Lavlna DOT Mitigation Wetland 



Climatic setting. The net annual precipitation balance for the 

 Lavina site (from the MAPS database) is -29 inches, placing WET43 

 near the more strongly evaporative extreme of the range shown by 

 the sample sites. Mean monthly precipitation for the Barber 

 climatic station shows a June maximum. The 3-year running average 

 of annual precipitation for the Barber station remained below often 

 well below) the long-term average throughout the 1984-1992 period. 

 Annual precipitation in 1993 (the year prior to sampling) exceeded 

 the long-term average by 4 inches. 



Geologic setting. The WET43 site is underlain by alluvium of the 

 Musselshell River and of the unnamed northern tributary draining 

 to the wetland site. The character of the alluvium in the 

 immediate vicinity of the wetland is undescribed; in the general 

 vicinity, the Musselshell alluvium is permeable enough to support 

 wells of low to moderate yield. The Judith River Formation 

 underlies surficial deposits at the wetland site; higher-elevation 

 areas within the northern tributary basin are underlain by Bearpaw 

 Shale. 



Hydrologic type. WET34 is a modified site, apparently receiving 

 inflow from the unnamed northern tributary and (probably) from the 

 groundwater system of the Musselshell River alluvium. The wetland 

 does not appear to have surface water outflow under the sampled 

 conditions. 



Basin characteristics. The contributing catchment for this small 

 site is not well defined. If the catchment is taken to be the 

 northern tributary drainage, the catchment to wetland area ratio 

 ranks mid-range with respect to other sample sites of the 

 unglaciated plains. However, the Musselshell River alluvium 

 (interacting with the Musselshell River throughout the upper river 

 basin) may provide ground-water inflow to the site. The U.S. 

 Highway 12 corridor and excavation for wetland enhancement affect 

 local site hydrology. 



Water chemistry. The WET43 site exhibits moderately alkaline, 

 "oligosaline" sodium-sulfate water chemistry. Mineral equilibria 

 indicate oversaturation with carbonate phases. Ammonium and 

 nitrate concentrations were below reporting limits at the time of 

 sampling; phosphorous (total and orthophosphate) and total organic 

 carbon concentrations are low with respect to sites in the same 

 classification. 



Boron and iron concentrations were reported at the lower end of the 

 ranges for Great Plains sample sites; most other trace elements 

 were below reporting limits. 



Chemical history. No other chemical data for this wetland are 

 known . 



