Download Examining food webs and trophic dynamics across a stream

Examining food webs and trophic dynamics
across a stream restoration intensity gradient
Lena Weiss, Brown University
Advised by Linda Deegan
Project Collaborators:
Andrew Miano, Connecticut College
Audrey Seiz, Clark University
Sam Stewart, Colorado College
12/19/2011
Key Words: Disturbance, stream restoration, food webs, trophic dynamics
Abstract: Stream ecosystems provide a plethora of important services to the local landscape;
however, many stream systems on Cape Cod have been heavily degraded due to the development
of cranberry agriculture. The organisms in these streams are most strongly impacted by the
removal of terrestrial inputs into the streams through riparian clearing, as well as the reduction of
habitat complexity in the stream channel itself. While there has been a recent push towards
restoring these heavily degraded systems, there is little examination of restoration on a systemlevel scale. By examining food webs and trophic dynamics within a stream restoration intensity
gradient, I was able to determine the effects of restoration on the stream systems as a whole. The
natural system had the most diversity, although it was the least productive, indicative of a system
with a high amount of resource specialization, and top-down control. In contrast, all of the
restored systems had more generalist species, with very few specialists, although the amount of
specialization increased generally with increasing restoration intensity. This indicates that, in the
long term, restoration which focuses on creating habitat complexity and riparian inputs similar to
a natural system will be more successful in returning the disturbed systems to a more natural
state.
Introduction
The clearing of land near stream systems for cranberry bogs in New England was a
common practice throughout the nineteenth century. This intense disturbance regime severely
altered the ecology of the streams involved. Riparian clearing reduced shading, causing increases
in stream temperatures, light penetration, and macroalgal growth, decreased bank stability and
the retention of nutrients and contaminants, reduced sediment trapping, and lowered the retention
of benthic organic matter; while the altering of the stream channel itself altered the runoff evapo-
transpiration balance, lowered base flow, and altered channel dynamics (Allan, 2004). These
disturbances both severely degraded the stream habitat and changed food web structure, thus
modifying community composition (Lake et al, 2007). In particular, stream systems are
extremely sensitive to changes in inputs of organic matter, since most streams have detritus
based food webs. For example, the exclusion of leaf litter from a detritus-based food web can be
detrimental to a vertebrate predator by reducing prey availability (Johnson & Wallace, 2005).
This bottom up control of food web structure acts most severely on basal members of the food
webs (Power and Dietrich, 2002), which in turn provide an food source for economically
important organisms, such as brook trout. As a result, there is a strong incentive for humans to
return these heavily degraded cranberry bogs to their natural state. In order to do so, many
communities and conservation organizations are turning to stream restoration, which aims to
return the environmental health of the ecosystem. However, stream restoration is often conducted
with little or no thought to the original ecology of the stream, and is given virtually no follow up
after the restoration event occurs (Lake et. al. 2007). Therefore, we have very little idea of the
effects of stream restoration on the ecosystem as a whole, especially whether the trophic
structure present attains complexity similar to unperturbed streams. This knowledge will allow
us to judge the relative success of a stream restoration, and will useful in helping to shape how
streams are restored in the future, in order to minimize harmful effects to the local biota and
community structure.
In order to examine the effects of a stream restoration on a system scale, I examined how
food webs and trophic dynamics differed in a restored system in comparison to a natural system,
as well as if there was a difference in trophic dynamics and food webs along a restoration
intensity gradient. I would expect the pristine system to have a more complex food web, with
more trophic links, and more organisms specialized for specific habitats in order to fully exploit
the different habitat types present. In addition, along a restoration intensity gradient, I would
expect the system with the least intensive restoration to have the least amount of system
complexity, the least diversity, and least amount of habitat specialists, since this system is closest
to the original, heavily disturbed state. This would shift to being more and more like the natural
system with increasing restoration intensity, since the higher the degree of restoration, the more
complex the altered habitat.
Methodology
Description of Field Sites (See Figure 1)
Four streams on and around Cape Cod were examined for this study. All of the streams
are groundwater fed, and of a similar size, so they would be expected to be capable of hosting
similar types and numbers of species. The reference stream, the Mashpee River, has been
completely undisturbed by farming or development, making it an ideal natural comparison to the
streams having undergone restoration. The Mashpee has an intact riparian zone, with the stream
receiving a large amount of terrestrial input, mainly from leaf fall. Additionally, due to the
shading from the trees, there is little submerged aquatic vegetation in the stream. Our three other
stream sites have been undergoing different levels of restoration for some years. The
Coonamessett River, which was abandoned as a cranberry bog, has been restoring naturally since
2001, with no human intervention. As a result, it still strongly resembles a bog, with no trees in
the riparian zone, and a fairly straight, sandy channel. The openness of the stream allows for
submerged aquatic vegetation as well as algae to become a dominant substrate cover. Red Brook
has undergone medium intensity restoration. In 2009, large woody debris was added to the
stream channel. In addition, bank planting has occurred, making the riparian zone appear fairly
similar to that of the reference stream. Furthermore, there is very little submerged aquatic
vegetation in this stream. Finally, Eel River, which has undergone high intensity restoration,
completed in 2010, has been reconfigured using a backhoe to create sinuosity. In addition, large
structures, such as woody debris and rocks, have been added to the stream. Although bank
planting has occurred, these are still very young trees, and the riparian zone is still very open. As
a result, there is a large amount of submerged and emergent vegetation in this stream. All these
sites were visited in November 2011.
Description of Field Methods
At each stream site, we chose a representative 150 metre reach as the study area. Within
this reach, stream depth, velocity, substrate cover, and bank class was determined at transects
every fifteen metres (Stewart, 2011). We sampled for benthic invertebrates in three different
types of microhabitats: runs with submerged aquatic vegetation, runs without submerged aquatic
vegetation, and detrital pools using a Surber sampler (Seiz, 2011). We collected fish using a two
pass depletion method in both run and pool areas of the stream (Miano, 2011). We measured and
weighed all fish collected this way on site, and kept only a small subset of fish for later analysis.
For sensitive fish species, such as brook trout and chain pickerel, we took a fin clipping and then
released the fish, rather than removing the organism from the stream. Additionally, in order to
create as complete a representation of the organisms in the stream as possible, I used a Noah’s
Ark sampling technique to collect as many different types of organisms as possible. I focused on
organisms that would not be collected in the Surber sampler or seine, such as amphibians and
larger insects in the stream channel. Some organisms, such as the common musk turtle, and
larger green frogs, were observed in the stream but were not collected. Additionally, at each site,
I collected a sample of detritus as well as many different species of aquatic vegetation as
possible.
Analysis of Samples
I examined the detrital samples before drying, removing any organisms found on the
material. Additionally, where possible, I noted the number of different plant species comprising
the organic matter, as well as if the sample comprised mainly of terrestrial or aquatic material. I
then placed the samples in a 60°C oven to dry overnight. Dry samples were ground into a fine
powder for isotopic analysis.
I gathered the quantitative submerged aquatic vegetation samples from the Surber
sampler. I first weighed the vegetation, then separated it by species and sub-sampled. I weighed
the samples and placed them in a 60°C oven to dry overnight. Once dry, the samples were reweighed, and then ground into a fine powder. I identified the qualitative submerged aquatic
vegetation samples and then dried and ground them if I considered them to comprise a
significant portion of substrate cover. For each stream, Potamageton was used for isotopic
analysis, since it was often a dominant substrate cover. Algae samples were also analyzed in
each stream (except for the reference stream, which did not have algae present in significant
enough quantities) to determine the relative importance of algae in each system. Other plants that
were considered to be significant producers in the stream systems were also used for isotopic
analysis.
Benthic invertebrates that were collected quantitatively were sorted by species and
microhabitat location for each stream, and then weighed (Seiz, 2011). I identified any species
collected qualitatively. I re-weighed the fish collected from the streams and then dissected them
to analyze gut contents. I also took tissue samples from the fish for isotopic analysis.
Using the organisms collected qualitatively via Noah’s Ark sampling, as well as the
quantitative organisms, I constructed food webs for each stream. I gathered species diets from
literature, although the information from the gut dissections was used for the fish and
amphibians. In the food webs, I limited each species to consuming three food types. I calculated
the interconnectedness of each of the food webs using the formula:
C = L/(s*(s-1)/2)
Where L is the number of actual trophic links in the web, and s is the number of species
in each system (Dunne et. al., 2002).
After the food webs were constructed, organisms appearing to be a central food source, as
well as species whose feeding relationships could not be determined were chosen for isotopic
analysis. Additionally, oligochates, amphipods, and Hirudinea from each stream were chosen for
isotopic analysis, to see how stable isotopes differed along the restoration intensity gradient. I
chose these organisms because they were present in all four streams in relatively high
abundance, and because these organisms are capable of feeding on more than one trophic level,
so examining differences in feeding habits along the restoration gradient was possible. I ran
stable isotopes using a standard mass spectrometer to determine δ13C and δ15N values for each
organism, as well as the percent carbon in each of the plant species.
Using the results from the stable isotopes, as well as from then food webs, organisms
were categorized into trophic levels. I then calculated abundance, biomass, and productivity for
each of the organisms found in the reach. These numbers were calculated for benthic
invertebrates by averaging the two replicates of each microhabitat together, and using the
average abundance and weight of the sample to calculate biomass and productivity (Seiz, 2011).
These values were scaled up to the reach by multiplying the results from each microhabitat by
area of each reach containing that type of habitat. Fish abundances were calculated using
formulas designed to determine the number of fish missed in the reach based on what was caught
in the first and second passes (Miano, 2011). I calculated biomass and productivity of each fish
species in the reach using the P/B ratio for fish established by Banse and Mosher (1980), using
the average wet weight of each species and assuming that the dry weight of each individual is
20% of the wet weight and that carbon is 50% of the dry weight (Banse and Mosher, 1980). I
estimated biomass for primary producers in the streams using the percent carbon values from the
isotopic analysis, as well as the dry weight of each species. I then scaled up by dividing the area
of the stream by the area covered by a Surber sampler and then multiplied this area by the
percent of the reach covered in aquatic vegetation.
Results
Species Composition and Food Web Characteristics
The reference stream had three distinct types of food source at its base: primary
producers, leaf pack, and fine detritus. Most secondary consumers in this system were feeding on
only one of these food sources, rather than multiple (Figure 2). Additionally, when organisms
were feeding on multiple food sources, it was a mix of leaf pack and fine detritus. Only one
organism, the isopod, found in the stream, was feeding on all three food sources. The only
organism specialized as a grazer in this system was Gastropoda Planorbidae. In general, the
second trophic level comprised mostly of detritivores, with many sensitive, and highly
specialized organisms, such as two classes of Ephemeroptera, the American Brook Lamprey (an
endangered species), and five distinct types of web-spinning caddisfly. The third trophic level
comprised mainly of predaceous insects, such as those in the Odonata and Megaloptera family,
as well as several species of insectivorous fish, such as the four spined-stickleback,
pumpkinseed, and white sucker. The most numerous and distinct member of the fourth trophic
level is the brook trout, an indicator of excellent water quality. Although brook trout were found
in all the systems except for the low intensity restoration, the brook trout in the reference stream
were the largest (Miano, 2011), and therefore capable of eating the widest variety of organisms.
The low intensity restoration stream had two distinct types of food at its base: primary
producers and detritus. Unlike the reference stream, the grazing pathway in this system is
stronger, with more organisms, such as Green frog tadpoles, specialized for consuming algae or
submerged aquatic vegetation (Figure 3). However, it is worthwhile to note that although there
are organisms feeding on the grazing pathway, these were not the most abundant organisms
feeding in this system, nor were they among the most common food sources for higher trophic
levels. Rather, it was detritivores, such as amphipods, crayfish, and Diptera Chironomidae,
which were most abundant in this system. Additionally, the low intensity restoration stream had
very few predaceous invertebrates on the third trophic level, instead having a more complex
network of fish feeding interactions. Smaller, insectivorous fish, such as the stickleback and
brown bullhead, were preyed upon by larger fish, such as the chain pickerel and largemouth bass.
The medium intensity restoration stream had three distinct base food types: primary
producers, leaf pack, and detritus, however, primary producers cannot be considered an integral
part of this system since it comprised less than 1% of substrate cover in this stream (Stewart,
2011). Most organisms in this system are feeding on either detritus alone, such as the American
eel, or on a combination of leaf pack and detritus, such as the amphipod (Figure 4). There are
very few specialists in this system, which mostly comprises of generalist detritivores
(amphipods, Chironomidae, isopods). The third trophic level is a combination of both
predaceous invertebrates, as well as some fish species, such as the pumpkinseed. The fourth
trophic level comprises of many different fish species, such as sticklebacks, killifish, and brook
trout.
The high intensity restoration stream has two main food sources at its base, primary
producers and detritus. Organisms in the second trophic level are either feeding on mostly
primary producers (Bivalvia Sphaeriidae, Gastropoda), or a combination of detritus as well as
primary producers (amphipods, isopods) (Figure 5). Additionally, unique to this system, is an
herbivorous fish, the golden shiner. This underlines the importance of primary producers to this
system. There are no real specialist organisms in the second trophic level, the majority of
organisms there being generalist detritivores. The third and fourth trophic levels consist almost
entirely of predaceous invertebrates (Odonata, Ranatra); with some exception (i.e. brook trout,
green frogs).
Overall, the reference stream had the lowest number of species of primary producer, with
the low and high intensity streams both having the highest number of different species (10)
(Figure 6). Interestingly, the medium intensity stream had a fairly high number of species,
despite the fact that an insignificant percentage (<1%) of the reach measured was covered with
aquatic vegetation. On the other hand, the reference stream had the highest number of benthic
invertebrate species, as well as the highest total number of species (Figure 7). However, it had
the lowest number of vertebrate species found in the reach. The high, medium, and low intensity
restorations all had similar overall numbers of species, although the medium intensity stream had
the fewest number of invertebrate species.
The reference stream also had the largest number of trophic links in the constructed food
web. The high intensity stream had the next largest amount of links, while the low and medium
intensity streams had the fewest total number of links (Figure 8). The connectedness value in
each of the streams did not vary very much; however, the reference stream had the lowest
connectedness value, while the high intensity stream had the highest (Figure 9).
Cross-System Comparison of Stable Isotopes
In the reference stream system, δ13C values ranged from -38 to -24, with most organisms
ranging between -27 and -29. Organic matter in this stream had a carbon signature most similar
to terrestrial values (-29, whereas the δ13C value for trees is -28). δ15 N values ranged from 1.7 to
15.9, with most organisms in the 7-9 range, what amounts to the third trophic level (assuming a
trophic level shift of 2.5) (Figure 10). Thus, the amphipod, oligochate, and philipomatidae, are
feeding on primarily the detrital pathway, which consists of terrestrial based organic matter.
The low intensity stream had δ13C values ranging from -35 to -26, with most organisms
ranging between -28 and -29. Organic matter in this system had a carbon signature most similar
to that of Potamageton. δ15 N values ranged from 5.8 to 14.6, with no clear clustering of N
values (Figure 11). Amphipods in this system are feeding on a combination or algae and organic
matter, whereas chironomidae is feeding on organic matter alone. Oligochaeta in this system is
feeding on a higher trophic level (is possibly eating chironomidae). The organisms tested in this
system appear to have a carbon value indicative of the detrital pathway, which is based off of
submerged aquatic vegetation.
The medium intensity stream had δ13C values ranging from -13 to -34.6, with most
organisms in the -28 to -29 range. Organic matter in this system had a value of -29.6, indicative
of terrestrial, rather than aquatic vegetation, origin. N values ranged from 1.6 to 13.1, with most
organisms in the 6-8 range, or the second trophic level (Figure 12). Organisms in this system,
such as amphipods, oligichates, and Sidlidae, are feeding off of organic matter (detrital
pathway), based off of terrestrial inputs.
The high intensity restoration had δ13C values from -25.8 to -35.6, with most organisms
occurring in the -28 to -29 range. Organic matter in this system had a δ13C value of -29, and
appears to originate from a combination of different types of submerged aquatic vegetation in the
stream, especially bur reed. N values ranged from 3.8 to 11.5, with no clear clustering of values
occurring (Figure 13). Organisms in this system, such as heptageniidae, isopods, and
oligochates, are feeding on a combination of submerged aquatic vegetation and organic matter
from the stream.
When examining the same species of organism across the restoration gradient, several
patterns emerge. After standardizing the nitrogen value against the base of all of the food webs
(the δ15N value for organic matter), all of the organisms in the reference stream are feeding
higher on the trophic scale (have overall higher δ15N values) than the other streams (Figure 14).
This effect is small at lower trophic levels, and is amplified as you move up the food web. For
example, the amphipod, which is a lower trophic level scavenger, has a δ15N of 2.4 in the high
intensity stream, 2.9 in the low intensity stream, 5.3 in the medium intensity stream, and 5.5 in
the reference stream. In comparison, the brook trout, which is a top predator in all of the systems,
has a δ15N of 6.5 in the high intensity stream, 8.8 in the medium intensity stream, and 13.2 in the
reference stream. In this case, the change in δ15N is much higher, as well as the difference in
δ15N between the reference and medium intensity stream. However, the pattern of trophic level
increasing from high to low to medium intensity restoration with the reference stream shifted
above them does not hold for all of the organisms tested. Hirudinea in the medium intensity
stream are feeding at the same trophic level as in the reference stream, while there is no shift in
trophic level between Hirudinea in the low and high intensity restored streams.
Cross- System Comparison of Abundance, Biomass, and Productivity
In terms of abundance, the reference stream had both the lowest overall abundance, as
well as the lowest abundance in each trophic level (Figure 15). The low intensity restoration
stream had the second largest overall abundance, although it had the most abundant third trophic
level. Additionally, this was the only system with five trophic levels (Figure 16). The medium
intensity restoration stream had the third most abundant system, although it had the most
abundance in its third trophic level (Figure 17). The high intensity restoration stream had the
most overall abundance, although this was in part only to the large abundance in the second
trophic level (Figure 18). All these systems had a pyramidal shape moving up the food web.
The reference stream had the second most total biomass out of every system, with the
most biomass in the base of the food web, and more biomass in the fourth level than the third.
This system however, had the lowest biomass in every level except for the primary producers
and the second trophic level (Figure 19). The low intensity stream had the third most total
biomass, although it had the most biomass out of every system in the third and fourth trophic
levels (Figure 20). The medium intensity stream had the lowest total biomass out of every
system, and had slightly more biomass on the fourth trophic level than on the third (Figure 21).
Finally, the high intensity stream had the most overall biomass, as well as the highest biomass in
the first and second trophic levels (Figure 22).
In terms of productivity, the reference stream was the least productive system, both
overall and among all the different trophic levels. However, the fourth trophic level was more
productive than the third trophic level (Figure 23). The low intensity stream was the second most
productive system, although it had the most productivity in all the streams at the third trophic
level (Figure 24). The medium intensity stream had the third most productive system, both
overall and among all the different trophic levels (Figure 25). Finally, the high intensity stream
was the most productive stream overall and in all the trophic levels except for the third.
Additionally, the fourth trophic level in this stream is more productive than the third (Figure 26).
Discussion:
Although the reference stream was the least productive stream out of the four systems
studied, this does not, by any means, indicate, that it is in poor shape, and not in the “pristine”
condition we would like for a control. Rather, this is an indication of the dependence on this
system as a whole on outside inputs, both energetically in terms of nutrients from litter fall, and
in terms of organisms, such as sea run brook trout, bringing and using energy from outside the
system into the stream. The importance of brook trout to this stream can also be seen in terms of
the wasp like shape in the biomass and productivity pyramids for the reference stream. From
this, we can infer that the fourth trophic level (i.e. brook trout), are exerting top-down control on
the third trophic level, which consists of larger invertebrates. This is an important point as it
illustrates that although the system is not overall very productive, nutrients at the bottom of the
food chain, are not limiting the overall production of the system. Rather, this system functions
well as it has many different organisms at its base, mostly specialists on some type of specific
food source or habitat type. For example, Trichoptera Hydropsychidae is limited to flowing
water with a gravel substrate, while Trichoptera Glossosomatidae feeds as a scraper and collector
of fine detritus (Schowalter, 2009). The fact that resource partitioning and resource specialization
is common in this system is also indicated by the fact that the reference stream has the most
diverse overall system, but has the lowest connectance value. This is indicative of specialization
because while organisms present can be feeding on many different food types, they are focusing
on a specific type, limiting the number of overall trophic links (Schmid-Araya et. al., 2002). A
final indicator of ecosystem complexity in the reference stream is the fact that all of the
organisms measured for stable isotopes were feeding higher than their counterparts in other
systems. Since the organisms tested were generalists and capable of omnivory, the fact that they
are feeding higher may be due to resource partitioning. These organisms may be getting
outcompeted by a specialized detritivore, for terrestrial matter and may be feeding higher
because there is less competition for resources as a scavenger. Overall, the patterns seen in the
reference system are indicative of a complex and well-developed system resulting from high
amounts of terrestrial inputs and high levels of habitat complexity.
The δ13C values of the organic matter from the low intensity restoration stream suggest
that the detritus in the stream comes from mainly Potamageton. Despite the fact that algae
comprises 8.2% of substrate cover in this stream (Stewart, 2011), it turns over and breaks down
too quickly to be represented in the stable isotopic composition of the organic matter, although it
may be an important component. In contrast, Potamageton has more structural complexity, and
therefore does not break down as easily and thus the organic matter sample taken from the
stream is more reflective of the importance of submerged aquatic vegetation, rather than algae, to
the detrital pathway. The similarity in the carbon value between Potamageton and the organic
matter makes it difficult to distinguish what pathway the organisms in the low intensity
restoration stream are feeding on primarily, however, it is evident that some organisms, such as
amphipods, and small eels are feeding on mostly organic matter, while others, such as dragonfly
larvae, are feeding off of mainly the grazing pathway. Although you would expect there to be a
stronger grazing pathway in this system as compared to the others, due to the larger amount of
primary producers, the proportion of detritivores to grazers in the second trophic level is the
same (~ 90% detritivores) as in the reference system. This may be due to the fact that as this
system is closest to its original, highly disturbed state, organisms specialized to exploit the
specific resources in this stream have yet to colonize. Rather, we see the dominance of generalist
organisms, such as amphipods and chironomidae, to this system. These organisms can be
successful because there is a uniform habitat type (sand), with little structural complexity in the
stream. Since these organisms are all competing for the same set of nutrients, inputs from
primary producers, in both the grazing and detrital pathways, the amount of aquatic vegetation in
the system ultimately limits productivity in this system (bottom up control).
The medium intensity restoration stream appears to exhibit many of the same patterns as
in the reference system. The organic matter in this system is mainly coming from terrestrial
inputs, as is evidenced by the similarity in carbon 13 values. Additionally, there is very little
(<1%) submerged aquatic vegetation in the measured reach (Stewart, 2011), with primary
producers contributing no measurable biomass to the system. As a result, the grazing pathway
can contribute little to the energy flow in this system, leading to the complete dominance of
detritivores. This can be seen in the cross-system comparison of isotopes, where scavengers,
such as amphipods, that can feed on multiple levels are feeding higher up on the trophic scale,
because the system supports dependence on more than one type of food source. Furthermore, due
to the fact that there is very little primary production in the stream, the entire system is driven by
both upstream and terrestrial inputs, as in the reference stream. Therefore, like in the reference
stream, there is very little overall productivity, especially in terms of the invertebrate community.
Since the system is dependent on outside inputs, and the communities present all seem to feed on
the detrital pathway, the system is ultimately limited by nutrient input into the stream from these
outside sources. Competition among unspecialized benthic invertebrates for these outside inputs
may be a reason for the low levels of secondary consumers in the stream.
The high intensity restoration stream is interesting because, due to the recent nature of the
restoration, there is a high amount of habitat complexity in the stream itself, but a very open
riparian zone, similar to that of the low intensity stream. So, there is a high amount of submerged
aquatic vegetation, suitable for a large number of invertebrates, and a fairly developed fish
population, due to the amount of suitable cover and habitat complexity. As a result, this system is
overall the most productive, as well as having the most overall biomass and abundance. This
would indicate a very diverse, complex, community; however, this system had a similar overall
number of species as the other restored streams, and a high connectance value, which, taken
together, indicates a large amount of generalist species, with only a few specialists, such as
golden shiners, the only solely herbivorous fish found in any stream. This pattern is also evident
when examining the isotopes in this system. Species such as oligochates, isopods, and
Heptigennidae, all of which are scavengers and collectors, are feeding on a mix of detritus and
submerged aquatic vegetation, rather than feeding mainly on one pathway, as in the reference
stream. The fact that the organisms in this stream are exploiting all of the available energy,
through both the grazing and detrital pathways, allows it to be the most productive. Additionally,
the beginnings of a wasp-shaped productivity pyramid suggest that this system is on its way to
having top-down control, which is freeing the second trophic level from predation. This may
allow for the beginning of competition for base nutrients, and drive the bottom organisms in this
system to begin to specialize to avoid overexploitation of resources.
Based on these results, and those of my fellow collaborators, it is clear that in order to
bring a stream back to a pristine state, restoration must focus on two components. One is the
restoration of tree cover and overhang into a stream to boost terrestrial input. This component is
important as terrestrial input into a stream drives stream production, and serves as the main food
and energy source into the stream. Increased shading from the riparian zone will also serve to
cool the stream, both reducing submerged aquatic vegetation in the water as well as allowing for
the return of cold water stream species, such as brook trout, to the streams. Additionally, the
restoration of habitat complexity, in the form of multiple microhabitats, the addition of sinuosity,
and large woody debris, is extremely important in returning a stream to its natural functioning.
Multiple habitat types allow for the specialization of different species of organism, contributing
to the complexity and diversity of the stream system. Taken together, these two components of
stream restoration will allow for the return from a disturbed system to a more pristine state.
Acknowledgements:
Thanks to Dr. Linda Deegan, my project mentor, project collaborators Andrew Miano, Audrey
Seiz, and Sam Stewart; teaching assistants Rich McHorney, Carrie Harris, Stef Strebel, and
Laura Van der Pol, as well as Dr. Marshall Otter. This project would not have been possible
without all of your help and advice.
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Appendix
Figure 1. Study sites
Figure 2. Food web for reference stream.
Figure 3. Food web for low intensity restoration stream
Figure 4. Food web for medium intensity restoration
Figure 5. Food web for high intensity restoration
Figure 6. Amount of diversity in species of primary producers along a stream restoration gradient.
Figure 7. Diversity of secondary consumers along a stream restoration gradient
Figure 8. Number of trophic links along a stream restoration gradient
Figure 9. Connectance level along a stream restoration gradient
Figure 10. Stable isotopes for reference stream
Figure 11. Stable isotopes for low intensity restoration
Figure 12. Stable isotopes for medium intensity restoration
Figure 13. Stable isotopes for high intensity restoration
Figure 14. Cross-system comparison of stable isotopes
Figure 15. Reference stream abundance
Figure 16. Low intensity restoration abundance
Figure 17. Medium intensity restoration abundance
Figure 18. High intensity restoration abundance
Figure 19. Reference stream biomass
\
Figure 20. Low intensity restoration biomass
Figure 21. Medium intensity restoration biomass
Figure 22. High intensity restoration biomass
Figure 23. Reference stream productivity
Figure 24. Low intensity restoration productivity
Figure 25. Medium intensity restoration productivity
Figure 26. High intensity restoration productivity