JUSTIFICATION FOR ADDING NUTRIENT LIMITED WATERSHED
DESIGNATIONS TO WATERBODIES IN APPENDIX A
Lake Tenkiller
Lake Thunderbird
October 21, 2005
WATER QUALITY PROGRAMS DIVISION
2
3
JUSTIFICATION FOR ADDING NUTRIENT LIMITED WATERSHED DESIGNATIONS
TO WATERBODIES IN APPENDIX A
Introduction
As part of the OWRB’s continuing efforts to monitor the health of the states waters,
OWRB staff have identified Tenkiller Reservoir and Lake Thunderbird as needing
Nutrient Limited Watersheds (NLW) designation. OWRB rule (OAC 785:45-1-2 and 46-
15-10) has for several years contained provisions for adding a NLW designation to any
lake or reservoir that could be shown to support a sufficiently large algal mass Such
watersheds are defined in785:45-1-2 as "Nutrient-limited watershed" means a
watershed of a waterbody with a designated beneficial use which is adversely affected
by excess nutrients as determined by Carlson's Trophic State Index (using chlorophyll-a)
of 62 or greater, or is otherwise listed as "NLW" in Appendix A of this Chapter.
Based upon a review of Clean Lakes studies and continued monitoring, Tenkiller
Reservoir and Lake Thunderbird are adversely affected by excess nutrients.
Process:
OWRB reviewed historical lakes studies to reveal gaps in the BUMP lakes sampling
process. Staff Reviewed 47 studies reporting on 48 different Oklahoma lakes that
included investigations by the Oklahoma Conservation Commission, Oklahoma Water
Resources Board, Tulsa District COE, University of North Texas, Oklahoma State
University, USDI Bureau of Reclamation, Oklahoma University, Oklahoma Department
of Environmental Quality and Oklahoma State Department of Health. Reports date
from 1979 to present spanning all ecoregions of Oklahoma with a common denominator
of intensive monitoring using established sampling sites throughout the reservoir
sampled at regularly set intervals. The first level of screening was whether a
relationship between nutrients and algae were determined; approximating a NLW Study
grade evaluation. The second level of screening was whether control of algae and
nutrient reductions were recommended. Finally, this short list of lakes was cross-referenced
against the list of lakes impaired due to low DO. Only Lake Tenkiller and
Lake Thunderbird fell within these guidelines.
Rationale behind the recommendations:
Dead and dying algae contribute to the hypolimnetic oxygen deficit in reservoirs. The
algae in reservoirs experiencing high to excessive algae growth ( TSI 50+) are
concluded to be a major determinant of the oxygen deficit rate. When a reservoir listed
as impaired due to dissolved oxygen (summer to fall values provide the proof for listing)
has high to excessive algae growth, it is reasonable to declare the high levels of algae
to be the pollutant source. Nutrients are the cause of the algae growth. Although this
rational implies that any reservoir impaired due to low DO and experiencing high to
excessive algae growth should be listed as an NLW, this was not the decision. Only
when data was used to establish a nutrient to algae relationship and a reduction of
nutrients recommended to control algae growth was the conclusion made that an NLW
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listing was necessary. OWRB staff recommends that new listings should be limited to
those with published burden of proof as opposed to imposing a general policy.
Proposal
Staff propose to add the designation NLW to the “REMARKS” column in Appendix A to
denote these reservoirs as being eutrophic. The proposed language can be found at
the end of this document.
Economic Considerations
OWRB requests that Oklahoma environmental agencies and all affected entities forward
to the OWRB estimates of financial or other impacts anticipated with implementation of
the NLW designation to these reservoirs.
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Seasonal TSI values for Tenkiller Ferry Lake
30
40
50
60
70
09/15/03 12/15/03 03/15/04 06/14/04
TSI (chlor-a)
Site 1 Site 2 Site 3 Site 4
Site 5 Site 6 Site 7
Oligotrophic
Mesotrophic
Eutrophic
Hypereutrophic
Tenkiller Lake
Tenkiller lake has been identified as a water body of concern for many years because of
an increasing trend in algae concentrations. The Clean lakes Study data from 1992 and
1993 show a substantial increase in chlorophyll-a over those observed in the 1974
national eutrophication study. Recent OWRB monitoring shows that the increased
algae levels persist 12 years later. Average chlorophyll in the national eutrophication
study was 6.6 ug/l(TSI 49) while average lacustrine chlorophyll a levels in the Clean
Lakes study and recent OWRB monitoring are 16.7 ug/l (TSI 59)and 14.6 ug/l (TSI 58)
respectively. While the average TSI is less than 62, it is frequently exceeded. The
Clean Lakes study called for nutrient reductions to limit the increased levels of algae
growth. Tenkiller Lake has been shown to be impaired by low dissolved oxygen in its
hypolimnion. Dissolved oxygen in the deeper waters of the lake frequently drops below
2 mg/l such that the Fish and Wildlife Propagation Beneficial Use is impaired. Lake
Tenkiller is listed in Oklahoma’s 303(d) list of impaired waters bodies for both nutrients
and dissolved oxygen. A NLW designation is recommended by staff to help implement
the nutrient reductions goal for Lake Ten killer.
For the most recent OWRB monitoring report for Tenkiller Lake see:
www.owrb.state.ok.us/studies/reports/bump/2004/bump_pdf/lakes/tenkiller_ferry.pdf
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Seasonal TSI values for Lake Thunderbird
30
40
50
60
70
09/09/03 12/09/03 03/03/04 06/08/04
TSI (chlor-a)
Site 1 Site 2 Site 3 Site 4
Site 5 Site 6 Site 7
Oligotrophic
Mesotrophic
Eutrophic
Hypereutrophic
Lake Thunderbird
Lake Thunderbird was constructed in 1965 and is owned by the Bureau of Reclamation. The
lake serves as a municipal water supply for flood control, fish and wildlife, and offers numerous
recreational opportunities to the public. OWRB studies on Lake Thunderbird have shown algae
growth to be problematic and causing taste and odor problems for the City of Norman water
supply. While the average TSI is less than 62, it is frequently exceeded. OWRB studies have
further shown that nutrient loading should be limited to help prevent the excessive algae levels
causing taste and odor problems.
From September 2003 through June 2004, water quality samples were collected at seven (7)
sites to represent the riverine, transitional, and lacustrine zones of the reservoir as well as any
major arms. Carlson's trophic state index TSI (chlorophyll-a), was calculated using values
collected at all sites (n=28). The average TSI was 58, classifying the lake as eutrophic,
indicative of high levels of productivity and nutrient rich conditions. This value is slightly higher
than the TSI in 2001 (TSI=56), although in the same trophic category. The TSI varied
seasonally from hypereutrophic in the fall and summer to mesotrophic and eutrophic in the
winter and spring quarters. The chlorophyll-a concentrations were generally lower at the dam
site and lacustrine areas of the lake (sites 1, 2, and 4) and higher at the upper end, or riverine
zones of the lake (sites 5, 6, and 7). In summary, Lake Thunderbird was eutrophic, indicative of
high primary productivity and nutrient conditions. The calculated TSI was very similar to that
sample year 2002 (TSI=56), indicating no significant change in productivity has occurred.
OWRB studies regarding Lake Thunderbird water quality can be found at:
www.owrb.state.ok.us/studies/reports/reports_pdf/ThunderbirdWaterQualityReport2004.pdf
www.owrb.state.ok.us/studies/reports/bump/2004/bump_pdf/lakes/thunderbird.pdf
www.owrb.state.ok.us/studies/reports/reports_pdf/ThunderbirdWaterQualityReport2003.pdf
www.owrb.state.ok.us/studies/reports/reports_pdf/thunderbird_report.pdf
Proposed language revision to Appendix A denoting the new NLW designations.
Lower Illinois River from headwater of
Robert S. Kerr Reservoir to Tenkiller Dam
121700
PPWS
Trout
1
●
PBCR
●
●
HQW
Upper Illinois River from Tenkiller Dam,
including Tenkiller Reservoir upstream to
Barren Fork confluence
121700
PPWS
CWAC
1
●
●
PBCR
●
HQW
NLW
Caney Creek
121700
PPWS
CWAC
●
PBCR
●
Tributary to Salt Creek at NW SW Sec. 33, T8N
R5E, IM
520800
WWAC
●
●
PBCR
●
Thunderbird Lake and Watershed
520810
PPWS
WWAC
1
PBCR
●
SWS
NLW
Tributary of Canadian River at SE 1/4, Sec.18,
T5N, R7E, IM
520600
HLAC
●
●
SBCR
●
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