Page 18 - The Freshwater Mussels of Oklahoma

addition of organic nutrients from some outside source. The most severe anoxia
conditions occur on the bottoms of aquatic systems. Fish and other aquatic organisms
can often move to the surface or other areas where oxygen levels are more favorable.
Mussels are unable to escape. Common sources of nutrients that result in anoxic
conditions include poultry wastes, cattle and hog feedlot wastes, municipal sewage
treatment overflow and fertilizer runoff.
Toxins: The variety of possible toxins that might pollute an aquatic system are
impossible to enumerate. Everything from pesticides and herbicides to heavy metals,
solvents, oil spills, salts and others. Just as in conditions of anoxia, the immobility of
mussels make it difficulty for them to escape or survive these events.
Sediments: Although erosion and deposition are natural processes that have
served to shape Oklahoma’s topography, any alteration in the process can have
significant effects on mussel species not adapted to the change. Most often the problem
is with increased erosion and deposition. This is usually associated with human activities
such as agriculture, logging, construction and overgrazing. Increased sediment loads in
our lakes and rivers can bury and smother mussels or perhaps alter the substrate say from
gravel to silt and thus making the habitat unsuitable for species adapted to gravel
substrates. Increased sediments can also alter the stability of a stream forcing channels to
constantly shift and meander. This creates conditions in which mussel populations have
great difficulty in establishing and also maintaining themselves.
Dams: Impounding rivers and streams have probably been the leading cause of
mussel declines in North America and in Oklahoma. Rivers contain the greatest diversity
of species and most of these species are adapted to flow regimes and temperature cycles
for their nutrient and reproductive needs. Impoundments obviously alter large stretches
of flowing river habitat into lakes. This restricts the number of species that can survive
lake conditions to only a few but also has drastic effects in the river both above and
below the lake. The dam itself is a barrier to the movement of anadromous fish that may
be required as hosts for mussel glochidia. If the proper fish hosts can’t reach those areas
of the river, the mussels can’t reproduce. Below the dams, a number of factors may come
into play. If water is released from the surface of the lake (hyperlimnetic discharge) then
it may follow fairly normal seasonal changes in temperature and nutrients. However, if
water is released from the bottom of the lake (hypolimnetic discharge) then the water
temperature will be much below normal and contain fewer nutrients. Both of these
factors can dramatically affect the mussel’s ability to survive and reproduce. Another
factor involves man’s control of the rate of discharge. If the discharge is too low,
stagnation and anoxia may result in damage to mussel populations. If the discharge is too
great, scouring of the streambed may result, thus removing the substrate needed for
mussel survival. This is almost inevitable because the dam itself blocks the passage of
any sediments from upstream and that can only mean that there will be a gradual loss of
substrate downstream.
Channelization: Channelization of rivers and streams is commonly done to
straighten a segment to shorten its length or to increase the rate of flow. It is also used to
deepen natural channels for the passage of large boats and barges. The channelization

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