The exchange of phosphorus between a euhaline vegetated marsh and the adjacent tidal creek

Abstract

Phosphorus exchange between a euhaline vegetated marsh and the adjacent tidal creek (North Inlet, South Carolina) was studied on 40 tidal cycles between 15 April 1983 and 19 June 1984. A flume was utilized to evaluate the net phosphorus exchange during tidal inundation, and a weir study was conducted to estimate the export of phosphorus from the marsh via runoff and seepage during low tide exposure (including storm events). Mean flood tide concentrations of PO 4 3− and particulate phosphorus (PP) varied seasonally between 0·1 and 1·3 μg at. P l −1 and 0·3 to 2·8 μg at. P l −1, respectively, with the highest values observed during the summer. PO 4 3− and PP were consistently removed from the tidal water inundating the marsh especially during the warmer months. There was a statistically significant (α = 0·05) import of PO 4 3− and PP to the vegetated marsh during tidal inundation of 0·46 gP m −2 year −1 and 2·01 gP m −2 year −1, respectively. For both constituents the removal rate on an areal basis was greater in the low marsh (tall Spartina alterniflora) than on the high marsh (medium and short S. alterniflora). The magnitude and direction of total phosphorus (TP) flux was similar to PP because the latter constituted up to 85% of the former. Export values of PO 4 3−, PP, and TP from the marsh via runoff and seepage during low-tide exposure (including rain events) were approximately 25% of the respective import values during tidal inundation. This study suggests a euhaline vegetated marsh is a sink for PO 4 3−, PP, and TP and therefore may not be the source of phosphorus outwelled in many marsh-estuarine systems.