Hoskins Lake Research Natiiral Area 



Climatic setting. The net annual precipitation balance for Hoskins 

 Lake (from the MAPS database) is 7 inches, placing the site among 

 the two wettest low-elevation sites in the sample set. Average 

 monthly precipitation for the Troy 18NE climatic station shows a 

 winter peak with a maximum in November. The records of annual 

 total precipitation for the station are incomplete; available 

 records from 1980 to 1991 show modest deviations from the average 

 in both directions. 



Geologic setting. Hoskins Lake occupies a glacially eroded trough 

 paralleling the Yaak River valley and following the trace of one 

 of a series of north-trending normal faults; preferential erosion 

 along the fault may have influenced the location and orientation 

 of the lake basin. The lake basin is underlain by paludal, 

 lacustrine and (probably) glacial deposits of undescribed 

 character. The underlying bedrock is composed of the Wallace 

 Formation of the Proterozoic-aged Belt series; the Wallace 

 Formation is dominantly argillaceous in composition but includes 

 a significant calcareous component. Locally, calcareous interbeds 

 in the Wallace Formation are described as frequently pyritic. 



Hydrologic type. The upper open-water portion of Hoskins Lake 

 (sometimes known as Hoskins Pond), where the WET28 site is located, 

 has a discrete surface water outflow to Hoskins Lake but no 

 channelized surface water inflow. Hoskins Lake itself has surface 

 water drainage to the Yaak River. The outflow from Hoskins Pond 

 has been described as intermittent, but no data regarding it's flow 

 characteristics are known. 



Basin cheuracteri sties. Hoskins Lake and Hoskins pond occupy a 

 single linear bedrock basin with a veneer of glacial(?) and 

 Holocene sediments, separated by a minor topographic high and a 

 vegetated wetland surface. The catchment to wetland area ratio is 

 mid-range for Rocky Mountain sites; local relief is steep. The 

 maximum depth reported for Hoskins Pond is 8.5 meters (27.5 feet). 

 Based on topographic position, the lake basin may receive ground- 

 water discharge from the Belt series bedrock. The dilute water 

 chemistry suggests ground-water to be a minor hydrologic input, 

 however . 



Water chemistry. Hoskins Pond exhibits mildly alkaline, very dilute 

 calcium-bicarbonate water. For a site of such dilute chemistry, 

 WET28 shows an unusually high ratio of sulfate to bicarbonate, 

 possibly reflecting the presence of sulfide minerals (pyrite) in 

 the local Wallace Formation outcrops. Equilibrium calculations 

 indicate substantial undersaturation with resect to carbonate 

 minerals. 



The nitrate and total organic carbon concentrations at WET28 ranked 

 mid-range among Rocky Mountain sites, while the ammonium 

 concentration was below detection limits. The orthophosphorous 



