Carbon, Nitrogen, and Phosphorus Accumulation in Floodplains of Atlantic Coastal Plain Rivers, Usa

Abstract

Net nutrient accumulation rates were measured in riverine floodplains of the Atlantic Coastal Plain in Virginia, Maryland, and Delaware, USA. The floodplains were located in watersheds with different land use and included two sites on the Chickahominy River (urban), one site on the Mattaponi River (forested), and five sites on the Pocomoke River (agricultural). The Pocomoke River floodplains lie along reaches with natural hydrogeomorphology and on reaches with restricted flooding due to channelization and levees. A network of feldspar clay marker horizons was placed on the sediment surface of each floodplain site 3-6 years prior to sampling. Sediment cores were collected from the material deposited over the feldspar clay pads. This overlying sediment was separated from the clay layer and then dried, weighed, and analyzed for its total carbon (C), nitrogen (N), and phosphorus (P) content.Mean C accumulation rates ranged from 61 to 212 g·m Ϫ2 ·yr Ϫ1 , N accumulation rates ranged from 3.5 to 13.4 g·m Ϫ2 ·yr Ϫ1 , and P accumulation rates ranged from 0.2 to 4.1 g·m Ϫ2 ·yr Ϫ1 among the eight floodplains. Patterns of intersite variation in mineral sediment and P accumulation rates were similar to each other, as was variation in organic sediment and C and N accumulation rates. The greatest sediment and C, N, and P accumulation rates were observed on Chickahominy River floodplains downstream from the growing metropolitan area of Richmond, Virginia. Nutrient accumulation rates were lowest on Pocomoke River floodplains that have been hydraulically disconnected from the main channel by channelization and levees. Sediment P concentrations and P accumulation rates were much greater on the hydraulically connected floodplain immediately downstream of the limit of channelization and dense chicken agriculture of the upper Pocomoke River watershed. These findings indicate that (1) watershed land use has a large effect on sediment and nutrient retention in floodplains, and (2) limiting the hydraulic connectivity between river channels and floodplains minimizes material retention by floodplains in fluvial hydroscapes.

Land Cover Changes (1963–2010) and Their Environmental Factors in the Upper Danube Floodplain

“…In other studies, poor connectivity and strong fragmentation of floodplain result in a lower rate of mineral sedimentation and P accumulation [104]. In this study agricultural intensification shifted the arable land into larger fields, which equalized the conditions and had negative impacts on species diversity, as also found by Harms et al [105].…”

Spatial variability in floodplain sedimentation: the use of generalized linear mixed-effects models

“…At the reach scale, TOC and TN exchange between the main channel and its adjacent floodplain plays a key role in the ecological functioning (Junk, 1999;Robertson et al, 1999;Tockner et al, 1999;Tockner at al., 2000;Thoms, 2003;Knosche, 2006;Preiner et al, 2008). Previous research has shown how human-induced changes at the basin and reach scale have decreased the potential of riverine floodplains to act as sediment-associated nutrient sinks (Noe and Hupp, 2005;Owens et al, 2005;Pierce and King, 2008;Cabezas et al, 2009;Cabezas and Comin, 2010). To accomplish knowledge-based management and restoration strategies at specific river reaches, TOC and TN deposition patterns must be properly understood.…”

“…scale by channel-floodplain geomorphology, which promotes spatial variability on sedimentation load and patterns for a given river section during a specific flood event (Hupp, 2000;Noe and Hupp, 2005;Piégay et al, 2008). At this scale, previous studies have indicated that distance from the main channel exerts more influence on spatial variability of overbank sedimentation than downstream variation (Walling and He, 1998;Middelkoop and Asselman, 1998;Thonon et al, 2007).…”

Nitrate leaching from short-hydroperiod floodplain soils

“…We did not observe significant erosion at any plot. It should be noted that N sedimentation is controlled by organic matter accumulation and hence is not equal to available N. Because of the linear relationship between N and organic C content of deposited sediments (C/N ratio of fresh sediments was around 11 in all FPZs, Weibel, 2011), we assume as in earlier studies (Stoeckel and Miller-Goodman, 2001;Noe and Hupp, 2005) that N is dominantly organic and has first to be mineralized. Furthermore, this low C/N ratio compared to that of the top 10 cm (C/N ratio = 15, Table 1) suggests that around 30 % of the organic matter in the newly deposited sediments is easily degradable.…”