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Bioswales are a type of permeable green infrastructure designed to slow stormwater and clean runoff by sequestering pollutants such as heavy metals. Measurements of dissolved pollutants before and after the bioswale often justify their ability to clean this runoff, but research addressing the physical and chemical sequestration of these pollutants is scarce. Soil samples were taken from an arid bioswale and analyzed for concentrations of aluminum, cobalt, chromium, copper, iron, magnesium, manganese, nickel, lead, vanadium and zinc. Heat maps of the concentration of these metals in soil were generated via Empirical Bayesian Kriging (EBK) and demonstrate that location-specific sequestration differs between metals within the same swale. Sequential extraction with a modified Tessier et al. (1979) protocol coupled with profiles of metal concentration versus distance along the main flow axis in the bioswale illustrate that the carbonate soil fraction contains elevated concentrations of zinc, lead, cobalt, and manganese, metals sequestered by the bioswale with statistical significance.

IntroductionThe US deports more Mexicans to Tijuana than any other borderland city. Returning involuntarily as members of a stigmatized underclass, many find themselves homeless and de-facto stateless. Subject to routinized police victimization, many take refuge in the Tijuana River Canal (El Bordo). Previous reports suggest Tijuana River water may be contaminated but prior studies have not accessed the health effects or contamination of the water closest to the river residents.MethodsA binational, transdisciplinary team undertook a socio-environmental, mixed methods assessment to simultaneously characterize Tijuana River water quality with chemical testing, assess the frequency of El Bordo residents' water-related diseases, and trace water contacts with epidemiological survey methods (n=85 adults, 18+) in 2019, and ethnographic methods in 2019-2021. Our analysis brings the structural violence framework into conversation with an environmental injustice perspective to documented how social forces drive poor health outcomes enacted through the environment.ResultsThe Tijuana River water most proximate to its human inhabitants fails numerous water-quality standards, posing acute health risks. Escherichia coli values were ∼40,000 times the Mexican regulatory standard for directly contacted water. Skin infections (47%), dehydration (40%) and diarrhea (28%) were commonly reported among El Bordo residents. Residents are aware the water is contaminated and strive to minimize harm to their health by differentially using local water sources. Their numerous survival constraints, however, are exacerbated by routine police violence which propels residents and other people who inject drugs into involuntary contact with contaminated water.DiscussionHuman rights to drinking water, sanitation and hygiene are routinely violated among El Bordo inhabitants. This is exacerbated by violent policing practices that force unhoused deportees to seek refuge in waterways, and drive water contacts. Furthermore, US-Mexico 'free-trade' agreements drive rapid growth in Tijuana, restrict Mexican environmental regulation enforcement, and drive underinvestment in sewage systems and infrastructure.

This study evaluates the presence of metal(loid) contamination from shrimp aquaculture effluent in a nearby mangrove ecosystem in Khung Krabaen Bay (KKB), Thailand. Our objectives were to: 1) examine how sediment metal(loid) concentrations change spatially in KKB relative to the aquaculture ponds; (2) compare mollusc trophic dynamics of elements associated with shrimp aquaculture; and (3) determine if certain mangrove mollusc species present better ecological indicators of aquaculture elemental contamination. We analyzed targeted elemental concentrations (As, Mn, Cu, Zn, Cr, Pb) in sediments sampled at increasing distance from intensive shrimp aquaculture and within the tissues of five species of molluscs. Differences in mollusc diet were studied using carbon (ẟ13C) and nitrogen (ẟ15N) stable isotopes, and biomagnification and biodilution of metal(loid)s were examined using ẟ15N values to infer trophic position. Elemental concentrations were low in farmed shrimp and pellet food relative to mangrove molluscs, but high in the sediments of drainage ponds filtering pond effluent. Declining elemental concentrations from the aquaculture drainage ponds to the mangrove sediments closest to shrimp farms suggested that the management settling ponds are effective at attenuating metal(loid) contamination. Large differences in mollusc mean ẟ13C (–25.8 to –20.1‰) and ẟ15N (1.9 to 8.3‰) values indicate variable diets across species, and trophically-elevated molluscs had greater marine-based diets resulting in a significant, positive correlation between mollusc ẟ13C and ẟ15N values. KKB molluscs biomagnify As, Zn, and Se, whereas declines in Mn and Cu with increasing trophic position indicate biodilution. The metals Pb, Fe, Al, Cr were elevated in the shrimp drainage pond sediments and in the tissues of the gastropods Ellobium aurisjudae, Cerithidea obtusa (both mud grazing), and Nerita lineata (algal grazing at low tide), identifying these gastropod species as probable bioindicators of aquaculture contamination in southeast Asian mangroves. Although we find biomagnification of some elements, mangrove mollusc metal(loid) concentrations are not likely to be of toxicological concern, and in fact, were lower than many mangroves elsewhere impacted by industrial and sewage contamination.

Cryptosporidium parvum, Giardia lamblia, and Toxoplasma gondii are waterborne protozoal pathogens distributed worldwide and empirical evidence suggests that wetlands reduce the concentrations of these pathogens under certain environmental conditions. The goal of this study was to evaluate how protozoal removal in surface water is affected by the water temperature, turbidity, salinity, and vegetation cover of wetlands in the Monterey Bay region of California. To examine how protozoal removal was affected by these environmental factors, we conducted observational experiments at three primary spatial scales: settling columns, recirculating wetland mesocosm tanks, and an experimental research wetland (Molera Wetland). Simultaneously, we developed a protozoal transport model for surface water to simulate the settling columns, the mesocosm tanks, and the Molera Wetland. With a high degree of uncertainty expected in the model predictions and field observations, we developed the model within a Bayesian statistical framework. We found protozoal removal increased when water flowed through vegetation, and with higher levels of turbidity, salinity, and temperature. Protozoal removal in surface water was maximized (~0.1 hour(-1)) when flowing through emergent vegetation at 2% cover, and with a vegetation contact time of ~30 minutes compared to the effects of temperature, salinity, and turbidity. Our studies revealed that an increase in vegetated wetland area, with water moving through vegetation, would likely improve regional water quality through the reduction of fecal protozoal pathogen loads.

Nonpoint sources of pollution, primarily from agricultural sources, are a major cause of water quality impairment. Yet policies to address this issue remain underexplored in the literature. This article first reviews the agricultural nonpoint source (NPS) pollution policy literature and categorizes its major findings. The North American literature, in particular, rarely analyses NPS policies already in force, and pays even less attention to overcoming implementation barriers to reaching desired environmental outcomes. Second, this paper evaluates a newly adopted policy approach that addresses nonpoint sources of nutrient contaminants in the surface waters of one of the United States’ most agriculturally productive and environmentally pristine areas, California's Central Coast. The article then reveals the political, budgetary and technical barriers faced by farmers, regulators, and other stakeholders. The article concludes by arguing that more analyses of implemented policies designed to address agricultural NPS pollution will better inform both local-level and federal policymakers towards the successful creation and implementation of policies that achieve environmental outcomes.

We investigated changes in vegetation composition of different grass buffer strips in a fragmented coastal agricultural landscape to evaluate the potential for native grass restoration of sites that receive agricultural runoff. Vegetative buffers bordering Elkhorn Slough, draining into Monterey Bay, California, were either seeded with a non-native annual grass (Hordeum vulgare) or with a mix of native perennial grasses (Bromus carinatus, Deschampsia cespitosa, Nassella pulchra), and above-ground biomass and cover of vegetation were measured over a 4-yr period. Based on preliminary results, we initiated a second, smaller-scale experiment to test establishment of native perennial grasses (Bromus carinatus, Elymus glaucus, Hordeum brachyantherum) at different seeding densities with combinations of non-native annual grasses (H. vulgare or Lolium multiflorum and Vulpia myuros) to optimize erosion control. In the first experiment, plots seeded with non-native annual grasses had greater biomass than nat...

The major ion chemistry of water from an 11.42-km reach of the Pajaro River, a losing stream in central coastal California, shows a consistent pattern of higher concentrations during the 2 nd (dry) half of the water year. Most solutes are conserved during flow along the reach, but (NO3 � ) decreases by ;30% and is accompanied by net loss of channel discharge and extensive surface-subsurface exchange. The corresponding net NO3 � uptake length is 37 6 13 km (42 6 12 km when normalized to the conservative solute Cl � ), and the areal NO3 � uptake rate is 0.5 lmol m � 2 s � 1 . The observed reduction in (NO3 � ) along the reach results from one or more internal sinks, not dilution by ground water, hill-slope water, or other water inputs. Observed reductions in (NO3 � ) and channel discharge along the experimental reach result in a net loss of 200-400 kg/d of NO3 � -N, ;50% of the input load. High-resolution (temporal and spatial) sampling indicates that most of the NO3 � loss occurs along the lower part of the reach, where there is the greatest seepage loss and surface-subsurface exchange of water. Stable isotopes of NO3 � , total dissolved P concentrations, and streambed chemical profiles suggest that denitrification is the most significant NO3 � sink along the reach. Denitrification efficiency, as expressed through downstream enrichment in 15 N-NO3 � , varies considerably during the water year. When discharge is greater (typically earlier in the water year), denitrification is least efficient and downstream enrichment in 15 N-NO3 � is greatest. When discharge is lower, denitrification in the streambed appears to occur with greater efficiency, resulting in lower downstream enrichment in 15 N-NO3 � .

Many tools exist for determining and mapping the bathymetry and topography of aquatic systems, such as freshwater wetlands. However, these tools often require time-consuming survey work to produce accurate maps. In particular, the large quantity of data necessary may be prohibitive for projects where determining bathymetry is not a central focus, but instead a necessary step in achieving some other goal. We present a method to produce bathymetric surface maps with a minimum amount of effort using global positioning system receiver and laser transit survey data. We also demonstrate that this method is surprisingly accurate, given the small amount of data we use to generate the bathymetry maps.

Bathymetry is the measurement of underwater topography. In wetlands, development of bathymetric maps can have many applications, including determining water storage capacity and hydroperiod (depth and timing of flooding) of a wetland, assisting with wetland design and restoration and land use planning, and facilitating legal boundary determination. This chapter provides practical steps for mapping and modeling wadeable wetland bathymetry. By characterizing the bathymetry of wetlands, investigators can better understand key hydrologic, geomorphologic, and ecological processes of wetlands. Using standard survey equipment, investigators can plan and implement a relatively simple survey of wetlands. These data can be used to model and quantitatively analyze the surface area, volume, and bottom topography (bathymetry) of wetlands using standard geographic information system software.

Natural groundwater recharge is inherently difficult to quantify and predict, largely because it comprises a series of processes that are spatially distributed and temporally variable. Infiltration ponds used for managed aquifer recharge (MAR) provide an opportunity to quantify recharge processes across multiple scales under semi-controlled conditions. We instrumented a 3-ha MAR infiltration pond to measure and compare infiltration patterns determined using whole-pond and point-specific methods. Whole-pond infiltration was determined by closing a transient water budget (accounting for inputs, outputs, and changes in storage), whereas point-specific infiltration rates were determined using heat as a tracer and time series analysis at eight locations in the base of the pond. Whole-pond infiltration, normalized for wetted area, rose rapidly to more than 1.0 m/d at the start of MAR operations (increasing as pond stage rose), was sustained at high rates for the next 40 d, and then decreased to less than 0.1 m/d by the end of the recharge season. Point-specific infiltration rates indicated high spatial and temporal variability, with the mean of measured values generally being lower than rates indicated by whole-pond calculations. Colocated measurements of head gradients within saturated soils below the pond were combined with infiltration rates to calculate soil hydraulic conductivity. Observations indicate a brief period of increasing saturated hydraulic conductivity, followed by a decrease of one to two orders of magnitude during the next 50 to 75 d. Locations indicating the most rapid infiltration shifted laterally during MAR operation, and we suggest that infiltration may function as a "variable source area" processes, conceptually similar to catchment runoff.

We quantify relations between rates of in situ denitrification and saturated infiltration through shallow, sandy soils during managed groundwater recharge. We used thermal methods to determine time series of point-specific flow rates, and chemical and isotopic methods to assess denitrification progress. Zero order denitrification rates between 3 and 300 μmol L(-1) d(-1) were measured during infiltration. Denitrification was not detected at times and locations where the infiltration rate exceeded a threshold of 0.7 ± 0.2 m d(-1). Pore water profiles of oxygen and nitrate concentration indicated a deepening of the redoxocline at high flow rates, which reduced the thickness of the zone favorable for denitrification. Denitrification rates were positively correlated with infiltration rates below the infiltration threshold, suggesting that for a given set of sediment characteristics, there is an optimal infiltration rate for achieving maximum nitrate load reduction and improvements to water supply during managed groundwater recharge. The extent to which results from this study may be extended to other managed and natural hydrologic settings remains to be determined, but the approach taken in this study should be broadly applicable, and provides a quantitative link between shallow hydrologic and biogeochemical processes.