December, 2013
Pennsylvania State University
Kletetschka, Karel
The Pennsylvania State University
Department of Geosciences
Understanding Stream Water Physiochemical Properties and
Dynamics in the Shaver’s Creek Watershed
Karel Kletetschka
Fall 2013
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December, 2013
Pennsylvania State University
Kletetschka, Karel
Abstract:
Using bulk geochemistry, cation analysis, natural tracers, and hydro-mechanical models,
the Shaver's Creek watershed was analyzed to determine the extent of groundwater-surface water
interactions and were compared to those in Shale Hills Critical Zone Observatory to help
ultimately understand whether anthropogenic projects such as the construction of the lake Perez
dam have an effect on them. Calcium and magnesium cation concentrations were measured and
analyzed with respect to the distance from the stream and the data showed that there was less of
both elements in the stream water. Temperature was used as a natural tracer and the data showed
that the stream water at Shaver's Creek was noticeably cooler than the groundwater which
suggests that there is little interaction between the groundwater and surface water however in
Shale Hills, the data showed the opposite trend and the stream water was warmer which is more
common at the time of collection since the sun would have warmed the upper layers of the
stream. This difference suggests that in Shaver's Creek, where the lake Perez dam once was,
there are legacy sediments that clog the pore spaces and subsequently reduce permeability.
Chloride ion concentrations also showed that in Shaver's Creek there was little interaction
between the two bodies on the same basis. Other analyses such were used to determine the water
gradient and it was determined that the stream was a losing stream at the time due to a recent
rainfall event prior to data collection however based on previous data the stream can be
considered a gaining stream. Mixing model diagrams were used to compare the sites to
precipitation as well as to further determine the extent of GW-SW interaction.
The results strongly suggest that the extent of groundwater-surface water interaction in
Shaver's Creek is minimal and comparison with Shale Hills Critical Zone Observatory data
indicates that this is likely due to legacy sediments that accumulated at the time when the lake
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Pennsylvania State University
Kletetschka, Karel
Perez dam was present in the Shaver's Creek area. Anthropogenic influences on GW-SW
interactions are critical areas of study as they can have significant effects on the hyporheic zone,
the ecology of the stream, water quality downstream(i.e. the Chesapeake Bay), and it can also
have structural implications that must be considered for potential geotechnical or architectural
projects that may take place there in the future.
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December, 2013
Pennsylvania State University
Kletetschka, Karel
Table of Contents
I.
Introduction and Background: ............................................................................................. 1
II.
Methods: .............................................................................................................................. 5
i.
ii.
Study Area: ....................................................................................................................... 5
Field Methods ...................................................................................................................... 5
iii. Laboratory Methods: ....................................................................................................... 7
III. Results: ................................................................................................................................. 8
i.
Field Results: .................................................................................................................... 8
ii.
Laboratory Results: .......................................................................................................... 9
IV. Discussion: ......................................................................................................................... 11
V.
Conclusion: ......................................................................................................................... 14
VI. References ......................................................................................................................... 15
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December, 2013
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I.
Pennsylvania State University
Kletetschka, Karel
Introduction and Background:
Quantifying groundwater-surface water interactions and their impact on the underlying
3
geology, transport of solutes and the health of ecosystems is an exigent task but can be
4
approximated using hydro-geochemical models and analysis. Differences in temperature between
5
groundwater and surface water can also be beneficial in characterizing their interaction and
6
oftentimes gaining streams will keep a stable sedimentary temperature while losing streams will
7
have a more fickle temperature distribution on the sediment as well as the surface water.
8
Groundwater and surface water interactions are also important in studying stream chemistry
9
because water contained in aquifers bears different chemical properties ranging from
10
composition, conductivity, and pH so analyzing its transport and exchange rate with stream
11
water is critical (Hoeksema et al., 1985). Measuring the differences in height of water to the
12
surface can be used to draw conclusions for the lateral hydromechanics of the water. Coupled
13
with depletion profiles for dissolved mineral cations, one can paint a much more clear picture of
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the physiochemical dynamics and GW-SW interactions occurring in the area of interest.
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Variable solute behavior in relation to discharge of water into a stream has been explored
16
by researchers for quite some time and two processes that are significant in these variability’s are
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advective pumping and mechanical dispersion which are related to stream flow along
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heterogeneous groundwater beds that direct distribution of groundwater pore flow paths and thus
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subsurface solute discharge rates (Wörman et al., 2002) . Essentially, irregular groundwater beds
20
mean that as water flows along them there will be different mechanical effects based on the
21
topography which, determine where water will discharge more and thus where solute discharge
22
rates will be higher or lower. Several mathematical models exist including the Transient Storage
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Pennsylvania State University
Kletetschka, Karel
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Model, a Log normal probability density function, First-order mass transfer relationships,
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Diffusive exchange, Advective pumping model yet all of the models have shown only limited
25
success in predicting solute variability with flow patterns (Wörman et al., 2002) due to the
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plethora of other influential factors and conditions that exist in each aquifer and the fact that
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groundwater surface-water interactions are often poorly accounted for in these models.
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Another important quantification in understanding geochemistry of streams is that of
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weathering rates. Weathering (dissolution) of bedrock results in the discharge of dissolved
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solutes and can significantly affect water chemistry. Using factors such as climate, biota,
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porosity, and atmospheric exposure to understand and quantify weathering will consequently
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help quantify and understand chemical characteristics of water including pH, conductivity, and
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composition. Vegetation will have an effect on CO2 levels as photosynthesis fixes CO2 , and
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furthermore, vegetation can increase the concentration of non-essential elements through
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transpiration while taking up essential nutrients such as potassium and calcium. There are other
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factors that should be considered as well such as closest factory’s etc. when it comes to
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monitoring Carbon.
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Climate plays a significant role in studying ground-water surface water interactions and
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temperature in particular is often used as a tool in monitoring these interactions. Heat is a natural
40
tracer that can be used for analyzing ground-water surface water exchange. As previously
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mentioned, methods for quantifying these ground-water surface water interactions have had
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limited success as seepage meters are erratic in flowing waters such as streams and rivers and
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techniques based on Darcy’s law rely on hydraulic conductivity data which is often only an
44
estimate due to great variability (Anibas 2009). If the heat transfer method, coupled with energy
45
balance calculations are done correctly then it may be a more useful technique in quantifying
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Pennsylvania State University
Kletetschka, Karel
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ground-water surface water interactions and that is why monitoring the ambient temperature and
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incorporating it into these temperature based studies may be important. Water levels and
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chemical profiles can also be used to assist in understanding the behavior of natural waters since
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they are related to porosity as well as mineral dissolution. These, as well as the tracer chloride
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ions and temperature values are quite useful in calculating the general water flux from ground
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water to surface water or vice-versa (Gleeson et al. 2009) so surface water temperature due to
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current climate is a large factor.
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Anthropogenic influences such as the creation of dams can have significant effects on the
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area in which they were constructed for example there is the issue of runoff sediments that
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become trapped in the dams and build up; they are known among geologists as legacy sediments.
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These legacy sediments likely play a significant role in erosion rates as well as water quality
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downstream (Merritts et al. 2006). Phosphorus in particular has shown to be transported with this
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eroded sediment raising concerns about pollution as phosphorus often causes increased algal
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growth and subsequently less sunlight penetration and dissolved oxygen concentrations
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(Sotomayor-Ramírez et al. 2004).
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Shaver's Creek and the Shale Hills Critical Zone Observatory are ideal locations for
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determining the behavior and chemistry of natural waters as well as the influence of man-made
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dams on such processes. Central Pennsylvania climate has an average annual temperature of
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about 15°C (National Climate Data Center 2013) and roughly 39.77 inches of precipitation
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annually for years 1981-2010 which plays a role in water levels as well as GW-SW mechanics
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and chemistry. In the Shaver's creek watershed, channel morphology may differ as streams
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transition from 3rd to 1st order streams as pressure and flow rate at the stream beds will differ,
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however the quantification of these phenomena that has yet to be fully outlined. The primary
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Kletetschka, Karel
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lithology of the area can be characterized by mostly Calcareous shale, Limestone, Quartzite,
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Sandstone, and Shale. The area where the majority of the surface water is concentrated has
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mostly Shale and Limestone which has implications on the mineralogy of the water. Limestone
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and shale are relatively easy to erode as opposed to sandstone for example and this means that
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the streams will have a higher concentration of calcium ions from the limestone/calcium
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carbonate (Boynton et al., 1966) and possibly traces of hydrous aluminum phyllosilicates, iron,
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magnesium and other cations in differing concentration from the shale (Velde et al., 1995).
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Weathering of bedrock can be significant in ground water surface water interactions because the
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dissolved minerals and particulate matter could increase sedimentation and consequently clog the
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streambed; preventing interactions between ground and surface water to some degree. Variability
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in Mg in soil water has much to do with the kinetics of clay mineral dissolution and rainfall
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intensity also has an effect on weathering by spurring water-rock interactions (Jin et al., 2011)
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One method of observing ground water surface water interactions and the weathering of
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minerals is to analyze ground water and surface water samples for cations characteristic to
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certain minerals. Much of the Valley and Ridge province of Pennsylvania has an abundance of
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Illite and Chlorite which are magnesium silicates that when weathered/reduced will release Mg+,
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K+, Si+, Fe+, Al+ (Jin et al., 2010). Looking at depletion profiles of these cationic species will
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shed light on the type of ground water-surface water interactions that are occurring as well as
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potential weathering patterns. Calcium and alkalinity profiles along the M5 transect as it goes
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farther from the stream can shed light on limestone dissolution as well as the porosity of the
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stream bed-rocks. Analyzing surface soil samples will be beneficial in understanding the role of
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water in changing the soil chemistry and the hydrological properties of the underlying geological
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materials. Once these characteristics are understood in both Shaver's Creek and Shale Hills,
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Pennsylvania State University
Kletetschka, Karel
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comparisons can be drawn that could shed light on the effects the dam had on the area that are
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still affecting the Shaver's Creek watershed but would only be seen in Shale Hills to a lesser
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extent.
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II.
Methods:
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i.
Study Area:
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Shaver's Creek is a tributary second order stream that is located in Huntingdon County,
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Pennsylvania within the Valley and Ridge province in central Pennsylvania. The stream is
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situated near the lake Perez basin and consists mainly of soil developed from the Marcellus Shale
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at coordinates 40°39'52.09"N 77°54'52.90"W and Elevation~250m with mostly grasslands.
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ii.
Field Methods
A total of seven water samples were taken from Shaver’s creek watershed in September,
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2013 and they included groundwater wells as well as the stream adjacent to them. The site
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consisted of mainly grasslands with thick vegetation along all the various transects. Unfiltered
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aliquots were tested from the sites mostly along transect M and N(Figure 1) towards the stream
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at 40°39'52.09"N 77°54'52.90"W , and were analyzed for Temperature and pH using a pH probe
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kit with standards (Mettler Toledo™). Electrical conductivity was measured at each site ((Multi-
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Parameter PCTeste ™ 35). Of the seven sites, six were ground water wells previously installed
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each 2-8 meters deep with a 0.15m diameter and the last site was the stream centered between
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wells M4 and M5. Water samples were collected from the wells using a peristaltic pump as well
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as a 0.45micron filter. The Well 4 water sample had to be hand filtered due to heavy particulate
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matter and Well M5 had an unknown layer of matter that had to be penetrated between the
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outside surface and the start of groundwater. The depth of the surface of water for each well was
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Kletetschka, Karel
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measured using a portable depth meter (Solinst 101 Water Level Meter), however well N6 failed
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to give a concise reading. Filtered samples were collected for analysis of cations, anions, and
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alkalinity and were stored in separate acid-prewashed HDPE plastic vials. Samples collected for
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cation analysis were acidified on site with three drops of concentrated nitric acid(16M). Samples
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collected for alkalinity testing were taken in vials without headspace air and capped. Two
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samples were collected for DIC and DOC analysis; DIC vials were acid-washed and combusted
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previously and capped with seals and septa. DOC samples were acidified using 3 drops of
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Hydrochloric Acid(1M) in the field. All samples were kept cool on ice as they were transported
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to the laboratory for analysis.
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Two surface soil samples were collected: Sample 1 at 40.66574°N 77.91087°W near the
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stream lower bank and Sample 2 was collected at 40.66547°N 77.90990°W and placed in plastic
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bags to be transported to the laboratory. Soil cores were also taken at various depths at various
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locations surrounding Shaver's creek, Shale hills, and Katy creek. Once at the laboratory, all
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water samples were stored at 4°C and soils samples were allowed to dry.
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An important principle in quantifying ground water surface water interactions is Darcy’s
law which describes fluid flow through a porous medium and is described as:
𝑑ℎ
𝑞 = −𝐾 𝑑𝑙
(Eq.1)
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where q is the flux(m/s) and K is the hydraulic conductivity, dh is the hydraulic head difference
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and dl is the distance however many other forms exist that rely on different data such as
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permeability and pressure change (Whitaker et al., 1986). The depths measured were correct to a
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known datum to estimate hydraulic head which was used for the three-point problem strategy
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that was utilized to determine the direction of groundwater flow as well as the hydraulic
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gradient(variation of Eq. 1) at the time of sample collection.
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iii.
Laboratory Methods:
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Sample from both Shaver's Creek watershed and Shale Hills Critical Zone Observatory
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were analyzed for comparison. Alkalinity was measured and calculated using a titrating device
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and sulfuric acid (1.6N). Alkalinity values were calculated using:
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Alk (ppm CaCO3) = ((2B-C) x N x 50 000) / V
(Eq. 2)
(American Public Health Association, 1915)
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Cation concentration was measured using an inductively coupled plasma-atomic emission
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spectrometer (ICP-AES), or optical emission spectrometer. The specific instrument used was the
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Perkin-Elmer Optima 5300 UV. Anion concentration was measured using a dionex ion
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chromatograph (Dionex ICS 2500). To measure isotope abundance in the water samples using
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Off-Axis-Integrated Cavity Output Spectroscopy (OA-ICOS).
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Soil cores sections were extracted at various depths (80-90cm, 130-140cm, 190-
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200cm,280-290cm). The two soil samples along with the cores were manually broken apart to
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prepare for homogenization via riffle splitting (~5 per sample) and sieving. Lithium metaborate
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fusion is a technique used to dissolve solid samples and it is often used for geological sampling
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of soils due to reliability and the fact that the high concentration salt environment dampens any
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inter-sample matrix differences. Sieved samples were finally prepared for lithium metaborate
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fusion by mixing lithium metaborate(1g) and a soil sample (100mg) to be placed into a high
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temperature furnace (900°C) in small graphite crucibles. After heating the samples to 900°C for
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approximately 10 minutes the molten beads from the crucibles were placed in a 5% nitric acid
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solution and diluted for elemental analysis(ICP-AES).
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Soil samples were also tested using X-ray diffraction techniques based upon Braggs law:
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(Eq. 3)
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The various soil samples were dissolved in de-ionized water and transferred via plastic pipettes
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onto small glass slides (75mm by 25mm) until fully covered. The slides were allowed to dry for
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a period of ~1 week and then tested for structural characteristics with X-ray diffraction (Titan X-
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FEG).
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III.
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i.
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Results:
Field Results:
The data from well M4 seemed to be inconsistent with the rest of the samples and
perhaps collecting more samples would be beneficial.
The pH of the wells in Shaver's Creek doesn't vary in any particular pattern with respect
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to the distance from the stream (Figure 14) however the groundwater samples were generally
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lower in pH than the surface water samples. For Shale Hills there also is not a noticeable trend in
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the pH vs. distance graph yet the groundwater samples are also lower in pH than the stream
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water samples. Overall, the Shale Hills pH values was noticeably higher than for Shaver's Creek
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in both stream water and groundwater.
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Temperature measurements in Shaver's Creek showed that Well M4 had a noticeably
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larger value than the rest of the wells including the stream water. The stream water temperature
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was curiously lower than the groundwater temperatures. In Shale Hills, the temperature values
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showed little variability on all the samples tested. The stream water had the highest value of the
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tested aliquots in Shale Hills. Overall, the Shale Hills temperatures were all lower than the
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Shaver's Creek Temperatures (Figure 15).
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Conductivity measurements were taken on site and proved to all be higher than the
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stream water conductivity except for well M10.(see figures 2,3). The depths of surface of the
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water for each well was recorded however well N6 failed to give a proper reading.
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The three-point problem showed that the Shaver's Creek stream was a losing stream at
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the time of data collection, however average water level data over a longer period of time for the
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area suggests that it is in fact a gaining stream(figure 15).
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ii.
Laboratory Results:
Stream water alkalinity values tended to be lower than the nearby groundwater values .
190
From 0-10 meters from the stream water the alkalinities were quite variable (Figure 3)
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ICP-AES results for the water samples showed concentrations(ug/mL) of dissolved cations: Al,
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Ba, Ca, Fe, K, Mg, Mn, Na, P, S, Si, Sr, Ti, Zr. Phosphorous, Titatium, and Zirconium all had no
193
variability in concentration across all of the different sites including those of Shale Hills, and
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Katy Creek(Table 2).
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Concentration of calcium showed a cluster of similar concentrations near the stream in
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Shaver's Creek perhaps suggesting a separate store within the catchment (Kirchner 2003, Figure
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5). For both Shaver's Creek and Shale Hills the stream water had a lower concentration than the
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groundwater. Magnesium concentration also showed that values away from the stream were
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higher than the stream water concentrations in both the Shaver's Creek watershed and the Shale
200
Hills critical zone observatory.(figure 6)
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The anion analysis showed that chlorine concentrations were very different in the stream
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of Shaver's Creek compared to the nearby groundwater wells(Figure 16), and in Shale Hills on
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the other hand the values are rather similar to each other. The concentrations in Shale Hills were
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all lower than those in Shaver's Creek. Oxygen 18 isotopes showed little variability in both areas
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however the stream values for Shale Hills were both somewhat higher than the groundwater
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wells.
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Non-purgiable dissolved carbon(NPDC), dissolved organic carbon(mg/L), and dissolved
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inorganic carbon data sets for Shaver's Creek can be seen in figure 7 and shows that as you get
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father away from the stream, there is more dissolved organic carbon.
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The data for the soil samples fused via lithium metaborate show significant variation
211
between the soil samples taken near the stream compared to the samples taken farther away. Soil
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1 refers to the sample taken near the stream, and soil 2 refers to the sample taken farther down
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the transect. Specific value can be seen in figure 8. The x-ray diffractograms for Shaver's Creek
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core M5 80-90cm had significantly less intensity in the illite peak than the complementary M11
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80-90cm peak.
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The hydrogeology(Three-point problem) results from Shaver's Creek showed that the
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stream was a losing stream at the time of data collection with a hydraulic gradient of 0.44. The
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XRD analysis yielded probable distributions of minerals in the core samples taken as well as the
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surface soil samples(figures 9, 10). The XRD from the deep core(200-210) at Shaver's Creek
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shows a more prominent illite primary and secondary peak.
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IV.
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Discussion:
Since the magnesium concentration results versus distance from the stream show that
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there is a higher concentration of magnesium in the ground water as the distance from the stream
225
increases, it is likely that there is little interaction between the ground water and the surface
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water as researchers such as Sakthivadivel have concluded that sediments can often clog pore
227
spaces and thus decrease permeability.
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The field results for temperature in Shaver's Creek showed that the stream water
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temperature was curiously lower than the groundwater which suggests that there is not much
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interaction between the two since stream water is generally higher in temperature due to sunlight
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warming the upper layer. In Shale Hills however the stream water temperature was slightly
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higher than the groundwater samples suggesting that in Shale Hills there is more groundwater-
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surface water interaction. Since overall the temperature of Shale Hills water was lower than
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Shaver's Creek water, there is a strong possibility that the stream water in SC was in fact water
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that flowed in from Shale Hills which is why it was cooler. The temperature data suggests that
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there is likely more interaction between groundwater and surface water in Shale Hills than in
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Shaver's Creek which could be interpreted as being a result of the dam that existed there causing
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legacy sediments to accumulate, thus clogging the pores in the bedrock (Sakthivadivel et al.
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1970)
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Chlorine, or Chloride ion rather is an excellent tracer element and examining differences
241
in concentration can help understand whether there are groundwater-surface water
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interactions(Gleeson et al. 2009). The data showed that in Shaver's Creek, the chloride ion
243
concentration was much noticeably higher than the adjacent ground water well concentrations
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which suggests that there is little interaction between the two systems or there is a possible
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contamination salt contamination in the stream. In Shale Hills, the values were more similar to
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each other however they were all lower than the Shaver's Creek values which suggests that the
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Shale Hills water isn't directly flowing towards Shaver's Creek or that there is a source of
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Chloride that is only present near Shaver's Creek.
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The measured pH values in the two regions show very different values for the two
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streams which would may suggest that there is some mineral dissolution (perhaps due to legacy
251
sediments) that causes the pH to decrease as it reaches the Shaver's Creek watershed.
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Alkalinity and calcium concentration as the distance from the stream increases showed
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very similar patterns which reinforces the integrity of the data as they are both based upon
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calcium carbonate concentrations in the water(Boynton 1966).
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Well M4 in the Shaver's creek transect shows outlying data across many different
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analyses which suggests error in collection and that more data may be needed. This is important
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since that was the only well sampled that was on the other side of the stream. M4 data could have
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reinforced or contradicted conclusions made based on the other wells.
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The three-point problem showed that the Shaver's Creek stream was a losing stream at
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the time of data collection, however the data was collected following a significant rainfall event
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which could have driven the direction of the water flow towards the groundwater(Brady 2008).
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The dissolved organic carbon(DOC) data in Shaver's Creek showed more DOC in the
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wells farther from the stream which suggests that perhaps the water farther from the stream is
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less mobile and thus has more dissolved organic carbon due to vegetation or any organic material
265
having a longer time to break down.
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When looking at the ratios of Mg:Ca and Na:K, it is evident that the stream water of the
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Shaver's Creek watershed has a significantly higher Na:K ratio than the groundwater
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samples(Figure4). Perhaps this is due to illite dissolution(Hower, 1900) due to weathering in the
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stream that would cause K ions to flow into the groundwater, particularly after the rainfall event
270
that occurred prior to data collection. Another explanation could simply be differences in
271
lithology between the groundwater farther from the stream as well a lack of significant
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interactions between the stream water and groundwater; in other words the mineralogy of the
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groundwater farther from the wells may have more illite which would decrease the Na:K ratio
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and the dissolved potassium ions may not be able to permeate into the stream. XRD analysis
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shows that illite is indeed a prominent element in the deeper soils of the area. The XRD
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diffractograms of well M5 did indeed have significantly less intensity in the illite peak than well
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M11, which was farther from the stream which supports the idea of less illite dissolution in the
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stream. The Na:K and Mg:Ca relations were also examined in the average precipitation in the
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region and they show that the large ratio in the surface water of Shaver's Creek isn't related to
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precipitation in terms of Na:K values since their values are significantly different. The Mg:Ca
281
ratio's however were nearly identical between the surface water and the average precipitation
282
suggesting that the water from the rainfall event was predominantly still in the stream. Another
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factor to consider is road salt, which would increase the sodium concentration in the stream
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water. The data showed that there was both more sodium, and less potassium which advocates
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both the road salt contamination theory and potentially the less illite dissolution in the stream.
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Magnesium and calcium concentrations may have to do with dolomite dissolution (Velde 1995).
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V.
Pennsylvania State University
Kletetschka, Karel
Conclusion:
The bulk geochemistry of the Shaver's Creek watershed shows that stream water and
289
groundwater have significant differences such as in their Na:K ratio, which is likely due to
290
sodium containing road salt getting into the stream but could also be due to illite dissolution near
291
the bottom of the stream flowing into the groundwater; raising the GW concentrations. Much of
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the specific chemical profiles showed that there is less interaction between groundwater and
293
surface water than could be expected and this is reinforced by the temperature values.
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Temperature is an excellent tracer and in Shaver's Creek, the value for the stream water is lower
295
than all of the groundwater values which indicates that there is not much interaction between the
296
two bodies. This is likely due to legacy sediments that arose from the historic dam (Merritts et al.
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2006) clogging the pores between the groundwater and the stream water. One method of
298
rationalizing the lower temperature is to consider Shale Hills which generally had lower values
299
for temperature. Topography indicates that water from Shale Hills may be flowing towards
300
Shaver's Creek and that could explain why the temperature of the stream is lower. The
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temperature in the stream water of Shale Hills is higher than the groundwater which is the
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common trend as sunlight tends to warm the surface of water. This indicates that there is likely
303
more interaction between the ground water and surface water of Shale Hills where the legacy
304
sediments would not be present. X-ray diffraction allowed for the testing for certain minerals and
305
revealed why certain elements may have been present for example the peak intensities for illite
306
were much larger in the well that was farther from the stream than the one that was closer.
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Anion concentrations showed that in Shaver's Creek there was a very noticeable
308
difference in chloride concentration compared to the wells which suggests that there is little
309
interaction between the groundwater and surface water or that there is an outside contamination
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such as road salt. The fact that the values are all smaller for Shale Hills and don't vary from GW
311
to SW suggest the former.
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Understanding ground water-surface water interactions in Central Pennsylvania can be
313
pivotal for various reasons including understanding the water quality downstream and in the
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Chesapeake Bay. The Shaver's Creek watershed is very important in that it used to be a dam, so
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it has the potential to shed light on how anthropogenic influences such as the construction of lake
316
Perez can effect water chemistry and biological systems. It has been documented various times
317
that the region where this exchange occurs: the hyporheic zone, has an important impact on an
318
ecological system. Perhaps the key to understanding/controlling water pollutants lies in
319
anthropogenic influences such as the building of dams and the accumulation of legacy sediments
320
that hinder interaction between the ground water and in many cases increase erosion rates.
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Eventually, a model to explain the hydromechanics and geochemistry of stream systems such as
322
this one may be perfected.
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330
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VI.
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