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Developing and Calibrating an Indicator for Biogeochemical Condition of Headwater of Riparian Ecosystems
Richard D. Rheinhardt 1,2, Mark M. Brinson 1, Robert R. Christian 1,
Kevin H. Miller1,3, and Greg F. Meyer1
1 Department of Biology, East Carolina University, Greenville, NC 27858
2 415 County Road, Pocasset, MA 02559, rrheinhardt@earthlink.net
3 Miller North Carolina Wetlands Restoration Program, Raleigh, NC 27699-1619
Vegetated buffers of headwater riparian ecosystems remove nitrate from surface and ground water in agricultural landscapes in the coastal plain of southeastern USA. We hypothesized that total organic matter, represented by live plant and detrital biomass, would be an effective indicator of riparian condition for nitrate removal, and thus a general indicator of biogeochemical functioning. Measuring biomass in riparian zones is not practical for rapid assessment, however. Therefore, we partitioned riparian zones into seven easily recognizable cover-types within a continuum of biomass, determined total biomass of each type, and developed a condition index for each cover type based on the biomass of the least altered type (mature forest). To calibrate the biomass index as an indicator for biogeochemical condition of low order streams, we determined the relationship between riparian zone biomass and nitrate concentrations in streams and in contributing ground water. Sites spanning the array of riparian conditions from least to most altered showed a pattern of low concentrations of nitrate nitrogen at sites with high biomass and high concentrations at sites with low biomass. The indicator of biogeochemical condition was arranged to give more weight to biomass near the channel than further away in the riparian zone. This approach may not be as useful in higher order streams, however, because they likely are more affected by contributing streams and ground water than by local riparian condition.
Keywords: riparian ecosystems, headwater streams, biomass, nitrate, indicator calibration, nutrient buffer, coastal plain, North Carolina