Flathead Basin Commission Flathead Lake Total Maximum Daily Load [TMDL] Recommended Water Quality Targets and Load Reduction (Revised December 1997) Download as Adobe Acrobat PDF File (42K) (Webmaster's Note. This is the FBC's statement regarding the Flathead Lake TMDL Report.) Background: After reviewing the recommendations of the TMDL Technical Committee at its August 15, 1997 meeting, the Flathead Basin Commission opted not to accept the committee's recommendation of 70 grams of carbon per cubic meter of surface water per year measured at the mid-lake site as a target to achieve the reduction of nutrient input sufficient to have Flathead Lake de-listed as an impaired water body. The Commission recognized that its initial obligation is to establish an interim target to allow the Voluntary Nutrient Reduction Strategy [VNRS] phase to begin, and that subsequent monitoring will determine whether or not the interim target of 80 grams of carbon is adequate to achieve the desired results. The members agreed that the interim target can be adjusted, either upward or downward after subsequent monitoring verifies the relative success, or lack of success of the VNRS effort. In light of those considerations, the Commission voted unanimously to set the lower interim target at 80 grams of carbon. The motion also specified that: "Monitoring at the mid lake deep site must provide: evidence of no measurable blooms of anabaena (or other pollution algae), no declining trend in oxygen concentrations in the hypolimnion, c. algal biomass measured as Chlorophyll a (e.g., near shore rocks on lake bottom) remains stable or exhibits a declining trend." The Commission also acknowledged the work of the TMDL Technical Committee and their recommended targets. In its motions the Commission further requested the TMDL Technical Committee to "adjust the other numerical targets" to the new target of 80 grams of carbon. TMDL Technical Committee Response: The Technical Committee's meeting on September 25,1997, determined that a simple incremental equation does not exist to allow the other numerical targets to be adjusted to the new target of 80 grams of carbon with assurance that the goals of the nutrient reduction effort will be achieved. The Technical Committee recommended that the targets for the lake be maintained as proposed except for the interim target of 80 grams of carbon as reflected in Table 1: Table 1 Flathead Lake Interim TMDL Targets Primary production 80.0 g C/m2/yr Chl a 1.0 micrograms/l no measurable blooms of Anabaena (or other pollution algae) no oxygen depletion in hypolimnion SRP <0.5 micrograms/l (BDL) Total Phosphorus 5.0 micrograms/l Total Nitrogen 95 micrograms/l Ammonia (NH3) <1.0 micrograms/l Nitrate Nitrite (NO2/3) 30 micrograms/l Algal bio-mass measured as Chl a (e.g. on near-shore rocks on lake bottom) remains stable or exhibits a declining trend. The Commission has chosen not to adopt interim TMDL targets for SRP total phosphorus, total nitrogen, ammonia (NH3) and nitrate. Therefore, while the Commission has not adopted interim TMDL nutrient targets, the Commission recommends their presence in Flathead Lake be routinely monitored to determine whether the necessary nutrient reductions are occurring within the watershed and to better define the relationship between available nutrients and primary productivity and algal growth in the lake. The Commission recognizes that the relationship between lake concentrations of nutrients (N and P), primary productivity, and algal growth is not a simple mathematical one. The Commission understands primary productivity and algal growth depend on nutrient concentrations within Flathead Lake. It recognizes any implementation strategy designed to meet the interim TMDL target for primary productivity (80.0 g C/m2/yr.), to eliminate anabaena blooms and oxygen depletion in the hypolimnion, and to reduce algal blomass measured as Chlorophyll a in Flathead Lake must lower N and P loading within the watershed. To achieve the interim target, the Technical Committee recommended that annual nutrient loading from nonpoint sources be reduced by 15 percent for the entire watershed, recognizing that when actual measures are adopted, some may achieve greater that a 15 percent improvement while others may achieve less. The Technical Committee also assumed that nutrient loading from point sources will not increase without a corresponding decrease in nonpoint sources. The Technical Committee also concluded that: primary productivity is a response to conditions that exist at any given moment, the health of Flathead Lake is a response to a constantly changing variety of natural and human-caused events, the interim target of 80 grams of carbon is reasonable in light of the uncertainty between the current understanding of linkage between loading, annual natural conditions, and the presence of nuisance algal blooms, interim targets are set at a level that will likely hold or restore the lake to the conditions that existed when the Flathead Basin Commission was established, the interim targets may need to be adapted and changed as monitoring and better understanding of nutrient input to Flathead Lake provide new information, the long-term success of the Flathead Basin Commission's Master Monitoring Program is critical to providing data needed to evaluate the effectiveness of the VNRS program in meeting the interim target and achieving the pollution reduction goals. 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