Riparian zones within the Appalachian Valley and Ridge physiographic province are often characterized by localized variability in soil moisture and organic carbon content, as well as variability in the distribution of soils formed from alluvial and colluvial processes. These sources of variability may significantly influence denitrification rates. This investigation studied the attenuation of nitrate (NO3- -N) as wastewater effluent flowed through the shallow ground water of a forested headwater riparian zone within the Appalachian Valley and Ridge physiographic province. Ground water flow and NO3- -N measurements indicated that NO3- -N discharged to the riparian zone preferentially flowed through the A and B horizons of depressional wetlands located in relic meander scars, with NO3- -N decreasing from > 12 to < 0.5 mg L(-1). Denitrification enzyme activity (DEA) attributable to riparian zone location, soil horizon, and NO3- -N amendments was also determined. Mean DEA in saturated soils attained values as high as 210 microg N kg(-1) h(-1), and was significantly higher than in unsaturated soils, regardless of horizon (p < 0.001). Denitrification enzyme activity in the shallow A horizon of wetland soils was significantly higher (p < 0.001) than in deeper soils. Significant stimulation of DEA (p = 0.027) by N03- -N amendments occurred only in the meander scar soils receiving low NO3- -N (<3.6 mg L(-1)) concentrations. Significant denitrification of high NO3- -N ground water can occur in riparian wetland soils, but DEA is dependent upon localized differences in the degree of soil saturation and organic carbon content.
A constructed wetland treatment system consisting of subsurface flow (SSF) wetland cells, sand filters, and final effluent wetlands was found to be effective in removing carbonaceous biochemical oxygen demand (CBOD) and total suspended solids (TSS) to below 30 and 10 mg L−1, respectively. Removal efficiency of total nitrogen (TN) loads improved from 60.1 to 88.5% over the 2‐yr study, primarily due to increased vegetation densities in the SSF wetland cells. In both years, parallel wetland treatment cells had significantly different (p < 0.001) plant densities of broadleaf cattail (Typha latifolia L.) and softstem bulrush [Schoenoplectus tabernaemontani (K.C. Gmel.) Palla], with significantly more TN removed from the more densely vegetated cell. Overall, the assimilation of N by plants removed less than 25% of the TN load, regardless of plant density, indicating that the primary role of deeply rooted macrophytes is supporting sequential nitrification‐denitrification within the anaerobic wetland substrate. More than 99% of the dissolved phosphate (PO3−4‐P) was removed within the entire system in both years, but removal efficiencies within the wetland cells decreased from 91.2% the first year to 66.1% the second year, indicating that adsorption sites for PO3−4‐P may be saturated despite increased plant assimilation. Experimental manipulation of waste applied to the sand filters demonstrated that a header‐type distribution system promoting horizontal flow was more effective at nitrifying ammonium (NH+4‐N) discharged to the sand filters than the surface application of waste promoting vertical flow.
In order to improve modeling accuracy and general understanding of lotic biochemical oxygen demand (BOD), this study characterized river metabolism with the current Georgia Environmental Protection Division method for the middle and lower Savannah River basin (MLSRB) and several alternative methods developed with 120-day, long-term biochemical oxygen demand (LTBOD) data from the MLSRB. The data were a subset of a larger two-year LTBOD study to characterize and understand BOD in the MLSRB, located approximately between Augusta, Georgia, and Savannah, Georgia, along the border of Georgia and South Carolina. The LTBOD data included total oxygen loss and nitrogen speciation for separately quantifying nitrification. Results support the following insights and opportunities for modeling methods: (1) it is important to modeling accuracy that residuals be checked for even dispersion to avoid areas of over-and underprediction; (2) modeling with bounded, yet unfixed, rates is a sufficiently simple alternative to fixed-rate modeling that can eliminate the need for manual adjustments and provide additional system understanding to inform regulation; (3) if fixed rates modeling is desired, model quality for this system might be improved through revising the current low rate (along with the associated f-ratio updates) from 0.02 ⁄ day rate to 0.006 ⁄ day and potentially adding a new rate at 1.0 ⁄ day in some cases; and (4) the current 57 ⁄ 43 ratio of slow ⁄ fast BOD is reasonable based on the 52 ⁄ 45 ⁄ 3 slow ⁄ fast ⁄ faster BOD proportions of this study.(KEY TERMS: environmental impacts; environmental regulations; microbiological processes; rivers ⁄ streams; simulation; total maximum daily load; transport and fate.) Rosenquist, Shawn E., Jason W. Moak, and Oscar P. Flite, 2012. Modeling Biochemical Oxygen Demand Through the Middle and Lower Savannah River.
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