Patrick L. Brezonik

Trace metal analysis by anodic stripping voltammetry: effect of sorption by natural and model organic compounds

Abstract A variety of model organic compounds representative of the types of organic substances occurring in natural waters were found to sorb onto hanging mercury drop electrodes in the anodic stripping voltammetric analysis of trace metals. Sorption effects on the ASV diagnostic parameters Ep and ip (peak current and peak potential) were pH dependent, with greater effect under acidic conditions in some cases, and were significant at organic concentrations in the ppm range. Compounds tested included gelatin and alkaline phosphatase as representatives of soluble proteins. Triton X100 (a nonionic surfactant), and a variety of polysaccharides, including agar, alginic acid and starch. Effects of sorption included depressed ip values, shifts in Ep to more positive values, and broader peaks. Implications of these effects on the interpretation of ASV measurements in terms of analysis and speciation of trace metals in natural waters are discussed.

Acid precipitation and sulfate deposition in Florida.

The acidity of rainfall in Florida has increased markedly in the past 25 years, and the average sulfate and nitrate concentrations have increased by factors of 1.6 and 4.5, respectively, over the period. Annual average pH values below 4.7 now occur over the northern three quarters of the state. Summer rainfall has average pH values 0.2 to 0.3 unit lower than winter rainfall, and sulfate concentrations at most sites are higher in summer. The annual deposition of H+ (about 300 to 500 equivalents per hectare) in northern Florida is a third to a half of the deposition in the heavily impacted northeastern United States; comparable figures for excess sulfate (derived from sulfur dioxide) are 7 to 11 kilograms of sulfur per hectare or 50 to 90 percent of the sulfate deposition rates at Hubbard Brook, New Hampshire.

Application of ATP to plankton biomass and bioassay studies

Abstract The use of adensine triphosphate (ATP) analysis for freshwate algal and plankton populations was evaluated as a measure of biomass and as a bioassay response parameter. ATP analysis was performed using the firefly luminescence procedure. In short term laboratory studies. ATP levels in cultured algae and lake plankton correlate well with other standard biomass parameters, including chlorophyll a and dry weight. Algal ATP responded rapidly to mercury addition and pH changes, indicating its usefulness as a measurement of toxicity. The rapid response of ATP following nutrient additions to starved algal cultures suggests ATP may be useful as a tool in nutrient bioassay studies.

DENITRIFICATION IN NATURAL WATERS

SUMMARY Denitrification is a bacterial process in which nitrate is used as the terminal electron acceptor and is reduced primarily to nitrogen gas (N 2 ). The bacterial agents, metabolic and environmental requirements and mechanisms for denitrification are described. The long-standing controversy over the role of oxygen in denitrification is summarized. Denitrification is essentially an anaerobic process; it can occur in the presence of low levels of oxygen only if the microorganisms are metabolizing in an anoxic microzone (such as within suspended particles). Chemical formation of gaseous nitrogen from nitrite has been found to occur in acidic soils, and possible mechanisms for this are reviewed. The ecological significance of denitrification relates to the fact that few organisms can use N 2 directly and the reaction thus serves as a sink of fixed nitrogen. The distribution and importance of denitrification in the environment are discussed, and measured rates of the reaction in anoxic marine, lake and sediment systems are summarized. The reaction may act as a significant sink for fertilizer nitrogen applied to soils, and in eutrophic lakes denitrification may eliminate 10 to 50 percent of the annual nitrogen loading. The reaction may also be important in removing nitrate from groundwater as it seeps through marsh or sublacustrine sediments and into a lake, but further studies are need to quantify this hypothesis.

Nitrogen Fixation in Some Anoxic Lacustrine Environments

Low rates of acetylene reduction to ethylene in water samples from two dystrophic lakes indicate the presence of nitrogenase and in situ nitrogen fixation. Highest rates were found in anoxic water from the aphotic zone. Environmental conditions in these lakes suggest the agents of fixation were bacteria.

The limnology of selected Guatemalan Lakes

During the summer of 1969, fourteen Guatemalan lakes were sampled, including eight in the lowland northern province of Peten and six in southern Guatemala. The majority of the Peten lakes exhibited thermal stratification and hypolimnetic oxygen depletion. In most cases, pollution tolerant bottom forms were found. Algal species and numbers in general corresponded to a subjective estimate of the degree of nutrient input to the lakes. Lyngbya was usually the organism found when blooms were noted. The lakes in the Peten are predominately calcium bicarbonate and calcium sulfate lakes, but magnesium is also high in several of them. The southern lakes were chemically more variable, with sodium being more important than in the northern lakes. Most of the southern lakes also exhibited thermal stratification and hypolimnetic oxygen depletion, with the flora and fauna dependent upon oxygen and nutrient conditions. The authors conclude that different criteria than those used to assess the trophic status of temperate lakes are needed to classify tropical lakes.

Application of nutrient loading models to the analysis of trophic conditions in Lake Okeechobee, Florida

Lake Okeechobee (surface area = 1830 km2, mean depth = 3.5 m), the largest lake in Florida, is eutrophic and has nitrogen and phosphorus loading rates in excess of nearly all established criteria. The lake is not homogeneous regarding trophic conditions, and spatial and temporal variations occur regarding nutrient limitation. Nonetheless, phosphorus loading rate and trophic state data fit reasonably well to various input-output models developed for temperate lakes. Modification of the models by regression analysis to fit data for Florida lakes resulted in improved predictions for most parameters. Analysis of nutrient management alternatives for the lake indicates that a 75% reduction of phosphorus loading from the largest source (the Taylor Creek-Nubbins Slough watershed) would reduce the average chlorophyll a concentration by less than 20%. Complete elimination of inputs from the largest nitrogen source (the Everglades Agricultural Area) would decrease the average nitrogen concentration in the lake by about 20%. Limitations of nutrient inputoutput models regarding analysis of trophic conditions and management alternatives for the lake are discussed.

Nitrifying population densities and inhibition of ammonium oxidation in natural and sewage-enriched cypress swamps

Abstract The occurrence of autotrophic nitrifiers in the peat from the floors of a natural cypress dome, a cypress dome receiving deep artesian groundwater, and two cypress domes amended with secondary treated sewage effluent, were assessed by surveying their population densities. The absence of ammonium oxidation in the surface waters of the natural dome was due to the low pH and not to any toxic organic chemical effects present in the humic-colored water. This probably explains the low density (0–56 cells cm−3) of autotrophic nitrifiers found associated with the peat from that dome.

Agricultural nitrogen model: A tool for regional environmental management

A detailed nitrogen budget was devised for agricultural activities in the Florida peninsula, based on routine data published by state agricultural agencies. The model demonstrates that important unmonitored fluxes of nitrogen can often be calculated by mass balance on individual model compartments, and that the reasonability of poorly quantified fluxes can be assessed. The results of such models can be very useful in designing and assessing the results of field experiments and in prioritizing environmental monitoring programs.