Headwater streams in the Piedmont region near Charlotte, NC, are subject to high levels of disturbance due to human activities. Many of these streams are quite small, being only a few centimeters deep and a meter wide, and they all drain subwatersheds of the Catawba and Yadkin River Basins. Many also have highly productive insect communities, with insect densities in the thousands per square meter. Stream hydrology, biodiversity, and ecosystem function within these bodies of water are in danger of being disrupted as land use in the surrounding watersheds changes. Impacts to these streams from human development primarily include loss of riparian buffer zones and increased sedimentation from erosion. Previous studies have linked loss of riparian vegetation with increased sedimentation in streams. Increased human activity, especially construction and suburban development, also increases erosion into surface waters. Sedimentation in small streams may decrease both surface water flow and insect biodiversity, which then disrupt ecosystem function, in particular, detrital processing. Benthic insect communities perform a variety of ecosystem functions, inhabit a diversity of habitats, and have a variety of responses to perturbations. Some taxa are sensitive to high sediment loads and will disappear from streams with high sediment. However, how sedimentation and buffer zones of different magnitudes interact in headwater streams to affect flow regimes and aquatic insect communities is not well known. There is likely a synergistic effect of these two factors, as construction within a riparian zone eliminates the buffer and contributes far more sediment and runoff to streams than construction outside a riparian zone, and width of the zone is an important consideration for adequate protection of surface waters.
Assessment of sedimentation, flow, and insect communities is critical in light of the high rate of development in this region and the importance of riparian forests near headwater streams for erosion control, water quality, and energy inputs into stream ecosystems. Headwater stream resources near Charlotte are being assessed by determining land use, changes in land use, the broad patterns of aquatic insect communities, sedimentation rates, and characteristics of riparian vegetation zones. This will allow us to determine effects of changing land use and erosion on sedimentation, benthic insect communities, and stream hydrology.
Objectives:
This project is being carried out on tributaries of the Catawba and Rocky Rivers in the north Charlotte region, where heavy suburban development is occurring. The research questions are:
The objectives are to:
Physical data includes
flow velocity, suspended sediment bedload sediment, substrate characteristics,
and discharge. Chemical data include alkalinity, dissolved oxygen, pH, and
conductivity, and biological data include benthic insect community sampling.
These parameters have been measured on ten streams in the proposed study area
from May 2001 to the present. Geographic information systems (GIS) and habitat
assessments will also be used to analyze land use characteristics from aerial
photographs, topographic map themes, and visual inspections.
One other objective is to involve students in aquatic field research, so they
may learn and appreciate the incredible, and often unseen, diversity, of benthic
macroinvertebrates and the threats to aquatic biodiversity.
The results so far:
In the study conducted by summer of 2001, the trend observed in preliminary analysis of the data indicates that streams with a high level of development and construction near them had less diverse insect communities with lower abundance than streams with more heavily forested watersheds. Numerous families were found in only in streams that drained highly undisturbed watersheds. Plecopterans, especially, are particularly sensitive to disturbance and have low tolerance values. Only one individual perlid stonefly in 45 kick net samples was found from streams draining the five most disturbed watersheds. In the five undisturbed watersheds, streams contained between two and five families of Plecoptera, often with more than one individual in a sample. Megalopterans, two families of Ephemeroptera (Heptageniidae and Leptophlebiidae), and some Diptera (Tabanidae and Ceratopogonidae) were also found only in streams draining undisturbed watersheds.
Changing land use and development patterns, including the construction of a new sewer line near Mooresville and of the new College Union here at Davidson College, may be affecting deposition of sediment and water flow patterns. During the few storm events we had this past summer, streams that had higher levels of disturbed watersheds seemed to have higher sediment loads. However, more data on suspended and bedload sediment, discharge, and flow are needed from multiple storm events to make stronger conclusions, as variability in these data is quite large.
In addition, two instances of direct adverse effects on streams were observed near a new sewer line being installed in the Mooresville area. On two sampling trips construction crews digging just upstream of our site were observed dumping dirt and mud directly into study streams, resulting in extremely high loads of sediment, to the point of completely muddying the water. High sediment loads may introduce pollutants into surface waters, or clog insect and fish gills, causing mortality or drift.
*indicates undergraduate author
