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Miyun Reservoir plays a vital role as a source of drinking water for Beijing, however it grapples with nitrogen contamination issues that have been poorly understood in terms of their distribution, source, and associated health risks. This study addresses this knowledge gap by employing data on nitrate nitrogen (NO3−–N), chloride (Cl−), dual isotopic compositions of NO3− (δ15N–NO3− and δ18O–NO3−) data in water ecosystems, systematically exploring the distribution, source and health risk of nitrogen contaminants in Miyun reservoir watersheds. The results showed that over the past 30 years, surface water runoff has exhibited a notable decrease and periodic fluctuations due to the combined influence of climate and anthropogenic activities, while the total nitrogen (TN) concentration in aquatic ecosystems presented an annual fluctuating upward trend. The TN concentration in the wet season was predominantly elevated because a large amount of nitrogen contaminants migrated into water ecosystems through heavy rainfall or river erosion. The concentration of NO3−–N, the main contaminant of the water ecosystems, showed distinct variations across different watersheds, followed as rivers over the Miyun reservoir. Moreover, NO3−–N levels gradually increased from upstream to downstream in different basins. NO3−–N in surface water was mainly derived from the mixture of agricultural ammonia fertilizer and sewage and manure, with a minority of samples potentially undergoing denitrification. Comparatively, the main sources of NO3−–N in groundwater were soil N and sewage and manure, while the denitrification process was inactive. The carcinogenic risks caused by NO3−–N in groundwater were deemed either nonexistent or minimal, while the focus should predominantly be on potential non-carcinogenic risks, particularly for infants and children. Therefore, it is crucial to perform proactive measures aimed at safeguarding water ecosystems, guided by an understanding of the distribution, sources, and associated risks of nitrogen contamination. [ABSTRACT FROM AUTHOR]

Nitrogen contamination is ubiquitous across the globe; as a result of this, the need to understand and predict the extent and effects of nitrogen contamination on microbial ecosystems is increasingly important. This paper utilises a dataset that provides a rare opportunity to observe varying contamination conditions in a single aquifer and understand the differences between potential background bores and two different types of contamination spread across the other bores. Using physicochemical and microbiological community analysis, this paper aims to determine the impacts of the two contaminants, nitrate and ammonia, on the microbial communities and the differences between polluted and physicochemical background bores. Total nitrogen (N) varied by a factor of over 2000 between bores, ranging from 0.07 to 155 mg L−1. Nitrate (NO3−) concentrations ranged from 150 to <0.01 mg L−1; ammonium (NH4+) concentrations ranged from 26 to <0.1 mg L−1. MANOVA analysis confirmed an overall significant relationship (p = 0.0052) between N variables and the physicochemical data (or status) of the three areas of contamination dubbed 'contamination zones'. The contamination zones were defined by no known presence of contamination in the uncontaminated bores, the presence of NO3− contamination and the presence of NO3− and NH4+ contamination. PERMANOVA analysis confirmed that there was an overall significant difference in the microbial communities between the three contamination zones (p = 0.0002); however, the presence of NH4+ had a significant effect (p = 0.0012). In general, the nitrate-contaminated bores showed a decrease in the abundance of individual OTUs. We further confirmed that NH4+ contamination had a significant relationship with an increased percentage of abundance occupied by the Planctomycetota phylum (specifically the Candidatus Brocadia genus). It was found that one of the two background bores (BS-004) was likely also representative of natural microbial background, and another (BS-002) showed characteristics that may be representative of past or intermittent contamination. This paper demonstrates a possible way to determine the microbial background and discusses the potential uses for this information. [ABSTRACT FROM AUTHOR]

Nitrate-nitrogen (NO3-N) contaminating groundwater is an environmental issue in many areas, and is difficult to treat by simple processes. A bio-electrochemical reactor (BER) using copper wire and graphite plate was developed to purify the NO3-N-contaminated groundwater. The low (of 10 mA) and high (of 20 mA) electric currents were applied to the BERs, and various influent hardness levels from 20 to 80 mg/L as CaCO3 due to groundwater characteristics were supplied to clarify the total nitrogen removal efficiency and NO3-N removal mechanisms. In the BER-10, the bio-electrochemical reactions caused 85% of total nitrogen to be removed through heterotrophic and autohydrogenotrophic denitrification in the suspended sludge and biofilm. However, the chemical deposit occurring at the cathode from water hardness affected the decreasing denitrification performance; 12.6% of Mg and 8.8% of Ca elements were observed in the biofilm. The enhancement of electrochemical reactions in the BER-20 caused integrating electrochemical and bio-electrochemical reactions; the NO3-N was electrochemically reduced to NO2-N, and it was further biologically reduced to N2. A better total nitrogen removal of 95% was found; although, a larger deposit of Mg (22.8%) and Ca (10.8%) was observed. The relatively low dissolved H2 in the BER-20 confirmed that the deposit affected the decreasing gaseous H2 transfer and inhibition of autohydrogenotrophic denitrification in the suspended sludge. According to the microbial analysis, both heterotrophic and autohydrogenotrophic denitrification were obtained in the suspended sludge of both BERs; Nocadia (26.8%) was the most abundant genus in the BER-10, whereas Flavobacterium (27.1%) and Nocadia (25.0%) were the dominant genera in the BER-20. [ABSTRACT FROM AUTHOR]

A comprehensive understanding of nitrogen pollution status, especially the identification of sources and fate of nitrate is essential for effective water quality management at the local scale. However, the nitrogen contamination of surface water across China was poorly understood at the national scale. A dataset related to nitrogen was established based on 111 pieces of literature from 2000 to 2020 in this study. The spatiotemporal variability, source tracing, health risk assessment, and drivers of China's surface water nitrogen pollution were analyzed by integrating multiple methods. These results revealed a significant spatiotemporal heterogeneity in the nitrogen concentration of surface water across China. Spatially, the Haihe River Basin and Yellow River Basin were the basins where surface water was seriously contaminated by nitrogen in China, while the surface water of Southwest Basin was less affected. Temporally, significant differences were observed in the nitrogen content of surface water in the Songhua and Liaohe River Basin, Pearl River Basin, Southeast Basin, and Yellow River Basin. There were 1%, 1%, 12%, and 46% probability exceeding the unacceptable risk level (HI＞1) for children in the Songhua and Liaohe River Basin, Pearl River Basin, Haihe River Basin, and Yellow River Basin, respectively. The primary sources of surface water nitrate in China were found to be domestic sewage and manure (37.7%), soil nitrogen (31.7%), and chemical fertilizer (26.9%), with a limited contribution from atmospheric precipitation (3.7%). Human activities determined the current spatiotemporal distribution of nitrogen contamination in China as well as the future development trend. This research could provide scientifically reasonable recommendations for the containment of surface water nitrogen contamination in China and even globally., Competing Interests: Declaration of Competing Interest ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐ The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:, (Copyright © 2024. Published by Elsevier Inc.)

Groundwater is a crucial natural resource in the state of Florida. since it supports to environmental, social, and economic aspects of the country. Groundwater will not be contaminated easily but it is difficult to restore once it is contaminated. Since its extensive usage in agricultural activities in the state of Florida, groundwater has degraded in recent years, resulting in many direct and indirect impacts, particularly nitrogen content in the form of nitrates using Geographical Information System (GIS) technology, the researchers investigated the effects of groundwater on Nitrogen (NO3) content in the study area by creating a spatial distribution of NO3 contamination, which was then analyzed using GIS, Kriging Interpolation, and the DRASTIC model to determine the susceptibility of groundwater to NO3 contamination. The final result depicts the model's performance as vulnerability groups, which are based on natural breaks showing places that are more susceptible to nitrogen pollution. The map highlighted that the south zone of Florida was more vulnerable to nitrogen contamination, necessitating more careful wastewater disposal system planning. [ABSTRACT FROM AUTHOR]

To determine nutrient fluxes derived from submarine groundwater discharge (SGD), we conducted monthly hydrological surveys on the coast of Jeju, a volcanic island located in the southern sea of Korea. The concentrations of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved silicon (DSi) were significantly correlated with salinity, indicating that fresh SGD (FSGD) is a major nutrient source in Jeju Island where no other coastal freshwater origins exist. Based on a DSi-mass balance model, seepage rate of FSGD was found to depend on 5-day precipitation before sampling campaigns, which immediately permeated via porous aquifers. Thus, the FSGD-driven nutrient fluxes were generally higher in rainy season (July–August) and September 2019 when typhoons occurred. However, high DIN and DIP fluxes were found during spring (March–May), even at low seepage rate, perhaps by a fertilizer input from agriculture activity. This study highlights that large variation of the SGD-driven nutrient fluxes was caused by environmental and anthropogenic factors and emphasizes on the importance of long-term investigation.

Nitrogen contamination is ubiquitous across the globe; as a result of this, the need to understand and predict the extent and effects of nitrogen contamination on microbial ecosystems is increasingly important. This paper utilises a dataset that provides a rare opportunity to observe varying contamination conditions in a single aquifer and understand the differences between potential background bores and two different types of contamination spread across the other bores. Using physicochemical and microbiological community analysis, this paper aims to determine the impacts of the two contaminants, nitrate and ammonia, on the microbial communities and the differences between polluted and physicochemical background bores. Total nitrogen (N) varied by a factor of over 2000 between bores, ranging from 0.07 to 155 mg L−1. Nitrate (NO3−) concentrations ranged from 150 to −1; ammonium (NH4+) concentrations ranged from 26 to −1. MANOVA analysis confirmed an overall significant relationship (p = 0.0052) between N variables and the physicochemical data (or status) of the three areas of contamination dubbed ‘contamination zones’. The contamination zones were defined by no known presence of contamination in the uncontaminated bores, the presence of NO3− contamination and the presence of NO3− and NH4+ contamination. PERMANOVA analysis confirmed that there was an overall significant difference in the microbial communities between the three contamination zones (p = 0.0002); however, the presence of NH4+ had a significant effect (p = 0.0012). In general, the nitrate-contaminated bores showed a decrease in the abundance of individual OTUs. We further confirmed that NH4+ contamination had a significant relationship with an increased percentage of abundance occupied by the Planctomycetota phylum (specifically the Candidatus Brocadia genus). It was found that one of the two background bores (BS-004) was likely also representative of natural microbial background, and another (BS-002) showed characteristics that may be representative of past or intermittent contamination. This paper demonstrates a possible way to determine the microbial background and discusses the potential uses for this information.

Aquifers provide integral freshwater resources and host ecosystems of largely uncharacterized, truncated endemic microorganisms. In recent history, many aquifers have become increasingly contaminated from various anthropogenic sources. To better understand the impacts of nitrogen contamination on native groundwater ecosystems, 16S rRNA sequencing of the groundwater microbial communities was carried out. Samples were taken from an aquifer known to be contaminated with nitrogen from multiple sources, including fertilizers and wastewater treatment plant effluents. In total, two primary contaminants were identified: NH4+ (−1 NH4+ min-median-max), and NO3− (−1 NO3− min-median-max). These contaminants were found to be associated with a decrease/increase in microbial species richness within affected groundwater for NH4+/NO3−, respectively. Important phyla were identified, including Proteobacteria, which had the highest abundance within samples unaffected by NH4+ (36–81% NH4+ unaffected, 4–33% NH4+ affected), and Planctomycetes (0.05–10% NH4+ unaffected, 43–72% NH4+ affected), which had the highest abundance within the NH4+ affected samples, likely due to its ability to perform anaerobic ammonia oxidation (ANAMMOX). Planctomycetes were identified as a potential indicator for the presence of NH4+ contamination. The analysis and characterization of sequencing data alongside physicochemical data showed potential to increase the depth of our understanding of contaminant behavior and fate within a contaminated aquifer using this type of data and analysis.

Research on the hydrochemical characteristics of groundwater can help to elucidate its evolution and distribution, as well as other hydrogeological conditions. The present study investigated the current status of groundwater hydrochemistry and nitrogen contamination in Yinchuan area, Yinchuan basin of northwest China. Piper and Gibbs diagrams were constructed and multivariate statistical methods were used to explore the groundwater hydrochemical characteristics and its controlling factors, as well as nitrogen contamination of groundwater and its sources. The results demonstrated that phreatic water was moderately salty with a large variation of TDS and major ion concentrations, while the confined water was mainly fresh water with TDS less than 1000 mg/L. Phreatic water was mainly HCO3·Cl–Na·Mg and HCO3·SO4–Na·Mg types, while the confined water was HCO3·Cl–Na·Ca and HCO3·SO4–Na·Ca types. The major ion chemistry of the confined water is governed by water–rock interactions, while evaporation plays a key role in phreatic water chemistry formation. Furthermore, the concentration of NO3− in phreatic water is significantly higher than that of confined water, and the opposite was observed for NH4+. The concentrations of NO3− and NH4+ exhibited an increasing tendency in groundwater in the last 26 years. The nitrogen sources in phreatic water involved human activities like nitrogen fertilizer application in agriculture, and industrial and domestic sewage. In confined aquifer, the higher NH4+ concentration is comprehensively affected by hydrogeological conditions, leakage of phreatic water and an anaerobic environment. Overall, the results of the present study are helpful for the groundwater protection in Yinchuan area, and will contribute to the effective management and reasonable development of groundwater resources in Yinchuan basin. [ABSTRACT FROM AUTHOR]

The increasing concentration of nitrogen compounds in the groundwater is of a growing concern in terms of human health and groundwater quality. Although an excess of nitrogen compounds in the groundwater of the Kathmandu Valley has been reported, the seasonal variations of the fate of the nitrogen compounds and their relationships to the subsurface sediments are unknown. In this study, spatially distributed shallow dug well samples were collected during both the dry and wet seasons of 2016, and the nitrogen compound, chloride (Cl−), and iron (Fe2+) concentrations were analyzed. Two shallow dug wells and one deep tube well were monitored monthly for 2 years. Although NH4-N concentrations were similar in the clay-dominated areas during both seasons (1 and 0.9 mg-N/L), they were lower in the gravel-dominated areas during wet season (1.8 > 0.6 mg-N/L). The NO3-N concentration differed depending upon the soil type which increased during the wet season (clay 4.9 < 13.6 mg-N/L and gravel 2.5 < 6.8 mg-N/L). The Fe2+ concentration, however, was low during the wet season (clay 2.7 > 0.4 mg/L and gravel 2.8 > 0.3 mg/L). Long-term analysis showed higher fluctuation of nitrogen compounds in the gravel-bearing areas than in the clay-bearing areas.

Aquifers provide integral freshwater resources and host ecosystems of largely uncharacterized, truncated endemic microorganisms. In recent history, many aquifers have become increasingly contaminated from various anthropogenic sources. To better understand the impacts of nitrogen contamination on native groundwater ecosystems, 16S rRNA sequencing of the groundwater microbial communities was carried out. Samples were taken from an aquifer known to be contaminated with nitrogen from multiple sources, including fertilizers and wastewater treatment plant effluents. In total, two primary contaminants were identified: NH4+ (<0.1–3.7–26 mg L−1 NH4+ min-median-max), and NO3− (<0.01–18–150 mg L−1 NO3− min-median-max). These contaminants were found to be associated with a decrease/increase in microbial species richness within affected groundwater for NH4+/NO3−, respectively. Important phyla were identified, including Proteobacteria, which had the highest abundance within samples unaffected by NH4+ (36–81% NH4+ unaffected, 4–33% NH4+ affected), and Planctomycetes (0.05–10% NH4+ unaffected, 43–72% NH4+ affected), which had the highest abundance within the NH4+ affected samples, likely due to its ability to perform anaerobic ammonia oxidation (ANAMMOX). Planctomycetes were identified as a potential indicator for the presence of NH4+ contamination. The analysis and characterization of sequencing data alongside physicochemical data showed potential to increase the depth of our understanding of contaminant behavior and fate within a contaminated aquifer using this type of data and analysis. [ABSTRACT FROM AUTHOR]

Through a detailed analysis of the FAO database, we have constructed a generalized representation of the nitrogen transfers characterizing the current agro-food system (GRAFS) of 12 macro-regions of the world in terms of functional relationships between crop farming, livestock breeding and human nutrition. Based on this model, and maintaining the current cropland areas and the performance of cropping and livestock systems in each region, we have assessed the possibilities of meeting the protein requirements of the estimated world population in 2050, according to various combinations of three critical drivers namely human diet (total amount of protein consumed and share of animal protein in this total), regional livestock production and crop fertilization intensity, in each region. The results show that feeding the projected 2050 world population would generally imply higher levels of inter-regional trade and of environmental nitrogen contamination than the current levels, but that the scenarios with less recourse to inter-regional trade generally produce less N losses to the environment. If an equitable human diet (in terms of protein consumption) is to be established globally (the same in all regions of the world), the fraction of animal protein should not exceed 40% of a total ingestion of 4 kgN capita ^−1 yr ^−1 , or 25% of a total consumption of 5 kgN capita ^−1 yr ^−1 . Our results show that slightly improving the agronomical performance in the most deficient regions (namely Maghreb, the Middle East, sub-Saharan Africa, and India) would make it possible not only to meet the global protein requirements with much less international trade (hence more food sovereignty), but also to reduce N environmental contamination the most efficiently.

Abstract: A 1.6ha plot of Atriplex canescens (fourwing saltbush) was established in a desert soil at a former uranium ore-processing plant, near Monument Valley, Arizona, to remediate nitrate and ammonium N contamination. The plants were irrigated to stimulate growth and N uptake. However, NO3 − loss from the soil was unexpectedly rapid. Initially, the soil contained approximately 180mgkg−1 NO3 −–N distributed at depths up to 4.6m, but concentrations decreased to 80mgkg−1 after 41 months. Losses occurred throughout the plot at all soil depths. NH4–N remained unchanged (ca.180mgkg−1). Soil moisture was generally below field capacity and soil–water flux showed no net downward movement over the course of the study. A salt balance showed a 10% decrease in soluble salts during the study, attributable to the loss in NO3 −. Residual soluble soil N became progressively enriched in 15N over time, consistent with biological denitrification. Additionally, microcosm studies indicate significant potential denitrification rates on the plot but not for control soils. Total losses of NO3 −–N were 1360kgha−1 yr −1. These findings of rapid denitrification in the vadose zone of a desert soil are unique and may offer a low-cost method for NO3 − remediation at similar sites. These findings are also of interest due to the depth at which the losses occurred and the possibility that considerable amounts of naturally occurring NO3 − in deep vadose zone desert soils in the southwestern US could be similarly mobilized by changing land use practices or climate change. [Copyright &y& Elsevier]

We present measurements of drift velocities and gains in gas mixtures based on Ar and Xe, with CO2, CH4, and N2 as quenchers, and compare them with calculations. In particular, we show the dependence of Ar- and Xe–CO2 drift velocities and gains on the amount of nitrogen contamination in the gas, which in real experiments may build up through leaks. A quantification of the Penning mechanism which contributes to the Townsend coefficients of a given gas mixture is proposed. [Copyright &y& Elsevier]

Nitrogen (N) contamination in the Yellow River mainstream and its tributaries was studied using data from 1960 to 2000 from 312 monitoring sites in the Yellow River system. Data showed that N concentrations in the Yellow River have increased since 1960, especially after 1990. N concentrations in the Yellow River mainstream increased from the upper reaches (less than 1.0 mg L-1 for TN and less than 0.10 mg L-1 for NH4+-N) to lower reaches (higher than 4–5 mg L-1 for TN and higher than 1.0 mg L-1 for NH4+-N). However, the highest N contaminations (50–250 mg L-1 for TN and 10–20 mg L-1 for NH4+-N) was found in some tributaries, which was attributed as an effect of industrial wastewater and municipal sewage. Nitrogen concentrations from several monitoring sites were positively correlated with several regional socio-economic indices, such as population density, fertilization rates, livestock, industrial input and GDP. Depending on location, seasonal N concentrations contrasted among watersheds. Monitoring stations located in rural and agricultural areas showed higher N concentrations during the flood season while those located in areas with urban and industrial centers showed higher N concentration during the dry season. Mainstream flow and N concentrations showed a strong inverse relationship; with higher N concentrations as the river flow declined. Intensive water extraction for agricultural irrigation and increasing N input to the river from fertilized agricultural fields could explain the increasing N concentrations during extensive droughts. [ABSTRACT FROM AUTHOR]

• Less than 5 kg nitrate-N ha−1 is annually leached from 1-m soil in northeast China. • Long term incorporation of full straw increases nitrate leaching intensity. • Reducing nitrogen doses is an effective way to reduce nitrate leaching intensity. • Nitrate leaching of cultivated Phaeozems is sensitive to climate warming. • Nitrogen dose, precipitation and temperature jointly regulate nitrate leaching. Nitrate (NO 3 −) leaching from agricultural soils poses a potential risk for water contamination and a reduction in nutrient use efficiency. However, NO 3 − leaching intensity and its driving forces of cultivated Phaeozems, well-known for its high soil organic content and productivity, is still unclear, especially in regions with cool climates. In this study, a process-oriented biogeochemical model named CNMM-DNDC was validated with observed variables including soil moisture, NO 3 − concentrations and crop yields, which are closely related to NO 3 − leaching. Next, this validated model was used to quantify the NO 3 − leaching intensity of Phaeozems cultivated with maize in northeastern China in 1990 − 2015. The regional simulations showed that NO 3 − leaching intensities of maize fields (0 − 5 kg N ha−1 yr−1 for most 10 × 10 km2 grids) were lower than those in other Phaeozem regions with warmer climates (29 − 49 kg N ha−1 yr−1). In addition, the results of temperature scenarios also imply that global warming could potentially increase the risk of NO 3 − leaching from cultivated Phaeozems in this study region with cool climates, due to the high temperature sensitivity. Reducing nitrogen doses would be an effective strategy to alleviate the risk of water contamination by reducing the regional leaching amount by 15 % with 5% less applied nitrogen. The scenario simulation indicates that the incorporation of full straw would lead to less NO 3 − leaching in the near term, but more intensive leaching in the long term. A significant nonlinear relationship was found between the simulated NO 3 − leaching intensity and the product of average annual nitrogen dose, average annual precipitation and exponential of average annual air temperature at the county scale. This relationship may provide a simple approach for identifying the potential vulnerable zones prone to nitrogen loss by NO 3 − leaching. As this study suggests, the process-oriented CNMM-DNDC model shows the capacity to quantify long term NO 3 − leaching at the regional scale, which is potentially a robust tool for developing the best management strategies to mitigate/prevent water nitrogen contamination in the Phaeozem regions. [ABSTRACT FROM AUTHOR]

The increasing concentration of nitrogen compounds in the groundwater is of a growing concern in terms of human health and groundwater quality. Although an excess of nitrogen compounds in the groundwater of the Kathmandu Valley has been reported, the seasonal variations of the fate of the nitrogen compounds and their relationships to the subsurface sediments are unknown. In this study, spatially distributed shallow dug well samples were collected during both the dry and wet seasons of 2016, and the nitrogen compound, chloride (Cl−), and iron (Fe2+) concentrations were analyzed. Two shallow dug wells and one deep tube well were monitored monthly for 2 years. Although NH4-N concentrations were similar in the clay-dominated areas during both seasons (1 and 0.9 mg-N/L), they were lower in the gravel-dominated areas during wet season (1.8 > 0.6 mg-N/L). The NO3-N concentration differed depending upon the soil type which increased during the wet season (clay 4.9 < 13.6 mg-N/L and gravel 2.5 < 6.8 mg-N/L). The Fe2+ concentration, however, was low during the wet season (clay 2.7 > 0.4 mg/L and gravel 2.8 > 0.3 mg/L). Long-term analysis showed higher fluctuation of nitrogen compounds in the gravel-bearing areas than in the clay-bearing areas. [ABSTRACT FROM AUTHOR]

A prototype decision support system, developed for the New Zealand meat processing industry, provides real-time estimates of potential groundwater contamination by nitrate-N from wastewater irrigation. Leachate is monitored in the vadose zone beneath the land treatment site so that remedial action can be taken before serious groundwater contamination occurs. Instrumentation at a site comprises at least two lysimeters, each containing a 500 mm diameter column of pasture and undisturbed soil to a depth of 700 mm. Leachate volumes are measured and solute samples are collected for laboratory analysis a few days aftereach irrigation or significant rainfall event. The results provide data on the mean concentration of nitrate-N for uneven intervals of soil-water drainage, which occur at irregular intervals of time throughout the year. These data are not directly useful for operational management of the treatment site because of the high noise level caused by natural variability of transformation and transport processes in the soil, as well as the nature of the relationship between nitrate-N concentration in the vadose zone and drinking water standards at a receptor site in the underlying aquifer. Both these issues were accounted for by means of a single-cell mixing model which transforms the data into continually updated estimates of the potential effect on groundwater and a control value related to the rate of change of contamination. The concept of the single-cell mixing model, with flow-based index, is discussed in relation to: simulation of advective-dispersive transport by means of mixing cells in series; exponentially-weighted-moving-average methods for statistical process control in the manufacturing industries; and Kalman filter estimation techniques for time-series with unequally-spaced data. [ABSTRACT FROM AUTHOR]