Effects of Pipeline Construction Clear-Cutting on
Water Quality in Northeastern Headwater Streams
Nicole K. Zenes
05/2015
Abstract
Clear cutting in hardwood forests has been shown to increase the concentration of
nitrates in stream water. The intensity of nitrate concentration ranged from a 2-fold to a
50-fold increase. My study was designed to test whether the deforestation from natural
gas pipeline construction was sufficient to cause an increase in nitrate levels and the
magnitude of the increase. I took water samples above and below fifteen streams
across Northeast Pennsylvania and North New Jersey. I found that the below pipeline
concentration of nitrate was significantly higher than the above stream concentration.
On average, there was a 63% increase. The dominant tree species did not have a
significant effect on the change in nitrate concentration. Contrary to other studies on
clear cutting, there was not a significant impact on water temperature. Impacts from
pipeline construction should be studied further and current methods may need to be
reevaluated to limit impact on water quality.
Acknowledgements
The completion of this thesis became more of a journey than I expected. I have spent
the past three years monitoring the progress of Tennessee Gas Pipeline Company‘s
Northeast Upgrade Project. I never thought my passion for protecting my home would
turn into a real study. Writing this at times felt like a chore, but I love the work that I
do and here is the final result of this endeavor.
I am indebted to my advisor, Stephen W. Pacala, for helping through all stages of
this process. While I knew what my motivation for this study was, his guidance in
narrowing my focus and developing a solid project was critical. His support and encouragement helped me stay calm through my set backs in the final stretch.
I would also like to thank Lars O. Hedin for his knowledge and all his assistance with
field protocol and laboratory work. Without his advice, I would have had a much
more difficult time completing this thesis. Thanks to Mingzhen Lu, as well, for his
assistance in the laboratory, analyzing my water samples.
Cooperation with the Delaware Riverkeeper Network and Faith Zerbe was invaluable
to the completion of my research. Access to their data and use of equipment allowed
me to further my insights and expand the scope of my project.
I thank the landowners, who allowed me access their land and streams to conduct my
sampling. Without them, this project could not have been completed.
This research was funded by the Office of the Dean of College and the Princeton
Environmental Institute. Finally, I would like to acknowledge Princeton University
for giving me the opportunity to complete this study.
Contents
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Results
3.1 Nitrate Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Dicussion
4.1 Nitrate Concentrations . .
4.1.1 Tree Species Effect
4.2 Stream Temperature . . . .
4.3 Soil Impacts . . . . . . . .
4.4 Ecosystem Recovery . . .
4.5 Future Directions . . . . .
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Literature Review
1.1 Nutrient Cycling . .
1.2 Thermal Impacts . .
1.3 Tree Species . . . . .
1.4 Motivation for Study
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Methods
2.1 Study Sites . . . . . . . .
2.2 Complete-Tree Harvesting
2.3 Pipeline Construction . . .
2.4 Nitrate Concentration . . .
2.5 Temperature . . . . . . . .
2.6 Vegetation . . . . . . . . .
2.6.1 Dominant Species
2.6.2 Regrowth . . . . .
Conclusion
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List of Figures
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Map of Stream Sites and Dominant Tree Species . . . . . . . .
Map of Pipeline Route from TGP‘s Public Notice (2010) . . . .
Changes in Shade Coverage for S005 . . . . . . . . . . . . . . .
Soil Disturbances during Construction . . . . . . . . . . . . . .
Nitrate/N Concentrations Above and Below Pipeline . . . . . .
Changes in Nitrate/N Concentrations Above and Below Pipeline
Nitrate Concentrations per Dominant Species . . . . . . . . . .
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Stream Information . . . . . . . . . . . . . . . . . . . . . . . . . . .
Mortality of Red Pine Saplings . . . . . . . . . . . . . . . . . . . . .
10
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List of Tables
1
2
1
1.1
Literature Review
Nutrient Cycling
In mature forests, the nutrient cycle and its outputs are highly predictable from year
to year. Their processes help minimize the amount of nutrients and sediments leaving
the system (Bormann et al. 1974). Nutrient cycling within the forest is rarely altered
therefore studying the export of solubilized substances is indicative of a problem. Concentrations of dissolved nutrients exiting the ecosystem in a stable, undisturbed forests
have high fidelity year to year. Following a disturbance, the immediate response is the
solubilization of nutrients in the soil and discharge into stream waters (Pierce et al.
1972, Bormann et al. 1974). The high increase in runoff from the cleared areas causes
a marked discharge of nutrients into streams (Federer 1968).
Studies involving clear-cutting have ranged in size from 0.25ha (Prescott
et al. 1992) to entire watersheds. While the minimum necessary gap size is unknown,
it is the gap itself is necessary to cause these effects rather than the removal of a
particular number of trees in a plot. Prescott et al. (2003) found that removing single
trees randomly throughout the forest, in the same quantity as removed in a gap, would
dampen or eliminate the loss of nitrates from the system. Partial cuts reported in Feller
et al. (2000) also showed smaller loss of nitrates than found in an undisturbed forest.
The occurrence of nitrification in stable forest is low (Bormann et al. 1968
). Following a disturbance like clear-cutting, nitrification increases in the soil (Frazer
et al. 1990, Dahlgren and Driscoll 1994) and increased nitrate concentrations are
found in streams (Vitousek et al. 1979, Feller et al. 2000). The effect can be seen in
less than a year and lasts 2-7 years (Prescott et al. 2003). The increase occurs because
Nitrobacter bacteria can quickly convert ammonium into nitrates when vegetation is
removed (Likens et al. 1969). In addition to this rapid conversion, the number of
Nitrobacter bacteria have been reported to increase 34 fold after clear cutting (Likens
et al. 1969).
Studies on nitrogen cycling and nitrate loading in streams, in particular,
have been on the rise due to an increased interest in downstream impacts of this
form of environmental pollution. Increased nitrate levels can have a negative effect
on plant and macro-invertebrate life, terrestrial forest health, and impact on human
health through water consumption. A wide variation in stream nitrate concentrations
1
was found within similar forest types (Berhardt et al. 2002). Differences could be
attributed to forest age, soil composition or hydrology of the surrounding area. Denitrifying bacteria and the biological assimilation of nitrogen impact nitrate levels in
streams (Bernhardt et al. 2002). The availability of organic carbon [C] also has been
shown in greatly influence the demand for nitrate in streams and soils (Prescott et
al. 2003). Each watershed has a unique set of characteristics and responses to clearcutting.
The conditions present after a disturbance are generally favorable for the
ecosystem to recover and return to stable conditions (Bormann et al. 1974). While
nutrients do exit the system, the increased decomposition can replenish the soil. An
increase in soil moisture in the first few years, along with these nutrients, can allow
adapted species to recolonize and prevent further leaching and erosion. This ability
to capitalize on the newly exposed clearing is what allows the system to recover, as
they would with naturally occurring disturbances such as fire, wind, and ice damage.
Altering the ecosystem beyond clearing the trees, however, can set back this process.
The more invasive the human made disturbances are, the higher the risk for long term
damage.
The majority of studies referenced are analyses of stem-only harvesting.
This includes only trunk removal while that debris and root systems remain in the gap.
In complete-tree harvesting, all of the above and belowground parts of the tree are
removed (Bormann & Likens pp. 216-219). Generally careful stem-only harvesting,
leaving the stump results in rapid regeneration. There is an abundance of resources
generally limited in a mature forest including access to sunlight, increased water, and
more nutrients (Bormann & Likens pp. 216). Ecosystems are able to rebound quickly
as long as there is not intensive disturbances.
Complete-tree harvesting can have a negative impact on regeneration in
the gap. The disruption of the soil can affect seeds buried in the ground and make it
harder for herbaceous vegetation, such as grasses and shrubs, to begin re-colonization.
There are no stumps allowing for basal shoots or root sprouts to grow. There is little
information available on the regeneration impacts of complete-tree harvesting because
it is not a method commonly practiced.
The Bormann et al. (1974) study differed from other clear-cutting studies
because they prevented regrowth for the first two years through the use of herbicide in-
2
stead of allowing for natural regeneration. This was to test the ability of the ecosystem
to prevent loss of nutrients as decomposition continued to increase the available nutrients. They found extremely high nitrate levels compared to other studies (Vitousek &
Melillo 1979). The return of vegetation is necessary to regulate the loss of nutrients
and stabilize the system.
The top layer of the soil contains the organic matter that is the target of
increased decomposition following clear cutting. In Bormann et al. (1974) the export
of nutrient by the ecosystem began as early as 6-10 months following clear-cutting.
Nitrate export from an ecosystem reaches its peak around 2-3 years then tapered off as
the supply of nutrient dwindled. Their study reported approximately twice the amount
of nitrogen taken up annually in the drainage waters. Two years is the amount of time
it takes for to exhaust the matter available for decomposition as well as the stock of nutrients in the soil prior to deforestation (Bormann et al. 1974). Additional disturbance
such as the removal of topsoil and root systems can compound the effects seen.
Dominski (1971) and Bormann et al. (1974) reported significant loss of
nitrogen stored in the top layers of the soil. In addition to increased nitrates being
produced and export from the ecosystem, the nitrates already stored prior to clearcutting were leached from the soil. While dissolved substances exported from the
system reach their peak around two years, particulate matter from erosion reaches its
peak approximately 3-4 years following clear cutting. This can continue to aid in the
export of nitrates through the physical removal of upper layers of soil.
Prescott et al. (2003) suggest that increased decomposition is not the cause
of increased nitrate concentrations. They found there was not an increase in the rate
of decomposition to accompany the increase in nitrate levels. Zhang and Liang (1995)
reported similar reults. Replicating clear-cut induced changes in soil temperature and
moisture levels in uncut forests does not yield the same change in nitrate concentrations (Prescott 1997, Prescott et al. 2003). Vitousek and Matson(1984) took soil from
a clear cut area and transplanted to the undisturbed forest and still reported an increase
in nitrate concentrations. The increase is being influenced by factors other than the
environmental conditions in the gap.
Hart et al. (1994) suggests that accumulation of nitrates in the soil is a
result of microorganism becoming carbon limited rather than nitrate limited. Mature
forests generally have lower concentrations of nitrates (Davidson et al. 1992) and
3
low rates of nitrification. This accumulation occurs only after the decomposition of
remaining roots and branches. Prescott et al. (2003) argues that their study shows
that an increase in nitrates is due to less microbial assimilation as a result of reduced
carbon input from leaf litter.
An increase in water exiting the system was seen during the growing season
(Pierce et al. 1970, Bormann et al. 1974). Nutrient cycles, especially nitrogen, do
fluctuate slightly throughout the year, as does stream flow. However, stream flow
and total water export are different. Loss of dissolved substances is independent of
stream flow, unlike particular matter. The loss of nutrients from an ecosystem can
be directly correlated with the amount of water leaving the ecosystem (Likens et al.
1967, Bormann et al. 1969, Bormann et al. 1974). Lack of vegetation to slow runoff
from precipitation can prevent water from seeping into the ground as it would in an
undisturbed ecosystem. Pierce et al. (1970), Likens et al. (1970) and Bormann et al.
(1974) found a significant increase in the total water leaving an ecosystem, resulting
in loss of nutrients carried away in the stream water.
Following a disturbance such as clear cutting, there is less vegetation available to perform transpiration, an important aspect of forests. The water that normally
be vaporized is now added to the stream flow and total export of water from the ecosystem. As several studies reported, the close relationship between water leaving the
system and loss of nutrients would also be impacted by loss of transpiration services
(Likens et al. 1967, Bormann & Likens 1969, 1972, Bormann et al. 1974). The
ecosystem, losing the biotic organisms that performed this duty, would struggle to
hold on to water and therefore dissolved nutrients, such as nitrates, exit the system
through streams.
When clear cuts impact streams that are only a small part of the larger
ecosystem, the uncut streams can usually diluted the impacts to the aquatic life and
ecosystems (Fisher and Likens 1973, Likens et al. 1978). Bormann and Likens (1979
pp. 216-219) emphasize that cutting a large portion of a basin can have a compound
impact on the environment. A pipeline is one long clear cut and crosses a large proportion of streams in multiple watersheds. Although, the cut is only 30m across, it
extends for miles compounding the effect on the larger drainage basin. There is no
opportunity for mitigation unlike commercial harvesting in a single part of the forest.
Downstream impacts are also intensified by a reduction in regeneration
4
from soil compaction and forest floor disturbance. Bormann and Likens (pp. 216-217)
state that to understand total environmental impacts, attention needs to be paid to all
cuts made in the ecosystem. There is an addictive effect from the loss of nutrients from
each section of the forest. Not only are there amplified negative effects in the stream
water, but also compound disruptions to the nutrient cycle of the larger ecosystem.
1.2
Thermal Impacts
Water temperature is a crucial component of water chemistry and overall environment.
Stream temperature is generally very stable in a mature forested ecosystem (Brown
and Krygier 1970). Therefore fluctuations or changes in temperature can have a strong
negative impact on water chemistry and aquatic life. Often temperature is factored into
determining the health of a stream. Dissolved oxygen levels and dissolved solids are
strongly influenced by temperature. Bacteria growth is also impact by temperature;
generally bacteria and algae prefer highly temperatures. Many species of macro invertebrates and fish species, such as trout, have difficulties surviving in warm waters.
Most studies conducted testing the effects of clear cutting on stream temperature were
conducted to study the impact on the fish population.
Solar radiation is one main factor altered by clear cutting. This is especially important to streams running through the gap. Meehan et al. (1969) reported a
significant increase in water temperatures following a clear cut. Another study found
conflicting results (Patric 1969). In one watershed, there was no increase in stream
temperature. The other watershed had an increase even though the cuts were the same
size (Brown and Krygier 1970). Creation of gaps does not necessary guarantee an
increase in stream temperatures.
Headwater streams generally are smaller with shallow flows. They are
more sensitive to changes in solar radiation and clear cuts (Brown and Krygier 1970).
The proportion of total water exposed to sunlight is much higher than in larger, deep
running streams. In these smaller streams, temperatures were found to have returned
to pre-logging levels as early as six years following a clear cut (Brown and Kyrgier
1970). The recovery was facilitated by vegetation growth along the stream edge. The
return of this buffer zone is essential to reducing the water temperature.
5
1.3
Tree Species
Increased nitrate concentration in streams is partially caused by the release of nutrient
stores within the soil. Breeman and Finzi (1998) discuss the impact tree species have
on soils‘ chemical and physical properties. These properties include nutrient storage,
availability, and cycling. Their research examined the question of whether the soil
conditions were impacting vegetation or vice versa. The trees do not always cause
the relationship seen between the soil properties and tree species. The soil conditions
can determine which tree species can survive best in that area. However, following
the colonization, the presence of the particular species can create a feedback loop that
affects the patterns of N and P cycling and other soil properties.
Breeman and Finzi (1998) examined the species-specific interactions by
looking at characteristics that were easily influenced by vegetation and those that were
not. The physical composition of the forest floor is less affected by the tree species
growing, while pH and C and N concentrations are more affected. They looked at six
species of trees, beech (Fagus grandifolia), eastern hemlock (Tsuga canadensis), sugar
maple (Acer saccharum), red maple (Acer rubrum), white ash (Fraxinus americana),
and red oak (Quercus rubra). These are all common species in the hardwood forests
of Pike County and Sussex County.
The main properties examined were the thickness of the forest floor, soil
pH, stores of C and N, and exchangeable cations. Two sites were studied and all six
tree species were present in both. The mean pH and mean depth of forest floor were
different between the two sites. However, the forest floor was thickest beneath the
sugar maples and thinnest beneath hemlocks, regardless of the site. The soil pH was
lowest underneath the hemlocks and highest underneath the sugar maples (Breeman et
al. 1997). The C/N ratio also differed between species; soil beneath sugar maples had
a 15:1 ratio while soil underneath hemlocks had a 20:1 ratio (Finzi et al. 1998).
Frehlich et al. (1993) investigated changes in soil properties caused by
each species and any competitive advantage. They found that sugar maples thrive
in an environment where there are higher concentrations of nitrates. Their leaf litter
creates an environment with high levels of available N so they are able to outcompete
other species. On the other hand, hemlock leaf litter decomposition results in low soil
pH (White 1986). The rate of nitrification is slower in soils with lower pH (Godbold &
Hutterman 1994), so the availability of N is reduced beneath hemlocks. The low levels
of nitrate beneath hemlock trees prevent sugar maples from growing there. Therefore,
6
concentrations of soil nitrates would be affected by the tree species growing there.
1.4
Motivation for Study
Bormann and Likens provided invaluable information about the processes and impacts
surrounding clear-cutting. Their full-scale watershed studies give a more complete
picture of how deforestation impacts hardwood forests. The scope of my project could
not include all the processes that were affected from the pipeline construction. My
study only tests for impacts on stream nitrate concentrations and on water temperatures. Other qualitative observations were made, but no extensive data collection or
analysis was performed. I explore the need to examine impacts, such as regrowth, soil
compaction, and ecosystem recovery, in the discussion section.
This project set out to investigate the impact of pipeline clear cutting specifically on water quality in NJ and PA. Complete-tree harvesting has not been investigated as thoroughly as the more commonly practiced stem-only harvesting. What is
unique about pipeline clear-cutting and disturbances associated with construction is
the need to removal the soil to place the pipe underground. Many of these studies limit
the impact solely to the cutting and/or the removal of the trees. The heavy vehicle traffic involved with construction a pipeline, as well as the direct disturbance of the soil
and streams, exceeds the level of disruption in past studies. Therefore, my research
was to add additional insights into how pipeline installation methods can affect nitrate
levels and overall water quality.
2
2.1
Methods
Study Sites
This study was conducted in Pike County, Pennsylvania and Sussex County, New
Jersey. Elevation of Pike County sites ranged from 190m to 330m. The annual mean
precipitation is 108.5cm, the majority falling from March to June. The annual mean
temperature is 8.7 ◦ C and the maximum mean temperature is 20.5 ◦ C in July. The mean
wind velocity is 5.80 m/s. The Sussex County streams, except S111F, were located in
High Point State Park and elevations range from 250m to 400m. Sussex County has
similar weather conditions with a mean annual temperature of 9.5 ◦ C, precipitation of
116.5cm and wind velocity of 5.60 m/s.
7
Originally all twenty-two streams crossed by the pipeline were to studied.
However, only fifteen streams are included in the analysis. There streams are part of
six different watersheds, but are all headwater streams of the Delaware River Basin.
Major tree species included Acer spp., Tsuga canadensis, Quercus spp. and Betula
spp. Craft Brook, Dimmick Brook, and Pinchot Brook are located in forests harvested
roughly 150 years ago. The remaining Pike County streams are located in forests
harvested over 200 years ago. These streams occur in large swaths of undisturbed land
exceeding 500 acres for each study site (Figure 1).
Figure 1: Map of Stream Sites and Dominant Tree Species
8
Figure 2: Map of Pipeline Route from TGP‘s Public Notice (2010)
2.2
Complete-Tree Harvesting
There were two sections of pipeline looked at in this study. Both sections were replacing the old pipeline installed in the 1970‘s. There was already a 7m wide permanent
easement cleared, except the 10km stretch that included Sites 2 & 3 cleared for the first
time. The first section was Loop 321 and clear cutting occurred in the fall of 2010.
Construction began in the spring of 2011. Only Craft Brook was affected by this clear
cut. Loop 323 crossed all other streams mentioned in this study. Clear cutting occurred in the fall of 2012 and construction began in the spring of 2013. The clear-cut
area is a continuous cut 23km in length and approximately 30m wide. Near Pinchot
Brook, Laurel Swamp, S111F, S038, and S005 the width of the pipeline was extended
to 40m.
For both loops, the method of clear-cutting was complete-tree removal.
The crown, trunk, and root systems were removed in the fall before construction. Cut
9
timber was preserved and stacked on the side of the right-of-way (ROW) only near
Deep Brook, for the landowner to utilize. Prior to pipeline construction in May 2011
and 2013, all leaf litter and organic forest floor matter was removed to prep the land
and build access roads to these remote forest locations. Pipeline construction and soil
disturbance lasted through the summer until September 2011 and 2013.
Table 1: Stream Information
Stream
Site Number
Craft Brook
1
Pinchot Brook
1
Dimmick Brook
1
Laurel Swamp
2
Deep Brook
2
Cummins Creek
3
S061
3
S060
3
Evergreen Creek
3
S111F
4
S037
5
S038
5
S039
5
Shimer Brook
5
S005
6
2.3
Number of Visits
4
5
6
8
10
4
2
2
7
3
2
7
7
8
5
Percent Coverage
>50%
>50%
>50%
>50%
<50%
<50%
>50%
<50%
<50%
<50%
<50%
>50%
>50%
>50%
>50%
Dominant Species
Acer spp.
Quercus spp.
Acer spp.
Acer spp.
Tsuga canadensis
Tsuga canadensis
Tsuga canadensis
Tsuga canadensis
Tsuga canadensis
Tsuga canadensis
Acer spp.
Acer spp.
Tsuga canadensis
Acer spp.
Acer spp.
Pipeline Construction
Natural gas pipelines are below ground systems. There is additional disturbance in
the ecosystem following the clear-cut. The next stage of construction is trenching.
A backhoe is used to dig the hole, which must be at least 1.5m deep. This trench
is roughly 3-4m across (Figure 4 b). Large boulders or solid rock in the ground are
removed or blasted with explosives. Explosives were used intensively near S111F
although unknown for other locations.
Protocol for soil removal dictates that topsoil should be removed and piled
10
separately. Soil should be returned in the reverse order to prevent layer mixing. Observations made during the construction process of Loop 323 showed that this protocol
was not followed. Top-soil was removed and placed into the same pile as the rest of
the soil removed from the trench. Soil is supposed to be screened before replacement
to remove any rocks larger than 30cm in diameter. This was also not done and large
boulders dug from the trench were left in the top layer of soil.
2.4
Nitrate Concentration
No baseline data was collected prior to pipeline construction. A paired design was
used to determine if nitrate concentrations in stream water above the gap differed significantly from the concentrations below. Water samples were taken 30m upstream
and downstream of the gap. An HDPE 60ml bottle and 60ml syringe were was rinsed
three times with stream water. The water was filter into the bottle through a 1.2 µm
Acrodisc filter. Samples were placed on ice in a cooler and transferred to a freezer
within a maximum of three hours. For every four samples taken, a second sample
of water was collected to ensure the sampling method was effective and consistent.
Samples were collected from May until October.
Samples were kept frozen until placed in a refrigerator two weeks prior to
analysis. Analysis of anions was performed use a Dionex Ion Chromatograph. Individual adjustments to curve were made to ensure an accurate measurement of nitrate.
Samples that differed from their double by more than 10% were not included in the
analysis. Data was log transformed to satisfy normality. A repeated measures ANOVA
was performed to determine whether the above stream concentration of nitrates differed from the below stream concentration. The samples were grouped by stream and
by dominant tree species to determine whether these had a significant effect.
2.5
Temperature
Water temperature was taken at the same time as water samples at each location using
a Tracer Pockettester. Two long-term HOBO Water Temperature Pro v2 Data Loggers
were installed 30m above and below the cut in Pinchot Brook in May 2014. They were
removed in August 2014, but water levels dropped exposing the loggers. The data was
unable to be analyzed. Hand recorded temperatures above and below the clear cut
were normally disturbed and analysis was done using a repeated measures ANOVA.
11
2.6
2.6.1
Vegetation
Dominant Species
Transects were laid above and below each stream. They extended 30m into the forest
and 10m to either side of the stream. Inside the 20m x 30m rectangle, all trees with
a diameter at breast height (DBH) greater than 12cm were counted and recorded. At
Deep Brook and Shimer Brook, DBH was taken for every tree in the plot. The assumption was made that the forest around two streams accurately represented the forest type
around the other streams. The size distribution for each species in the plot was approximately the same. Therefore, total counts were used to determine the dominant tree
species in each plot.
2.6.2
Regrowth
Pinus resinosa was replanted along a 3.5km section that crossed Craft Brook and Pinchot Brook in the spring of 2012, 2013, and 2014. Saplings were approximately 30cm
high and planted only on 10m of the ROW. They were planted in rows of fifteen
with rows roughly 1-2m apart. 100 trees were counted and marked as either living
or dead/dying. This was repeated every 500m along the 3.5km stretch to estimate the
percent mortality. Saplings were also planted near S005 in High Point State Park.
Mortality rates were not analyzed for those trees.
Following completion of pipeline construction, the restoration crew planted
grass seed and spread lime to facilitate regrowth. During August 2014, the percent of
ground covered by grass or other herbaceous vegetation was estimated. This was done
for 30m on either side of the stream. 5m squares were recorded as mainly grass or
exposed soil. This data was used to determine whether more or less than 50% of the
ground was covered by vegetation (Table 1).
3
3.1
Results
Nitrate Analysis
The nitrate concentration downstream of the pipeline was significantly higher than the
upstream concentration (P = 0.0002) (Figure 5). The average increase in nitrate/N
was from 0.065 mg/L to 0.107 mg/L, an increase of 63%. There was a significant
12
stream effect on the nitrate concentration (P <<0.001) and the degree of change (P
<< 0.001) (Figure 6).
The dominant tree species did not a significant effect on the change in
nitrate concentration (P = .0715). However, the mean nitrate concentration of streams
differed significantly for each tree type (P <0.001). The oak dominated stream had a
mean of 0.034 mg/L, the maple dominated streams had a mean of 0.080 mg/L , and
the hemlock dominated ones had a mean of 0.125 mg/L (Figure 7).
3.2
Temperature
The temperatures above and below the clear-cut were not significantly different (P =
0.291). There was a significant difference in mean temperatures between streams (P
<<0.001).
4
4.1
Dicussion
Nitrate Concentrations
Nitrate concentrations were found to be significantly higher in the below stream water
samples than above. This indicates that the disturbance from the pipeline construction
has an impact on the water quality in these high quality headwater streams. However,
the level of increase was much lower than previous studies had reported (Federer 1968,
Likens et al. 1970). Liken et al. (1969) saw an increase in over 50-fold following stemonly clear-cutting. This is much higher than other North American temperature forest
studies, but the majority reported at least a two-fold increase in nitrate concentrations
in stream water (Vitousek & Melillo).
The gap characteristics may impact the interpretation of results in comparison to previous studies. The pipeline clear-cut is a long continuous strip, which makes
it hard to determine the size of the gap. In terms of nitrate runoff, the area of land
draining into each stream can impact the effective gap size. Looking at Figure 6, we
can see that there was a large variation in the degree of change between streams. The
majority of the streams not do appear have a significant difference in upstream and
below stream nitrate values. The five streams that appear to have the largest change
13
are all located at the bottom of steep slopes. This offers evidence that there is a topographic component affecting the nitrate losses seen.
Increase in nitrate concentration in complete-tree harvesting further supports the literature suggesting that nitrate losses are caused by limitations in microorganism uptake rather than an increase in litter and root decomposition. No decomposition can occur after the removal of excess of organic material. The absence severely
limits C availability from the beginning. Microorganism productivity would decline
quickly following the harvest. This could impact the rate of nitrate loss because of fast
depletion of the C reservoir. This study would benefit from supplementary data on soil
nitrate concentrations.
The amount of change we would expect to see from the disturbance could
be affected by factors such as organic carbon availability (Bernhhardt and Likens
2002), stream hydraulics, and canopy damage from storms (Houlton et al. 2003).
Evergreen Creek had the highest concentration of nitrates and the largest change. This
stream was not only impacted by the pipeline clear cutting, but also by the loss of
additional trees from Hurricane Sandy in October 2012. This could be a factor that
added to the high nitrate levels found. Given the wide variation in factors affecting
nitrate concentration outside of the clear-cutting focused on in this study, more intensive long-term monitoring would be valuable to determine the impact solely from
clear-cutting.
Nitrate release into streams can extend up to seven years (Prescott et al.
2003). This study would benefit from expanding the timeline in future years to track
changes in loading. Studies saw a peak loss of nitrate two years following clear cutting
(Vitousek et al. 1979, Feller et al. 2000, Prescott et al 2003). Nitrate losses similar in
magnitude to those in my study were reported by Douglass and Swank(1977). Nitrate
losses were not exceptionally high, but were still elevated 20 years later. Impacts
of watershed disturbance can be very long-lived. More thought needs to be taken
before approving pipeline construction and alternative routes should be considered to
minimize damage.
4.1.1
Tree Species Effect
The difference in soil nitrate composition from tree species composition (Frehlich et
al. 1993, Breeman and Finzi 1998) should have an effect on the stream water con-
14
centrations as well. The nutrient runoff into streams comes directly from the soil.
However, there was not a significant difference in above and below concentrations
when grouped by the dominant tree species. The majority of the stands were very heterogeneous with an average of 10 different species per 30mx20m section. No stream
had more than 50% coverage by a single species. Therefore, soil composition across
the plot could have had less variation from stream to stream then predicted from tree
counts.
The significant difference found between mean nitrate concentrations in
the different forest types was expected. However, I did expect to find higher concentrations in the hemlock streams and lower concentrations in the maple dominated
streams. Mentioned above, hemlock leaf litter decomposition reduces the pH of the
soil and therefore the rate of nitrification. I would have expected the hemlock dominated streams to have lower levels of nitrates because the runoff would be coming
from nutrient poor soils.
A factor to consider is the method of determining the dominant species. I
counted trees above and below each stream to extrapolate what trees were removed
when clear-cutting. The percent coverage varied drastically for some streams even
though only 30m separated the two plots. There is no guarantee that the trees above
and below the pipeline accurately represent the trees that were removed or the properties of the soil. A baseline tree survey would be more beneficial in analyzing whether
the tree species, and its effect on soil chemistry, have an effect on the nutrient leaching
following pipeline construction. Analyzing soil concentration, as well as water concentrations, would allow us to better understand the relationship between the two in
complete-tree harvesting.
4.2
Stream Temperature
There was no significant increase in stream water temperature down stream of the
pipeline. This could indicate that the gap was not large enough to cause a marked
increase in solar radiation. However, I believe that my sampling method may not
have been able to accurately detect any changes. Temperature was generally taken
early in the morning, before the streams were exposed to notable amount of sunlight.
Because solar radiation is the key component to changes in water temperature, 24 hour
measurements would make any effects from the clear cutting more clear.
15
The temperature data taken during this project should be redone in order to
fully assess the impact from clear cutting. Long-term temperature probes were placed
in three streams that are not included in this analysis because the streams completely
ran dry during the summer months. Past data, collected with the Delaware Riverkeeper
Network, indicated that there were massive fluctuations of water temperature during
the daytime hours. Downstream Pinchot Brook reached temperatures greater than
27 ◦ C, an increase of 10 ◦ C from nighttime temperatures. More successful paired temperature monitoring is needed to determine if this increase in normal during summer
months or as a result of the pipeline.
While the temperature data analyzed in my study was inconclusive, other
past data also suggests that the pipeline is causing thermal pollution. A temperature
logger was placed in W038, a wetland located 1km east of Craft Brook, from May
2012 to August 2013 and from May 2014 to August 2014. The data from the logger
showed water temperatures exceeding 32 ◦ C. Stream water feeding into the wetland
did not exceed 22 ◦ C. Because full analysis of this data is not included in this study,
definitive conclusions can not be drawn. It does indicate, at the very least, a need to
redeploy temperature probes to determine the extent of the thermal impact.
Greene (1950) reported that stream temperatures quickly dropped further
into the forest, away from the clear-cut. The thermal pollution was not propagated
downstream for an extended distance once solar radiation was limited. The study suggested that leaving buffer trees along the edges of the stream help to offset the thermal
impacts. Increasing the amount of shade on the surface of the water is important, especially in shallow headwater streams. Stream banks are often where the additional
10m are taken during pipeline construction. Phragmites has been one species that has
capitalized on the newly exposed land surrounding streams, but often there is limited
regrowth of any vegetation on the streams‘ banks (Figure 3). Without the buffer‘s
return, solar radiation will continue to impact the stream and its return to pre-logged
water conditions.
4.3
Soil Impacts
One of the larger impacts from pipeline clear cutting and construction is the effect
of construction vehicles and equipment on soil. Scientists with the Delaware Riverkeeper Network performed soil compaction analyses that indicated extremely high
levels of compaction (Faith Zerbe, personal correspondence). Even three years after
16
clear-cutting there is little to no herbaceous regeneration along Loop 321. Attempts
to replant have resulted in up to 100% mortality within a year of planting (Table 2). I
would like to further investigate whether the inability of tree to grow is due to a lack
of water in the soil or from nutrient depletion. Analysis of soil nutrient levels would
have given more insight into the bigger picture and a prognosis of the future recovery
of the system.
In my study was the absence of decomposition that usually occurs following clear-cutting. All trees, roots, leaf litter, and other vegetation were completely
removed from the site. As discussed above, increased decomposition is suggested to
cause an increase in the nitrate concentration. If this is true, complete-tree harvest may
actually limit the influx of nitrates into the stream, off setting some of the anticipated
impacts.
The Bormann et al. (1974) study kept the products of the clear cutting in
order in decrease soil erosion. By doing this they also left the forest floor undisturbed
and the topsoil containing organic matter intact. The complete removal of much of the
forest floor from pipeline construction mixes this nutrient rich topsoil in with lower
layers containing far fewer nutrients. The impacts of this may be a smaller amount of
nitrate runoff due to nutrient rich soil being buried and compacted. Another possibility
to be considered is the accelerated loss of nutrients during the initial construction year.
Heavy summer rains could have caused more runoff when the topsoil was loosely piled
along side the pipeline clearing.
The environmental conditions following clear cutting in my study are ideal
for maximizing nutrient leaching. The lack of regrowth prevents the clearing from
beginning a return to a stable state in terms of nutrient cycling and water export. In
this regard, construction clear cutting may have more long-term impact than commercial harvesting. I believe greater care needs to be taken to prevent excessive soil
compaction and attempts for landscape rehabilitation need to be more thorough. The
damage done to the ecosystem is more complete and cannot recover as quickly as
other studies, such as Bormann et al. (1974), have shown. Erosion and nutrient leaching would be able to continue until the natural barriers are restored. Severe disturbance
of the natural soil layers adds an additional impact beyond the removal of trees.
17
4.4
Ecosystem Recovery
Stem-only clear cutting, when done properly, can work with the natural processes of
the ecosystem (Bormann & Likens 1979, pp. 216-219). The release of nutrients,
changes in water availability, and increased access to sunlight allow for some species
to capitalize on the newly cleared land. However, pipeline installation causes additional forest floor disturbance that can disrupt the recovery processes. There needs
to be reconciliation between the current practice and a process that allows for forest
recovery.
TGP claims that disturbance from their installation methods are temporary
and there is a return to the natural forest state afterwards. They have not presented any
evidence to support this claim. This study has shown some of the negative impacts of
the pipeline construction, but there is a need to test the ability for recovery. If careless
stem-only cutting can delay or disrupt the regeneration process, complete-tree cutting
would be expected to have much stronger impacts. The extent of the disturbance is
outside of what has been studied before and indicates that there could be long-term
degradation of the ecosystem.
Buried seeds and rooting substrates in the soil plays an important role in regeneration following a disturbance. The removal or disruption of these during pipeline
construction can severely impact the ability of the system to recover (Bormann &
Likens 1979, pp. 216-219). Stored nutrients in the forest floor are also important for
regulating the nutrient cycle within the system. Excessive disturbance of the floor,
seen in complete-tree harvesting, can lead to an even greater release than would occur in stem-only harvesting or natural events. This would cause further depletion of
nutrient stores, affecting the stability and recovery of the nitrogen cycle.
In some studies, the land is prepared for replanting following the clear-cut.
A mixing of the organic and mineral layers of the soil can occur. The mixing has
been reported to increase nitrification (Chase et al. 1968). Bormann & Likens (1979
pp. 216-219) suggest that this could result in greater nutrient losses. The process
of placing the pipe in the ground causes a much more extreme mixing of soil layers.
There is an alternative method to the trenching process involved removing an entire
section of the forest floor, keeping the soil layers intact. Employment of this more
expensive method may be able to offset some additional nutrient losses and prevent
declines in the productivity of the ecosystem (pp. 216-219).
18
Table 2: Mortality of Red Pine Saplings
Year
2012
2013
2014
2014
Month
Mortality
August
100%
August
80-90%
July
50%
September 70-80%
(a) Before clear-cut Fall 2012
(b) After clear-cut Fall 2014
Figure 3: Changes in Shade Coverage for S005
(b) Completed installation of pipe in
trench
(a) Soil disturbance prior to trenching
Figure 4: Soil Disturbances during Construction
19
4.5
Future Directions
Many of the impacts discussed were not a result of clear cutting, but rather the entire
process of pipeline construction. This study only looked at a small part of the overall
impact to the ecosystem. My study focused mainly on the immediate impact of deforestation on nitrate concentrations. However, over the 3 years I have spent monitoring
the entire process of pipeline construction, the other data and observations gathered
have suggested there is long term or permanent damage done to the ecosystem. There
is a need to go more in depth on impacts of soil compaction, ability for regrowth of
vegetation, soil nutrient depletion and water temperature impact on aquatic life.
Current regulations require TGP to perform an Environmental Assessment
rather than an Environmental Impact Study prior to construction. TGP argues that
only 10m of ROW will be permanently impacted. The remaining 20m and additional
workspace taken should be able to return quickly to the original state of the surrounding undisturbed forest. Evidence presented from other studies suggests the intensity
of disturbance on the forest floor will have long lasting repercussions.
Many of the issues I raised will need to be studied for multiple years. Most
studies addressing the recovery of an ecosystem following a clear cut saw substantial
changes around the seventh year. It is important to begin addressing things now so that
changes can be tracked long term. At the present time, natural gas fracking is being
delayed in states like PA and NY. There is no immediate demand for more pipelines to
be built. Long term monitoring of the ones already in place can help with development
of a plan that will lessen the impact to the environment should more be necessary in
the future.
5
Conclusion
This study illustrates the need to re-evaluate current methods of pipeline construction.
There was a significant increase in stream water nitrate concentration from completetree harvesting. Temperature impacts were inconclusive and require further evaluation
to determine any and all effect. Investigation of the ramifications of soil compaction
and forest floor disturbance would lead to a greater understanding of the overall damage to the ecosystem, as well as, offer a prognosis for the future recovery of the forest. This study should encourage stricter regulations and better enforcement of current
ones for pipeline construction through these delicate forested streams. I highlight mul-
20
tiple gaps in knowledge of the outcome of this highly disruptive process. Documented
impacts of less intensive forest disturbances indicate that there could be drastic repercussions from pipeline construction. Natural gas may become an important resource
in the future and require the installment of pipelines. However, currently, we need to
understand the full impact to the health of our forests and find a way to develop the
infrastructure in a less harmful and invasive manner.
21
Figure 5: Nitrate/N Concentrations Above and Below Pipeline
22
Figure 6: Changes in Nitrate/N Concentrations Above and Below Pipeline
23
Figure 7: Nitrate Concentrations per Dominant Species
24
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