MODELING OF NONPOINT SOURCE POLLUTION OF NITROGEN AT THE WATERSHED SCALE1

ABSTRACT: The Watershed Nutrient Transport and Transformation (NTT-Watershed) model is a physically based, energy-driven, multiple land use, distributed model that is capable of simulating water and nutrient transport in a watershed. The topographic features and subsurface properties of the watershed are refined into uniform, homogeneous square grids. The vertical discretization includes vegetation, overland flow, soil water redistribution and groundwater zones. The chemical submodel simulates the nitrogen dynamics in terrestrial and aquatic systems. Three chemical state variables are considered (NO₃^-_-, NH₄⁺, and Org-N). The NTT-Watershed model was used to simulate the fate and transport of nitrogen in the Muddy Brook watershed in Connecticut. The model was shown to be capable of capturing the hydrologic and portions of the nitrogen dynamics in the watershed. Watershed planners could use this model in developing strategies of best management practices that could result in maximizing the reductions of nitrogen export from a watershed.     

Comparison of Measured and MM5 Modeled Meteorology Data for Simulating Flow in a Mountain Watershed1

Herr, Joel W., Krish Vijayaraghavan, and Eladio Knipping, 2010. Comparison of Measured and MM5 Modeled Meteorology Data for Simulating Flow in a Mountain Watershed. Journal of the American Water Resources Association (JAWRA) 46(6):1255–1263. DOI: 10.1111/j.1752-1688.2010.00489.x Abstract: Accurate simulation of time-varying flow in a river system depends on the quality of meteorology inputs. The density of meteorology measurement stations can be insufficient to capture spatial heterogeneity of precipitation, especially in mountainous areas. The Watershed Analysis Risk Management Framework (WARMF) model was applied to the Catawba River watershed of North and South Carolina to simulate flow and water quality in rivers and a series of 11 reservoirs. WARMF was linked with the AMSTERDAM air model to analyze the water quality benefit from reduced atmospheric emissions. The linkage requires accurate simulation of meteorology for all seasons and for all types of precipitation events. WARMF was driven by the mesoscale meteorology model MM5 processed by the Meteorology Chemistry Interface Processor, which provides greater spatial density but less accuracy than meteorology stations. WARMF was also run with measured data from the National Climatic Data Center (NCDC) to compare the performance of the watershed model using measured data vs. modeled meteorology as input. A one year simulation using MM5 modeled meteorology performed better overall than the simulation using NCDC data for the volumetric water balance measure used for calibration, but MM5 represented precipitation from a dissipated hurricane poorly, which propagated into errors of simulated flow.     

MODELING ACID MINE DRAINAGE ON A WATERSHED SCALE FOR TMDL CALCULATIONS1

ABSTRACT: The Cheat River of West Virginia is impaired by acid mine drainage (AMD). Fifty‐five of its river segments were placed on the 303(d) list, which required calculations of total maximum daily load (TMDL) to meet the water quality criteria for pH, total iron, aluminum, manganese, and zinc. An existing watershed model was enhanced to simulate AMD as nonpoint source load. The model divided a watershed into a network of catchments and river segments. Each catchment was divided into soil layers, which could contain pyrite, calcite and other minerals. A kinetic expression was used to simulate pyrite oxidation as a function of oxygen in the soil voids. Oxygen in the soil voids was consumed by pyrite oxidation and replenished by earth breathing. The by‐products of pyrite oxidation were calculated according to its mass action equations. Chemical equilibrium was used to account for the speciation of ferrous and ferric irons and precipitation of metal hydroxides. Simulated hydrology and water quality were compared to available data. The USEPA used the calibrated model to calculate the TMDLs in the Cheat River Watershed.     

Effect of reservoir flushing on downstream river water quality

The effect of short-term reservoir flushing on downstream water quality in the Geum River, Korea was studied using field experiments and computer simulations. The reservoir release was increased from 30 to 200 m(3)/s within 6 h for the purpose of this experiment. The flushing discharge decreased the concentrations of soluble nitrogen and phosphorus species considerably, but the experimental results revealed a negative impact on organic forms of nutrients and biochemical oxygen demand (BOD). A dynamic river water quality model was applied to simulate the river hydraulics and water quality variations during the event. The model showed very good performance in predicting the travel time of flushing flow and the variations of dissolved forms of nitrogen and phosphorus constituents. However, it revealed a limited capability in simulating organic forms of nutrients and BOD because it does not consider the re-suspension mechanism of these constituents from sediment during the wave front passage.     

WATERSHED SCALING EFFECT ON BASE FLOW NITRATE,VALLEY AND RIDGE PHYSIOGRAPHIC PROVINCE1

ABSTRACT: A study of stream base flow and NO₃‐N concentration was conducted simultaneously in 51 subwatersheds within the 116‐square‐kilometer watershed of East Mahantango Creek near Klingerstown, Pennsylvania. The study was designed to test whether measurable results of processes and observations within the smaller watersheds were similar to or transferable to a larger scale. Ancillary data on land use were available for the small and large watersheds. Although the source of land‐use data was different for the small and large watersheds, comparisons showed that the differences in the two land‐use data sources were minimal. A land use‐based water‐quality model developed for the small‐scale 7.3‐square‐kilometer watershed for a previous study accurately predicted NO₃‐N concentrations from sampling in the same watershed. The water‐quality model was modified and, using the imagery‐based land use, was found to accurately predict NO₃‐N concentrations in the subwatersheds of the large‐scale 116‐square‐kilometer watershed as well. Because the model accurately predicts NO₃‐N concentrations at small and large scales, it is likely that in second‐order streams and higher, discharge of water and NO₃‐N is dominated by flow from smaller first‐order streams, and the contribution of ground‐water discharge to higher order streams is minimal at the large scale.     

Application of an Environmental Decision Support System to a Water Quality Trading Program Affected by Surface Water Diversions

Environmental decision support systems (EDSSs) are an emerging tool used to integrate the evaluation of highly complex and interrelated physicochemical, biological, hydrological, social, and economic aspects of environmental problems. An EDSS approach is developed to address hot-spot concerns for a water quality trading program intended to implement the total maximum daily load (TMDL) for phosphorus in the Non-Tidal Passaic River Basin of New Jersey. Twenty-two wastewater treatment plants (WWTPs) spread throughout the watershed are considered the major sources of phosphorus loading to the river system. Periodic surface water diversions to a major reservoir from the confluence of two key tributaries alter the natural hydrology of the watershed and must be considered in the development of a trading framework that ensures protection of water quality. An EDSS is applied that enables the selection of a water quality trading framework that protects the watershed from phosphorus-induced hot spots. The EDSS employs Simon’s (1960) three stages of the decision-making process: intelligence, design, and choice. The identification of two potential hot spots and three diversion scenarios enables the delineation of three management areas for buying and selling of phosphorus credits among WWTPs. The result shows that the most conservative option entails consideration of two possible diversion scenarios, and trading between management areas is restricted accordingly. The method described here is believed to be the first application of an EDSS to a water quality trading program that explicitly accounts for surface water diversions.     

WATER QUALITY AND SOURCE OF FRESHWATER DISCHARGE TO THE CALOOSAHATCHEE ESTUARY,FLORIDA1

ABSTRACT: The Caloosahatchee River has two major sources of freshwater one from its watershed and the other via an artificial connection to Lake Okeechobee. The contribution of each source to the freshwater discharge reaching the downstream estuary varies and either may dominate. Routine monitoring data were analyzed to determine the effects of total river discharge and source of discharge (river basin, lake) on water quality in the downstream estuary. Parameters examined were: color, total suspended solids, light attenuation, chlorophyll a, and total and dissolved inorganic nitrogen and phosphorus. In general, the concentrations of color, and total and dissolved inorganic nitrogen increased, and total suspended solids decreased, as total discharge increased. When the river basin was the major source, the concentrations of nutrients (excepting ammonia) and color in the estuary were relatively higher than when the lake was the major source. Light attenuation was greater when the river basin dominated freshwater discharge to the estuary. The analysis indicates that water quality in the downstream estuary changes as a function of both total discharge and source of discharge. Relative to discharge from the river basin, releases from Lake Okeechobee do not detectably increase concentrations of nutrients, color, or TSS in the estuary.     

WATER QUALITY MODELING FOR THE FEITSUI RESERVOIR IN NORTHERN TAIWAN1

ABSTRACT: Field data collected from the Feitsui Reservoir in Taiwan indicate that the water is at a stage between mesotrophic and eutrophic. Recent measurements such as total phosphorus, chlorophyll a and Secchi depth levels suggest that the water quality has been declining. A two‐dimensional, laterally averaged, finite difference hydrodynamic and water quality model was used to simulate the water quality in the Feitsui Reservoir in an effort to determine sound water quality management strategies. The model was calibrated and verified using data collected in 1996 and 1997. The calibrated model was used to simulate algal biomass (in terms of chlorophyll a) levels under various wasteload reduction scenarios. Model results show that 50 percent reduction of the total phosphorus load will improve the existing water quality, shifting the trophic status from eutrophic/mesotrophic to oligotrophic. The modeling effort has yielded valuable information that can be used by decision makers for the evaluation of different management strategies of reducing watershed nutrient loads.     

ORIGIN AND TRANSPORT OF DISSOLVED CHEMICALS IN A KARST WATERSHED,SOUTHWESTERN ILLINOIS1

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.     

THE EFFECTS OF CLIMATE CHANGE ON STREAM FLOW AND NUTRIENT LOADING'

ABSTRACT: This study assesses the potential impact of climate change on stream flow and nutrient loading in six watersheds of the Susquehanna River Basin using the Generalized Watershed Loading Function (GWLF). The model was used to simulate changes in stream flow and nutrient loads under a transient climate change scenario for each watershed. Under an assumption of no change in land cover and land management, the model was used to predict monthly changes in stream flow and nutrient loads for future climate conditions. Mean annual stream flow and nutrient loads increased for most watersheds, but decreased in one watershed that was intensively cultivated. Nutrient loading slightly decreased in April and late summer for several watersheds as a result of early snowmelt and increasing evapotranspiration. Spatial and temporal variability of stream flow and nutrient loads under the transient climate scenario indicates that different approaches for future water resource management may be useful.     

EFFECTS OF NO-FLOW RIVER CONDITIONS ON THE PLATTE RIVER WELL FIELD1

ABSTRACT: Effects of no-flow river conditions on the quantity and quality of water in the Platte River well field of the City of Grand Island, Nebraska, were examined utilizing a finite-difference computer simulation model specifically developed for this well field. Results suggest that the effects of these no-flow periods on water quality may be most important. In particular, the no-flow periods eliminate the hydraulic barrier between the well field and an area north of the River that is contaminated with nitrate (concentrations in the 20 to 40 mg/1 NO₃-N range). They also change the direction and velocity of movement of the contaminated ground water. Simulation results indicate that contaminated ground water moves toward the well field with a velocity of 0.42 ft/d after 30 days of no-flow and 1.43 ft/d after 180 days of no-flow. Limiting no-flow conditions to 10 consecutive days would protect the well field.     

An innovative modeling approach using Qual2K and HEC-RAS integration to assess the impact of tidal effect on River Water quality simulation

Water quality modeling has been shown to be a useful tool in strategic water quality management. The present study combines the Qual2K model with the HEC-RAS model to assess the water quality of a tidal river in northern Taiwan. The contaminant loadings of biochemical oxygen demand (BOD), ammonia nitrogen (NH₃-N), total phosphorus (TP), and sediment oxygen demand (SOD) are utilized in the Qual2K simulation. The HEC-RAS model is used to: (i) estimate the hydraulic constants for atmospheric re-aeration constant calculation; and (ii) calculate the water level profile variation to account for concentration changes as a result of tidal effect. The results show that HEC-RAS-assisted Qual2K simulations taking tidal effect into consideration produce water quality indices that, in general, agree with the monitoring data of the river. Comparisons of simulations with different combinations of contaminant loadings demonstrate that BOD is the most import contaminant. Streeter-Phelps simulation (in combination with HEC-RAS) is also performed for comparison, and the results show excellent agreement with the observed data. This paper is the first report of the innovative use of a combination of the HEC-RAS model and the Qual2K model (or Streeter-Phelps equation) to simulate water quality in a tidal river. The combination is shown to provide an alternative for water quality simulation of a tidal river when available dynamic-monitoring data are insufficient to assess the tidal effect of the river.     

CALIBRATION OF STORM LOADS IN THE SOUTH PRONG WATERSHED,FLORIDA, USING BASINS/HSPF1

ABSTRACT: The South Prong watershed is a major tributary system of the Sebastian River and adjacent Indian River Lagoon. Continued urbanization of the Sebastian River drainage basin and other watersheds of the Indian River Lagoon is expected to increase runoff and nonpoint source pollutant loads. The St. Johns River Water Management District developed watershed simulation models to estimate potential impacts on the ecological systems of receiving waters and to assist planners in devising strategies to prevent further degradation of water resources. In the South Prong system, a storm water sampling program was carried out to calibrate the water quality components of the watershed model for total suspended solids (TSS), total phosphorous (TP), and total nitrogen (TN). During the period of May to November 1999, water quality and flow data were collected at three locations within the watershed. Two of the sampling stations were located at the downstream end of major watercourses. The third station was located at the watershed outlet. Five storm events were sampled and measured at each station. Sampling was conducted at appropriate intervals to represent the rising limb, peak, and recession limb of each storm event. The simulations were handled by HSPF (Hydrologic Simulation Program‐Fortran). Results include calibration of the hydrology and calibration of the individual storm loads. The hydrologic calibration was continuous over the period 1994 through 1999. Simulated storm runoff, storm loads, and event mean concentrations were compared with their corresponding observed values. The hydrologic calibration showed good results. The outcome of the individual storm calibrations was mixed. Overall, however, the simulated storm loads agreed reasonably well with measured loads for a majority of the storms.     

MODELING THE FOREST HYDROLOGY OF WETLAND-UPLAND ECOSYSTEMS IN FLORIDA1

ABSTRACT: Few hydrological models are applicable to pine flat-woods which are a mosaic of pine plantations and cypress swamps. Unique features of this system include ephemeral sheet flow, shallow dynamic ground water table, high rainfall and evapotranspiration, and high infiltration rates. A FLATWOODS model has been developed specifically for the cypress wetland-pine upland landscape by integrating a 2-D ground water model, a Variable-Source-Area (VAS)-based surface flow model, an evapotranspiration (ET) model, and an unsaturated water flow model. The FLATWOODS model utilizes a distributed approach by dividing the entire simulation domain into regular cells. It has the capability to continuously simulate the daily values of ground water table depth, ET, and soil moisture content distributions in a watershed. The model has been calibrated and validated with a 15-year runoff and a four-year ground water table data set from two different pine flat woods research watersheds in northern Florida. This model may be used for predicting hydrologic impacts of different forest management practices in the coastal regions.     

Beyond water data: benefits to volunteers and to local water from a citizen science program

Survey results of citizen science water data collection volunteers are presented, indicating personal benefits (e.g., being in nature, helping local water quality), and suggesting potential long-term benefits of improved watershed health (e.g., behavior change). These results can inform citizen science program development and contribute to watershed planners’ understanding of the broad benefits of such programs. We suggest that respondents’ positive feelings toward the watershed's major river and desire to learn about science and nature are place-specific elements that watershed and citizen science program managers could utilize in program development. Moreover, we explore the potential of social diffusion and behavior change and suggest the need for further research in these areas. We conclude that citizen science has potential not just as a means to collect large amounts of data (cheaply), but as a means to engage citizens to make environmentally friendly decisions.     

Assessment of a turfgrass sod best management practice on water quality in a suburban watershed

The disposal of manure on agricultural land has caused water quality concerns in many rural watersheds, sometimes requiring state environmental agencies to conduct total maximum daily load (TMDL) assessments of stream nutrients, such as nitrogen (N) and phosphorus (P). A best management practice (BMP) has been developed in response to a TMDL that mandates a 50% reduction of annual P load to the North Bosque River (NBR) in central Texas. This BMP exports composted dairy manure P through turfgrass sod from the NBR watershed to urban watersheds. The manure-grown sod releases P slowly and would not require additional P fertilizer for up to 20 years in the receiving watershed. This would eliminate P application to the sod and improve the water quality of urban streams. The soil and water assessment tool (SWAT) was used to model a typical suburban watershed that would receive the sod grown with composted dairy manure to assess water quality changes due to this BMP. The SWAT model was calibrated to simulate historical flow and estimated sediment and nutrient loading to Mary's Creek near Fort Worth, Texas. The total P stream loading to Mary's Creek was lower when manure-grown sod was transplanted instead of sod grown with inorganic fertilizers. Flow, sediment and total N yield were the same for both cases at the watershed outlet. The SWAT simulations indicated that the turfgrass BMP can be used effectively to import manure P into an urban watershed and reduce in-stream P levels when compared to sod grown with inorganic fertilizers.     

流域污染物通量测算方法研究

流域水系内污染物通量不仅能够用于评价各类污染源的水污染物入河负荷,也是对流域污染特征,水污染物在河流水体中复杂迁移、转化过程的最直观反应。准确测算流域水系内污染物跨界通量及其时空分布是进行流域水环境风险预警和风险管理的重要前提之一。针对目前多种污染物通量测算方法在进行污染物年通量估算时,结果不确定性大这一突出问题,以流域水质监测站年内逐日流量、悬浮颗粒物监测数据作为悬浮颗粒物年通量参考值,基于以月、半月、周为周期的监测策略,将逐日流量、悬浮颗粒物监测数据重新筛选抽样构造,由此,系统分析了不同流域集水面积、污染通量监测频次和目前常用通量估算方法对污染物年通量估算不确定性的影响。所得方法和结论可为进一步制定流域污染物通量的测算规范提供方法指引和技术支持。     

WATERSHED MODELS AND THEIR APPLICABILITY TO CONJUNCTIVE USE MANAGEMENT1

ABSTRACT: Techniques employed to simulate infiltration and subsurface ground-water flow were examined for a number of available watershed models. The large number of processes that these models simulate prohibits detailed analysis of subsurface flow, due to excessive computer and data requirements. Such models emphasize surface flow and include only that portion of water lost to the subsurface and the portion returned to the stream as baseflow. Problems were examined in adopting conjunctive use models, which allow the coordinated exploitation and management of both surface and ground-water resources. The application of conjunctive use models in water resources management is expected to increase dramatically over the next decade.     

COMPUTATION OF UNSTEADY FLOWS IN THE ALABAMA RIVER1

ABSTRACT: An application is described of the branch-network flow model, BRANCH, to the upper Alabama River system in central Alabama. The model is used to simulate one-dimensional unsteady flows and water surface elevations in approximately 60 river miles of the Alabama River system. Preliminary calibration was made using 72 hours of observed data. Simulated discharges are about 10 percent lower than observed discharges at higher discharge rates and computed flows lag observed flows by about 30 minutes.     

A Comparative Assessment of Runoff Nitrogen from Turf,Forest, Meadow,and Mixed Landuse Watersheds

Landscaping paradigms that encourage high‐input, intensively managed and mono‐culture turf/lawn landscapes have raised concerns about water quality. We conducted a watershed‐scale assessment of landscaping practices that included turf, urban, forest, native meadow, and mixed landuse watersheds with a professional golf course and a parking lot. The turf site was moderately managed and had lower fertilizer inputs than those typically used by homeowners and golf courses. Stream water sampling was performed during base flow and storm events. Highest nitrate and total nitrogen concentrations in runoff were observed for the mixed watershed draining the golf course. In contrast, concentrations in base flow from the turf watershed were lower than expected and were comparable to those measured in the surrounding meadow and forest sites. Total nitrogen concentrations from the turf site increased sharply during the first storms following fertilization, suggesting that despite optimal management there exists a risk for nutrient runoff following fertilization. Overall, this study suggests that turf or lawns, when managed properly, pose minimal water quality risk to surface waters. Rate, timing of application, and the type of fertilizer appear to be the key factors affecting water quality. Better education of homeowners and landscaping professionals with regard to these factors may be a cost‐effective strategy to reduce nonpoint source pollution.