Ecological status and dynamics of a salt marsh restoration in the Salmon River Estuary, Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/kk91fp79c

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  • In 1978, a 22 ha diked pasture in the Salmon River estuary, Oregon, was restored to tidal influence. The goal was to re-establish the original salt marsh. The pasture had been diked for 17 years and was dominated by upland pasture species. The site had also subsided by 30- 40 cm relative to surrounding, undiked high salt marsh. This study evaluates the restoration process from 1980 to 1988. Data on species cover and frequency, surface elevation, soil texture, soil-water salinity, and standing biomass were collected at 49 permanent plots established in 1978 by Mitchell (1981) After dike removal, there was a rapid die-off of pasture species. Potentilla pacitica and Agrostis alba remained as residuals at higher tidal elevations but diminished or disappeared at lower elevations. Newly barren flats were revegetated by colonizing species that were mostly absent in 1978, but comprised 31% cover by 1980 and 91% cover by 1988. Ephemeral colonizers Spergularia marina, Puccinellia purnila and Cotula coronopifolia never became abundant and did not persist. Persistent colonizers dominated the restoration site by 1988; of particular importance are Salicornia virqinica, Distichlis spicata, and especially Carex lyngbyei (67% cover). The behavior of residuals and colonizers are clearly expressed in 1988 plant conuiiunities. Mid-transitional marsh elevations (1.21 - 1.50 m MLLW) support a residual Potentilla/Agrostis community. Due to surface subsidence, restoration has been to low rather than high salt marsh. Two colonizing communities, Salicornia/Distichlis and Carex, occupy the low-transitional marsh zone (1.01 - 1.35 m MLLW). The widespread Carex community is a nearly monotypic (98% cover) stand of Carex lyngbyei. Although the Carex and Salicornia/Distichlis communities occupy a similar elevational range, the latter community is situated in closer proximity to the ocean and sand spit at the mouth of the estuary. Both Salicornia and Distichlis are positively correlated with substrate sand (r=0.48, p=0.O01; r=0.56, p=0.000 respectively) and salinity (r=0.59, p=0.002; r8=O.66, p=0.000). Carex has a weak negative correlation with both sand (r8= -0.42, p=0.005) and salinity (r8= -0.423, p=0.003). In 1988, peak standing biomass of the restored marsh was 1645 g/m2, more than twice that of the 1978 pasture bioinass (758 g/m2). Results of this study suggest that the diked pasture has been restored to a functioning salt marsh system. It has not, however, been restored to its pre-impact condition. Lowered marsh surface elevation as a result of diking has had a major effect on restoration results, and will continue to exert a strong influence on hydrology and vegetation. While changes in species composition and biomass production were most rapid between 1980 and 1984, significant changes continued to occur between 1984 and 1988, the last year reported in this study.
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