Early biotic and abiotic assessment of soil amendment as a wetland restoration technique

Background/Question/Methods

Inherent in any wetland restoration is the question of the ecological success of the project. Numerous studies aim at evaluating the success of projects in terms of producing natural levels of biodiversity and ecosystem function. Most times these studies consist of pre- and post-observational experiments. Rarely are wetland restorations evaluated as manipulative field experiments nor focused on early pathways of development. Here we use a manipulative in-situ field design to evaluate the biogeochemical consequences of soil amendment use in wetland restoration. Our study was conducted at the Cockroach Bay Aquatic Preserve in Ruskin, FL. We compared the effects of amended and un-amended dredge soil on interstitial water pH, salinity, and sulfide concentrations, sediment C:N, Spartina alterniflora tissue C:N, and soil macroinvertebrates. We placed S. alterniflora plants, potted within perforated pots filled with our experimental soil types, directly into the marsh at low marsh level and collected data on our parameters between August 2007 and September 2008. Data collection consisted of monthly abiotic sampling and quarterly pot-harvests for biotic sampling. Additionally, we collected data on the same parameters from the surrounding marsh in which our pots were placed. Our experimental design was a randomized block with 3 sites within the preserve.

Results/Conclusions

We harvested a total of 120 pots (2 soil types * 4 time periods * 5 replicates * 3 sites) and the same number of ambient marsh cores for comparison. Initial ANOVA results demonstrate significant site differences that overshadow differences in most abiotic variables between sediment types. Also, differences in most abiotic conditions between our experimental pots and the ambient marsh were non-significant. The exception to this early trend is in total soil nitrogen and carbon which were consistently higher in the amended soil and more consistent with values measured from the ambient marsh. Early results from tissue C:N analysis of S. alterniflora demonstrates non-significant differences between soil types and ambient marsh plant tissue. In terms of zoological effects, the diversity of below-ground macro-invertebrates colonizing our pots increased over time with taxon-specific variations in rate and significant site differences. The most diverse taxa were, in order of decreasing diversity, crustaceans, bivalves, gastropods, polychaetes, and nematodes. With completion of our data analysis we expect to be able to advocate for the use of organically-amended soil in the restoration of coastal wetlands because of the similarities in attributes between amended-soil conditions and natural marshes in terms of ecosystem biodiversity and function.