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Effects of Streambank Fencing of Pasture Land on Benthic Macroinvertebrates and the Quality of Surface Water and Shallow Ground Water in the Big Spring Run Basin of Mill Creek Watershed, Lancaster County, Pennsylvania, 1993-2001

U.S. Geological Survey Scientific Investigations Report 2006-5141

By Daniel G. Galeone, Robin A. Brightbill, Dennis J. Low, and David L. O’Brien


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ABSTRACT

Streambank fencing along stream channels in pastured areas and the exclusion of pasture animals from the channel are best-management practices designed to reduce nutrient and suspended-sediment yields from drainage basins. Establishment of vegetation in the fenced area helps to stabilize streambanks and provides better habitat for wildlife in and near the stream. This study documented the effectiveness of a 5- to 12-foot-wide buffer strip on the quality of surface water and near-stream ground water in a 1.42-mi2 treatment basin in Lancaster County, Pa. Two miles of stream were fenced in the basin in 1997 following a 3- to 4-year pre-treatment period of monitoring surface- and ground-water variables in the treatment and control basins. Changes in surface- and ground-water quality were monitored for about 4 years after fence installation.

To alleviate problems in result interpretation associated with climatic and hydrologic variation over the study period, a nested experimental design including paired-basin and upstream/downstream components was used to study the effects of fencing on surface-water quality and benthic-macroinvertebrate communities. Five surface-water sites, one at the outlet of a 1.77-mi2 control basin (C-1), two sites in the treatment basin (T-3 and T-4) that were above any fence installation, and two sites (one at an upstream tributary site (T-2) and one at the outlet (T-1)) that were treated, were sampled intensively. Low-flow samples were collected at each site (approximately 25-30 per year at each site), and stormflow was sampled with automatic samplers at all sites except T-3. For each site where stormflow was sampled, from 35 to 60 percent of the storm events were sampled over the entire study period. Surface-water sites were sampled for analyses of nutrients, suspended sediment, and fecal streptococcus (only low-flow samples), with field parameters (only low-flow samples) measured during sample collection. Benthic-macroinvertebrate samples were collected in May and September of each year; samples were collected at the outlet of the control and treatment basins and at three upstream sites, two in the treatment basin and one in the control basin. For each benthic-macroinvertebrate sample: Stream riffles and pools were sampled using the kick-net method; habitat was characterized using Rapid Bioassessment Protocols (RBP); water-quality samples were collected for nutrients and suspended sediment; stream field parameters were measured; and multiple biological metrics were calculated.

The experimental design to study the effects of fencing on the quality of near-stream shallow ground water involved a nested well approach. Two well nests were in the treatment basin, one each at surface-water sites T-1 and T-2. Within each well nest, the data from one deep well and three shallow wells (no greater than 12 ft deep) were used for regional characterization of ground-water quality. At each site, two of the shallow wells were inside the eventual fence (treated wells); the other shallow well was outside the eventual fence (control well). The wells were sampled monthly, primarily during periods with little to no recharge, for laboratory analysis of nutrients and fecal streptococcus; field parameters of water quality also were measured.

Ancillary data collected during the study included precipitation amounts, inorganic and organic nutrient applications in both basins, and the number of cows in both basins. Precipitation during the pre-treatment period averaged about 5 in. more per year than during the post-treatment period; streamflow was about 56-63 percent less during the post-treatment period relative to the calibration period. Agricultural activity did show some changes from the pre- to post-treatment period. The estimated amount of nitrogen (N) and phosphorus (P) applied to the land as inorganic and organic fertilizers decreased 27 and 33 percent, respectively, from the pre- to the post-treatment period in the treatment basin. Over the same period, estimated N and P applications in the control basin decreased by 3 percent and increased by 7 percent, respectively. The number of cows decreased from the pre- to post-treatment period, primarily during the latter part of the study. The control basin showed an approximate 50-percent decrease in cow numbers over the last 2 years; the treatment basin showed a similar decrease during the last year of the study.

Improvements relative to control or untreated sites in surface-water quality (nutrients and suspended sediment) during the post-treatment period were evident at the outlet (T-1) of the treatment basin; however, a tributary site (T-2) (0.36 mi2 drainage) showed reductions only in suspended sediment. N species at the outlet showed reductions of 18 percent (dissolved nitrate) to 36 percent (dissolved ammonia); yields of total P were reduced by 14 percent. Conversely, the tributary site showed increases in N species of 10 percent (dissolved ammonia) to 43 percent (total ammonia plus organic N), and a 51-percent increase in yield of total P. The average reduction in suspended-sediment yield for the treated sites was about 40 percent.

The results indicated that effects on suspended sediment were fairly consistent in the treatment basin, but this was not true for nutrients. The cumulative effect of 2 miles of fencing in the treatment basin helped to reduce nutrient yields at the outlet; in the upper parts of the treatment basin, however, other factors affected measurable water-quality improvements. Two factors were evident at T-2 that helped to overshadow any positive effects of fencing on nutrient yields. One was the increased concentration of dissolved P in shallow ground water. This influx of P through the ground-water system partially helped to increase P yield during the post-treatment period at T-2. This indicates that nutrient management in a basin is critical to reducing P yields, and that streambank fencing with small buffer widths cannot compensate for increased dissolved P moving to the stream system through shallow subsurface zones. Another factor that appeared to affect water quality at T-2 was that the cattle crossings were embedded in the stream, which was necessary for a drinking-water supply for the cattle and was less costly than installation of culverts and raising the crossing above the stream. Cattle excretions at the crossings appeared to increase concentrations of dissolved ammonia plus organic N and dissolved P. This factor would be one reason to install crossings using culverts if at all possible, but an alternative water supply would need to be provided for the animals.

After the fencing was installed, the treated sites sampled for benthic macroinvertebrates showed improvement relative to control sites in riparian and instream habitat as assessed through Rapid Bioassessment Protocols (RBP III). Habitat characteristics such as bank stability, bottom substrate available cover, and bottom scouring and deposition all showed relative improvements at the outlet and upstream sites in the treatment basin.These improvements were attributable to the fence keeping the cows out of the stream and allowing the vegetation to establish itself and stabilize the banks. Water-quality data collected during the benthic-macroinvertebrate sampling, along with data collected for the surface-water aspect of this study, indicated suspended-sediment loads decreased at treated sites relative to control sites during the post-treatment period. This suspended-sediment reduction helped to cause some of the habitat improvements detected in the treatment basin.

Using the macroinvertebrate metric data at the generic- and family-identification levels also showed improvement at treated sites relative to control sites during the post-treatment period. The treatment sites showed a relative increase in taxa richness and in the Ephemeroptera, Plecoptera, and Trichoptera (EPT) index, and a decrease in the percent oligochaetes during the post-treatment period. Responses were varied in other biological metrics, such as the Hilsenhoff Biotic Index (HBI), which showed improvement at the outlet of the treatment basin, but not at the upstream sites. Overall, slightly more improvement in structure of the benthic-macroinvertebrate community was detected at the outlet of the treatment basin relative to upstream sites. More detected improvement at the outlet could have been because of more overall area to habitat because the outlet sites had a larger stream width and deeper pools and riffles than the upstream sites.

Ground-water data for the shallow wells in the treatment basin showed markedly different flow patterns. The shallow ground-water flow system appeared to be controlled by bedrock geology, and the shallow and deep ground-water flow systems were not well-connected. Shallow ground-water flow at the nest at T-2 showed ground water contributing to the flow of the stream; at the T-1 well nest, however, the stream was actually losing water to the shallow ground-water system.

The difference in shallow ground-water flow patterns between the two well nests caused water-quality improvements during the post-treatment period to be mainly evident only at the T-2 well nest. This site, where shallow ground water was contributing to streamflow, showed relative improvements in water temperature, dissolved oxygen, N species, and counts of fecal streptococcus for treated wells during the post-treatment period. Concentrations of dissolved P in these wells did not show improvement during the post-treatment period, primarily because of an upland source of P from an agricultural field affecting these wells during the post-treatment period. Nevertheless, the relative improvements for the shallow wells at T-2 indicated that, even though the buffer width was small, there was still a noticeable improvement in the quality of shallow ground water. Improvements to the quality of shallow ground water because of streambank fencing, however, appeared to be dependent on the flow paths of that water.

Given the small buffer width within the fenced area (5 to 12 ft), it was unclear from this study to what extent water-quality changes would occur. Results of the study indicated that even a small buffer width can have a positive influence on surface-water quality, benthic macroinvertebrates, and near-stream shallow ground-water quality. Results do show, however, that streambank fencing in itself cannot alleviate excessive nutrient inputs that may be transported through subsurface zones into the stream system. Overland runoff processes that move suspended sediment to the stream can be controlled (or reduced) to some extent by the vegetative buffer established inside the fenced area.

Table of Contents

Abstract
Introduction
Purpose and Scope
Study Area Description
     Land Use
     Hydrogeologic Setting
     Geology
     Geohydrology
          Structural Framework
          Geohydrologic Framework
          Soils
          Regolith
          Fractured Bedrock
Study Design
     Experimental Design
     Implementation of Best Management Practices
     Data Collection and Analysis
          Ancillary Data
               Precipitation
               Agricultural Activity
          Surface Water
               Streamflow
               Water Quality
               Data Analysis
          Benthic Macroinvertebrates and Habitat Assessments
               Benthic Macroinvertebrates
               Algae
               Habitat
               Water Quality
               Data Analysis
          Ground Water
               Structural Framework
               Fractured Bedrock
               Ground-Water Levels
               Water Quality
               Data Analysis
Quality Control
     Surface Water
     Benthic Macroinvertebrates
     Ground Water
Effects of Streambank Fencing
     Ancillary Data
          Precipitation
          Agricultural Activity
          Surface Water
     Streamflow
     Water Quality
          Low Flow
               Changes in Pre- and Post-Treatment Constituent Concentrations and Field Water-Quality Characteristics
               Changes in Instantaneous Yields of Nutrients and Suspended Sediment
               Post-Treatment Changes
          Stormflow
               Changes in Pre- and Post-Treatment Constituent Concentrations
               Changes in Stormflow Yields of Nutrients and Suspended Sediment
               Post-Treatment Changes
          Annual Yields
          Summary
     Benthic Macroinvertebrates and Habitat
          Habitat
          Water Quality
          Benthic Macroinvertebrates
          Canonical Correspondence Analysis
          Summary
     Ground Water
          Structural Framework
          Ground-Water Flow
               Age Dating
               Water-Level Fluctuations
          Water Quality
               Description of Data
               Relation to Agricultural Activities
                    Manure Application
                    Soil Type
               Relation to Storm Events
               Relation to Water Levels
               Relation to Streambank Fencing
                    Paired Wells
                    Pre- and Post-Treatment Comparisons
                    Dissolved Ammonia
                    Dissolved Ammonia Plus Organic Nitrogen (DKN)
                    Dissolved Nitrate
                    Dissolved Nitrite
                    Dissolved Phosphorus
          Summary
Conclusions
Acknowledgments
References

This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.

View the full report in PDF 8.1 MB

For more information about USGS activities in Pennsylvania contact:
Director
USGS Pennsylvania Water Science Center
215 Limekiln Road
New Cumberland, Pennsylvania 17070
Telephone: (717) 730-6960
Fax: (717) 730-6997
or access the USGS Water Resources of Pennsylvania home page at:
http://pa.water.usgs.gov/.



U.S. Department of the Interior, U.S. Geological Survey
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Last modified: Thursday, January 10 2013, 05:27:58 PM
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