Stormwater Retention Ponds: Hydrogen Sulfide Production, Water Quality and Sulfate-Reducing Bacterial Kinetics

Title: Stormwater Retention Ponds: Hydrogen Sulfide Production, Water Quality and Sulfate-Reducing Bacterial Kinetics
Authors: D'Aoust, Patrick Marcel
Date: 2016
Abstract: Stormwater retention basins are an integral component of municipal stormwater management strategies in North America. The province of Ontario’s Ministry of the Environment and Climate Change obligates land developers to implement stormwater management in their land use and development plans to mitigate the effects of urbanization (Bradford and Gharabaghi, 2004). When stormwater retention ponds are improperly designed or maintained, these basins can fail at improving effluent water quality and may exasperate water quality issues. Intense H2S production events in stormwater infrastructure is a serious problem which is seldom encountered and documented in stormwater retention ponds. This study monitored two stormwater retention ponds situated in the Riverside South community, Ottawa, Ontario, Canada for a period of 15 consecutive months to thoroughly characterize intense hydrogen sulfide (H2S) production in a stormwater retention pond under ice covered conditions during winter operation and during periods of drought under non-ice covered conditions during the summer. Field experiments showed a strong relationship (p < 0.006, R > 0.58, n = 20+) between hypoxic conditions (dissolved oxygen (DO) concentration < 2 mg/L) and the intense production of H2S gas. Ice-capping of the stormwater ponds during winter severely hindered reaeration of the pond and led to significant production of total sulfides in the Riverside South Pond #2 (RSP2), which subsequently resulted in the accumulation of total sulfides in the water column (20.7 mg/L) during winter in this pond. There was a perceived lag phase between the drop in DO and the increase in total sulfides near the surface, which was potentially indicative of slow movement of total sulfides from the benthic sediment into the water column. These high-sulfide conditions persisted in RSP2 from early January 2015 until the spring thaw, in mid-April, 2015. Riverside South Pond #1 (RSP1), the reference pond studied in this work, showed significantly less production of total sulfides across a significantly shorter period of time. Analysis of the microbial communities showed that there was little change in the dominant bacterial populations present in the benthic sediment of the pond demonstrating significant total sulfide production (RSP2) and the pond that did not demonstrate significant total sulfide production (RSP1). Additionally, it was found that locations with the most accumulated sediment had the highest propensity for the production of H2S gas. Furthermore, there was no perceivable community shift in the two ponds throughout the seasons, indicating that the sulfate-reducing bacteria (SRB) in stormwater benthic sediment are ubiquitous, exist in an acclimatized microbial population and are robust. Study of the microbial abundances revealed that SRB represented approximately 5.01 ± 0.79 % of the microbes present in the benthic sediment of RSP2. Likewise, in the stormwater pond which did not experience intense H2S gas production, RSP1, 6.22 ± 2.11 % of microbes were of the SRB type, demonstrating that H2S gas production does not correspond to higher concentrations of SRB or the proliferation of dominant species, but rather is a symptom of increased bacterial activity due to favourable environmental conditions. In addition, this work also covers the kinetics of sediment oxygen demand (SOD), ammonification and sulfate-reduction, and attempts to understand the processes leading to H2S gas production events. In doing so, it was observed that kinetics obtained full-scale field studies were greater than in laboratory kinetic experiments. Laboratory experiments at 4°C identified total SOD, ammonification and sulfate-reduction kinetics to be 0.023 g/m2/day, 0.027 g N/m2/day and 0.004 g S/m2/day, respectively. Meanwhile, kinetics calculated from the field study of stormwater retention ponds for total SOD, ammonification and sulfate-reduction were of 0.491 g/m2/day, 0.120 g N/m2/day and 0.147 g S/m2/day, respectively. It is expected that this difference is due to the depth of active sediment influencing the total rates of production/consumption, making area-normalized daily rates of production/consumption (g/m2/day) unsuitable for the comparison of field and laboratory studies, without some scaling factor. This study also measured supplementary kinetic parameters such as the Arrhenius coefficients and the half-saturation coefficient, to add to existing knowledge of sulfate-reduction.
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