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Untreated stormwater discharge has been found to have major impacts on urban watercourses. Despite the acknowledgement of the importance of adopting broader-scale approaches to managing stormwater, there is limited information describing the subwatershed benefits of implementing numerous best management practices (BMPs). Operational monitoring of stormwater management facilities (SWMFs) and streams in three subwatersheds undergoing urbanization was undertaken over a five-year period to measure potential changes in suspended solids concentrations, hydrology and temperature. SWMFs at construction sites had elevated total suspended solids (TSS) discharges relative to facilities in stable catchments, but reduced TSS discharges in comparison to uncontrolled construction sites. The discharge from single facilities was found to have the potential to increase downstream watercourse TSS concentrations in headwater areas, but increases were often not detectable further downstream. TSS discharges from SWMFs in stable catchments were similar to published ranges, and were a useful tool to identify facilities that were not functioning as designed. Based upon the current subwatershed imperviousness levels, water quality impacts from cumulative SWMF discharges appear to be less likely to be significant than some other factors, such as the changes in the subwatershed hydrological response. No increase in peakflow or duration of midbankfull flow for the 25-mm and 2-year storm event and no trend in baseflow or water temperature were detectable over the study period, despite the increase in imperviousness due to watershed urbanization. The findings from this operational monitoring study suggest that implementation of BMPs may help to mitigate urban impacts at the subwatershed level.

We assessed the response of phytoplankton communities in aquatic microcosms to single applications of liquid creosote. The creosote was applied to 14 microcosms at concentrations ranging from 0.06 to 109 mg/L. Two microcosms served as controls. Phytoplankton samples were collected from each microcosm one week and 1 d before treatment and at 7 and 21 d after treatment. Temporal changes (response-recovery) in phytoplankton community composition were assessed with principal response curves. Creosote had no direct toxic effect on the phytoplankton community based on total abundance and number of taxa. Population levels declined in all treatments between day -1 and day 7, but this trend mirrored a similar decline in the control microcosms. At both 7 and 21 d after treatment, population densities and number of taxa in most treatments exceeded those in the controls and exhibited a parabolic relationship relative to creosote concentration. This relationship was most pronounced at 21 d, at which time population densities and number of taxa at intermediate concentrations were up to twice those at low and high concentrations. This response pattern seems to represent an indirect response to impacts on zooplankton and a corresponding reduction in grazing pressure. In contrast, total algal biomass declined 52 to 97% relative to the controls at all but the lowest creosote concentration at 7 d. This apparent decline was due to a significant proliferation of the alga Closterium moniliforme in the controls and low creosote concentration. At 21 d, no difference was found in total biomass between treated and control microcosms. The results of this study suggest that creosote does not pose a significant direct risk to phytoplankton at concentrations likely to be encountered in most contaminated aquatic environments; however, stimulation of algal populations could occur in situations of long-term chronic exposure or spill events that remove predatory zooplankton populations.

Temporal changes in the distribution and relative composition of 15 priority polycyclic aromatic hydrocarbons (PAHs) in water, sediment, and absorbed to polyvinylchloride (PVC) strips were assessed following direct application of liquid creosote to aquatic microcosms. Fourteen microcosms were treated with nominal creosote concentrations ranging from 0.06 to 109 mg/L and two microcosms served as controls. Quantitative analysis of PAHs was performed using high-performance liquid chromatography equipped with a fluorescence detector. Post-treatment concentration of PAHs in water decreased exponentially with time. At 2 d posttreatment, total PAHs (Σ PAH) ranged from 7.3 μg/L (lowest treatment) to 5.803.2 μg/L (highest treatment): by 84 d, Σ PAH in the same microcosms was reduced to between 0.8 μg/L and 13.9 μg/L. respectively. The relative composition of PAHs in the water also changed with time: at 2 d posttreatment, Σ PAH in the lowest treatment (7.3 μg/L) reflected contribution from nine PAHs. whereas only two PAHs contributed to this concentration (0.8 μg/L) at 84 d. Low and high molecular weight (mol. wt.) PAHs were lost first from the water column, followed by PAHs of intermediate mol wt. In sediments, a dose-dependent increase in Σ PAH was observed above 0.59 mg/L creosote up to 28 d. followed by a decline thereafter in all but the highest treatment. Total PAHs in sediment ranged from 0.91 μg/g (lowest treatment) to 63.9 μg/g (highest treatment) at 28 d. A dose-dependent relationship was also observed in PVC strips, with Σ PAH on PVC ranging from 0.05 to 88 μg/cm 2 at 31 d and 0.04 to 18.4 μg/ cm 2 at 58 d posttreatment. A mass balance evaluation showed that 88.3% of PAHs was lost from the system after I month, indicating that liquid creosote is attenuated relatively quickly in aquatic environments.

Temporal changes in the concentration and relative composition of 15 priority polycyclic aromatic hydrocarbons (PAHs) in water, sediment, and polyvinylchloride (PVC) strips were assessed to evaluate the fate of creosote leached from impregnated wood pilings in aquatic environments. The study consisted of single microcosms containing one of 0.5, 1, 2, 3, 4, or 6 creosote-impregnated pilings and two microcosms containing untreated pilings. Quantitative analyses of PAHs were performed using high-performance liquid chromatography equipped with a fluorescence detector. For each treatment, total PAHs(∑ PAH) in water increased rapidly up to 7 d posttreatment yielding a clear dose-dependant concentration gradient ranging from 7.3 (0.5 pilings) to 97.2 μg/L (6 pilings). Total PAHs declined exponentially after 7 d and was reduced close to background concentrations (0.8–6.7 μg/L) by the end of the study (84 d). No increase in ∑ PAH was observed in sediments at any treatment, nor was there any relationship between sediment PAHs and distance from each piling cluster. However, a slight increase in PAHs was observed on PVC liner strips that exhibited a concentration gradient similar to that in water. The PVC-bound ∑ PAH ranged from 0.3 to 2.4 μg/cm2 and 0.2 to 2.2 μg/cm2 at 31 and 58 d posttreatment, respectively. Based on these data, we estimated a rate loss of creosote from the pilings of approximately 50 μg/cm2/d (273 mg/piling/d). The low concentration of PAHs on the PVC, along with the absence of accumulation of PAHs in sediments, suggests that creosote was lost primarily from water via degradative pathways such as photolysis and microbial decomposition and adsorption onto PVC. The rapid loss of creosote from water in conjunction with the slow rate of leaching from the pilings suggests that risks associated with the use of creosote-impregnated pilings in aquatic environments may be minimal.