Big Lake 



Climatic setting. The MAPS database value for the net annual 

 precipitation balance at Big Lake is -28 inches, placing the site 

 among the most strongly evaporative of the sample wetlands. Mean 

 monthly values for the Rapelje climatic station show a strong May- 

 June peak in precipitation. The 3-year running average of total 

 annual precipitation appears to show periodicity, with 6 to 9 years 

 between peaks. Between 1975 and 1992, the 3-year average remained 

 at or above the long-term mean during most year. Data for 1993 and 

 1994 were not retrieved for this station. 



Geologic setting. According to published geologic mapping, the Big 

 Lake basin is underlain by the Bearpaw Shale and lies along the 

 eastern limb of the Lake Basin Anticline, a structural trap for 

 hydrocarbons which supports oil and gas production in the area. 

 Outcrops in the immediate vicinity of WET06 are a well-cemented, 

 medium grained sandstone believed to be the Virgelle Sandstone. 

 Surficial sediments at the sampling site are composed of moderately 

 well-sorted sand, with finer grained material accumulated in 

 surface depressions created during the alteration excavation and 

 alteration of the site. 



Hydrologic type. Big Lake proper is a structurally controlled 

 depression lacking surface outflow, which receives runoff from the 

 entire Cedar Creek basin. The WET06 site is a reconstructed basin 

 at the inlet to Cedar Creek, intended to retain water from Cedar 

 Creek during low-water periods. The WET06 site drains to the 

 greater Big Lake basin, which has slightly lower elevation than the 

 reconstructed wetland. Water also probably exits the sample site 

 by infiltration into the sandy, recently disturbed substrate. 



Basin characteristics. The large ephemerally flooded Big Lake 

 basin has a low ratio of catchment to wetland area. The small 

 wildlife enhancement site sampled at WET06, however, has a very 

 high catchment to wetland ratio. The enhancement site is controlled 

 by overflow to Big Lake proper at a maximum water depth of 

 approximately 3 feet, or about 1.5 feet deeper than during the 

 conditions observed in October 1994. Turnover of water in the 

 sample site would be relatively rapid during Cedar Creek runoff 

 events. Excavated depths vary within the enhancement site. 



Water chemistry. At the time of sampling, the WET06 site contained 

 "hypersaline" sodium sulfate water with relatively low bicarbonate 

 and carbonate concentrations. Mineral equilibria indicate 

 substantial oversaturation with carbonate species and near- 

 equilibrium with gypsum (corroborated by the formation of 

 authigenic gypsum(?) in samples collected in October 1994). 



Phosphorous concentrations were moderate in comparison to 

 hydrologically similar sites, while the ammonium and total organic 

 carbon concentrations were toward the high end of the range for 

 sites of this type. 



