Dr. Ewel described the relationship between an exotic herbivorous fish and hydrilla, which is an invasive aquatic weed that is widespread in the southern United States. She constructed a model to simulate the effect on a lake ecosystem of using this fish as a biological control agent.
Her current research interests are concentrated in wetlands. The characteristic elements of wetlands are hydroperiod (length of flooding), flow rate, water quality, and fire frequency. Management practices that affect these elements can therefore change the species richness and productivity of wetland ecosystems. When a wetland is used for wastewater recycling, for instance, the increased nutrient supply may combine with the longer hydroperiod to alter both plant and animal communities. Draining a wetland, both by constructing berms to reduce water inflow and by building canals to speed water outflow, also changes the plant community; this common practice has frequently opened up avenues for invasion by both native and alien species.