Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-04, (2) surveys by IDNR Fisheries Bureau, and (3) ISU reports on lake plankton communities from 2000-05.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "fully supporting”. The Class B(LW) aquatic life uses are assessed (evaluated) as "fully supporting." 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 sponsored by IDNR and conducted by Iowa State University (ISU) from 2000 through 2004, (2) surveys by IDNR Fisheries Bureau, and (3) information on plankton communities collected at Iowa lakes from 2000 through 2005 as part of the ISU lake survey.
Note: A TMDL for noxious aquatic plants at Lake Smith was prepared by IDNR and approved by EPA in 2005. The basis of the impairment at this lake was high populations of bluegreen algae (=noxious aquatic plants) at this lake. Based on recent monitoring, a fish kll in the winter of 2000-01 and a subsequent lake renovation has sigificantly improved the water quaity of this lake. Recent ISU lake monitoring data strongly suggest that the impairment due to noxious aquatic plants no longer exists. Although non-bluegreen algal populations remain elevated at this lake, the current data suggest "full support" of both the Class A and Class B(LW) uses. Thus, this waterbody is appropriate for IR Category 2a (some uses met; no data to assess other uses) for the 2006 assessment/listing cycle.
EXPLANATION: According to the IDNR Fisheries Bureau, Lake Smith previously suffered from nuisance blue-green algae blooms. During the winter of 2000-2001, however, this lake suffered a severe winterkill. Because the sportfish population was reduced dramatically, IDNR Fisheries chemically renovated the lake in September of 2001. Both common carp and grass carp were successfully eliminated. The water quality in 2002 was very good: the water was clear and submergent vegetation was reestablished. Although the relative permanence of these positive changes is difficult to determine, the IDNR Fisheries does not consider this lake to be currently "impaired" for aquatic life uses.
Results from the ISU statewide survey of Iowa lakes, which includes data collected before and after the fish kill, suggest that the high levels of algal turbidity that had adversely affected the Class A and Class B(LW) uses of Lake Smith have improved such that this lake exhibited good water quality during the 2002-2004 assessment period. Using the median values from this survey from 2000 through 2004 (approximately 15 samples), Carlson's (1977) trophic state indices for total phosphorus, chlorophyll-a, and secchi depth were 75, 64, and 58, respectively. According to Carlson (1977), the index value for total phosphorus continues to places this lake in range of hyper-eutrophic lakes; the index values for chlorophyll-a is in the middle 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 very to extremely high levels of phosphorus in the water column, somewhat elevated levels of chlorophyll-a (suspended algae), 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 ISU lake data suggest that algal production at Lake Smith is likely limited by a combination of inorganic turbidity and zooplankton grazing. 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. Of 131 lakes sampled, Lake Smith had the 56th lowest median level of inorganic suspended solids (4.2 mg/l), thus suggesting that non-algal turbidity may contribute to limiting the production of algae at this lake. The annual average ISS values have declined (improved) greatly over the 2000-2005 period: 2000: 40 mg/l; 2001: 6 mg/l; 2002 = 4 mg/l; 2003 = 3 mg/l; 2004 = 2 mg/l and 2005 = 3 mg/l. This trend likely reflects the impact of the 2000-2001 winterkill that removed common carp and grass carp from the lake and allowed the reestablishment of littoral zone vegetation.
The presence of very large populations of zooplankton at Lake Smith that graze on algae, however, may explain the discrepancy between the TSI value for phosphorus (75) and that for chlorophyll-a (64). In terms of all Iowa lakes sampled, data from the ISU survey show 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 approximately just over half 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 (156 mg/l) was the 33rd highest of the 131 lakes sampled. This population of zooplankton grazers suggests the potential for this type of non-phosphorus limitation on algal production at Lake Smith.
Based on median values from ISU sampling from 2000 through 2002, the ratio of total nitrogen to total phosphorus for Lake Smith is 31, thus suggesting that nitrogen is not likely a limiting nutrient in this lake.
The levels of nuisance (=noxious) algal species (i.e., bluegreen algae) at this lake do not suggest an impairment of Class A uses. Data from the ISU survey from 2000 through 2004 suggest that bluegreen algae (Cyanophyta) comprise a relatively low portion (about one-third%) of this lake’s summertime phytoplankton community. Sampling from 2000 through 2004 showed that the median per summer sample mass of bluegreen algae at Lake Smith (0.6 mg/l) was the 4th lowest of the 131 lakes sampled: This extremely low level is in the lowest 10% 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.
The conditions at this lake suggest good water quality and “full support" of the Class A uses. Additional years of data, however, will be needed to determine the relative permanence of these improved water quality conditions.
Recent information from the IDNR Fisheries Bureau suggests that water quality of this lake is improving, with a shift from a turbid, algae-dominated system to one with clear water and abundant rooted aquatic vegetation. Results from the ISU lake survey that show improvements in TSI values from the 2000-01 period to the 2000-02 and 2002-04 periods support this conclusion. Information from the IDNR Fisheries Bureau suggests that the Class B(LW) aquatic life uses should, due to recent improvements in water quality at this lake, be assessed as "fully supported". The ISU lake survey data show no violations of the Class B(LW) criteria for dissolved oxygen in the 14 samples collected during summers of 2000 through 2004. Three of 14 samples, however, exceeded the Class B(LW) criterion for pH (maximum = 9.7; minimum = 8.2 pH units). Based on IDNR’s assessment methodology, however, these results do not suggest that significantly more than 10 percent of the samples exceed Iowa’s pH criteria and thus do not suggest an impairment of the Class A and Class B(LW) uses of this lake. These violations likely reflect the excessive primary productivity at Lake Smith and do not reflect the input of pollutants into this lake.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring a this lake.
