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Title:Influence of riparian forest and agricultural land use on community structure and ecosystem function in headwater streams
Author(s):Effert, Eden L
Director of Research:Wahl, David H.
Doctoral Committee Chair(s):Schneider, Daniel W.
Doctoral Committee Member(s):Cáceres, Carla E.; Fischer, Robert U
Department / Program:Natural Res & Env Sci
Discipline:Natural Res & Env Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):stream community
riparian buffers
food web structure
Abstract:Riparian forest buffers are often promoted to improve stream water quality and instream habitat in agricultural areas because the vegetation can filter runoff, reduce bank erosion, and restore channel morphology. However, previous studies have found that protecting narrow strips of riparian areas, typically 30-50 meters wide along streams, may be insufficient for restoring stream biological integrity in highly degraded watersheds. I examined nine headwater streams that varied in the amount of riparian forest and watershed agriculture to determine the extent to which riparian forest buffers can mitigate the effects of cropland agricultural activities. The nine sites were equally divided into three land use groups: 1) “Forested” streams with high percent riparian forest and low watershed agriculture, 2) “Buffered” streams with high percent riparian forest and high watershed agriculture, and 3) “Agricultural” streams with low percent riparian forest and high watershed agriculture. Sampling was conducted seasonally over three years to explore temporal patterns in community structure and ecosystem function related to land use, instream habitat, and water quality parameters. While there were significant seasonal and annual differences, relationships among streams within different land use groups remained relatively consistent throughout the study. Streams with low percent forest buffer had significantly higher daily maximum temperature, nitrate-nitrogen levels, and primary productivity than the two high forest buffer land use groups. Although there were greater abundances of macroinvertebrates and fish in streams with low forest buffer, assemblages were dominated by pollution tolerant taxa. In contrast, streams with high percent forest buffer and low watershed agriculture had the best biotic integrity. Greater proportions of piscivores in these streams was attributed to increased maximum depth and improved habitat structure from woody debris along with better water quality. Ordinations based on fish community composition revealed significant differences among all three land use groups due to differences in trophic structure. In addition, the fish assemblage matrix was significantly correlated to environmental patterns that clustered streams into each land use group. Macroinvertebrate assemblages were less sensitive to land use changes at both the riparian zone and watershed scale likely due to the dominance of sandy, unstable substrates in all sites. Results suggest instream conditions that were strongly controlled by the amount of riparian forest buffer in the watershed (e.g., basal resources, nutrient levels, and depth) had the greatest influence on stream community structure. Stable isotope analysis (13C and 15N) was performed to examine food web structure and energy flow within each stream to determine how land use changes affect ecosystem function and identify potential mechanisms for observed differences in community structure. To date, few studies have used a food web approach to investigate effects of row crop agriculture on headwater streams. Agricultural streams with low percent riparian forest had compressed food webs with low trophic diversity and high trophic redundancy. In contrast, forested and buffered streams had larger trophic niche areas with greater variability in both resource use and trophic position among invertebrates and fishes. Results suggest fish communities in agricultural streams occupied lower trophic positions and had greater reliance on periphyton production than forested and buffered streams. Although trophic diversity measures tended to be smaller in buffered sites, food web structure in forested and buffered streams were relatively similar despite a large range in watershed agriculture (48% - 81%) between these two land use groups. To further examine differences in food web structure, stable isotope and gut content analyses were combined to better quantify fish diets and explain variation in trophic position among species and land use groups. Gut content analysis revealed that fish in forested streams had a more diverse diet that included greater numbers of terrestrial invertebrates and aquatic invertebrate predators, whereas fish in agricultural streams consumed more aquatic herbivores (e.g., gastropods) and decapods. Diets shifts of the omnivorous creek chub followed differences in basal resource biomass among streams, with greater proportions of algae consumed by creek chubs in agricultural sites contrasted by greater detritus consumption in forested sites. Stable isotope analysis mixing model results supported differences indicated by gut content analysis, particularly increased contributions of terrestrial invertebrates to fish diets in forested streams. Results suggest the higher trophic positions of fish in forested streams were due to greater consumption of predatory invertebrates that inserted an intermediate link in the food chain. Together these studies highlight the importance of riparian forest buffers for restoring community structure, maintaining trophic diversity in food webs, and elevating fish trophic position in agricultural headwater streams. My research provides further support for conservation programs that target riparian areas in efforts to protect stream ecosystem function in agriculturally impacted watersheds.
Issue Date:2015-07-09
Rights Information:Copyright 2015 Eden Effert
Date Available in IDEALS:2015-09-29
Date Deposited:August 201

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