Dudley Slough Preserve 



Climatic setting. The net annual precipitation balance for the 

 Dudley Slough (from the MAPS database) is -12 inches, ranking the 

 site as one of the more strongly evaporative of Rocky Mountain 

 sites. Mean monthly precipitation for the Fortine climatic station 

 shows a relatively even seasonal distribution with a June maximum. 

 Annual totals show the 3-year running mean remaining below the long 

 term mean for most of the period from 1970 to 1987. Total 

 precipitation in 1993 (the year prior to sampling) was about 5 

 inches above the long-term mean. 



Geologic setting. Dudley Slough lies in glaciated terrain and is 

 inferred to be underlain by till and possibly other late 

 Pleistocene glacial sediments. Based on available source 

 lithologies, glacial deposits can be inferred to be calcareous. 

 Bedrock formations underlying the site are of the Proterozoic Belt 

 series, including the calcareous Siyeh Formation. Glacial 

 processes have given the general area a prominent northwest 

 trending drumlinoid lineation. 



Hydrologic type. Dudley Slough is a natural glacial depression with 

 channelized surface water inflow and outflow. 



Basin Chzuracter istics . The catchment area to wetland surface area 

 ratio for Dudley Slough ranks mid-range among sample sites of 

 similar type. The maximum reported depth of the pond is 6 meters. 



Water chemistry. Dudley Slough contains relatively dilute, 

 moderately alkaline calcium-magnesium/bicarbonate water. Mineral 

 saturation indices indicate moderate oversaturation with carbonate 

 species; authigenic carbonate deposition appears to be verified by 

 the exceptionally high extractable calcium concentration reported 

 for Dudley Slough sediments. Nitrate, ammonium and 

 orthophosphorous concentrations were below detection limits. The 

 total phosphorous concentration ranked in the mid-range for sample 

 sites of this type, and the total organic carbon concentration was 

 toward the lower end of the range for all sample sites. Copper was 

 reported at the detection limit, and other trace elements were 

 below detection limits. 



Chemical history. A single previous partial chemical analysis is 

 known for a sample collected in July of 1988. The reported 

 specific conductance at that time was 75% of the August 1994 value. 

 The concentrations of major cations and of alkalinity were very 

 close in the two samples (raising some doubt about the 1988 

 specific conductance measurement.) Trace element concentrations 

 were not analyzed for the 1988 sample. Generally, variability is 

 not expected to be very great at this site. 



Sediments. A very high extractable calcium concentration probably 

 indicates a high fraction of authigenic calcium carbonate in Dudley 

 Slough's sediments. Arsenic, aluminum and iron concentrations were 



