Effects of water hardness on slough-wet prairie plant communities of the A. R. M. Loxahatchee National Wildlife Refuge

Alterations to ground-water and surface-water hydrology and water chemistry in South Florida have contributed to increased flows of mineral-rich (hard water) canal water into historically rain-fall driven (soft water) areas of the Everglades. The interior of the A. R. M. Loxahatchee National Wildlife Refuge largely has retained its historic low conductivity or soft water condition due to its relative isolation from canal flows. However, recent sampling by USGS and the Refuge has shown that canal influences on water quality extend several kilometers into the Refuge in some areas, and Refuge managers and scientists are concerned that these influences may increase depending on future changes in water management operations. A survey across existing mineral gradients will be performed to document patterns of vegetation change and their relationship to changes in water hardness and other environmental factors. Laboratory and field experiments will test these correlative relationships to determine the relative importance of increasing water hardness as a cause of observed vegetation changes across canal gradients.

Intrusion of canal waters into the Refuge increases the availability of Phosphorus (P), the primary limiting plant nutrient in the Everglades, as well as concentrations of major mineral ions such as Ca 2+, Mg 2+ and SO4 2-. While the ecological effects of P enrichment on the Everglades is fairly well understood, potential impacts caused by increased mineral concentrations in this soft-water wetland are largely unknown. Understanding the types and magnitude of these impacts is particularly important given that the area of the Refuge exposed to mineral enrichment is much greater than that exposed to P enrichment. The objective of this project is to determine the effects of increased flows of mineral-rich water on the aquatic plant community of the Refuge interior. Slough-wet prairie (SWP) habitats area a major landscape feature in the Refuge and several SWP plant species may be adapted to the soft-water conditions in the Refuge interior. Increased mineral loads to the Refuge may result in a shift towards a more species-poor and spatially homogeneous community, In addition, there is a small amount of evidence to suggest that mineral enrichment may favor the growth and expansion of sawgrass and a consequent decline in the coverage of the SWP habitats.