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The convergence of urban expansion, deteriorating infrastructure, and a changing climate will escalate the risks of stormwater pollution and urban flooding in the coming decades. Using outputs from an ensemble of global climate models to drive a high spatial resolution stormwater model, we analyzed climate change impacts on urban stormwater runoff and control measures for 23 cities across the United States. Runoff model outputs for two future emissions scenarios ending in 2055 were compared against a historical scenario to assess changes. All cities showed increases in average annual stormwater runoff, with changes up to 30% over the next 30 years due to a greater frequency of high intensity storm events. Runoff model outputs showed substantial variation across cities with untreated stormwater runoff increasing by as much as 48%. Patterns of future runoff impacts within cities will affect the performance of distributed treatment strategies such as Green Stormwater Infrastructure (GSI) to meet municipal water quality improvement and runoff reduction goals. Results indicate that adoption of adaptable design standards and decision support tools that readily accommodate projected precipitation changes are critical for supporting more resilient designs of stormwater control measures. [ABSTRACT FROM AUTHOR]

Two laboratory microcosm experiments were conducted to mimic an annual spring diatom bloom in South Sao Francisco Bay by isolating the phytoplankton community from the benthic grazing pressure to induce a phytoplankton bloom. The purpose of these experiments was to isolate the impact of a spring diatom bloom on the nutrient and trace metal geochemical cycling. Microcosms were created in 2.5 L incubation bottles and subjected to one of 4 treatments (control, copper [Cu] addition, manganese [Mn] additions, and both Cu and Mn addition) to investigate the toxicity of Cu on the resident plankton and the potential antagonistic effects of Mn on reducing Cu toxicity. Dissolved macronutrient (nitrate + nitrite, phosphate. and silicate), and dissolved and particulate trace metal (Cu, Ni, Mn) concentrations were monitored it: the grow-out incubations on a daily basis. Chlorophyll a concentrations were also monitored over the course of the experiment and used to calculate diatom-specific growth rates. In the experiments containing ambient South San Francisco Bay surface waters, average specific growth rates were nit the order of 1.1 d-1. The induced diatom blooms resulted to significant removal of macronutrients from the microcosms over the course of the experiments. Our research supports previous suggestions that dissolved Ni and Cu concentrations in South San Francisco Bas have a very low biological availability as a result of organic chelation. Ni(EDTA)2- has been to be the dominant dissolved Ni species by other researchers and Cu speciation analyses from this study and others indicate that >99% of the dissolved Cu in South San Francisco Bay is strongly chelated as CuL1. The free cupric ion concentration was on the order of 10-12 M. Marked removal of dissolved Mn was observed in the control treatments, well exceeding expected dissolved Nm removal by diatom uptake. Additions of 375 nM Cu resulted in the complete titration of the chelating ligand (L1) concentrations. The elevated [Cu2+] (≈ 10-8 M) appeared to have a toxic effect on the diatom community observed in the significant decreases in their specific growth rates (μ = 0.4 d-1). The suppression of dissolved Nm removal front solution was also observed in treatments spiked with high levels of dissolved Cu, providing support that Mn precipitation was due to biologically mediated oxidation not phytoplankton assimilation. The observed geochemical behavior in the concurrent Cu and Mn addition treatments provide evidence in support of Mn alleviation of Cu toxicity. The biological role in the ambient short-term biogeochemical cycling of Cu and Ni in Smith San Francisco Ray appears to be minimal due to the inert character of the organic ligand-metal complexes. A significant portion of the annual macronutrient and Mn cycling occurs as a result of spring diatom blooms in South San Francisco Bay. [ABSTRACT FROM AUTHOR]

A diel biogeochemical study was performed to assess the influence that periods of elevated biological activity have on the biogeochemicalcycling of macronutrients and redox-sensitive elements in a natural estuarine environment. High-resolution data (15 min sampling) illustrates periodic extreme variations in dissolved oxygen (DO) in the shallow waters of Azevedo Pond, Elkhorn Slough, California. During periods of low tidal flushing, DO values can range from highly oxic (> 560 Mu M O2: > 250% saturation) during sunny days to suboxic conditions (< 5 Mu M) at night. Nutrient cycling and redox-sensitive trace element biogeochemistry were evaluated in response to the extreme daily DO fluctuations. A diel sampling study was conducted over a 26-h period, where O2 concentrations ranged from 346 Mu M to sustained non-detectable levels in the night hours. In concert withthe DO fluctuations, diet phosphate cycling was on the order of 4 MuM in response to tidal flushing events and biological assimilation and regeneration. The I03- /I- redox couple quickly responded to suboxic conditions in the water column bya marked increase in I- concentrations and corresponding depletion of I03-. The extreme fluctuations of the pe in the water column resulted in diel dissolved Mn2+variations of nearly 5 Mu M, with observed dissolved Mn removal rates on the order of 1 Mu M h-1. The elevated biogeochemical cycling of oxygen, nitrogen, phosphorus, iodine, manganese, and iron found in this shallow estuarine environment suggest that tidal restrictions and anthropogenic nutrient enrichments can amplify diel variations and potentially hinder the functional and ecological stability of these systems. These data suggest that accurate chemical monitoring of the health of an estuarine ecosystem must account for the diel variability inherent in these highly productive environments. [ABSTRACT FROM AUTHOR]