Urban Stream Ecology
Presiding: R Northington, University of North Carolina-Greensboro; H Rushforth, University of North Carolina-Greensboro
NB24B-01 15:30h
Nitrogen Retention in Three Streams in the Piedmont Region of North Carolina Using a 15N Tracer Addition
Stream restoration is often done as a compensatory mitigation project, but it is unresolved as to what extent restoration helps restore natural nutrient cycling within streams. During the summer of 2004 we ran a stable isotope drip of 15 NH 4Cl for 4 weeks in a forested pristine stream, an unrestored urban stream (but with a restored riparian zone), and a restored urban stream (restored channel and riparian zone). All three streams were located in the piedmont region of North Carolina. By collecting and analyzing samples along a 500m reach in each stream we were able to trace 15N uptake into the food web components. Preliminary results indicate that the restored stream was less retentive of 15N in periphyton and other food web components than the unrestored stream. Differences between these two urban streams likely reflect continued nitrogen loading rather than the instream conditions. The unrestored urban stream had consistently higher mean algal biomass than the other two streams. Grazers were consistently more enriched than periphyton in all streams. Hydropsychid caddisflies were isotopically similar to grazers in the forested and unrestored stream, but tracked seston in the restored stream indicating considerable variability in their trophic status.
NB24B-02 15:45h
An Examination of the Importance of Terrestrial Food Sources in the Diets of Fishes in Three Piedmont North Carolina Urban Streams
Urban streams are greatly impacted by runoff, construction, and the loss of riparian buffers. Past studies have shown the importance of terrestrial subsidies to aquatic communities in pristine, non-urban systems. During the summer of 2004, I examined how urban stream fish communities are impacted by the degradation of streamside vegetation, which typically provides allochthanous input into their diets. North and South Buffalo Creeks in Greensboro, NC and Little Sugar Creek in Charlotte, NC were used in this study. Stable isotope natural abundances of periphyton, CPOM, benthic and drifting macroinvertebrates, terrestrial macroinvertebrates, seston, FBOM, and fish were examined in restored, unrestored, and forested sites on each stream. Macroinvertebrate samples were also taken for NCBI and EPT. Seston, periphyton, and FBOM showed significant site type differences in isotopic composition in the forested reaches. Fish data also show a significant effect of site type on isotopic composition, with forested sites showing the most dramatic differences. These data suggest that, thus far, these urban stream restorations efforts have not resulted in significant restoration of riparian subsidies to the fish community. The results of this study should be considered in stream restoration projects, which attempt to bring about a rejuvenation of aquatic communities.
NB24B-03 16:00h
A 28-Year Comparison of Urbanization Effects on Stream Macroinvertebrate Richness and Secondary Production
Long term changes in urbanization and stream invertebrate communities were investigated from analysis of data collected 28 years apart in the Atlanta, Georgia metropolitan region. Twenty-one streams were selected for study in 1975, and the same streams were studied in 2003 (minus two streams flooded by reservoir construction). Watersheds ranged in land use from 0 to 97% urban across years, but the degree of urbanization increased substantially for many of the previously more natural sites after 28 years. Four modified Hester-Dendy samplers were placed in each stream in July of each year of study for a period of 4-5 weeks. Upon collection, all macroinvertebrates were identified to the lowest possible taxonomic resolution (species or genus) and lengths were measured. Macroinvertebrate richness and an index of secondary production were determined for each sampler in all streams. Biomass was estimated using taxon-specific length-mass regressions, and production was estimated using empirical models of production/biomass values. Richness ranged from <7 to 32 taxa per sampler and production ranged from 0.1 to 4.9 mg dry mass sampler-1 day-1. Both taxa richness and production had a significant relationship with percent urban land-use (p<0.01). The relationship of invertebrate richness and production with increasing urbanization will be discussed.
NB24B-04 16:15h
The Effects of Urbanization on the Food Web of a Mid-order Stream in Rio de Janeiro, Brazil
Stream degradation caused by point source and non-point source pollution, loss of riparian vegetation, erosion and sedimentation can alter aquatic food webs. Due to the lack of proper sewage treatment, the main polluter in urban streams of Brazil is raw sewage. The purpose of this study is to determine if sewage-derived carbon and nitrogen are incorporated into the aquatic system and how this may affect the food web. We collected food web components at four sites along an urban stream, Rio Paineiras, and a reference stream, Rio Andorinha. Samples were analyzed for natural abundance of 13C and 15N. Raw sewage signatures were distinct and enriched compared to primary sources. Riparian vegetation and CPOM samples became significantly more enriched in 15N along the urban stream, compared to the reference stream. Periphyton 15N and 13C signatures were not significantly different between streams. Fish (Astyanax hastatus and Poecilids) showed some incorporation of sewage-derived 13C and 15N, in distinct trophic groups. Macroinvertebrate Hetaerina sp. reflected some incorporation of sewage-derived 15N. We also observed a reduction in functional feeding groups in the sewage-influenced reach of Rio Paineiras. Collectors, gatherers, and shredders were absent as stream degradation increased. Downstream communities were composed mostly of fish.
NB24B-05 16:30h
A Simple Flow Time Series Estimation (FTSE) Tool
We developed a tool to estimate daily flow time series at ungaged locations based on the neighboring flow gage stations. The tool is composed of two components: (1) an ArcView GIS interface to analyze spatially distributed data, and (2) a Microsoft Excel based flow time series generator. The GIS component processes the spatially distributed input data such as land use, soil, elevation, and weather station locations and determines the hydrologic parameters including drainage area, mean curve number, mean vegetation cover factor, and elevation for both gaged and ungaged locations. The flow time series generator calculates the flow time series at the ungaged locations using a simple hydrologic model that takes consideration of both the landscape information and daily weather information (precipitation and mean temperature). The estimated flows are used to automatically calculate indicators of hydrologic alteration for ecosystems. These indicators provide significant information regarding surface and ground water features that influence aquatic, wetland, and riparian ecosystems. The tool was used to estimate flow time series and, subsequently, the hydrologic alteration indicators at about 1300 locations in the Baltimore-Washington DC region for a comparative biological assessment study.