Watersheds & Wetlands

Mica Creek Study

The Mica Creek Experimental Watershed is a paired and nested watershed study in Shoshone County in northern Idaho. This long-term watershed study (1990 – current), which is evaluating effects of best management practices (BMPs) of roads, clear cut, and partial cut harvesting, has been largely supported and funded by PotlatchDeltic, with supplemental support from NCASI.

The primary goals are to assess BMP effectiveness on fish populations, evaluate potential to use well-validated models as virtual control watersheds, and develop novel approaches to use dissimilarly-sized watershed pairs to assess BMP effectiveness. We will also work with cooperators to assess effectiveness of the Idaho forest practice rules in protecting water quality, including seasonal and long-term trends.

This includes analyzing water samples for orthophosphate, nitrate/nitrite, and total nitrogen.

Participating organizations include PotlatchDeltic Corporation, University of Idaho, and NCASI. Partial funding support has been provided by USDA’s National Research Initiative.

Below is the abstract of a paper from the Mica Creek study titled: “Nutrient concentration dynamics in an inland Pacific Northwest watershed before and after timber harvest” (Forest Ecology and Management 257:1663-1675).

Authors of the study include J.A. Gravelle (University of Idaho), G. G. Ice (NCASI), T.E. Link (University of Idaho) and D.L. Cook (NCASI). Study outcomes include post-harvest increases in NO3 + NO2 concentrations were statistically significant but small in magnitude (<1 mg L-1).


“The nutrient loads of water draining forested watersheds are generally lower than the loads in water draining basins with other dominant land uses. Commercial forest management activities including timber harvesting, site preparation, road construction, and maintenance can alter the chemical properties of headwater forest streams, and there are concerns this can result in cumulative effects at downstream locations. Monthly water samples were collected from 1992 to 2006 in the Mica Creek Experimental Watershed (MCEW) in northern Idaho. This period of record included a pre-treatment time interval from 1992 to 1997; post-road construction period from 1997 to 2001; and post-harvest period from 2001 to 2006. Samples were analyzed for total Kjeldahl nitrogen (TKN), total ammonia nitrogen (TAN), nitrate + nitrite (NO3 + NO2), total phosphorus (TP), and orthophosphate (OP). Statistically significant increases (p < 0.001) were observed in NO3 + NO2 concentrations following both clearcut and partial cut harvest practices. Downstream of the clearcut harvest activity, mean monthly increases of 0.29 mg-N L-1 were observed. Statistically significant increases were also observed at sites further downstream, but changes were smaller than those immediately below the harvest sites and reflected dilution and possibly instream processing and/or uptake. Continued monitoring at these sites will help evaluate nutrient concentration trends during stand regrowth and hydrologic recovery.”