ENVS 160
Problem Set 4
Part 1—Do Salmon Add Marine-Derived Nitrogen to the Stream Ecosystem?
Questions (5 points each)
1. Do marine-derived nutrients (MDNs) from salmon get incorporated into the stream food
web? If so, what parts (trophic levels or feeding categories)? Refer specifically to ...
Part 1—Do Salmon Add Marine-Derived Nitrogen to the Stream Ecosystem?
Questions (5 points each)
1. Do marine-derived nutrients (MDNs) from salmon get incorporated into the stream food
web? If so, what parts (trophic levels or feeding categories)? Refer specifically to the data
in the figures to support your answer.
Yes, but they are more incorporated in the Grizzly Creek (Nitrogen) than the Stream 0372
(Nitrogen). In the case of Carbon, it is more proficient in the Grizzly Creek as well. The specific
trophic levels in the case of Nitrogen is Cutthroat Trout (predator). In the case of Carbon, it is still
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the Cutthroat Trout. We can see that the bar for cutthroat trout is higher than the rest of the stream
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bars; in the case of Nitrogen this indicates a higher MDN level. We can see that in Figure 1b the
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bars for cutthroat trout are less negative than the other cutthroat trout stream bars, which indicates
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MDN presence. rs e
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2. (a) What is the significance of looking at both N and C stable isotope ratios? (Think
about—or review, if you can’t remember them—how the biogeochemical cycles of these
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two elements differ, particularly in how they move within a food web.)
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The significance is that evaporation doesn’t apply to heavy isotopes and heavy isotopes of
Nitrogen build up in consumers because of what they eat. If heavy nitrogen isotopes build up in
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the ecosystem, and lower trophic level organisms consume heavy nitrogen isotopes, it travels
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through the feed web to consumers. This will create an unbalanced ecosystem because there will
be different levels of heavy isotopes on each level. The carbon ratio is important because Carbon
is
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plays a part in cellular respiration and photosynthesis. The nitrogen is important because it plays a
role in all consumers.
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(b) Compare the patterns of N and C in Figure 1. What does this tell us about how the
MDN are entering the food web?
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, It tells us that MDN is entering the food web at the lowest trophic level. The figure can tell us this
because if you look at the graphs, you can see that for figure 1a the bars are relatively low, but
raise up. This is a buildup of MDN in the ecosystem. The carbon portion, figure 1b, shows that it
enters the system at the lowest trophic level as well. We can see this because as we move through
the graph, the bars get relatively smaller, indicating less MDN
3. What do the seasonal changes in enrichment (Figure 1) tell us about the source of the
MDN?
Seasonal changes show a decrease in MDN from Winter to Autumn (figure 1a and b). this tells us
that the source of MDN is more present in the winter than autumn; post-spawning has more MDN
than pre-spawning.
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4. Both studies measured MDNs in fish. Aside from examining different species, does the
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experiment (Chaloner et al. 2002; Figure 2) tell you anything different than the
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observational study (Bilby et al. 1996; Figure 1)? If so, what?
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Figure 2 shows us more of a comparison between Nitrogen and Carbon, whereas in Figure 1 they
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were separated and harder to compare, this isn’t a difference between the two studies, just a
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personal observation. The difference is that carcasses were controlled and in all aspects of the
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study, not just an assumption of the Grizzly Creek. The more carcasses in the artificial stream
meant the higher nitrogen and carbon values.
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Part 2A—Do Marine-Derived Nutrients Affect Stream Organisms?
Questions (2 points each)
1. Does the presence of salmon carcasses affect the abundance of biofilm or macroinvertebrates?
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Support your answer by referring to specific data in the figures.
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The presence of salmon carcasses affects the abundance of both biofilm and
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macroinvertebrates. In Figure3a, we can see the shaded bar is significantly larger than the
open bar. The shaded bar means carcasses were present. This indicates that Biofilm increases
with the presence of salmon carcasses. In Figure 3b we can see the same. All three shaded
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