UVM Theses and Dissertations
Format:
Print
Author:
Hackman, Alexander M.
Title:
Dept./Program:
Rubenstein School of Environment and Natural Resources
Year:
2008
Degree:
M.S.
Abstract:
The "urban stream syndrome" (Meyer et al. 2005, Walsh et al. 2005a) describes a wellstudied and consistent pattern of biological, chemical, and physical degradation to lotic systems. However, the impact of urbanization on key ecosystem-scale ecological processes (e.g. rates of primary production, respiration, nutrient uptake) is still unclear, despite increasing calls to include these integrated measures in holistic assessments of stream health (Bunn et al, 1999; Walsh et al, 2005). Our ability to understand, diagnose, and mitigate the impacts of urbanization - and restore ecosystem services linked to these processes - is thus limited.
To better understand how watershed development has impacted ecological processes in northwestern Vermont, we measured whole-ecosystem metabolism in 7 streams in over two years. Study streams were selected based upon a prior classification by the Vermont Department of Environmental Conservation (VT DEC) as either "impaired" for urban stormwater runoff (303d listed) or in "attainment" of state standards according to prior monitoring of biotic indicators (macroinvertebrates and fish). We confirmed and augmented these classifications by conducting additional assessments of biological community structure, stream geomorphic and habitat conditions, and stream water chemistry.
We used the open-channel, single-station approach (Odum 1956, Bott 1996) with several modifications to conduct nearly continuous monitoring of whole-stream metabolism. We modeled relationships between discharge and stream dimension, and incorporated these as dynamic variables in the metabolism calculations. We estimated 271 daily rates of gross ecosystem production (GEP), ecosystem respiration (ER), net daily metabolism (NDM), as well as the ratio of production to respiration (PIR) split almost evenly between the impaired and attainment condition stream groups.
GEP was significantly higher in the stormwater-impaired streams, particularly during the spring and summer months; ER was closely linked to the production of autochthonous resources. The attainment condition streams, on the other hand, were characterized by more consistent and less vigorous in-stream primary production. Attainment condition streams were more heterotrophic, and processed organic matter from a more diverse resource base throughout the year. At the individual stream level, we also found significant correlations between PIR ratio and benthic macroinvertebrate community metrics, geomorphic and habitat scores, mean PO4 concentration, and specific conductivity.
We propose that the altered 'metabolic regime' observed in our stormwater-impaired study streams may represent andther aspect of the urban stream syndrome associated with this particular level of watershed development. We suggest that measures to limit the drivers of in-stream primary production (i.e. sunlight, temperature, nutrients) may help encourage a more 'natural' metabolic regime in urban stormwater-impaired streams in some areas.
To better understand how watershed development has impacted ecological processes in northwestern Vermont, we measured whole-ecosystem metabolism in 7 streams in over two years. Study streams were selected based upon a prior classification by the Vermont Department of Environmental Conservation (VT DEC) as either "impaired" for urban stormwater runoff (303d listed) or in "attainment" of state standards according to prior monitoring of biotic indicators (macroinvertebrates and fish). We confirmed and augmented these classifications by conducting additional assessments of biological community structure, stream geomorphic and habitat conditions, and stream water chemistry.
We used the open-channel, single-station approach (Odum 1956, Bott 1996) with several modifications to conduct nearly continuous monitoring of whole-stream metabolism. We modeled relationships between discharge and stream dimension, and incorporated these as dynamic variables in the metabolism calculations. We estimated 271 daily rates of gross ecosystem production (GEP), ecosystem respiration (ER), net daily metabolism (NDM), as well as the ratio of production to respiration (PIR) split almost evenly between the impaired and attainment condition stream groups.
GEP was significantly higher in the stormwater-impaired streams, particularly during the spring and summer months; ER was closely linked to the production of autochthonous resources. The attainment condition streams, on the other hand, were characterized by more consistent and less vigorous in-stream primary production. Attainment condition streams were more heterotrophic, and processed organic matter from a more diverse resource base throughout the year. At the individual stream level, we also found significant correlations between PIR ratio and benthic macroinvertebrate community metrics, geomorphic and habitat scores, mean PO4 concentration, and specific conductivity.
We propose that the altered 'metabolic regime' observed in our stormwater-impaired study streams may represent andther aspect of the urban stream syndrome associated with this particular level of watershed development. We suggest that measures to limit the drivers of in-stream primary production (i.e. sunlight, temperature, nutrients) may help encourage a more 'natural' metabolic regime in urban stormwater-impaired streams in some areas.