nitrate-N Pollution Research Articles

Qualitative risk aggregation problems for the safety of multiple aquifers exposed to nitrate, fluoride and arsenic contaminants by a ‘Total Information Management’ framework

The aquifer at Varzeqan plain, with multiple confined/unconfined and hard-rock boundaries, is exposed to risks from several contaminants (nitrate-N, fluoride and arsenic) originated by anthropogenic and/or geogenic activities, which are possibly accelerating by anthropogenic activities. The study is a research initiative driven by impacts of poor or non-existent planning/ regulation practices to produce insights despite the sparsity of the available data and the unknown baseline. A methodology is given, which seeks ‘total information management’ by pooling together the following five dimensions: (i) a perceptual model to collect existing knowledge-base; (ii) a conceptual model to analyse a sample of ion-concentrations by a set of existing techniques (e.g. statistical, graphical and multivariate analysis); (iii) risk cells to contextualise each contaminant; (iv) “soft modelling” to firm up information by learning from convergences and/or divergences within the conceptual model; and (v) study the processes within each risk cell through the OSPRC framework (Origins, Sources, Pathways, Receptors and Consequence). The research caters for inherent variabilities in the study area by 15 risk cells delineated within the boundaries of confined, unconfined and hard-rock aquifers as follows: 4 risk cells account for minor ions of nitrate-N pollution of anthropogenic origins; 6 for minor ions of fluoride and 5 for trace ions of geogenic arsenic anomalies. It further identifies the possibility of anthropogenic activities encouraging geogenic anomalies. The findings are presented as a descriptive model but this will be transformed into quantitative models in due course when more data become available.

Evaluation of a Digital Camera and a Smartphone Application, Using the Dark Green Color Index, in Assessing Maize Nitrogen Status

ABSTRACT Nitrogen (N) fertilization is crucial for maximizing maize (Zea mays L.) yield, but optimizing the amount of N to apply for maize must also consider potential impact on the environment from nitrate-N pollution. The dark green color index (DGCI) technology determines the greenness of maize leaves to assess maize N status. Spectrum Technologies used this DGCI technology to develop a smartphone app called Greenindex+. The objective of this study was to determine if DGCI values made by the app (DGCIapp) agree with values determined by a digital camera (DGCIcam), and to identify the sources of potential discrepancies between the camera and the app for determining DGCI. Field experiments were conducted at six sites across the state of Arkansas during 2013 and 2014 with N rates ranging from 0 to 360 kg N ha−1. Dark green color index measurements were made at tasseling both in the field using the app under ambient lighting conditions and in the laboratory under fluorescent lighting using the camera and the app. There was a significant linear–plateau relationship (P ≤ 0.05, R2 = 0.60, 0.89) between DGCIcam and leaf N concentration. However, the relationship between DGCIapp and leaf N concentration was more variable (R2 = 0.33, 0.69) than between DGCIcam and leaf N concentration when measured in the laboratory. Under field conditions, DGCIapp was also more variable than DGCIcam measured in the laboratory. The variability between DGCIcam and DGCIapp is because DGCIcam uses the whole leaf for color analysis while DGCIapp uses only the center portion of the leaf for color analysis.

Developing a reliable model for aquifer vulnerability

The assessment of aquifer vulnerability to pollution is crucial for planning a sound management strategy of groundwater quality protection and farmland fertilizer use. This study establishes a reliable model for aquifer vulnerability assessment with an excellent performance for predicting groundwater nitrate-N contamination in the Choushui River alluvial fan, Taiwan based on the DRASTIC method. To promote the prediction performance of aquifer vulnerability assessment, discriminant analysis (DA) was applied to determine the weights of factors in the DRASTIC model by comparing the model results with the observed nitrate-N data. Key factors influencing the presence of groundwater nitrate-N pollution were characterized for different concentration thresholds. The results of analysis reveal that the modified DRASTIC model using DA significantly improves prediction performance for aquifer vulnerability assessment, and groundwater protection zones can be determined correctly based on the modified DRASTIC index. Furthermore, the sensitivity of the factors in the modified DRASTIC model indicates that the depth to the groundwater and aquifer media are critical when the nitrate-N concentration is less than 3 mg/L, while the impact of the vadose zone plays a vital role in controlling nitrate-N pollution of over 5 mg/L.

Integrating indicator-based geostatistical estimation and aquifer vulnerability of nitrate-N for establishing groundwater protection zones

Summary Groundwater nitrate-N contamination occurs frequently in agricultural regions, primarily resulting from surface agricultural activities. The focus of this study is to establish groundwater protection zones based on indicator-based geostatistical estimation and aquifer vulnerability of nitrate-N in the Choushui River alluvial fan in Taiwan. The groundwater protection zones are determined by univariate indicator kriging (IK) estimation, aquifer vulnerability assessment using logistic regression (LR), and integration of the IK estimation and aquifer vulnerability using simple IK with local prior means (sIKlpm). First, according to the statistical significance of source, transport, and attenuation factors dominating the occurrence of nitrate-N pollution, a LR model was adopted to evaluate aquifer vulnerability and to characterize occurrence probability of nitrate-N exceeding 0.5 mg/L. Moreover, the probabilities estimated using LR were regarded as local prior means. IK was then used to estimate the actual extent of nitrate-N pollution. The integration of the IK estimation and aquifer vulnerability was obtained using sIKlpm. Finally, groundwater protection zones were probabilistically determined using the three aforementioned methods, and the estimated accuracy of the delineated groundwater protection zones was gauged using a cross-validation procedure based on observed nitrate-N data. The results reveal that the integration of the IK estimation and aquifer vulnerability using sIKlpm is more robust than univariate IK estimation and aquifer vulnerability assessment using LR for establishing groundwater protection zones. Rigorous management practices for fertilizer use should be implemented in orchards situated in the determined groundwater protection zones.

Use of Nitrification Inhibitor DMPP to Improve Nitrogen Uptake Efficiency in Citrus Trees

In citrus orchards, nitrogen uptake efficiency (NUE) is between 40 to 60% where any excess of nitrate is subjected to leaching below the rooting zone. The compound, 3,4-dimethylpyrazole phosphate (DMPP) inhibits the nitrification process in soil thus reducing/delaying nitrate leaching. The objective of this study was to evaluate the performance of DMPP added to ammonium sulphate (AS+DMPP), compared to ammonium sulphate (AS) and calcium-potassium nitrate (CPN), in fertigation of bearing orange trees grown outdoors in drainage lysimeters. Fertilizers were 15N-labeled to trace N through soil-plant-drainage system. Soil was sampled monthly from April to December and trees were destructively harvested in December. In trees fertilized with AS+DMPP, increased biomass was observed with a more profuse development of root system and higher fruit yield. Fertilizer 15N uptake significantly increased with DMPP addition. In AS+DMPP amended soils, increased values of -15N and lower -N concentrations were recorded from April to June as evidence of the inhibitory effect of DMPP on the nitrification process during this period. In CPN and AS fertilized soils, 15N losses in drainage solutions represented 9-10% of the fertilizer supplied whereas less than 3% was leached when DMPP was added. At the end of the cycle, highest NUE was recorded in the AS+DMPP treatment (69%), while CPN and AS had lower values (61% and 54%, respectively). Therefore, the use of DMPP enables a more efficient utilization of the fertilizer-N in citrus trees, minimizing the risk of nitrate-N pollution in groundwater. However, DMPP supply should be considered during spring fertilization, since high temperatures of summer months significantly reduced its activity.

Assessing nitrate contamination and its potential health risk to Kinmen residents

Kinmen is located in the southwest of Mainland China. Groundwater supplies 50% of the domestic water use on the island. Residents of Kinmen drink groundwater over the long term because surface water resources are limited. Nitrate-N pollution is found and distributed primarily in the western part of groundwater aquifer whereas saline groundwater is distributed to the northeastern Kinmen. This work applied the DRASTIC model to construct the vulnerability map of Kinmen groundwater. MT3D was then used to evaluate the contamination potential of nitrate-N. The health risk associated with the ingestion of nitrate-N contaminated groundwater is also assessed. The results from DRASTIC model showed that the upland crop and grass land have high contamination potential, whereas the forest, reservoir and housing land have low contamination potential. The calibrated MT3D model inversely determined the high strength sources (0.09-2.74kg/m(2)/year) of nitrate contaminant located in the west to the north west area and required 2-5years travel time to reach the monitoring wells. Simulated results of MT3D also showed that both the continuous and instantaneous contaminant sources of nitrate-N release may cause serious to moderate nitrate contamination in the western Kinmen and jeopardize the domestic use of groundwater. The chronic health hazard quotient (HQ) associated with the potential non-carcinogenic risk of drinking nitrate-N contaminated groundwater showed that the assessed 95th percentile of HQ is 2.74, indicating that exposure to waterborne nitrate poses a potential non-cancer risk to the residents of the island. Corrective measures, including protecting groundwater recharge zones and reducing the number of agricultural and non-agricultural nitrogen sources that enters the aquifer, should be implemented especially in the western part of Kinmen to assure a sustainable use of groundwater resources.

Analysis of spatial–temporal distributions of nitrate-N concentration in Shitoukoumen catchment in northeast China

This article discusses the generation and migration process of nitrate-N pollution in shallow groundwater caused by agricultural nonpoint source pollution in the catchment area of Shitoukoumen Reservoir in northeast China. By monitoring the shallow groundwater nitrate-N in the low-water period, the normal season, and high-flow period in the study area for a year, it was found that the nitrate-N concentration in the shallow groundwater of this area had a seasonal variation in both spatial and time distribution. In the time distribution, the peak value appeared in July, the high-flow period, and the valley value appeared in April, the low-water period, and showed a significant correlation with the time distribution of fertilization rate and rainfall. In the spatial distribution of nitrate-N pollution, when the distribution in shallow groundwater was analyzed separately in the three different periods (low-water period, the normal season, and high-flow period) and the discipline transference and enrichment of nitrate-N pollution in shallow groundwater was determined, this indicated that the region in the southeast study area where runoff conditions were better was less contaminated, and the region where runoff conditions were poor, as well as the region along the river were seriously polluted. The nitrate-N concentration in shallow groundwater was distributed mainly along the path of groundwater flow and was excreted in the drainage region. This showed that the spatial distribution of nitrate-N concentration in the shallow groundwater of the entire region was mainly controlled by the groundwater flow system. At the same time, in the middle and lower reaches of the study area, the seasonal changes in the recharged-excreted relationship between groundwater and river caused seasonal differences in the spatial distribution of nitrate-N pollution in groundwater. The combined effects of the groundwater mobility and the surface river resulted in a poor correlation between the groundwater nitrate-N concentration and land-use types. Only in the plain area where there was little influence from groundwater runoff and the surface river did the groundwater nitrate-N concentration correlate with land-use types. The spatial and time distribution of nitrate-N concentration in the shallow groundwater of the study area was impacted by agricultural nonpoint source pollution, the groundwater flow system, and the surface river and formed a concentration response system which uses basins as a unit.

Seasonal variation of nitrate-N in surface and ground-waters of South Western Nigeria: a preliminary survey

Two surveys of nitrate-N concentrations in surface and ground water in Ogun and parts of Lagos and Oyo States of south-western Nigeria were undertaken between October 1997 and December 1998, and between July 2000 and May 2001 (covering both dry and rainy seasons). The study was conducted to ascertain the extent of nitrate-N pollution of the surface/ground water in some parts of the three states. Seventy-two water points (33 rivers/streams, 21 wells and 18 boreholes) were sampled three times during each of the two seasons. Nitrate-N was detected in all the river/stream samples analysed with concentrations ranging from 0.5 to 15.3 mg/l and 1.0 to 7.7 mg/l during the rainy and dry seasons, respectively (average value 2.7 and 2.4 mg/l for rainy and dry season, respectively). 98.5% of the rivers/streams sampling points contained nitrate-N in amounts equal to or less than 10 mg/l. 88.1% of wells and 97.2% of boreholes had a nitrate-N content less than 5 mg/l. Nitrate-N concentrations in the sampled wells ranged from 1.4 to 7.4 mg/l and 1.1 to 6.0 mg/l during the rainy and dry seasons, respectively (average value 2.6 and 2.2 mg/l, respectively). The sampled boreholes had a lower nitrate-N concentration ranging from 0.1 to 5.2 mg/l and from below the detection limit to 5.0 mg/l during the rainy and dry seasons, respectively (average value 1.8 and 1.6 mg/l, respectively). Nitrate-N concentrations in boreholes were below detection limit in 22% of the samples. Generally, for most of the sampling points, nitrate-N concentrations were slightly higher during the rainy season compared with the dry season. The present results indicated that nitrate-N concentrations in all the water points (except one) were below the World Health Organization (WHO) maximum acceptable limit in potable waters (10 mg/l). Therefore, contamination of the surface and ground water of the study area is not indicated. This study provides background data against which future changes in nitrate-N concentrations of surface and ground waters in the study area can be measured.

Regional differentiation of non-point source pollution of agriculture-derived nitrate nitrogen in groundwater in northern China

Abstract Nitrate is one of the major agriculture-derived pollutants leaching to groundwater. This paper discusses the contamination process and spatial distribution of nitrate-N concentrations in groundwater in a typical high-yielding area of northern China. On-site monitoring of nitrate-N concentrations in groundwater from two separated regions that had been managed similarly indicated different trends of nitrate-N elevation during the past 4 years: one remained relatively stable while the other one significantly increased. Statistical analyses show that nitrate-N concentrations in groundwater were significantly correlated with the sampling depth of 60 m and deeper and nitrate had diffused to the depth of 150–200 m. Results of surface interpolation analyses based on a large number of groundwater samples indicate that the distribution and pollution patterns of nitrate-N were mainly influenced by groundwater flow in horizontal direction. It was found that some regions were more obviously contaminated than others and a few regions were less polluted or even absent of pollution. The spatial variation in pollution patterns of nitrate-N could be mainly attributed to the diffusion and translocation of nitrate-N in three dimensions after being leached into groundwater. The differentiation of nitrate-N concentration in groundwater resulted in poor correlation between land use types on the ground and nitrate-N concentrations in the underlying water. Nitrate-N pollution of groundwater might be directly related to management practices in situations where relatively stable groundwater tables and negligible water flow existed. Therefore, the observed nitrate-N concentration in groundwater at a specific site could be a static appearance of dynamic distribution of the agriculture-derived nitrate-N within a watershed. The importance of this study is in recognition of the guidelines on managing and controlling agriculture-derived pollution within a watershed—the basic ecologic unit.

ROLE OF SOIL AND GRASS STRIPS IN REDUCING NITRATE-N POLLUTION IN SUBSURFACE DRAINED FARMLANDS: LYSIMETER RESULTS

A two-year study was carried out to investigate the role of soil and grass strips, coupled with water table management, in reducing nitrate-N residues from agricultural drainage waters. Twelve lysimeters, 1 m long and 450 mm diameter, were packed with a sandy soil and subjected to two water table management practices: free drainage and controlled drainage. Each treatment had either grass (sod) cover or bare soil in triplicate. Nitrate-N contaminated water was applied at the top to each lysimeter and samples of drain effluent were collected at the bottom. Significant reductions (1% level) in nitrate-N concentrations were found in all treatments. However, the controlled drainage treatment was found to be more effective for reducing nitrate levels than the free drainage treatment.In the second year, the cumulative volume of applied water and drain outflow was used to perform a mass balance and estimate the nitrate residues in drainage waters after treatment. The total amount of nitrate applied to each column, 13 g, was reduced to one-third in the controlled drainage lysimeters, and to one-half in the free drainage lysimeters. The controlled drainage lysimeters covered with grass were found to be the most effective for reducing nitrate residues. The results of this study reinforce the contention that grass filter strips can reduce nitrate-N pollution of drainage water from agricultural land.

IMPROVING SWEET CORN FERTILIZER-NITROGEN EFFICIENCY

Improving sweet corn fertilizer-N efficiency promotes a more vigorous and healthy crop, rewards the grower with greater profits, and protects our water resources from nitrate-N pollution. Two areas of research that have the potential to improve the efficiency of fertilizer-N applications are the Minolta SPAD 502 chlorophyll meter and the presidedress soil N test. The SP meter is a rapid and nondestructive technique for assessing sweet corn leaf levels, and SP readings have been correlated to leaf N concentration. A presidedress soil N test measures the amount of soil N that will be available to the plant during the remainder of the growing season. SP meter readings combined with presidedress soil N analyses may be used to determine crop N needs and fertilizer-N sidedress application rates. Basing fertilizer-N sidedress application rates on actual crop N needs will reduce excess fertilizer-N applications and the resulting leaching of nitrates.