Total Suspended Solids Loads Research Articles

Estimating Suspended Solids from Turbidity in the Robeson Creek, NC Watershed

AbstractThe purpose of this project was to assess the effect of estimating total suspended solids (TSS) concentrations from turbidity on TSS loads for streams in the Robeson Creek watershed. Discharge was monitored continuously and base‐flow grab and storm event composite samples were collected and analyzed for TSS and turbidity from five sites during five years of monitoring. For base‐flow samples, the TSS‐turbidity relationship for all five sites was poor indicating that TSS concentrations in base flow cannot be estimated from a TSS‐turbidity relationship. To test the effect of analyzing fewer samples, TSS from every third and the first 20 samples collected from each site was used to develop TSS‐turbidity relationships. In addition, the TSS‐turbidity relationship developed from the most downstream site was used to estimate TSS concentrations from turbidity measured at the other four sites. For four of the five sites, analyzing every third sample for TSS and using the TSS‐turbidity relationship to estimate the missing TSS concentrations would result in mean TSS loads that were not significantly different from the observed. Using the TSS‐turbidity relationship from the outlet to estimate TSS from turbidity measured at the other four sites resulted in significantly different mean TSS loads at three of the four sites. These results indicate that estimating TSS concentrations from turbidity using a TSS‐turbidity relationship developed from a subset of the overall dataset should be done with great caution.

Modelling the effects of changes in rainfall event characteristics on TSS loads in urban runoff

AbstractThe effect of changes in rainfall event characteristics on urban stormwater quality, which was described by total suspended solids (TSS), was studied by means of computer simulations conducted with the Storm Water Management Model for a climate change scenario for northern Sweden. The simulation results showed that TSS event loads depended mainly on rainfall depth and intensity, but not on antecedent conditions. Storms with low‐to‐intermediate depths and intensities showed the highest sensitivity to changes in rainfall input, both for percentage and absolute changes in TSS wash‐off loads, which was explained by the contribution of pervious areas and supply limitations. This has significant implications for stormwater management, because those relatively frequent events generally carry a high percentage of the annual pollutant load. Copyright © 2013 John Wiley & Sons, Ltd.

Comparison of runoff quantity and quality under annual cropping and forages

Conversion from annual cropping to perennial forages may be a beneficial management practice (BMP) to reduce runoff quantity and improve surface water quality. Runoff variables were determined in two 30 ha producer's fields over 4 years (2004–2007) using a rainfall simulator. Field 1 was cropped to barley (Hordeum vulgare L.) in 2004 and then an alfalfa (Medicago sp.) and grass mix used for hay and fall grazing was grown from 2005 to 2007. Field 2 was cropped to barley-winter triticale (WT) (Triticosecale Rimpavi Wittm.) in 2005 and alfalfa-grass for hay was grown in 2006 and 2007. Runoff variables measured were runoff depth, electrical conductivity, and concentrations and loads of total suspended solids, total N, total P, and dissolved reactive P fractions. Conversion from barley to alfalfa-grass for hay and fall grazing in Field 1 resulted in reductions for only 13% of the 10 runoff variables, 33% of runoff variables were unaffected, and 53% of variables were significantly increased. Conversion from barley-WT to alfalfa-grass used for hay in Field 2 significantly reduced 25% of the 10 variables, 40% were unaffected, and 35% were significantly increased. Converting from annual cropping to forage did not improve the majority of runoff variables.

Measuring bluff erosion part 2: pairing aerial photographs and terrestrial laser scanning to create a watershed scale sediment budget

ABSTRACTEffectively managing and reducing high suspended sediment loads in rivers requires an understanding of the magnitude of major sediment sources as well as erosion and transport processes that deliver excess fine sediments to the channel network. The focus of this research is to determine the magnitude of erosion from tall bluffs, a primary sediment source in the 2880 km2 Le Sueur watershed, Minnesota, USA. We coupled analyses of seven decades of aerial photographs with four years of repeat terrestrial laser scanning (TLS) to determine erosion rates on bluffs. Together, these datasets provide decadal‐scale retreat rates throughout the entire watershed and high‐resolution geomorphic change detection on a subset of bluffs to both constrain erosion rates and document how environmental conditions affect bluff retreat. Erosion rates from aerial photographs and TLS were extrapolated from 243 and 15 measured bluffs, respectively, to all 480 bluffs in the Le Sueur watershed using multiple techniques to obtain estimates of sediment loading from these features at the watershed‐scale. Despite different spatial and temporal measurement scales, the aerial photograph and TLS estimates yielded similar results for bluff retreat rate and total mass of sediment derived from bluffs, with bluffs in the Le Sueur watershed yielding 135 000 ± 39 000 Mg/yr of fine sediment. Comparing this value to the average annual total suspended solids (TSS) load determined from gauging from 2000 to 2010, we determined that bluffs comprise 57 ± 16% of the total TSS load, making bluffs the single most abundant fine sediment source in the basin. Copyright © 2012 John Wiley & Sons, Ltd.

Crop Residue Biomass Effects on Agricultural Runoff

High residue loads associated with conservation tillage and cover cropping may impede water flow in furrow irrigation and thus decrease the efficiency of water delivery and runoff water quality. In this study, the biomass residue effects on infiltration, runoff, and export of total suspended solids (TSS), dissolved organic carbon (DOC), sediment-associated carbon (TSS-C), and other undesirable constituents such as phosphate (soluble P), nitrate (), and ammonium () in runoff water from a furrow-irrigated field were studied. Furrow irrigation experiments were conducted in 91 and 274 m long fields, in which the amount of residue in the furrows varied among four treatments. The biomass residue in the furrows increased infiltration, and this affected total load of DOC, TSS, and TSS-C. Net storage of DOC took place in the long but not in the short field because most of the applied water ran off in the short field. Increasing field length decreased TSS and TSS-C losses. Total load of , , and soluble P decreased with increasing distance from the inflow due to infiltration. The concentration and load of P increased with increasing residue biomass in furrows, but no particular trend was observed for and . Overall, the constituents in the runoff decreased with increasing surface cover and field length.

High Pollutant Removal Efficacy of a Large Constructed Wetland Leads to Receiving Stream Improvements

Hewletts Creek, in Wilmington, North Carolina, drains a large suburban watershed and as such is affected by high fecal bacteria loads and periodic algal blooms from nutrient loading. During 2007, a 3.1-ha wetland was constructed to treat stormwater runoff from a 238-ha watershed within the Hewletts Creek drainage. A rain event sampling program was performed in 2009-2010 to evaluate the efficacy of the wetland in reducing pollutant loads from the stormwater runoff passing through the wetland. During the eight storms sampled, the wetland greatly moderated the hydrograph and retained and/or removed 50 to 75% of the inflowing stormwater volume. High removal rates of fecal coliform bacteria were achieved, with an average load reduction of 99% and overall concentration reduction of >90%. Particularly high (>90%) reductions of ammonium and orthophosphate loads also occurred, and lesser but still substantial reductions of total phosphorus (89%) and total suspended solids loads (88%) were achieved. Removal of nitrate was seasonally dependent, with lower removal occurring in cold weather and a high percentage (90%+) of nitrate load removal occurring in the growing season when water temperature exceeded 15°C. Long-term before-and-after sampling in downstream Hewletts Creek proper showed that, after wetland construction, statistically significant average decreases of 43% for nitrate, 72% for ammonium, and 59% for fecal coliform bacteria were realized. Wetland features contributing to the high pollutant control efficacy included available space for a large wetland, construction of deep forebays, and a dense and diverse aquatic and shoreline plant assemblage.

Influence of Sampling Frequency on Estimation of Annual Total Phosphorus and Total Suspended Solids Loads1

Abstract: The determination of sediment and nutrient loads is typically based on the collection and analysis of grab samples. The frequency and regularity of traditional sampling may not provide representation of constituent loading, particularly in systems with flashy hydrology. At two sites in the Little Bear River, Utah, continuous, high‐frequency turbidity was used with surrogate relationships to generate estimates of total phosphorus and total suspended solids concentrations, which were paired with discharge to estimate annual loads. The high frequency records were randomly subsampled to represent hourly, daily, weekly, and monthly sampling frequencies and to examine the effects of timing, and resulting annual load estimates were compared to the reference loads. Higher frequency sampling resulted in load estimates that better approximated the reference loads. The degree of bias was greater at the more hydrologically responsive site in the upper watershed, which required a higher sampling frequency than the lower watershed site to achieve the same level of accuracy in estimating the reference load. The hour of day and day of week of sampling impacted load estimation, depending on site and hydrologic conditions. The effects of sampling frequency on the determination of compliance with a water quality criterion were also examined. These techniques can be helpful in determining necessary sampling frequency to meet the objectives of a water quality monitoring program.

Water Quality Effects of Herded Stream Crossings by Domestic Sheep Bands

Livestock impacts on total suspended solids (TSS) and pathogen (e.g., ) levels in rangeland streams are a serious concern worldwide. Herded stream crossings by domestic sheep () are periodic, necessary managerial events on high-elevation rangelands, but their impacts on stream water quality are largely unknown. We evaluated the effects of herded, one-way crossings by sheep bands (about 2000 individuals) on TSS and concentration and load responses in downstream waters. Crossing trials were conducted during the summers of 2005 and 2006 on two reaches within each of three perennial streams in the Centennial Mountains of eastern Idaho and southwestern Montana. Water samples were collected at 2-min intervals at an upstream background station and at stations 25, 100, 500, and 1500 m downstream just before and during each crossing trial. Crossings produced substantial increases in TSS and concentrations and loads downstream, but these concentration increases were localized and short lived. Maximum TSS concentration was highest 25 m downstream, declined as a function of downstream distance, and at 500 m downstream was similar to background. Post-peak TSS concentrations at all downstream stations decreased to <25 mg L within 24 to 48 min after reaching their maxima. Findings for concentration and load responses were similar to that of TSS but less clear cut. Stream-crossing sheep do affect water quality; therefore, producers and resource managers should continue to evaluate the efficacy of herdsmanship techniques for reducing water quality impact.

Side effects of cultured bacteria addition in wastewater collection system on plant operations – a case study

Cultured bacteria addition is one of the technologies used for odor control and FOG (fat, oil, and grease) removal in wastewater collection systems. This study investigated the efficiency of bacterial addition on wastewater odor control by conducting a set of full scale trials in a 60,000 cubic meter per day system for a period of two years. The objectives of this study were: (i) to identify factors that could impact wastewater treatment plant (WWTP) operations due to the effect of bacterial addition in the collection system, (ii) to estimate/understand the level of those impacts, and (iii) to present some interesting findings from the completed case study. The plant operation data before and during the bacterial addition were reviewed. The application of the cultured bacteria presented in the study was found to have significant impacts on the operation of the WWTP in terms of influent biological oxygen demand (BOD) and total suspended solids (TSS) loading, primary settling, sludge production, energy use, dissolved sulfides concentration, and methane production.

Evaluating upgrade possibilities of activated sludge wastewater treatment plants utilizing biofilm-based treatment technologies – an experimental study at the South Pest WWTP

As more and more wastewater treatment plants (WWTPs) arrive to a point in their lifecycles when their original capacities are not sufficient anymore, the demand for good WWTP retrofitting solutions becomes increasingly critical. One of the typical problems is the suspended solids overload of secondary clarifiers, which is one of the main concerns at the South Pest WWTP as well. Pilot scale studies were carried out at the WWTP with a biofilm based technology applying biofilm carriers imitating plant root structures in order to characterize the potentials of clarifier TSS load reduction while maintaining the existing biodegradation performance of the activated sludge stage. The research demonstrated that the clarifier load can be reduced by more than 90%, while the original biodegradation performance of the system does not decrease. In addition to this, it was demonstrated that the biomass amount in the reactors can be increased substantially opening potentials for further biodegradation capacity.

Characteristics of run-off quality and pollution loading from a highway toll-gate

The Ministry of Environment of the Republic of Korea has been seriously considering implementing a TMDL (Total Maximum Daily Load) as a mandatory requirement on watersheds because of the potential water pollution from highway toll-gates. The purpose of this study was to investigate the characteristics of run-off quality and pollution loading during rainfall events at a highway toll-gate. Samples were analysed for run-off quantity and quality parameters such as CODcr, TSS, total petroleum hydrocarbons, nutrients (TKN, NO3, TP and PO4) and several heavy metals (As, Cu, Cd, Ni, Pb and Zn). Based on a hydrograph and pollutant graph analysis, the pollutant concentration peak occurred in the run-off 10 minutes after the onset of rainfall. The typical first flush effect on the concentration depended on the rainfall intensity and the number of antecedent dry days. The relationships between the run-off and the event mean concentrations of the pollutants (e.g. TSS and COD) were described by general nonlinear equations. For governmental implementation of TMDL policies, the estimation of the cumulative TSS load was 1032 kg/(ha·yr) in 2007, 963.44 kg/(ha·yr) in 2008 and 847.21 kg/(ha·yr) in 2009. This information can lead to improved practical water quality management practices and reduced costs of improving water quality.

Measured Copper Toxicity toCnesterodon decemmaculatus(Pisces: Poeciliidae) and Predicted by Biotic Ligand Model in Pilcomayo River Water: A Step for a Cross-Fish-Species Extrapolation

In order to determine copper toxicity (LC50) to a local species (Cnesterodon decemmaculatus) in the South American Pilcomayo River water and evaluate a cross-fish-species extrapolation of Biotic Ligand Model, a 96 h acute copper toxicity test was performed. The dissolved copper concentrations tested were 0.05, 0.19, 0.39, 0.61, 0.73, 1.01, and 1.42 mg Cu L−1. The 96 h Cu LC50 calculated was 0.655 mg L−1 (0.823 − 0.488). 96-h Cu LC50 predicted by BLM for Pimephales promelas was 0.722 mg L−1. Analysis of the inter-seasonal variation of the main water quality parameters indicates that a higher protective effect of calcium, magnesium, sodium, sulphate, and chloride is expected during the dry season. The very high load of total suspended solids in this river might be a key factor in determining copper distribution between solid and solution phases. A cross-fish-species extrapolation of copper BLM is valid within the water quality parameters and experimental conditions of this toxicity test.

The use of long-term on-line turbidity measurements for the calculation of urban stormwater pollutant concentrations, loads, pollutographs and intra-event fluxes

This paper presents one of the largest databases on the quality of urban wet weather discharges measured since the development of continuous in-sewer water quality sensors in the late 1990s. Five years of continuous turbidity measurements enabled the validation of 263 and 239 rainfall events, respectively on two experimental catchments in Lyon (France), Chassieu (185ha separate sewer) and Ecully (245ha combined sewer). Except for high rainfall events of summer and second half of winter, analysis of database representativeness showed that all seasons were relatively well represented. As a first analysis of the database, traditional tools used in the urban drainage field were applied to assess: i) statistics and analysis of distributions of TSS and COD events loads and event mean concentrations (EMCs) and ii) the correlations between these statistics and events characteristics and iii) M(V) curves describing the intra-event mass distribution. Results showed that: i) EMCs and loads were approximately log-normally distributed, with a clear impact from wastewater contribution in Ecully, ii) EMCs are not correlated with storm event characteristics, whereas loads have shown significant correlation with key storm event variables such as total event volume, rainfall depth, maximum rainfall intensity and discharge and iii) M(V) curves dynamic could be classified in three categories, however with no clear correlation with storm event characteristics. The visual analysis of continuous time series of TSS and COD pollutographs, derived from turbidity time series showed that event pollutographs were highly variable, due to complex interacting processes during and between events, and suggests that further progress in knowledge and modelling of urban wet weather pollutant loads and pollutographs should be based on more detailed analyses of continuous time series rather, than on the traditional single event approach.

Towards ecologically relevant targets for river pollutant loads to the Great Barrier Reef

Degradation of coastal ecosystems in the Great Barrier Reef (GBR), Australia, has been linked with a decline in water quality from land-based runoff. This paper examines the reduction in current end-of-catchment loads required for total suspended solids (TSS) and dissolved inorganic nitrogen (DIN) to achieve GBR water quality guidelines. Based on first-order estimates of sustainable pollutant loads, current TSS and DIN loads would need to be reduced by approximately 7000ktons/y (41%) and 6000tons/y (38%), respectively. Next, these estimated reductions for TSS and DIN are compared with Reef Plan targets for anthropogenic sediment (−20% by 2020) and nitrogen (−50% by 2013) loads. If successful, these targets will accomplish approximately 40% of TSS and 92% of DIN load reductions required to achieve sustainable loads to the GBR lagoon. These first-order estimates elucidate the need to establish ecologically relevant targets for river pollutant loads to the GBR for management and policy.

Off-site transport of nutrients and sediment from three main land-uses in the Mt Lofty Ranges, South Australia

► Generally the highest TSS concentrations were found in surface drainage from a vineyard rather than the apple or cherry orchard. ► TSS was found generally to only be high in the first few flow events but TN did not show any consistent trend with flow volumes. ► TN concentration exceeded the Australian environmental trigger value in >50% of the samples from the apple orchard and >90% of the samples from the cherry orchard and vineyard. ► The TP concentrations exceeded the Australian environmental trigger value in <10% of the samples from the apple and the cherry orchard but in >90% of the samples from the vineyard. ► Current remedial strategies may not be very effective in this environment. This paper reports on the edge-of-field loads of sediment, nitrogen, phosphorus and organic carbon transported from three main land uses, namely an apple and a cherry orchard and a vineyard, in the Mt Lofty Ranges (MLR), South Australia over a three year period. There is a plethora of data in Australia on nutrient losses from dairy but prior to this study there was limited data from horticultural activities which are predominant in the MLR. Generally the highest total suspended solids (TSS) were found in surface drainage from the vineyard. At all three sites the highest TSS load was found in the first runoff event of the year but large flow events were accompanied by spikes in TSS concentration. Generally, within an event, the highest TSS concentration was found at the peak of flow and decreased on the receding limb of the hydrograph. The total nitrogen (TN) concentration exceeded the Australian environmental trigger value of 1 mg/L in >50% of the samples from the apple orchard and >90% of the samples from the cherry orchard and vineyard. The total phosphorus (TP) concentrations exceeded the Australian environmental trigger value of 0.1 mg/L in <10% of the samples from the apple and the cherry orchard but in >90% of the samples from the vineyard. Trends in the timing of the transport of TN, TP and TOC were only clearly observed when flow was large. After the initial seasonal flush of contaminants, generally only a very large runoff volume was sufficient to generate large loads of TN, TP and TOC during the season. Generally, the concentration of TP and TOC but not TN during a flow event was high at the start and declined with flow rate. In low flow situations, these trends were not clear. The transport of TN during an event was variable and unpredictable.

Cargas de Fósforo Total e Material em Suspensão em um Reservatório do Semi-Árido Brasileiro

Normal 0 21 false false false PT-BR X-NONE X-NONE SUSPENDED SOLIDS AND PHOSPHORUS LOAD IN A BRAZILIAN SEMI-ARID RESERVOIR. Semi-arid reservoirs are highly vulnerable to eutrophication and siltation, as they have a large catchment: surface area ratio (AD: AL), and high water residence time, which underlies their potential for high retention of nutrients and sediments exported from the watershed . Nevertheless, the external loads of nutrients and suspended solids to these reservoirs and their retention coefficients are unknown. In order to quantify the loads of total phosphorus and suspended solids exported from the watershed of Cruzeta (RN) reservoir, and to describe the patterns of temporal variation in total phosphorus, suspended solids and chlorophyll a concentrations in the water, five sampling points in the reservoir were monitored between March 2007 and May 2008 (n = 26). The annual exportation coefficients of total phosphorus and suspended solids were respectively, 0.03g and 7.08g per square meter of watershed. The annual loads of total phosphorus and suspended solids were respectively, 4.8g and 1160.7g per square meter of reservoir . The mass balance results shows that the reservoir retained 94% of the incoming suspended solids and 50% of the incoming total phosphorus load. The median concentrations of total phosphorus and chlorophyll a were 0,12mg L -1 and 12?g L -1 respectively, over the study period. The TN:TP ratio (atomic) were often below 16:1 suggesting nitrogen limitation. The observed negative correlation (r²=0.40; p 0.001) between fixed suspended solids and transparency (secchi depth) indicates that the major source of turbidity was abiogenic and suggests potential light limitation of primary production. The likely light and/or nitrogen limitation might explain the lower than expected chlorophyll a per total phosphorus concentrations observed in the reservoir . Keywords: Water balance; mass balance; eutrophication; reservoir; semi-arid.

Evaluation of undersized bioretention stormwater control measures for treatment of highway bridge deck runoff

Two grassed bioretention cells were constructed in the easement of a bridge deck in Knightdale, North Carolina, USA, in October, 2009. One was intentionally undersized ('small'), while the other was full sized ('large') per current North Carolina standards. The large and small cells captured runoff from the 25- and 8-mm events, respectively. Both bioretention cells employed average fill media depths of 0.65 m and internal water storage (IWS) zones of 0.6 m. Flow-proportional, composite water quality samples were collected and analyzed for nitrogen species, phosphorus species, and TSS. During 13 months of data collection, the large cell's median effluent concentrations and loads were less than those from the small cell. The small cell's TN and TSS load reductions were 84 and 50%, respectively, of those achieved by the large cell, with both cells significantly reducing TN and TSS. TP loads were not significantly reduced by either cell, likely due to low TP concentrations in the highway runoff which may have approached irreducible levels. Outflow pollutant loads from the large and small cell were not significantly different from one another for any of the examined pollutants. The small cell's relative performance provides support for retrofitting undersized systems in urbanized areas where there is insufficient space available for conventional full-sized stormwater treatment systems.

Analysis of rainfall runoff characteristics from a subtropical urban lawn catchment in South-east China

Characteristics of rainfall runoff from a 3.26 hm2 urban catchment with predominant land-use as lawn in Xiamen City, South-east China were investigated and analyzed. Water quality and quantity measurements of rainfall runoff were conducted for ten rainfall events over the period March, 2008 to April, 2009. The results indicated that chemical oxygen demand (COD) and total phosphorus (TP) were the major pollutants with event mean concentrations of 56.09 and 0.44 mg·L−1. From hydrograph and pollutograph analysis of two typical rainfall events, it was clear that the peak rainfall preceded the peak flowrate by about 15–20 min. Meanwhile, concentrations of major pollutants showed multiple peaks and these peaks usually preceded peak flowrate. There were no distinctive first-flush effects except for the rainfall events with the longest rainfall duration and largest runoff volume, which was verified by the fact that the first 30% runoff volume (FF30) carried 39.36% of the total suspended solids (TSS) load, 35.17% of the COD load, 28.13% of the TP load and 39.03% of the nitrate nitrogen load. Multivariate regression analysis further demonstrated that the total runoff volume had a positive correlation with the FF30 of TSS and COD.

Assessing dry weather flow contribution in TSS and COD storm events loads in combined sewer systems

Continuous high resolution long term turbidity measurements along with continuous discharge measurements are now recognised as an appropriate technique for the estimation of in sewer total suspended solids (TSS) and Chemical Oxygen Demand (COD) loads during storm events. In the combined system of the Ecully urban catchment (Lyon, France), this technique is implemented since 2003, with more than 200 storm events monitored. This paper presents a method for the estimation of the dry weather (DW) contribution to measured total TSS and COD event loads with special attention devoted to uncertainties assessment. The method accounts for the dynamics of both discharge and turbidity time series at two minutes time step. The study is based on 180 DW days monitored in 2007-2008. Three distinct classes of DW days were evidenced. Variability analysis and quantification showed that no seasonal effect and no trend over the year were detectable. The law of propagation of uncertainties is applicable for uncertainties estimation. The method has then been applied to all measured storm events. This study confirms the interest of long term continuous discharge and turbidity time series in sewer systems, especially in the perspective of wet weather quality modelling.

Metals, nutrients and total suspended solids discharged during different flow conditions in highly urbanised catchments

Stormwater discharged from highly urbanised catchments on the southern shore of Sydney estuary, Australia, has been identified as the primary source of contaminants responsible for ecological degradation and reduction in recreational value of the waterway. Effective management of this pollution requires knowledge of contaminant loads associated with various stormwater flow conditions in three highly urbanised catchments in Sydney estuary catchment. The majority (>90%) of metal (Cu, Pb and Zn) and total suspended solid annual loads were contributed during high-flow conditions (>50 mm rainfall day(t1)), whereas ≤55% of TN and ≤21% of total phosphorus were contributed to annual loading by dry weather base-flow conditions. All flow conditions posed an in-stream ecological threat because contaminant concentrations exceeded water quality guidelines for all analytes measured, except Pb. Irregular, temporal variability in contaminant concentrations associated with base-flow (within day and amongst days), high-flow (amongst events) and irregular discharges indicated that contaminant contributions in stormwater were strongly controlled by human activity in the three catchments. Significant variation in contaminant concentrations under all flow conditions revealed unique chemical signatures for each catchment despite similarities in land uses, location and geology amongst catchments. These characteristics indicate that assessment and management of stormwater pollution needs to be conducted on an individual-catchment basis for highly urbanised regions of Sydney estuary catchment.