PS 68-116
Hydrologic regimes revealed bundles and tradeoffs among six wetland services
Current ecological theory suggests that biodiversity support and other ecosystem services can be bundled, or provided together at high levels. Restoration practitioners regularly put that idea to the test by attempting to recover native vegetation, flood regulation, and water quality improvement in individual wetland restoration projects. We asked if six commonly-sought ecosystem services could be provided together in three created wetlands within a site at the University of Wisconsin-Madison Arboretum. Wetlands were similar in size, shape, inflows (quantity and quality), soils, and plantings, but differed in drainage rate due to natural variation in subsoils. We sought to explore how differences in hydrologic regime would affect ecosystem services and how levels of services would covary. We measured: flow attenuation and stormwater retention by monitoring flows through the inlet and outlet weirs of each wetland, net primary productivity (NPP) and diversity support by repeatedly sampling and harvesting vegetation, erosion resistance by measuring the stress required to detach surface soil particles, and water quality improvement by analyzing removal of four common contaminants.
Results/Conclusions
On average, the fastest-draining wetland infiltrated inflows five times faster than the slowest-draining wetland. The resulting differences in hydrologic regime (including duration and extent of inundation) led wetlands to differ significantly in levels of all measured services (ANOVA P<0.05). The fastest-draining wetland provided the highest level of five services but the lowest level of NPP, whereas the slowest-draining wetland provided the highest NPP but lowest levels of all other services. Hydrologic regime explained some patterns, e.g., inundation favored highly productive emergent vegetation (and high NPP) but also allowed phosphorus export (leading to low or no water quality improvement). Other patterns indicated interactions among services, e.g., high NPP limited light levels and appeared to limit the formation of moss and algal mats that stabilized surface soils and increased erosion resistance in areas with low NPP. In our system, some, but not all services, were bundled. Our results highlight the important effect of hydrologic regime on wetland services and the potential for unexpected trade-offs to occur among services (with NPP in our case). Further multi-service assessments in restoration projects could help reveal underlying relationships among services and guide restoration planning.