Created vernal pools: How well do they function compared to natural pools?
Vernal pools are small, isolated, ephemeral wetlands that undergo cyclical periods of drying and inundation. In the Northeast, they typically occur in forested landscapes and are an important ecological resource, providing key breeding habitat for several amphibian and invertebrate species. Due to their small size and ephemeral nature, vernal pools often lack adequate legal protection and are subject to destruction. Because of their importance, vernal pools have been created as mitigation for development projects or as management efforts to enhance existing habitat. Although monitoring of created pools is often required, it is rarely long term and efforts to more fully evaluate how well created pools mimic the ecology of natural pools has been less well studied.
To address this question, we compared 7 vernal pools in southeastern New York that were created in 2006 with 6 established vernal pools in northeastern Connecticut. The 6 established “reference” pools have a long history of supporting breeding populations of wood frogs and spotted salamanders, two amphibian species that are a primary target of vernal pool conservation efforts in the northeastern US. In 2013 and 2014, we collected data from spring through mid- to late- summer on: physical, habitat, water chemistry, productivity, and community composition of amphibians and macroinvertebrates.
The physical habitat structure showed some stark differences between constructed and reference pools. Specifically, created pools were smaller in area, had shallower basins, more open canopies, and greater amounts of duckweed, cattail, and Phragmites. The created pools were less likely to dry. Several differences in water chemistry were evident: created pools had higher pH, conductivity, and total dissolved solids, and did not demonstrate a seasonal increase in dissolved organic carbon that occurred in reference pools. Created and reference pools were similar in dissolved nitrogen, dissolved phosphorus, and algal biomass. There were also interesting differences between amphibian and macroinvertebrate assemblages among created and reference pools. Created pools had fewer egg masses of key vernal-pool breeding amphibians (wood frogs and spotted salamanders), with both amphibian species present in only 4 of the 7 created sites; however, overall amphibian species richness and composition did not differ. Macroinvertebrate richness was similar across sites, but composition differed greatly between created and reference pools. Our results indicate that although created vernal pools can provide habitat for a variety of species, the ability to mimic the physical conditions and ecological functions of natural vernal pools is suspect.