THE RELATIONSHIP BETWEEN HYDROLOGIC AND MACROINVERTEBRATE METRICS ALONG AN URBANIZATION GRADIENT IN PIEDMONT HEADWATER STREAMS

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Black, R. (2019). THE RELATIONSHIP BETWEEN HYDROLOGIC AND MACROINVERTEBRATE METRICS ALONG AN URBANIZATION GRADIENT IN PIEDMONT HEADWATER STREAMS. Unc Charlotte Electronic Theses And Dissertations.
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Abstract

Urban streams are characterized by altered hydrographs, increased nutrient concentrations, altered geomorphology, and decreased biodiversity. This study asked how the hydrologic flow regime impacts stream macroinvertebrates in Piedmont headwater streams by quantifying bed mobility using tractive force and threshold discharge to integrate flow impacts on stream organisms. These hydrologic metrics are used to assess the impacts of grain size movement during peak flows based on the dimensions of the stream. Tractive force (τ) is the average shear stress, the amount of force required to move a specific area of water in the bed of the channel, that is required to move the size of the material at initial motion. Tractive force depends on 1) the depth of flow and 2) the slope of the water surface. Threshold discharge (Qc) is the flow value that results in the mobilization of a specific sediment size and depends on 1) the median grain size and 2) the two-year flood discharge value. I sampled watersheds that ranged from 0.47 to 9.51 square kilometers and 4.84 to 41.7 % impervious cover in Mecklenburg County, North Carolina. Macroinvertebrates, water quality (dissolved oxygen, specific conductivity, pH, temperature, nutrients), and Wolman pebble counts were collected during fall 2018 and winter 2019. Nearby USGS gages were used to assess flow data for two years prior to sampling. The background environmental parameters and water quality assessed for the study resulted in positive relationships with increasing impervious cover. The water quality concentrations studied yielded mixed results when compared to impervious cover. The distribution of grain sizes found for the study locations varied between sites and sampling dates due to past restoration efforts of varying magnitude, that included bank stabilization to full restoration of the study location. Macroinvertebrates diversity, species richness, and species evenness decreased along the impervious cover gradient. The collector functional feeding group was dominant throughout the study compared to the predator, shredder, and scraper functional feeding groups. The percentage of tolerant species were dominant compared to the percentage of intolerant species found throughout the study.Qc did not vary systematically with %IC due to local variability in streambed D50. The D50 tractive force and the D50 threshold discharge relationships with the macroinvertebrate metrics yielded mixed positive and negative correlations that were not significant. Species richness, diversity and evenness had a significant moderate positive correlation with the D50 percent bed mobility. Threshold discharge and the percent of EPT and tolerant species positive correlation shows that the flow that moves the median grain size increases similarly as the number of tolerant species and sensitive species are found. By linking sediment mobilization and macroinvertebrate diversity, new insights into best practices for stream restoration design for controlling sediment transport and improving ecological health can be determined.

Details
Author

Black, Rebecca

Title

THE RELATIONSHIP BETWEEN HYDROLOGIC AND MACROINVERTEBRATE METRICS ALONG AN URBANIZATION GRADIENT IN PIEDMONT HEADWATER STREAMS

Physical Description

1 online resource (137 pages) : PDF

Date

2019

Degree Granting Institution

University of North Carolina at Charlotte

Abstract

Urban streams are characterized by altered hydrographs, increased nutrient concentrations, altered geomorphology, and decreased biodiversity. This study asked how the hydrologic flow regime impacts stream macroinvertebrates in Piedmont headwater streams by quantifying bed mobility using tractive force and threshold discharge to integrate flow impacts on stream organisms. These hydrologic metrics are used to assess the impacts of grain size movement during peak flows based on the dimensions of the stream. Tractive force (τ) is the average shear stress, the amount of force required to move a specific area of water in the bed of the channel, that is required to move the size of the material at initial motion. Tractive force depends on 1) the depth of flow and 2) the slope of the water surface. Threshold discharge (Qc) is the flow value that results in the mobilization of a specific sediment size and depends on 1) the median grain size and 2) the two-year flood discharge value. I sampled watersheds that ranged from 0.47 to 9.51 square kilometers and 4.84 to 41.7 % impervious cover in Mecklenburg County, North Carolina. Macroinvertebrates, water quality (dissolved oxygen, specific conductivity, pH, temperature, nutrients), and Wolman pebble counts were collected during fall 2018 and winter 2019. Nearby USGS gages were used to assess flow data for two years prior to sampling. The background environmental parameters and water quality assessed for the study resulted in positive relationships with increasing impervious cover. The water quality concentrations studied yielded mixed results when compared to impervious cover. The distribution of grain sizes found for the study locations varied between sites and sampling dates due to past restoration efforts of varying magnitude, that included bank stabilization to full restoration of the study location. Macroinvertebrates diversity, species richness, and species evenness decreased along the impervious cover gradient. The collector functional feeding group was dominant throughout the study compared to the predator, shredder, and scraper functional feeding groups. The percentage of tolerant species were dominant compared to the percentage of intolerant species found throughout the study.Qc did not vary systematically with %IC due to local variability in streambed D50. The D50 tractive force and the D50 threshold discharge relationships with the macroinvertebrate metrics yielded mixed positive and negative correlations that were not significant. Species richness, diversity and evenness had a significant moderate positive correlation with the D50 percent bed mobility. Threshold discharge and the percent of EPT and tolerant species positive correlation shows that the flow that moves the median grain size increases similarly as the number of tolerant species and sensitive species are found. By linking sediment mobilization and macroinvertebrate diversity, new insights into best practices for stream restoration design for controlling sediment transport and improving ecological health can be determined.

Genre

masters theses

Subjects--Topics

Environmental sciences
Ecology
Hydrology

Degree

M.S.

Keywords

Bed Mobility
Headwater Streams
Macroinvertebrate
Piedmont
North Carolina
Threshold Discharge
Tractive Force

Subject Area

Earth Sciences

Advisor(s)

Clinton, Sandra

Committee Members

Gagné, Sara
Allan, Craig

Degree Note

Thesis (M.S.)--University of North Carolina at Charlotte, 2019.

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Rights Holder Information

Copyright is held by the author unless otherwise indicated.

Identifier

Black_uncc_0694N_12162

Permalink

http://hdl.handle.net/20.500.13093/etd:2155