HGM vs. IBI hydrology
landscape success criteria
floristic quality Abby Rokosch
Jessen Book Siobhan Fennessy
In 1985 a 12 hectare plot in the Sweetwater National Wildlife Refuge was created to replace a similar sized plot of land destroyed for construction purposes. At first glance, the wetland appears to be fully functional. It fulfilled the government mandated requirements by establishing wetland vegetation, and consequently resembles a natural wetland. However, the created wetland still did not meet the project's goals. In this case, the wetland was created in order to help provide habitat for the endangered Light-footed Clapper Rail. This wetland was planted with cordgrass, the necessary habitat for Clapper nesting. The cordgrass was planted, and seemed to thrive. Yet, the Clapper did not nest. Superficially, the wetland was successful in its establishment of the cordgrass, but for some reason the Clapper would not use it for nesting. Upon closer examination it was determined that the Clapper would not nest because the cordgrass community planted did not grow tall enough to support nests (Zedler, 1993 in Gibson et al., 1994). Under flooding conditions, the nests of the Clappers would have been washed away. By looking closely at the wetland, it was determined the failure was in the nitrogen (N) depauperate soils. The soils did not contain the necessary N to promote full growth. This was because the base of the wetland was laid on sand substrate, and not on a richer layer of organic matter (Gibson et al., 1994). This is a classic example of hasty restoration projects; while the proximate goal of establishing cordgrass was realized, the ultimate goal of reestablishing the Clapper was unfulfilled.
Observation: Mitigated wetlands (marshes) in San Diego Bay, California, USA, have soils with low organic matter and nitrogen stores (compared to local-natural-sites) and have stunted cordgrass populations.
Hypothesis: Organic and nitrogen amendments would accelerate plant growth and enrich soil nitrogen pools.
Experimental Design: A newly created marsh was used for the experiments. The marsh was: