Groundwater In Agricultural Areas Research Articles

Evaluation of the Health Risk and Distribution Characteristics of Pesticides in Shallow Groundwater, South Korea

In this work, a method of simultaneously analyzing pesticide concentration and assessing its risks was developed. Assessments were conducted to evaluate the distribution characteristics and risks to human health of pesticides in shallow groundwater in agricultural areas. We developed multi-residue analytical methods using liquid chromatography (LC-MS/MS) and gas chromatography–tandem mass spectrometry (GC-MS/MS) to analyze 57 pesticides in groundwater. In addition, risk assessments were performed by setting scenarios considering the routes of pesticide infiltration into groundwater. For the simultaneous analysis of 57 pesticides, the liquid–liquid extraction method was applied twice using dichloromethane under acidic and alkaline conditions. The extract was concentrated and analyzed using LC-MS/MS (41 pesticides) and GC-MS/MS (16 pesticides). The precision and accuracy ranges of the analytical methods were 0.1~12.9% (within ±15%) and 80.3~113.6% (within ±20%), respectively. The limit of quantification was found to range from 0.0004 to 0.0677 μg/L. In total, 57 pesticides were monitored in 200 groundwater wells from 2019 to 2020. Twenty-six pesticides, including metolachlor and imidacloprid, were detected, with an average concentration of 0.0008 μg/L in groundwater. The pesticide types and detection levels differed depending on the survey period and surrounding land. When the risks associated with alachlor, metolachlor, and carbofuran were assessed, their health risks when found in groundwater were evaluated to be negligible (non-carcinogenic risk: less than 10−3, carcinogenic risk: less than 10−6).

Human biomarkers associated with low concentrations of arsenic (As) and lead (Pb) in groundwater in agricultural areas of Thailand

Human biomarkers were used to evaluate the lead (Pb) and arsenic (As) exposure of local people who lived in an agricultural area with intense agrochemical usage and who consumed groundwater. Although the heavy metals/metalloids in the groundwater were at low concentrations, they could cause adverse effects due to a high daily water intake rate over the long term. Biomarkers (hair, fingernails and urine) were collected from 100 subjects along with the local shallow groundwater and tap water, which is the treated deep groundwater, and investigated for the concentrations of As and Pb. Shallow groundwater had an average pH of 5.21 ± 1.90, ranging from 3.77 to 8.34, with average concentrations of As and Pb of 1.311 µg/L and 6.882 µg/L, respectively. Tap water had an average pH of 5.24 ± 1.63, ranging from 3.86 to 8.89, with the average concentrations of As and Pb of 0.77 µg/L and 0.004 µg/L, respectively. The levels of both As and Pb in the hair, fingernails and urine of shallow groundwater-consuming residents were greater than those in the hair, fingernails and urine of tap water-consuming residents. Interestingly, the As level in urine showed a linear relationship with the As concentration in groundwater (R2 = 0.91). The average water consumption rate was approximately two-fold higher than the standard; thus, its consumption posed a health risk even at the low As and Pb levels in the groundwater. The hazard index (HI) ranged from 0.01 to 16.34 (average of 1.20 ± 2.50), which was higher than the acceptable level. Finally, the concomitant factors for As and Pb in the urine, hair and nails from both binary logistic regression and odds ratio (OR) analysis indicated that groundwater consumption was the major concomitant risk factor. This study suggested that direct consumption of this groundwater should be avoided and that the groundwater should be treated, especially before consumption. In conclusion, urine is suggested to be a biomarker of daily exposure to As and Pb, while for long-term exposure to these metals, fingernails are suggested as a better biomarker than hair.

Impact of fertilization with pig slurry on the isotopic composition of nitrate retained in soil and leached to groundwater in agricultural areas

The isotopic composition of N and O of nitrate (NO3−) is usually employed to trace its sources of pollution in groundwater. In agricultural areas, the amount of NO3− that reaches the aquifers after fertilization is controlled by different transformation processes that can affect the nitrogen species isotopic composition. Aiming to address the reliability of using isotope tools to trace sources of groundwater NO3−, the goal of this study was to check the effect of fertilization on the isotopic composition of N compounds retained and leached from soils. The concentration and isotopic composition (δ15N and δ18O) of ammonium (NH4+), NO3− and nitrite (NO2−) was characterized after the application of pig slurry in lysimeters containing either soil under fallow (LF) or the same soil continuously cropped and fertilized (LC) during the previous six years. Results showed that the leached NO3− isotopic signature did not directly reflect the isotopic composition of the applied pig slurry. Just after fertilization, nitrification led to lower δ15NNO3 values in soil extracts and leachates (e.g. from +5.9 ± 0.9‰ to +3.8 ± 3.1‰ in soil extracts of LF lysimeters). These values increased after complete nitrification (+11.5 ± 1.3‰) towards the δ15Nbulk of pig slurry (+19.6 ± 0.5‰). Later on, due to soil organic matter and plant debris mineralization and subsequent nitrification, values decreased towards the initial δ15NNO3 of soil but remained above them (+8.6 ± 1.0‰). Both LF and LC experiments showed a similar trend and the latter ones allowed to reinforce that long-term fertilization with pig slurry can increase the soil δ15NNO3. Concerning the δ18O of NO3− from soil extracts and leachates, it mainly depended on the δ18O of irrigation water and oxygen, after nitrification of NH4+ from pig slurry. Therefore, studies aiming to trace groundwater NO3− pollution sources in rural areas by using an isotopic approach should consider the fertilization history of each setting. Also, analyzing the δ15Nbulk of soil is recommended, since it could mask the isotopic signature of the N applied through fertilization.

Delineating the impacts of poultry burial leachate on shallow groundwater in a reclaimed agro-livestock farming area, using multivariate statistical analysis of hydrochemical data.

Burial is applied to dispose of livestock carcasses due to its convenience and cost efficiency despite concerns about groundwater contamination by leachate from burial pits. In particular, the burial method has caused debates about groundwater contamination sources around on-farm livestock burial sites because of pre- and coexisting contamination from livestock production and agriculture. To assess the causes of groundwater contamination around poultry burial pits that were constructed after an outbreak of avian influenza in 2010-11 in Korea, hydrochemical data of groundwater samples from monitoring wells (MWs, n = 14) and household wells (HWs, n = 30) were monitored to differentiate contamination sources. Hydrochemical data indicated that groundwater from MWs is characterized by higher enrichments of inorganic constituents including electrical conductivity (EC), NH4, Ca, Mg, K, SO4, HCO3, Fe(Total), and Mn(Total), but lower concentrations of DO than groundwater from HWs. The combined use of the principal component analysis (PCA) and K-means cluster analysis (KCA) indicated that groundwater in seven MWs was affected by leachate. The parameters such as NH4, Ca, Mg, K, SO4, HCO3, Fe(Total), and Mn(Total) are expected to be useful to identify the impact of leachate on groundwater in agricultural areas. This study suggests that (1) regional hydrochemical characteristics should be assessed to distinguish the effect of livestock burial leachate from other contamination sources and (2) the combined use of PCA and KCA is effective to identify the weakened impact of leachate leakage among overlapping multiple sources and processes of groundwater contamination.

Nitrate-dependent Uranium mobilisation in groundwater

Nitrate is a critical substance that determines the prevailing redox conditions in groundwater, and in turn the behaviour of Uranium (U). Therefore, the excessive use of nitrate-fertiliser in agricultural catchments could exert a significant influence on U mobilisation. This is a significant issue in catchments, where groundwater resources are increasingly being exploited for drinking water production. Past studies on U mobility in groundwater have considered individual hydro-geochemical factors influencing U concentrations, rather than as a single system with multiple factors. This research study investigated nitrate-dependent U mobility within a catchment in Brazil, where a range of intensive agricultural activities are undertaken and the giant Guarani aquifer is located. The study used direct measurements of groundwater redox conditions and other hydro-geochemical parameters. The research outcomes indicated that U could have two hydro-geochemical systems based on positive and negative redox potential of groundwater. The pH, HCO3− and temperature pose the largest influence, respectively, on U mobilisation, and these impacts are greater in agricultural lands than urban areas. Acidic and less reducing (positive redox) groundwater across the aquifer and basic and highly reducing (negative redox) groundwater in agricultural areas make U more mobile. The alkalinity increases U mobility in less reducing groundwater across the aquifer and in highly reducing groundwater in agricultural areas. Further, U can be mobile in hot and less reducing groundwater across the aquifer, but hot and highly reducing groundwater in agricultural areas can limit U mobility. More importantly, the study revealed that U can be mobile under high NO3− concentrations in reducing groundwater in non-agricultural areas. However, anthropogenic inputs of NO3− are expected to be lower than natural NO3− inputs in areas where the groundwater is highly reducing. Hence, fertiliser use in agricultural lands is less likely to increase U mobility in highly reducing groundwater.

Microbial nitrate removal efficiency in groundwater polluted from agricultural activities with hybrid cork treatment wetlands

Agricultural practices have raised the level of nutrients reaching aquifers. In Europe, nitrate pollution is considered as one of the main threats for the quality of groundwater in agricultural areas. Treatment wetlands (TWs), also known as Constructed Wetlands, are used for groundwater treatment in areas with an important concentration of nitrogen compounds; total nitrogen removal depends on the type and operation scheme. Cork by-product from the industry has shown clear adsorbent properties to remove organic pollutants. The work is focused on the characterization of microbial communities involved in the nitrate‑nitrogen removal process in groundwater polluted from agricultural activities. The experimental design allowed the comparison of nitrate removal efficiency depending on the filter media material, cork by-product or gravel, used in two hybrid TWs (a vertical flow cell followed by a horizontal subsurface flow cell), installed in areas close to two irrigated agricultural plots at the Lleida plain area (Spain). Both physicochemical and microbial results were consistent and confirm the nitrate removal efficiency using cork as a filter media. A significant (p = 0.0025) higher removal in Bellvís TW using cork compared with the Vilanova de la Barca gravel system was observed, achieving a removal rate from 80 to 99% compared to the 5–46%, respectively. Regarding the community composition of the two different TWs, microorganisms were mainly related to the phylum Proteobacteria, and included members found to be key players in the nitrogen cycle, such as ammonia and nitrite oxidizers, as well as denitrifiers. Also, the group Bacteroidetes turns to be another abundant phylum from our bacterial dataset, whose members are suggested to be strongly involved in denitrification processes. Some groups showed to prevail depending on the type of media (cork or gravel); Firmicutes and Delta and Epsilonproteobacteria had a significant higher abundance in the TW with cork, while Acidobacteria and Planctomyces were prevalent in gravel. Therefore, cork could be an alternative material used by treatment wetlands to minimize the impact in the environment caused by nitrogen pollution in groundwater bodies.

Metamodeling and mapping of nitrate flux in the unsaturated zone and groundwater, Wisconsin, USA

Nitrate contamination of groundwater in agricultural areas poses a major challenge to the sustainability of water resources. Aquifer vulnerability models are useful tools that can help resource managers identify areas of concern, but quantifying nitrogen (N) inputs in such models is challenging, especially at large spatial scales. We sought to improve regional nitrate (NO3−) input functions by characterizing unsaturated zone NO3− transport to groundwater through use of surrogate, machine-learning metamodels of a process-based N flux model. The metamodels used boosted regression trees (BRTs) to relate mappable landscape variables to parameters and outputs of a previous “vertical flux method” (VFM) applied at sampled wells in the Fox, Wolf, and Peshtigo (FWP) river basins in northeastern Wisconsin. In this context, the metamodels upscaled the VFM results throughout the region, and the VFM parameters and outputs are the metamodel response variables. The study area encompassed the domain of a detailed numerical model that provided additional predictor variables, including groundwater recharge, to the metamodels. We used a statistical learning framework to test a range of model complexities to identify suitable hyperparameters of the six BRT metamodels corresponding to each response variable of interest: NO3− source concentration factor (which determines the local NO3− input concentration); unsaturated zone travel time; NO3− concentration at the water table in 1980, 2000, and 2020 (three separate metamodels); and NO3− “extinction depth”, the eventual steady state depth of the NO3− front. The final metamodels were trained to 129 wells within the active numerical flow model area, and considered 58 mappable predictor variables compiled in a geographic information system (GIS). These metamodels had training and cross-validation testing R2 values of 0.52 – 0.86 and 0.22 – 0.38, respectively, and predictions were compiled as maps of the above response variables. Testing performance was reasonable, considering that we limited the metamodel predictor variables to mappable factors as opposed to using all available VFM input variables. Relationships between metamodel predictor variables and mapped outputs were generally consistent with expectations, e.g. with greater source concentrations and NO3− at the groundwater table in areas of intensive crop use and well drained soils. Shorter unsaturated zone travel times in poorly drained areas likely indicated preferential flow through clay soils, and a tendency for fine grained deposits to collocate with areas of shallower water table. Numerical estimates of groundwater recharge were important in the metamodels and may have been a proxy for N input and redox conditions in the northern FWP, which had shallow predicted NO3− extinction depth. The metamodel results provide proof-of-concept for regional characterization of unsaturated zone NO3− transport processes in a statistical framework based on readily mappable GIS input variables.

Assessment of Groundwater Quality in Areas Irrigated with Food Industry Wastewater: a Case of Wastewater Utilisation from Sugar and Yeast Factories

This work presents the outcomes from two independent studies evaluating the chemical quality of groundwater in agricultural areas irrigated with wastewater from sugar and yeast industries. The evaluation was determined using chemical parameters representing typical contaminants of sugar industry wastewater (SIWW) and yeast industry wastewater (YIWW), and characterising the content of organic matter (BOD5), nutrients (NH4-N, NO3-N, TN and TP) and salts (Cl, SO4, Na and K). The studies reveal that food industry wastewater constitutes a valuable water-nutrient-rich medium that can be reused in agricultural applications as an alternative water resource for irrigation and nutrients for fertilisation. Furthermore, the reuse facilitates the sustainable discharge of wastewater through a soil-aquifer zone to the natural environment. This does not affect chemical quality of groundwater, which was comparable in areas irrigated and non-irrigated with SIWW and YIWW. Although some parameters (NO3-N, NH4-N, SO4, Cl and Na) displayed higher concentrations in groundwater from the fields irrigated with wastewater, these contents were within recommended health-based guideline limits defined in either the groundwater quality standards or the drinking water quality norms. Only the contents of K revealed an exclusive groundwater impact from wastewater irrigation. This was confirmed in statistical tests employing the Ward’s hierarchical clustering method, which exposed excessive amounts of K introduced into groundwater through irrigation with both SIWW and YIWW. However, this parameter is not considered to pose any health risk to humans or the environment, and its content is not restricted by quality guideline values for either groundwater or drinking water.

Impact of water pollution on human health in the Central African Republic

Bacterial contamination of waters and their impacts on human health in the Central African Republic is a pollution problem that goes far back in time. Today, water quality is impaired, including the contamination of fecal microorganisms, excessive use of agrochemicals, uncontrolled discharges from industries and solid and liquid waste from households and municipal. Most of people in Central Africa use water directly from the wells and rivers water for their domestic activities include drinking. These works highlight the bacteriological and nitrate pollution of surface and groundwater streams and how can impair public health. Many reports concluded that this pollution came from poor sanitation wastes/extracts. Other studies have revealed the presence of nitrates and coliform bacteria in groundwater in agricultural areas it concludes that, this pollution comes from the reuse of untreated wastewater in agriculture. Rivers and lakes seem to be most contaminated sources because are most exposed to waste. Human activities and poor municipal waste control contribute to water pollution and results to serious health problems. Main data in this review study are collected in various existing studies by many researchers and published in international and national journals, but also by non-governmental organizations and the Central African Government reports.

Impact of Polluted River Water on Ground Water of Agricultural Area and its Suitability for Irrigation

This paper describes the impact of polluted river water on ground water of agricultural area and its suitability for irrigation. In this study seven villages were selected for investigating river and groundwater contamination. Hence 11 river and 54 well water samples were obtained from either side of Kham River. Pollution by TDS, Cl, NO3, Ca, Mg, and Na in 22 river water sample during pre-monsoon and post-monsoon period was observed. 6 groundwater sample during pre-monsoon period and 8 well water samples during post-monsoon period have NO3 concentration more than 45 mg/lit as per Indian Irrigation and drinking water standard. The suitability of river and groundwater for irrigation was determined on the basis of chemical indices like Sodium adsorption ratio (SAR), Soluble Sodium percentage (SSP), Kelly’s ratio (KR). IS 11624:1986 and analytical data plotted on US salinity diagram illustrates that, 22 river water samples during pre-monsoon and post monsoon period are having SAR above 26 and EC above 6000 micromhos/ cm. This suggests that river water is unsuitable for irrigation. 6, 13 groundwater samples along left and right bank of Kham river respectively have SAR between 18 to 26 and EC 3000 to 6000 micromhos/cm. Such water when used for irrigation decreases soil solution capacity and irrigated water is not available to plant even though soil appears wet. A statistical correlation was attempted on above mentioned water quality parameter. River and groundwater sample analysis shows increased concentration of sodium, calcium, magnesium, nitrate and chloride which indicates the influence of domestic and industrial effluent on river and groundwater hydrochemistry in village Waluj, Patoda, Naigaon, Valdgaon of Aurangabad and Gangapur taluka. This was clarified in Spatial relationship between river water and groundwater.

Determination of Nitrate Concentration in Groundwater in Agricultural Areas in Babol, Iran

Background and Purpose: Elevated nitrate concentrations in drinking water c an cause methemoglobinemia in infants, stomach cancer in adults and nitrate poisoning in animals as well. Modeling of nitrate fate and transport in groundwat er to minimize nitrate concentration in groundwater has been studied by numerous researchers. Materials and Methods: In order to determine the potential nitrate and nit rite ions contamination of groundwater, 93 groundwater samples were collected. All the observation wells were located in agricultural areas. In order to measure the amou nt of nitrogen in the soil, 45 samples from the entire region were randomly selected and analyzed . Results: The results showed that in 82% of groundwater samples nitrate concentration has exceeded the standard level of 10 mg/l as N. Water level in orchard fields were between 1m to 3.7 m below the ground surface. Nitrate concentration in all sample s from the citrus orchard fell within the standard levels. Simulation of potential nitrate movement wa s performed in 4 different areas. Results indicated that in the rice field nitrate penetrated to the de pth of 3.2 m that was the deepest nitrate seepage between four areas. Probable reasons of different r esults in these areas are discussed. Conclusion: The simulated and observed measured data showed that the model was able to predict the groundwater quality changes within the soil profile and the aquifer. [*Ehteshami M, Biglarijoo N. Determination of Nitrate Concentration in Groundwater in Agricultural Area in Babol County, Iran . IJHS 2014; 2(4): 1-9] http://jhs.mazums.ac.ir

Soil and groundwater quality with reference to nitrate in a semiarid agricultural region

Nitrate is a common pollutant in surface water and groundwater of agricultural areas. It is essential to monitor this pollutant in groundwater, especially when it is used for drinking purposes without treatment. The present study was carried out in an intensively irrigated area which forms a part of Nalgonda district, Andhra Pradesh, India where groundwater meets all the water needs of the rural population living in this area. The objective was to assess the spatiotemporal variation in the concentration of nitrate in groundwater and soil. Based on the analysis of 496 groundwater samples collected from 45 wells over a period of 2 years from March 2008 to January 2010 by sampling every 2 months, it was observed that groundwater in 242 km2 of the total 724 km2 area had nitrate above the maximum permissible limit of 45 mg/l for drinking purposes. Nitrate concentration in groundwater showed a positive relation with potassium, chloride, and sulfate, indicating their source from fertilizers. Reasons for the high concentration of nitrate in domestic areas were the dumping of animal wastes and leakage from septic tanks. The pH of the soil samples showed that most of the area had basic soil. Apart from pH, organic carbon, available phosphorous, available potassium, ammoniacal nitrogen, and nitrate nitrogen were also analyzed in the 97 soil samples.

Estimating nitrate travel time to groundwater in agricultural areas in the Tone River basin from deep soil properties and layer characteristics

Estimating nitrate travel time to groundwater in agricultural areas in the Tone River basin from deep soil properties and layer characteristics

Application of Indicator kriging to Evaluate the Probability of Exceeding Nitrate Contamination Thresholds

Nitrate contamination is one of the main risks for groundwater in agricultural areas. Theevaluation of the effect of agricultural practices on groundwater nitrate concentration, especially in highlysensitive areas, is crucial for a correct land planning, and a good agronomic intervention scheduling. Aim of this paper is to map the probability to exceed nitrate regulatory threshold applying a non-parametric geostatistical approach, the Indicator Kriging (IK). A study in the Fucino Plain (Abruzzo, Central Italy), characterized by highly profitable intensive agriculture with mainly irrigated horticultural and short rotation crops, was carried out. The Plain has a shallow and controlled groundwater table, and channels draining the surplus water during winter. Water samples were collected monthly from piezometers and analysed for nitrate. IK provided a model of spatial uncertainty, representing the probability that the threshold of 50 mg/L fixed by the European Nitrate Directive is exceeded, and results were transferred into a GIS. Maps obtained for each month showed how the probability to exceed the threshold changes during an average year. The methodology can provide an effective operative tool to support decision-makers for the identification and the designation of nitrate vulnerable zones.

Regression Models for Estimating Concentrations of Atrazine plus Deethylatrazine in Shallow Groundwater in Agricultural Areas of the United States

Tobit regression models were developed to predict the summed concentration of atrazine [6-chloro--ethyl--(1-methylethyl)-1,3,5-triazine-2,4-diamine] and its degradate deethylatrazine [6-chloro--(1-methylethyl)-1,3,5,-triazine-2,4-diamine] (DEA) in shallow groundwater underlying agricultural settings across the conterminous United States. The models were developed from atrazine and DEA concentrations in samples from 1298 wells and explanatory variables that represent the source of atrazine and various aspects of the transport and fate of atrazine and DEA in the subsurface. One advantage of these newly developed models over previous national regression models is that they predict concentrations (rather than detection frequency), which can be compared with water quality benchmarks. Model results indicate that variability in the concentration of atrazine residues (atrazine plus DEA) in groundwater underlying agricultural areas is more strongly controlled by the history of atrazine use in relation to the timing of recharge (groundwater age) than by processes that control the dispersion, adsorption, or degradation of these compounds in the saturated zone. Current (1990s) atrazine use was found to be a weak explanatory variable, perhaps because it does not represent the use of atrazine at the time of recharge of the sampled groundwater and because the likelihood that these compounds will reach the water table is affected by other factors operating within the unsaturated zone, such as soil characteristics, artificial drainage, and water movement. Results show that only about 5% of agricultural areas have greater than a 10% probability of exceeding the USEPA maximum contaminant level of 3.0 μg L. These models are not developed for regulatory purposes but rather can be used to (i) identify areas of potential concern, (ii) provide conservative estimates of the concentrations of atrazine residues in deeper potential drinking water supplies, and (iii) set priorities among areas for future groundwater monitoring.

Factors controlling nitrate fluxes in groundwater in agricultural areas

The impact of agricultural chemicals on groundwater quality depends on the interactions of biogeochemical and hydrologic factors. To identify key processes affecting distribution of agricultural nitrate in groundwater, a parsimonious transport model was applied at 14 sites across the U.S. Simulated vertical profiles of NO3−, N2 from denitrification, O2, Cl−, and environmental tracers of groundwater age were matched to observations by adjusting the parameters for recharge rate, unsaturated zone travel time, fractions of N and Cl− inputs leached to groundwater, O2 reduction rate, O2 threshold for denitrification, and denitrification rate. Model results revealed important interactions among biogeochemical and physical factors. Chloride fluxes decreased between the land surface and water table possibly because of Cl− exports in harvested crops (averaging 22% of land‐surface Cl− inputs). Modeled zero‐order rates of O2 reduction and denitrification were correlated. Denitrification rates at depth commonly exceeded overlying O2 reduction rates, likely because shallow geologic sources of reactive electron donors had been depleted. Projections indicated continued downward migration of NO3− fronts at sites with denitrification rates <0.25 mg‐N L−1 yr−1. The steady state depth of NO3− depended to a similar degree on application rate, leaching fraction, recharge, and NO3− and O2 reaction rates. Steady state total mass in each aquifer depended primarily on the N application rate. In addition to managing application rates at land surface, efficient water use may reduce the depth and mass of N in groundwater because lower recharge was associated with lower N fraction leached. Management actions to reduce N leaching could be targeted over aquifers with high‐recharge and low‐denitrification rates.

Nitrate and Escherichia coli NAR analysis in tile drain effluent from a mixed tree intercrop and monocrop system

Contamination of groundwater in agricultural areas by nitrate and Escherichia coli can potentially lead to several harmful health effects for those who consume or are exposed to it. The objective of this study was to determine if trees can reduce loadings of these contaminants to the groundwater. Tile drain effluent from two adjacent agricultural systems (a mixed tree intercrop and a monocrop) was collected from April to November during 2005 and 2006 from a mini watershed area of 17,200 m 2. An area of 1100 m 2 (6.4%) in each system was subject to application of a mixture of water and a biotracer E. coli NAR, a naturally occurring strain that is resistant to naladixic acid and has been shown to be safe for introduction into the environment. The effluent was analyzed for concentrations of the biotracer and NO 3 −-N. The premise of this study is to determine if the safety-net hypothesis is valid in a temperate intercropping system. This hypothesis states that the incorporation of trees into agricultural systems will allow for a more efficient use of resources, since the rooting system of the trees capture nutrients that are not captured by the crop component of the system. The quantities of NO 3 −-N in the leachate were similar in 2005: 57.37 and 54.74 kg ha −1 leached from the monocrop and intercrop sites, respectively. However, in 2006, NO 3 −-N levels were significantly higher ( p < 0.05) in the monocrop effluent: 164.67 kg ha −1 compared to that of the intercrop, 88.59 kg ha −1. Few significant differences were found in E. coli NAR outputs during both years: for the same number of samples collected, the total colony forming units (CFUs) found in the monocrop and intercrop effluents, respectively were 4040 and 3558 in 2005 and 34,025 and 28,401 in 2006. This indicates that intercropping systems and perhaps trees in general have a potential mitigating effect on E. coli movement to the groundwater.

Decadal‐Scale Changes of Pesticides in Ground Water of the United States, 1993–2003

Pesticide data for ground water sampled across the United States between 1993-1995 and 2001-2003 by the U.S. Geological Survey National Water-Quality Assessment Program were evaluated for trends in detection frequency and concentration. The data analysis evaluated samples collected from a total of 362 wells located in 12 local well networks characterizing shallow ground water in agricultural areas and six local well networks characterizing the drinking water resource in areas of variable land use. Each well network was sampled once during 1993-1995 and once during 2001-2003. The networks provide an overview of conditions across a wide range of hydrogeologic settings and in major agricultural areas that vary in dominant crop type and pesticide use. Of about 80 pesticide compounds analyzed, only six compounds were detected in ground water from at least 10 wells during both sampling events. These compounds were the triazine herbicides atrazine, simazine, and prometon; the acetanilide herbicide metolachlor; the urea herbicide tebuthiuron; and an atrazine degradate, deethylatrazine (DEA). Observed concentrations of these compounds generally were < 0.12 microg L(-1). At individual wells, changes in concentrations typically were < 0.02 microg L(-1). Data analysis incorporated adjustments for changes in laboratory recovery as assessed through laboratory spikes. In wells yielding detectable concentrations of atrazine, DEA, and prometon, concentrations were significantly lower (alpha = 0.1) in 2001-2003 than in 1993-1995, whereas detection frequency of these compounds did not change significantly. Trends in atrazine concentrations at shallow wells in agricultural areas were found to be consistent overall with recent atrazine use data.

Initial transformation step of dicamba by a sulfate-reducing consortium enriched from sediment of the Pearl River of China

Dicamba is a readily detectable chemical in run-off and groundwater of agricultural areas. Biotransformation of dicamba was investigated in laboratory anaerobic microcosms incubated at two temperatures (15 and 25 °C) under sulfate-reducing condition using sediment from the Pearl River of Southern China as a source of microorganisms. Initial results of sulfate-reducing microcosms showed that dicamba was transformed by 86% in 120 days of incubation at 25 °C compared with the sterile controls. In comparison, only <60% of the initial dicamba concentrations disappeared at 15 °C. Subsequent enrichment cultures were established from the initial microcosms and accelerated transformation of dicamba was observed in the enrichment transfer cultures by 30 days of incubation for 95% and 78% removal at 25 and 15 °C, respectively. Through enrichment transfer technique, the lag phase and the time required for dicamba biotransformation were all shortened from the initial microcosms, indicating the enrichment of microorganisms capable of transforming dicamba. Addition of 0.1% yeast extract enhanced the dicamba biotransformation by the dicamba-transforming consortium. Transformation of dicamba was further investigated by incubating 14C-ring labeled dicamba with the dicamba-transforming consortium. Results confirmed that dicamba was transformed by the consortium but no substantial amount of 14CO 2 was recovered, suggesting that the initial degradation was an demethoxylation reaction removing the o-methyl group forming 2-hydroxy-3,5-dichlorobenzoic acid. Our results suggest that dicamba is quickly transformed through demethoxylation, but further degradation of the transformation intermediate is much slower in the environment.

Temporal variations in the abundance of heterotrophic bacteria in ground water according to land use patterns in Mysore district, India

Temporal variations in the abundance of heterotrophic bacteria were studied from February 2005 to January 2007, in ground waters from Agricultural, Domestic and Industrial land use areas. The lowest mean abundance (AODG ml -1 ) of Free Living Bacteria (2.2 × 10 5 ), Particle Bound Bacteria (0.07 ×10 5 ) and Total Bacteria (2.28 ×10 5 ) was recorded in ground water of Agricultural area; and the highest (1.07 × 10 6 , 1.13 ×10 5 and 1.70 ×10 6 , respectively) in that of Domestic area. In this investigation, 2.79% of the total bacteria determined by Acridine Orange staining in the ground water of Agricultural area could be grown on the artificial nutrient agar media and the comparative proportion in groundwater under the industrial area was 3.60 and 4.69% in the domestic area. Statistical analysis of the data revealed that several Physico-chemical parameters (Lab pH, air temperature, water temperature, conductivity, rainfall, BOD, CO 2 , alkalinity, hardness, ca, Mg, PO 4 , CL 2 , NO 3 , SO 4 , Total Anion of Strong Acid, Total Solids, Total Dissolved Solids and Total Suspended Solids) (p < .05) were potentially responsible for some of the temporal variations in heterotrophic bacterial abundance, suggesting the influence of landusespecific environmental stressors on the biota in these ecosystems. Key words : Temporal variation, heterotrophic bacterial abundance, colony forming units, Acridine Orange Direct Count, Direct Epifluroscence Microscopic Technique, ground water, land use patterns.