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1.
J Environ Qual ; 49(1): 119-127, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33016350

RESUMO

Eutrophication is an issue of concern in many brackish lakes with an agricultural watershed. The amount of snowfall in snowy areas is anticipated to decline because of global climate change. The aim of this study was to assess the impact of changes in the inflow of snowmelt on the nutrient concentrations of a downstream brackish lake. In Lake Ogawara, a brackish lake in a snow-covered agricultural area of Japan, we examined the relationships between inflowing river discharge (D/C) during spring and total nitrogen (TN) and total phosphorus (TP) concentrations in the mixolimnion of the lake ([TNmix ] and [TPmix ], respectively) using 29 yr of monitoring data. In addition, we assessed the causal relationship between the D/C and the lake nutrient concentrations. There was large year-to-year variation in D/C during April (D/CApr ), which accounted for 7-31% of the mixolimnion volume. Significant positive correlations were observed between D/CApr and [TNmix ] from the ensuing April to September. On an annual basis, 49% of the interannual variation of the mean [TNmix ] during the ensuing April to September was explained by the interannual variation of D/CApr . Therefore, D/CApr could be useful as a simple index to [TNmix ] in the ensuing spring to summer. It is notable that the relationships between D/CApr and [TNmix ] from April to September was indicated to be acausal by statistical causal inference. Common climate conditions that increase D/CApr (i.e., a cold winter with a high level of precipitation) were found to drive other biogeochemical processes that increased [TNmix ] during the ensuing spring to summer.


Assuntos
Lagos , Poluentes Químicos da Água/análise , Monitoramento Ambiental , Nitrogênio/análise , Fósforo/análise
2.
J Environ Qual ; 49(1): 38-49, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33016359

RESUMO

Grain producers are challenged to maximize crop production while utilizing nutrients efficiently and minimizing negative impacts on water quality. There is a particular concern about nutrient export to the Gulf of Mexico via loss from subsurface drainage systems. The objective of this study was to investigate the effects of crop rotation, tillage, crop residue removal, swine manure applications, and cereal rye (Secale cereale L.) cover crops on nitrate-N (NO3 -N) and total reactive phosphorus (TRP) loss via subsurface drainage. The study was evaluated from 2008 through 2015 using 36 0.4-ha plots outfitted with a subsurface drainage water quality monitoring system. Results showed that when swine manure was applied before both corn (Zea mays L.) and soybean [Glycine max (L.) Merr.], drainage water had significantly higher 8-yr-average flow-weighted NO3 -N concentrations compared with swine manure applied before corn only in a corn-soybean rotation. The lowest NO3 -N loss was 15.2 kg N ha-1  yr-1 from a no-till corn-soybean treatment with rye cover crop and spring application of urea-ammonium nitrate (UAN) to corn. The highest NO3 -N loss was 29.5 kg N ha-1  yr-1 from swine manure applied to both corn and soybean. A rye cover crop reduced NO3 -N loss, whereas tillage and residue management had little impact on NO3 -N loss. Losses of TRP averaged <32 g P ha-1  yr-1 from all treatments. Corn yield was negatively affected by both no-till management and cereal rye cover crops. Results showed that cropping management affected N leaching but impacts on P leaching were minimal.


Assuntos
Agricultura , Qualidade da Água , Animais , Nitrogênio/análise , Soja , Suínos , Zea mays
3.
J Environ Qual ; 49(1): 140-151, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33016365

RESUMO

Watershed managers generally focus on P reduction strategies to combat freshwater eutrophication despite evidence that N co-limits primary production. Our objective was to test the role of P in limiting stream periphyton biomass within the Buffalo River watershed in Arkansas by conducting a 31-d streamside mesocosm experiment. To represent potentially different starting states, cobbles were transplanted from two different tributary streams and initially exposed to a range of P (0, 0.012, 0.025, 0.05, 0.1, and 0.2 mg L-1 P) to assess benthic ash-free dry mass (AFDM) and chlorophyll-a (chl a) and responses during a P only enrichment period. Later, the experiment was continued under a N/P (10:1 molar ratio) enrichment gradient to examine co-limitation. Mean AFDM was higher on Day 31 of the N+P enrichment compared with Day 17 of the P-only enrichment (p < .001). Overall differences in AFDM and chl a were observed between cobbles from different stream sites. Phosphorus enrichment stimulated benthic chl a biomass, but enrichment effects were greater when streams were enriched with N+P (p < .001). Chlorophyll-a increased (4.4-57.9 mg m-2 ) with increasing P concentrations (p < .001) after P enrichment but was threefold greater after N+P enrichment, increasing from 13.3 to 171.1 mg m-2 across the enrichment gradient. Results support the need to consider both N and P limitation in freshwater systems and demonstrate that potential increases in nutrient concentrations may influence accumulation of algae on cobble substrates from the Buffalo River watershed.


Assuntos
Nitrogênio/análise , Fósforo/análise , Arkansas , Biomassa , Nutrientes
4.
J Environ Qual ; 49(3): 735-744, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-33016396

RESUMO

Nonpoint-source nitrogen (N) loads in the U.S. Corn Belt are a major concern both for local impacts on receiving waters and for contributing to hypoxia in the Gulf of Mexico. Nonpoint-source nutrient loads can be ameliorated by a combination of in-field and offsite practices, and wetland restoration is a particularly promising approach for reducing N loads from agricultural drainage. However, there is considerable variability among wetlands, and adequate performance data are available for relatively few systems receiving unregulated nonpoint-source loads. We measured N mass balances of 26 restored wetlands receiving a wide range of unregulated, naturally varying hydraulic and nutrient loads to evaluate the N removal performance of these systems and the effects of major factors controlling their performance. Nitrogen loads were primarily in the form of nitrate, and all of the wetlands were effective in reducing both nitrate and total N loads. Nitrate N and total N removal rates averaged 1,500 and 1,440 kg N ha-1  yr-1 , respectively, with the slightly lower total N removal rates reflecting a small net export of reduced N (averaging 66 kg N ha-1  yr-1 ). Average nitrate and total N removal rates were substantially higher than typically reported for Corn Belt wetlands but comparable with highly loaded systems elsewhere. Nitrate removal efficiency ranged from 9 to 92% and was strongly related to hydraulic loading rate and temperature. Results demonstrate the substantial capacity of wetlands to reduce unregulated and highly variable nonpoint-source N loads over a broad range of weather and loading conditions and provide a reasonable basis for predicting average wetland performance based on hydraulic loading rate, temperature, and nitrate concentration.


Assuntos
Qualidade da Água , Áreas Alagadas , Desnitrificação , Nitratos , Nitrogênio/análise
5.
J Environ Qual ; 49(2): 292-303, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-33016415

RESUMO

Artificial subsurface drainage is necessary to maintain agricultural production in the soils and climate of north-central Iowa. However, it can result in adverse environmental impacts, because it intercepts and diverts some water and soluble NO3 -N directly to streams. We investigated the impact of no-till and a winter rye cover crop (Secale cereale L.) on seasonal and annual NO3 -N concentration and loading in leachate from a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation. The eight treatments are chisel plow (CT), chisel plow with winter cereal rye (CTr), no-till (NT), and no-till with winter cereal rye (NTr), with "-C" indicating corn and "-S" indicating soybeans. Plots with artificial subsurface drainage were monitored for water quality from 2011 to 2015. The NT and CTr treatments consistently decreased NO3 -N loss on the seasonal and annual scales compared with CT. Compared with NT, NTr did not reduce NO3 -N loading nor concentration in leachate, probably because of low NO3 leaching potential from NT combined with low rye cover crop biomass throughout the study with NT. The 5-yr average annual NO3 -N concentrations were: 16.9 mg L-1 with CT-S, 16.7 mg L-1 with CT-C, 12.6 mg L-1 with NT-S, 12.0 mg L-1 with CTr-S, 11.8 mg L-1 with CTr-C, 11.4 mg L-1 with NTr-S and NTr-C, and 11.1 mg L-1 with NT-C. Overall, both no-till and a cover crop showed potential for improving N management for water quality.


Assuntos
Nitrogênio/análise , Secale , Agricultura , Iowa , Estações do Ano
6.
J Environ Qual ; 49(2): 324-334, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-33016426

RESUMO

Managing a sustainable dairy farm requires balancing phosphorus (P) imports and exports that enter and leave through the farm gate. Over the long term, P surpluses will elevate soil-test P concentrations above crop requirements through routine land applications of manure. The objectives of this study were aimed at Virginia dairy farms (a) to determine P mass balances, (b) to define potential guidelines for a sustainable and feasible zone of operation based on P balance and P use efficiency, and (c) to assess risk factors driving P surplus and P use inefficiencies. Data on farm-gate P imports and exports via feed, manure, crops, fertilizers, bedding, animals, and milk were collected for 58 dairy farms in Virginia. There was no relationship between farm P balance and milk production, indicating that a P surplus was not necessary for good milk productivity. A feasible P balance limit was calculated below which 75% of farms could operate, and this was 18.7 kg P ha-1 . Two risk factors were identified for farms having a P balance above this limit: (a) land application of poultry litter and (b) excessive import of P through feed. Combined dairy and beef operations generally had more land and a lower P balance, whereas having combined dairy and poultry did not raise the P balance as long as poultry litter was exported. Dairy farms in Virginia can operate with a sustainable P balance as long as they avoid using excessive poultry litter and pay attention to P imported through purchased feed.


Assuntos
Indústria de Laticínios , Fósforo/análise , Ração Animal/análise , Animais , Bovinos , Fazendas , Nitrogênio/análise , Virginia
7.
J Environ Qual ; 49(2): 304-313, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-33016428

RESUMO

Excess nitrogen (N) loading in the Mississippi River basin is a major water quality issue, encompassing large spatial scales and feedbacks between social and biophysical entities. Effective management depends on reductions in agricultural N loading, mainly from the Corn Belt region in the upper reaches of the basin. In this study, we evaluated the role of federal Nutrient Task Force policy on N management from 2000 to 2015. We analyzed trends in nitrate (NO3 - ) concentrations from monitoring data in 148 priority watersheds. We compared water quality trends with state nutrient reduction strategies, monitoring efforts, and land use. Of the 148 watersheds, 13 displayed a significant decrease in NO3 - concentrations, 24 displayed a significant increase, 51 displayed a nonsignificant trend, and 60 had insufficient data to analyze. We demonstrate that policy efforts on a large scale are slow to establish, but states and watersheds that showed signs of policy acting successfully could serve as examples for improved N management moving forward. Despite considerable variability, states with the most comprehensive strategies, evidenced by word count and presence of recommended elements, were almost exclusively located in the Corn Belt region. States with more thorough nutrient reduction strategies also tended to have a larger number of monitoring sites in priority watersheds (R = .42), demonstrating the potential for adaptive management. States with the most consistent improvements in NO3 - concentrations tended to have the most comprehensive policies, whereas variation in water quality trends was partly attributed to land use factors including slope and dominance of corn (Zea mays L.) and soy [Glycine max (L.) Merr.].


Assuntos
Nitrogênio/análise , Rios , Agricultura , Mississippi , Qualidade da Água
8.
J Environ Qual ; 49(2): 483-495, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-33016434

RESUMO

To manage nitrogen (N) efficiently, organic growers must be able to predict the amount and timing of plant-available N from organic amendments. In this study, we measured N mineralization from a variety of organic amendments, including composted animal manures and plant material, pelleted and granular organic fertilizer formulations, slaughter waste products, and hydrolyzed liquid fertilizers. In a laboratory incubation, we measured net N mineralization from materials mixed with either organically or conventionally managed soil at 23°C and 60% water holding capacity after 0, 7, 21, 42, and 84 d. We found that net mineral N change in the amended soils after 84 d of incubation fell into four categories: immobilization to 5% of applied N for yard trimmings composts, 15-30% for poultry manure composts, 35-55% for granular fertilizers, and 60-90% for quick release products. However, across all amendments the amount of plant-available N after 84 d of incubation was well correlated with the carbon (C)/N ratio (R2  = 0.92). Within amendment types, the C/N ratio predicted N mineralization for yard trimmings composts (R2  = 0.91), manure composts (R2  = 0.81), and specialty fertilizer and slaughter products (R2  = 0.88) but not liquid products (R2  = 0.11). Soil management history did not consistently affect net N mineralization but may have influenced timing.


Assuntos
Compostagem , Nitrogênio/análise , Animais , Fertilizantes , Esterco , Solo
9.
J Environ Qual ; 49(4): 812-834, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-33016477

RESUMO

Despite decades of effort toward reducing nitrogen and phosphorus flux to Chesapeake Bay, water-quality and ecological responses in surface waters have been mixed. Recent research, however, provides useful insight into multiple factors complicating the understanding of nutrient trends in bay tributaries, which we review in this paper, as we approach a 2025 total maximum daily load (TMDL) management deadline. Improvements in water quality in many streams are attributable to management actions that reduced point sources and atmospheric nitrogen deposition and to changes in climate. Nutrient reductions expected from management actions, however, have not been fully realized in watershed streams. Nitrogen from urban nonpoint sources has declined, although water-quality responses to urbanization in individual streams vary depending on predevelopment land use. Evolving agriculture, the largest watershed source of nutrients, has likely contributed to local nutrient trends but has not affected substantial changes in flux to the bay. Changing average nitrogen yields from farmland underlain by carbonate rocks, however, may suggest future trends in other areas under similar management, climatic, or other influences, although drivers of these changes remain unclear. Regardless of upstream trends, phosphorus flux to the bay from its largest tributary has increased due to sediment infill in the Conowingo Reservoir. In general, recent research emphasizes the utility of input reductions over attempts to manage nutrient fate and transport at limiting nutrients in surface waters. Ongoing research opportunities include evaluating effects of climate change and conservation practices over time and space and developing tools to disentangle and evaluate multiple influences on regional water quality.


Assuntos
Baías , Fósforo/análise , Nitrogênio/análise , Nutrientes , Qualidade da Água
10.
J Environ Qual ; 49(3): 613-627, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-33016388

RESUMO

Regulatory watershed mitigation programs typically emphasize widespread adoption of best management practices (BMPs) to meet total maximum daily load (TMDL) goals. To comply with the Chesapeake Bay TMDL, jurisdictions must develop watershed implementation plans (WIPs) to determine the number and type of BMPs to implement. However, the spatial resolution of the bay-level model used to determine these load reduction goals is so coarse that the regulatory plan cannot consider heterogeneity in local conditions, which affects BMP effectiveness. Using the Topo-SWAT modification of the Soil and Water Assessment Tool (SWAT), we simulated two BMP adoption scenarios in the Spring Creek watershed in central Pennsylvania to determine if leveraging fine-scale spatial heterogeneity to place BMPs could achieve the same (or better) nutrient and sediment reduction at a lower cost than the state-level WIP BMP adoption recommendations. Topo-SWAT was initialized with detailed land use and management practice information, systematically calibrated, and validated against 12 yr of observed data. After determining individual BMP cost effectiveness, results were ranked to design a cost-effective BMP adoption scenario that achieved equal or greater load reduction as the WIP scenario for 74% of the cost using eight management-based BMPs: no-till, manure injection, cover cropping, riparian buffers, land retirement, manure application timing, wetland restoration, and nitrogen management (15% less N input). Because watersheds of this size typically represent the smallest modeling unit in the Chesapeake Bay Model, results demonstrate the potential to use watershed models with finer inference scales to improve recommendations for BMP implementation under the Chesapeake Bay TMDL.


Assuntos
Nitrogênio/análise , Solo , Conservação dos Recursos Naturais , Pennsylvania , Áreas Alagadas
11.
Sci Total Environ ; 741: 140451, 2020 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-32886973

RESUMO

The present study aimed to determine the spatial and temporal variations in trophic state and identify potential causes for these variations in 60 Korean reservoirs. Empirical models were developed using the relations of nutrients (total phosphorus, TP, and total nitrogen, TN) with chlorophyll-a (CHL-a) for efficient lake managements. The empirical models indicated that TP was the key regulating factor for algal growth in agricultural (R2 = 0.69) and power generation (R2 = 0.50) reservoirs. The CHL-a:TP and TN:TP ratios, indicators of phosphorus limitation, were used to validate the phosphorus reduction approach. The mean CHL-a:TP ratio of agricultural reservoirs was 0.60, indicating that algal chlorophyll is potentially limited by TP than any other factors. Agricultural, multipurpose, and power generation reservoirs, based on the N:P ratios, were more P- limited systems than natural lakes and estuarine reservoirs. The trophic state index (TSI) of Korean reservoirs varied between mesotrophy to hypereutrophy based on values of TSI (TP), TSI (CHL-a), and TSI (SD). Agricultural reservoirs were hypereutrophic using the criteria of TSI (CHL-a) and blue-green algae dominated the algal community. Analysis of trophic state index deviation (TSID) indicated that agricultural reservoirs were primarily P limited and other factors had minor effect. In contrast, the trophic status of estuarine and power generation reservoirs and natural lakes was largely modified by non-algal turbidity. Our outcomes may be effectively used for Korean lakes and reservoirs management.


Assuntos
Monitoramento Ambiental , Eutrofização , China , Clorofila/análise , Lagos , Nitrogênio/análise , Nutrientes , Fósforo/análise , República da Coreia
12.
Sci Total Environ ; 741: 140494, 2020 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-32886976

RESUMO

Here, we examined the effects of low and high concentrations of perfluorooctanesulfonate (PFOS) on rhizosphere soil N cycling processes in the presence of Lythrum salicaria and Phragmites communis over 4 months. Compared with the control group, the nitrate nitrogen (NO3--N) content of the bulk soil in the low PFOS (0.1 mg kg-1) treatment significantly decreased (27.7%), the ammonium nitrogen (NH4+-N) content significantly increased (8.7%), and the pH value and total organic carbon (TOC) content slightly increased (0.3% and 1.1%, respectively). Compared with the low PFOS treatment, the content of NO3-N, NH4+-N and pH value in the bulk soil of the high PFOS treatment (50 mg kg-1) significantly increased (1.0%, 53.8% and 61.8%, respectively), and the TOC content significantly decreased (8.2%). Soil protease levels were high in the low PFOS treatment, but low in the high PFOS treatment. PFOS produced inverted U-shaped responses in the potential nitrification (1.5, 3.0, and 1.1 mg N d-1 kg-1 in no, low, and high PFOS, respectively), denitrification (0.19, 0.30, and 0.22 mg N d-1 kg-1 in no, low, and high PFOS, respectively), and N2O emission rates (0.01, 0.03, and 0.02 mg N d-1 kg-1 in no, low, and high PFOS, respectively) of bulk soil. The abundance of the archaea amoA gene decreased with increasing PFOS concentration, whereas that of bacterial amoA increased; inverted U-shaped responses were observed for narG, nirK, nirS, and nosZ. In the PFOS-contaminated rhizosphere soil, the observed changes differed from those in the bulk soil and differed between treatments. P. communis tended to upregulate each step of the nitrogen cycle under low PFOS conditions, whereas L. salicaria tended to inhibit them. Under high PFOS conditions, both test plants tended to act as inhibitors of the soil N-cycle; thus, the effects of PFOS on soil N transformation were plant-specific.


Assuntos
Rizosfera , Solo , Ácidos Alcanossulfônicos , Desnitrificação , Fluorcarbonetos , Nitrificação , Nitrogênio/análise , Ciclo do Nitrogênio , Microbiologia do Solo
13.
Sci Total Environ ; 741: 140488, 2020 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-32887004

RESUMO

Nitrogen fertilization significantly increases greenhouse gases (GHGs) emission, when applied from inorganic or organic sources. Minimizing GHGs from agroecosystems without compromising crop yield for stabilization of green production systems remains a challenge. Being an integral component of wheat production technology, the nitrogen (N) application deems to be indispensable. Thus, to reduce the application of N fertilizer and keep in view the minimization of GHGs emission, without compromising soil fertility and wheat production, field experiments were performed with treatments included maize straw mulch (S1: 0, S2: 4500, S3: 9000 kg ha-1) and nitrogen fertilizer (N1: 0, N2: 192 and N3: 240 kg ha-1) during 2015-17. Results showed that the cumulative CO2 and N2O emission from 9000 kg ha-1 of maize straw mulch with 192 kg N ha-1 (S3N2) significantly decreased by 0.67% and 33.7%, respectively, averaged over two years compared with that of 9000 kg ha-1 of maize straw mulch with 240 kg N ha-1 (S3N3). Likewise, the average soil moisture content significantly increased by 10% and 10.6% for S3N2 and S3N3 treatments at 0-10 cm soil depth, respectively, compared to S1N1. Similarly, the S3N2 and S3N3 treatments had lowered the soil temperature by 0.2 and 0.1 °C, respectively, over S1N1 in wheat grown fields. The grain yield of wheat was increased by 45% and 45% under S3N3 and S3N2 treatments than S1N1, respectively. The S3N2 treatment was more economical than S3N3 for wheat crop. Therefore, maize straw mulch (S3) combined with 20% less N fertilizer (N2) from commercial source were considered as a viable production technology to improve crop yield, and reduce soil CO2 and N2O emissions.


Assuntos
Fertilizantes/análise , Triticum , Agricultura , Dióxido de Carbono , China , Nitrogênio/análise , Óxido Nitroso/análise , Solo , Zea mays
14.
Water Sci Technol ; 82(2): 281-291, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32941170

RESUMO

Biofilters based on earthworms-microorganisms represent, particularly in developing countries, an interesting alternative for domestic wastewater treatment due to their easy operation and low cost. However, there are several operational aspects that should be better understood in order to improve their performance. This paper studies the effect of using intermittent hydraulic loading rates to improve organic matter and nutrient removal from domestic wastewater using these biofilters. Three laboratory-scale columns, operating at a 2.5 m3 m-2day-1 hydraulic loading rate, were used. The B1-24 h, B2-8 h, B3-4 h column loading rates indicate that the columns were operated continuously for 24, 8 and 4 h, respectively. Each column (biomass biofilm/earthworms, redox potential, and head loss) and its corresponding operational performance parameters (TCOD, NH4+, NO3-, NO2-, TP) were monitored. The results showed that the B2-8 h intermittent hydraulic loading rate results in the best global performance, with 74%, 57%, and 20% average removal efficiencies for TCOD, nitrogen, and phosphorus, respectively. Moreover, it showed the best biomass growth (biofilm and earthworms), activity (as redox potential changes) and the lowest clogging effects (up to -1.0 cm). The intermittent operation influences the behavior of the earthworm-microorganism biofilters and offers the possibility of optimizing its global performance and achieving a resilient technology.


Assuntos
Oligoquetos , Águas Residuárias , Animais , Reatores Biológicos , Filtração , Nitrogênio/análise , Nutrientes , Fósforo , Eliminação de Resíduos Líquidos
15.
Water Sci Technol ; 82(2): 351-363, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32941176

RESUMO

The migration of nitrogen (N) and phosphorous (P) from farmland to river not only results in fertilizer inefficiency, but also aggravates water pollution and eutrophication. It is of great significance to construct a reasonable vegetation buffer zone between the river and farmland to protect water quality. By using constructed buffer strips and runoff hydrometric devices, quantitative research was conducted on removal loads of N and P in a field experiment of different vegetated and slope strips. Results showed that removal rates of TN, NH4+-N, and TP by different vegetated strips were 2-3 times higher than the control group. The removal ratios of seepage accounted for 73.6%, 66.9%, 73.9% of total seepage and runoff in three vegetated strips, respectively. On the 2% gradient strips with Cynodon dactylon, the removal ratios of TN, NH4+-N, and TP were 36%, 34%, 37%, which were higher than that with 5% gradient, respectively. And removal ratios from the seepage of 2%, 3%, 4%, and 5% gradient strips were 71.66%, 68.14%, 64.39%, and 61.93% of the total, respectively. The conclusion can provide the basis of vegetation and slope optimization for the design and construction of a riparian buffer zone, so as to control non-point source pollution effectively.


Assuntos
Nitrogênio/análise , Fósforo , Fertilizantes , Rios , Poluição da Água
16.
Water Sci Technol ; 82(2): 386-400, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32941179

RESUMO

For the utilization of nitrogen and phosphorus in rural sewage tailwaters after biological treatment, four systems were examined regarding their ability to purify tailwaters of rural domestic sewage: a hydroponic vegetable system (HV), a subsurface flow constructed wetland (SFCW), a compound system with HV followed by SFCW (HV-SFCW), and a compound system with SFCW followed by HV (SFCW-HV). Parameters of the four systems were optimized to maximize the utilization efficiency of nitrogen and phosphorus, and the characteristics and pollutant removal efficiency of the process were investigated. Moreover, the edible security of vegetables was also evaluated. Results showed that the optimal hydraulic loadings for the four systems were 0.2, 0.3, 0.3, and 0.3 m3/(m2·d) (the lowest being the HV), respectively. In the combined system of HV-SFCW, high contribution proportions of the HV unit to the removal of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) were obtained, reaching 46.7%, 58.1%, and 53.7%. The heavy metal content of plants harvested met the standards of the National Food Safety Standard Limit of Pollutants in Food (GB 2762-2012). Overall, the compound HV-SFCW system achieved the best performance, ensuring that effluent water quality met national standards and realized the effective utilization of nitrogen and phosphorus.


Assuntos
Ipomoea , Esgotos , Hidroponia , Nitrogênio/análise , Fósforo , Verduras , Eliminação de Resíduos Líquidos , Áreas Alagadas
17.
Sci Total Environ ; 740: 139740, 2020 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-32927530

RESUMO

Most wetlands have been subject to changes in flooding regimes by climate change and human activities, resulting in widespread alteration of wetland plants at different organizational levels. However, scaling the responses of wetland plants to changes in flooding regimes is still challenging, because flooding could indirectly affect wetland plants through affecting environment factors (e.g. soil properties). During the non-flooding period, we investigated leaf N and P stoichiometry at three organizational levels (intra-species, inter-species, inter-community) along a flooding duration gradient in a lakeshore meadow of Poyang Lake floodplain, China. At the intra-species level, leaf N and P stoichiometry showed species-specific responses to flooding duration. At the inter-species level, leaf N or P contents or N:P ratio showed no significant response to flooding duration. At the inter-community level, leaf N and P contents significantly increased with flooding duration, while leaf N:P ratio decreased. At each organizational level, leaf N and P stoichiometry showed poor correlation with soil N and P stoichiometry. Moreover, intra-specific responses of leaf N and P contents to flooding duration and soil nutrient content increased with mean flooding duration of species distribution, which was the index of species hydrological niche. Intraspecific variation had lower contribution than species turnover to variations in community leaf nutrient stoichiometry. In all, flooding duration affected leaf N and P stoichiometry mainly through direct pathway at the intra-species and inter-community level, rather than the indirect pathway via soil nutrient stoichiometry. Therefore, our results have implications for scaling up from environmental conditions to ecosystem processes via wetland plant communities.


Assuntos
Ecossistema , Nitrogênio/análise , China , Nutrientes , Fósforo , Folhas de Planta/química , Solo
18.
Sci Total Environ ; 740: 140169, 2020 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-32927550

RESUMO

Hydrological extremes of unusually high or low river discharge may deeply affect the biogeochemistry of coastal lagoons, but the effects are poorly explored. In this study, microbial nitrogen processes were analyzed through intact core incubations and 15N-isotope addition at three sites in the eutrophic Sacca di Goro lagoon (Northern Adriatic Sea) both under high discharge (spring) and after prolonged low discharge (late-summer) of the main freshwater inputs. Under high discharge/nitrate load, denitrification was the leading process and there was no internal recycling. The site located at the mouth of the main freshwater input and characterized by low salinity exhibited the highest denitrification rate (up to 1150 ± 81 µmol N m-2 h-1), mostly sustained by nitrification stimulated by burrowing macrofauna. In contrast, we recorded high internal recycling under low discharge, when denitrification dropped at all sites due to low nitrate concentrations, reduced bioturbation and nitrification. The highest recycling was measured at the sites close to the sea entrance and characterized by high salinity and particularly at the clams cultivated area (up to 1003 ± 70 µmol N m-2 h-1). At this site, internal recycling was sustained by ammonification of biodeposits, bivalve excretion and dissimilatory nitrate reduction to ammonium (DNRA), which represented 30% of nitrate reduction. Flash floods and high nitrate loads may overwhelm the denitrification capacity of the lagoon due to the reduced residence time and to the saturation of microbial enzymatic activity, resulting in high transport of nitrate to the sea. Prolonged dry periods favor large internal recycling, due to a combination of high temperatures, low oxygen solubility and low bioturbation, which may prolong the extent of algal blooms with negative effects on lagoon biogeochemical services. We conclude that hydrological extremes, which are expected to become more frequent under climate change scenarios, strongly alter N cycling in coastal sediments.


Assuntos
Compostos de Amônio/análise , Animais , Desnitrificação , Sedimentos Geológicos , Hidrologia , Nitratos/análise , Nitrogênio/análise
20.
Ambio ; 49(11): 1747-1758, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32918719

RESUMO

Land use and climate change can impact water quality in agricultural catchments. The objectives were to assess long-term monitoring data to quantify changes to the thermal growing season length, investigate farmer adaptations to this and examine these and other factors in relation to total nitrogen and nitrate water concentrations. Data (1991-2017) from seven small Norwegian agricultural catchments were analysed using Mann-Kendall Trend Tests, Pearson correlation and a linear mixed model. The growing season length increased significantly in four of seven catchments. In catchments with cereal production, the increased growing season length corresponded to a reduction in nitrogen concentrations, but there was no such relationship in grassland catchments. In one cereal catchment, a significant correlation was found between the start of sowing and start of the thermal growing season. Understanding the role of the growing season and other factors can provide additional insight into processes and land use choices taking place in agricultural catchments.


Assuntos
Monitoramento Ambiental , Rios , Agricultura , Conservação dos Recursos Naturais , Nitrogênio/análise , Noruega
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