Master of Science (MS)
Oceanography and Coastal Sciences
Naturally vegetated areas converted to urban uses increases impervious surfaces in a watershed with corresponding increases in nutrient, sediment, and metal loadings to downstream ecosystems. Wetlands mitigate detrimental impacts by transforming or retaining pollutants. Current and historic sedimentation and metal retention rates were measured in an urban, depressional wetland in Baton Rouge, Louisiana to evaluate landscape position and watershed development on these processes. Sedimentation disks, feldspar marker horizons, and Cs137 analyses were used in three distinct landscape positions. Inflow channels had the highest elevation and water velocity while the interior was located in the lowest elevations with the longest hydroperiod. An intermediate elevation between the channel and interior was designated as the transitional landscape position. Sedimentation disks yielded significant differences (p = 0.009) in sedimentation rates between the channel (23.8 ± 5.43 g/m2/d) and transitional (37.1 ± 5.09 g/m2/d) landscapes. The interior (27.9 ± 4.65 g/m2/d) position was not significantly different. Feldspar data yielded comparable values for the transitional (29.6 ± 2.57 g/m2/d) and interior (27.2 ± 3.64 g/m2/d) locations, which were not significantly different (p = 0.35). A historic sedimentation rate of 0.49 cm/yr ± 0.11 cm/yr, calculated from Cs137 analysis, was significantly lower than the current rate of 2.95 ± 1.10 (p = 0.010). Lead, Cd, Cu, Zn, Ni, and P sediment concentrations were significantly greater (p < 0.05) in the interior than the transition based on sedimentation disks. Sediment metal concentrations were normalized with Al to compensate for increases in metal concentration with increasing clay content. Significantly higher Al content in the interior resulted in either no differences between the interior and transitional locations or significantly lower concentrations in the interior after Al-normalization. Historic metal retention rates (background concentrations) were calculated for depths below the 1963 Cs137 peak. Metal/Al ratios from soil cores yielded significantly higher Cd, Cr, Cu, Zn, Ni, and P concentrations in sediments deposited since 1963. These higher concentrations correspond with a seven percent increase in developed area surrounding Bluebonnet Swamp from 1963 to 2000. This urban wetland functions as an important sediment and pollutant sink, and protects downstream aquatic ecosystems.
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Sanders, Renee Lynn, "Sedimentation rates and metal retention in an urban Louisiana swamp" (2002). LSU Master's Theses. 879.