to be below 0.5 ppm), field-scale adjusted unsaturated zone nitrogen input for the 1975 time period, average difference between precipitation and evapotranspiration during the years 1971–2000, and 1992 total landscape nitrogen input.

Twenty-five variables were selected for the final model for log-transformed nitrate. In general, increasing probability of anoxic conditions and increasing precipitation relative to potential evapotranspiration had a corresponding decrease in nitrate concentration predictions.

Conversely, increasing 1975 unsaturated zone nitrogen leaching flux and 1992 total landscape nitrogen input had an increasing relative impact on nitrate predictions.

Three-dimensional visualization indicates that nitrate predictions depend on the probability of anoxic conditions and other factors, and that nitrate predictions generally decreased with increasing groundwater age.

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A Water Resources Data-Network Evaluation for Monterey County, California, Phase 3: Northern Salinas River Drainage Basin
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A Water Resources Data-Network Evaluation for Monterey County, California, Phase 3: Northern Salinas River Drainage Basin
U.S. Geological Survey, Monterey County Flood Control and Water Conservation District | December 15, 1990...
Summary
This report presents an evaluation of water resources data collection networks in the northern Salinas River drainage basin, Monterey County, California. The evaluation,...

This report presents an evaluation of water resources data collection networks in the northern Salinas River drainage basin, Monterey County, California. The evaluation, done in cooperation with the Monterey County Flood Control and Water Conservation District, covers both quantity and quality monitoring by precipitation, surface-water, and ground-water networks. The report describes existing networks in the study area and possible additional data collection.

The study identified 34 precipitation gages in the study area, of which 20 are active. The stations are concentrated in the northwestern part of the study area. Data are lacking for the eastern and southern parts of the study area, as well as the southwestern slopes of the Gabilan Range. No precipitation-quality networks were identified. Possible data-collection efforts for precipitation quality include monitoring for acid rain and for pesticides in precipitation.

The study identified 10 streamflow-gaging stations, of which 6 are active. To meet the objectives for streamflow networks that are outlined in the report, all sites could be reactivated, and two of the inactive sites could be relocated to improve the reliability of the data. Besides these stations, nine possible additional streamflow-gaging sites were identified.

The Monterey County Flood Control and Water Conservation District samples one surface-water site for suspended sediment, specific conductance, and chlorides. Several agencies have done water-quality sampling in the past, but only five sites are active. Reactivation of the 45 inactive sites might help to meet the various surface-water-quality objectives described in the report. Development of a stream-reach rating system also could help to identify parts of the study area most in need of sampling.

The Monterey County Flood Control and Water Conservation District maintains three networks to measure ground-water levels on a monthly basis, during peak irrigation, and at the end of the irrigation season. The District measures water levels in 318 wells. The only other network identified for this report was operated by the U.S. Geological Survey, and none of its five wells are active. The study identified 128 sections in which no ground-water-level monitoring is presently done. Well coverage is densest in the saltwater-intrusion areas near Castroville, California. Wells in the rest of the study area are more sparsely distributed and are concentrated down the center of the drainage basin in the alluvial ground-water basin.

The ideal initial baseline network of ground-water-quality wells would be an evenly spaced grid of index wells within each aquifer, with a density of one per section. Once baseline conditions were established, representative wells could be selected and monitored annually. As of 1985, the Monterey County Flood Control and Water Conservation District monitored 379 study wells in the area for various water-quality conditions. Other networks monitor (or propose the monitoring of) 135 wells. The District collects samples in summer months to monitor saltwater intrusion near Castroville.

Annual samples also are analyzed for chloride, specific conductance, and nitrate. Every 5 years, the District does a complete mineral analysis on each study well. Improvements in network coverage are suggested to better approximate ideal network coverage. The adequacy of wells in existing monitoring networks for representing actual conditions in the ground-water basins was not established conclusively.

Possible redundancy of information from existing networks was not evaluated statistically. Despite these limitations, this report does provide a basis for assessing the adequacy of ground-water-level networks in the study area. The computerized Geographic Information System (GIS) that is planned for Monterey County could easily use the information in this report for the needed initial analysis of network adequacy. The feasibility of management and analysis of large complicated data bases (such as the ground water networks identified in this report) is substantially improved through the use of state-of-the-art GIS tools now available.

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Adapting to Change: Utility Systems and Declining Flows

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Adapting to Change: Utility Systems and Declining Flows
California Urban Water Agencies (CUWA) | November 1, 2017...
Summary
During the recent historic drought, Californians responded to the call for emergency statewide water use reductions, which the state has recognized as a...

During the recent historic drought, Californians responded to the call for emergency statewide water use reductions, which the state has recognized as a highly successful outcome. However, this significant reduction in water demands has brought to light some unintended consequences of declining flows that ripple throughout the interconnected urban water cycle. These observations offer a preview into the potential impact of establishing permanent indoor water use targets at or below the thresholds achieved as a result of the governor’s emergency conservation mandate.

California’s water industry leaders, including regulators and purveyors, are working to understand the system-wide impacts of increased conservation so that decision makers are better informed as they address California’s current and future water challenges.

Through a partnership with California Association of Sanitation Agencies (CASA), Water Research Foundation(WRF), WateReuse California, and California Water Environment Association(CWEA), California WaterUrban Agencies(CUWA) has developed this white paper to provide decisionmakers, water/wastewater system managers, and other stakeholders an understanding of the impacts of declining flows resulting from substantial reductions in indoor water use and how utilities are adapting to these circumstances.

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Advancement of Salinity and Flow Monitoring in the San Francisco Bay Delta, San Francisco Bay Delta Action Plan Implementation Support, FINAL REPORT

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Advancement of Salinity and Flow Monitoring in the San Francisco Bay Delta, San Francisco Bay Delta Action Plan Implementation Support, FINAL REPORT
U.S. Geological Survey, U.S. Environmental Protection Agency | February 1, 2017...
Summary
This report evaluates the cost and utility of adding coupled surface and near-bottom salinity monitors along the axis of the San Francisco Estuary,...

This report evaluates the cost and utility of adding coupled surface and near-bottom salinity monitors along the axis of the San Francisco Estuary, and the types of equipment and approximate costs of this additional monitoring effort. Expanding the monitoring network by adding downstream monitoring stations, adding stations at depth, and increasing the resolution of monitoring stations along the axis of the estuary will generate data that capture tidal dynamics and may be used to derive equations that predict salinity and other hydrodynamic endpoints with greater precision than currently possible. The proposed monitoring is expected to enhance the hydrodynamic modeling of the salt field and the accuracy of compliance and prediction methods in the estuary.

Springtime outflows through the San Francisco Estuary are managed through the position of the 2 parts per thousand bottom salinity isohaline (X2) along the center-line of the estuary, measured in kilometers relative to the Golden Gate Bridge. X2 is calculated from surface salinity measurements with a constant vertical conversion factor. The current framework of sampling stations does not collect near-bottom salinity along the estuary center-line, does not extend far enough down-estuary to adequately characterize X2 during high flows, and the separation of monitoring locations limits the precision with which the position of X2 can be calculated.

Near-surface and near-bed salinity and turbidity sensors and ancillary hardware could be added to the estuary for an estimated cost of ~ $780K in capital costs and $500K/yr in operation, maintenance, and data processing costs based on a proposed addition to an existing surface salinity network in San Francisco Estuary operated by the US Geological Survey. While this document does not recommend a particular plan for implementation, the compiled information provides rough costs for planning considerations. Data collected through a network of this kind could improve precision of compliance methods with the existing Delta outflow standard. With data collected over time, it would support modifications to a new/modified Delta outflow standard, improve our ability to assess the effectiveness of water quality standards, and improve protection of water supply and aquatic life habitat. These data would also improve the salinity modeling capability and accuracy for future predictions and past evaluations. Expanding the monitoring network also provides a platform to connect hydrodynamic and biological measurements which is necessary for integrating biological and hydrodynamic modeling and advancing knowledge of estuarine mechanisms that influence fish population trends. The specific design of a monitoring network and whether or not the improvements can be optimized for their potential outputs was beyond the scope of the present document and needs to be based on a broader discussion among science experts, regulators, and the regulated community.

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An Index of Biotic Integrity (IBI) for Perennial Streams in California’s Central Valley

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An Index of Biotic Integrity (IBI) for Perennial Streams in California’s Central Valley
California State Water Resources Control Board | December 1, 2008...
Summary
Bioassessment is the science of using aquatic organisms as indicators of ecological condition in streams in rivers. Many types of organisms can be...

Bioassessment is the science of using aquatic organisms as indicators of ecological condition in streams in rivers. Many types of organisms can be used as indicators, for example fish or algae, but bioassessment is most frequently based on benthic macroinvertebrates (BMIs), which are small but visible bottom-dwelling organisms such as insects. BMI data sets typically consist of long lists of species (or taxa) found in a sample and their relative abundances. These data can be simplified into measures of biological condition such as indices of biotic integrity (IBIs) that are designed to be sensitive to human-caused alterations to the landscape, to stream channels and riparian zones, and to water chemistry. IBIs function much like economic indicators: high IBI scores reflect good ecological conditions while low IBI scores reflect poor ecological conditions.

Bioassessment is increasingly used throughout California by water quality monitoring programs, but in the Central Valley bioassessment is more challenging than in other regions of the state because the entire landscape and most streams are highly altered by human activities such as urbanization, agriculture and water diversions. This makes it impossible to evaluate how BMIs respond across a complete gradient of human disturbance within the region, that is, from minimally disturbed reference sites where human activity is absent or minimal and which therefore set the benchmark for biological expectations, to the most altered sites with degraded biology. In the Central Valley, minimally disturbed reference sites are no longer available. Even the ‘least-disturbed’ sites, which represent the best-available chemical, physical and biological habitat conditions given the current state of the landscape, are markedly disturbed. Reference sites in other parts of California, such as the Sierra Nevada or the Sierra foothills, may be significantly less disturbed than Central Valley reference sites.

In this study, BMI data sets from 11 studies conducted at various intervals over the last 14 years were compiled to build an IBI for Central Valley streams. Data were not collected consistently by the different studies, and many gaps were present in associated physical habitat and water chemistry data sets. This could be corrected for BMI samples by standardizing to a consistent level of taxonomic effort. Gaps in other data could not be addressed. Criteria for defining ‘best-available’ reference sites were established as data allowed and were based on local urban and agricultural intensity, stream channel and riparian condition, and stream substrate composition. Eighty BMI metrics were evaluated for inclusion in the IBI based on 4 criteria: 1) sufficient range for scoring; 2) responsiveness to land use and/or local disturbance variables measured at the 150-meter sampling reach (as data allowed); 3) good discrimination between reference and test sites; 4) lack of correlation with other responsive metrics. Five final metrics were selected and scored for inclusion in the IBI: collector richness (number of taxa that are collector- feeders), predator richness (number of taxa that are predators), percent EPT taxa (percent of taxa that are mayflies, stoneflies, or caddisflies), percent clinger taxa (percent of taxa that cling to vegetation) and Shannon diversity (a composite measure of taxonomic richness and evenness of abundance). The final IBI showed good discrimination between reference and test sites, and was validated with an independent data set. BMI metrics and the final IBI were more strongly related to reach-scale physical habitat variables than to water chemistry or land use variables, but detailed water chemistry was lacking for many sites, and some studies have shown that response to land use diminishes when more than 10% of a watershed is degraded by human activities.

Despite data gaps that were less than ideal for indicator development, this study is the first to set expectations for Central Valley BMI assemblages based on best-available reference sites. The Central Valley IBI can be used as a general interpretive framework for benthic samples collected from perennial streams on the valley floor and provides an objective means for rating biological condition in a region with high urban and agricultural intensity. The ability to rank sampling sites relative to explicitly defined biological expectations is essential to any biological monitoring program. Therefore, this index may prove useful in several monitoring applications, including California’s non- point source CMAP program where sampling was stratified to assess and compare stream condition in urban, agricultural and forested watersheds, in stormwater monitoring programs, in point-source pollution investigations, and in stream restoration monitoring. Key recommendations include: 1) that all future bioassessment projects in the Central Valley should collect quantitative physical habitat and water chemistry with consistent protocols at all sites; in situ chemistry and rapid (qualitative) physical habitat are not sufficient for screening reference sites or evaluating BMI responses to stressor gradients; 2) that bioassessment should be added to NPS monitoring where programs are already collecting more intensive stressor data such as pesticides, nutrients and metals. This will provide California’s monitoring programs with better datasets to support future analyses.

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Assessment of Interim Flow Water-Quality Data of the San Joaquin River Restoration Program and Implications for Fishes, California, 2009–11
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Assessment of Interim Flow Water-Quality Data of the San Joaquin River Restoration Program and Implications for Fishes, California, 2009–11
U.S. Geological Survey (USGS), San Francisco Water Department | June 29, 2015...
Summary
After more than 50 years of extensive water diversion for urban and agriculture use, a major settlement was reached among the U.S. Departments...
After more than 50 years of extensive water diversion for urban and agriculture use, a major settlement was reached among the U.S. Departments of the Interior and Commerce, the Natural Resources Defense Council, and the Friant Water Users Authority in an effort to restore the San Joaquin River.

The settlement received Federal court approval in October 2006 and established the San Joaquin River Restoration Program, a multi-agency collaboration between State and Federal agencies to restore and maintain fish populations, including Chinook salmon, in the main stem of the river between Friant Dam and the confluence with the Merced River. This is to be done while avoiding or minimizing adverse water supply effects to all of the Friant Division contractors that could result from restoration flows required by the settlement.

The settlement stipulates that water- and sediment-quality data be collected to help assess the restoration goals. This report summarizes and evaluates water-quality data collected in the main stem of the San Joaquin River between Friant Dam and the Merced River by the U.S. Bureau of Reclamation for the San Joaquin River Restoration Program during 2009–11. This summary and assessment consider sampling frequency for adequate characterization of variability, sampling locations for sufficient characterization of the San Joaquin River Restoration Program restoration reach, sampling methods for appropriate media (water and sediment), and constituent reporting limits.

After reviewing the water- and sediment-quality results for the San Joaquin River Restoration Program, several suggestions were made to the Fisheries Management Work Group, a division of the San Joaquin River Restoration Program that focuses solely on the reintroduction strategies and health of salmon and other native fishes in the river. Water-quality results for lead and total organic carbon exceeded the Surface Water Ambient Monitoring Program Basin Plan Objectives for the San Joaquin Basin, and results for copper exceeded the U.S. Environmental Protection Agency Office of Pesticide Programs’ aquatic-life chronic and acute benchmarks for invertebrates. One sediment sample contained detections of pyrethroid pesticides bifenthrin, lambda-cyhalothrin, and total permethrin at concentrations above published chronic toxicity thresholds.

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Benthic Invertebrate and Deposited Sediment TMDL Guidance for the Pajaro River Watershed

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Benthic Invertebrate and Deposited Sediment TMDL Guidance for the Pajaro River Watershed
California State Water Resources Control Board | March 1, 2016...
Summary
The Pajaro River and its tributaries are exposed to sediments from a variety of sources. To establish limits for regulating this pollutant, it...

The Pajaro River and its tributaries are exposed to sediments from a variety of sources. To establish limits for regulating this pollutant, it is necessary to understand how and where deposition of sediments impact biological health. Benthic, or bottom-dwelling, invertebrates offer a direct way to assess the impacts of deposited sediment on the integrity of stream ecosystems. The channel bed is where sediments accumulate and persist, so benthic macroinvertebrates that live in this ha bitat provide a responsive indicator of the effect of these sediments. Previous criteria for bedded sediment fines in spawning gravels have been established for salmonids, but these may not be appropriate to all stream segments, are not typically measured in stream assessments, and are confounded by other factors limiting steelhead vitality. Instead, the effects of sediment cover can be evaluated using benthic macroinvertebrates (BMIs) as indicators of stream condition to assess any stream segment and can be related to the bioassessment and stream habitat surveys of the Surface Water Ambient Monitoring Program (SWAMP) . The approach taken in this study was to select 25 sites throughout the perennial Pajaro watershed and in the adjacent upper Coyote Creek watershed that represented a cross-section of land uses, above and below reservoirs (unregulated/regulated flows), and in varied geographic settings that would permit examining source area influences on sediment deposition.

Rather than define conventional TMDL estimates for daily loads of sediment, a more relevant survey of the cover of deposited fine and sand (FS) sediments on the stream bed was used here to find the level at which BMIs lost integrity of species c omposition and diversity. BMI responses we re-examined at the reach scale (50-meter channel length ) and at local patch scales (30x3 0 cm) of varied FS sedim ent cover . The data were used to define target levels at which sediment impairs stream bed habitat quality. Reaches of varied sediment cover were compared to conditions at relatively undisturbed reference streams of the Central Coast region to evaluate sediment impacts.

Significant loss of species diversity and altered community type occurred above a sediment cover range of 40% FS at both reach and local-patch scales. In a range of 20-40% FS , BMI diversity declined, showing incipient losses of biological integrity . Richness of mayfly, stonefly and caddisfly taxa richness (EPT) was used as an indicator of biological effects of sediment, and reduced diversity associated with sediment increase corresponded to declines below the criterion 10th percentile of reference site EPT found in other central coast streams . Because of multiple stressors, some streams may not achieve these sediment or EPT targets just by improving the local sediment condition . For example, streams that are regulated (below reservoirs) or in arid regions may be influenced by temperature, dissolved minerals and/or elevated pH , in addition to sediment .

Rankings of streams surveyed were based either on sediment cover within the wetted stream width or the entire bankfull channel profile, accounting for both current habitat conditions and recent environmental exposure . Although the design of this study examined sediment deposition at different spatial scales and used a variety of sediment measures, the results are compatible with habitat and bioassessment surveys using standard SWAMP protocols. Only three to five of the 25 streams surveyed in the Pajaro region showed sediment and diversity levels indicating likely sediment deposition impacts. Results from this study can be used to identify streams where sediment degradation to biological integrity is likely (at >40% FS) , and those in a warning range (20-40% FS) that should be flagged for further assessment.

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Bioaccumulation of Pollutants in California Waters: A Review of Historic Data and Assessment of Impacts on Fishing and Aquatic Life

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Bioaccumulation of Pollutants in California Waters: A Review of Historic Data and Assessment of Impacts on Fishing and Aquatic Life
California State Water Resources Control Board, San Francisco Estuary Institute | October 24, 2007...
Summary
This report was written for the State Water Resources Control Board’s Surface Water Ambient Monitoring Program (SWAMP) as a step toward the development...

This report was written for the State Water Resources Control Board’s Surface Water Ambient Monitoring Program (SWAMP) as a step toward the development of an improved bioaccumulation monitoring program for California. The report provides a review of bioaccumulation monitoring data generated under three historic State Board programs (the Toxic Substances Monitoring Program, the State Mussel Watch Program, and the Coastal Fish Contamination Program) and other major bioaccumulation studies since 1970. Future monitoring will be guided by assessment questions developed for the SWAMP. The objective of this report was to evaluate how well the historic data from the State Board programs and from other major monitoring efforts since 1970 address these questions. This exercise has provided a substantial amount of information about present and historical impacts of pollutant bioaccumulation on shing and aquatic life in California, and has also highlighted areas where improved sampling approaches can better address the assessment questions.

Present concentrations of pollutants in many California water bodies are high enough to cause concern for possible effects on human health and to have a significant impact on the fishing beneficial use. Consumption advisories, 303(d) listings, and the bioaccumulation database as a whole provide three indices of the status of this impact. Consumption advisories exist for an increasing number of water bodies, but these represent only a fraction of the areas likely to need them. Lack of suitable data is a major impediment to developing advice for additional water bodies. A US E.P.A. evaluation of the 2002 303(d) List indicated that large portions of the state had not been assessed, especially rivers and coastline. Most of the lake area in the state (61%) had been assessed, and a relatively small percentage of the total area (6%) was classified as impaired. Assessment of lakes, however, has focused primarily on the largest lakes, leaving the vast majority of smaller lakes unsampled. Many of these small lakes are near population centers and are popular for shing. Bays and estuaries had been thoroughly assessed (98% of the area) and 93% of the total area was impaired.

Evaluation of the most recent monitoring data (collected from 1998-2003) indicates that, for the locations sampled, 32% had low concentrations of pollutants, 42% had moderate concentrations, 18% had high concentrations, and 8% had very high concentrations (Figure 1). Concentrations in the low category are in a range where consumption is generally encouraged by the California Office of Environmental Health Hazard Assessment (OEHHA) (Klasing and Brodberg 2006). OEHHA is the agency responsible for managing health risks due to contaminated sport fish in California. Concentrations in the very high category are in a range where OEHHA discourages consumption (Klasing and Brodberg 2006). Lakes assigned to the moderate, high, or very high concentration categories were primarily affected by mercury, with PCBs also playing a lesser role.

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A Bayesian approach to infer nitrogen loading rates from crop and land-use types surrounding private wells in the Central Valley, California

A Bayesian approach to infer nitrogen loading rates from crop and land-use types surrounding private wells in the Central Valley, California

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A Field Guide to the Identification of the Ordinary High Water Mark (OHWM) in the Arid West Region of the Western United States: A Delineation Manual

A Field Guide to the Identification of the Ordinary High Water Mark (OHWM) in the Arid West Region of the Western United States: A Delineation Manual

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A hybrid machine learning model to predict and visualize nitrate concentration throughout the Central Valley aquifer, California, USA

A hybrid machine learning model to predict and visualize nitrate concentration throughout the Central Valley aquifer, California, USA

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A Water Resources Data-Network Evaluation for Monterey County, California, Phase 3: Northern Salinas River Drainage Basin

A Water Resources Data-Network Evaluation for Monterey County, California, Phase 3: Northern Salinas River Drainage Basin

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Adapting to Change: Utility Systems and Declining Flows

Adapting to Change: Utility Systems and Declining Flows

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Advancement of Salinity and Flow Monitoring in the San Francisco Bay Delta, San Francisco Bay Delta Action Plan Implementation Support, FINAL REPORT

Advancement of Salinity and Flow Monitoring in the San Francisco Bay Delta, San Francisco Bay Delta Action Plan Implementation Support, FINAL REPORT

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An Index of Biotic Integrity (IBI) for Perennial Streams in California’s Central Valley

An Index of Biotic Integrity (IBI) for Perennial Streams in California’s Central Valley

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Assessment of Interim Flow Water-Quality Data of the San Joaquin River Restoration Program and Implications for Fishes, California, 2009–11

Assessment of Interim Flow Water-Quality Data of the San Joaquin River Restoration Program and Implications for Fishes, California, 2009–11

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Benthic Invertebrate and Deposited Sediment TMDL Guidance for the Pajaro River Watershed

Benthic Invertebrate and Deposited Sediment TMDL Guidance for the Pajaro River Watershed

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Bioaccumulation of Pollutants in California Waters: A Review of Historic Data and Assessment of Impacts on Fishing and Aquatic Life

Bioaccumulation of Pollutants in California Waters: A Review of Historic Data and Assessment of Impacts on Fishing and Aquatic Life

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