Total Suspended Solids Loads Research Articles

Evaluating the hydrologic and water quality performance of novel infiltrating wet retention ponds

Abstract Wet retention ponds temporarily store and slowly release stormwater to mitigate peak flow rates and remove particulate-bound pollutants. However, with sandy underlying soils, wet retention ponds may provide additional benefits through infiltration, thereby recharging groundwater and supporting baseflow in streams. Current design guidance often requires lining wet ponds to prevent infiltration; however, modern stormwater management strategies recommend maximizing runoff volume reduction through infiltration. Two infiltrating wet retention ponds in Fayetteville, NC, USA, were monitored for one year to assess volume reduction, peak flow mitigation, and water quality. In some months, 100% of stormwater runoff infiltrated and evaporated, with cumulative annual volume reductions of 60 and 51% for the two ponds. For events up to 76 mm (equivalent to the local 1-yr, 24-hr storm), measured peak flow reductions were similar to those of typical (non-infiltrating) wet ponds (median 99% reduction). Dissolved nitrogen species, total and dissolved phosphorus, and total suspended solids (TSS) concentrations were significantly reduced in both ponds; mean percent reductions were greater than 30% for each of these pollutants. Effluent concentrations were on par with typical (non-infiltrating) wet ponds previously monitored in North Carolina. Due to the aforementioned runoff reduction, nutrient and TSS loads were reduced by (at minimum) 35 and 67%, respectively. Infiltrating wet ponds were able to meet both peak flow and volume mitigation goals, suggesting that they could be a common tool in regions with sandy soils.

Water quality of an integrated crop–livestock system in the northern Great Plains

AbstractImpacts of integrated crop–livestock (ICL) systems on water quality have not been well studied. Water quality parameters were quantified for two 30‐min rainfall simulations in wheat (Triticum aestivum L.)–cover crop, cover crop, and rangeland grass control phases of a long‐term ICL study site in Mandan, ND, in 2017 and 2018. Both pre‐graze and post‐graze simulations were conducted. Nitrate‐N (NO3−–N), nitrite‐N (NO2−–N), ammonia‐N (NH4+–N), phosphate‐P (PO43−–P), and total suspended solid (TSS) concentrations and loads were evaluated in surface runoff water, along with concentrations of NO3−–N, NO2−–N, NH4+–N, and PO43−–P in infiltration water. Non‐parametric ranked two‐way analysis of variance was used to evaluate differences for vegetation type and grazing as fixed effects, with year as a random effect. Surface runoff concentrations of NO3−–N and NH4+–N were significantly different with cover crop and wheat phases being greater than grass. A grazing effect was also observed with pre‐graze significantly greater than post graze for NO2−–N, NH4+–N, PO43−–P, and TSS surface runoff concentrations. For infiltration water concentrations, similar significant effects of vegetation type were observed for NO3−–N and PO43−–P, while pre‐graze was also greater than post‐graze for NO2−–N and PO43−–P. Due to variable runoff volumes, no significant differences were observed for loads of any parameters. Minimal runoff volumes (0–6.7 L) and significant vegetation and grazing effects in nutrient infiltration water concentrations highlight the importance of infiltration in such studies, particularly at sites in the northern Great Plains.

Mercury increase in Lake Champlain fish: links to fishery dynamics and extreme climatic events.

Mercury concentrations in Lake Champlain fish increased (2011-2017) for the first time in more than two decades. The increase, however, was not consistent among species or throughout the lake. Mercury concentrations in smallmouth bass and yellow perch from the three Main Lake segments increased significantly while concentrations in the eastern portions of the lake (Northeast Arm and Malletts Bay) remained unchanged or decreased; mercury concentrations in white perch remained unchanged. Factors examined to explain the increase included: atmospheric deposition, lake temperature, chlorophyll-a, fishery dynamics, lake flooding and loading of total suspended solids (TSS). This paper examines how each factor has changed between study periods and the spatial variability associated with the change. We hypothesize fishery dynamics, flooding and TSS loading may be partially responsible for the increase in fish mercury. Both growth efficiency and biomass of fish suggest mercury concentrations would increase in the Main Lake segments and decrease in the eastern portion of the lake. Additionally, two extreme climate events in 2011 resulted in extensive flooding and a four-fold increase in annual TSS loading, both potentially increasing biotic mercury with the impact varying spatially throughout the lake. Changes to the fishery and disturbance caused by extreme climatic events have increased biotic mercury and the processes responsible need further study to identify possible future scenarios in order to better protect human and wildlife health.

Analysis of load variation on chicken slaughterhouse waste water treatment using GAS-SBR

In general, chicken slaughterhouses have capacity of slaughtering more than 40,000 chickens per day so its produce a high waste water. It takes sewage treatment appropriate technology, Granular Aerobic Sludge which use Sequencing Batch Reactor (GAS-SBR) due to the high of BOD and COD. The purpose of this research was to explore GAS ability in decreasing parameter of COD, BOD, TSS and ammonia. The initial concentration COD influent was 6,406.4 mg/L then it was varied into three concentrations were 6,144 mg/L (100%), 4,608 mg/L (75%) and 3,072 mg/L (50%) of diluted pure water. As the result with four hours’ aeration time, the highest removal of 100% BOD load was 56.25% and an effluent was 1,400 mg/L. The highest removal of 50% COD load was 75% and an effluent was 768 mg/L. The highest removal of 100% TSS load was 36.73% an effluent was 1.79 mg/L. And the highest removal of 75% Ammonia load was 67.91% and an effluent was 1.11 mg/L. The parameter for the TSS and ammonia have meet the quality ministry environment no.5 2014 law for slaughterhouses, while the BOD and COD parameters are exceeding the standards due to its high organic content.

Evaluating the Impact of Climate Change on Water Quality and Quantity in an Urban Watershed Using an Ensemble Approach

Considerable efforts are underway to restore watersheds and estuaries downstream impacted by urban development; however, climate change (CC) may be undermining them. Current methods are limited in their ability to predict hydrology and water quality with CC and assess its effect on the efficiency of stormwater control measures (SCMs). We developed a method using downscaled global climate models (GCMs) from the Coupled Model Intercomparison Project Phase 5 (CMIP5) to project precipitation and temperatures; these were used to force a Storm Water Management Model (SWMM). Three scenarios, a historical and two Representative Concentration Pathways (RCP 4.5 and 8.5) with five GCMs, were used to produce ensemble results. All GCMs in both RCP scenarios projected increases in precipitation and temperature compared to historical conditions. Both RCPs exhibited their largest increases in precipitation, streamflow, total suspended solids (TSS), total nitrogen (TN), and total phosphorous (TP) loads in the winter, summer exhibited the largest increase in temperature. Median loads of TSS, TN, and TP increased 3.1%, 2.5%, and 9.9%, respectively, for RCP 4.5, and increased 3.8%, 3.1%, and 10.4%, respectively, for RCP 8.5. Median reductions in TSS, TN, and TP SCM efficiency for RCP 4.5 were projected to be 6%, 7%, and 11%, respectively; and 11%, 12%, and 17% for RCP 8.5, respectively. Thus, it is likely that additional efforts will be needed to meet water quality goals in the future. Methods such as these can help create climate resilient watershed improvement strategies and guide urban stormwater planning against likely future changes as a result of CC.

Responses of river discharge and sediment load to climate change in the transboundary Mekong River Basin

AbstractClimate change is expected to alter streamflow and sediment load in the transboundary Mekong River Basin (MRB), thereby affecting aquatic ecosystem and people’s livelihoods. Thus, future decisions on sustainable management of water resources in the basin should take climate change impact into consideration. In this study, the responses of river discharge and sediment (total suspended sediment [TSS]) load to future climate change in the transboundary MRB have been investigated. The Soil and Water Assessment Tool (SWAT) model is used as a simulation tool, which has been carefully calibrated and validated against the observation data in the period of 1982–2005 before applying to evaluate the impact of climate change scenarios for the near‐future period of 2016–2040. The climate change scenarios, which are acquired from four different Regional Climate Models (RCMs) downscaled from the Hadley Centre Global Environmental Model version 2‐Atmosphere (HadGEM2‐AO), are applied in the present study. In regard to the effect of changing climate, the annual river discharge and TSS load are forecasted to rise from 3.35 to 9.13% and from 7.45 to 13.15%, respectively. Generally, the TSS loading projection varies larger than the streamflow projection concerning changing climate. The findings here are also agreed with the conclusions of previous investigations on the future impacts of changing climate in the MRB.

The effect of sampling frequency and strategy on water quality modelling driven by high-frequency monitoring data in a boreal catchment

With conventional water quality monitoring based on grab sampling, usually carried out once a month, it is quite challenging to obtain reliable sediment and nutrient loading estimates, which is a pre-requisite for testing of water quality models. Despite the growing availability of high-frequency water quality monitoring data obtained by using modern sensors, their use in the calibration of water quality models is still limited. The main objective of this study is to evaluate six years of continuous, high-frequency water quality monitoring data set from a case study carried out in a medium-sized, boreal catchment in southern Finland to be used as a source for the calibration and testing of the Soil & Water Assessment Tool (SWAT). This objective is accomplished by developing a set of ‘sub-sampling’ scenarios focused on quantifying the effect of the sampling frequency (12 vs. 26 samples per year) and strategy (regular vs. flow-proportional sampling) on the model performance and output uncertainty. The goodness-of-fit of the model calibrated against high-frequency data (‘benchmark’), evaluated using the Kling-Gupta Efficiency index for total suspended solids (TSS), nitrate and total nitrogen (NO3-N and TN) and total phosphorus (TP) daily loads ranged between 0.76 and 0.83 (0.69 and 0.73 in validation period). Overall, the model calibrated against low-frequency data performed worse when evaluated against high-frequency data and compared with the benchmark model for each of the studied water quality parameters. The results show that increasing the sampling frequency from 12 to 26 samples per year leads to an improvement in the model performance, particularly for TSS and TP loads. In contrast to the sampling frequency, the evidence for the effect of the sampling strategy on the model performance was much weaker. The model output uncertainty due to different realizations of sub-sampling scenarios was high for four analysed output indices: basin-averaged, long-term average annual values of soil erosion rate, denitrification rate, NO3-N yield and soluble P yield. This study demonstrates that more attention should be paid to the calibration data as a source of uncertainty in model predictions. It also provides evidence for either a wider adoption of modern sensors providing high-frequency data, or for increasing the grab sampling frequency to reduce the uncertainty of loading estimates, particularly in rivers with flashy flow regime such as the Vantaanjoki River.

A game theoretical low impact development optimization model for urban storm water management

Abstract This study presents a novel framework to optimize Low Impact Development (LID) practices for urban storm water management. First, the Storm Water Management Model (SWMM) model was executed for different possible scenarios of input parameters and various LIDs to simulate runoff volume, Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS) loads. Next, a neural network (MLP-ANN) was trained and validated, as a surrogate model, against the set of inputs and output variables from the SWMM model simulations. The inherent uncertainties in the rainfall-runoff modeling were accounted for using a Nonlinear Interval Number Programming (NINP) model, and stakeholders' interactions are considered using a leader-follower game model. Velenjak urban watershed in Tehran, Iran, with four key stakeholders was considered as the study area. Tehran Municipality is the financial service provider that makes the first decision the leader-follower structure, and is considered as the leader with the priority of minimizing LIDs’ construction and maintenance costs. Tehran Department of Environmental Protection, Tehran Regional Water company, and Tehran Province Water and Wastewater company are the main followers in the decision making structure in the study area. This game theoretical framework yields several Pareto optimal solutions given the conflicting utilities of various players, and a Multi Criteria Decision Making procedure – i.e. PROMETHEE model – selects the most preferred compromised option. Fourteen weighting scenarios were considered in the PROMETHEE model to determine the compromise solution among the 52 solutions on the trade-off curve. The novelty of this study lies in using a nonlinear interval conflict resolution multi-objective optimization model for urban storm water management based on a leader-follower game. The proposed methodology warrants BOD and TSS loads, as well as storm water volume, are all reduced, with the highest reductions of 93, 86 and 90 percent, respectively. Results testify to the efficacy of the proposed model for urban storm water management.

Impact of Urban Stormwater Runoff on Cyanobacteria Dynamics in A Tropical Urban Lake

Worldwide, eutrophication and cyanobacteria blooms in lakes and reservoirs are a great concern for water resources management. Coupling a catchment hydrological model and a lake model has been a strategy to assess the impact of land use, agricultural practices and climate change on water quality. However, research has mainly focused on large lakes, while urban reservoirs and their catchments, especially in tropical regions, are still poorly studied despite the wide range of ecosystem services they provide. An integrated modelling approach coupling the hydrological model Storm Water Management Model SWMM and the lake ecological model DYRESM-CAEDYM is proposed for Lake Pampulha (Brazil). Scenarios of increased imperviousness of the catchment and of reduction in the load of nutrients and total suspended solids (TSS) in dry weather inflow were simulated. Runoff water quality simulations presented a fair performance for TSS and ammonium (NH4+) while the dynamics of total phosphorus (TP) and nitrate (NO3−) were poorly captured. Phytoplankton dynamics in the lake were simulated with good accuracy (Normalized Mean Absolute Error, NMAE = 0.24 and r = 0.89 in calibration period; NMAE = 0.55 and r = 0.54 in validation period). The general trends of growth, decline and the magnitude of phytoplankton biomass were well represented most of the time. Scenario simulations suggest that TP reduction will decrease cyanobacteria biomass and delay its peaks as a consequence of orthophosphate (PO43−) concentration reduction in the lake surface layers. However, even decreasing TP load into Lake Pampulha by half would not be sufficient to achieve the water quality objective of a maximum concentration of 60 µg chla L−1. Increased imperviousness in the catchment will raise runoff volume, TSS, TP and NO3− loads into Lake Pampulha and promote greater cyanobacteria biomass, mainly in the beginning of the wet season, because of additional nutrient input from catchment runoff. Recovering Lake Pampulha water quality will require the improvement of the sanitation system. The lake water quality improvement will also require more sustainable and nature-based solutions for urban drainage in order to reduce non-point pollution through infiltration and retention of stormwater and to enhance natural processes, such as chemical sorption, biodegradation and phytoremediation. The integrated modelling approach here proposed can be applied for other urban reservoirs taking advantage of existing knowledge on Lake Pampulha.

Utilizing SWMM and GIS to identify total suspended solids hotspots to implement green infrastructure in Lucas County, OH

AbstractThis research demonstrates that modeling approaches can be used to identify priority areas to implement green stormwater infrastructure (GSI) resulting in improved water quality outcomes. The total suspended solids (TSS) washoff loading from watersheds in Lucas County, Ohio due the municipal separate storm sewer system (MS4) was reported based on 2015 rain data. The highest TSS loading was experienced in the winter season in 80% of the watersheds. Subcatchments with the highest predicted TSS washoff loadings were identified as priority areas or hotspots. In subsequent simulations, GSI implementation in hotspots improved water quality by more than twofold as compared to indiscriminate implementation of GSI. These hotspot maps are being used by regional stormwater stakeholders to focus their urban water quality efforts and to identify site characteristics that may be used to inform environmental policy.

Drying system of sewage sludge - wastewater treatment plant in Gdansk

The 'Wschod' wastewater treatment plant, with average flow of sewage equal to 110 000 m3 /day, is the biggest plant in the voyevodship of Gdansk. The volume of treated sewage amounts to 60% of the total quantity of sewage in the community of Gdansk. Until 1993 treatment of sewage was carried out in the facilities that ensured only mechanical removal of contaminants. Poor sanitary conditions of the coastal water of the Gulf of Gdansk was the main reason for introducing primary chemical precipitation (dephosphatation), using coagulant called PIX. Chemical process of precipitation resulted first of all in effective elimination of phosphates, between 77.6 - 81.8% during the period 1993-95. The removal of organic matter also improved. Due to this the load of total suspended solids in 1995 decreased by 49.1% in comparison to 1992. The removal of organic matter expressed as BOD5 and CODcr equaled respactively 34.7% and 32,8%. However, after the introduction of chemical precipitation, the increase of the sludgefrom 600 m3 /d (before introducing of chemical precipitation) to 1100 m3 /d (after introducing of chemical precipitation) was observed. For this reason it was decided to provide support for the coagulation process with anionic polimer. The anionic polimer was introduced in 1995, which resulted in the decrease of the total production of sludge to the amount of 600 - 650 m3 /d.
 Modernization of the WWTP also caused the necessity of replacing the formerly used method of dewatering on drying beds (total area of 7.4 ha) by mechanical dewatering in centrifuges of capacity of 8-25 m3 /h and maximum load of sludge of 800 kg DS/h. As a result the operation of the treatment plant became easier, though the problems with utilization of the sludge are not completely solved yet.

Water quality characterization of storm and irrigation runoff from a container nursery

Commercial nurseries grow specialty crops for resale using a variety of methods, including containerized production, utilizing soilless substrates, on a semipervious production surface. These “container” nurseries require daily water application and continuous availability of mineral nutrients. These factors can generate significant nutrients [total nitrogen (TN), and total phosphorus (TP)] and sediment [total suspended solids (TSS)] in runoff, potentially contributing to eutrophication of downstream water bodies. Runoff is collected in large ponds known as tailwater recovery basins for treatment and reuse or discharge to receiving streams. We characterized TSS, TN, and TP, electrical conductivity (EC), and pH in runoff from a 5.2 ha production portion of a 200-ha commercial container nursery during storm and irrigation events. Results showed a direct correlation between TN and TP, runoff and TSS, TN and EC, and between flow and pH. The Storm Water Management Model (SWMM) was used to characterize runoff quantity and quality of the site. We found during irrigation events that simulated event mean concentrations (EMCs) of TSS, TN, and TP were 30, 3.1 and 0.35 mg·L−1, respectively. During storm events, TSS, TN and TP EMCs were 880, 3.7, and 0.46 mg·L−1, respectively. EMCs of TN and TP were similar to that of urban runoff; however, the TSS EMC from nursery runoff was 2–4 times greater. The average loading of TSS, TN and TP during storm events was approximately 900, 35 and 50 times higher than those of irrigation events, respectively. Based on a 10-year SWMM simulation (2008–2018) of runoff from the same nursery, annual TSS, TN and TP load per ha during storm events ranged from 9230 to 13,300, 65.8 to 94.0 and 9.00 to 12.9 kg·ha−1·yr−1, respectively. SWMM was able to characterize runoff quality and quantity reasonably well. Thus, it is suitable for characterizing runoff loadings from container nurseries.

Emerging contaminants in sediment core from the Iron Gate I Reservoir on the Danube River

The Iron Gate I Reservoir is the largest impoundment on the Danube River. It retains >50% of the incoming total suspended solids load and the associated organic contaminants. In the sediment core of the Iron Gate I Reservoir we report the presence and fate of four classes of emerging contaminants (pharmaceuticals, pesticides, steroids and perfluorinated compounds), predominantly not covered by the EU monitoring programs, but considered as future candidates. Based on contaminant's partitioning behavior in the water/sediment system and the suspected ecotoxicological potential asserted from the literature data, the risk of recorded concentrations for sediment-dwelling organisms was discussed. The high anticipated risk was associated with antibiotics sulfamethoxazole and erythromycin, and pesticides linuron and carbendazim (banned in the EU, but still approved for use in the investigated area) and malathion. This indicated the need for better control of release of these compounds into the river, and implied their inclusion in future regular monitoring. Higher concentrations of pharmaceuticals and most pesticides and sterols were recorded in the fragment of allochthonous coarser sediment, assumed to have entered the reservoir during a high discharge event. Only one perfluorinated compound was recorded in the upper part of the sediment core. The vertical concentration profiles of pesticides propazine and malathion indicated their uniform source, most likely atmospheric transport and deposition of particles deriving from agricultural land.

Landscape characteristics driving spatial variation in total phosphorus and sediment loading from sub-watersheds of the Nottawasaga River, Ontario

Eutrophication from agricultural runoff is a global problem, often resulting in formation of anoxic zones in receiving water bodies. The Nottawasaga River Watershed (NRW) is dominated by agricultural land-use, and drains into Nottawasaga Bay, Georgian Bay (Lake Huron). A fundamental feature of the NRW is the Minesing Wetlands, a Ramsar site and the largest inland wetland in southern Ontario. We used total phosphorus (TP) concentration-discharge relationships to estimate annual loading from six sub-watersheds and compared these against published models, which did not offer a way to account for the unique properties of the Minesing Wetlands. We developed predictive loading models specifically for the NRW to account for these characteristics, which accurately predict daily summer base-flow TP (r2 = 0.76, p = <0.0001) and total suspended solids (TSS; r2 = 0.65, p = <0.0001) loads for 11 subwatersheds using geomorphic and land-cover variables. Drainage area and % pasture land were the most significant predictive variables driving spatial variability in TP and TSS loading rates among subwatersheds. The positive relationship between TP and % wetland (r2 = 0.22, p = 0.0063) also suggested that the Minesing Wetlands are a source of nutrients to the Nottawasaga River. Watershed geomorphology (e.g. slope) was a good predictor of land cover, and produced accurate loading estimates. This study is the first to offer a new approach to predict TP and TSS loading rates during the growing season using readily available geospatial data.

Catchment management influence on the magnitude of the total solids load conveyed by the stormwater sewer system – a comparative case study

The aim of the investigations was to make a comparative analysis of TSS concentration and variability in TSS loads as well as to analyse first flush phenomena. That issue is related to the characteristics of two urban catchments located in the city of Kielce. The runoff events observed in the period of investigations (years 2009 – 2016) showed a great diversity. The analyses performed for the study revealed substantial differences in the values of TSS concentration and loads in stormwater from the catchments of concern. The highest TSS concentration in the stormwater for the catchment located at the city outskirts was 252 mg.dm-3, whereas for the catchment in the city centre that value was almost 30 – fold higher and amounted to 7432 mg.dm-3. The analysis of the runoff first flush with respect to the mass of total solids in individual rainfall events showed substantial differences in the course of the process depending on the type of catchment management. In the densely built-up area, the initial 25% and 30% of the volume of runoff transported 25-41% and 30-48% of the solids mass, respectively. In the other catchment, with low and sparsely located buildings, the maximum values of TSS mass were considerably higher and amounted to 22-83% and 28-87%.

Analysis of Rainfall Runoff Pollution Characteristics and Non-point Source Pollution Simulation

In view of the impact of non-point source pollution on the quality of water environment, the campus area of Shenyang Jianzhu University was taken as the research object, and the empirical model---SCS runoff curve number method is used to estimate the annual load of different runoff pollutants generated on the underlying surface of the roof and the underlying surface of the pavement. The results show that the load TSS of annual runoff pollutants in the campus is 38,975.66 kg/a, COD is 10,102.12 kg/a, TN is 454.78 kg/a, TP is 49.1 kg/a, and NH3-N is 171.88 kg/a; In 2015, the annual runoff pollutant TSS loading was 38189.14kg/a, COD was 19293.5kg/a, TN was 833.68kg/a, TP was 77.59kg/a, and NH3-N was 567.89kg/a.

Scale-dependent impacts of urban and agricultural land use on nutrients, sediment, and runoff

We coupled a spatially-explicit land use/land cover (LULC) change model, Dinamica EGO, (Environment for Geoprocessing Objects), with the Chesapeake Bay Watershed Model (CBWM) to project the impact of future LULC change on loading of total nitrogen (TN), total phosphorous (TP) and total suspended solids (TSS) as well as runoff volume in the watersheds surrounding Virginia's Shenandoah National Park in the eastern United States. We allowed for the dynamic transition of four LULC classes, Developed, Forest, Grasses (including both pasture and hayfields) and Crops. Using 2011 as a baseline scenario and observed differences in LULC between 2001 and 2011, we estimated the temporal and spatial patterns of LULC change as influenced by physiographic and socio-economic drivers 50 years in the future (2061). Between transitions of the four LULC classes, the greatest absolute change occurred between the gain in total Developed land and loss in total Forest. New Developed land was driven primarily by distance to existing Developed land and population density. Major findings on the effect of LULC change on watershed model outputs were that: the impact of LULC change on pollutant loading and runoff volume is more pronounced at finer spatial scales; increases in the area of Grasses produced the greatest increase in TP loading, while loss of Forest increased TN, TSS, and runoff volume the most; and land-river segments with a greater proportion of Developed or a smaller proportion of Forest in the 2011 scenario experienced a greater change in runoff than other land-river segments. Results of this study illustrate the potential impact of projected LULC change on nutrient and sediment loads which can adversely impact water quality. Studies like this contribute to a broader understanding of how ecosystem services such as fresh water respond to LULC change, information relevant to those in planning and watershed management.

The Green Bay saga: Environmental change, scientific investigation, and watershed management

Abstract The Green Bay watershed, draining a total area of approximately 40,468 km2, comprises about a third of the Lake Michigan drainage. In the early years, fur trade was the dominant economic activity within the watershed. Later, when timber harvesting, papermaking, and agriculture came on the scene in the 19th and early 20th centuries, major environmental changes occurred in a relatively short period of time. Nutrient and sediment loadings, accompanied by organic wastes from sawmills and paper mills, resulted in a pollutant overload in the Fox River and in the eutrophication of the waters of lower Green Bay. Citizen complaints about these severely degraded conditions initiated a period of scientific investigation. Starting slowly with a few studies and surveys in the first half of the 20th century, serious investigatory work began at mid-century with support from the University of Wisconsin Sea Grant Institute. Examples of topics that have been investigated since then with support from numerous sources are: biological oxygen demand (BOD), phosphorus and total suspended solids loads, trophic status and food chain efficiencies, coastal wetland characterization, dynamics of the benthic layer, algae and abiotic solids, phosphorus cycling and mass balance, PCBs, seasonal hypoxia, and climate change impacts. These studies have provided the scientific foundation for government-led programs such as the Green Bay Remedial Action Program, the PCB clean-up program, and the TMDL program. Progress has been made—reduction in BOD is an example—but a fuller rehabilitation of this large-scale ecosystem remains an elusive goal. The saga goes on.

Distribution-Based Calibration of a Stormwater Quality Model

Stormwater quality models are usually calibrated using observed pollutographs. As current models still rely on simplified model concepts for pollutant accumulation and wash-off, calibration results for continuous pollutant concentrations are highly uncertain. In this paper, we introduce an innovative calibration approach based on total suspended solids (TSS) event load distribution. The approach is applied on stormwater quality models for a flat roof and a parking lot for which reliable distributions are available. Exponential functions are employed for both TSS buildup and wash-off. Model parameters are calibrated by means of an evolutionary algorithm to minimize the distance between a parameterized lognormal distribution function and the cumulated distribution of simulated TSS event loads. Since TSS event load characteristics are probabilistically considered, the approach especially respects the stochasticity of TSS buildup and wash-off and, therefore, improves conventional stormwater quality calibration concepts. The results show that both experimental models were calibrated with high goodness-of-fit (Kolmogorov–Smirnov test statistic: 0.05). However, it is shown that events with high TSS event loads (&gt;0.8 percentile) are generally underestimated. While this leads to a relative deviation of −28% of total TSS loads for the parking lot, the error is compensated for the flat roof (+5%). Calibrated model parameters generally tend to generate wash-off proportional to runoff, which is indicated by mass-volume curves. The approach itself is, in general, applicable and creates a new opportunity to calibrate stormwater quality models especially when calibration data is limited.

Evaluation of two statistical approaches for estimating pollutant loads at adjacent combined sewer overflow structures.

Quantifying pollutant loads from combined sewer overflows (CSOs) is necessary for assessing impacts of urban drainage on receiving water bodies. Based on data obtained at three adjacent CSO structures in the Louis Fargue catchment in Bordeaux, France, this study implements multiple linear regression (MLR) and random forest regression (RFR) approaches to develop statistical models for estimating emitted loads of total suspended solids (TSS). Comparison between hierarchical clustering selection and random selection of CSO events for model calibration is included in model development. The results indicate that selection of the model's explanatory variables depends on both the type of approach and the CSO structure. By using the cluster technique to select representative events for model calibration, model predictability is generally improved. For the available dataset, MLR may have advantages over RFR in terms of verification performance and lower range of error due to splitting events for calibration and verification. But RFR model uncertainty bands are considerably narrower than the MLR ones.