Effects of in-stream restorations on stream hydrodynamics, nutrient uptake, and ecosystem metabolism at Fort Benning, GA.
Roberts, Brian*,1, Mulholland, Patrick1, Houser, Jeffrey2, 1 Oak Ridge National Laboratory, Oak Ridge, TN2 USGS, La Crosse, WI
ABSTRACT- Spatial variability in military training intensity results in a wide range of upland disturbance intensity that, in turn, affects streams at the Fort Benning Military Reservation (near Columbus, GA). We selected streams within 8 catchments with contrasting levels of upland denudation and stream ecosystem impacts. In October 2003, 4 of these streams (spanning the disturbance gradient) received in-stream restorations in the form of coarse woody debris additions every 10 m for the 100 m study reaches. Stream hydrodynamic properties, NH4+ uptake, and whole-stream metabolism were examined both prior to and after restoration in all 8 streams. We used a replicated before-after control-intervention (BACI) approach to examine the effects of coarse woody debris additions. Wood additions resulted in immediate (within one month) impacts on stream hydrodynamic complexity (water velocity decreased while the absolute and relative size of the transient storage zone, the fraction of median travel time due to transient storage, and the hydraulic retention factor all increased after restoration). These hydrodynamic changes corresponded to increases in both NH4+ uptake rate and velocity as the ability of stream biota to control stream NH4+ concentration increased. After two years post-restoration, woody debris additions have increased stream respiration rates but have had little effect on gross primary production rates relative to the unrestored streams.
Key words: Stream, nutrient uptake, ecosystem metabolism
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