Influences of land use on the structure and function of headwater streams: A multiple scale analysis
Sponseller, Ryan Allen
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The structure and function of stream ecosystems may be strongly influenced by land-use practices within watersheds. The magnitude of land-use impacts may depend upon the spatial arrangement of development in watersheds. This study examines the relationship between land-cover patterns and stream structure and function in 9 southern Appalachian headwater basins. Using a GIS/remote sensing approach, land-cover patterns were quantified at several spatial scales, including the entire watershed, riparian corridor, and riparian sub-corridors extending upstream in 200 m increments for 2 km. In-stream physico-chemical variables were related to land-cover patterns at different spatial scales. Dissolved constituents (e.g., TIN, alkalinity) were frequently related to physical features or land-cover patterns at the watershed scale. Conversely, mean substrate particle size and stream temperature were most strongly related to land-use practices at the entire riparian corridor scale. Finally, maximum stream temperature was best explained from land-cover patterns at the 200 m sub-corridor scale. The relationship between land-cover patterns and benthic macroinvertebrate communities is examined in Chapter 1. Macroinvertebrate assemblage structure was quantified using the slope of rank-abundance plots, and further described using standard diversity and evenness indices. Macroinvertebrate taxa richness ranged from 24 to 54 among sites, and the analysis of rank-abundance curves defined three distinct groups with high, medium, and low diversity. In general, other macroinvertebrate indices were in accord with rank-abundance groups, with richness and evenness decreasing among sites with maximum stream temperature. Macroinvertebrate indices were most strongly related to land cover patterns evaluated at the 200 m sub-corridor scale, suggesting local, streamside development effectively alters assemblage structure. The relationship between land-cover patterns and leaf breakdown is examined in Chapter 2. Breakdown rate for American sycamore (Plantanus occidentalis) leaf packs varied significantly among sites (k = 0.0051 to 0.0180 d-1), but fell within the range reported in the literature for sycamore. Leaf breakdown rate increased among sites with shredder density and biomass. Further, breakdown rate and shredder density and biomass were positively related to mean substrate particle size. Though several instream variables were related to watershed-scale features, leaf breakdown rate was not related to land cover at the watershed scale. Leaf breakdown rate was inversely related to % non-forest within riparian sub-corridors of approximately 1 km. Results suggest that the distribution of shredders is critical to leaf processing in these streams. In some streams, increased sediment inputs as a result of agricultural activity or residential development in riparian corridors may limit the distribution of shredders and thus influence leaf breakdown rates. Alternatively, near stream development may reduce the quantity and/or quality of allochthonous inputs to streams, and thus indirectly influence the distribution of shredders.
- Masters Theses