The Salmon River estuary: restoring tidal inundation and tracking ecosystem response
The Salmon River estuary offered a unique opportunity to simultaneously evaluate several estuarine restoration projects and make comparisons with a reference, undiked portion of the estuary. Dikes installed in three locations in the estuary during the early 1960s were removed in 1978, 1987 and 1996 creating a "space-for-time substitution" chronosequence. I analyzed marsh community response to assess development state of three recovering marshes and make comparisons with the reference. During spring and summer from 1998--2002, I assessed juvenile salmon habitat development by comparing wild Oncorhynchus tshawytscha (Chinook salmon) density, diet composition and modeled growth potential among marshes. I also explored differences in invertebrate abundance and composition among marshes, and determined repeatable and exclusive indicators to marsh age. In my analysis, I applied techniques, such as bioenergetics modeling and indicator analysis, to evaluate ecosystem development. A bioenergetics model was used to compare growth potential with site-specific diet composition and temperature, estuary-specific prey energy, average fish size and calculated consumption rates. Modeled growth potential was positive, ranged from 0.001--0.07 g/g/d, and was unrelated to marsh age. Growth rates approximating the reference were found in the newest restoration site with higher variability. Density and taxonomic richness of benthic macroinvertebrates was related to marsh age, but unrelated to marsh surface insects. Invertebrate communities were also compared among marshes. Benthic communities in the 1996 marsh were different from all other marshes, and insect communities were distinct by site except for several cases when no difference between the reference and the 1978 marsh was found. Using indicator analysis I determined several reliable indicators of marsh age, including Staphylinidae (rove beetles) and Chironomidae larvae (midge flies) in the 1996 marsh. Insect communities were more affected by landscape positioning than benthic communities, but tracking both, and evaluating the key indicators of community response was the most informative for describing and assessing recovery state across marsh conditions. The range of metrics I used to track ecosystem development at the Salmon River estuary provided broad indication as to the state of ecosystem re-development after restoring tidal inundation and revealed differences among the marshes related to landscape position and marsh age.
- Fisheries