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Terrestrial-aquatic linkages: Herbaceous vegetation and headwater streams.
Menninger, Holly*,1, Palmer, Margaret2, 1 Behavior, Ecology, Evolution & Systematics Program, College Park, MD, USA2 Department of Entomology, College Park, MD, USA
ABSTRACT- Open-canopy streams with dense edges of herbaceous vegetation are common throughout agricultural landscapes in the Mid-Atlantic region, yet the interaction between vegetation and invertebrate dynamics of such streams is rarely studied. Along headwater streams, edge vegetation bridges the terrestrial−aquatic interface and may play important roles in channel shading, creating habitat structure, and providing a detrital resource. We removed the edge vegetation from three open-canopy headwater streams and measured the removal effects on 1.) rates of key ecosystem processes (primary production, organic matter decomposition) and 2.) diversity of aquatic invertebrates as compared to reference streams and pre-manipulation observations. We predicted that vegetation removal would result in a shift from an apparent detritus-based system to a primarily algal-driven system. With changes in food resource base, we anticipated a decrease in the abundance of detritivorous invertebrates as well as an increase in algivorous invertebrates. We also predicted that removing edge habitat structure would result in a decline of sedentary invertebrate predators. We found increases in primary production, the result of greater insolation to the stream channel, although algae did not grow homogeneously throughout the stream reaches. Rates of leaf decomposition of a common grass did not change significantly as a result of vegetation removal. Shredding invertebrates (Isopoda, Lepidostomatidae) declined across reference and experimental streams, suggesting no effect of manipulation on this feeding guild. Other invertebrate feeding groups, however, did respond to the removal treatment. Algivorous midge larvae (Chironomidae) increased nearly four-fold following vegetation removal and the subsequent increase in algal production. The number of predaceous odonate larvae (Calopterygidae) declined significantly following vegetation removal, a consequence of the elimination of important habitat structure. These results suggest that herbaceous vegetation growing along the edges of open-canopy headwater streams may play key roles in regulating in-stream food resources and structuring the aquatic invertebrate community.
Key words: stream, invertebrate, headwater, vegetation