Numeric biological assessment thresholds for lakes, reservoirs and impounded flowing waters

Numeric biological assessment thresholds for lakes, reservoirs and impounded flowing waters. Numeric biological assessment thresholds for lakes, reservoirs and impounded flowing waters. This section contains numeric biological assessment thresholds for evaluating the biological condition of lakes, reservoirs, and impounded flowing waters and determining whether applicable designated uses are being attained. Numeric biological assessment thresholds used to assess attainment of designated uses include all of the following: (1) Aquatic life use thresholds. (a) Chlorophyll a. 1. ‘Assessment thresholds.’ a. A lake or reservoir other than a stratified two-story fishery lake is not attaining its aquatic life use if its arithmetic mean suspended chlorophyll a concentration exceeds 27 ug/L. b. A two-story fishery lake is not attaining its aquatic life use if its arithmetic mean suspended chlorophyll a concentration exceeds 8 ug/L. 2. ‘Assessment methods.’ Data requirements for chlorophyll a are the same as those specified for phosphorus in s. NR 102.07 (1) (a) , except that the sampling period for chlorophyll a is July 15 to September 15. To determine attainment of the chlorophyll a threshold under subd. 1. , the department shall compare the waterbody’s mean suspended chlorophyll a concentration during the sampling period to the threshold, using the confidence interval approach described under s. NR 102.52 (2) (b) to (c) to determine if additional samples are needed. (b) Aquatic plants. 1. ‘Assessment thresholds.’ Thresholds for evaluating the general health of an aquatic plant community in a lake or reservoir to determine whether its aquatic life use is attained are shown in Table 8. Thresholds used in the macrophyte assessment of condition indicate the acceptable percentage of a lake or reservoir’s vegetated area supporting species that are in each of three tolerance categories. The tolerance categories specify whether a plant species is sensitive to, moderately tolerant of, or tolerant of disturbance. 2. ‘Assessment methods.’ The percentage of a lake or reservoir’s vegetated area supporting each tolerance category shall be determined using department-approved protocols for assessing macrophyte condition. The sampling period for southern lakes is June 15 to September 15, and for northern lakes is July 1 to August 31 unless the department determines that an extension from June 15 to September 15 is appropriate during warmer than average years. The department shall consider the threshold attained if the most recent plant survey conducted within the past 10 years, or other more representative survey, attains the applicable threshold in Table 8. (2) Recreation use thresholds. (a) Definition. In this section, “moderate algae level” means a chlorophyll a concentration of 20 ug/L or greater. (b) Frequency of moderate algae levels. Thresholds in Table 9 shall be used when determining if a lake, reservoir, or impounded flowing water is attaining its recreational use. (c) Assessment methods. Data requirements for chlorophyll a are the same as those specified for phosphorus in s. NR 102.07 (1) (a) , except that the sampling period for chlorophyll a in all waterbody types is July 15 to September 15. To determine attainment of the threshold, the department shall determine a waterbody’s frequency of moderate algae levels during the chlorophyll a summer sampling period using the confidence interval for a percentile of a normal distribution, and use the approach described under s. NR 102.52 (2) (b) and (c) to compare that frequency to the applicable threshold in Table 9.