Semds Waterfowl Production Area 



Climatic setting. The net annual precipitation balance for the 

 Sands WPA (from the MAPS database) is -27 inches, placing Sands 

 toward the more evaporatively intense end of the range shown for 

 sites of the glaciated plains. Mean monthly precipitation for the 

 Havre climatic station shows a prominent June maximum. Total 

 annual precipitation for the Havre station shows apparent 

 periodicity, with peaks in the 3-year running average every 4 or 

 5 years. From 1988 to 1990, the running average was below the 

 long-term mean. From 1991 through 1993, the running average met 

 or exceeded the long-term average. 



Geologic setting. The WET61 site (part of the Sands WPA situated 

 on Halfway Lake, but not to be confused with nearby Sands Lake) is 

 underlain sandstone and shale of the late Cretaceous Judith River 

 Formation and, at the northern end of the lake, the late Cretaceous 

 Bearpaw Shale. The catchment contributing to Halfway Lake exposes 

 significant areas of Tertiary volcanic rocks in addition to the 

 sedimentary rocks underlying Halfway Lake. Surficial deposits are 

 inferred to include lacustrine sediments within the lake basin and 

 glacial deposits(?) in lower-elevation portions of the Halfway Lake 

 catchment; descriptions of surficial sediments are not available 

 for the area, however. 



Hydrologic type. Halfway Lake has surface water inflow from a 

 large catchment and no apparent surface water outflow. The origin 

 of the lake basin is uncertain; glacial processes and structural 

 geologic controls may both contribute to the basin's presence. 

 Basin characteristics. Halfway Lake has a relatively large natural 

 catchment and a catchment to wetland area ratio ranking mid-range 

 among Great Plains sampling sites. Water is also imported into the 

 catchment from the Beaver Creek basin to the west; some of this 

 imported water may contribute to Halfway Lake. The depth and 

 volume of the lake are unknown, but low basin gradients suggest 

 shallow lake depths and transient shoreline position. The WET61 

 site is very near one the lake's inlet streams and may during 

 runoff conditions show more dilute water chemistry than other point 

 in the lake. 



Water chemistry. At the time of sampling, WET61 exhibited near- 

 neutral, "oligosaline" sodium-bicarbonate water quality 

 characteristics and a depressed dissolved oxygen concentration. 

 The sampling hour (8:30 am) suggests that the DO depression may be 

 due to overnight plant respiration in a productive setting. The 

 ammonium concentration ranked mid-range in comparison to sites in 

 this classification; phosphorous and total organic carbon 

 concentrations were high, with the phosphorous concentrations 

 (total and orthophosphate) exceeded mainly at sites much more 

 saline than Halfway Lake. 



Arsenic and boron concentrations rank mid-range within this site 

 class, while copper, iron, lead and zinc concentrations were 



