Date of Award
Summer 2024
Document Type
Thesis
Degree Name
Master of Science (MS) in Biology
Department
Biology
Committee Chair
Lori Tolley-Jordan
Abstract
Land cover changes, driven by urbanization, agriculture, and deforestation, significantly affect the physical and chemical characteristics of water bodies at both the watershed and riparian levels. At the larger spatial scale, a stream’s surrounding watershed facilitates lateral inputs into the stream that are essential for biodiversity support, hydrological stability, and water quality. When a stream becomes disconnected from the lateral inputs due to urban or agricultural development, the morphology of the stream is significantly altered. On a smaller spatial scale, the riparian zone can act as a buffer to pollutants. The vegetation surrounding the stream bank promotes stability to the instream morphology. Riparian zones trap sediments, preventing excessive sedimentation in the stream. In aquatic systems, the sensitivity of organisms to degraded rivers is most apparent in benthic (stream bottom-dwelling) macroinvertebrates such as insects, crustaceans, mollusks, and annelids. Benthic macroinvertebrates, key indicators of water quality and ecosystem health, are highly sensitive to alterations in their habitats. This, in turn, reduces macroinvertebrate diversity by favoring tolerant species over sensitive ones, leading to homogenized communities. Our research analyzed LULC from three time periods in the Choccolocco Creek watershed in Northeast Alabama at two spatial scales (watershed and riparian) to assess their impacts on benthic macroinvertebrate diversity over time. This study design was based on two previous sample periods, 2000 and 2012, where macroinvertebrate samples were collected at four sites in Choccolocco Creek. LULC data was made available from the NLCD Landsat imagery database for all years sampled (2000,2012,2022). Urban, agriculture, and forest percent changes in LULC were determined among the three study intervals for both watershed and riparian zones. Over time, changes in the biodiversity of benthic macroinvertebrates were crucial in determining the resilience of a stream system to changes in land use and land cover (LULC) in the Choccolocco Creek watershed in Northeast Alabama. All three studies used standardized EPA biomonitoring benthic invertebrate collection protocols in riffles. Four riffles in the watershed were sampled during all 3 decades that occurred in April, July, and October. All macroinvertebrates collected were pooled for each event and were identified at the family level for all three studies. Invertebrate diversity statistics of richness, evenness as the Shannon-Wiener index, were determined for each of the four sites across the three sampling events. These values were correlated to changes in LULC across sites and sampling events. Differences in invertebrate community structure among sites and sampling events were with non-metric multi-dimensional scaling analysis. In addition, comparisons of beta diversity (community stability) across sites were used to assess change in communities through time. Results showed that all sites had forest as the most abundant land cover in both watershed and riparian zones across all sampling locations and events (WS- 45 to 80%, Riparian 40 to 65%), agriculture was second (WS 15 to 37%, Riparian 32 to 47%) and urban had the smallest cover (WS 3 to 25%, Riparian 0 to 10%). However, at both the watershed and riparian buffer scales, the urban land cover had the highest percentage increase at each site 5 to 115%), except site one found in the national forest exhibited little change in land cover at either watershed or riparian scales. Results also showed that declines in macroinvertebrate richness and evenness from 2000 to 2022 were correlated to increasing agriculture and urban land cover and decreasing forest cover and that these relationships were similar at both the riparian and watershed scales. NMDS showed that differences in community composition differed across sites although communities did not vary across time. Still, beta diversity estimates were highest in site 3 which also had the largest percent change in land use. This study highlights the need for continued monitoring on multiple spatial scales to maintain biological integrity within a stream.