Total Nitrogen Mass Research Articles

The role of magnetite for enhancing reduction of N-nitrosodimethylamine by zero-valent iron

Mixed-valent iron mineral has significant effects in redox reaction and engineering applications. Magnetite (Fe3O4) combined with zero-valent iron (ZVI) were chosen to reduce N-nitrosodimethylamine (NDMA). Enhancement had been shown in ZVI-Fe3O4 system than the sum of removals of ZVI and Fe3O4 systems. Lower solution pH value facilitated the removal of NDMA, the concentration of dissolved oxygen (DO) had little effect. The main reduction products of NDMA by ZVI-Fe3O4 were 1,1-dimethylhydrazine (UDMH) and dimethylamine (DMA). The total nitrogen mass was unbalanced. By capturing the active species in the ZVI-Fe3O4 system, active hydrogen atoms had been determined. Catalytic hydrogenation was proposed to be the mechanism. Electrochemical tests showed that ZVI-Fe3O4 had a lower open circuit potential and a higher corrosion current than ZVI, the presence of Fe3O4 promoted the corrosion of ZVI. Scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses of solid powders showed that the corrosion was more serious and no other substances were formed on the surface of powders in ZVI-Fe3O4 system after reaction. X-ray photoelectron spectroscopy (XPS) showed that the value of ratio of peak area of Fe(III) to Fe(II) of ZVI-Fe3O4 surfaces was lowest. The Fe(III) on the powders’ surface could be reduced by ZVI and the surface passivation of ZVI would be prevented, which would be benefit for the generation of active hydrogen atoms.

Effect of floating treatment wetland coverage ratio and operating parameters on nitrogen removal: toward design optimization.

Floating treatment wetlands (FTWs) have the potential to improve the quality of wastewater discharges, yet design basics are unavailable to size these systems. This study investigates the effect of FTWs' coverage ratio and hydraulic retention time on agri-food wastewater treatment. This was studied in a pilot-scale experiment comprising four lagoons (6.5 m3 each) fed with real effluent from an existing tertiary treatment lagoon. An evaluation of FTW of different sizes (L24, L48, and L72 representing 24, 48, and 72% of pilot lagoons surface areas) and a control, L0 (without FTW), was performed over 16 months. Overall, L72 and L48 moderately improved total nitrogen (TN) mass removal compared to L0 (p < 0.05), while L24 exhibited similar TN mass removal (p = 0.196). The highest improvement was observed for L72, exhibiting up to 55% (mean of 13%) greater N mass removal than the control. The net increase in TN removal by FTWs was mainly related to denitrification, promoted by decreasing dissolved oxygen for increasing FTW coverage ratio. Residence time, temperature, and dissolved oxygen were the main parameters driving TN removal by FTWs. Retrofitting existing lagoons with FTW can facilitate N retrieval through plant harvesting, thereby reducing N remobilization from sediment (common in conventional lagoons).

Nitrogen mass balance and uptake velocity for eutrophic reservoirs in the Brazilian semiarid region.

The nitrogen (N) cycle from the catchment to the downstream reservoir is complex, particularly the quantification of N losses. However, in order to assess the nitrogen impact in a reservoir ecosystem, simplified models may be applicable regarding the TN load production and the magnitude of lake TN removal. This study presented a methodology to perform and validate a TN mass balance to further calibrate a simplified coefficient for TN losses (vf.) in 29 tropical semiarid reservoirs. The study reservoirs were highly productive ecosystems with an average total nitrogen (TN) concentration, accounting for all measurements in all reservoirs, ranging from 0.59 to 3.84 mg L-1. Regarding the production of TN load, the median values ranged from 4.35 to 2,499.43 t year-1 with median of 80.34 t year-1. The TN loads were estimated through an annual mass balance over a 24-year period. The median of the estimates was compared with reference values obtained by using the export modelling coefficient. The correlation between the median estimated and reference loads resulted in satisfactory agreement (r2 0.88) and reinforced the reliability of the mass balance alternative. From the validated TN loads, the TN uptake velocity (vf) was estimated for all reservoirs (44.9 ± 20.1 m year-1) and could be described as a general function of the water residence time. The reservoirs of the study region have demonstrated higher vf than temperate lakes and reservoirs and similar vf with Latin America/Caribbean ones. As expected, reservoirs of warmer climates tend to present intensified N loss processes compared to lakes and reservoirs of temperate regions. The methodology proposed in the present study can be used to potentially improve water quality management in tropical semiarid reservoirs.

Strengthen the purification of eutrophic water and improve the characteristics of sediment by functional ecological floating bed suspended calcium peroxide and sponge iron jointly

To overcome the shortcomings of conventional ecological floating bed (CEFB) in purifying landscape water, this study constructed a functional ecological floating bed (FEFB) through the suspension of calcium peroxide (CP) and sponge iron (SI) jointly below the CEFB. The purification effect of water quality and influence of sediment were compared in control check, CEFB, and FEFB systems, which were loaded the same sediment and reclaimed water in a field experiment. Results showed that the FEFB suspended with CP and SI had evident purification effect on the quality of landscape water supplied with reclaimed water and can maintain stably the nutrient status of the water body at mesotrophic levels and low turbidity. The FEFB promoted the degradation of humus, thus eliminating the chroma risk in water body caused by the decay of plants from the CEFB. Moreover, the FEFB can control the sediment mass produced, reduce the total nitrogen (TN) mass of sediment, and decrease the transformable TN (TTN) content in the sediment. The FEFB enhanced the stability of phosphorus (P) in the sediment, where the relative content of Ca–P and stable P reached 42.18% and 64.27%, respectively. To sum up, the FEFB suspended with SI and CP can not only effectively control the eutrophication and sensory index of landscape water but also change the TTN content and P forms in sediment, making the sediment more stable. Thus, the FEFB provides an innovative approach to reduce endogenous nutrient release for landscape water along with recharging with reclaimed water.

Response of sedimentation rate to environmental evolution in Da River Reservoir in Southwest China.

Lake sediment records the evolution process of the interaction between human and nature. It is important to master the lacustrine sedimentation rate for the ecological environment assessment of catchment. A 60-cm sediment core was collected in the Da River Reservoir during 2019 to analyze radionuclides (210Pb and 137Cs) massic activities, grain size, total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), and metals (Mn, Cu, Al, and Pb) mass fractions to reconstruct the response of sedimentation rate to environmental evolution. The environmental changes in the small catchment were classified into the following three stages through cluster analysis (CA) for geochemical parameters in the sediment core: phase I (1881-1985), phase II (1987-1999), and phase III (2000-2018). The average depth sedimentation rates (ADSRs) of the three stages were 0.33, 0.90, and 1.50cm/year, respectively. The sedimentation rates increased from the bottom to the surface layer, indicating that the exogenous inputs into the reservoir have been occurring. The sediment deposition in phase III was strongly disturbed by the environmental changes (such as warmer climate and intensified land use). Therefore, sedimentation rates showed a rapid increase. Both Pearson correlation analysis and redundancy analysis (RDA) showed that sedimentation rates were positively correlated with climatic factors, particle size, nutrients and metals mass fractions, elemental ratios, and socioeconomic parameters. Sedimentation rates show high sensitivity to anthropogenic activities and climatic change, which can be used to reconstruct the environmental evolution process at a small catchment scale.

Effect of Operational Conditions on Ammonia Recovery from Simulated Livestock Wastewater Using Gas-Permeable Membrane Technology

Gas-permeable membrane (GPM) technology is a novel alternative to reduce N content in wastewater while recovering N in the form of an ammonium salt solution that can be used as fertilizer. This work aims to elucidate the effects of three operational conditions on the performance of GPM technology for ammonia recovery in batch conditions using synthetic wastewater that simulates livestock wastewater. Firstly, the effect of the ratio of the initial mass of total ammonia nitrogen (TAN) per membrane surface from 197 to 936 g N per m2 of membrane was investigated. The highest ratio presented the highest TAN recovery rate (90 g N m−2 d−1). Secondly, the influence of the ratio of the volume of wastewater per volume of acidic trapping solution in the range from 7.8 to 33.3 L L−1 was studied. In this case, the higher the ratio, the higher the N concentration in the trapping solution, achieving a N concentration of 43,773 mg N L−1 with a ratio of 33.3 L L−1. Finally, two different TAN concentrations (&lt;0.1 and 30 g N L−1) in the acidic trapping solution were evaluated. The use of a trapping solution with a TAN concentration of 30 g N L−1 led to a reduction in the TAN recovery rate, which meant that the diffusion of ammonia through the membrane was more difficult as the trapping solution became saturated with TAN. Overall, the tested conditions highly influence the performance of GPM technology, and therefore, these conditions should be set to optimize the ammonia recovery and reduce nitrogen losses.

Inoculation of growth-promoting bacteria in the lettuce crop

Plant growth promoting bacteria (PGPB) are an alternative to increase the productivity of several crops, including lettuce. Several reports are found in the literature with the use of plant growth-promoting bacteria in lettuce cultivation, but most seek increments during the production of seedlings. Aiming to provide increments in the cultivation of lettuce in the field and to generate subsidies to technicians and producers, the present work aimed to study the influence of the application of commercial products based on Azospirillum brasilense, Bacillus subtilis + B. megaterium and Pseudomonas fluorescens, on agronomic characteristics and quality of crisp lettuce. The experiment was implemented in two locations, in a randomized block design, in a 4 x 3 factorial scheme, with four replications. The first factor refers to the application of different PGPB: control, without inoculation; inoculations with A. brasilense; B. subtilis + B. megaterium and P. fluorescens. The second factor was composed of three times of application of PGPB, the first being on the day of seedling transplantation (DAT), the second at 15 STR and the third on the day of seedling transplantation + 15 DAT. At 15 DAT, the relative chlorophyll content, plant height, head diameter, number of leaves per plant, leaf area, leaf dry mass, stem dry mass, root dry mass, total dry mass, root volume were evaluated. and root length. At harvest, the same variables analyzed at 15 DAT + leaf fresh mass, stem fresh mass, head fresh mass, root fresh mass, total fresh mass and leaf contents of nitrogen, phosphorus and potassium were analyzed. The inoculated plant growth-promoting bacteria did not promote a significant increase in the development of the lettuce cultivar Vera when compared to the control (without PGPB application).

Finite size corrections on the estimation of the effective diffusion coefficients through the dynamical behavior of the diffusion zone during gaseous nitriding of pure iron

Effective diffusion coefficients in monolayer and bilayer growth experiments during gaseous nitriding of pure iron have been previously determined by assuming a diffusion zone of infinite size. In this work, finite size corrections to the effective diffusion coefficients are determined by imposing total mass balance of nitrogen in a sample with a diffusion zone of finite size. The proposed model incorporates an equation of motion for the diffusion zone thickness, which is consistent with total mass balance. The model does not have an exact analytical solution; therefore, semi-analytical methods are used to find approximate solutions to the problem. The effective diffusion coefficients are estimated through a double minimization process. Experimental data from other authors are used to define a least squares error function for the layer thicknesses and another error function for the total mass of nitrogen. The steepest descent method is used to determine a set of diffusion coefficients that minimize the error in the layer thicknesses. The effective diffusion coefficients that best approximate the total mass of nitrogen in the sample are estimated by solving the model for each of the local minima previously determined. The values of the effective diffusion coefficients are validated by comparing the numerical and semi-analytical solutions obtained from the proposed model, with the experimental values for the total nitrogen mass at different nitriding conditions. Finally, non-parabolic growth behavior is captured by the proposed model in experiments where the assumption of a diffusion zone of infinite size or saturated substrate is arguable.

Distribution Characteristics of Carbon, Nitrogen, and Phosphorus Bearing Pollutants in the Ancient Town Rivers of Suzhou

Suzhou is a water-deficient city with water quality issues. Despite water conservation measures, emission reductions, source control, and pollution interception, water quality remains poor. To understand the total mass and distribution characteristics of carbon, nitrogen, and phosphorus bearing pollutants and inform decisions regarding river dredging, sediment and water samples were collected from 20 representative sections in the town's rivers during the spring of 2019. The depths of the sediments were measured along with the concentrations of carbon, nitrogen, and phosphorus bearing pollutants in the sediments and water, and the pollution degree was evaluated. Variations in various parameters were predicted for change water, diversion water, rainfall, and dredging. The results show that the sediment depths ranged between 22 and 1025 mm (average=266 mm), and the total mass of sediment was approximately 5.2×105 t in the ancient town rivers of Suzhou. The average proportions and concentrations of TOC, TN, NH4+-N, TP, and AP in the sediments were 3.4%, 2074 mg·kg-1, 140.2 mg·kg-1, 1765 mg·kg-1, and 57.2 mg·kg-1, respectively, indicating a moderate level of pollution. The concentration of TP in the sediments at 90% of the sampling points exceeds the national standard. Huancheng River was found to have the highest concentration of TP, suggesting that dredging shuld be targeted here first. In the water samples, the average concentrations of TOC, BOD5, COD, TN, NH4+-N, Kjeldahl nitrogen, TP, and PO43--P were 7.8, 0.6, 13.1, 2.5, 0.643, 1.3, 0.18, and 0.09 mg·L-1, respectively, indicating a severe level of pollution. Overall, water quality in these rivers falls below Class V surface water, and the concentration of TN seriously exceeds the national standard. Based on the patterns of total carbon mass and nitrogen and phosphorus bearing pollutants, the recommended order of dredging in Suzhou is the Huancheng River, the northern rivers of the ancient town, Ganjiang River, and the southern rivers of the ancient town. Under the rainfall scenario, the initial concentrations of pollutants in runoff were high, which leads to a decline in water quality. The total mass of TN in the water was reduced by 0.2 t under the change water and diversion water scenarios, and was further reduced by 4.58 t and 2.19 t, respectively, after dredging. Phosphorus bearing pollutants in the sediment were mainly imported from other sources, meaning that the total mass of TP in the water may increase following dredging activities.

Non-point source pollution and long-term effects of best management measures simulated in the Qifeng River Basin in the karst area of Southwest China

Abstract Non-point source (NPS) pollution has caused serious threats to water quality on a global scale. However, the investigation using a single measure with multi-scenarios for the long-term simulation in karst agricultural watershed is still lacking. In this study, the Annualized Agricultural Non-Point Source Pollution (AnnAGNPS) model was developed to verify the applicability in a karst agricultural watershed. Then, the model was used to determine the best management measures (BMPs) and the reduction rate characteristics under long-term effects (about 10 years) in the watershed. The AnnAGNPS model perform well in simulating in NPS pollution with R2 (0.95 for runoff, 0.93 for TN, and 0.93 for TP, respectively) and NSE (0.95 for runoff, 0.53 for TN, and 0.57 for TP, respectively). The output of total nitrogen (TN) and total phosphorus (TP) primarily occurred in the rainy season (up to 80%). The loss of mass of TN and TP were mainly observed in orchards and woodlands in the upstream of each sub-basin. The results from AnnAGNPS model demonstrated that different BMPs had significant impacts on the reduction of NPS pollution. Furthermore, a same BMPs measure showed it was closely related to land use in the watershed. In the Qifeng River watershed, stubble tillage (ST) showed to be useful with relatively good reduction rates (16.64% for sediment, 17.85% for TN, and 17.80% for TP, respectively). The simulation results indicated that AnnAGNPS was a valuable tool after validation for the planning and management of the watershed in karst areas.

Greenhouse gas and ammonia emissions from stored manure from beef cattle supplemented 3-nitrooxypropanol and monensin to reduce enteric methane emissions

The investigative material 3-nitrooxypropanol (3-NOP) can reduce enteric methane emissions from beef cattle. North American beef cattle are often supplemented the drug monensin to improve feed digestibility. Residual and confounding effects of these additives on manure greenhouse gas (GHG) emissions are unknown. This research tested whether manure carbon and nitrogen, and GHG and ammonia emissions, differed from cattle fed a typical finishing diet and 3-NOP [125–200 mg kg−1 dry matter (DM) feed], or both 3-NOP (125–200 mg kg−1 DM) and monensin (33 mg kg−1 DM) together, compared to a control (no supplements) when manure was stockpiled or composted for 202 days. Consistent with other studies, cumulative GHGs (except nitrous oxide) and ammonia emissions were higher from composted compared to stockpiled manure (all P < 0.01). Dry matter, total carbon and total nitrogen mass balance estimates, and cumulative GHG and ammonia emissions, from stored manure were not affected by 3-NOP or monensin. During the current experiment, supplementing beef cattle with 3-NOP did not significantly affect manure GHG or NH3 emissions during storage under the tested management conditions, suggesting supplementing cattle with 3-NOP does not have residual effects on manure decomposition as estimated using total carbon and nitrogen losses and GHG emissions.

Investigating the ideal mixture of soil and organic compound with Bacillus sp. and Trichoderma asperellum inoculations for optimal growth and nutrient content of banana seedlings

Organic compounds from the compost of agricultural waste have been increasingly used in the formulation of substrates for fruit seedlings production. Microorganisms can enhance the beneficial effects of fertilizers on the plant, but reports on the use of endophytic strains to promote banana plant growth are rare. The goal of this study was to investigate the ideal mixture of soil and organic compound with Bacillus sp. and Trichoderma asperellum inoculations for optimal growth and nutrient content of banana seedlings. A Greenhouse experiment was arranged in a factorial scheme (3 × 2 × 2)+3, five times replicated, with the following factors: (a) substrates consisting of three organic compound and soil ratios – 20:80, 40:60, 60:40 (v/v); (b) Bacillus sp. inoculation – with [B+] and without [B-]; and (c) Trichoderma asperellum inoculation – with [T+] and without [T-]. Additionally, the following controls for substrates consisting of soil free of organic compound (0:100) were also considered: [B+T-], [B-T+], and [B-T-]. After 100 days from planting, plant height (H), pseudostem diameter (D), H/D ratio, number of leaves, total leaf area, root volume, shoot and root dry mass, net photosynthesis, and contents of chlorophyll, carotenoid, nitrogen (N), phosphorus (P) and potassium (K) were evaluated. Results showed that the substrate 40:60 with Bacillus sp. or Trichoderma asperellum inoculation provides the best morphophysiological quality to banana seedlings. The strains also showed potential to promote plant growth in different ways, either by helping phosphate solubilization or by favoring auxins and hydrolytic enzymes synthesis.

Sweet corn nitrogen accumulation, leaf photosynthesis rate, and radiation use efficiency under variable nitrogen fertility and irrigation

Virtually no information exists on the response of sweet corn (Zea mays L. saccharata) to nitrogen fertility and irrigation treatments in terms of leaf nitrogen accumulation and the consequent impact on leaf CO2 assimilation rate and on crop growth as measured as radiation use efficiency (RUE). A two-year field experiment was undertaken in which a sweet corn cultivar was subjected to all combinations of five nitrogen fertility and three irrigation treatments. Leaf photosynthesis measurements were made at stages of 7–9 leaves, tasseling, silking, blistering, and milking. Leaf nitrogen per unit area was also measured at these five stages plus two additional stages before and after the five core measurements. Total nitrogen and plant mass was accumulated at the seven stages to track total nitrogen accumulation and to calculate RUE. The overall patterns in the measured variables were similar to those reported for field maize. However, leaf nitrogen per unit area for sweet corn under optimum conditions was greater than reported for field maize. The higher leaf nitrogen per unit area in sweet corn did not, however, result in greater leaf photosynthesis rates and RUE than reported for field maize. The results of these unique observations on sweet corn indicate the possibility of greater nitrogen storage in sweet corn leaves that is not directly linked with photosynthesis and carbon accumulation.

Dynamic Process of Nitrogen and Phosphorus Export and Loss Load in an Intensive Orchard with Ridge and Furrow Plantation in the Three Gorges Reservoir Area

To comprehend the runoff load of nitrogen (N) and phosphorus (P) and the impact on the receiving river in an agricultural area with an intensive orchard plantation and a longitudinal ridge and furrow morphology in the Three Gorges Reservoir Area, the runoff and N and P concentrations were dynamically monitored in a typical citrus orchard catchment in Wanzhou Country, Chongqing, China. The results showed that the nutrient concentration in runoff water from the intensive citrus planting catchment was very high. The average annual event mean concentrations (EMC) were 9.31 mg·L-1 for total nitrogen (TN), 8.11 mg·L-1 for dissolved nitrogen (DN), 5.66 mg·L-1 for nitrate nitrogen (NN), 0.51 mg·L-1 for ammonium nitrogen (AN), 0.87 mg·L-1 for total phosphorus, 0.56 mg·L-1 for solved phosphorus (DP), and 0.32 mg·L-1 for particulate phosphorus (DP). In addition, the annual loss loads were 13.43, 12.20, 8.77, 0.75, 1.26, 0.84, and 0.42 kg·(hm2·a)-1 for TN, DN, NN, AN, TP, DP, and PP, respectively. The annual average concentrations of TN and TP were 8.49 mg·L-1 and 0.87 mg·L-1, respectively, which exceeded the category V values of the surface water quality standards (GB3838-2002) by 4.25 times and 2.2 times, respectively, and also exceeded the internationally recognized thresholds for the eutrophication of waterbodies. The TN and TP loss load from storm runoff was one of the main reasons for the degradation of the river water quality, thus suggesting the need to treat surface runoff and control runoff nutrient losses, especially during the first storm events after fertilization. During two typical long-duration springtime rainfall events after fertilization, the loads of nitrate nitrogen (NN) and dissolved phosphorus (DP) were 4.94 kg·hm-2 and 0.28 kg·hm-2, respectively, which accounted for 92.90% and 64.69% of the total annual TN and TP loss loads, respectively. The loads of NN and DP in a short-duration high-intensity rainfall event were 0.52 and 0.05 kg·hm-2 respectively, which accounted for 65.92% and 74.88% of the total annual TN and TP loss loads, respectively. The DN and DP were the main forms of nitrogen and phosphorus losses from the intensive citrus orchard with a longitudinal ridge and furrow morphology. Meanwhile, the catchment showed a significant first-flush phenomenon during a typical rainfall event, with a total of 58.0%, 57.0%, 58.5%, 79.0%, 62.0%, 63.5%, and 60.0% of the mass of TN, DN, NN, AN, TP, DP, and PP in the initial 20% of the runoff, respectively. Hence, controlling the surface runoff at the early runoff stage plays an important role in reducing nutrient losses.

Riverine nitrate source apportionment using dual stable isotopes in a drinking water source watershed of southeast China

It is crucial to quantitatively track riverine nitrate (NO3−) sources and transformations in drinking water source watersheds for preventing current and future NO3− pollution, and ensuring a safe drinking water supply. This study identified the significant contributors to riverine NO3− in Zhaoshandu reservoir watershed of Zhejiang province, southeast China. To achieve this goal, we used hydrochemistry parameters and stable isotopes of NO3− (δ15N-NO3− and δ18O-NO3−) accompanied with a Markov Chain Monte Carlo mixing model to estimate the proportional contributions of riverine NO3− inputs from atmospheric deposition (AD), chemical nitrogen fertilizer (NF), soil nitrogen (SN), and manure and sewage (M&S). Results indicated that the main form of riverine nitrogen in this region was NO3−, constituting ~60% of the total nitrogen mass on average (total organic nitrogen ~37% & ammonium ~3%). Variations in the isotopic signatures of NO3− demonstrated that microbial nitrification of NF, SN and M&S was the primary nitrogen transformation process within the Zhaoshandu reservoir watershed, whereas denitrification was minimal. A classical dual isotope bi-plot incorporating chloride concentrations suggested NF, SN and M&S were the major contributors of NO3− to the river. Riverine NO3− source apportionment results were further refined using the Markov Chain Monte Carlo mixing model, which revealed that AD, NF, SN and M&S contributed 7.6 ± 4.1%, 22.5 ± 12.8%, 27.4 ± 14.5% and 42.5 ± 11.3% of riverine NO3− at the watershed outlet, respectively. Finally, uncertainties associated with NO3− source apportionment were quantitatively characterized as: SN > NF > M&S > AD. This work provides a comprehensive approach to distinguish riverine NO3− sources in drinking water source watersheds, which helps guide implementation of management strategies to effectively control NO3− contamination and protect drinking water quality. Summary of the main finding from this works (Capsule)We utilized NO3− stable isotope analysis and a Markov Chain Monte Carlo mixing model to quantify riverine nitrate pollution sources in a drinking water source watershed in Zhejiang province, southeast China. Markov Chain Monte Carlo mixing model output showed that NF, SN and M&S were the dominant sources of riverine NO3− during the sampling period in Zhaoshandu watershed. Uncertainty analysis characterized the variation strength associated with contributions of individual nitrate sources and indicated the greatest uncertainty for SN, followed by NF, M&S and AD.

Response of Nitrogen Loading to the Chesapeake Bay to Source Reduction and Land Use Change Scenarios: A SPARROW‐Informed Analysis

AbstractIn response to concerns regarding the health of streams and receiving waters, the United States Environmental Protection Agency established a total maximum daily load for nitrogen in the Chesapeake Bay watershed for which practices must be in place by 2025 resulting in an expected 25% reduction in load from 2009 levels. The response of total nitrogen (TN) loads delivered to the Bay to nine source reduction and land use change scenarios was estimated using a Spatially Referenced Regression on Watershed Attributes model. The largest predicted reduction in TN load delivered to the Bay was associated with a scenario in which the mass of TN as fertilizer applied to agricultural lands was decreased. A 25% decrease in the mass of TN applied as fertilizer resulted in a predicted reduction in TN loading to the Bay of 11.3%, which was 2.5–5 times greater than the reductions predicted by other scenarios. Eliminating fertilizer application to all agricultural land in the watershed resulted in a predicted reduction in TN load to the Bay of 45%. It was estimated that an approximate 25% reduction in TN loading to the Bay could be achieved by eliminating fertilizer applied to the 7% of subwatersheds contributing the greatest fertilizer‐sourced TN loads to the Bay. These results indicate that management strategies aimed at decreasing loading from a small number of subwatersheds may be effective for reducing TN loads to the Bay, and similar analyses are possible in other watersheds.

Potential release of legacy nitrogen from soil surrounding onsite wastewater leaching pools

This study examined whether the accumulation of nitrogen (legacy nitrogen) within and surrounding leaching pools for onsite wastewater treatment may act as a source of nitrogen contamination to groundwater upon changes to the quantity and/or composition of the influent to the pool. In this study, one concrete leaching pool with neutral pH (A, pH 6.9) and one leaching pool after acid washing (B, pH 3.7) were selected to examine the quantity and composition of legacy nitrogen in the surrounding soil, as well as evaluate the potential release of this nitrogen under two environmentally relevant leaching scenarios: (i) the concrete leaching pool serves as the final discharge unit for aerobic treatment unit (ATU) effluent; (ii) extreme weather events (flash flood/heavy rains) act to increase the quantity and dilute the composition of flow to the pool. Core sample analysis showed that organic nitrogen accounts for the majority (97.3–99.7%) of the total nitrogen (TN) at site A (4.1 ± 0.6 mg N/g soil) and site B (3.0 ± 0.4 mg N/g soil); while ammonium was the major form of inorganic nitrogen present at the sites. The TN accumulated under the two leaching pools was equivalent to approximately 17–39 days of nitrogen loading to the system. pH had a significant impact on the mass of TN leached from the soil, while no significant difference in leached TN was observed for the two leaching scenarios. The amount of TN leached from the soil matrix was not affected by the flow rate (18.6 mL/d in scenario i vs. 547.2 mL/d in scenario ii) or flow pattern (intermittent dosing vs. continuous flow). The quantity of TN leached from soils in both scenario (i) and (ii) was low and accounted for 2.6–8.9% of the total nitrogen in the soil.

Treatment of landfill leachate in a constructed free water surface wetland system over a decade – Identification of disturbance in process behaviour and removal of eutrophying substances and organic material

An 8 ha free water surface wetland system in Örebro, Sweden, which has sediment traps followed by 10 ponds for treatment of landfill leachate in the methanogenic stage, was studied from 2003 to 2012. The wetland was irregularly loaded and the leachate characteristics showed high temporal and spatial variability, so Multivariate Statistical Process Control was chosen as the diagnostic tool for detecting anomalies prior to assessing removal efficiency for eutrophying substances and organics. Disturbances in process behaviour included those due to intermittent flow, dilution due to snowmelt, an episode of high pollutant load, and sampling technique. The wetland total nitrogen mass removal was 89%, resulting in a first order rate coefficient of 1.7 m/year. Total phosphorus mass removal was 98%, while mass reduction was lower for TOC (60%), although this was still below discharge limits. The low amount of labile organic material and phosphate are probably the main reasons for the low denitrification rate.

Influence of rainfall intensity and pollution build-up levels on water quality and quantity response of permeable pavements

Permeable pavements are part of stormwater management practices known as sustainable urban drainage systems (SUDS). This study describes the influence of several environmental variables, such as the rainfall regime or the pollution build-up level, on the hydraulic and water quality performance of permeable pavements. Four infiltrometers with different configurations of pavement layers were used to study the influence of two rainfall regimes (Atlantic and Mediterranean) and two rainfall intensities (0.5 and 2.2mm/min). The influence of the progressive pollution build-up level was studied by dry sprinkling of road deposited sediments collected with a mechanical street sweeper with a dose of 5g/m2/d. The results show that permeable pavements retained a significant rainwater volume and improved the infiltrated water quality in terms of suspended solids, organic matter and nutrients when compared to the corresponding surface runoff potentially generated from an impervious pavement. The volume of rainwater retained inside them varied between 16 and 66% depending on the variables studied. The water infiltrated from permeable pavements subjected to a Mediterranean rainfall regime contained, in general, higher concentrations of organic matter (22 to 89mg Chemical Oxygen Demand/l) and nutrients (0.6 to 2.1mg Total Nitrogen/l and 0.05 to 0.45mg Total Phosphorus/l) than those under Atlantic regime. However, the latter infiltrated higher loadings in terms of mass. Nitrogen was the substance that infiltrated the most, reaching a 25% of the total mass of nitrogen deposited on the pavements surface. The concentration and mass loading in infiltrated water increased as the pollution build-up level did. The leachability of nutrients and organic matter was greater for high rainfall intensities. The results suggest that it is essential to carry out an adequate cleaning in dry conditions, especially when high intensity rainfall events are foreseen, because of its greater capacity to mobilize pollutants.

Predicting bioretention pollutant removal efficiency with design features: A data-driven approach

The objective of this study is to synthesize previous research findings from bioretention experiments and identify design features that lead to the best performance of bioretention pollutant removal with a data-driven approach. A bioretention database was built from 79 bioretention publications, composed of 182 records of bioretention cells with their design features and the corresponding pollutant removal efficiency data. Non-parametric correlation analysis, multiple linear regression (MLR), and decision tree classifiers were applied to investigate the relationships between bioretention design features and pollutant removal efficiencies. Non-parametric statistics and MLR results indicated that bioretention surface area, media depth, the presence of an internal water storage (IWS) layer, soil composition, and vegetation cover are all significantly correlated with pollutant removal efficiencies. The impacts of design features are significantly different under different climate and inflow conditions. Decision tree classifiers showed that non-vegetated bioretention cells with sand filter media generally have higher than 80% total suspended solid (TSS) mass removal efficiencies; bioretention cells with minimum organic matter and greater than 0.58 m soil media depth tend to remove more than 51% of total nitrogen (TN); and vegetated bioretention cells with minimum organic matter remove more than 67% of total phosphorus (TP). The overall accuracy of decision tree classifiers in the test set is around 70% to predict TSS, TN, and TP mass removal efficiency classes. This study suggests that the data-driven approach provides insights into understanding the complex relationship between bioretention design features and pollutant removal performance.