Physical-Chemical and Biological Characterization of Small Streams Following Intensive Forest Management Practices in the Coastal Plain of Alabama
Type of DegreeThesis
Fisheries and Allied Aquacultures
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This study measured changes in five first-order streams (S 1 through S 5) following management techniques including clearcut logging and chemical (S 2 and S 3) and mechanical site preparation (S 4 and S 5). The herbicides used in this study included a mixture of Imazapyr and Glyphosate. Streams in two watersheds (S 3 and S 5) were left with 35-foot (11 m) wide streamside management zones (SMZ) while S 2 and S 4 had no SMZ. The fifth stream (S 1) draining an undisturbed watershed of similar size was used as a control. During each phase of the study (predisturbance, harvest and site preparation) periphyton, macroinvertebrates and physicochemical data were collected at least two times per season from August 1993 to December 1995. Statistical analyses utilized randomized intervention analysis (RIA). Pre-disturbance phase data showed similar seasonal variation among all streams regarding water temperature, dissolved oxygen and algal biomass, except for S 3 that was strongly influenced by springs. Water temperature in clearcuts with SMZ was not significantly different from the control while those without SMZ increased significantly following harvest. Among biological communities, when compared to the control stream, algal biomass (as chlorophyll a) from periphyton showed the greatest change and significantly increased in all streams after harvest, particularly in those with no SMZ. These changes probably resulted from the reduced canopy cover and increased sunlight reaching the streams because nitrogen and phosphorous changed little following harvest or site preparation. Following site preparation, chlorophyll a values remained high compared to the pre-disturbance phase. The herbicide had no apparent detrimental effect on periphyton biomass. Macroinvertebrate population densities were highly variable during the study period. Following harvest, macroinvertebrates in S 2 and S 4 with no SMZ had greater increases in density than that measured in the streams with SMZ. However, only in S 4 was this difference significant. This density difference probably reflected the increase in algal biomass in S 2 and S 4. After site preparation macroinvertebrate densities were unaffected when compared with the control using RIA. Taxa richness and diversity (i.e. both Shannon-Weaver and EPT) were not affected during harvest or site preparation according to RIA. Even with a 35-foot SMZ, timber harvest as practiced in the southeastern USA increased algal biomass as a result of additional light reaching the streams, especially streams with no SMZ. However, the presence of SMZ seemed to mitigate any dramatic changes to macroinvertebrate communities. Chemical and mechanical site preparation techniques did not significantly affect periphyton biomass and macroinvertebrate communities during this study. Timber harvest without SMZ appeared to be the management practice that most affected the stream biota.