Single Water Quality Research Articles

Eutrophication in the Yunnan Plateau lakes: the influence of lake morphology, watershed land use, and socioeconomic factors

Lakes play an important role in socioeconomic development and ecological balance in China, but their water quality has deteriorated considerably in recent decades. In this study, we investigated the spatial-temporal variations of eutrophication parameters (secchi depth, total nitrogen, total phosphorus, chemical oxygen demand, chlorophyll-a, trophic level index, and trophic state index) and their relationships with lake morphology, watershed land use, and socioeconomic factors in the Yunnan Plateau lakes. Results indicated that about 77.8% of lakes were eutrophic according to trophic state index. The plateau lakes showed spatial variations in water quality and could be classified into high-nutrient and low-nutrient groups. However, because watersheds were dominated by vegetation, all eutrophication parameters except chlorophyll-a showed no significant differences between the wet and dry seasons. Lake depth, water residence time, volume, and percentage of built-up land were significantly related to several eutrophication parameters. Agricultural land use and social-economic factors had no significant correlation with all eutrophication parameters. Stepwise regression analyses demonstrated that lake depth and water residence time accounted for 73.8% to 87.6% of the spatial variation of single water quality variables, respectively. Redundancy analyses indicated that lake morphology, watershed land use, and socioeconomic factors together explained 74.3% of the spatial variation in overall water quality. The results imply that water quality degradation in the plateau lakes may be mainly due to the domestic and industrial wastewaters. This study will improve our understanding of the determinants of lake water quality and help to design efficient strategies for controlling eutrophication in the plateau region.

A review of sediment and nutrient concentration data from Australia for use in catchment water quality models

Land use (and land management) change is seen as the primary factor responsible for changes in sediment and nutrient delivery to water bodies. Understanding how sediment and nutrient (or constituent) concentrations vary with land use is critical to understanding the current and future impact of land use change on aquatic ecosystems. Access to appropriate land-use based water quality data is also important for calculating reliable load estimates using water quality models. This study collated published and unpublished runoff, constituent concentration and load data for Australian catchments. Water quality data for total suspended sediments (TSS), total nitrogen (TN) and total phosphorus (TP) were collated from runoff events with a focus on catchment areas that have a single or majority of the contributing area under one land use. Where possible, information on the dissolved forms of nutrients were also collated. For each data point, information was included on the site location, land use type and condition, contributing catchment area, runoff, laboratory analyses, the number of samples collected over the hydrograph and the mean constituent concentration calculation method.A total of ∼750 entries were recorded from 514 different geographical sites covering 13 different land uses. We found that the nutrient concentrations collected using “grab” sampling (without a well defined hydrograph) were lower than for sites with gauged auto-samplers although this data set was small and no statistical analysis could be undertaken. There was no statistically significant difference (p<0.05) between data collected at plot and catchment scales for the same land use. This is most likely due to differences in land condition over-shadowing the effects of spatial scale. There was, however, a significant difference in the concentration value for constituent samples collected from sites where >90% of the catchment was represented by a single land use, compared to sites with <90% of the upstream area represented by a single land use. This highlights the need for more single land use water quality data, preferably over a range of spatial scales. Overall, the land uses with the highest median TSS concentrations were mining (∼50,000mg/l), horticulture (∼3000mg/l), dryland cropping (∼2000mg/l), cotton (∼600mg/l) and grazing on native pastures (∼300mg/l). The highest median TN concentrations are from horticulture (∼32,000μg/l), cotton (∼6500μg/l), bananas (∼2700μg/l), grazing on modified pastures (∼2200μg/l) and sugar (∼1700μg/l). For TP it is forestry (∼5800μg/l), horticulture (∼1500μg/l), bananas (∼1400μg/l), dryland cropping (∼900mg/l) and grazing on modified pastures (∼400μg/l). For the dissolved nutrient fractions, the sugarcane land use had the highest concentrations of dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP). Urban land use had the highest concentrations of dissolved inorganic phosphorus (DIP). This study provides modellers and catchment managers with an increased understanding of the processes involved in estimating constituent concentrations, the data available for use in modelling projects, and the conditions under which they should be applied. Areas requiring more data are also discussed.

Testing for allocation efficiencies in water quality tenders across catchments, industries and pollutants: a north Queensland case study*

The design of competitive tenders to purchase environmental services requires judgements to be made about the funding scale and tender scope, with the latter incorporating considerations of geographic area, industries involved and the types of environmental outputs required. Increasing the scale and scope of tenders increases the likelihood that a larger range of proposals will be proposed and cost‐effective ones selected. However, the use of larger and more broadly scoped tenders may reduce landholder participation and increase asking bids. In the study reported here, these issues have been tested with a single water quality tender run in north‐eastern Australia in 2007 and 2008. Post hoc tests and workshop exercises show that while larger‐scale and scope tenders can generate efficiency gains, care has to be taken to maintain participation and avoid higher bid levels.

Minimizing health risks during secondary effluent application via subsurface drip irrigation

Health risks posed on consumers due to the use of agricultural products irrigated with reclaimed wastewater were assessed by numerical simulation. The analysis is based on defining of an Exposure Model (EM) which takes into account several parameters: (i) the quality of the applied wastewater, (ii) the irrigation method, (iii) the elapsed times between irrigation, harvest, and product consumption, and; (iv) the consumers' habits. The exposure model is used for numerical simulation of human consumers' risks by running the Monte Carlo simulation method. Although some deviations in the numerical simulation which are probably due to uncertainty (impreciseness in quality of input data) and variability due to diversity among populations reasonable results were accepted. Accordingly, there is a several orders of magnitude difference in the risk of infection between the different exposure scenarios with the same water quality. The variability indicates the need for setting risk-based criteria for wastewater reclamation, including the application method and environmental conditions, rather than single water quality guidelines. Extra data is required to decrease uncertainty in the risk assessment. Future research needs to include definite acceptable risk criteria, more accurate dose-response modeling, information regarding pathogen survival in treated wastewater, additional data related to the passage of pathogens into and in the plants during irrigation, and information referring to the consuming habits of the human community.

Assemblage grouping of European benthic diatoms as indicators of trophic status of rivers

River benthic diatoms are routinely used to monitor water quality in rivers throughout Europe. Many diatom indices have been developed to monitor a single water quality variable such as phosphorus concentration, or organic pollution, and there is a need to develop diatom monitoring methods for the Water Framework Directive (WFD) which can monitor and quantify a range of environmental variables. The identification of benthic diatom assemblages, or biotypes, is an alternative method that may allow monitoring of ecological status throughout European rivers. Multivariate analysis showed that diatom species composition corresponded most strongly to altitude, temperature, pH and conductivity, while nutrient variables were of secondary importance. To assess the use of biotypes as indicators of eutrophic status benthic diatom samples collected from five European countries were grouped on the basis of their species composition using TWINSPAN. Eight diatom biotypes, some with two subgroups, were identified. Canonical Correspondence Analysis was used to investigate the relationship between these diatom groupings and nutrient concentrations, with and without the effects related to altitude and pH. A number of communities which may act as indicators of eutrophication were identified, though issues arose concerning the identification of these communities and the lack of sample sites from a range of altitudes, pH and conductivities. Finally the use of such diatom based methods to set river quality boundaries and monitor trophic status for the WFD is considered in light of their predictive strength, practicability in application and international differences in river monitoring standards.

Trading pollutant discharge permits in rivers using fuzzy nonlinear cost functions

Transferable Discharge Permit (TDP) programs in water quality management produce environmental benefit, which closely achieves the same benefit through a command-and-control approach, with comparatively lower costs. Estimating abatement cost functions is one of the greatest challenges in these trading programs. According to the fact that water flows to the lowest level uni-directionally, the Trading Ratio System (TRS) is utilized for water quality management in river systems. TRS considers the river assimilative capacity and provides the optimum trading pattern. TRS has been designed for a single water quality variable and the existing uncertainties are not incorporated. In this study, an extended version of TRS is utilized which considers the uncertainties in treatment cost functions and can be used for BOD/DO management in rivers. Then, by combining the extended TRS and a fuzzy nonlinear regression, a novel model is proposed to configure a permit trading structure and provide decision maker with a wealth of cost-effective management strategies. The proposed model has been used for trading water pollutant discharge permits in the Zarjub river in northern part of Iran. The results show that trading discharge permit in this river system is a cost-effective strategy. It is also shown that the uncertainty in the wastewater treatment cost functions can be easily considered using the fuzzy set theory.

Impact of catchment land use on bacterial communities within stream biofilms

The bacterial community structure in epilithic biofilms within 18 different streams was characterised using a community DNA fingerprinting technique (automated ribosomal intergenic spacer analysis—ARISA). Each stream has previously been described in terms of the dominant catchment land use, relative level of human disturbance and using a broad suite of water quality variables. Combination of ARISA with multivariate statistical analysis and ordination revealed that bacterial communities in streams located within rural catchments were significantly different to those within urban catchments. Broad-scale catchment land use described the largest component of the observed variation with no single water quality variable found to be a dominant determinant of the observed bacterial community variability, assessed using distance based redundancy analysis (dbRDA) of the ARISA data. This study highlights the potential of bacterial ARISA to provide a rapid and cost-effective approach to monitor the impact of catchment land use on aquatic ecosystems, such as the influence of encroaching urban development on the ecological health of rural streams.

Developing real time operating rules for trading discharge permits in rivers: Application of Bayesian Networks

Transferable discharge permit (TDP) programs show potential cost-effective methods of pollution control in river systems. Nevertheless, there remain uncertainties that, if not adequately addressed, might impair their success. Trading Ratio System (TRS) suggested by Hung and Shaw [2005. A trading-ratio system for trading water pollution discharge permits. Journal of Environmental Economics and Management 49, 83–102] is a cost-effective tool for water quality management in river systems, which provides the optimum trading pattern among dischargers. TRS has been designed for a single conservative water quality variable and the existing uncertainties are not incorporated. In this study, TRS is extended to be applicable to Biochemical Oxygen Demand (BOD) and Dissolved Oxygen (DO) management in river systems and uncertainties in input variables of river water quality simulation model are also considered. In the proposed methodology, low water quality is also quantified as a fuzzy event and fuzzy risk of violating the water quality standards is estimated at each checkpoint along the river. The Extended Trading Ratio System (ETRS) is used in a Monte Carlo Analysis to provide the required data for training and validating a Bayesian Network (BN). The trained BN can be used for real time river water quality management and provides the probability density functions of treatment levels and trading discharge permit policies. The methodology is successfully applied to the Zarjub River in the northern part of Iran to show its usefulness as a cost-effective and risk-informed decision-making tool in real time river water quality management.

Site selection and production performance of rainbow trout(Oncorhynchus mykiss)cage operations in small farm reservoirs: the Western Cape experience, South Africa

Cage farming of rainbow trout (Oncorhynchus mykiss) has expanded rapidly into private farm reservoirs of the Western Cape. During the grow-out season 2006, water quality problems such as increased mortality rates and off-flavour of the final product caused economic losses. To set criteria for improved site selection, water quality information of surface and near-bottom water was correlated with morphometric reservoir data, fish production data as well as the observed production difficulties. The data revealed good linkage between reservoir information and fish production data as well as production problems. The production problems correlated (P<0.01) with single water quality parameters so that suggestions for risk management indicators can be made. By ranking the data, threshold values for better production practice were determined. Thereafter, reservoirs of a minimum surface area of at least 3 ha would be recommended as well as reservoirs with good water exchange rates (>1 per year) to avoid oxygen problems. Reservoirs of larger surface area (>5 ha) produced significantly larger fish that grew faster and showed lower mortality rates.

Fuzzy Waste Load Allocation Model: Application to a Case Study

A fuzzy optimization model, developed earlier to address uncertainty due to imprecision in management goals in river water quality management problems is applied to a case study in this paper by addressing uncertainty due to randomness implicitly through Monte Carlo simulations. Municipal and industrial effluents, characterized by their Biochemical Oxygen Demand (BOD) loads are considered as point sources of pollution and the Dissolved Oxygen (DO) level at specified checkpoints in the river stretch is taken as the single water quality indicator. Conflicting goals related to water quality and fraction removal levels are expressed as fuzzy sets with appropriate membership functions in the model. The fuzzy optimization model is solved for a number of simulated sets of inputs to obtain optimal solutions, thus generating a large set of optimal objective function values and associated decisions. This information is used to obtain waste-load allocation decisions for a specified level of reliability.

Defining the sources of low-flow phosphorus transfers in complex catchments

Nutrient transfers from the land to rivers have the potential to cause persistent eutrophic impacts at low flows even though the transfers may constitute a minor percentage of total annual fluxes. In rural catchments, the contribution from agricultural soils during storm events can be particularly large and untangling the relative contributions from multiple sources that vary in time and space is especially problematic. In this study, the potential for domestic septic tank system pollution during low flows was investigated in 3 small catchments (3 to 5 km(2)) using an integrated series of methods. These included septic system surveys, continuous (10 min) total phosphorus (TP) monitoring at the outlet of each catchment, repeated low-flow water quality surveys in sub-catchments upstream of the catchment outlets and single day river-walk water quality surveys. A series of faecal matter and grey-water fingerprinting techniques were also employed. These included determining sterol ratios in stream sediments, monitoring the presence of proteins, E. coli and enterococci bacterial signatures and boron. The total density and density of poorly maintained septic systems mirrored the magnitude of frequent TP concentrations in the catchments although this relationship was less apparent in the nested sub-catchments. The exception was possibly related to the simple hydraulics in one particular catchment and indicated temporary effluent attenuation in the other catchments. Repeated low-flow and river-walk water quality surveys highlighted discrete areas and reaches where stepped changes in nutrient concentration occurred. Bio-chemical fingerprinting showed that between 7% and 27% of sediments were contaminated with human faecal material and correlation matrices indicated that, at least during low flows, P fractions were positively correlated with some markers of faecal and grey-water contamination.

Modelling discolouration in a Melbourne (Australia) potable water distribution system

Reducing customer complaints of discoloured water is a major challenge for the water industry. The ability to predict the spatial probability and severity of discolouration events in distribution systems could lead to the implementation and optimisation of proactive operational and maintenance strategies to minimise discolouration. This paper explores the transfer of a predictive, semi-empirical model developed to describe iron dominated discolouration problems in the UK to an Australian system, where discolouration is primarily associated with clay type material. The paper presents the application of the model to a large diameter water main that forms part of the Melbourne system within a single source water quality zone. The model is based on cohesive transport theory and for this application includes the concept of a ‘self-cleaning threshold’, defined as a shear stress that the pipe experiences regularly, due to normal daily demand, that prohibits the accumulation of sufficient material within the pipe and hence poses no discolouration risk. Results presented here show that the model can be calibrated to simulate the turbidity response measured in real systems due to changes in hydraulic conditions, for clay driven discolouration problems. These changes in hydraulic condition resulted from various ‘natural’ events which occurred during the available data period. Through such simulation the semi-empirical model parameters were evaluated. These simulations demonstrate the capabilities of the model, which could be applied to operational and maintenance practice. For example, to identify and prioritise network cleaning operations to minimise discolouration risk, at pipe level, through simulation of discolouration responses to various possible events (burst, fire fighting etc) and ranking the resulting predicted discolouration, or through prior simulation to identify the cleaning necessary to mitigate discolouration risk of planned operations such as valve movements.

Reduction of Malodorous Compounds from Liquid Swine Manure by a Multi-Stage Treatment System

A full-scale swine wastewater treatment system was designed and implemented to replace anaerobic lagoon treatment systems with a three-stage process of solids separation, biological nitrogen (N) removal, and phosphorus recovery. Our study had the objectives of evaluating both the system's efficiency for odor control and water quality parameters that better indicate odor reduction. This report presents data on the concentration in liquid of six selected malodorous compounds (phenol, p-cresol, p-ethylphenol, p-propylphenol, indole, and skatole) and 15 water quality parameters measured at the three successive stages of the treatment process. Solid phase extraction of odor compounds showed that the concentrations of malodorous compounds were reduced by almost 98% in the treated effluent as compared to untreated raw flushed manure. The majority of this odor reduction occurred during biological N treatment. No single water quality parameter served as the sole indicator for the levels of all six odor compounds that we measured in wastewater. Except for phenol, the levels of ammonia N and electrical conductivity (EC) measurements were highly correlated with reduction of individual malodorous compounds in wastewater. Seven out of 15 parameters measured (soluble COD, soluble BOD, TKN, ammonia-N, nitrate-N, alkalinity, and EC) were found to be highly related to reduction of total measured malodorous compounds. These results suggest that selected water quality parameters in swine wastewater could assist to evaluate odor control measures when no sensory analysis or appropriate analytical equipment is available. They also indicate that treatment systems incorporating biological N removal can greatly reduce malodorous compounds in liquid swine manure.

ORIGIN AND TRANSPORT OF DISSOLVED CHEMICALS IN A KARST WATERSHED, SOUTHWESTERN ILLINOIS

ABSTRACT: An extensive base of water quality information emphasizing the effects of land use and hydrology was obtained in the karstified Fountain Creek watershed of southwestern Illinois to help resolve local water quality issues. Agrichemicals dominate the loads of most water quality constituents in the streams and shallow karstic ground water. Only calcium (Ca), magnesium (Mg), Aluminum (A1), and sulfate (SO4) ions are predominantly derived from bedrock or soils, while agrichemicals contribute most of the sodium (Na), potassium (K), chlorine (Cl), nitrate (NO3), fluorine (F), phosphorus (P), and atrazine. Concentrations of individual ions correlate with discharge variations in karst springs and surface streams; highly soluble ions supplied by diffuse ground water are diluted by high flows, while less soluble ions increase with flow as they are mobilized from fields to karst conduits under storm conditions. Treated wastewater containing detergent residues dominates the boron load of streams and provides important subordinate loads of several other constituents, including atrazine derived from the Mississippi River via the public water supply. Average surface water concentrations at the watershed outlet closely approximate a 92:8 mixture of karst ground water and treated wastewater, demonstrating the dominance of ground water contributions to streams. Therefore the karst aquifer and watershed streams form a single water quality system that is also affected by wastewater effluent.

Water quality aspects of optimal operation of rural water distribution systems for supply of irrigation and drinking water

AbstractThis paper considers the control of quality in rural water supply systems by means of dilution and treatment plants. Diverse quality sources can be used to supply consumers with differing quality requirements, such as irrigation of agricultural crops with differing water quality tolerance levels, domestic requirements at drinking water standards, and industrial and municipal uses. Models for optimal operations of such systems are difficult to develop due to the complexity of formulating dilution conditions at junctions as functions, for which the derivative can be calculated (because the flow directions at incident pipes change as the solution procedure progresses); strong scaling effects due to the treatment plants; and the presence of several water quality parameters.The model presented here solves the operation problem for a single period under steady state conditions. The formulation is simplified by representing the hydraulics by a conveyance cost in each pipe with bounds on the maximum allowed discharges (the authors have also developed a model that includes the hydraulics explicitly). The model is therefore suited both to canal and pipe systems for supply of irrigation and drinking water. Improvement of water quality by treatment plants located at the supply system is also considered here. This improvement has been achieved by lowering the concentration of conservative substances (those whose concentration remain time invariant) in the water only such as in the reverse osmosis process. The applicability of the model to practical situations is demonstrated by a case study of a regional rural water supply system with 39 pipes and 37 nodes (of which 11 are source nodes with different qualities, 10 are agricultural consumers with different quality requirements, and 4 are domestic consumers requiring high quality drinking water). The model determines the optimal discharges in all pipes, values of quality parameters at consumer nodes, and removal ratios of the treatment plants. Three cases were studied: (1) a single water quality parameter (salinity) without treatment plants; (2) three quality parameters (salinity, sulphur, and magnesium) without treatment plants; and (3) three quality parameters and eight treatment plants, each located at a different source node. Water quality requirements are represented by constraints on the maximum allowable concentrations at consumer nodes, and, for the case of irrigation, a crop yield function that relates yield loss to salinity. The value of the objective function for Case 3 was 10% lower than for the other cases due to savings in yield loss at the agricultural consumers that were obtained by improvement of the quality of the irrigation water. Copyright © 2004 John Wiley &amp; Sons, Ltd.

QUANTIFICATION OF &lt;I&gt;ESCHERICHIA COLI&lt;/I&gt; AND ENTEROCOCCI LEVELS IN WET WEATHER AND DRY WEATHER FLOWS

Forty percent of rivers, 45% of lakes and 50% of estuaries assessed by the National Water Quality Inventory (2000) were not clean enough to support designate d fishing and swimming uses. Pathogens were found to be one of the leading causes of impairments in these waters. Urban runoff is recognized as a leading source of organisms potentially indicating the presence of pathogens. Urban runoff can be defined as any discharge from a separate storm drainage system. Urban runoff traditionally had been defined to in clude precipitation and wash off from lawns and other landscaped areas, buildings, roadways and parking lots. However, other flows may enter the storm drainage system from such sources a s infiltrating groundwater, leaking domestic water supplies and sewage, washwaters, and other inappropriate entries to the storm drainage system. This research was conducted to quantify th e levels of indicator bacteria, and their sources, in urban areas. The main objective of t his research was to identify possible sources of E. coli and enterococci bacteria in dry and wet-weather flows in storm drainage systems. An urban area consists of many different kinds of land uses such as residential, institutional, commercial, industrial open spaces, etc. Each type of la nd use consists of various types of source areas, such as roofs, parking lots, landscaped areas, play grounds, driveways, undeveloped areas, sidewalks. Four representative source area types were sa mpled during this research; including rooftops, parking lots, open spaces, and streets. Two paralle l sites were sampled for each source area type; one affected by birds and other animals, and an other set with less influence from birds and other animals. A section of Cribbs Mill Creek in Tusc aloosa, Alabama, was also selected for dry weather sampling at outfalls. The section of the cr eek was selected such that the drainage areas contributing to outfalls had either commercial or residential land uses. Potential inappropriate discharge water samples were also obtained, including influent samples from the Tuscaloosa sewage treatment plant, local springs, irrigati on runoff water, domestic water taps, car wash, and laundry water. Overall, total coliforms, E. coli and enterococci bacterial analyses were conducted on 202 wet weather and 278 dry weather flow water samples. All samples were analyzed using IDEXX Quantitray enumeration procedures. E. coli and enterococci levels larger than 2,400 and 24,000 MPN/100 mL, r espectively, were observed in wet weather samples collected from various source areas which could not possibly be contaminated with sanitary sewage. The levels of ind icator bacteria present in the urban runoff source area samples exceeded the EPA 1986 single sa mple maximum value water quality criteria in 31% of the samples for E. coli and in 74% of the samples for enterococci. The geometric mean criteria were exceeded in 100% of the source area samples. Since both the indicator organisms studied ( E. coli. and enterococci) only originate in intestines of warm

Risk-Based Assessment of the Impact of Aluminium on a Riverine Ecosystem

The Dawesley Creek–Bremer River drainage system, in South Australia, is affected by the potentially costly problem of acid drainage from the Brukunga mine site. This paper contrasts geochemical model predictions of water quality with detailed measurement of water chemistry in the field. This information is also used in the ecological risk assessment code, AQUARISK, to predict the degree of ecological detriment. These predictions are then assessed against independent, field-based biomeasures of algal and bacterial communities to test the performance of the code. The study demonstrates that the assessment of ecological risk obtained using AQUARISK, when coupled with geochemical modelling, accords quite well with the independent data from the biomeasures. Results from the study also suggest that only a single water-quality guideline value is required for aluminium, the major toxicant in the Dawesley Creek–Bremer River system.

Particle Backtracking Algorithm for Water Distribution System Analysis

A novel input-output model of water quality in water distribution systems is presented as a particle (water parcel) backtracking algorithm (PBA). The PBA is a simpler and more efficient version of that described by Zierolf et. al. in 1998 and is extended to allow storage tanks and multiple water sources and quality inputs. For simplicity the algorithm details are described for networks with a single water quality input at the water source, and the necessary extensions to allow multiple water sources and quality inputs are described separately. The PBA provides information that is not available using traditional simulation approaches: the various paths that water takes between a particular input source and output node, and their associated time delays and impact on output node water quality. Such information constitutes a complete description of the input-output behavior under typical assumptions of first-order chemical decay or production reactions. Thus the output behavior can be calculated for any source quality input, and the explicit mathematical form of the input-output behavior is useful information for certain applications such as feedback control. More generally, the PBA is a tool to understand flow-path-dependent water quality processes in distribution systems, since those paths and their characteristics are made explicit and thus available for analysis. The potential utility of input-output analysis is illustrated by several examples.

Risk assessment of consuming agricultural products irrigated with reclaimed wastewater: An exposure model

This study assesses health risks to consumers due to the use of agricultural products irrigated with reclaimed wastewater. The analysis is based on a definition of an exposure model which takes into account several parameters: (1) the quality of the applied wastewater, (2) the irrigation method, (3) the elapsed times between irrigation, harvest, and product consumption, and (4) the consumers' habits. The exposure model is used for numerical simulation of human consumers' risks using the Monte Carlo simulation method. The results of the numerical simulation show large deviations, probably caused by uncertainty (impreciseness in quality of input data) and variability due to diversity among populations. There is a 10–orders of magnitude difference in the risk of infection between the different exposure scenarios with the same water quality. This variation indicates the need for setting risk‐based criteria for wastewater reclamation rather than single water quality guidelines. Extra data are required to decrease uncertainty in the risk assessment. Future research needs to include definition of acceptable risk criteria, more accurate dose‐response modeling, information regarding pathogen survival in treated wastewater, additional data related to the passage of pathogens into and in the plants during irrigation, and information regarding the behavior patterns of the community of human consumers.

Optimization of Regional Water Quality Monitoring Strategies

A conceptual framework is presented for optimizing the operation of regional monitoring networks which assist water quality management. The primary objective of the studied network is to determine the annual nutrient load carried into a lake by its tributaries. Following the description of the basic (single time–period, single water quality indicator) model, several extension possibilities and computational aspects are highlighted. The suggested methodology is illustrated by a numerical example, concerning the surveillance system on the tributaries of Lake Balaton (Hungary).