Salt Marsh Diking and Restoration: Biogeochemical Implications of Altered Wetland Hydrology |
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Authors: | John W Portnoy |
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Institution: | (1) National Park Service, Cape Cod National Seashore, 99 Marconi Site Road, Wellfleet, Massachusetts 02667, USA , US |
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Abstract: | Experimental short-term desalination and drainage of salt marsh cores in greenhouse microcosms caused Spartina production to increase after one growing season, reflecting decreased salt stress and sulfide toxicity. However, production
thereafter declined, likely due to pyrite oxidation and acidification in drained treatments and sulfide accumulation in waterlogged
treatments.
A survey of longer-term (decadal) effects of diking on peat composition of Cape Cod, Massachusetts, USA, marshes revealed
acidification, Fe(II) mobilization, and decreased organic content in drained sites. Despite the aerobic decomposition of organic
matter, abundant nutrients remained as sorbed NH4 and mineral-bound PO4. In diked, seasonally waterlogged sites, porewater alkalinity, sulfide, ammonium and orthophosphate were much lower, and
organic solids higher, than in adjacent natural marsh.
Seawater was added to cores from diked marshes to study the effects of tidal restoration. Salination of the drained peat increased
porewater pH, alkalinity, ammonium, orthophosphate, Fe, and Al; copious ammonium N, and Fe(II) for sulfide precipitation favored
Spartina growth. Salination of diked–waterlogged peat increased sulfate reduction and caused 6–8 cm of sediment subsidence. The resulting
increase in porewater sulfides and waterlogging decreased vigor of transplanted Spartina alterniflora. Results indicate that seawater restoration should proceed cautiously to avoid nutrient loading of surface waters in drained
sites or sulfide toxicity in diked–waterlogged marshes. |
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Keywords: | : Salt marsh Diking Biogeochemical cycling Restoration Massachusetts |
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