Fluxes of water and solute in a coastal wetland sediment. l. The contribution of regional groundwater discharge

doi:10.1016/0022-1694(94)02561-O

Journal of Hydrology

Volume 164, Issues 1–4, January 1995, Pages 89-107

https://doi.org/10.1016/0022-1694(94)02561-O Get rights and content

Abstract

Upward discharge of fresh groundwater into a mid-Atlantic intertidal wetland contributed 62% of the water needed to replace evapotranspiration losses from the sediment during an 11 day period in September. Infiltration during flooding by tides provided most of the balance; thus there was a net advection of salt into the sediment. The amount of groundwater discharge was estimated from changes in water storage in the sediment, as inferred from measurements of hydraulic head made every 10 min. We argue that this approach is inherently more accurate than calculating the flux as the product of hydraulic conductivity and head gradient. Evapotranspiration was estimated from direct measurements of net radiation. On an annual time-scale, our results suggest that groundwater discharge at this site may exceed the evapotranspiration flux during months of reduced evapotranspiration. Should this occur, groundwater-driven advection would supplement diffusion, during flooding, in removing salt from the sediment.

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Different salt marsh macrophytes have different tolerances to salinity, so the ecological zonation of salt marsh macrophytes is significantly affected by soil salinity (Julkowska and Testerink, 2015; Xue et al., 2018)). Many studies have shown that these abiotic factors are related to the elevation and hydrological processes of salt marshes (Silvestri et al, 2005), especially in relation to groundwater processes in shallow soil (Gardner, 1973; Hemond and Fifield, 1982; Harvey et al., 1987; Harvey and Odum, 1990; Nuttle and Harvey, 1995). Groundwater process is the main route of solute migration in soil (Guo et al., 2008, 2011, 2013, 2014, 2016, 2019; Famiglietti, 2014).
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In a typical tidal creek, no direct freshwater input from upstream rivers/streams occurs. At a daily time scale, water outflow, evapotranspiration and intertidal storage account for losses in the water budget (Michot et al., 2011; Nuttle and Harvey, 1995; Speer et al., 1991). Mutual feedback processes between hydrodynamics and geomorphology define the natural system of tidal creeks.
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This chapter provides a very brief background on salt marshes and then focuses on: the role of N in regulating primary production, plant zonation, and community structure, the input and output N budget of salt marshes, and the cycling of N in the plant-sediment system. Marshes have experienced increased input of anthropogenic N loads over the last century. There is growing evidence that fixation, denitrification and even sedimentation rates are altered by increased external N inputs but these responses need to be much better understood and quantified. There are large fluxes of N between marshes and tidal creeks and between marsh creek complexes and estuarine and coastal waters. The net direction of the fluxes is not consistent and the rules governing exchange are not well understood. A review of a small number of studies has suggested that marshes generally export N to coastal waters, although some specific forms, such as nitrate may be imported. Marshes play a large role in altering both the timing and the form of N flowing from land to sea. The degree to which this interaction buffers coastal systems from land-based nutrient inputs and supports estuarine food webs needs to be better understood. It also includes a brief discussion of marshes and eutrophication and place marshes in the context of the global N-cycle.
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Fluxes of water and solute in a coastal wetland sediment. l. The contribution of regional groundwater discharge

Abstract

J. Hydrol.

Estuarine Coastal Shelf Sci.

Estuarine Coastal Shelf Sci.

J. Hydrol.

J. Hydrol.

J. Hydrol.

J. Hydrol.

Estuarine Coastal Shelf Sci.

Interannual patterns of watertable height and groundwater derived nitrate in near-shore sediments

Biogeochemistry

Ammonium and phosphate dynamics in a Virginia salt marsh

Estuaries

Applied Regression Analysis

A Water Balance Estimate at Brownsville, Virginia

Calibration, comparison, and correction of net radiation instruments used during FIFE

J. Geophys. Res.

Groundwater