Effect of water column, sediment and time over the tidal cycle on the chemical composition of tidal water in a mesohaline marsh

Abstract

A detailed nutrient exchange study, supported by experimental chamber work, indicates that location on the marsh, depth within the water column, and time over the tidal cycle all affect the chemical composition of tidal water which inundates the marsh surface. On the flood tide, over the low marsh (tall Spartina alterniflora), ammonia and orthophosphate apparently are released into the water column and taken up by the sediment, while on the high marsh (medium S. alterniflora) these constituents are removed from the tidal water the year round. Later in the tidal cycle these nutrients are released from low marsh sediments and removed from the water column. This implies ammonium and orthophosphate are tightly cycled within the vegetated marsh system. Nitrite and nitrate are always removed from the tidal water, except during fall when a large release of nitrite into the tidal water was observed. There is evidence to suggest that when the water volume to sediment surface area is small, nitrite and nitrate are used by the sediment whereas later in the tidal cycle near high tide most of the available NO2-' and NO3-' is used within the water column. DON and DOP are both released and taken up from the tidal water over the low marsh depending on season of the year and whether it is a flood or ebb tide while these nutrients are always removed from the tidal water over the high marsh. Most of the particulate nitrogen and phosphorus was removed over the low marsh on the flood tide.