The Effects of Seasonal Change and Urbanization on Macroinvertebrate Communities in Streams
Kristen A. Beckert
ABSTRACT:
Increasing urbanization has become a significant
factor and possible threat to stream communities and ecosystems. Stream macroinvertebrates respond to changes caused by this introduced factor in addition to natural cyclic changes such as seasonal variation. The U.S. Geological Survey (USGS) created the Urban Land Use Gradient (ULUG) that rates a stream’s urbanization level on a scale of 0-100, with 100 being the most urbanized. This index takes into account measures including riparian buffers, population, impervious surfaces, industry, and agriculture. Five streams at different points on the ULUG in the cities of Raleigh and Chapel Hill in North Carolina were sampled for macroinvertebrates once in August and again in January. Five discrete sample bottles were taken from riffle zones within an established 150 meter reach, a good representation of overall stream characteristics. All organisms were classified to the lowest resolvable taxa and analyzed for their abundance, richness, diversity, and coefficient of variation among bottles and streams in both the summer and winter. By using the USGS Invertebrate Data Analysis Software (IDAS) additional indices and metrics were calculated.
Although summer metrics such as richness and diversity showed a significant decreasing trend along the ULUG’s increasing urbanization gradient, the winter samples did not show a similar pattern. From summer to winter, organism tolerance increased for every stream as well as the abundance of Chironomids (very tolerant) over Ephemoptera, Pleicoptera, and Tricoptera combined. Feeding group composition varied greatly in the summer samples but obtained a constant configuration in the winter for all streams. These results suggest that mechanisms indirectly influenced by urbanization (stream flow, sedimentation, temperature, runoff effects) may have a greater impact on streams in the summer than in the winter. The effects of stream urbanization are important because of their contribution to large-scale ecosystem functions.
Research Advisor: Dr. Seth R. Reice
Research Mentors: Dr. Thomas Cuffney and Michael Thure Caire
Beckert, K.A., 2004, The effects of seasonal change and urbanization on macroinvertebrate communities in streams [abs]: John K. Koeppe Undergraduate Research Symposium in Biology, The University of North Carolina at Chapel Hill, November 2.
