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Abstract
The influence of catchment-scale disturbance from military training maneuvers was assessed in 12 streams within the Fort Benning Military Installation, Georgia, USA. Contemporary military training resulted in increased erosion potential and associated sedimentation of stream channels.
A comparison of 3 methods (instability index based on shear stress and bed particle size and 2 measures of bedload movement, erosion pins and cross-stream transects) to quantify streambed stability was conducted to assess method efficacy. Bedload movement estimates over the entire 8-mo period (Jan. to Sept. 2003), as well as length of sampling interval (2, 4, 6, or 8 mo), revealed that absolute measures of a cross-stream transect method was the best estimate of streambed stability.
Another study examined the relationships between catchment disturbance and stream physical and organic matter variables. Stream flashiness (response to precipitation event) positively related to storm magnitude and % catchment with sandy soils, whereas streambed stability related to % of catchment with nonforested land. Instream coarse woody debris, benthic organic matter, and streamwater dissolved organic carbon all negatively related to catchment disturbance.
Irrespective of season, a multitude of macroinvertebrate richness measures were all negatively correlated with catchment disturbance. Other than the number and % of macroinvertebrates that cling to habitat, no composition or feeding group measure was related to catchment disturbance. Regional multimetric indices, the Florida Stream Condition Index (FLSCI) and the Georgia Stream Condition Index (GASCI) were both consistently negatively related to catchment disturbance.
Fish were sampled seasonally in 8 streams in 2003. Assemblage measures (richness, diversity, and number collected) were negatively related to catchment disturbance only in the spring but not summer and winter, whereas relative abundance of the 2 most abundant populations consistently showed opposite associations with disturbance, Pteronotropis euryzonus (negative) and Semotilus thoreauianus (positive).
Contemporary land use (1999) better predicted stream physicochemistry and short-lived, high turnover biota (e.g., periphyton, chironomids), whereas historic land use (1944) was more related to streambed stability and longer-lived, low turnover biota (non-chironomid macroinvertebrates and fish). Results suggest rapid recovery of catchment to disturbance and a possible increasing magnitude of legacy effects with increasing organism longevity and time to maturity of taxa in the stream community.