Turtle LciXe 



Climatic setting. The net annual precipitation balance for Turtle 

 Lake (from the MAPS database) is approximately -11 inches. This 

 places the site toward the less evaporative end of the climatic 

 spectrum for hydrologically similar sample sites, but toward the 

 more evaporative extreme for Rocky Mountain sample sites . Monthly 

 average precipitation for the Fortine climatic station shows 

 relatively even distribution throughout the year, with a moderate 

 peak in May and June. Annual records from the Fortine station show 

 the 3-year running average precipitation has been below the long- 

 term mean during most of the last 30 years. Annual precipitation 

 during the sample year of 1993 exceeded the average for the period 

 of record by approximately 5 inches . 



Geologic setting. The Turtle Lake basin is underlain by calcareous 

 till and possibly other glacial sediment types of late(?) Wisconsin 

 age. Bedrock geologic units are of the Proterozoic Belt Series, 

 probably including the calcareous and dolomitic Helena Formation. 



Hydrologic type. Turtle Lake is a glacial depression with surface 

 water inflow from an intermittent stream but lacking surface water 

 outflow at current water levels. Groundwater outflow is inferred 

 from the moderate salinity of this topographically closed basin, 

 contrasting with nearby Thirsty Lake, which has high salinity and 

 apparently restricted ground-water outflow. 



Basin characteristics. Turtle Lake has a larger surface catchment 

 and considerably larger catchment to wetland area ratio than nearby 

 Alkali Lake. The cluster of lakes in the vicinity display disjunct 

 water quality; Thirsty Lake, nearby and at a lower elevation, 

 exceeds Turtle Lake and Alkali Lake in specific conductance by more 

 than an order of magnitude. Alkali Lake and Turtle Lake display 

 generally similar water chemistry. 



Water chemistry. Turtle Lake is proportionately high in magnesium 

 and is nearly depleted in calcium; equilibrium calculations 

 indicate supersaturation with calcium and magnesium carbonate 

 species. Low calcium concentrations appear to be maintained by 

 solubility controls; deposition of authigenic carbonate minerals 

 is inferred from relatively high extractable calcium concentrations 

 in sediment and from observed marl formation in nearby Alkali Lake. 

 High relative magnesium concentrations are typical of 

 hydrologically similar sample sites. 



The ammonium and total organic carbon concentrations rank toward 

 the upper end of the ranges shown by Rocky Mountain sites. The 

 orthophosphorous concentration ranks mid-range in comparison to the 

 site class. Trace element concentrations are comparatively low 

 with the exception of selenium, which was reported at the detection 

 limit. 



Chemical history. A single previous partial chemical analysis from 

 this water body is known. Dating from June of 1987, this partial 



