Wagner Basin Research Natural Area 



Climatic setting. The net annual precipitation balance for Wagner 

 Basin (from the MAPS database) is -6 inches, ranking mid-range 

 among sample sites of the Rocky Mountains. Mean monthly 

 precipitation for the Gibson Reservoir climatic station shows a 

 May-June peak. Total annual precipitation for the Gibson Reservoir 

 station shows apparent periodicity, with the 3-year running average 

 peaking every 4 to 7 years. The 3-year average remained near or 

 below the long-term average throughout the 1980s and was near the 

 long-term average in the early 1990s. In 1993 (the year of the 

 DHES sampling) precipitation exceeded the long-term mean by nearly 

 5 inches. 



Geologic setting. Wagner Basin is underlain by a faulted slice of 

 Paleozoic sedimentary rocks including the Mississippian-aged 

 Madison Group. The wetland is supported by a large spring 

 discharging ground water from the Madison Group(?), or possibly 

 from another carbonate formation in the Paleozoic section. 

 Recharge to the ground-water system probably occurs locally within 

 Wagner Basin. The location of the spring may be controlled by 

 cavernous zones within carbonate aquifer (s) or, possibly, by thrust 

 faults underlying basin. Discharging ground water flows across 

 outwash and terrace gravel sediments fringing the wetland and to 

 the Sun River. Surficial sediments include travertine and tufa 

 deposits precipitated from the discharging ground water. 



Hydrologic type. Wagner Basin receives perennial ground-water 

 discharge from a discrete spring source and intermittent(?) surface 

 runoff. Outflow occurs via an outlet stream and probably by 

 seepage into terrace gravels fringing the wetland. 



Basin characteristics. The catchment to wetland area ratio for 

 Wagner Basin is relatively high compared to most other Rocky 

 Mountain sample sites. Carbonate rocks underlie a large portion 

 of the steep catchment and are inferred to receive ground-water 

 recharge readily. 



Water chemistry. Water sampled at the WET73 site was relatively 

 dilute, slightly alkaline and calcium-sulf ate/bicarbonate in 

 composition. The calcium-sulf ate character of this site is unusual 

 among the unimpaired sample sites; the few other sites with similar 

 proportions of major ion equivalents are in wetlands impacted by 

 acid mine drainage or underlain by notably gypsiferous Colorado 

 Group shales. Wagner Basin's water composition is believed to be 

 influenced by dissolution of calcium sulfate evaporites (gypsum or 

 anhydrite) within the carbonate aquifer(s) drained by the Wagner 

 Basin springs. Mineral equilibria indicate slight over-saturation 

 with carbonate phases and undersaturation with gypsum. 



WET73 was among the minority of sites with reportable nitrate; the 

 orthophosphate concentration ranked mid-range in comparison to 



