Spatial and temporal variations of nutrient concentration in the groundwater of a floodplain: effect of hydrology, vegetation and substrate

Abstract

Abstract:Spatio-temporal variations in nitrogen and phosphorus concentrations in groundwater were analysed and related to the variations in hydrological conditions, vegetation type and substrate in an alluvial ecosystem. This study was conducted in the Illwald forest in the Rhine Plain (eastern France) to assess the removal of nutrients from groundwater in a regularly¯ooded area. We compared both forest and meadow ecosystems on clayey-silty soils with an anoxic horizon ( pseudogley) at 1 . 5±2 m depth (eutric gley soil) and a forest ecosystem on a clayeysilty¯uviosoil rich in organic matter with a gley at 0 . 5 m depth (calcaric gley soil). Piezometers were used to measure the nutrient concentrations in the groundwater at 2 m depth in the root layer and at 4 . 5 m depth, below the root layer. Lower concentrations of nitrate and phosphate in groundwater were observed under forest than under meadow, which could be explained by more ecient plant uptake by woody species than herbaceous plants. Thus NO 3 -N inputs by river¯oods were reduced by 73% in the shallow groundwater of the forested ecosystem, and only by 37% in the meadow. Compared with the super®cial groundwater layer, the lowest level of nitrate nitrogen (NO 3 -N) and the highest level of ammonium nitrogen (NH 4 -N) were measured in the deep layer (under the gley horizon at 2 . 5 m depth), which suggests that the reducing potential of the anoxic horizon in the gley soils contributes to the reduction of nitrate. Nitrate concentrations were higher in the groundwater of the parcel rich in organic matter than in the one poorer in organic matter. Phosphate (PO 4 -P) concentrations in both shallow and deep groundwater are less than 62 to 76% of those found in surface water which can be related to the retention capacity of the clay colloids of these soils. Moreover, the temporal variations in nutrient concentrations in groundwater are directly related to variations in groundwater level during an annual hydrological cycle. Our results suggest that variations in groundwater level regulate spatio-temporal variations in nutrient concentrations in groundwater as a result of the oxidation±reduction status of soil, which creates favourable or unfavourable conditions for nutrient bioavailability. The hydrological variations are much more important than those concerning substrate and type of vegetation.

Subsurface Mobilization of Phosphorus in an Agricultural Riparian Zone in Response to Flooding from an Upstream Reservoir

“…This suggests that the P in the groundwater system originates from the riparian zone surface and surface soil, rather than from the adjacent agricultural fields. Previous studies have shown that high water tables in riparian zones can cause leaching of decayed vegetation (Takatert et al, 1999), which increases concentrations of particulate organic P in groundwater. At this site, groundwater subsequently migrates into the Beverly Swamp, south of the research site.…”

Nitrogen dynamics in the shallow groundwater of a riparian wetland zone of the Garonne, SW France: nitrate inputs, bacterial densities, organic matter supply and denitrification measurements

“…The reduction of phosphorus concentrations in groundwater by riparian forests has usually been attributed to root absorption (Sánchez-Pérez et al 1991a), chemical precipitation and adsorption processes (Reddy and Rao 1983;Patrick 1990). Some other studies have documented the effects of factors as well as the interactions which regulate the transfer of nutrients to groundwater, for example geomorphology (Pinay et al 1995), catchment hydrology (Cooper 1990) and vegetation type (Takatert et al, 1999;Sánchez-Pérez and Trémolières, in press).…”

Shallow groundwater nitrogen responses to different land use managements in the riparian zone of Yuqiao Reservoir in North China

“…Many reports have indicated that the woodland in the riparian zone could effectively remove nutrients from the upland (Cey et al, 1999;Takatert et al, 1999;Clement et al, 2003). In our research, the woodlands were located at the lower slope of the croplands.…”

“…Moreover, during the developing process of the ephemeral stream from incised gully, cracks created by many stones with different sizes in the stream bed favored the water and nitrogen transport from the upland. When ammonium-N in shallow groundwater reached woodland, the anoxic environment created by high groundwater table was favorable to the existence of ammonium-N, as shown by other researchers (Takatert et al, 1999;Clement et al, 2003).…”

“…Research on these processes has focused on the hydrogeochemical processes in the stream riparian zone or the river floodplain, where surface water level often fluctuates at the scales of hours, days or weeks (Takatert et al, 1999;Martin et al, 2004;Rassam et al, 2006). However, little research is done on the riparian zone of reservoirs, where surface water level only changes seasonally and is mainly adjusted for flood management and maintenance of water supply.…”