The food web of a severely contaminated site following reclamation with warm season grasses

We used the stable isotope 13C to distinguish between food web components that depended on warm season grasses with the C4 photosynthetic pathway and those that depended on plants with the C3 pathway. The study site was contaminated by heavy metals from a zinc smelter that operated near Palmerton, Pennsylvania, U.S.A. C3 plants only contributed 1.16% of aboveground primary productivity, whereas recently seeded (5–7 year old) warm season C4 grasses contributed the remaining 98.84%. Analyses of tissue samples revealed that the carbon content of invertebrates and vertebrates did not reflect the composition of the vegetation. Of 135 samples, 48 (36%) had greater than 75% of their carbon from C4-derived sources, while 32 (24%) of the samples had less than 25%. However, carbon from C4 grasses passed through to higher trophic levels, as shown by the abundance of predators with a high proportion of C4-derived carbon. We document three channels of carbon flux through the food web, one based on warm season grasses, now supporting a functioning ecosystem at all key trophic levels, one based on C3 plants, and a third based on detritus. Theoretical and empirical studies have shown that relative configurations of such channels are important to ecosystem stability. Our results suggest that functional groupings of plants based on photosynthetic pathway or other plant traits likely form the basis for food web compartments. By using diverse functional groups of plants for reclamation or restoration, practitioners may be able to aid the development of channels and thereby promote desired ecosystem states.