Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-04, (2) ISU reports on lake plankton communities from 2000-05, (3) surveys by IDNR Fisheries Bureau, and (4) an IDNR investigation of a fish kill in May 2005.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "fully supporting", although somewhat elevated levels of chlorophyll-a and moderately high levels of inorganic suspended solids remain water quality concerns at this lake. The Class B(WW) aquatic life uses are assessed (evaluated) as "partially supporting" due to occurrence of a fish kill in May 2005. Nutrient loading to the water column and siltation remain water quality concerns at this lake. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake. The sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2000 through 2004 by Iowa State University (ISU), (2) information from the IDNR Fisheries Bureau, (3) information on plankton communities collected from 2000 through 2005 for the ISU lakes survey, and (4) results of an IDNR investigation of a fish kill in May 2005.
Note: The occurrence of the fish kill in May 2005 resulted in changing the 2004 assessment: this waterbody was moved from Category 4a of the Integrated Report (impaired, but a TMDL has been completed and approved) to Category 2b (at least one use assessed as "fully supported" with at least one other use "evaluted" as "impaired").
EXPLANATION: Using the median values from the ISU lake survey from 2000 through 2004 (approximately 15 samples), Carlson's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth are 67, 62, and 59, respectively, for Upper Pine Lake. According to Carlson (1977), the index value for total phosphorus places this lake in the upper range between eutrophic and hyper-eutrophic lakes; the index value for chlorophyll-a is in the lower range between eutrophic and hyper-eutrophic lakes, and the index value for Secchi depth is in the upper range of eutrophic lakes. These index values suggest moderately high to very high levels of phosphorus, somewhat elevated levels of chlorophyll-a, and relatively good water transparency.
According to Carlson (1991), the occurrence of a high TSI value for total phosphorus with relatively low values for chlorophyll-a and secchi depth indicate that some factor (e.g., nitrogen limitation, zooplankton grazing, or some other factor) other than phosphorus limits production of algae. The results of ISU monitoring suggest that the moderately high levels of inorganic suspended solids at this lake likely limit algal production; algal production at this lake does not appear to be limited by nitrogen availability or by zooplankton grazing. Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for Upper Pine Lake is 100. This ratio is very high and suggests that the production of algae at this lake is limited by the availability of phosphorus and that this lake has an excess of nitrogen (the 2000-04 median level of total nitrogen at this lake (7.7 mg/l) was the 12th highest of the 131 lakes sampled).
The presence of moderately large populations of zooplankton at Upper Pine Lake that graze on algae likely has only a minor influence on the discrepancy between TSI value for phosphorus (67) and those for chlorophyll-a (62) and secchi depth (59). In terms of all Iowa lakes sampled, data from the ISU survey show moderately large populations of zooplankton species at this lake that graze on algae. Sampling from 2000 through 2005 showed that Cladoceran taxa (e.g., Daphnia) comprised about 40% of the dry mass of the zooplankton community of this lake. The average per summer sample mass of Cladoceran taxa over the 2000-2005 period (83 mg/l) was the 62nd lowest of the 131 lakes sampled. These results suggest a minor potential for non-phosphorus limitation on algal production due to zooplankton grazing at Upper Pine Lake.
The levels of inorganic suspended solids at this lake are moderately high and suggest the potential for limiting algal production at this lake. The median level of inorganic suspended solids in the 131 lakes sampled for the ISU lake survey from 2000 through 2004 was 5.2 mg/l; the median level at Upper Pine Lake was 5.6 mg/l.
Levels of nuisance algal species (i.e., bluegreen algae) at this lake appear to be low and neither threaten nor impair designated uses. While data from the ISU survey from 2000 through 2004 suggest that bluegreen algae (Cyanophyta) comprise a significant portion (50%) of this lake’s summertime phytoplankton community, sampling from 2000 through 2004 showed that the median per summer sample mass of bluegreen algae at Upper Pine Lake (4.9 mg/l) was the 24th lowest of the 131 lakes sampled. This level is in the lowest 25% of the 131 Iowa lakes sampled. The presence of a relatively small population of bluegreen algae at this lake does not suggest a potential violation of Iowa’s narrative water quality standard protecting against occurrence of nuisance aquatic life. This assessment, however, is based strictly on a distribution of the lake-specific median bluegreen algae values for the 2000-2004 monitoring period. Median levels less than the 75th percentile of this distribution (~29 mg/l) were arbitrarily considered by IDNR staff to not represent an impairment of the Class A uses of Iowa lakes. No criteria exist, however, upon which to base a more accurate identification of impairments due to bluegreen algae. Thus, while the ability to characterize the levels of bluegreen algae at this lake has improved over that of the previous (2004) assessment due to collection of additional data, the assessment category for assessments based on level of bluegreen algae nonetheless remains, of necessity, "evaluated" (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).
Although results of the ISU lake surveys suggest "full support" of the Class A uses, the somewhat elevated levels of chlorophyll-a, as well as the moderately high levels of inorganic suspended solids, remain water quality concerns regarding the full support of these uses at Upper Pine Lake.
Information from the IDNR Fisheries Bureau suggests that the Class B(WW) aquatic life uses should be assessed as "fully supported". Nutrient loading to the water column and siltation, however, remain concerns regarding support of aquatic life uses at this lake. Also, results of ISU monitoring from 2000 through 2004 suggest generally good chemical water quality at this lake. Results of this monitoring show that only one of the 15 samples collected exceeded the Class B(WW) criteria for dissolved oxygen and that only two of the 15 samples collected exceeded Iowa’s Class A,B(WW) criteria for pH (maximum = 9.4; minimum = 7.3 pH units). Based on IDNR’s assessment methodology, these results do not suggest violation frequencies are significantly greater than 10% for either parameter and thus do not suggest impairment of either the Class A and Class B(WW) uses of Upper Pine Lake.
Despite indications of "full support" of the Class B(WW) uses based on IDNR information and on ISU chemical/physical monitoring data, a fish kill that occurred at this lake in May 2005 suggests that the Class B(WW) uses should be assessed (evaluted) as "partially supported. This kill was attributed to natural causes (spawning stress). The kill affected bluegill and crappie; no estimated were made of the number of dead fish. The kill was believed due to fluctuating water temperatures that contributed to spawning stress. According to the IDNR assessment/listing methodology, the occurrence of a single pollutant-caused fish kill, or a fish kill of unknown origin, on a waterbody or waterbody reach during the most recent assessment period (2002-2005) indicates a severe stress to the aquatic community and suggests that the aquatic life uses should be assessed as “impaired”. If a cause of the kill was not identified during the IDNR investigation, or if the kill was attributed to non-pollutant causes (e.g., winterkill), the assessment type will be considered “evaluated.” Such assessments, although suitable for Section 305(b) reporting, lack the degree of confidence to support addition to the state Section 303(d) list of impaired waters (IR Category 5). Waterbodies affected by such fish kills will be placed in IR subcategories 2b or 3b and will be added to the state list of waters in need of further investigation.
Fish consumption uses remain "not assessed” due to the lack of recent fish contaminant monitoring at this lake.
