Subtidal advective water flux as a potentially important nutrient input to southeastern U.S.A. Saltmarsh estuaries

An initial study was conducted to assess the importance of the advective movement of interstitial water from subtidal creek sediments in enriching the overlying creek water of the estuary. The process of advection was measured in two creeks of a South Carolina estuarine saltmarsh and results indicated that significant amounts of inorganic nutrients (NH₄⁺ and PO₄^-3) were added to the overlying creek water by this process. The nutrient concentrations in the advected water were as much as an order of magnitude higher than in the overlying water column. A comparison of runoff from the marsh surface during low tide to advection from subtidal creek bottoms indicated the importance of the latter in contributing NH₄⁺ and PO₄^-3 to the estuarine water column. Data indicated, however, that runoff from the marsh surface appeared to be a greater source of NO₃^- + NO₂^- to the tidal creek waters. Mean (n = 5 sites) advective flux across one of the creeks was 3·1 mg NH₄⁺-N m^-2 tide^-1, 0·02 mg NO₃^-+NO₂^--N m^-2 tide^-1 and 0·31 mg PO₄^-3-P m^-2 tide^-1 which was 6 times and 2·5 times higher for NH₄⁺ and PO₄^-3, respectively, than surface runoff (a process known to export nutrients to tidal creek water) from the nearby vegetated marsh. When normalized over the areal extent of subtidal creek bottom in the estuary, subtidal advection is estimated to contribute approximately 3 times as much NH₄⁺ and 1·3 times as much PO₄^-3 to the estuarine water column than low tide runoff from the vegetated marsh surface.