Date of Award

8-2003

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology and Environmental Sciences

Advisor

Alexander D. Huryn

Second Committee Member

A. Randall Alford

Third Committee Member

Christopher S. Cronan

Abstract

The objective of this study was to investigate the effects of N enrichment and flow permanence on stream organic matter dynamics at the Bear Brook Watershed in Maine (BBWM). BBWM is a paired-catchment manipulation of atmospheric (NH4)2SO4 deposition, and the goal of the experiment is to understand how increased N affects forested catchments. The treatment has increased stream nitrate and foliar N concentrations in the treatment watershed. Because streams draining BBWM are intermittent, this investigation provided an opportunity to investigate the combined effects of stream flow permanence and human alteration of N cycling in a forested watershed. Several lines of evidence suggested that stream drying affects streams more than N deposition. For leaf-litter processing, elevated dissolved N concentrations played a minimal role in regulating stream leaf-litter processing. Increased foliar N, however, did influence detritus processing by increasing microbial activity, and possibly increasing detritivore biomass. Based on these findings, I concluded that physical similarities between streams regulated leaf litter loss rates. For stream organic matter dynamics, BBWM did not have different inputs or storage, and only modest differences in export of coarse organic matter. These results support the conclusion that N additions at BBWM do not affect these streams, and that physical characteristics regulate what happens to organic matter. Utilization of organic matter, measured as invertebrate secondary production, was also the same between streams, but varied temporally. Increased production in the second year was attributed to increased stream permanence and organic matter biomass. These results again suggest that N deposition at BBWM has little effect on organic matter dynamics, specifically utilization. Differences in drying for streams did affect production and invertebrate assemblage structure. To further assess stream drying effects, secondary production was quantified in 6 reaches with differing drying regimes. Production ranged from 1.7 to 2.9 g AFDM m-2 yr-1 among all reaches, and flow permanence and organic matter biomass appeared to influence these patterns. This work suggests that chemical changes in streams because of atmospheric N deposition are less important than gradients in flow permanence in regulating organic matter in intermittent streams.

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