Environmental Determinants of Allomyia bifosa Larvae in an Alpine Fen of Glacier National Park, Montana
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Authors
Schonfeld, Darcy
Issue Date
1998
Type
Thesis
Language
en_US
Keywords
Alternative Title
Abstract
The ecology of alpine headwater streams differs drastically from that portrayed by
accepted theories on river and stream ecosystems. Alpine streams lack traditional
allochthonous energy sources and light is limited by direction of the slope face rather then
by canopy. Autotrophy of alpine streams is limited not by light but by nutrients (Ward
1994).
Baring Creek, a first-order alpine stream and associated fen, fed by the waters of a
permanent snowfield in Glacier National Park, Montana has been recognized as the home
of a rare caddisfiy, Allomyia bifosa (Trichoptera) It was found that nitrate in the stream
was high at the source and dropped within the first 100 m (the presence of Allomyia
bifosa dropped along with the nitrate); this trend differs from the general view that nitrate
is gradually added to the water column by the additive action of blue-green algae
(Cyanophyta) and other sources of fixed nitrogen. Latrine sites made by small mammals,
thought to be the unique source of nitrate, were found in abundance in the headwaters of
Baring Creek. It was postulated that Baring Creek would experience a change in
periphyton structure from blue-green dominated (blue-greens have the exclusive ability to
fix nitrogen in aquatic ecosystems and resistance to extreme situations )to diatoms
(Bacillariophyta). As an obligate grazer, Allomyia bifosa, would be restricted to streams
with this unique fen association, high nitrate levels, and diatom dominated periphyton.
Four streams on a continuum of fen-association were assayed, an upstream and
downstream site at each. It was found that nitrate levels were high at the source of all
streams and dropped longitudinally; periphyton carbon levels increased, strongly
suggesting the periphyton was taking up nitrate. Nitrogen to phosphorus ratios suggest
that phosphorus limitation is occurring at some sites. Allomyia bifosa were later found at
all sites when in close proximity with groundwater and fen. Algae in Baring Creek were
not found and the periphyton is now thought to be primarily microbially mediated by
heterotrophs.
Description
vii, 39 p.
Citation
Publisher
Kalamazoo College
License
U.S. copyright laws protect this material. Commercial use or distribution of this material is not permitted without prior written permission of the copyright holder.