Catastrophes, Near-Catastrophes and the Bounds of Expectation: Success Criteria for Macroscale Marsh Restoration

Abstract

Most tidal marsh on Delaware Bay has a history of diking for purposes ofsalt hay (Spartina patens) production and wildlife management. Extensiveditching for drainage and mosquito control has also altered naturalhydrological cycles, and combined with diking or other water controlstructures has provided suitable conditions for invasion by Phragmitesaustralis. Where diking and other water control measures have been inplace for extended periods, in some instances back to colonial times,marsh surfaces have subsided by oxidation and compaction, and high marshspecies of plants are maintained artificially at low marsh elevations.These conditions lead to potential catastrophic ``blow-outs{''} whendikes are rapidly breached, principally by storms. Although seawater mayenter the breaches and fill the marsh, the absence of a typical fourthorder drainage system (long filled by farming practices andsedimentation) prevents efficient return of tidal water to the adjacentbay. Massive circulation patterns and standing water combined with thelow marsh plain elevation kill extant plants and prevent recolonizationby low marsh species. The result may be destruction of the root mat and``fluidization'' of the entire marsh surface-replaced by an open waterlagoon environment. It may take many decades for the marsh to begin toreestablish itself, if ever. Without further intervention, the slowlyrecovering marsh is characterized by `'tree-like'' drainageconfigurations that appear to exhibit low drainage density downstream,low overall sinuosity and higher order intertidal streams. It is in thisframework that the ecological engineering of macroscale marshrestoration and the criteria that determine its success, the `'bound ofexpectation,'' is undertaken.