Trade-offs between soil-based functions in wetlands restored with soil amendments of differing lability

Soil amendments have been proposed as a means to speed the development of plant and soil processes that contribute to water quality, habitat, and biodiversity functions in restored wetlands. However, because natural wetlands often act as significant methane sources, it remains unknown if amendments will also stimulate emissions of this greenhouse gas from restored wetlands. In this study, we investigated the potential trade-offs of incorporating soil amendments into wetland restoration methodology. We used controlled field-scale manipulations in four recently restored depressional freshwater wetlands in western New York, USA to investigate the impact that soils amended with organic materials have on water-quality functions and methane production in the first three years of development. Results showed that amendments, topsoil in particular, were effective for stimulating the development of a suite of biological (microbial biomass increased by 106% and respiration by 26%) and physicochemical (cation exchange capacity increased by 10%) soil properties indicative of water-quality functions. Furthermore, increases in microbial biomass and activity lasted for a significantly longer period of time (years instead of days) than studies examining less recalcitrant amendments. However, amended plots also had 20% times higher potential net methane production than control plots three years after restoration. Wetlands restoration projects are implemented to achieve a variety of goals, commonly including habitat provision, biodiversity, and water-quality functions, but also carbon sequestration, flood abatement, cultural heritage and livelihood preservation, recreation, education, and others. Projects should strive to achieve their specific goals while also evaluating the potential tradeoffs between wetland functions.