Journal of environmental quality最新文献

Although wetland restoration is a promising strategy to reduce nonpoint source nitrogen (N) loads, there is some concern over the potential for increased nitrous oxide (N₂O) emissions. We examined the production and emission of N₂O and methane (CH₄) from wetlands designed to intercept and reduce elevated, nonpoint source nitrate (NO₃⁻) loads. We measured N₂O and CH₄ flux rates at three wetlands subject to a wide range of NO₃⁻ loading rates. Nitrate, dissolved N₂O, and dissolved CH₄ associated with inflows and outflows were estimated using measured flows and concentrations, and N₂O and CH₄ emissions were estimated using floating chambers. Nitrate removal, N₂O production, and CH₄ production were estimated by mass balance analyses. Methane emission rates averaged 1,010 mg m⁻² day⁻¹, similar to rates for restored depressional wetlands, and N₂O emission rates averaged 4.49 mg m⁻² day⁻¹, similar to rates from cropland. Inflows and outflows contributed little to CH₄ fluxes but were significant components of N₂O budgets. Dissolved N₂O loads to the wetlands from inflow streams ranged from 8.1% to 70% of the total N₂O inputs, and dissolved N₂O export from the wetlands through outflow to streams ranged from 7.3% to 63% of the total N₂O outputs. Nitrous oxide production and emission increased with NO₃⁻ loading; however, these wetlands also exhibited very high NO₃⁻ conversion efficiencies, with N₂O-N production and emission averaging approximately 0.5% of NO₃⁻ removal. The fraction of N loading that would be transformed to N₂O in these wetlands is much lower than in cropland or downstream riverine systems.

Riparian zones are a critical terrestrial-aquatic ecotone. They play important roles in ecosystems including (1) harboring biodiversity, (2) influencing light and carbon fluxes to aquatic food webs, (3) maintaining water quality and streamflow, (4) enhancing aquatic habitat, (5) influencing greenhouse gas production, and (6) sequestering carbon. Defining what qualifies as a riparian zone is a first step to delineation. Many definitions of riparian boundaries focus on static attributes or a subset of potential functions without recognizing that they are spatially continuous, temporally dynamic, and multi-dimensional. We emphasize that definitions should consider multiple ecological and biogeochemical functions and physical gradients, and explore how this approach influences spatial characterization of riparian zones. One or more of the following properties can guide riparian delineation: (1) distinct species, elevated biodiversity, or species with specific adaptations to flooding and inundation near streams relative to nearby upland areas; (2) unique vegetation structure directly influencing irradiance or organic material inputs to aquatic ecosystems; (3) hydrologic and geomorphic features or processes maintaining floodplains; (4) hydric soil properties that differ from the uplands; and/or (5) elevated retention of dissolved and suspended materials relative to adjacent uplands. Considering these properties for an operational and dynamic definition of riparian zones recognizes that riparian boundaries vary in space (e.g., variation of riparian corridor widths within or among watersheds) and time (e.g., responses to hydrological variance and climate change). Inclusive definitions addressing multiple riparian functions could facilitate attainment of research and management goals by linking properties of interest to specific outcomes.

Per- and polyfluoroalkyl substances (PFAS) in biosolid-amended soils can transfer and accumulate in crops, cattle, and people. Bioaccumulation factors (BAFs) are often applied to estimate the transfer of contaminants from soil to crops. However, they can vary widely and introduce uncertainty to exposure and risk estimates. We, therefore, aimed to quantify this uncertainty in a case study of an agricultural field with elevated soil concentrations of perfluorooctane sulfonic acid (PFOS) using literature-derived BAF versus measured concentrations of PFOS in corn (Zea mays L.) kernels and stover. PFOS was the predominant PFAS detected in soil and corn stover (<100 and 19 ng/g), and no detectable PFAS were identified in kernels. The median BAF (0.17) for PFOS was similar to that derived from a review of previous studies, while the maximum (0.2) was over an order of magnitude lower. Median PFOS concentrations in stover from our samples were comparable (16.60 ng/g) to those calculated using the literature-based BAF (16.28 ng/g). For cattle consuming stover, median and upper bound concentrations of PFOS in beef (30 ng/g) were similar and 60% lower using measured versus literature-derived BAF concentrations in stover. Finally, the central tendency exposure for children (27 ng/kg-bw/day) was similar using measured versus literature-derived BAF concentrations in stover and higher compared to adults (15 ng/kg-bw/day). Overall, these results indicate that (1) corn kernels accumulate little to no PFAS even when soil concentrations are elevated, (2) direct measurement of PFAS in crops can reduce uncertainty in exposure and risk assessment, and (3) PFOS can biomagnify via the soil-stover-cattle-human pathway and is found to pose a potential risk in our case study.

Brazil is the world's largest producer and exporter of soybeans (Glycine max L. Merr.). Assessing yield gaps (Yg) is essential for improving resource use efficiency and guiding farmers’ management strategies. The objective of this study was to estimate soybean yield potential (Yp), water-limited yields (Yw), and Yg based on water and agricultural practices across Brazil's five soybean macroregions. We have quantified yield losses due to delayed sowing and evaluated interannual yield variability caused by environmental and climatic factors. The results revealed that the southern regions had the highest Yp values but also the largest Yg values, which were strongly influenced by climatic factors. In contrast, the Brazilian Midwest had the lowest Yp yet minimal water-related Yg, with relatively stable yields over time; here, Yg were primarily due to crop management rather than climatic constraints. In northern macroregions, lower Yp was observed with moderate climatic influences. Delayed sowing reduced Yp across all macroregions, with the greatest losses occurring in regions with initially high Yp, particularly in the south. Each macroregion has unique environmental conditions that lead to different patterns of Yp, Ya (actual yield), and Yw. In the southern macroregions, Yg are primarily due to water constraints, indicating potential benefits of irrigation, while the Midwest, which has the lowest Yg, improved crop management practices offer the most significant opportunity for yield gains.

Public concerns exist over whether land application of biosolids is a pathway of introducing large amounts of per- and polyfluorinated alkyl substances (PFAS) into terrestrial ecosystems. Ongoing research is investigating a variety of high organic matter (OM) and Al/Fe phases for use as amendments to reduce PFAS leaching from matrices including biosolids. Drinking water treatment residuals (DWTRs) have characteristics (e.g., high OM, oxalate-extractable Al (Alo_x), and/or oxalate-extractable Fe (Fe_Ox) content) linked with PFAS retention and are widely available at low cost. We investigated sorption and desorption of a suite of eight PFAS, including sulfonates and carboxylates varying from C4 to C9, in biosolids amended with Al, Ca, and Fe DWTRs at rates from 2.5% to 10% wt/wt. Three biosolids were used: (1) high OM, low Fe_Ox; (2) high OM, high Fe_Ox; and (3) low OM, high Al_Ox. For all biosolids and DWTRs tested, amendment with 2.5% and 5% DWTR resulted in no significant increase of partition coefficient (Kd) value in sorption for the examined PFAS when compared to controls, and only a few inconsistent significances in desorption. However, at 10% DWTR, significantly increased Kd values were observed in both sorption and desorption in some of the DWTR-treated biosolids, particularly those treated with Al DWTR. These results suggest that DWTRs (especially Al DWTRs) can enhance the retention of PFAS, and that DWTR amendment rate appeared to be more influential on PFAS sorption and desorption than physical characteristics of the DWTRs and biosolids or PFAS properties.

Korea and the Netherlands historically developed highly fertilized cropping systems, resulting in the highest nitrogen (N) and phosphorus (P) surpluses among Organization for Economic Cooperation and Development (OECD) countries. However, their nutrient balances changed differently over the past three decades. The Netherlands reduced its N and P balances dramatically, from 328 to 166 kg ha⁻¹ and 35 to 4 kg ha⁻¹, respectively, while Korea's balances remained unchanged with the highest levels in 2019 (230 kg N ha⁻¹ and 46 kg P ha⁻¹). To find solutions for Korea's persistent nutrient surpluses, changes in nutrient balances and related parameters were compared using OECD statistics. Despite Korea's efforts to reduce chemical fertilizer use, a 33% decline in agricultural land area and increased manure production offset the reduction. Conversely, the Netherlands rapidly decreased nutrient balances by reducing N and P inputs by 35% and 52%, respectively. Nutrient outputs in the Netherlands, primarily driven by forage harvest, were over twice as high as in Korea, helping lower its balances despite minor output declines. By the late 2010s, Dutch P input and output were nearly equilibrated, indicating no P surplus. As a result, the Netherlands has improved its nutrient use efficiency substantially, which inversely correlates with nutrient balance, but Korea has not shown considerable changes. Therefore, to address Korea's nutrient balances, nutrient inputs should be reduced while increasing outputs. Determining the level of nutrient inputs, coupled with advanced agronomic practices and technologies to improve nutrient use efficiency, is essential for achieving reductions in nutrient balances while enhancing crops and forage production.

Heavy metal contamination in coastal ecosystems can significantly impact biological activity, metal retranslocation, and biogeochemical cycling. This study assessed the concentrations of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) in mangrove sediments and leaves of two ecosystems in Puerto Rico that differed in their proximity to urban areas: La Parguera and Laguna Grande. Metal bioconcentration factors and retranslocation percentages (RT%) were determined. Relationships between metals, between metals and sediment carbon, and metal retranslocation and bioavailability differed between the sites. Metals with high retranslocation percentages by plants, such as zinc and lead at La Parguera, suggest that plant-mediated stabilization processes can reduce immediate bioavailability but may pose latent risks under changing environmental conditions. Conversely, cadmium, with low retranslocation, and nickel, with high retranslocation and high bioavailability at Laguna Grande, indicate greater potential for biological uptake and ecosystem stress. Results suggest that differences in relationships between metals and between metals and carbon may help identify sources and effects of metals. Further research is needed to explore the direct physiological effects of metal exposure on plants and their implications for carbon storage and ecosystem health in mangrove-dominated systems.

Nitrogen Leaching Estimation System version 5 (NLES5) is an empirical model extensively used for estimating annual nitrate leaching from the root zone. The model is based on leaching data obtained by multiplying the measured nitrate concentration below the root zone depth by the percolation calculated using a hydrological model, which together provides estimates of annual nitrate leaching from the root zone. However, this approach has some limitations, including redundancy and unclear error propagation in the relationship between nitrate concentration and percolation without considering seasonal variability. This study presents an approach to estimate the monthly distribution of nitrate concentration based on measurements of soil water samples taken with suction cells installed below the root zone. Our workflow includes screening algorithms to identify the most relevant predictors, testing the predictive performance, reducing the number of predictions for practical implementation, and evaluating the impact on the final nitrate leaching calculations. The workflow was applied to the suction cup measurement dataset in the NLES5 support database of field experiments. The results show that the regression tree-based Extreme Gradient Boosting algorithm effectively estimates monthly variations in nitrate concentrations without relying on percolation data, by using time, management, soil, and weather covariates such as month, spring mineral fertilization, main crop, winter crop, clay content, mean monthly temperature, and accumulated precipitation in the harvest year. A cross-validated error of 34% was achieved for nitrate concentration, and a correlation of 0.8 with nitrate leaching calculated from observed concentrations demonstrates a consistent description of the seasonal distribution of nitrate concentrations below the root zone.

Eutrophication enhances emissions of greenhouse gases (GHGs) from surface waters. Policies designed to ameliorate eutrophication by limiting nutrient loadings to surface waters can reduce these GHG emissions and, in turn, reduce future climate damages (e.g., from heat stress, sea-level rise, etc.)—yet this benefit has not been considered in benefit-cost analyses of water quality policies. We address this gap by using a set of linked watershed, lake, and aquatic GHG models to estimate emission reductions from a large-scale nutrient management program in the America's largest estuary, the Chesapeake Bay. The modeling system predicts reductions in chlorophyll-a, total phosphorus, and GHG emission rates in waterbodies throughout the watershed, but those in the southern portion of the watershed are predicted to exhibit greater reductions than those in the north, likely due to strong climate (e.g., ice-cover duration) and land-cover gradients across the domain. We estimate climate benefits from changes in GHG emissions from these water bodies of over $300 million over the first 50 years of the program (2025–2075)—similar in magnitude to commonly quantified categories of water quality benefits. We then extrapolate our results to the third largest drainage basin in the world—the Mississippi-Atchafalaya River Basin—to estimate climate benefits of reduced GHG emissions from lakes and reservoirs in the basin resulting from a similarly stringent nutrient management policy. Our findings suggest that reductions in GHG emissions from nutrient management programs should not be overlooked when evaluating the societal benefits of such policies.

Separation and pyrolysis of the solid fractions of biogas digestate and animal slurry offer potential solutions to environmental and logistical challenges associated with direct slurry application as fertilizer. However, thermochemical transformations during pyrolysis typically reduce P availability. This study evaluated biochars produced at 400°C, 500°C, and 600°C from the solid fractions of biogas digestate (BDF) and pig manure (PMF) for their P-fertilization effects using a pot experiment with perennial ryegrass (Lolium perenne var. Soriento) and the ³³P dilution approach. The ryegrass biomass across two harvests remained similar for all biochar treatments but was significantly lower than for the mineral fertilizer (KH₂PO₄) treatment. Significant differences were evident in P contribution from biochars and raw feedstocks, as well as in total P uptake rates between treatments. The readily available P contents of biochar and P-recovery rates in plant shoots were negatively correlated with pyrolysis temperature, which was especially pronounced for digestate-derived biochars. All materials except high-temperature biochar (600°C) had mineral fertilizer replacement values exceeding 50%, indicating substantial P-recycling potential. Biochars produced at 400°C and 500°C had a similar fertilizer value as their original feedstocks. Therefore, low-temperature pyrolysis of separated solid fractions represents a promising approach that preserves the P fertilizer value while providing climate benefits through soil C sequestration and reduced energy requirements for transport.