Hewitt Lake National Wildlife Refuge 



Climatic setting. The net annual precipitation balance for the 

 Hewitt Lake site (from the MAPS database) is -28 inches, placing 

 the site at the more evaporative end of the range shown by sites 

 in this classification. Monthly mean precipitation for the Malta 

 7NE climatic station shows a broad summer peak with a maximum in 

 May; the Malta climatic station, with a longer period of record but 

 farther from Hewitt Lake, shows a pronounced June maximum. Annual 

 totals for the Malta 7NE station, shows the years 1988 to 1992 

 below the average for the period of record. The total for 1993 

 (the year prior to sampling) exceeded the average for the period 

 of record by about 2 . 5 inches . 



Geologic setting. The Hewitt Lake catchment is underlain by the 

 Late Cretaceous Claggett Shale. Although the area is within the 

 extent of Pleistocene glaciation, glacial deposits in the immediate 

 Hewitt Lake area may be thin or absent. Hewitt Lake lies near the 

 apex of the Bowdoin structural dome, apparently the trap for 

 natural gas reservoirs exploited by the well field surrounding the 

 refuge. 



Hydrologic type. Hewitt Lake is an impounded reservoir with a 

 surface water outlet structure; Hewitt Lake is the at the 

 downstream end of a series of intermittent natural lakes and ponds, 

 and may have a pre- impoundment history as a smaller natural basin. 

 Hewitt Lake has been dry or essentially dry during some recent 

 drought years. The history of discharge from the Hewitt Lake 

 outlet structure is not known. 



Basin characteristics. Hewitt Lake's catchment to wetland area 

 ratio ranks in the mid-range among sample sites in it's 

 classification. Depth and volume of the Hewitt Lake basin are not 

 known. Based on the geologic setting, ground water is not thought 

 to be an important contributor to Hewitt Lake's water budget. 

 Storage in (and evaporation from) intermittent lakes and ponds in 

 the Hewitt Lake catchment probably influence the runoff 

 characteristics of the basin. 



Water chemistry. At the time of sampling, Hewitt Lake contained 

 alkaline, "oligosaline" water of sodium sulfate character. Mineral 

 equilibria indicate moderate oversaturation with respect to 

 carbonate phases. The nitrate concentration was below detection 

 limits, and the ammonium concentration ranked mid-range among sites 

 in the same classification. The orthophosphorous concentration 

 ranked mid-range for sample sites of this classification, but the 

 total phosphorous concentration ranked near the upper end of the 

 range shown by the sample set overall. 



The Hewitt Lake water column contains an enriched suite of trace 

 metals relative to other sites of the glaciated plains, looking 

 more like sample sites of south-central Montana in this respect. 

 Concentrations of chromium, copper, iron, lead and zinc rank at the 



