 |
|
|
||||
| Publications— Scientific Investigations Reports |
In cooperation with the Pennsylvania Department of Environmental Protection
U.S. Geological Survey Scientific Investigations Report 2006-5141
By Daniel G. Galeone, Robin A. Brightbill, Dennis J. Low, and David L. O’Brien
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
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.
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/.
| AccessibilityFOIAPrivacyPolicies and Notices | |
  |
|