Abstract Soils are increasingly receiving treated wastewater (TWW) to support crop production and protect natural resources. However, besides water, various inputs, such as soil nutrients (salts), organic carbon, and various contaminants of emerging concern, including antibiotics, antibiotic resistance genes, pharmaceutical compounds, heavy metals, and microplastics, can be delivered. This review aims at (a) an integrated and mechanistic synthesis of current knowledge on potential impacts of TWW irrigation on key soil nitrogen turnover processes, such as nitrogen mineralization, nitrification, denitrification, and ammonia volatilization, and their drivers, and (b) identification of key knowledge and conceptual uncertainties to support future studies. Across the synthesis, no single, uniform TWW effect emerges. In fact, outcomes are consistently conditional on several co‐factors, such as treatment level, irrigation duration, soil type, and plant species, with the latter two sometimes exerting effects exceeding those of water quality itself. TWW alters soil conditions through substrate availability, redox dynamics, soil acidity and salinity, and contaminant exposure, but the mechanistic evidence linking specific drivers to specific nitrogen‐process outcomes is itself uneven. Identified knowledge and methodological gaps suggest long‐term field studies across TWW regimes, soil types, and climates; designs capable of disentangling co‐varying drivers at field scale; and laboratory studies addressing contaminant‐specific impacts, microbial functional persistence, and potential decoupling between nitrogen and carbon dynamics, an effect already evident, though unexplored as a general phenomenon, within the reviewed literature. Overall, this review offers an integrated, system‐level framework to support the evidence‐based management of environmentally and climate‐vulnerable soils receiving reclaimed or even conventional irrigation water.
Abstract In the United States, private well owners are responsible for monitoring and maintaining their drinking water but have little control over neighboring contamination sources and limited information about daily water quality. Potential for rapid contamination in karst settings exacerbates the challenge. The Runoff Risk Advisory Forecast (RRAF) is a real‐time online tool available in five US states that helps nutrient applicators avoid times and locations of high runoff risk. We wanted to determine if RRAF could be repurposed in areas susceptible to groundwater contamination to inform well owners of conditions when contamination is likely. Private wells were repeatedly sampled on seven dates (32–36 wells per date) and analyzed for nitrate‐nitrogen, total coliforms, and bovine manure markers. Three‐day windows of RRAF risk prior to sampling were selected post hoc, ranging from 1 to 3 days prior for manure markers to 10–12 days prior for nitrate. Contaminants were associated with RRAF values of ≥75% within these windows based on observed weather. A hydrologic association between RRAF risk and groundwater depth was also apparent. Overall, results suggest the RRAF model anticipates conditions of elevated contamination risk for susceptible wells. For nitrate, between‐well variation and delayed peak concentration suggested that well location and construction factors may be more informative than runoff events. Microbial contamination was rapid and distributed among wells, with one or more detections of coliforms in 31% of wells and bovine markers in 61% of wells. Thus, a warning system based on the RRAF model could help identify conditions of acute pathogen exposure.
Abstract Asian and European regions are characterized by huge inequalities, with the levels of cadmium, lead, and zinc tending to rise above safe concentrations by 1.26–6.01 times, disrupting nutrient cycling and microbial communities due to more than 37% of arable land at risk of high levels of metal mobilization. This literature review summarizes the patterns of spatial pollution, pyrolysis‐based biochar engineering, adsorption mechanisms, soil property transformation, remediation performance, nutrient synergies in enhancing agricultural productivity, and emergent soil–plant–microbe interactions to create a biochar development model (BDM) as a multifunctional biochar usage tool in sustainable agriculture. Under controlled experimental conditions, engineered biochars have demonstrated sorption capacities ranging from , reduced heavy metal bioavailability by 25%–62%, increased crop yields by 10%–32%, and enhanced soil organic carbon stocks by up to 595% in specialized degraded karst grassland restoration systems. However, these quantitative benefits are highly context‐dependent, and long‐term field evidence remains considerably more limited than that obtained from controlled laboratory and pot‐scale studies. This review integrates these findings into a BDM, a practical decision‐support framework that links spatial contamination patterns and climate‐driven redox dynamics with speciation‐informed pyrolysis engineering to optimize biochar design and guide field‐scale implementation for sustainable agricultural systems.
