Deported, homeless, and into the canal: Environmental structural violence in the binational Tijuana River.

INTRODUCTION: The 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. METHODS: A 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. RESULTS: The 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. DISCUSSION: Human 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.

Robust spatial analysis of sequestered metals in a Southern California Bioswale.

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.

Estimating environmental conditions affecting protozoal pathogen removal in surface water wetland systems using a multi-scale, model-based approach.

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.

Spatial and temporal infiltration dynamics during managed aquifer recharge.

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.