Prediction of groundwater nitrate concentration in a semiarid region using hybrid Bayesian artificial intelligence approaches

Environmental Science and Pollution Research - Nitrate is a major pollutant in groundwater whose main source is municipal wastewater and agricultural activities. In the present study, Bayesian...     

The groundwater contribution to surface water contamination in a region with intensive agricultural land use (Noord-Brabant, The Netherlands)

Traditionally, monitoring of soil, groundwater and surface water quality is coordinated by different authorities in the Netherlands. Nowadays, the European Water Framework Directive (EU, 2,000) stimulates an integrated approach of the complete soil-groundwater-surface water system. Based on water quality data from several test catchments, we propose a conceptual model stating that stream water quality at different discharges is the result of different mixing ratios of groundwater from different depths. This concept is used for a regional study of the groundwater contribution to surface water contamination in the Dutch province of Noord-Brabant, using the large amount of available data from the regional monitoring networks. The results show that groundwater is a dominant source of surface water contamination. The poor chemical condition of upper and shallow groundwater leads to exceedance of the quality standards in receiving surface waters, especially during quick flow periods.     

Effect of land use changes on non-carcinogenic health risks due to nitrate exposure to drinking groundwater

Environmental Science and Pollution Research - This study aimed to determine the effect of land-use changes on the non-carcinogenic health risk of nitrate ion exposure of underground drinking water...     

Nitrogen balance and groundwater nitrate contamination: comparison among three intensive cropping systems on the North China Plain

The annual nitrogen (N) budget and groundwater nitrate-N concentrations were studied in the field in three major intensive cropping systems in Shandong province, north China. In the greenhouse vegetable systems the annual N inputs from fertilizers, manures and irrigation water were 1358, 1881 and 402 kg N ha(-1) on average, representing 2.5, 37.5 and 83.8 times the corresponding values in wheat (Triticum aestivum L.)-maize (Zea mays L.) rotations and 2.1, 10.4 and 68.2 times the values in apple (Malus pumila Mill.) orchards. The N surplus values were 349, 3327 and 746 kg N ha(-1), with residual soil nitrate-N after harvest amounting to 221-275, 1173 and 613 kg N ha(-1) in the top 90 cm of the soil profile and 213-242, 1032 and 976 kg N ha(-1) at 90-180 cm depth in wheat-maize, greenhouse vegetable and orchard systems, respectively. Nitrate leaching was evident in all three cropping systems and the groundwater in shallow wells (<15 m depth) was heavily contaminated in the greenhouse vegetable production area, where total N inputs were much higher than crop requirements and the excessive fertilizer N inputs were only about 40% of total N inputs.     

Measuring ammonia concentrations and emissions from agricultural land and liquid surfaces: a review

Aerial ammonia concentrations (Cg) are measured using acid scrubbers, filter packs, denuders, or optical methods. Using Cg and wind speed or airflow rate, ammonia emission rate or flux can be directly estimated using enclosures or micrometeorological methods. Using nitrogen (N) recovery is not recommended, mainly because the different gaseous N components cannot be separated. Although low cost and replicable, chambers modify environmental conditions and are suitable only for comparing treatments. Wind tunnels do not modify environmental conditions as much as chambers, but they may not be appropriate for determining ammonia fluxes; however, they can be used to compare emissions and test models. Larger wind tunnels that also simulate natural wind profiles may be more useful for comparing treatments than micrometeorological methods because the latter require larger plots and are, thus, difficult to replicate. For determining absolute ammonia flux, the micrometeorological methods are the most suitable because they are nonintrusive. For use with micrometeorological methods, both the passive denuders and optical methods give comparable accuracies, although the latter give real-time Cg but at a higher cost. The passive denuder is wind weighted and also costs less than forced-air Cg measurement methods, but it requires calibration. When ammonia contamination during sample preparation and handling is a concern and separating the gas-phase ammonia and aerosol ammonium is not required, the scrubber is preferred over the passive denuder. The photothermal interferometer, because of its low detection limit and robustness, may hold potential for use in agriculture, but it requires evaluation. With its simpler theoretical basis and fewer restrictions, the integrated horizontal flux (IHF) method is preferable over other micrometeorological methods, particularly for lagoons, where berms and land-lagoon boundaries modify wind flow and flux gradients. With uniform wind flow, the ZINST method requiring measurement at one predetermined height may perform comparably to the IHF method but at a lower cost.     

Impact of land use on shallow groundwater quality characteristics associated with human health risks in a typical agricultural area in Central China

Environmental Science and Pollution Research - Groundwater pollution seriously threatens water resource safety due to high-intensity land use throughout the world. However, the relationship between...     

Fertilizer-N use efficiency and nitrate pollution of groundwater in developing countries

Around 76% of the world's population lives in developing countries where more fertilizer-N is currently applied than in developed countries. Fertilizers are applied preferentially in regions where irrigation is available, and soil and climatic conditions are favorable for the growth of crop plants. Due to low N application rates during the last 3 or 4 decades, negative N balances in the soil are a characteristic feature of the crop production systems in developing countries. In the future, with increasing fertilizer-N application rates, the possibility of nitrate pollution of groundwater in developing countries will be strongly linked with fertilizer-N use efficiency. A limited number of investigations from developing countries suggest that, in irrigated soils of Asia or in humid tropics of Africa, the potential exists for nitrate pollution of groundwater, especially if fertilizer-N is inefficiently managed. In a large number of developing countries in West and Central Asia and North Africa, the small amount of fertilizer applied to soils (mostly Aridisols) that remain dry almost all the year, do not constitute a major threat for nitrate pollution of groundwater, except possibly when soils are irrigated. In Asia and the Pacific regions, where 70% of the fertilizers are used to grow wetland rice on soils with low percolation rates, leaching of nitrates is minimal. Climatic water balance and soil moisture conditions do not favor leaching of nitrates from the small amount of fertilizer-N applied to Oxisols and Ultisols in Latin America. In developing countries located in the humid tropics, attempts have not been made to correlate fertilizer-N use with nitrate level in groundwater; however, fertilizers are being increasingly used. Besides high rainfall, irrigation is becoming increasingly available to farmers in the humid tropics and substantial leaching of N may also increase.     

A land use regression for predicting fine particulate matter concentrations in the New York City region

We developed regression equations to predict fine particulate matter (PM_2.5) at air monitoring locations in the New York City region using data on nearby traffic and land use patterns. Three-year averages (1999–2001) of PM_2.5 at US Environmental Protection Agency (EPA) monitors in the 28 counties including and surrounding New York City were calculated using daily data from the EPA's Air Quality Subsystem. As the secondary contribution to PM_2.5 concentrations is lowest in the winter, we also calculated and modeled average winter 2000 PM_2.5 to conduct a preliminary evaluation of model sensitivity to source contribution. Candidate predictor variables included traffic, land use, census and emissions data from local, state and national sources and were tabulated for a series of circular buffer regions at varying distances around the monitors using a geographic information system. In total, more than 25 variables at 5 different buffer distances were considered for inclusion in the model. Before evaluating the variables we removed several samples from the modeling for validation. For comparison and validation purposes we computed both a model using data for the full 28-county region as well as a more urbanized 9-county region. We found that traffic within a buffer of 300 or 500 m explains the greatest proportion of variance (37–44%) in all 3 models. Measures of urbanization, specifically population density, explain a significant amount of the residual variation (7–18%) after including a traffic variable. Finally, a measure of industrial land use further improves the 28-county and 9-county models based on the 3-yr annual averages, explaining an additional 4% and 11% of the variation, respectively, while vegetative land use improves the winter model explaining an additional 6%. The final models predicted well at validation locations. In total, the final land use regression models explain between 61% and 64% of the variation in PM_2.5.     

Socioeconomic outcomes of agricultural land use change in Southeast Asia

Agricultural land use is transforming rapidly in Southeast Asia, often supported by development policies aiming primarily at economic growth. However, the socioeconomic outcomes of these changes for smallholder farmers remain unclear. Here, we systematically review cases of agricultural land use change in Southeast Asia to assess their socioeconomic outcomes and potential trade-off and synergies in these outcomes. Of the 126 reviewed cases, we find mostly positive outcomes for income (SDG 1, 100 cases) and employment (SDG 8, 11 cases), while outcomes on health (SDG 3, 9 cases) were mixed, and outcomes for food security (SDG 2, 44 cases), gender equality (SDG 5, 13 cases), and economic equality (SDG 10, 14 cases) were mostly negative. Studies describing multiple outcomes show indications of synergies between income and food security, and between income and employment, but also potential trade-offs between income and economic equality. In addition, we find that economic land concessions result in multiple negative outcomes more often than other types of land governance regimes. The results provide evidence that economic gains from agricultural land use change often come at a cost of other dimensions of sustainable development.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13280-022-01712-4.     

Validation of regression models for nitrate concentrations in the upper groundwater in sandy soils

For Dutch sandy regions, linear regression models have been developed that predict nitrate concentrations in the upper groundwater on the basis of residual nitrate contents in the soil in autumn. The objective of our study was to validate these regression models for one particular sandy region dominated by dairy farming. No data from this area were used for calibrating the regression models. The model was validated by additional probability sampling. This sample was used to estimate errors in 1) the predicted areal fractions where the EU standard of 50 mg l⁻¹ is exceeded for farms with low N surpluses (ALT) and farms with higher N surpluses (REF); 2) predicted cumulative frequency distributions of nitrate concentration for both groups of farms.Both the errors in the predicted areal fractions as well as the errors in the predicted cumulative frequency distributions indicate that the regression models are invalid for the sandy soils of this study area.     

Air and groundwater pollution in an agricultural region of the Turkish Mediterranean coast

Air pollution and groundwater pollution in conjunction with agricultural activity were investigated in Antayla province on the Turkish Mediterranean coast. The air pollution was investigated in terms of gas-phase nitric acid (HNO3), sulfur dioxide (SO2), ammonia (NH3), and particulate matter for a 6-month period in the atmosphere using a "filter pack" system, which was developed and optimized in our laboratory. Ozone was measured by using an automated analyzer. Among all of the gas-phase pollutants, HNO3 had the lowest concentration (0.42 microg x m(-3)) followed by NH3. Agricultural activities seem to be the major source of observed NH3 in the air. The current state of water pollution was investigated in terms of organochlorine and organophosphorus pesticides around the greenhouses, in which mainly tomato, pepper, and eggplant are cultivated. Water samples were collected from 40 points, 28 of which were wells and 12 of which were surface water. The pesticide concentrations in water samples were determined by means of solid-phase extraction (SPE) followed by a gas chromatography (GC)-electron capture detector (ECD)/nitrogen phosphorus detector (NPD) system. In general, surface water samples were more polluted by the pesticides than groundwater samples. The most frequently observed pesticides were chlorpyriphos (57%) and aldrin (79%) in groundwater, and chlorpyriphos (75%), aldrin, and endosulfan sulfate (83%) in surface water samples. The highest concentrations were observed for fenamiphos (394.8 ng/L) and aldrin (68.51 ng/L) in groundwater, and dichlorvos (322.2 ng/L) and endosulfan sulfate (89.5 ng/L) in surface water samples. At least one pesticide had a concentration above the health limit in 38% of all the water samples analyzed.     

Predicting natural attenuation of xylene in groundwater using a numerical model.

The aquifer beneath an abandoned refinery in the Lower Rhine area, Germany, was contaminated with a number of different mineral oil products. Groundwater sampling in the area around the former xylene plant revealed that a xylene plume had developed in the underlying groundwater, and moreover, that there is strong evidence for in situ microbial xylene degradation with oxygen, nitrate, sulfate and ferric iron as electron acceptors. In order to prevent further xylene spreading, three pumping wells extracting contaminated water were installed downgradient of the spill zone. The numerical reactive transport code Transport Biochemisty Chemistry (TBC) was applied to this situation to quantify the relation of microbial degradation to xylene removal by the pumping wells. It could be shown that the unamended in situ degradation was an appreciable xylene removal process that contributed to about one-third to the total xylene removal (degradation plus extraction). A further objective of the model application was to predict xylene spreading under regional flow conditions, i.e. without operation of the three pumping wells, to consider the possible effects of natural xylene attenuation. To accomplish this, the model calibrated for the situation with operating wells was transferred to the hydraulic situation of regional flow while retaining the parameters of the biochemical model. It turned out that the xylene plume that is expected to develop downgradient of the source area will be limited to an extension of not more than 1000 m. An interesting feature of the simulations results was that xylene degradation under iron-reducing conditions, which was of minor importance for the situation with operating pumping wells, becomes the dominant degradation mechanism under regional flow conditions. Moreover, iron reduction will be the key process in controlling plume evolution. The model application illustrates that multi-species reactive transport models are needed to adequately transfer reactive processes from one hydraulic situation to another, while single species models are not suited for this predictive task.     

Scale-dependence of land use effects on water quality of streams in agricultural catchments

The influence of land use on water quality in streams is scale-dependent and varies in time and space. In this study, land cover patterns and stocking rates were used as measures of agricultural development in two pasture and one native grassland catchment in New Zealand and were related to water quality in streams of various orders. The amount of pasture per subcatchment correlated well to total nitrogen and nitrate in one catchment and turbidity and total phosphorous in the other catchment. Stocking rates were only correlated to total phosphorous in one pasture catchment but showed stronger correlations to ammonium, total phosphorous and total nitrogen in the other pasture catchment. Winter and spring floods were significant sources of nutrients and faecal coliforms from one of the pasture catchments into a wetland complex. Nutrient and faecal coliform concentrations were better predicted by pastural land cover in fourth-order than in second-order streams. This suggests that upstream land use is more influential in larger streams, while local land use and other factors may be more important in smaller streams. These temporal and spatial scale effects indicate that water-monitoring schemes need to be scale-sensitive.     

Removal of added nitrate in cotton burr compost, mulch compost, and peat: mechanisms and potential use for groundwater nitrate remediation

We conducted batch tests on the nature of removal of added nitrate in cotton burr compost, mulch compost, and sphagnum peat that may be potentially used in a permeable reactive barrier (PRB) for groundwater nitrate remediation. A rigorous steam autoclaving protocol (121 degrees C for 2h each day for three consecutive days) for the cotton burr compost and autoclaving of all labware and the nitrate working solutions resulted in drastically different results compared to the non-autoclaved treatment. In the non-autoclaved cotton burr compost, added nitrate at 20 mg N l(-1) decreased rapidly and was not detected after 3d; whereas, the autoclaved cotton burr compost showed persistent nitrate above 15.5 mg N l(-1) even after 10d, which is comparable with nitrate concentrations above 17.6 mg N l(-1) in a treatment using NaN(3) at 1000 mg l(-1). Dewaxed cotton burr compost showed decreased nitrate reduction compared to the pristine cotton burr compost. No nitrate reduction was detected in the dewaxed sphagnum peat. It is concluded that nitrate removal in the organic media is controlled by microbiologically mediated processes. The use of readily available cotton burr and mulch composts may offer a cost-effective method of nitrate removal from contaminated groundwater.     

The re-imagining of a framework for agricultural land use: A pathway for integrating agricultural practices into ecosystem services,planetary boundaries and sustainable development goals: This article belongs to Ambio’s 50th Anniversary Collection. Theme: Agricultural land use

This paper reflects on the legacy of the Ambio papers by Sombroek et al. (1993), Turner et al. (1994), and Brussaard et al. (1997) on the study of agricultural land use and its impacts on global carbon storage and nutrient dynamics. The papers were published at a time of transition in ecology that involved the integration of humans as components of ecosystems, the formulation of the ecosystem services, and emergence of sustainability science. The papers offered new frameworks to studying agricultural land use across multiple scales in a way that captured causality from interacting components of the system. Each paper argued for more comprehensive data sets; foreseeing the power of network-based science, the potential of molecular technologies to assess biodiversity, and advances in remote sensing. The papers have contributed both conceptual framings and methodological approaches to an ongoing movement to identify a pathway to study agricultural land use and environmental change that fit within the concepts of ecosystem services, planetary boundaries and sustainable development goals.     

Comparison of biotic and abiotic treatment approaches for co-mingled perchlorate, nitrate, and nitramine explosives in groundwater

Biological and abiotic approaches for treating co-mingled perchlorate, nitrate, and nitramine explosives in groundwater were compared in microcosm and column studies. In microcosms, microscale zero-valent iron (mZVI), nanoscale zero-valent iron (nZVI), and nickel catalyzed the reduction of RDX and HMX from initial concentrations of 9 and 1 mg/L, respectively, to below detection (0.02 mg/L), within 2 h. The mZVI and nZVI also degraded nitrate (3 mg/L) to below 0.4 mg/L, but none of the metal catalysts were observed to appreciably reduce perchlorate ( approximately 5 mg/L) in microcosms. Perchlorate losses were observed after approximately 2 months in columns of aquifer solids treated with mZVI, but this decline appears to be the result of biodegradation rather than abiotic reduction. An emulsified vegetable oil substrate was observed to effectively promote the biological reduction of nitrate, RDX and perchlorate in microcosms, and all four target contaminants in the flow-through columns. Nitrate and perchlorate were biodegraded most rapidly, followed by RDX and then HMX, although the rates of biological reduction for the nitramine explosives were appreciably slower than observed for mZVI or nickel. A model was developed to compare contaminant degradation mechanisms and rates between the biotic and abiotic treatments.     

The use of wind fields in a land use regression model to predict air pollution concentrations for health exposure studies

A methodology is developed to include wind flow effects in land use regression (LUR) models for predicting nitrogen dioxide (NO₂) concentrations for health exposure studies. NO₂ is widely used in health studies as an indicator of traffic-generated air pollution in urban areas. Incorporation of high-resolution interpolated observed wind direction from a network of 38 weather stations in a LUR model improved NO₂ concentration estimates in densely populated, high traffic and industrial/business areas in Toronto-Hamilton urban airshed (THUA) of Ontario, Canada. These small-area variations in air pollution concentrations that are probably more important for health exposure studies may not be detected by sparse continuous air pollution monitoring network or conventional interpolation methods. Observed wind fields were also compared with wind fields generated by Global Environmental Multiscale-High resolution Model Application Project (GEM-HiMAP) to explore the feasibility of using regional weather forecasting model simulated wind fields in LUR models when observed data are either sparse or not available. While GEM-HiMAP predicted wind fields well at large scales, it was unable to resolve wind flow patterns at smaller scales. These results suggest caution and careful evaluation of regional weather forecasting model simulated wind fields before incorporating into human exposure models for health studies. This study has demonstrated that wind fields may be integrated into the land use regression framework. Such integration has a discernable influence on both the overall model prediction and perhaps more importantly for health effects assessment on the relative spatial distribution of traffic pollution throughout the THUA. Methodology developed in this study may be applied in other large urban areas across the world.     

Stochastic analysis to assess the spatial distribution of groundwater nitrate concentrations in the Po catchment (Italy)

A large database including temporal trends of physical, ecological and socio-economic data was developed within the EUROCAT project. The aim was to estimate the nutrient fluxes for different socio-economic scenarios at catchment and coastal zone level of the Po catchment (Northern Italy) with reference to the Water Quality Objectives reported in the Water Framework Directive (WFD 2000/60/CE) and also in Italian legislation. Emission data derived from different sources at national, regional and local levels are referred to point and non-point sources. While non-point (diffuse) sources are simply integrated into the nutrient flux model, point sources are irregularly distributed. Intensive farming activity in the Po valley is one of the main Pressure factors Driving groundwater pollution in the catchment, therefore understanding the spatial variability of groundwater nitrate concentrations is a critical issue to be considered in developing a Water Quality Management Plan. In order to use the scattered point source data as input in our biogeochemical and transport models, it was necessary to predict their values and associated uncertainty at unsampled locations. This study reports the spatial distribution and uncertainty of groundwater nitrate concentration at a test site of the Po watershed using a probabilistic approach. Our approach was based on geostatistical sequential Gaussian simulation used to yield a series of stochastic images characterized by equally probable spatial distributions of the nitrate concentration across the area. Post-processing of many simulations allowed the mapping of contaminated and uncontaminated areas and provided a model for the uncertainty in the spatial distribution of nitrate concentrations.     

Effects of land use and land cover, stream discharge, and interannual climate on the magnitude and timing of nitrogen, phosphorus, and organic carbon concentrations in three coastal plain watersheds.

In-stream nitrogen, phosphorus, organic carbon, and suspended sediment concentrations were measured in 18 subbasins over 2 annual cycles to assess how land use and land cover (LULC) and stream discharge regulate water quality variables. The LULC was a primary driver of in-stream constituent concentrations and nutrient speciation owing to differences in dominant sources and input pathways associated with agricultural, urban, and forested land uses. Stream discharge was shown to be a major factor that dictated not only the magnitude of constituent concentrations, but also the chemical form. In high discharge agricultural subbasins, where nitrate was the dominant nitrogen form, there was a negative correlation between discharge and nitrate concentration indicating groundwater inputs as the dominant pathway. In urban settings, however, nitrate was positively correlated with discharge, and, in forested subwatersheds, where dissolved organic nitrogen (DON) was the dominant nitrogen form, there was a positive correlation between discharge and DON, indicating washoff from the watershed as the dominant input pathway. Similarly, phosphorus concentrations were strongly regulated by LULC, discharge, and seasonality. This comparative study highlights that different mechanisms regulate different forms of nitrogen, phosphorus, and carbon, and thus field programs or water quality models used for regulatory purposes must assess these nutrient forms to accurately apply management plans for nutrient reductions.