Leihrity Lake Southwest wetland 



Climatic setting. The net annual precipitation balance for the 

 Lahrity Lake Southwest site (from the MAPS database) is -17 inches, 

 placing the site toward the middle of the range for hydrologically 

 and regionally similar sites. Monthly average precipitation for 

 the Ovando 9 SSE climatic station shows a bimodal distribution, 

 with a primary June peak and a secondary January peak. The 3-year 

 moving average of total annual precipitation remained below (often 

 considerably below) the long-term average from the mid-1970s 

 through 1993. The total precipitation for 1993 (the year prior to 

 sampling) was very near the long-term average. 



Geologic setting. Lahrity Lake Southwest occupies a shallow 

 glacial ice-block(?) depression in till (and other glacial 

 sediments?) deposited by ice advancing into the Ovando Valley from 

 the Monture Creek drainage. The adjacent bedrock outcropping of 

 Monture Hill is a prominent resistant knob underlain by the 

 Snowslip Formation of the Proterozoic Belt series. The Monture 

 Creek source area for the glacial deposits in the area includes 

 large exposures of the calcareous and dolomitic Helena Formation. 



Inspection of the glacial sediments surrounding Lahrity Lake shows 

 abundant cobbles and boulders in a calcareous silty matrix. 



Hydrologic type. The Lahrity Lake southwest site is a relatively 

 shallow glacial depression with at least seasonal surface water 

 outflow. The outlet elevation prevents water levels in the wetland 

 from rising substantially above that observed at the time of 

 sampling. The wetland surface was approximately 7.9 feet higher 

 than the surface elevation of adjacent Lahrity Lake, possibly 

 restricting ground-water outflow from Lahrity Lake to the south. 



Basin characteristics. The Lahrity Lake Southwest wetland appears 

 to capture a larger area of surface drainage than Lahrity Lake 

 proper, and has a higher catchment to wetland area ratio. Surface 

 drainage and low volume (estimated maximum depth of 3-5 feet) imply 

 relatively rapid flux of water and solutes through the site when 

 compared to Lahrity Lake. Head relationships preclude this site 

 from receiving ground-water outflow influenced by the Lahrity Lake 

 brine. 



Water chemistry. At the time of sampling, WET35 exhibited 

 moderately alkaline "oligosaline" water lacking strongly dominant 

 cation characteristics. Calcium, magnesium, sodium and potassium 

 concentrations (in raeg/1) were all within a factor of five of each 

 other - an unusual distribution among the sample sites. C02 

 species (bicarbonate and carbonate) dominate the anion 

 distribution. Eguilibrium calculations indicate substantial 

 oversaturation with carbonate minerals. 



The ammonium concentration reported for WET35 was the highest of 

 any of the sample sites. Total organic carbon, orthophosphorous 



