South Coast

DDT Residues in Pacific Sea Birds: a Persistent Insecticide in Marine Food Chains

Nature Portfolio (Springer Nature) | November 1st, 1967

THE accumulation and biological concentration of DDT and its metabolites*within food chains of terrestrial, freshwater and estuarine ecosystems have been well doc

THE accumulation and biological concentration of DDT and its metabolites*within food chains of terrestrial, freshwater and estuarine ecosystems have been well documented. Significant residue concentrations have occasionally been reported in marine organisms, but these have usually been attributed to local sources of contamination4. The present study, which is based on analyses of collections of birds, fish and invertebrates from Pacific Ocean localities, indicates that DDT is also a component of marine ecosystems and that pelagic species may accumulate high concentrations of DDT residues. The results of the work with fish will be published elsewhere.

Debris flow occurrence under changing climate and wildfire regimes: A southern California perspective

Geomorphology (Elsevier) | December 2nd, 2022

In southern California, wildfire incidents are increasing in frequency and magnitude. There is a great deal of research predicting the impact of climate change on large s

In southern California, wildfire incidents are increasing in frequency and magnitude. There is a great deal of research predicting the impact of climate change on large scale fire regimes. These impacts, now the new normal, include increases in future fire incidents and burn severities. Yet predictive studies on how ecosystems respond to changing fire regimes are lacking. Identifying trends in post-fire erosion patterns, such as post-fire debris flows, is critical for increasing human resiliency and adaptation to changing weather patterns and eventual long-term climate change. The relative historical abundance of post-fire debris flows in southern California presents this concern: will worsening wildfire regimes result in more post-fire debris flows? Our research addresses this concern by utilizing a descriptive approach to analyze post-fire debris flows in southern California from 2001 to 2018 to elucidate possible trends. We found that 84 % of debris flows originate from watersheds with soils burnt at moderate soil burn severity. We found that debris flow occurrence is more reliant on the percent coverage of a soil burn severity classification than its areal extent. Further, larger fires also tended to produce more debris flows and most (73 %) debris flow watersheds occurred in predominantly bedrock areas. Our research suggests that the number of post-fire runoff-generated debris flows in the region will increase if fires continue to increase in size, occur on slopes of at least 20°, burn south-facing watersheds with bedrock of igneous or sedimentary origin to at least a moderate severity, and peak rainfall intensity return intervals do not change. These findings highlight the interconnectivity between natural erosive processes, wildfires, humans, and climate change.

Decadal Shifts in Groundwater Age Detected by Environmental Tracers Across California

American Geophysical Union (AGU) | March 23rd, 2026

Groundwater age tells us how long water has been underground since it last infiltrated the land surface. Monitoring changes in groundwater age helps identify aquifer stre

Groundwater age tells us how long water has been underground since it last infiltrated the land surface. Monitoring changes in groundwater age helps identify aquifer stress from pumping or shifts toward new hydrologic conditions—key factors for sustainable water management. In this study, changes in groundwater age were tested by comparing chemical tracer data collected about 10 years apart from hundreds of wells across California. Chemical tracers are dissolved substances with known historical records and decay rates that can be used to infer groundwater age. Using models that estimate expected tracer concentrations under steady-age conditions, this study found that nearly one-third of the wells showed significant changes in groundwater age over time. These changes were most common in areas with heavy agricultural use, where pumping and irrigation have altered how water moves underground. These shifts in age can also affect water quality, especially when younger water carries contaminants like nitrate. By using a statistical modeling approach, this study shows how changes in groundwater age can help identify aquifers under stress and support efforts to manage groundwater sustainably.

Decadal trends in the quality of groundwater used for public drinking-water supply in California, 2004–2023, California groundwater ambient monitoring and assessment program, priority basin project

U.S. Geological Survey (USGS) | February 25th, 2026

This study provides a comprehensive assessment of decadal changes in the quality of groundwater used for public drinking-water supply at 444 monitoring site

This study provides a comprehensive assessment of decadal changes in the quality of groundwater used for public drinking-water supply at 444 monitoring sites across California during 2004–2023. We assessed decadal step trends in groundwater quality for 145 water-quality constituents and geochemical indicators statewide and across geographic and land-use based network groups. We evaluated the statistical significance of directional changes (predominant increase or decrease of constituent concentrations) and the magnitude of those changes across all network groups. Uranium showed the most widespread directional and high-magnitude increases of all constituents with regulatory benchmarks statewide, particularly in the agriculture-dominated Central Valley as well as urban- and desert-dominated regions of Southern California. Fluoride and perchlorate showed the most widespread directional and high-magnitude decreases of all constituents with regulatory benchmarks statewide, which were also most pronounced in Southern California. Although arsenic and nitrate did not often register significant directional changes across network groups, they showed widespread, high-magnitude changes in both directions (increase and decrease) at levels often exceeding 10 percent of respective regulatory benchmarks statewide. Triazine herbicides (atrazine and simazine) and the gasoline oxygenate methyl tert-butyl ether (MTBE) showed significant directional decreases statewide, but not at levels considered to be of high magnitude compared to respective regulatory benchmarks. We observed significant directional and high-magnitude increases of total dissolved solids (TDS) statewide, which were most pronounced in agricultural areas. Analysis of explanatory geochemical indicators indicated that prevalent statewide increases of alkalinity and calcium were the predominant components of the observed statewide increases in TDS by mass. Widespread increases in groundwater alkalinity and calcium across agricultural and urban areas may be related, in part, to warm-season irrigation and other anthropogenic factors that have shifted soil weathering dynamics over the long term. Increasing alkalinity concentrations were related to increasing uranium concentrations, particularly in areas with aquifer materials derived from granitic rocks. Conversely, increasing calcium concentrations were related to decreasing fluoride concentrations, particularly in areas where fluoride occurred naturally at elevated concentrations. Decrease of perchlorate, triazine herbicides, and MTBE are likely related to decreased anthropogenic source inputs over time and natural attenuation in aquifers.

Decadal trends in the quality of groundwater used for public drinking-water supply in California, 2004–23

U.S. Geological Survey (USGS) | July 30th, 2026

This study provides a comprehensive assessment of decadal changes in the quality of groundwater used for public drinking- water supply at 444 monitoring sites across Cali

This study provides a comprehensive assessment of decadal changes in the quality of groundwater used for public drinking- water supply at 444 monitoring sites across California during 2004–23. We assessed decadal step trends in groundwater quality for 145 water- quality constituents and geochemical indicators statewide and across geographic and land- use based network groups. We evaluated the statistical significance of directional changes (predominant increase or decrease of constituent concentrations) and the magnitude of those changes across all network groups.

Decline of the world's saline lakes

Nature Portfolio (Springer Nature) | October 23rd, 2017

Many of the world's saline lakes are shrinking at alarming rates, reducing waterbird habitat and economic benefits while threatening human health. Saline lakes are long-t

Many of the world's saline lakes are shrinking at alarming rates, reducing waterbird habitat and economic benefits while threatening human health. Saline lakes are long-term basin-wide integrators of climatic conditions that shrink and grow with natural climatic variation. In contrast, water withdrawals for human use exert a sustained reduction in lake inflows and levels. Quantifying the relative contributions of natural variability and human impacts to lake inflows is needed to preserve these lakes. With a credible water balance, causes of lake decline from water diversions or climate variability can be identified and the inflow needed to maintain lake health can be defined. Without a water balance, natural variability can be an excuse for inaction. Here we describe the decline of several of the world's large saline lakes and use a water balance for Great Salt Lake (USA) to demonstrate that consumptive water use rather than long-term climate change has greatly reduced its size. The inflow needed to maintain bird habitat, support lake-related industries and prevent dust storms that threaten human health and agriculture can be identified and provides the information to evaluate the difficult tradeoffs between direct benefits of consumptive water use and ecosystem services provided by saline lakes.

Declining Freshwater Availability in the Colorado River Basin Threatens Sustainability of Its Critical Groundwater Supplies

American Geophysical Union (AGU) | May 27th, 2025

Climate change is causing more frequent and intense droughts around the world, including in the Colorado River Basin, which supplies water to seven U.S. states and Mexico

Climate change is causing more frequent and intense droughts around the world, including in the Colorado River Basin, which supplies water to seven U.S. states and Mexico, and is facing severe water shortages. This study investigates how changes in water storage components (e.g., snow, surface water, soil moisture and groundwater) and water use are contributing to these shortages, and impacting agriculture and municipal water supplies, using data from the NASA GRACE and GRACE Follow-On (GRACE-FO) satellite missions, land surface models, and in situ data over the past two decades. Results show significant losses of groundwater: 7.8.0 ± 5.3 km3 in the Upper CRB (UCRB) and 25.5 ± 7.4 km3 in the Lower CRB (LCRB). Progress toward sustainable groundwater could be achieved by reducing groundwater extraction, in line with current rates of depletion (0.35 km3 in the UCRB and 1.15 km3 in the LCRB). This research highlights the importance of understanding the factors affecting groundwater levels to create sustainable water management strategies that can help secure water resources for the region's future.

Declining Reservoir Reliability and Increasing Reservoir Vulnerability: Long‐Term Observations Reveal Longer and More Severe Periods of Low Reservoir Storage for Major United States Reservoirs

American Geophysical Union (AGU) | August 22nd, 2024

Delta Adapts: Creating a Climate Resilient Future

Delta Stewardship Council (DSC) | June 25th, 2025

The Delta Stewardship Council (Council) was established, in part, to provide sustainable management for the Delta ecosystem, and climate adaptation is a critical consider

The Delta Stewardship Council (Council) was established, in part, to provide sustainable management for the Delta ecosystem, and climate adaptation is a critical consideration to achieve that mission in future decades. To respond to the challenge of climate adaptation,the Council developed this initiative, Delta Adapts: Creating a Climate Resilient Future (Delta Adapts). Climate change must be considered to attain the state’s coequal goals, as established by the 2009 Delta Reform Act: securing a reliable water supply for California, protecting and restoring the ecosystem and wildlife it supports, and enhancing the Delta as a unique place, with its community, tribal, and agricultural heritage. The Council adopted the Delta Plan, which has regulatory policies that protect land for restoration and agriculture, help manage flood risk, and improve water supply reliability. The Delta Plan directs the Council to guide and regulate actions of the 200+ state and local agencies in the Delta to ensure they support statewide water supply reliability and Delta ecosystem restoration.

Demographic predictors of urinary arsenic in a low-income predominantly Hispanic pregnancy cohort in Los Angeles

Journal of Exposure Science & Environmental Epidemiology (Springer) | July 27th, 2020

Arsenic (As) is a contaminant of top public health concern, due to its range of detrimental health effects. Arsenic exposure has not been well-characterized among the US

Arsenic (As) is a contaminant of top public health concern, due to its range of detrimental health effects. Arsenic exposure has not been well-characterized among the US Hispanic populations and has been particularly understudied in this population during pregnancy. As part of the MADRES ongoing pregnancy cohort of predominantly lower-income, Hispanic women in Los Angeles, CA, we examined levels of maternal first trimester urinary As, including total As and As metabolites (inorganic (iAs), monomethylated (MMA) and dimethylated As (DMA)), in relation to participant demographics, lifestyle characteristics, and rice/seafood consumption, to identify factors that may influence As exposure and its metabolites during pregnancy (N = 241). Total As concentrations ranged from low to high (0.8–506.2 μg/L, mean: 9.0 μg/L, SD: 32.9) in our study population. Foreign-born Hispanic women had 8.6% higher %DMA (95% CI: 3.3%, 13.9%) and −7.7% lower %iAs (95% CI: −12.6%, −2.9%) than non-Hispanic women. A similar trend was observed for US-born Hispanic women. In addition, maternal age was associated with 0.4% higher %iAs (95% CI: 0.1%, 0.6%) and 0.4% lower %DMA (95% CI: −0.7%, −0.1%) per year, which may indicate poor As methylation capacity. Individual factors may predict As exposure and metabolism in pregnancy, and in turn, greater risk of adverse health effects.