Blackfoot Waterfowl Production Area 



Climatic setting. The net annual precipitation balance for the 

 Blackfoot WPA (from the MAPS database) is -12 inches, putting the 

 site toward the moist end the range shown by this site class. Mean 

 monthly precipitation for the Ovando 9SSE climatic station shows 

 a bimodal distribution, with a primary June maximum and a secondary 

 January peak. The 3-year running average of total annual 

 precipitation for this station has remained below (often well 

 below) the long-term average for most of the period since the mid- 

 1970s. Total precipitation in 1993 (the year of sampling) 

 approximated the long-term average. 



Geologic setting. The Blackfoot WPA site is underlain by late 

 Pleistocene glacial outwash(?) elevated a few feet above, and 

 graded to, the floodplain of the nearby Blackfoot River. The 

 source area for the glacial sediments is the basin of the North 

 Fork of the Blackfoot River. 



Bedrock in the small contributing catchment includes formations of 

 the Ravalli Group of the Proterozoic Belt series and Cretaceous and 

 Tertiary igneous rocks. Mineralization associated with these 

 igneous rocks occurs nearby. Formations exposed in the North Fork 

 basin include Proterozoic and Cambrian limestone and dolomite. 



Hydrologic type. The Blackfoot WPA site is a shallow glacial basin 

 (kettle?) augmented by dikes and equipped with an outlet control 

 structure. Prior to the WPA enhancement project, the natural 

 wetland had been ditched and largely drained. Inflow to the 

 wetland is via culverts beneath Highway 200, which isolates the 

 site from most of it's natural surface catchment and from reported 

 spring sources on the upgradient side of the road. 



Basin characteristics. The broad, shallow(?) natural basin of this 

 wetland has been altered by both diking and excavation to provide 

 deeper-water and more perennial conditions. The natural catchment 

 is relatively small relative to the wetland area, but ground-water 

 discharge apparently supporting the wetland would not necessarily 

 be expected to follow the low northern drainage divide. Surface 

 drainage from upgradient areas is altered by the existence of 

 Highway 200. 



Water chemistry. Water collected from the Blackfoot WPA was 

 relatively dilute, mildly alkaline and dominated by bicarbonate, 

 calcium and magnesium ions. Mineral equilibria indicate slight 

 undersaturation with carbonate phases. Nitrate, ammonia and 

 orthophosphorous concentrations were low; the total organic carbon 

 concentration was mid-range for sample sites similarly classified. 



Arsenic and copper were found at concentrations near the lower end 

 of the ranges shown by sites of this class. Most other trace 

 element concentrations were below detection limits. 



