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Abstract Crop water productivity (CWP) metrics can reveal how the dynamics of crop production and water use change across space and time. We use field-scale satellite inputs from 2016–2021 to estimate potential water savings for four crops (almonds, grapes, walnuts, and citrus—which collectively account for approximately one-third of California’s cropland area), within critically overdrafted groundwater sub-basins of California’s San Joaquin Valley. These annual estimates of field-level water savings potential are based on locally achievable CWP values for each crop type. Our findings show considerable spatial variation in CWP and potential water savings within each sub-basin. We find that increasing CWP to peak efficiency (defined as improving fields to the 95th percentile of observed CWP) for four crops could meet up to 36% of the estimated annual overdraft in San Joaquin Valley. For comparison, fallowing 5% of the four crop type fields in the same study area could potentially reduce annual overdraft by 11%. By delivering results at the field scale, our work can inform targeted interventions by irrigation district managers and more efficient allocation of state incentives for improved water management. For example, we estimate that state grant funding for water efficiency upgrades could have amplified potential water savings threefold by targeting investments to the least efficient fields. 

Multiphysics modelling reveals how the electric double layer governs nitrate transport and how a more negative catalyst potential-of-zero-charge promotes ammonia formation. 

Underutilized wastewaters containing dilute levels of reactive nitrogen (Nr) can help rebalance the nitrogen cycle. 

Electrocatalyst-in-a-box, a novel reactive separation process, enables a molecular catalyst to convert wastewater nitrate into purified ammonia. 

This study reports the accuracy and applications of an attenuated total reflectance–surface-enhanced infrared absorption spectroscopy (ATR–SEIRAS) technique to indirectly measure the interfacial pH of the electrolyte within 10 nm of the electrocatalyst surface. This technique can be used in situ to study aqueous electrochemical reactions with a calibration range from pH 1–13, time resolution down to 4 s, and an average 95% confidence interval of 14% that varies depending on the pH region (acidic, neutral, or basic). The method is applied here to electrochemical nitrate reduction at a copper cathode to demonstrate its capabilities, but is broadly applicable to any aqueous electrochemical reaction (such as hydrogen evolution, carbon dioxide reduction, or oxygen evolution) and the electrocatalyst may be any SEIRAS-active thin film (e.g., silver, gold, or copper). The time-resolved results show a dramatic increase in the interfacial pH from pH 2–7 in the first minute of operation during both constant current and pulsed current experiments where the bulk pH is unchanged. Attempts to control the pH polarization at the surface by altering the electrochemical operating conditions—lowering the current or increasing the pulse frequency—showed no significant change, demonstrating the challenge of controlling the interfacial pH.