Assessment Comments
Assessment is based on results of (1) ISU lake survey from 2000-04, (2) surveys by IDNR Fisheries Bureau, (3) ISU report on lake phytoplankton communities from 2000-05, and (4) an IDNR investigation of a fish kill in March 2004.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "not supporting" primarily due to very poor water transparency due to high levels of non-algal turbidity. The Class B(LW) aquatic life uses remain assessed (evaluated) as "partially supporting" due to high levels of nutrients, non-algal turbidity, and siltation impacts. Although not directly affecting the assessment of the Class B(LW) uses, a fish kill occurred in this lake in March 2004. The Class C drinking water uses are "not assessed" due to lack of data upon which to base an assessment. 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, (3) information on plankton communities collected at Iowa lakes from 2000 through 2005 as part of the ISU lake survey, and (4) results of an IDNR investigation of a fish kill in March 2004.
Note: A TMDL for siltation at Orient Lake was prepared by IDNR and approved by EPA in 2001; thus, this waterbody was placed into IR Category 4a (TMDL approved) for the 2004 assessment/listing cycle. Because all Section 303(d) impairments identified for the 2006 assessment/listing cycle (nutrients, non-algal turbidity, and siltation) are addressed by the TMDL, this waterbody remains in IR Category 4a.
EXPLANATION: Results from the ISU statewide survey of Iowa lakes suggest that high levels of non-algal turbidity may impair the Class A and Class B(LW) uses of Orient Lake. Using the median values from the Iowa State University statewide surveys of Iowa lakes from 2000 through 2004 (approximately 15 samples), Carlson’s trophic state indices for total phosphorus, chlorophyll-a, and secchi depth at Lake Orient are 80, 60, and 72, respectively. According to Carlson (1977), the index value for total phosphorus places this lake in the range of 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 lower range of hyper-eutrophic lakes. Together, these index values suggest extremely high levels of phosphorus in the water column, somewhat elevated (but less than expected) levels of chlorophyll-a, and very poor 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 Orient is limited primarily by inorganic turbidity but also (potentially) by nitrogen availability 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. The median level of inorganic suspended solids at Lake Orient (13.0 mg/l) was the 21st highest of the 131 lakes, thus strongly suggesting that non-algal turbidity is responsible for light attenuation that limits the production of algae. In addition, the ratio of total nitrogen to total phosphorus for this lake is relatively low (12) and suggest that algal production at the lake is, at times, nitrogen-limited.
The presence of extremely large populations of zooplankton at Lake Orient that graze on algae, however, may explain the discrepancy between the TSI value for phosphorus (80) and that for chlorophyll-a (60). Sampling from 2000 through 2005 showed that while Cladoceran taxa (e.g., Daphnia) comprised only 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 (256 mg/l) was the 10th highest of the 131 lakes sampled. The large population of zooplankton grazers at Lake Orient suggest the potential for limiting algal production at this lake.
Thus, the conditions at this lake suggest that very high levels inorganic suspended solids and the resultant very poor water transparency indicate impairment of the Class A (primary contact) uses due to violation of Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions.
The IDNR Fisheries Bureau concurs that Lake Orient is impaired by non-algal turbidity but believes that algae contribute to this impairment.
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 Orient (0.7 mg/l) was the 5th 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 hyper-eutrophic conditions at this lake, along with information from the IDNR Fisheries Bureau, suggest that the Class B(LW) aquatic life uses are "partially supported" due to excessive nutrient loading to the water column, high levels of non-algal turbidity, and siltation in the lake. The ISU lake survey data suggest relatively good chemical/physical water quality at this lake. The results of this monitoring show no violations of the Class B(LW) criteria for dissolved oxygen in the 14 samples collected during summers of 2000 through 2004. One of 15 samples, however, exceeded the Class B(LW) criterion for pH (maximum = 9.6; minimum = 7.8 pH units). Based on IDNR’s assessment methodology, this violation does not suggest that violation frequency is significantly greater than 10% for pH and thus does not suggest impairment of either the Class A and Class B(LW) uses of Lake Orient.
The occurrence of a fish kill at this lake in March 2004 is consistent with the assessment of the Class B(LW) uses as "partially supported". This kill occurred on or before March 2, 2004. This kill was attributed to natural causes (winterkill). An estimated 475 fish were killed with an estimated value of $7,125. Bluegill (75), crappie (150), and channel catfish (250) were observed killed. According to the investigation conducted by Adair County, the kill was caused by low oxygen conditions that developed during the winter. This lake has a maximum depth of eight feet and was approximately 3 feet low at the time of the investigation. According to IDNR’s 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.
Drinking water uses are "not assessed" due to a lack of relevant water quality information upon which to base an assessment. The only parameter collected as part of the ISU lake survey relevant to support of Class C (drinking water) uses is nitrate. While the results of the ISU survey from 2000-04 show that nitrate levels are low at this lake (maximum value = 5.5 mg/l; median = 1.4 mg/l), these data are not sufficient for developing a valid assessment of support of the Class C uses.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
