Water Stewardship Information Sources

Citation Chow, JK. 2007. Nutrient linkages between freshwater and marine ecosystems: Uptake of salmon-derived nutrients in estuaries. MSc Thesis, Uvic.
Organization Uvic
URL https://dspace.library.uvic.ca:8443/bitstream/handle/1828/1231/Jenn%20Chow%20M.Sc.%20Thesis.pdf?sequence=1&isAllowed=y
Abstract/Description or Keywords Anadromous Pacific salmon (Oncorhynchus spp.) return annually from marine
ecosystems to their natal freshwater habitat to spawn and die. Runs of spawning salmon
provide an important source of nutrients and energy to watersheds. However, in coastal
systems, substantial amounts of salmon-derived nutrients can be exported back to
estuaries. Human land use, including agriculture and urban development, also contribute
substantial nutrients to coastal ecosystems, and have the potential to confound results
from salmon-derived nutrient studies.
This thesis examines the influences of spawning salmon and human land use on
stream nutrient and particulate dynamics, including export to estuaries. It also
investigates the use of the stable isotope composition (δ13C and δ15N) of estuarine clams,
the varnish clam (Nuttalia obscurata: Reeve, 1857) and the manila clam (Tapes
philippinarum), and their food sources, as indices of the freshwater export of salmonderived
nutrients to estuaries. Samples were collected from three nearby river-estuary
systems along Southeast Vancouver Island, British Columbia. Study systems had either a
large number of returning salmon and little human land use (Goldstream), few returning salmon and extensive human land use (Shawnigan), or few returning salmon and little
human land use (Holland).
In Goldstream River, high abundance of salmon carcasses increased
concentrations of total nitrogen and total phosphorus stream water below a barrier to
upstream salmon migration. Carcasses also contributed substantial amounts of organic
matter to the stream, as indicated by high δ13C and δ15N, and corresponding low C:N
ratios in suspended particulate organic matter. My calculations indicate that between 51-
77% of the phosphorus transported upstream by migrating salmon, was exported back to
the estuary. Human land use also increased downstream nutrient concentrations and
raised baseline δ15N in stream ecosystems, which is cause for concern and caution for
salmon-derived nutrient studies in land use-affected watersheds, or in the reverse
situation, for anthropogenic nutrient studies in watersheds that support runs of
anadromous salmon.
The high δ15N of anthropogenic nitrogen was not evident in the Shawnigan
Estuary. In the Goldstream Estuary salmon-derived nutrients appeared to increase the
δ15N of clams, and both the δ13C and δ15N of sedimentary organic matter (SOM), with
more enrichment in the high intertidal zone near the river mouth, than in the midintertidal
zone. The stable isotope composition of clams and SOM was relatively
constant across the period of salmon spawning and carcass decay, indicating that they
may reflect a legacy salmon-derived nutrient input into estuaries.
This study demonstrates that substantial amounts of salmon-derived nutrients are
exported back downstream to the Goldstream Estuary where they appear to become
integrated into the estuarine food web. Data from a series of estuaries receiving a range
of nutrients inputs from salmon is needed to confirm indices of salmon-derived nutrients
in estuaries. There is also need for more extensive examination regarding the
downstream effects of salmon-derived nutrients in areas such as estuarine productivity,
community composition, and positive feedback mechanisms that influence salmon
populations. This last area of research is of particular importance considering the high
number of salmon stocks at risk in B.C..
Information Type thesis
Regional Watershed Vancouver Island South
Sub-watershed if known Goldstream, Shawnigan, Holland River
Aquifer #
Project status complete
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