Title page for ETD etd-05072010-214046

Type of Document Dissertation
Author Ely, Damon Thomas
URN etd-05072010-214046
Title Stress-induced alterations in ecosystem function: the role of acidification in lotic metabolism and biogeochemistry
Degree PhD
Department Biology
Advisory Committee
Advisor Name Title
Valett, H. Maurice Committee Chair
Jones, Robert H. Committee Co-Chair
Burger, James A. Committee Member
Daniels, Walter Lee Committee Member
Webster, Jackson R. Committee Member
  • aquatic fungi
  • DIN
  • 15N
  • spiraling
  • qCO2
  • nitrogen uptake
  • respiration
  • chlorophyll a
  • stream metabolism
Date of Defense 2010-03-31
Availability unrestricted

I investigated how anthropogenic acidification influences stream metabolism and nitrogen (N) cycling by considering the stress response of microbial compartments responsible for these ecosystem processes. Microcosm incubations of leaf biofilms from streams of differing pH revealed greater rates of fungal biomass-specific respiration (i.e. the stress metric qCO2) and biomass-specific N uptake (i.e. qN) with increasing acidity. The positive relationship between qCO2 and qN indicated alternate fates for N other than structural biomass, possibly related to increased exoenzyme production as part of the stress response.

Whole-stream 15N experiments and measurements of respiration and fungal standing crop across the pH gradient resulted in similar patterns in qCO2 and qN found in microcosm experiments, supporting qCO2 as an ecosystem-level stress indicator and providing insight towards controls over N cycling across the pH gradient. Fungal biomass and ecosystem respiration declined with increasing acidity while N uptake metrics were not related to pH, which suggested qN in acid streams was sufficiently high to counteract declines in fungal abundance.

During spring, chlorophyll a standing crops were higher in more acidic streams despite lower nutrient concentrations. However, N uptake rates and gross primary production differed little between acid and circumneutral streams. Reduced heterotrophy in acid streams was apparent in lower whole-stream respiration rates, less ability to process organic carbon, and little response of N uptake to added carbon resources. Overall, acid-induced stress in streams was found to impair decomposer activity and caused a decoupling of carbon and nitrogen cycles in these systems.

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