STATEWIDE EMPIRICAL MODELING OF BACTERIAL CONTAMINATION OF SURFACE WATERS1

ABSTRACT: Bacterial contamination of surface waters is attributed to both urban and agricultural land use practices and is one of the most frequently cited reasons for failure to meet standards established under the Clean Water Act (CWA) (P.L. 92–500). Statewide modeling can be used to determine if bacterial contamination occurs predominantly in urban or agricultural settings. Such information is useful for directing future monitoring and allocating resources for protection and restoration activities. Logistic regression was used to model the likelihood of bacterial contamination using watershed factors for the state of Maryland. Watershed factors included land cover, soils, topography, hydrography, locations of septic systems, and animal feeding operations. Results indicated that bacterial contamination occurred predominantly in urban settings. Likelihood of bacterial contamination was highest for small watersheds with well drained and erodible soils and a high proportion of urban land adjacent to streams. The number of septic systems and animal feeding operations and the amount of agricultural land were not significant explanatory factors. The urban infrastructure tends to “connect” more of the watershed to the stream network through the creation of roads, storm sewers, and wastewater treatment plants. This may partly explain the relationship between urbanization and bacterial contamination found in this study.     

LAND USE AND STREAMWATER NITRATE-N DYNAMICS IN AN URBAN-RURAL FRINGE WATERSHED1

ABSTRACT: Agricultural and residential activities are key non-point sources of nitrogen pollution in urban-rural fringe areas. A GIS-based watershed approach was used to compare land use indicators (septic system and animal unit densities), to streamwater nitrate-N in the Salmon River near Vancouver, B.C., Canada. The density of septic systems was used as an indicator of residential development while animal unit density was used as an indicator of the intensity of agricultural activity. Nitrate-nitrogen (nitrate-N) concentrations as high as 7.1 mg·L^?1 were found in the mid-portion of the watershed during the summer months, when streamflow is low and groundwater comprises a large proportion of water in the stream. The major aquifer supplying water to the midsection of the watershed is contaminated with nitrate-N. A comparison of the relationships between septic system and animal unit density and nitrate-N in the upstream to downstream direction provided evidence that both residential and agricultural activities contribute to elevated nitrate-N in the Salmon River mainstem. In contrast, only septic system density corresponded to the pattern of streamwater nitrate-N in Coghlan Creek, the main tributary to the Salmon River.     

Model evaluation of potential impacts of on-site wastewater systems on phosphorus in Turkey creek watershed

Nutrient loading to surface water systems has traditionally been associated with agricultural sources. Sources such as on-site wastewater systems (OWS) may be of concern especially in rural, nonagricultural watersheds. The impact of various point and nonpoint sources including OWS in Turkey Creek Watershed was evaluated using the Watershed Analysis Risk Management Framework, which was calibrated using 10 yr of observed stream flow and total P concentrations. Doubling the population in the watershed or OWS septic tank effluent P concentration increased mean stream total P concentration by a factor of 1.05. Converting all the OWS to a conventional sewer system with a removal efficiency of 93% at the wastewater treatment plant increased the mean total P concentration at the watershed outlet by a factor of 1.26. Reducing the soil adsorption capacity by 50% increased the mean stream total P concentration by a factor of 3.2. Doubling the initial P concentration increased the mean stream total P concentration by a factor of 1.96. Stream flow and sediment transport also substantially affected stream P concentration. The results suggest that OWS contribution to stream P in this watershed is minimal compared with other factors within the simulated time frame of 10 yr.     

A comparison of disposal methods for on-site sewage facilities within the state of Texas,USA

Currently, 1.5 million homes in Texas, USA utilize an on-site sewage facility to manage their household waste. This study compares the conventional septic dispersal technology of perforated pipe drain field with two of the new technologies recently implemented in Texas, multi-pipe and chamber systems, determining if soil classification and climate are influencing factors in functional ability for each of the technologies. There is no statistical significance for failure of a system with respect to system type or climate zone. The textural classification of soil is a statistically significant variable in septic system failures. Soil type III, which includes the clay groups except pure clays and silty clay, appears to significantly influence system failures. Additionally, occupant misuse and lack of maintenance are contributing factors to system failure.     

GENERATING DESIGN HYDROGRAPHS BY DEM ASSISTED GEOMORPHIC RUNOFF SIMULATION: A CASE STUDY1

ABSTRACT: The geomorphic instantaneous unit hydrograph (GIUH) may be one of the most successful methodologies for predicting flow characteristics in ungauged watersheds. However, one difficulty in applying the GIUH model is determination of travel time, and the other difficulty is the large amount of geomorphologic information required in the study watershed. Recently, using the kinematic-wave theory Lee and Yen (1997) have analytically determined the travel times for overland and channel flows in watersheds. The limitation of using an empirical velocity equation to estimate the runoff travel time for a specified watershed is then relaxed. To simplify the time-consuming work involved in geomorphic parameter measurement on topographic maps, the GIUH model is linked with geographic information systems to obtain geomorphic parameters from digital elevation models. In this paper, a case study performed for peak flow analysis in an ungauged watershed is presented. The geomorphic characteristics of the study watershed were analyzed using a digital elevation model and were used to construct the runoff simulation model. The design storm was then applied to the geomorphic runoff simulation model to obtain the design hydrograph. The analytical procedures proposed in this study can provide a convenient way for hydrologists to estimate hydrograph characteristics based on limited hydrologic information.     

SPATIAL DISTRIBUTION OF POINT SOIL MOISTURE ESTIMATES USING LANDSAT TM DATA AND FUZZY-C CLASSIFICATION1

ABSTRACT: Many hydrologic models have input data requirements that are difficult to satisfy for all but a few well-instrumented, experimental watersheds. In this study, point soil moisture in a mountain watershed with various types of vegetative cover was modeled using a generalized regression model. Information on sur-ficial characteristics of the watershed was obtained by applying fuzzy set theory to a database consisting of only satellite and a digital elevation model (DEM). The fuzzy-c algorithm separated the watershed into distinguishable classes and provided regression coefficients for each ground pixel. The regression model used the coefficients to estimate distributed soil moisture over the entire watershed. A soil moisture accounting model was used to resolve temporal differences between measurements at prototypical measurement sites and validation sites. The results were reasonably accurate for all classes in the watershed. The spatial distribution of soil moisture estimates corresponded accurately with soil moisture measurements at validation sites on the watershed. It was concluded that use of the regression model to distribute soil moisture from a specified number of points can be combined with satellite and DEM information to provide a reasonable estimation of the spatial distribution of soil moisture for a watershed.     

Effect of the Spatial Variability of Land Use,Soil Type,and Precipitation on Streamflows in Small Watersheds1

Abstract: The spatial variability of the data used in models includes the spatial discretization of the system into subsystems, the data resolution, and the spatial distribution of hydrologic features and parameters. In this study, we investigate the effect of the spatial distribution of land use, soil type, and precipitation on the simulated flows at the outlet of “small watersheds” (i.e., watersheds with times of concentration shorter than the model computational time step). The Soil and Water Assessment Tool model was used to estimate runoff and hydrographs. Different representations of the spatial data resulted in comparable model performances and even the use of uniform land use and soil type maps, instead of spatially distributed, was not noticeable. It was found that, although spatially distributed data help understand the characteristics of the watershed and provide valuable information to distributed hydrologic models, when the watershed is small, realistic representations of the spatial data do not necessarily improve the model performance. The results obtained from this study provide insights on the relevance of taking into account the spatial distribution of land use, soil type, and precipitation when modeling small watersheds.     

Preliminary evaluation of septic-system absorption-field architecture types in a profile-limited soil

Managing household wastewater is an issue that affects hundreds of thousands of people in rural communities nationwide, many of whom rely on septic systems as their primary means of household wastewater disposal. Septic system absorption field products with architectures quite different from traditional pipe-and-gravel systems are being installed in many states with variances from initial design specifications. The objective of this study was to evaluate the performance, as measured by the in-product height of stored solution, of four differing absorption-field product architecture types in a profile-limited soil that was loaded at the maximum allowable rate based on soil morphology. Five chamber, two gravel-less pipe, two polystyrene aggregate, and four pipe-and-gravel systems were installed in a profile-limited, Captina silt loam soil (fine-silty, siliceous, active, mesic Typic Fragiudult) and dosed with raw effluent at rates determined by current State of Arkansas regulations via individual peristaltic pumps. Free-solution monitoring ports were installed within each product, where the depth to free solution was measured periodically and used to evaluate product performance. Data collected from January through August 2009 indicated that preliminary system performance was unaffected by product architecture type. All products performed similarly under dry soil conditions. However, differences among individual products were observed during periods of hydrologic stress (i.e., wet soil conditions). Surfacing of effluent was not observed atop any product, indicating that the current loading rate design method is functioning properly. Preliminary results indicate that some alternative absorption-field products perform similarly to the traditional pipe-and-gravel system, thus providing flexibility and options for homeowners.     

Making or breaking waste facility siting successes with a siting framework

Waste facility siting successes depend on many linked factors of facility design and impacts, site characteristics, and community beliefs and values. A facility siting framework is constructed to combine important elements and cause–effect linkages that affect the siting outcome. The framework consists of three main components: (1) core elements of facility design, effects, and community beliefs, attitude and response; (2) contributing factors of site and community characteristics, community beliefs and values that affect the interpretation of the facility and its effects; and (3) siting management interventions to manage the process and facility impacts. The framework is applied in an unsuccessful and a successful siting case to determine the key elements that contribute to siting outcome: (1) thorough need justification for the facility from the proponent's and the community's perspective; (2) careful facility design and prediction of the impacts and to select impact management compensation measures; (3) screening and selection of communities where the beliefs and values are compatible with the type of facility and its effects, (4) cooperatively selected impact reduction (i.e., prevention, control, and mitigation) measures followed by compensation and incentives; and (5) intensive process management to balance the community characteristics and values with the proponent's efforts to plan, design, assess and manage impacts, and ultimately, gain approval of the facility. The siting framework provides a comprehensive and robust structure of key factors that contribute to siting outcome and, therefore, provides the tool to identify, evaluate, and design siting interventions to enhance the chances of successful siting outcome.     

Laboratory degradation studies of bentazone, dichlorprop, MCPA, and propiconazole in Norwegian soils

Laboratory degradation studies were performed in Norwegian soils using two commercial formulations (Tilt and Triagran-P) containing either propiconazole alone or a combination of bentazone, dichlorprop, and MCPA. These soils included a fine sandy loam from Hole and a loam from Kroer, both of which are representative of Norwegian agricultural soils. The third soil was a highly decomposed organic material from the Froland forest. A fourth soil from the Skuterud watershed was used only for propiconazole degradation. After 84 d, less than 0.1% of the initial MCPA concentration remained in all three selected soils. For dichlorprop, the same results were found for the fine sandy loam and the organic-rich soil, but in the loam, 26% of the initial concentration remained. After 84 d, less than 0.1% of the initial concentration of bentazone remained in the organic-rich soil, but in the loam and the fine sandy loam 52 and 69% remained, respectively. Propiconazole was shown to be different from the other pesticides by its persistence. Amounts of initial concentration remaining varied from 40, 70, and 82% in the reference soils after 84 d for the organic-rich soil, fine sandy loam, and loam, respectively. The organic-rich soil showed the highest capacity to decompose all four pesticides. The results from the agricultural soils and the Skuterud watershed showed that the persistence of propiconazole was high. Pesticide degradation was approximated to first-order kinetics. Slow rates of degradation, where more than 50% of the pesticide remained in the soil after the 84-d duration of the experiment, did not fit well with first-order kinetics.     

USING A GIS FOR ESTIMATING INPUT PARAMETERS IN URBAN STORMWATER QUALITY MODELING1

ABSTRACT: Geographic Information Systems (GIS) are being used increasingly as a method of preparing, analyzing, and displaying data for watershed analysis and modeling. Although GIS technology is a powerful tool for integrating and analyzing watershed characteristics, the initial preparation of the necessary database is often a time consuming and costly endeavor. This demonstration project assesses the viability of creating a cost-effective spatial database for urban stormwater modeling from existing digital and hard-copy data sources. The GIS was used to provide input parameters to the Source Loading and Management Model (SLANM), an empirical urban stormwater quality model. Land use characteristics, drainage boundaries, and soils information were geocoded and referenced to a base data layer consisting of transportation features. GIS overlay and data manipulation capabilities were utilized to preprocess the input data for the model. Model output was analyzed through postprocessing by GIS, and results were compared to a similar recent modeling study of the same watershed. The project, undertaken for a small urban watershed located in Plymouth, Minnesota, successfully demonstrates that the use of GIS in stormwater management can allow even small communities to reap the benefits of stormwater quality modeling.     

Development of a risk-based index for source water protection planning, which supports the reduction of pathogens from agricultural activity entering water resources

Source water protection planning (SWPP) is an approach to prevent contamination of ground and surface water in watersheds where these resources may be abstracted for drinking or used for recreation. For SWPP the hazards within a watershed that could contribute to water contamination are identified together with the pathways that link them to the water resource. In rural areas, farms are significant potential sources of pathogens. A risk-based index can be used to support the assessment of the potential for contamination following guidelines on safety and operational efficacy of processes and practices developed as beneficial approaches to agricultural land management. Evaluation of the health risk for a target population requires knowledge of the strength of the hazard with respect to the pathogen load (massxconcentration). Manure handling and on-site wastewater treatment systems form the most important hazards, and both can comprise confined and unconfined source elements. There is also a need to understand the modification of pathogen numbers (attenuation) together with characteristics of the established pathways (surface or subsurface), which allow the movement of the contaminant species from a source to a receptor (water source). Many practices for manure management have not been fully evaluated for their impact on pathogen survival and transport in the environment. A key component is the identification of potential pathways of contaminant transport. This requires the development of a suitable digital elevation model of the watershed for surface movement and information on local groundwater aquifer systems for subsurface flows. Both require detailed soils and geological information. The pathways to surface and groundwater resources can then be identified. Details of land management, farm management practices (including animal and manure management) and agronomic practices have to be obtained, possibly from questionnaires completed by each producer within the watershed. To confirm that potential pathways are active requires some microbial source tracking. One possibility is to identify the molecular types of Escherichia coli present in each hazard on a farm. An essential part of any such index is the identification of mitigation strategies and practices that can reduce the magnitude of the hazard or block open pathways.     

Local recycling of plant nutrients from small-scale wastewater systems to farmland—A Swedish scenario study

Reducing the negative impact from on-site systems and promoting recycling are important tasks for municipal authorities, especially as regards phosphorus. The objective of this scenario study was to compare energy turnover in a life cycle perspective, recycling potential and expected reduction of nitrogen and phosphorus emissions for three upgraded small-scale wastewater systems based on local recycling of plant nutrients. The systems studied were urine separation, blackwater separation and chemical precipitation in the septic tank. The urine was sanitised through storage, the blackwater through liquid composting and the precipitated sludge through chemical treatment with urea before reuse in agriculture. The system boundaries included the operational phase as well as investment in capital goods required for upgrading the existing on-site systems.The urine separation system used least energy. The potential recycling and reduction of phosphorus was lower than for the other two systems, while that of nitrogen was higher than for the chemical precipitation system but lower than for the blackwater separation system. The blackwater separation system reduced both nitrogen and phosphorus to a high extent and also enabled a large proportion of both nitrogen and phosphorus to be recycled to arable land. However, a major drawback with this system was its significantly higher use of electricity, related to the aeration and stirring required when sanitising the blackwater by liquid composting. When urea treatment replaced liquid composting, the use of electricity decreased substantially in the blackwater separation system. The chemical precipitation system was efficient in reducing and recycling phosphorus, while inefficient for nitrogen. The use of fossil fuels was significantly higher than for the other two systems, primarily due to the production of the precipitation chemical.     

Identification of Sediment Sources in Forested Watersheds With Surface Coal Mining Disturbance Using Carbon and Nitrogen Isotopes1

Abstract: Sediments and soils were analyzed using stable carbon and nitrogen isotope ratio mass spectrometry and carbon and nitrogen elemental analyses to evaluate the their ability to indicate land‐use and land management disturbance and pinpoint loading from sediment transport sources in forested watersheds disturbed by surface coal mining. Samples of transported sediment particulate organic matter were collected from four watersheds in the Southern Appalachian forest region of southeastern Kentucky. The four watersheds had different surface coal mining history that were classified as undisturbed, active mining, and reclaimed conditions. Soil samples were analyzed including reclaimed grassland soils, undisturbed forest soils, geogenic organic matter associated with coal fragments in mining spoil, and soil organic matter from un‐mined grassland soils. Statistically significant differences were found for all biogeochemical signatures when comparing transported sediments from undisturbed watersheds and surface coal mining disturbed watersheds, and the results were attributed to differences in erosion sources and the presence of geogenic organic matter. Sediment transport sources in the surface coal mining watersheds were analyzed using Monte Carlo mass balance un‐mixing and it was found that: δ¹⁵N showed the ability to differentiate streambank erosion and surface soil erosion; and δ¹³C showed the ability to differentiate soil organic matter and geogenic organic matter. Results from the analyses suggest that streambank erosion downstream of surface coal mining sites is an especially significant source of sediment in coal mining disturbed watersheds. Further, the results suggest that the sediment transport processes governing streambank erosion loads are taking longer to reach geomorphologic equilibrium in the watershed as compared with the surface erosion processes. The dual‐isotope technique provides a useful method for further investigation of the impact of surface coal mining in the uplands of the watershed upon the geomorphologic state of the channel and the source of organic matter in aquatic systems impacted by surface coal mining.     

Translation of user requirements into house designs: A multi-dimensional scaling analysis

An experiment was conducted to determine how user requirements for single-storey houses are translated into actual design layouts. Architectural students were asked to provide floorplans of houses for four quite different hypothetical users. The briefs contained information either about spatial requirements or about life-style characteristics. Another group of architectural students later evaluated the appropriateness of the designs for the intended user. An INDSCAL analysis of the data (inter-room distances) produced a 4-dimensional solution that accounted for 65% of the variance between house designs. The salience of the dimensions seemed to be more a function of the designer than of the requirements of the user.It was found that when users' requirements are expressed in spatial terms only, the designs produced are clearly a function of the user, not the designer. The more information supplied about the user, the greater the tendency for congruence in the designs. When the brief consisted of life-style characteristics only, the results remained equivocal. There appeared to be little consensus on what designs were appropriate for the hypothetical users.The experiment strongly suggested that (a) architecture students handle information about spatial requirements with ease and with a good deal of consensus on what they consider to be the appropriate design solution for each user; (b) information about life-style characteristics and activity profiles, on the other hand, is handled quite differently by different students. In the latter case, the house designs produced probably follow implicit design-behaviour theories that are quite idiosyncratic. A number of theoretical and methodological issues that require further investigation are raised in the discussion.     

Nitrous oxide accumulation in soils from riparian buffers of a coastal plain watershed carbon/nitrogen ratio control

Riparian buffers are used throughout the world for the protection of water bodies from nonpoint-source nitrogen pollution. Few studies of riparian or treatment wetland denitrification consider the production of nitrous oxide (N2O). The objectives of this research were to ascertain the level of potential N2O production in riparian buffers and identify controlling factors for N2O accumulations within riparian soils of an agricultural watershed in the southeastern Coastal Plain of the USA. Soil samples were obtained from ten sites (site types) with different agronomic management and landscape position. Denitrification enzyme activity (DEA) was measured by the acetylene inhibition method. Nitrous oxide accumulations were measured after incubation with and without acetylene (baseline N2O production). The mean DEA (with acetylene) was 59 microg N2O-N kg(-1) soil h(-1) for all soil samples from the watershed. If no acetylene was added to block conversion of N2O to N2, only 15 microg N2O-N kg(-1) soil h(-1) were accumulated. Half of the samples accumulated no N2O. The highest level of denitrification was found in the soil surface layers and in buffers impacted by either livestock waste or nitrogen from legume production. Nitrous oxide accumulations (with acetylene inhibition) were correlated to soil nitrogen (r2=0.59). Without acetylene inhibition, correlations with soil and site characteristics were lower. Nitrous oxide accumulations were found to be essentially zero, if the soil C/N ratios>25. Soil C/N ratios may be an easily measured and widely applicable parameter for identification of potential hot spots of N2O productions from riparian buffers.     

Improvement of sand filter and constructed wetland design using an environmental decision support system

With the aim of improving effluent quality of waste stabilization ponds, different designs of vertical flow constructed wetlands and intermittent sand filters were tested on an experimental full-scale plant within the framework of a European project. The information extracted from this study was completed and updated with heuristic and bibliographic knowledge. The data and knowledge acquired were difficult to integrate into mathematical models because they involve qualitative information and expert reasoning. Therefore, it was decided to develop an environmental decision support system (EDSS-Filter-Design) as a tool to integrate mathematical models and knowledge-based techniques. This paper describes the development of this support tool, emphasizing the collection of data and knowledge and representation of this information by means of mathematical equations and a rule-based system. The developed support tool provides the main design characteristics of filters: (i) required surface, (ii) media type, and (iii) media depth. These design recommendations are based on wastewater characteristics, applied load, and required treatment level data provided by the user. The results of the EDSS-Filter-Design provide appropriate and useful information and guidelines on how to design filters, according to the expert criteria. The encapsulation of the information into a decision support system reduces the design period and provides a feasible, reasoned, and positively evaluated proposal.     

Dynamic modeling of chemical fate and transport in multimedia environments at watershed scale-I: theoretical considerations and model implementation

A geo-referenced environmental fate model was developed for analyzing unsteady-state dispersion and distribution of chemicals in multimedia environmental systems. Chemical transport processes were formulated in seven environmental compartments of air, canopy, surface soil, root-zone soil, vadose-zone soil, surface water, and sediment. The model assumed that the compartments were completely mixed and chemical equilibrium was established instantaneously between the sub-compartments within each compartment. A fugacity approach was utilized to formulate the mechanisms of diffusion, advection, physical interfacial transport, and transformation reactions. The governing equations of chemical mass balances in the environmental compartments were solved simultaneously to reflect the interactions between the compartments. A geographic information system (GIS) database and geospatial analysis were integrated into the chemical transport simulation to provide spatially explicit estimations of model parameters at watershed scale. Temporal variations of the environmental properties and source emissions were also considered in the parameter estimations. The outputs of the model included time-dependent chemical concentrations in each compartment and its sub-compartments, and inter-media mass fluxes between adjacent compartments at daily time steps.     

VARIABILITY OF SOIL WATER PROPERTIES AND CROP YIELD IN A SLOPED WATERSHED1

ABSTRACT: Spatial distribution of soil and water properties and the correlations between them and crop yield were determined for a natural rainfall environment. Hydraulic conductivity, soil texture, water retention, and soil-water flux were variables used to investigate their relationship to crop yield using multiple regression techniques. Variations in crop yields on a watershed with a 3 to 4 percent slope and moderately erosive soils were related to soil-water characteristics and soil properties along slope and with depth. Climatic conditions to sustain crop growth and yield ranged from inadequate soil water in 1983 to adequate soil water in 1984. Crop yield was predicted with models using both available and measured soil-water content. Available water content provided a better model for the prediction of water yield and does not require field measurements of actual soil-water content. Soil water holding capacity was more significant for predicting crop yield in soils with moderate to high silt content than infiltrability of water into the soil.     

Modeling Agricultural Nonpoint Source Pollution Using a Geographic Information System Approach

Agricultural non-point source (NPS) pollution, primarily sediment and nutrients, is the leading source of water-quality impacts to surface waters in North America. The overall goal of this study was to develop geographic information system (GIS) protocols to facilitate the spatial and temporal modeling of changes in soils, hydrology, and land-cover change at the watershed scale. In the first part of this article, we describe the use of GIS to spatially integrate watershed scale data on soil erodibility, land use, and runoff for the assessment of potential source areas within an intensively agricultural watershed. The agricultural non-point source pollution (AGNPS) model was used in the Muddy Creek, Ontario, watershed to evaluate the effectiveness of management strategies in decreasing sediment and nutrient [phosphorus (P)] pollution. This analysis was accompanied by the measurement of water-quality parameters (dissolved oxygen, pH, hardness, alkalinity, and turbidity) as well as sediment and P loadings to the creek. Practices aimed at increasing year-round soil cover would be most effective in decreasing sediment and P losses in this watershed. In the second part of this article, we describe a method for characterizing land-cover change in a dynamic urban fringe watershed. The GIS method we developed for the Blackberry Creek, Illinois, watershed will allow us to better account for temporal changes in land use, specifically corn and soybean cover, on an annual basis and to improve on the modeling of watershed processes shown for the Muddy Creek watershed. Our model can be used at different levels of planning with minimal data preprocessing, easily accessible data, and adjustable output scales.