Mulching effects on the seasonally flooded zone of west-central Florida, USA wetlands

Abstract

Wetland mulching is the transfer of surface soil (often from a wetland that will be filled or otherwise impacted) onto the surface of a wetland creation area to provide wetland vegetation, organic matter, and soil organisms. A total of 33 herbaceous wetland creation areas (17 mulched and 16 non-mulched) in the Tampa, Florida, USA region were studied at the end of the wet season (November) and subsequent dry season (June) to determine the effects of mulching. All wetland creation areas were constructed between 5 and 11 years prior to the study. Using the seasonally flooded zone of each wetland, we examined the effects that mulching has on 1) percent organic matter in the soil, 2) the Prevalence Index (measure of hydrophytic vegetation occurrence) of plant communities present, 3) species richness, eveness, and diversity (Shannon Index), 4) total vegetation cover, 5) above-ground biomass production, 6) soil pH, and 7) nutrient content. Mulched wetlands had a higher percent organic matter in the soil than non-mulched wetlands (5.9±0.5% vs 2.6±0.3%, respectively). In November, the mulched wetlands had lower Prevalence Index values, species richness, and diversity values than non-mulched wetlands. Between November and June, nonmulched wetlands decreased in species richness (10.6±0.7 to 6.6±0.6 per m²) and overall diversity (Shannon Index values 1.74±0.08 to 1.28±0.10), while no change in diversity was detected for mulched wetlands. In a subsample of wetland sites, the concentrations of secondary macro-elements (Mg, Ca, and K) were greater in the mulched than in non-mulched wetlands. No significant differences were detected for primary nutrients (NO₃−N and P), soil pH, or above-ground plant biomass. Even 5–10 years after construction, initial mulching still seems to still have an influence on ecosystem development in these created wetlands.