Journal of environmental quality最新文献

Understanding and predicting dissolved phosphorus release from soils is critical to proper land management for maximizing P uptake by agronomic crops and minimizing losses to surface waters. In this study, we investigate the amount and rate of P release for 22 diverse soils using flow cells operating at low and high velocity. P release data were fit to a one-dimensional advection-dispersion equation assuming two P pools (Q₁ and Q₂) each with their own kinetic desorption rate. The model provided exceptionally good fits to the P release data at both flow velocities. The high-flow velocity desorbed P at a higher rate, while the slow-flow velocity released more P and at higher concentrations; although when normalized for residence time, the rate of P desorption was greater in the slow-flow velocity columns. Fitted values of the readily available P pool (Q₁) for the two flow velocities were well correlated, with Q₁ values for the slow flow velocity being consistently greater than the high flow velocity. Conversely, kinetic desorption parameters between the two flow velocities were not as well correlated. Fitted Q₁ values were strongly correlated with oxalate-extractable P (P_Ox), Mehlich-3 P (P_M3), and water-extractable P (P_W). Q₁ values were much lower than P_Ox and P_M3 but similar to P_W. We only found weak correlations between the kinetic desorption rates and measured soil properties. Our results show that the use of flow-through cells can provide useful information on P release from soils, but results will be dependent on flow velocity.

The development of phytoplankton communities in hypereutrophic shallow lakes, often used for aquaculture, is not fully understood and can sometimes be unpredictable. Focusing on the abiotic factors that regulate their succession, we recorded short-term mixing events in a shallow lake and examined their relationship with nutrient release from sediments in the lab. In situ measurements reveal a dynamic cycle of mixing and stratification during summer, when the lake mostly stratifies during the day and mixes at night, depending on wind conditions. The studied lake was stratified 45% of the time and, on average, mixed every 1.5 days. In terms of hydrodynamics, the velocities of surface and bottom waters are similar in magnitude, regardless of whether conditions are calm or windy. Stirred-core experiments recreated both lake hydrodynamic regimes and the observed patterns of destratification at the study site. Temporal destratification experiments show that the sediment releases more solutes during complete mixing than during partial destratification, due to an increase in sediment/water concentration gradients. This results in more phosphorus and ammonia being released, and more nitrate being consumed by sediments, when the water column is fully mixed compared to when a bottom layer remains unmixed. The effect of dissolved oxygen did not directly influence nutrient release by Fe-P compounds dissolution, as oxygen above the sediment did not fall below 50% saturation, but mixing enhanced the transport of electron acceptors to the sediment. The cycle of stratification and mixing appears to be a key factor in internal loading under oxic conditions.

Excess nitrogen and phosphorus export from agricultural lands is a primary contributor to water quality degradation in the United States. To improve water quality, significant investments have been made to implement conservation practices on agricultural lands, including through mandated spending in the Farm Bill and the Inflation Reduction Act. Effectively guiding conservation implementation requires assessment of practice efficacy at regional and national scales, consistent with the scales of water quality goals. To evaluate whether existing resources are sufficient for such conservation efficacy assessments, we review prior efforts and publicly available data and tools to evaluate the effects of agricultural conservation on water quality outcomes. We find that practice records from programs that fund agricultural conservation have a unique and substantial potential for secondary use to generate insights about conservation effects from local to national scales, but modifications would help maximize the potential of these data for assessing conservation efficacy. Such assessments would benefit from improved consistency in reporting units and geographic scales across program datasets; quantification of the duration of water quality benefits from conservation practices; publication of practice data aggregated across programs, to increase the spatial resolution of conservation insights while maintaining legal protections of producer privacy; and collection of water quality and conservation practice data at similar temporal and spatial scales. Enhancing existing and future datasets could deliver high return on effort by generating valuable insights to improve the use of conservation practices for water quality management.

Frass—the main by-product of insect rearing for animal feed—is emerging as a promising soil amendment and plant growth promoter. However, basic agronomic information is lacking and prevents frass’ widespread use as a biofertilizer. This study assessed impacts of black soldier fly (Hermetia illucens L. [Diptera: Stratiomyidae]) frass on soil fertility, crop growth, and quality compared to poultry litter (PL). Irrigated and non-irrigated soybean (Glycine max L. Merr.) and non-irrigated switchgrass (Panicum virgatum L.) plots received either PL (5.6 Mg ha⁻¹), low frass rate (LF; 5.6 Mg ha⁻¹), high frass rate (HF; 11.2 Mg ha⁻¹), besides the unamended control (CT). In general, soil nutrients and enzymes at the soil surface (0–15 cm) were unaffected by soil amendments. Irrigated-HF soybean had 7% higher grain P concentration than non-irrigated-HF, and 13% greater P concentration than the non-irrigated CT. Additionally, HF increased K concentration in switchgrass by 25% relative to the CT. HF reduced soybean leaf damage by 35% and 48% relative to the non-irrigated CT and PL-irrigated plots, illustrating for the first time frass’ potential to enhance plant resistance to herbivory, likely owing to the presence of chitin. LF had 2–4 times greater nutrient use efficiency than HF and PL in organic soybean and switchgrass systems, reflective of similar yields despite lower nutrient inputs. These findings provide foundational knowledge for frass utilization as an organic fertilizer and biostimulant, closing nutrient loops through waste recovery during insect rearing, and supporting the development of an emerging sustainable industry.

Organic production aims to diversify crop rotation and use organic fertilizer sources to build soil fertility and improve soil health indicators. The impact of organic farming on water quality in artificially drained midwestern Mollisols has received limited attention. This 7-year study compares tile nitrate loss and yields under three cropping systems: (1) conventional corn (Zea mays L)-soybean (Glycine max L.), (2) organic corn–soybean–oat (Avena sativa L.)/alfalfa (Medicago sativa L)–alfalfa, and (3) organic perennial pasture. Nitrogen (N) fertilization consisted of sidedress urea ammonium nitrate for conventional corn (168 kg N ha⁻¹) and spring-applied composted manure for organic corn (168 kg N ha⁻¹) and oats (56 kg N ha⁻¹). Overall, the 4-year organic rotation reduced N loads by 50% and pasture reduced loads by 93% compared with the conventional 2-year corn–soybean rotation. Reductions in N loads were related to the diversified cropping system as no difference in N losses was detected when only corn–soybean phases of the organic rotation were compared with the conventional system. Annual variations in N loads were explained by precipitation and varied by crop. Soil health indicators sampled in the fall showed minimal influence on N losses. Organic corn (4 of 7 years) and soybean (6 of 7 years) yields were equivalent to or higher than conventional in most years. Results of this study suggest that organic farming practices that combine use of animal manure and inclusion of small grains, forage legumes, and green manures can improve water quality in artificially drained landscapes while maintaining crop yields.

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.