Evaluating water quantity and quality of Canadian Great Lakes Watershed using LTHIA GIS Model.

Surface water quality impairment in agricultural watersheds is a major environmental concern in the United States. To assess seasonal and spatial variability of surface water quality and identify factors associated with surface water quality variability, we monitored surface water quality at seven locations in Bayou Plaquemine Brule Watershed in Louisiana twice monthly from March of 2002 to February of 2008 and performed multivariate analyses of the dataset. Using the Soil and Water Assessment Tool (SWAT) model, we identified critical areas of nonpoint source pollution in the watershed. While temperature, turbidity, dissolved oxygen (DO), conductivity and pH were determined in the field using YSI Sonde (YSI Incorporated, Yellow Springs, Ohio), surface water samples were analyzed for total nitrogen (TN), total phosphorus (TP), nitrate/nitrite-N (NO₃/NO₂-N), soluble reactive phosphate (SRP), total suspended solids (TSS), and five-day biological oxygen demand (BOD₅) in laboratory. The monthly water quality sampling included a regular sampling and an after-rain-event sampling. Average DO for the summer months, March through November, was 4.91 ± 0.08 mg L⁻¹ (4.91 ± 0.08 ppm), while average DO for the winter months, December through February, was 8.32 ± 0.12 mg L⁻¹ (8.32 ± 0.12 ppm). Dissolved oxygen was negatively correlated with TN (<em>r</em> = −0.22, <em>p</em> ≤ 0.001), SRP (<em>r</em> = −0.17, <em>p</em> ≤ 0.001), TP (<em>r</em> = −0.17, <em>p</em> ≤ 0.001), BOD₅ (<em>r</em> = −0.25, <em>p</em> ≤ 0.001), and surface water temperature (<em>r</em> = −0.70, <em>p</em> ≤ 0.001). Turbidity was strongly correlated with TSS (<em>r</em> = 0.59, <em>p</em> ≤ 0.001), suggesting that most turbidity in the water body comes from suspended solids. Similarly BOD₅ was significantly positively correlated with TN (<em>r</em> = 0.43, <em>p</em> ≤ 0.001), NO₃/NO₂-N (<em>r</em> = 0.26, <em>p</em> ≤ 0.001), TP (<em>r</em> = 0.25, <em>p</em> ≤ 0.001), and SRP (<em>r</em> = 0.18, <em>p</em> ≤ 0.001). Results of factor analyses showed sediment, phosphorus (P), nitrogen (N), surface water temperature, dissolved solids, and acidity/alkalinity as the most important factors associated with surface water quality variability in this watershed. Although relatively higher concentrations of sediments, TP, and TN were observed in the upper reaches of the watershed based on water quality monitoring, the SWAT simulation results showed the critical nonpoint source pollution areas of sediment, P, and N in the lower reaches of the watershed. Lower reaches of the watershed have mainly rice and crawfish production, while the upper reaches include primarily sugarcane, pasturelands, and soybean production. Information on seasonal variability of surface water quality, factors associated with surface water quality variability, and the critical areas for nonpoint source pollution will be valuable inputs for developing a watershed management plan for effective nonpoint source pollution control in an agricultural watershed.

Best management practices (BMPs) are the tools which are adopted to run any activity while inflicting least negative impacts on the surrounding environment. Since, water pollution is one of the most important issues in today's world; it is indispensable to discuss the activities which are deteriorating its quality. Although, a number of treatment technologies and methods are in place for treating the point sources of pollution, there is a need to address nonpoint sources of pollution. There are many successful practices which are capable of curtailing the impacts of nonpoint source pollution, if adopted. In this paper an attempt has been made to evaluate the performance and trade‐offs of various management practices to address the issues of agricultural nonpoint source pollution. Nevertheless, there is a dearth of guiding principles which can pave a way for adoption of these practices. Therefore, an attempt has also been made to explore the aspects of policy formulations along with emphasizing the factors which can lead to adoption/ non‐adoption of such practices.

ABSTRACT: Water quality and nonpoint source (NPS) pollution are important issues in many areas of the world, including the Inner Bluegrass Region of Kentucky where urban development is changing formerly rural watersheds into urban and mixed use watersheds. In watersheds where land use is mixed, the relative contributions of NPS pollution from rural and urban land uses can be difficult to separate. To better understand NPS pollution sources in mixed use watersheds, surface water samples were taken at three sites that varied in land use to examine the effect of land use on water quality. Within the group of three watersheds, one was predominately agriculture (Agricultural), one was predominately urban (Urban), and a third had relatively equal representation of both types of land uses (Mixed). Nitrogen (N), phosphorus (P), total suspended solids (TSS), turbidity, pH, temperature, and streamflow were measured for one year. Comparisons are made among watersheds for concentration and fluxes of water quality parameters. Nitrate and orthophosphate concentrations were found to be significantly higher in the Agricultural watershed. Total suspended solids, turbidity, temperature, and pH, were found to be generally higher in the Urban and Mixed watersheds. No differences were found for streamflow (per unit area), total phosphorus, and ammonium concentrations among watersheds. Fluxes of orthophosphate were greater in the Agricultural watershed that in the Urban watershed while fluxes of TSS were greater in the Mixed watershed when compared to the Agricultural watershed. Fluxes of nitrate, ammonium, and total phosphorus did not vary among watersheds. It is apparent from the data that Agricultural land uses are generally a greater source of nutrients than the Urban land uses while Urban land uses are generally a greater source of suspended sediment.

Many agricultural watersheds in the United States have impaired waterbodies due to nonpoint source pollution from agricultural activities and related processes. To understand the physical, chemical, and biological integrity of surface water in a coastal agricultural watershed, spatial and seasonal patterns of physicochemical and biological properties were investigated in Bayou Lacassine watershed (BLW) in Louisiana, United States. The relationship between the physicochemical and biological properties were also investigated. Sampling sites were located in the Bayou Chene and Lacassine Bayou subwatersheds within the BLW. Dissolved oxygen (DO), turbidity, conductivity, temperature, pH, total suspended solids (TSS), total dissolved solids (TDS), total solids (TS), five-day biological oxygen demand (BOD5), nitrate and nitrite-nitrogen (NO3/NO2-N), total Kjeldahl nitrogen (TKN), soluble reactive phosphorus (SRP), total phosphorus (TP), chloride (Cl−), fluoride (F−), and sulfate (SO4) were determined weekly from samples collected during 2012 to 2015. Fish and benthic invertebrate diversity and abundance in the two subwatersheds were determined in early summer and in fall of 2012 and 2013 at nine sites. Water quality was generally better at the most downstream site than at the most upstream site where agricultural intensity was highest, with significant differences in turbidity, TSS, TDS, TS, NO3/NO2-N, TKN, TP, and BOD5. There was also seasonal variation for the water quality parameters due to variability in agricultural activities and climatic conditions within the watershed. Results of the relationship between physicochemical properties and fish community variables showed that species richness, diversity, and abundance were negatively affected by elevated TS, NO3/NO2-N, and conductivity. For the benthic invertebrates, diversity was negatively related to BOD5. This study demonstrated unexpected longitudinal and seasonal patterns in physicochemical and biological properties of surface waters in a coastal agricultural watershed. This information is valuable in developing nonpoint source pollution control strategies for these subwatersheds.

In semi-arid and semi-humid areas, the occurrence of non-point source nutrient pollution is mainly driven by rainfall-runoff events, and nutrient loss under rainfall events determines annual total pollution load. Therefore, research on riverine nutrient dynamics under rainfall-runoff events in flood seasons is critical for simulating and controlling pollution load in semi-arid and semi-humid areas. The Chaohe River watershed, upstream watershed of Miyun Reservoir in Beijing was considered as study area, water quantity and quality of rainfall-runoff process at Gubeikou and Xiahui stations were monitored synchronously in flood seasons in 2018 and 2019. The results indicated the following:① Among the three rainfall events (E1, E2, and E3), E1 had the highest precipitation and rainfall intensity, and the corresponding discharge and pollutant concentrations were the highest. ② Under different rainfall events, the pollutant concentrations and their variations were different. The variations of concentrations of total nitrogen (TN), ammonia (NH4+-N), nitrate (NO3--N), total phosphorus (TP), and total suspended solids (TSS) were similar to the discharge process under the heavy rainstorm event (E1) and the rainstorm event (E3). The concentrations of total nitrogen (TN), ammonia (NH4+-N), total phosphorus (TP), and total suspended solids (TSS) were similar to the discharge process under the heavy rain events (E2), but the variations of nitrate (NO3--N) concentrations were opposite to those in the discharge process. ③ The concentrations and variations of different forms of pollutants were different under different rainfall events. Under the event of strong rainfall erosion (E1 and E2), the concentrations of particulate pollutants varied significantly, being positively correlated with that of total suspended solids (TSS). For the rainfall event that did not cause soil erosion (E3), the forms of nitrogen and phosphorus were dominated by total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) respectively, whose variations were mainly related to discharge. ④ The discharge and pollutant concentrations at each station varied under different rainfall events. Heavy rainfall erosion was more obvious at Gubeikou station, causing significant variations in discharge, TP, and TSS. Therefore, these results can be used to determine migration patterns of non-point source pollutants caused by rainfall-runoff events and provide references for water quality prediction and control in flood seasons.

The Muskingum River basin (MRB) of Ohio is the fourth most polluted watershed in the United States. To address water quality issues in the MRB, it is important to identify critical source areas (CSAs) that contribute disproportionately to high amounts of nonpoint source pollution. The Soil and Water Assessment Tool (SWAT) was used to develop a hydrological model in the MRB to identify conditions that cause land to be classified as CSAs in the basin. The model was calibrated for 10 years (1995 to 2004) and validated for 6 years (2005 to 2010) for streamflow, total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP) on a monthly scale. The validated model was then used to locate CSAs and the contributing sources of high nutrient discharges at the subbasin level in the MRB. Performance of conservation practices including terraces, buffer strips, 10% reduction in commercial and manure fertilizer use, and conservation tillage practices in the cropland of the CSAs were examined for their effectiveness in reducing nutrient loads at subbasin and watershed scales. In the MRB, average annual (1995 to 2010) subbasin yield for TSS, TN, and TP ranged from 0.02 to 1.23 Mg ha−1 y−1, 0.82 to 17 kg ha−1 y−1, and 0.03 to 2.6 kg ha−1 y−1, respectively. The slope of the landscape combined with land use practices were found to influence the water quality in the region. The cropland that comprises 22% of the basin was found to generate 70%, 63%, and 71% of the TSS, TN, and TP, respectively. Two percent of the cropland that is in steep landscape (>10% slope) was found to contribute to 29%, 6%, and 22% of the TSS, TN, and TP loads. While pasture land was found to generate 18% TSS, 15% TN, and 15% TP loads in the entire basin, these loadings were found to be significantly higher (53% TSS, 32% TN, and 64% TP) in the subbasins with intensive grazing activities. Evaluation of five conservation practices in the MRB suggested that terraces, vegetative filter strips, and controlled manure application are the most effective conservation practices to mitigate water quality issues in steep agricultural landscapes with complex management practices. The use of terraces was found to reduce the TSS (4% to 44%), TN (4% to 26%), and TP (5% to 53%) loads. Similarly, TSS, TN, and TP loads were reduced by 4% to 45%, 5% to 28%, and 7% to 45%, respectively, with filter strips practice in the basin. Nevertheless, none of the conservation practices in the cropland helped reduce sediment and nutrient loads by more than 12% in the outlet of the basin, suggesting that the conservation practices should be expanded to other land uses of the basin.

We quantified annual nutrient inputs to the Patuxent River estuary from point and nonpoint sources and from direct atmospheric deposition. We also compared nonpoint source (NPS) discharges from Piedmont and Coastal Plain regions and from agricultural and developed lands. Using continuous automated-sampling, we measured discharges of water, nitrogen, phosphorus, organic carbon (C), and suspended solids from a total of 23 watersheds selected to represent various proportions of developed land and cropland in the Patuxent River basin and the neighboring Rhode River basin. The sampling period spanned two years that differed in annual precipitation by a factor of 1.7. Water discharge from the watershed to the Patuxent River estuary was 3.4 times higher in the wet year than in the dry year. Annual water discharges from the study watersheds increased as the proportion of developed land increased. As the proportion of cropland increased, there were increases in the annual flow-weighted mean concentrations of nitrate (NO3 −), total nitrogen (TN), dissolved silicate (Si), total phosphate (TPO4 3−), total organic phosphorus (TOP), total P (TP), and total suspended solids (TSS) in NPS discharges. The effect of cropland on the concentrations of NO3 − and TN was stronger for Piedmont watersheds than for Coastal Plain watersheds. As the proportion of developed land increased, there were increases in annual mean concentrations of NO3 −, total ammonium (TNH4 +), total organic N (TON), TN, total organic C (TOC), TPO4 3−, TOP, TP, and TSS and decreases in concentrations of Si. Annual mean concentrations of TON, TOC, forms of P, and TSS were highest in the wet year. Annual mean concentrations of NO3 −, TNH4 +, TN, and Si did not differ significantly between years. We directly measured NPS discharges from about half of the Patuxent River basin and estimated discharges from the other half of the basin using statistical models that related annual water flow and material concentrations to land cover and physiographic province. We compared NPS discharges to public data on point source (PS) discharges. We estimated direct atmospheric deposition of forms of N, P, and organic C to the Patuxent River estuary based on analysis of bulk deposition near the Rhode River. During the wet year, most of the total terrestrial and atmospheric inputs of forms of N and P came from NPS discharges. During the dry year, 53% of the TNH4 + input was from atmospheric deposition and 58% of the NO3 − input was from PS discharges; NPS and PS discharges were about equally important in the total inputs of TN and TPO4 3−. During the entire 2-yr period, the Coastal Plain portion of the Patuxent basin delivered about 80% of the NPS water discharges to the estuary and delivered similar proportions of the NPS TNH4 +, TN, TOP, and TSS. The Coastal Plain delivered greater proportions of the NPS TON, TOC, Si, and TP (89%, 90%, 93%, and 95%, respectively) than of water, and supplied nearly all of the NPS TPO4 3− (99%). The Piedmont delivered 33% of the NPS NO3 − while delivering only 20% of the NPS water to the stuary. We used statistical models to infer the percentages of NPS discharges supplied by croplands, developed lands, and other lands. Although cropland covers only 10% of the Patuxent River basin, it was the most important source of most materials in NPS discharge, supplying about 84% of the total NPS discharge of NO3 −; about three quarters of the TPO4 3−, TOP, TP, and TSS; and about half of the TNH4 + and TN. Compared to developed land, cropland supplied a significantly higher percentage of the NPS discharges of NO3 −, TN, TPO4 3−, TOP, TP, and TSS, despite the fact development land covered 12% of the basin.

Evaluating the joint effects of climate and land use change on runoff and pollutant loading in a rapidly developing watershed

A better understanding of relationships between human activities and water chemistry is needed to identify and manage sources of anthropogenic stress in Great Lakes coastal wetlands. The objective of the study described in this article was to characterize relationships between water chemistry and multiple classes of human activity (agriculture, population and development, point source pollution, and atmospheric deposition). We also evaluated the influence of geomorphology and biogeographic factors on stressor-water quality relationships. We collected water chemistry data from 98 coastal wetlands distributed along the United States shoreline of the Laurentian Great Lakes and GIS-based stressor data from the associated drainage basin to examine stressor-water quality relationships. The sampling captured broad ranges (1.5-2 orders of magnitude) in total phosphorus (TP), total nitrogen (TN), dissolved inorganic nitrogen (DIN), total suspended solids (TSS), chlorophyll a (Chl a), and chloride; concentrations were strongly correlated with stressor metrics. Hierarchical partitioning and all-subsets regression analyses were used to evaluate the independent influence of different stressor classes on water quality and to identify best predictive models. Results showed that all categories of stress influenced water quality and that the relative influence of different classes of disturbance varied among water quality parameters. Chloride exhibited the strongest relationships with stressors followed in order by TN, Chl a, TP, TSS, and DIN. In general, coarse scale classification of wetlands by morphology (three wetland classes: riverine, protected, open coastal) and biogeography (two ecoprovinces: Eastern Broadleaf Forest [EBF] and Laurentian Mixed Forest [LMF]) did not improve predictive models. This study provides strong evidence of the link between water chemistry and human stress in Great Lakes coastal wetlands and can be used to inform management efforts to improve water quality in Great Lakes coastal ecosystems.

Costs of Meeting Water Quality Goals under Climate Change in Urbanizing Watersheds: The Case of Difficult Run, Virginia

Since sediment and nutrient concentrations vary with landuses in different climatic conditions, it is critical in understanding the connection between different landuses activities and water quality, and developing appropriate management strategies for a catchment.The objective of this paper is to assess the effects of climate and landuse activities on nutrient and sediment loads at 5 selected water quality monitoring stations in the Yarra River catchment of Victoria, Australia for 1994-2008 periods.A data-based technique was applied to achieve the above objective using long-term in-stream water quality data and other readily available tools.The methodology addressed the issues of selecting water quality stations, catchment disaggregation, identification of major landuse types, analysis of pollutant concentrations and loads in different climatic conditions, and suitable data-based method (regression model LOADEST) to estimate pollutant loadings.Climatic data were collected from the SILO climate database and the Bureau of Meteorology.Precipitation data from 16 stations and temperature data from 4 stations located in the Middle Yarra segment were collected for the period of 1980-2008.Daily streamflow and monthly water quality grab sample data of Total Suspended Solid (TSS), Total Nitrogen (TN) and Total Phosphorus (TP) were available for the 5 stations from Melbourne Water.ArcGIS 9.3 tool was used for catchment disaggregation and major landuse type identification using ASTER 30m global digital elevation model and landuse map (50m grid raster data collected from Australian Bureau of Agricultural and Resource Economics and Sciences).The water quality monitoring stations were selected based on data availability and dominant major landuse types (urban, agriculture and forest).The dominant landuse type in the tributary stations was either agriculture or urban where as in the main Yarra River stations; it was forest-agriculture mix type.There was an abrupt drop in rainfall after 1996 known as millennium drought in the catchment, and the most extreme rainfall event occurs in that drought period.The study period was categorised into wet, dry and average years based on rainfall for water quality analysis purposes.Since the correlations between the concentrations of TSS, TN, TP, and streamflow (TSS: 0.57-0.72;TN: 0.50-0.57and TP: 0.50-0.57except station 5) were high and statistically significant (p<0.01), a regression method based model LOADEST was used to estimate constituent loads from the grab sample data.The LOADEST model is well documented, and is accepted as a valid means of calculating constituent load from a limited number of water quality data.The LOADEST model performed well in estimating TSS, TN and TP loads.Coefficients of determination (R 2 ) for the regression models in LOADEST were greater than 0.84, 0.94 and 0.88 for TSS, TN and TP respectively at all stations.In general, TSS, TN and TP mean concentrations were higher in wet years than in the dry and average years, except at stations 2 and 3 where TN mean concentrations were higher in the average years.Also, TSS and TP mean concentrations were higher in the dry years than in the average years.This is due to the direct correlation of TSS and TP, and high runoff events.In addition, TSS, TN and TP mean concentrations were higher in the urban areas, and then in the agricultural areas.The four wet years (1995, 1996, 2000 and 2004) carried out on average 60% of TSS, 51% of TN and 53% of TP loadings in the monitoring stations.During the study period (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008), the highest export rates of TSS, TN and TP were from urban areas, and the lowest export rates of TSS and TP were from forest areas, and TN from agricultural areas.Overall, water quality and constituent concentrations were influenced by rainfall events and landuse types.

Recent concerns about excessive algal (Cladophora) growth in the nearshore area have prompted a comprehensive study of phosphorus concentrations and loads in the Milwaukee watershed (2000–2008). During this period, total phosphorus (TP) decreased slightly for Outer Harbor water monitoring Station 1 (OH-1) representing the confluence of the three rivers into the Outer Harbor; whereas TP remained the same or slightly increased for Outer Harbor water monitoring Station 2 (OH-2) near the Jones Island Water Reclamation Facility (WRF) outfall. Concentrations of TP at OH-2 (0.095±0.005 mg/L) are higher than at OH-1 (0.073±0.006 mg/L). Years with high rainfall and river discharge during May through June produce high daily and annual average TP loads. This appears to be caused by resuspension and erosion of sediments containing TP in the river beds. Jones Island WRF contributes 39,500 kg/year or less than 34% of the total load to the Harbor. An estimate of TP load to Lake Michigan from rivers is 76,500 kg/year (65.7%). Stepwise regression results show that total soluble phosphorus (TSP), total suspended solids (TSS), and biochemical oxygen demand (BOD), in that order, are important predictors of TP except for Station OH-2.

The Cisangkuy basin is part of the upstream Citarum sub-basin, which flows through the Bandung regency’s. total suspended solid (TSS), nitrogen (N), and phosphorus (P) in the Cisangkuy River are potentially polluted due to human activities like agriculture. This study aims to reveal the daily trend of total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP) at the Cisangkuy River, the upper Citarum in the period of March-May 2023. The study was conducted from March to May 2023 in the Cisangkuy sub-basin. The measured water quality parameters included total suspended solids, nitrogen, and phosphorus. Data were analyzed visually and statistically using MS Excel 2013. From the results of observations at rainfall observation stations, the intensity of rain at the study location tends to be low to moderate (0.5- 50 mm), with the highest intensity occurring in early May. Generally, this pattern is followed by the values from observations of water level TSS concentration at Lamajang and Kamasan tended to follow the rainfall pattern with concentration values that exceeded standard water quality criteria for river. TP concentrations followed the TSS pattern relatively with concentrations exceeding standard water quality criteria during some of the study period. TN concentrations at both study locations showed high value and still met the standard criteria. Water pollution control should be prioritized based on crucial characteristics that contribute significantly to pollution in the Cisangkuy basin.

Better management of water quality in streams, rivers and lakes requires precise and accurate estimates of different contaminant loads. We assessed four sampling frequencies (2days, weekly, fortnightly and monthly) and five load calculation methods (global mean (GM), rating curve (RC), ratio estimator (RE), flow-stratified (FS) and flow-weighted (FW)) to quantify loads of nitrate-nitrogen (NO3--N), soluble inorganic nitrogen (SIN), total nitrogen (TN), dissolved reactive phosphorus (DRP), total phosphorus (TP) and total suspended solids (TSS), in the Manawatu River, New Zealand. The estimated annual river loads were compared to the reference 'true' loads, calculated using daily measurements of flow and water quality from May 2010 to April 2011, to quantify bias (i.e. accuracy) and root mean square error 'RMSE' (i.e. accuracy and precision). The GM method resulted into relatively higher RMSE values and a consistent negative bias (i.e. underestimation) in estimates of annual river loads across all sampling frequencies. The RC method resulted in the lowest RMSE for TN, TP and TSS at monthly sampling frequency. Yet, RC highly overestimated the loads for parameters that showed dilution effect such as NO3--N and SIN. The FW and RE methods gave similar results, and there was no essential improvement in using RE over FW. In general, FW and RE performed better than FS in terms of bias, but FS performed slightly better than FW and RE in terms of RMSE for most of the water quality parameters (DRP, TP, TN and TSS) using a monthly sampling frequency. We found no significant decrease in RMSE values for estimates of NO3-N, SIN, TN and DRP loads when the sampling frequency was increased from monthly to fortnightly. The bias and RMSE values in estimates of TP and TSS loads (estimated by FW, RE and FS), however, showed a significant decrease in the case of weekly or 2-day sampling. This suggests potential for a higher sampling frequency during flow peaks for more precise and accurate estimates of annual river loads for TP and TSS, in the study river and other similar conditions.

본 연구에서는 시화호로 유입되는 다양한 비점오염원 중 도심유역을 흐르는 안산천 및 화정천과 산업지역인 반월산단 토구를 통한 강우유출수 내 총부유물질, 화학적산소요구량, 용존영양염, 총인 및 총질소 등의 비점오염물질의 유출특성 및 총유출부하량을 조사하였다. 조사지역 및 조사 시기에 따라 차이는 있으나 강우 시작 후 비점오염물질의 농도가 증가한 뒤 감소하는 경향을 보였다. 총부유물질의 평균농도는 안산천이 315 ㎎/L로 가장 높았으며 반월산단 토구에 비해 약 2~5배 정도 높았으나 화학적산소요구량, 총인 및 총질소의 평균농도는 반월산단 토구가 도심하천에 비해 높은 것으로 나타났다. 총부유물질은 화학적산소요구량 및 총인과 양의 상관성을 보였으며 용존영양염과는 음의 상관성을 나타냈다. 반월산단 토구를 통한 비점오염물질의 총유출량은 토구의 유역면적에 비례하였으며 가장 유역면적이 넓은 3토구에서의 비점오염물질의 유출량이 가장 높았다. 조사기간 내 약 30시간 동안 반월산단토구를 통하여 총부유물질 187,536 ㎏, 화학적산소요구량 17,118 ㎏, 총인 922 ㎏, 총질소 13,519 ㎏의 비점오염물질이 유출되는 것으로 나타났다. 반월공단 토구 유역면적은 전체 시화호 소유역 중 3%를 차지하는 것을 고려할 때 막대한 양의 비점오염물질이 별다른 처리과정 없이 시화호로 직접 유출되고 있음을 알 수 있었다. 이러한 강우시 비점 오염물질의 유출은 시화호 수질을 더욱 악화 시킬 것이기 때문에 비점오염원 관리 및 저감대책이 시급하게 요구되며 본 연구결과는 향후 시행예정인 시화호 연안오염총량제의 비점오염 최적관리기법 개발에 유용한 정보를 제공하고 있다.