Sulfate reduction and other sedimentary biogeochemistry in a northern New England salt marsh

Sulfate reduction rates, dissolved iron and sulfide concentrations, and titration alkalinity were measured in salt marsh soils along a transect that included areas inhabited by both the tall and short forms of Spartina alterniflora and by Spartina patens. Pore waters were collected with in situ “sippers ” to acquire temporal data from the same location without disturbing plant roots. During 1984, data collected at weekly intervals showed rapid temporal changes in belowground biogeo-chemical processes that coincided with changes in S. alterGj7ora physiology. Rates of SO, * re-duction increased fivefold (to>2.5 pmol ml I d-l) when plants began elongating aboveground yet decreased fourfold upon plant flowering. This rapid increase in rates of Sod2 reduction must have been fueled by dissolved organic matter released from roots only during active growth. Once plants flowered, the supply of oxidants to the soil decreased and sulfide and alkalinity concentrations increased despite decreases in SO,*- reduction and increases in SOd2-: Cl- ratios. Sulfide concen-trations were highest in soils inhabited by tallest plants. During 1985, S. alterniflora became infested with fly larvae (Chaetopsis apicaiis John) and aboveground growth ceased in late June. This cessation was accompanied by decreased rates o