Linking extant and historical aquatic vegetation communities in karst springs of the Ozark Highlands to assess status and threats to these highly groundwater-dependent ecosystems

Background/Question/Methods

Karst aquifers of the Ozark highlands of southern Missouri and northern Arkansas discharge thousands of springs, and among the largest springs in the US by volume.   Karst springs are particularly sensitive to contamination because subsurface conduits allow rapid movement of water through the aquifers with little filtration.  However, historical water quality data from most springs are sparse or inconsistent and information about spring flora and fauna are restricted to isolated records or anecdotal information.  Further, spring recharge areas often are not congruous with surface watershed boundaries, which complicates assessments of anthropogenic threats. 

Spring flora, including vascular hydrophytes, bryophytes, and macroalgae, are diverse communities that respond to the physical and chemical properties of the groundwater discharge, including flow rates, temperature, specific conductance, and nutrient concentrations.  In addition, some spring vegetation communities are threatened by nonnative species introductions and physical alterations to spring habitats by humans.  We surveyed the aquatic vegetation communities of first order to third order springs across the Ozark Plateau.  Our purpose is to analyze current and historical aquatic vegetation data in Ozarks springs to 1) compare the extant communities to those observed in a major aquatic vegetation survey of Ozarks Springs in the 1930’s, 2) document the extent of nonnative species introductions into spring habitats, and 3) evaluate potential physical and chemical factors that affect diversity and species composition.

Results/Conclusions

Diversity was strongly related to discharge, where first order springs with discharges greater than 100 cubic feet per second contained three or more times the number of species than third order springs with flow rates between 1 and 10 cfs.  Several species that were documented in the 1930’s have been apparently extirpated from springs, or have reduced distribution.  Nonnative species introductions into Ozarks springs have occurred, but they account for a low percentage of the total vegetation cover.    Our analysis show that vegetation communities in the larger springs have remained largely intact while those of smaller magnitude springs are more susceptible to anthropogenic disturbances.