California Groundwater Research Articles

Genetic potential for aerobic respiration and denitrification in globally distributed respiratory endosymbionts

The endosymbiont Candidatus Azoamicus ciliaticola was proposed to generate ATP for its eukaryotic host, an anaerobic ciliate of the Plagiopylea class, fulfilling a function analogous to mitochondria in other eukaryotic cells. The discovery of this respiratory endosymbiosis has major implications for both evolutionary history and ecology of microbial eukaryotes. However, with only a single species described, knowledge of its environmental distribution and diversity is limited. Here we report four complete, circular metagenome assembled genomes (cMAGs) representing respiratory endosymbionts inhabiting groundwater in California, Ohio, and Germany. These cMAGs form two lineages comprising a monophyletic clade within the uncharacterized gammaproteobacterial order UBA6186, enabling evolutionary analysis of their key protein complexes. Strikingly, all four cMAGs encode a cytochrome cbb3 oxidase, which indicates that these endosymbionts have the capacity for aerobic respiration. Accordingly, we detect these respiratory endosymbionts in diverse habitats worldwide, thus further expanding the ecological scope of this respiratory symbiosis.

Could California's groundwater resource management lessons be beneficial to England?

In California, Groundwater Sustainability Agencies (GSAs) are basin/catchment-specific water organizations mandated by the Sustainable Groundwater Management Act of 2014 to manage groundwater sustainably by 2040/2042. A GSA can charge replenishment fees for pumped groundwater and these fees can be used to: (a) monitor basin hydrologic conditions; (b) improve the water budget accuracy; (c) increase water availability through management actions and projects; (d) mitigate undesirable results; and/or (e) pay for activities including issuing allocations and limiting production to allocations. In England, housing is frequently proposed in river basin catchments that face water resource challenges. High profile examples are the Arun Valley and Cambridge. The current National Planning Policy Framework manages water resource planning strategically through water company Water Resource Management Plans or Environment Agency River Basin Management Plans. These processes can be slow to respond to development requirements. England might look to California's practices that require water users and developers to pay for ‘water credits’ or fees. This could involve a ‘Watermaster’ charged with local or catchment scale resource management and project implementation. This Watermaster could engage all stakeholders including the local water company, farmers, the Environment Agency and the local authority, none of whom is well positioned to act in isolation.

Will there be water? Climate change, housing needs, and future water demand in California

Climate change in California is expected to alter future water availability, impacting water supplies needed to support future housing growth and agriculture demand. In groundwater-dependent regions like California's Central Coast, new land-use related water demand and decreasing recharge is already stressing depleted groundwater basins. We developed a spatially explicit state-and-transition simulation model that integrates climate, land-use change, water demand, and groundwater gain-loss to examine the impact of future climate and land use change on groundwater balance and water demand in five counties along the Central Coast from 2010 to 2060. The model incorporated downscaled groundwater recharge projections based on a Warm/Wet and a Hot/Dry climate future from a spatially explicit hydrological process-based model. Two urbanization projections from a parcel-based, regional urban growth model representing 1) recent historical and 2) state-mandated housing growth projections were used as alternative spatial targets for future urban growth. Agricultural projections were based on recent historical trends from remote sensing data. Annual projected changes in groundwater balance were calculated as the difference between land-use related water demand, based on historical estimates, and climate-driven recharge plus agriculture return flows. Results indicate that future changes in climate-driven groundwater recharge, coupled with cumulative increases in agricultural water demand, result in overall declines in future groundwater balance, with a Hot/Dry future resulting in cumulative groundwater decline in all but Santa Cruz County. Cumulative declines by 2060 are especially prominent in San Luis Obispo (−2.9 to −5.1 Bm3) and Monterey counties (−6.5 to −8.7 Bm3), despite limited changes in agricultural water demand over the model period. These two counties show declining groundwater reserves in a Warm/Wet future as well, while San Benito and Santa Barbara County barely reach equilibrium. These results suggest future groundwater supplies may not be able to keep pace with regional demand and declining climate-driven recharge, resulting in a potential reduction in water security in the region. However, our county-scale projections showed new housing and associated water demand does not conflict with California's groundwater sustainability goals. Rather, future climate coupled with increasing agricultural groundwater demand may reduce water security in some counties, potentially limiting available groundwater supplies for new housing.

Drought Characterization With GPS: Insights Into Groundwater and Surface‐Reservoir Storage in California

AbstractDrought intensity is commonly characterized using meteorologically‐based metrics that do not provide insight into water deficits within deeper hydrologic systems. In contrast, global positioning system (GPS) displacements are sensitive to both local and regional hydrologic‐storage fluctuations. While a few studies have leveraged this sensitivity to produce geodetic drought indices, hydrologic drought characterization using GPS is not commonly accounted for in drought assessment and management. To motivate this application, we produce a new geodetic drought index (GDI) and quantify its ability to characterize hydrologic drought conditions in key surface and sub‐surface hydrologic reservoirs/pools across California. In northern California, the GDI exhibits a strong regional association with surface‐reservoir storage at the 1‐month time scale (correlation coefficient: 0.83) and groundwater levels at the 3‐month time scale (correlation coefficient: 0.87), along with moderate associations with stream discharge at the daily (instantaneous) time scale (correlation coefficient: 0.50). Groundwater in southern California is best characterized with a 12‐month GDI (correlation coefficient: 0.77), and surface‐reservoir storage is optimized with the 3‐month GDI (correlation coefficient: 0.72). Two sigma uncertainties are ±0.03. Differences between northern and southern California reveal that the GDI is sensitive to unique aquifer and drainage basin characteristics. In addition to capturing long‐term hydrologic trends, rapid changes in the GDI initiate during clusters of large atmospheric river events that closely mirror fluctuations in traditional hydrologic and meteorological observations. We show that GPS‐based hydrologic drought indices provide a significant opportunity to improve drought assessment, in California and beyond, by improving our understanding of the hydrologic cycle.

Access for sale? Overlying rights, land transactions, and groundwater in California

Climate change intensifies longstanding tensions over groundwater sustainability and equity of access among users. Though private land ownership is a primary mechanism for accessing groundwater in many regions, few studies have systematically examined the extent to which farmland markets transform groundwater access patterns over time. This study begins to fill this gap by examining farmland transactions overlying groundwater from 2003–17 in California. We construct a novel dataset that downscales well construction behavior to the parcel level, and we use it to characterize changes in groundwater access patterns by buyer type on newly transacted parcels in the San Joaquin Valley groundwater basin during the 2011–17 drought. Our results demonstrate large-scale transitions in farmland ownership, with 21.1% of overlying agricultural acreage statewide sold at least once during the study period and with the highest rates of turnover occurring in critically overdrafted basins. By 2017, annual individual farmland acquisitions had halved, while acquisitions by limited liability companies increased to one-third of all overlying acres purchased. Together, these trends signal increasing corporate farmland acquisitions; new corporate farmland owners are associated with the construction, on comparable parcels, of agricultural wells 77–81 feet deeper than those drilled by new individual landowners. We discuss the implications of our findings for near-term governance of groundwater, and their relevance for understanding structural inequities in exposure to future groundwater level declines.

"Candidatus Subterrananammoxibiaceae," a New Anammox Bacterial Family in Globally Distributed Marine and Terrestrial Subsurfaces.

Bacteria specialized in anaerobic ammonium oxidation (anammox) are widespread in many anoxic habitats and form an important functional guild in the global nitrogen cycle by consuming bio-available nitrogen for energy rather than biomass production. Due to their slow growth rates, cultivation-independent approaches have been used to decipher their diversity across environments. However, their full diversity has not been well recognized. Here, we report a new family of putative anammox bacteria, "Candidatus Subterrananammoxibiaceae," existing in the globally distributed terrestrial and marine subsurface (groundwater and sediments of estuary, deep-sea, and hadal trenches). We recovered a high-quality metagenome-assembled genome of this family, tentatively named "Candidatus Subterrananammoxibius californiae," from a California groundwater site. The "Ca. Subterrananammoxibius californiae" genome not only contains genes for all essential components of anammox metabolism (e.g., hydrazine synthase, hydrazine oxidoreductase, nitrite reductase, and nitrite oxidoreductase) but also has the capacity for urea hydrolysis. In an Arctic ridge sediment core where redox zonation is well resolved, "Ca. Subterrananammoxibiaceae" is confined within the nitrate-ammonium transition zone where the anammox rate maximum occurs, providing environmental proof of the anammox activity of this new family. Phylogenetic analysis of nitrite oxidoreductase suggests that a horizontal transfer facilitated the spreading of the nitrite oxidation capacity between anammox bacteria (in the Planctomycetota phylum) and nitrite-oxidizing bacteria from Nitrospirota and Nitrospinota. By recognizing this new anammox family, we propose that all lineages within the "Ca. Brocadiales" order have anammox capacity. IMPORTANCE Microorganisms called anammox bacteria are efficient in removing bioavailable nitrogen from many natural and human-made environments. They exist in almost every anoxic habitat where both ammonium and nitrate/nitrite are present. However, only a few anammox bacteria have been cultured in laboratory settings, and their full phylogenetic diversity has not been recognized. Here, we present a new bacterial family whose members are present across both the terrestrial and marine subsurface. By reconstructing a high-quality genome from the groundwater environment, we demonstrate that this family has all critical enzymes of anammox metabolism and, notably, also urea utilization. This bacterium family in marine sediments is also preferably present in the niche where the anammox process occurs. These findings suggest that this novel family, named "Candidatus Subterrananammoxibiaceae," is an overlooked group of anammox bacteria, which should have impacts on nitrogen cycling in a range of environments.

Prediction of 35 Target Per- and Polyfluoroalkyl Substances (PFASs) in California Groundwater Using Multilabel Semisupervised Machine Learning

Prediction of 35 Target Per- and Polyfluoroalkyl Substances (PFASs) in California Groundwater Using Multilabel Semisupervised Machine Learning

Using machine learning to predict 1,2,3-trichloropropane contamination from legacy non-point source pollution of groundwater in California's Central Valley

1,2,3-tricholoropropane (TCP) is an impurity common in nematicides applied to agricultural soils from the 1940s to the 1980s. Evidence from animal studies indicates that TCP is a probable human carcinogen. TCP leaches through the soil into groundwater where it persists and contaminates thousands of wells in Asia, Europe, and North America. In California, TCP contaminates drinking water wells, with the highest levels of TCP beneath agricultural land used to grow grapevines. This study performs a mass balance and evaluates the ability of three types of tree-based machine learning models to predict TCP concentration in California's Central Valley aquifer system: classification and regression trees (CART), Random Forest (RF), and Boosted Regression Trees (BRT). To construct the models, multiple spatial explanatory variables were used, including historical agricultural land use data, irrigation levels, precipitation, soil type, groundwater age, redox state, and the presence of the co-contaminant nitrate. To estimate the amount of TCP applied to farmland in California, state historical pesticide and land use documents were used in the mass balance. Between 110,000 and 4,300,000 kg of TCP are estimated to have accumulated in the subsurface. Machine learning models indicate that the most important explanatory variables to predict TCP contamination of groundwater are precipitation, redox state, and the presence of the co-contaminant nitrate. Additionally, a 1000-m buffer area offers a slightly higher predictive performance as compared to 500-m and 1500-m buffers. Furthermore, the RF model outperforms CART and BRT for predictive performance. Finally, modeling using decision trees can predict TCP contamination levels in areas where monitoring is lacking, help target future TCP monitoring efforts, and aid in identifying areas to avoid when drilling new drinking water wells.

Tertiary butyl alcohol plumes in southern california groundwater from leaking underground storage tank sites

Tertiary butyl alcohol in the groundwater was evaluated using closed leaking underground storage tank sites in Southern California between 2016 and 2019. Tertiary butyl alcohol is not regulated and lacks a maximum contaminant level in California. The current level of 12 µg per liter in drinking water (notification level) is advisory and not enforceable. As high as 88% of sites during 2018–2019 fiscal year were closed with tertiary butyl alcohol higher than its notification level in groundwater. Twenty-five percent of the time, the maximum tertiary butyl alcohol concentrations in the groundwater at closure were higher than 2,300 µg per liter during 2016–2017, 7,600 µg per liter during 2017–2018, and 4,400 µg per liter during 2018–2019, respectively. The plume length of the maximum tertiary butyl alcohol increased from 649 feet in 2016 to 1,128 feet in 2019. Considering the proximity of drinking water wells to the leaking underground storage tank sites in California, this points to an increase risk of impact on the drinking water resources. Tertiary butyl alcohol remained above 12 µg/L in a substantial percentage (70% in 2016–1017, 72% in 2017–2018, and 88% in 2018–2019) of sites. Site closure practices at Los Angeles Regional Water Quality Control Board should be more stringent toward tertiary butyl alcohol contamination. Despite documented health hazards, tertiary butyl alcohol has not received sufficient attention from government agencies. The toxicological evaluation of tertiary butyl alcohol indicates significant human health concerns. Based upon the toxicological evidence, an MCL should be considered for tertiary butyl alcohol in drinking water.

Using Machine Learning to Predict 1,2,3-Trichloropropane Contamination from Legacy Non-Point Source Pollution of Groundwater in California's Central Valley

Using Machine Learning to Predict 1,2,3-Trichloropropane Contamination from Legacy Non-Point Source Pollution of Groundwater in California's Central Valley

Patterns in Radon Activity in California Groundwater

Naturally occurring radon-222 (222Rn) is an effective marker of groundwater inflow to streams, lakes, and coastal environments. However, 222Rn activity in groundwater is difficult to predict, and e...

Do Environmental Markets Improve on Open Access? Evidence from California Groundwater Rights

Environmental markets are widely prescribed as an alternative to open-access regimes for natural resources. We develop a model of dynamic groundwater extraction to demonstrate how a spatial regression discontinuity design that exploits a spatially-incomplete market for groundwater rights recovers a lower bound on the market’s net benefit. We apply this estimator to a major aquifer in water-scarce southern California and find that a groundwater market generated substantial net benefits, as capitalized in land values. Heterogeneity analyses point to gains arising in part from rights trading, enabling more efficient water use across sectors. Additional findings suggest the market increased groundwater levels.

Innovations in Sustainable Groundwater and Salinity Management in California’s San Joaquin Valley

The Sustainable Groundwater Management Act (SGMA) of 2014 and the Central Valley Salinity Alternatives for Long-Term Sustainability (CVSALTS) initiative were conceived to reverse years of inaction on the over-pumping of groundwater and salination of rivers that both threaten agricultural sustainability in the State of California. These largely stakeholder-led, innovative policy actions were supported by modern tools of remote sensing and Geographic Information System technology that allowed stakeholders to make adjustments to existing resource management and jurisdictional boundaries to form policy-mandated Groundwater Sustainability Agencies (GSAs) and Salinity Management Areas (SMAs) to address future management responsibilities. Additional resources mobilized by the California Department of Water Resources (CDWR) and other water resource and water quality management agencies have been effective in encouraging the use of spreadsheet accounting and numerical simulation models to develop robust and coherent quantitative understanding of the current state and likely problems that will be encountered to achieve resource sustainability. This activity has revealed flaws and inconsistencies in the conceptual models underpinning this activity. Two case studies are described that illustrate the disparity in the challenges faced by GSAs in subregions charged with developing consensus-based Groundwater Sustainability Plans (GSPs). These case studies also illustrate the unique aspect of SGMA: that alongside mandates and guidelines being imposed statewide, local leadership and advocacy can play an important role in achieving long-term SGMA and CVSALTS goals.

Increasing threat of coastal groundwater hazards from sea-level rise in California

Projected sea-level rise will raise coastal water tables, resulting in groundwater hazards that threaten shallow infrastructure and coastal ecosystem resilience. Here we model a range of sea-level rise scenarios to assess the responses of water tables across the diverse topography and climates of the California coast. With 1 m of sea-level rise, areas flooded from below are predicted to expand ~50–130 m inland, and low-lying coastal communities such as those around San Francisco Bay are most at risk. Coastal topography is a controlling factor; long-term rising water tables will intercept low-elevation drainage features, allowing for groundwater discharge that damps the extent of shoaling in ~70% (68.9–82.2%) of California’s coastal water tables. Ignoring these topography-limited responses increases flooded-area forecasts by ~20% and substantially underestimates saltwater intrusion. All scenarios estimate that areas with shallow coastal water tables will shrink as they are inundated by overland flooding or are topographically limited from rising inland. Sea-level rise raises water tables, causing flooding from below and saltwater intrusion. A modelling study predicts that coastal California groundwater flooding will expand 50–130 m inland with 1 m of sea-level rise, with areal flooding extent strongly dependent on topography and drainage capacity.

Status and trends of orthophosphate concentrations in groundwater used for public supply in California

Phosphorus is a necessary nutrient for all organisms. However excessive phosphorus can cause eutrophication in surface water. Groundwater can be an important nonpoint contributor of phosphorus to surface water bodies. Most groundwater phosphorus is in the form of orthophosphate and orthophosphate concentrations in California groundwater vary temporally and geographically. This study quantifies orthophosphate concentrations in water samples from public supply wells in California, evaluates temporal trends (both step and monotonic trends) in orthophosphate concentration for different areas of the state, and explores potential explanatory factors for the trends observed. Orthophosphate concentrations are low in 42 percent of the groundwater used for public supply in California, moderate in 43 percent, and high in 15 percent of this groundwater relative to reference conditions and a goal expressed by the USEPA for streams overlying the aquifers. The findings also suggest that orthophosphate concentrations increased in approximately one-third of this groundwater during the study period (2000 to 2018). The timing of orthophosphate increases observed in time-series evaluations coincided approximately with the timing of increases observed in step-trend evaluations, with both suggesting that the increasing trend occurred mostly before 2011. Principal component analysis (PCA) of the statewide dataset indicates that orthophosphate concentrations are antithetically related to dissolved oxygen (DO), and weakly associated with boron, arsenic, and fluoride. Step trend and time-series trend analyses using PCA were inconclusive.

Path Dependence, Evolution of a Mandate and the Road to Statewide Sustainable Groundwater Management

SGMA is a landmark transition in California water policy. For local governments engaged in managing at-risk groundwater basins, SGMA brought a transformation of responsibility and authority. These changes reflect a continuation of California water policy, rather than a disjuncture. This policy analysis describes the changing role of state government in groundwater management in California, explaining that role, including the passage of SGMA, through the lens of path-dependent policy evolution. We identify three phases in state groundwater policy: initially the State enabled, subsequently the State incentivized, and with SGMA the State mandated local action. Later phases built upon previous ones and added to existing state policies rather than replacing them, resembling an evolution within the constraints established by earlier decisions. The changing role of the State in California groundwater management demonstrates how initial decisions can push policy along a trajectory, within which there remain opportunities for adjustment and change.

Rapid and Efficient Arsenic Removal by Iron Electrocoagulation Enabled with in Situ Generation of Hydrogen Peroxide.

Millions of people are exposed to toxic levels of dissolved arsenic in groundwater used for drinking. Iron electrocoagulation (FeEC) has been demonstrated as an effective technology to remove arsenic at an affordable price. However, FeEC requires long operating times (∼hours) to remove dissolved arsenic due to inherent kinetics limitations. Air cathode Assisted Iron Electrocoagulation (ACAIE) overcomes this limitation by cathodically generating H2O2 in situ. In ACAIE operation, rapid oxidation of Fe(II) and complete oxidation and removal of As(III) are achieved. We compare FeEC and ACAIE for removing As(III) from an initial concentration of 1464 μg/L, aiming for a final concentration of less than 4 μg/L. We demonstrate that at short electrolysis times (0.5 min), i.e., high charge dosage rates (1200 C/L/min), ACAIE consistently outperformed FeEC in bringing arsenic levels to less than WHO-MCL of 10 μg/L. Using XRD and XAS data, we conclusively show that poor arsenic removal in FeEC arises from incomplete As(III) oxidation, ineffective Fe(II) oxidation and the formation of Fe(II-III) (hydr)oxides at short electrolysis times (<20 min). Finally, we report successful ACAIE performance (retention time 19 s) in removing dissolved arsenic from contaminated groundwater in rural California.

Integrated Hydrologic Modeling to Untangle the Impacts of Water Management During Drought.

Over the past century, groundwater levels in California's San Joaquin Valley have dropped by more than 30 m in some areas mostly due to excessive groundwater extraction used to irrigate agricultural lands and sustain a growing population. Between 2012 and 2015, California experienced the worst drought in its recorded history, depleting surface water supplies and further exacerbating groundwater depletion in the region. Due to a lack of groundwater regulation, exact quantities of extracted groundwater in California are unknown and hard to quantify. Recent adoption of the Sustainable Groundwater Management Act has intensified efforts to identify sustainable groundwater use. However, understanding sustainable use in a highly productive agricultural system with an extremely complex surface water allocation system, variable groundwater use, and spatially extensive and diverse irrigation practices is no easy task. Using an integrated hydrologic model coupled with a land surface model, we evaluated how water management activities, specifically a suite of irrigation and groundwater pumping scenarios, impact surface water-groundwater fluxes and storage components and how those activities and the relationships between them change during drought. Results showed that groundwater pumping volume had the most significant impact on long-term water storage changes. A comparison with total water storage anomaly (TWSA) estimates from NASA's Gravity Recover and Climate Experiment (GRACE) provided some insight regarding which combinations of pumping and irrigation matched the GRACE TWSA estimates, lending credibility to these scenarios. In addition, the majority of long-term water storage changes during the recent drought occurred in groundwater storage in the deeper subsurface.

Deglacial water-table decline in Southern California recorded by noble gas isotopes

Constraining the magnitude of past hydrological change may improve understanding and predictions of future shifts in water availability. Here we demonstrate that water-table depth, a sensitive indicator of hydroclimate, can be quantitatively reconstructed using Kr and Xe isotopes in groundwater. We present the first-ever measurements of these dissolved noble gas isotopes in groundwater at high precision (≤0.005‰ amu−1; 1σ), which reveal depth-proportional signals set by gravitational settling in soil air at the time of recharge. Analyses of California groundwater successfully reproduce modern groundwater levels and indicate a 17.9 ± 1.3 m (±1 SE) decline in water-table depth in Southern California during the last deglaciation. This hydroclimatic transition from the wetter glacial period to more arid Holocene accompanies a surface warming of 6.2 ± 0.6 °C (±1 SE). This new hydroclimate proxy builds upon an existing paleo-temperature application of noble gases and may identify regions prone to future hydrological change.

Groundwater in California: From Juridical and Biopolitical Governmentality to a Political Physics of Vital Processes

This article analyzes the emergence of a political rationality of groundwater in contemporary California. It contrasts a new government of nature that we call a ‘political physics of vital processes’, operative in the case of the Orange County Water District, with juridical and biopolitical rationalities of groundwater governance. To do so, we propose a genealogical account grounded in a reading of a key concept in Aristotle’s first book of Politics. The case is analyzed along the axes of subjectivity, space, and temporality, opening to a novel way of conceptualizing the relation between power and nature.