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Nitrate (NO3-) is a ubiquitous groundwater contaminant in agricultural and wastewater discharge areas. The prediction of microbial mediated NO3- removal in subsurface environments requires an understanding of the rates at which electron donors are utilized by denitrifying microbes. This study focuses specifically on the following organic carbon compounds as electron donors: glucose, acetate, adenine, cysteine and fulvic acid. Six triplicate series of flow through reactors (FTRs) containing 35 cm3 of natural, organic-poor sediment were supplied for 10 weeks with solutions containing nitrate and the individual carbon compounds, along with a no-carbon added control. The organic carbon compounds were selected to yield a range of different types of organic carbon (sugars, amino acids etc.) as well as a range of Gibbs Free Energy (???G) values when their oxidation is coupled to denitrification. The initial flow rate of the FTRs was 1 ml h-1. Once steady NO3- concentrations were reached in the outflow, the flow rate was increased to 2 ml h-1 and, subsequently, 4 ml h-1. Potential denitrification rates (RD) measured for the different carbon substrates spanned a range of 0 to 114 nmol cm-3 h-1. Fulvic acid did not induce denitrification, while acetate yielded the highest rate. The outflow solutions for FTRs supplied with adenine and cysteine contained ammonia and sulfate, respectively. These results are consistent with the molecular structure of adenine, which contains an amine group, and of cysteine, containing an amine and thiol group. The results show that the addition of C-substrates to the sediment promotes denitrification, and the rate at which it occurs are dependant on which C-substrate is provided. RD results were used to determine if the denitrification rates imposed by the different carbon substrates could be predicted using theoretical approaches such as ???GR or the nominal oxidation state of carbon (NOSC). However, predictions determined by thermodynamics alone were not significantly correlated with the observed trends in denitrification rates.

Toxicity of copper to larval <I>Mercenaria mercenaria</I> was evaluated with static non-renewal and continuous renewal methods that permitted daily observation of mortality, activity, development, and metamorphosis without subsampling. Clam larvae, 100 - 150 microns, were held for up to two weeks in small, 30 mm, sealed petri plates during static assays with excellent survival of control organisms, low evaporative losses, and relatively low between replicate variability. An eight day LC50 of 12 micrograms / liter for six day old organisms was determined as well as EC50s (active swimming). EC50s at 24 hours were as much as much as seven times lower than LC50s after 24 hours of exposure. Flow - through assays were conducted with a modified petri dish design. Two sections from opposing sides of a 30 mm petri dish were removed and covered with 35 micron polyester screening. This dish (organism dish) was placed in an outer catch dish that captured the effluent toxin as it passed through the screening and routed it to a catch bottle for water quality analysis. The toxicant feed line entered through the catch dish cover and slowly dripped toxin into the organism dish. Water quality in the flow - through assay remained excellent. Survival of control organisms in the flow - through assay was lower than in static assays, but metamorphosis was not delayed as had been observed in static assays. Data variability was low enough that statistical distinctions were made between the effects of copper on metamorphosis. A non-standard "M" shaped survival response was observed in all assays. The responses generating the "M" shaped response in the static petri assay were statistically different from each other. Activity, as judged by swimming, in organisms was not observed to follow the "M" shaped pattern. Instead, it decreased exponentially with increasing copper concentrations. Static experiments with unfed clams, observations of activity, and data from experiments in copper accumulation by algae led to a theory relating the unusual dose response to food consumption and its relationship to the effective dose of copper to which the larval clams were exposed. / Master of Science

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