Journal of environmental quality最新文献

Agricultural practices in the Everglades Agricultural Area (EAA) of South Florida have focused on managing accelerated organic matter (OM) decomposition in Histosols, which leads to soil subsidence. Rotating flooded rice (Oryza sativa L., variety Diamond) during the summer fallow period of sugarcane (Saccharum officinarum L.) has been proposed to reduce soil oxidation and loss by creating anaerobic conditions. However, limited research exists on the oxidation–reduction (redox) dynamics of these unique organic soils under rice cultivation and the associated OM decomposition, hindering the development of effective water management practices. This study aimed to understand the effects of flooded rice cropping on OM decomposition and loss by unraveling the intricacies of the redox conditions and their relationship with irrigation practices. Soil redox indicators, including dissolved oxygen (DO) and redox potential (E_h), along with flood depth, soil temperature, and acidity level (pH) were monitored in two rice fields. Soil samples were collected before planting and after harvest and their OM and active carbon concentrations were compared to quantify the effects of rice cultivation. Results showed that prolonged flooding shifted the soil from aerobic to moderately reduced conditions. Increased flood depth, elevated soil temperatures, and higher pH from alkaline limestone mixing contributed to lower DO and E_h. The observed reduction in active carbon suggests that flooded rice cultivation can slow the rate of OM decomposition and loss. Improved water management practices, including extended irrigation periods, consistent water levels, and optimized field conditions, are recommended to further mitigate soil loss and support sustainable farming in the EAA.

Plant-available soil extractable P is used for making P fertilizer recommendations and can be helpful in assessing P loss potential in surface runoff water. Current efforts to relate soil test P (STP) to soluble P concentration in snowmelt surface runoff in the Canadian Prairie Pothole Region do not account for the relative solubility of the P source used nor crop productivity as influenced by the properties of the receiving soil. These factors also potentially influence the utility of STP as an indicator of runoff P losses. In this study, the relationship between STP (modified Kelowna extraction) and P concentration in simulated snowmelt runoff was evaluated across eight inorganic P fertilizer sources applied for 3 years at three sites of variable topography and soil properties in south-central Saskatchewan, Canada. Over 3 years, lower solubility P fertilizer sources had lower P concentrations in runoff that were predicted by assessment of soil residual P level in the fall. Phosphorus fertilizer applications, landscape positions, and crops grown that gave rise to higher crop P uptake and removal over time tended to lead to lower P losses in snowmelt runoff. In contrast, soil conditions that limited crop P uptake, including elevated salinity and low soil moisture, promoted P losses in surface runoff. These influences were also predicted by STP content, demonstrating the utility of the STP measure.

The transition from conventional to more regenerative cropping systems can be economically risky due to variable transition period yields and unforeseen costs. We compared yields and economic returns for the first 3 years of the transition from a business as usual (BAU) conventional corn (Zea mays)–soybean (Glycine max) rotation to an aspirational (ASP) five-crop (corn-soybean-winter wheat [Triticum aestivum]–winter canola [Brassica napus]-forage) rotation in the Upper Midwest United States. Regenerative ASP cropping practices included the more diverse crop rotation, continuous no-till, cover crops, precision inputs, and livestock (compost) integration. For the first two transition years, BAU corn yields were 8%–12% higher than ASP while in the third transition year, BAU corn yields were 5% lower. Soybean yields were similar for the first 2 years but higher in BAU in the third year due to an ASP pest outbreak. Equivalent yields for other ASP crops were lower than BAU in the first 2 years but similar in the third year except for canola, which suffered from slug damage. Whole-system economic returns narrowed across years; by year three, whole system comparisons for the ASP corn and soybean entry points (corn-soybean-wheat and soybean-wheat-canola, respectively) showed equivalent economic returns for BAU and ASP, despite yield differences, owing largely to the ASP system's reduced operational costs. Overall findings suggest that early regenerative systems can be as profitable as conventional systems with careful attention to rotation entry points and inputs.

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.