Urban channel incision, water table decline, and nitrate attenuation in floodplain aquifers, Greenville, NC / by David F. Harnsberger.
| Author/creator | Harnsberger, David F. author. |
| Other author | O'Driscoll, Michael (Michael Anthony), degree supervisor. |
| Other author | East Carolina University. Department of Geological Sciences. |
| Format | Theses and dissertations |
| Production | 2009. |
| Description | 132 leaves : illustrations (some color), color maps ; 28 cm |
| Supplemental Content | Access via ScholarShip |
| Subjects |
| Summary | Water table decline in riparian areas has been linked to the incision of urban stream channels by increased stormwater runoff. The contact of riparian groundwater with shallow, organic-rich surface soils in riparian zones of both urban and agricultural watersheds may be affected by channel incision. Therefore, channel incision has notable implications for nitrate (N03') attenuation via denitrification and plant uptake in groundwater of riparian, floodplain areas of urban watersheds. In this study, three sediment cores (nine cores total; 3.5 to 6.9 m depth) were collected across transects in the floodplains of three progressively incised, low-order Coastal Plain streams. Standard loss on ignition (LOI) method was used to assess changes in percent organic matter (% OM) with depth for the full length of each core. Three well transects were installed in line with floodplain transects to determine if water table decline adjacent to incised Coastal Plain streams notably impacts the contact of floodplain groundwater and shallow organic matter (OM). The impact of water table decline on NO3'-attenuation in floodplain aquifers was also assessed. Water samples were collected monthly from eighteen monitoring wells (six per site) from October, 2007 to September, 2008 and were analyzed for nitrate-N (NO3'-N), ammonium-N (NH4'^-N), dissolved organic carbon (DOC), and dissolved oxygen (DO). Results of this investigation suggest organic matter in riparian areas is not confined to the upper few centimeters of riparian sediment profiles in low order Coastal Plain watersheds. Buried soil horizons and isolated hotspots of OM were found in 8 of9 cores at depths of 54 to 230 cm. Despite the occurrence of deep and laterally extensive peat layers at the urban and suburban sites, water table decline caused a notable reduction in contact between floodplain groundwater and shallow organic matter at the urban and suburban sites. Though groundwater-organic matter contact was reduced adjacent to incised channels, buried peats contributed high (> 6 mg/L) concentrations of DOC to floodplain groundwater. High DOC concentrations in association with low DO concentrations (< 1 mg/L) provided conditions suitable for denitrification across all three floodplain aquifers. Median N03'-attenuation (decrease, loss and/or retention) values (N = 12/site) were calculated as a percent difference in monthly NO3'-N concentrations between up-gradient and near-stream locations for each floodplain study site. NO3'-N concentrations were attenuated 99%, 58%, and 46% at the rural, suburban, and urban floodplain sites. This decrease in percentage NO3'-attenuation with increasing near stream water table depth (0.82 m, 0.99 m, and 1.47 m for the rural, suburban, and urban sites) suggests that water table decline and impaired NO3'-attenuation across the urban and suburban floodplains may be related. Though near-stream N03'-N concentrations were significantly higher at the incised study sites than at the rural site, they were low in comparison to near-stream concentrations in unbuffered agricultural settings of the US and Canada. Marked variability in groundwater discharge from each floodplain, caused by variable hydraulic conductivity of floodplain sediments at each site, prevented a clear relationship between water table decline and the loading ofNO3' to surface water at each site. |
| General note | Presented to the faculty of the Department of Geological Sciences. |
| General note | Advisor: Michael A. O'Driscoll |
| Dissertation note | M.S. East Carolina University 2009 |
| Bibliography note | Includes bibliographical references (leaves 71-79). |
| Genre/form | Academic theses. |
| Genre/form | Academic theses. |
| Genre/form | Thèses et écrits académiques. |
Availability
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