Biological Opinions - Bureau of Reclamation

time allows temperatures to increase and facilitates photosynthetic and microbial processes that
further degrade water quality.
Figure 7.5 Model results of orthophosphate concentrations from just downstream of Klamath Straits Drain
discharge. The “With Klamath Straits Drain/Lost River Diversion Channel” results are from the 2002
calibration model (ODEQ 2010).
Excessive phosphorus loading linked to watershed development has been determined to be a key
factor driving the massive AFA blooms that now dominate UKL in the summer (ODEQ 2002,
NRC 2004). UKL was eutrophic prior to settlement by Anglo-Americans, but is now classified
as being hypereutrophic (highly enriched; ODEQ 2002, Bradbury et al. 2004, Eilers et al. 2004),
due in large part to human manipulations. Riparian and floodplain habitats, which can detain or
alter nutrients throughout the system, have been lost or degraded as a result of ditching and
diking to promote drainage and prevent overbank flows. The relatively high runoff and erosion
in the Sprague River drainage during high flow events have been identified as the major source
of bound phosphorus to UKL, but many external sources contribute to the nutrient loading of
UKL (ODEQ 2002). Ecosystem improvement efforts are implemented regularly to reduce
nutrient loading due to development and land management, but it is unclear to what degree
restoration can reduce nutrient availability because UKL sediments contain large amounts of
phosphorus that continue to support AFA blooms from sources within the lake (NRC 2004;
Kuwabara et al. 2007, 2009).
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