Biogeochemistry

, Volume 36, Issue 3, pp 275–303

Effects of historic tidal restrictions on salt marsh sediment chemistry

  • J.W. PORTNOY
  • A.E. GIBLIN
Article

DOI: 10.1023/A:1005715520988

Cite this article as:
PORTNOY, J. & GIBLIN, A. Biogeochemistry (1997) 36: 275. doi:10.1023/A:1005715520988

Abstract

The effects of tidalrestrictions by diking on salt marshbiogeochemistry were interpreted by comparingthe hydrology, porewater chemistry and solidphase composition of both seasonally floodedand drained diked marshes with adjacentnatural salt marshes on Cape Cod,Massachusetts. Flooding periods weregreatest in natural and least in drainedmarshes.

Differences between the chemistry of thenatural and diked marshes depended upon thedepth of the water table and the supply ofsulfate for anaerobic metabolism. Drainedmarsh sediments were highly acidic (pH <4)with porewaters rich in dissolved Fe; thenatural and diked flooded marshes had pH 6–7.5and Fe orders of magnitude lower. Porewater nutrients, sulfides and alkalinitywere much lower in both flooded and draineddiked marshes than in the natural marsh.

Sediments of the drained marsh had subsided90 cm relative to the natural site due toorganic matter decomposition and compaction. However, despite the loss of organic matter,much of the P and N was retained, withNH4 likely protected from nitrificationby low pH and PO4 adsorbed on Fe and Aloxides. Iron, and to a lesser degree sulfur,had also been well retained by the sediment. Despite eight decades of diking, substantialamounts of reduced S, representing potentialacidity, persisted near the top of the watertable.

In contrast, the surface of the seasonallyflooded marsh was only 15 cm below thenatural marsh. Accretion since dikingamounted to 25 cm and involved proportionallyless mineral matter.

The restoration of seawater flow to bothseasonally flooded and drained diked marsheswill likely extend flooding depth andduration, lower redox, increase cationexchange, and thereby increase NH4,Fe(II), and PO4 mobilization. Increasedporewater nutrients could benefitrecolonizing halophytes but may also degradesurface water quality.

acid sulfatesdikingrestorationsalt marshessulfur cycling

Copyright information

© Kluwer Academic Publishers 1997

Authors and Affiliations

  • J.W. PORTNOY
    • 1
  • A.E. GIBLIN
    • 2
  1. 1.National Biological ServiceCape Cod National SeashoreWellfleet
  2. 2.Ecosystems CenterMarine Biological LaboratoryWoods Hole