Physical, Biological & Chemical Assessment
of Lolo Creek, Montana, Summer 2002
A report to the Missoula County Water Quality District
By Sean Sullivan
Under direction of
Dr. Vicki Watson
UM Watershed Health Clinic
EXECUTIVE SUMMARY (full report available from the UM Watershed Health Clinic)
Lolo Creek drains a rapidly developing watershed in the Northern Rockies of western Montana. Parts of the Lolo Creek mainstem are listed as impaired (not fully supporting aquatic life, cold water fisheries and drinking water uses) by the Montana Department of Environmental Quality (MDEQ 2002a). Probable causes of impairment are listed as siltation, flow alteration, and other habitat alterations, and the probable sources are listed as silviculture, agriculture, construction, land development and habitat modification (other than hydromodification)
A water quality restoration plan for sediment has been developed for the upper watershed and the creek’s headwater tributaries (MDEQ 2002b). Because of the pace of development in this area, a baseline assessment of key physical, nutrient and biological parameters in the main stem was desired. This assessment was intended to determine if nutrients and algae have become problems and to identify and describe any other possible causes of impairment.
Purpose: The purpose of this report is to describe and report the current conditions of Lolo Creek’s main stem, noting any apparent water quality problems and sources of impairment.
1) Summarize key available information on the Lolo watershed (climate, hydrology, soils, geology, land cover/uses);
2) Classify 5 study reaches along the creek by channel type and riparian community type;
3) Assess the physical condition of the stream’s bed and banks at those sites, using the Montana Department of Environmental Quality’s Stream Reach Assessment Form;
4) Measure nutrient concentrations and stream flows in Lolo Creek through the spring and summer of 2002 and estimate nutrient loading to the Bitterroot River. Note any reaches with high nutrient concentrations and potential sources of nutrients;
5) Assess biological indicators of stream condition (attached algae biomass levels and benthic macroinvertebrate community composition);
6) Use the above information to assess support of aquatic life;
7) If uses are impaired, attempt to identify possible causes of impairment and make recommendations for restoring and protecting stream uses and health.
The purpose of this study was to describe and report on the nature and current condition of Lolo Creek’s mainstem, noting any apparent water quality problems and causes of impairment.
1) All the study sites on Lolo Creek were classified as B3 channels types and Populus trichocarpa/ Cornus stolonifera riparian communities except the most upstream site (Lee Creek Campground) which was classified as a B4 stream channel type and a Salix exuga riparian community. A relatively undisturbed reach of Rattlesnake Creek in the Rattlesnake Creek Recreational Area that shared these characteristics was selected as a reference reach for the Lolo Creek study sites.
3) Results of applying the Montana DEQ’s Stream Reach Assessment procedure suggest that much of the creek below the Lee Creek campground is moderately impaired in its aquatic life habitat.
4) Nitrogen concentrations from April through September were below standards and targets set to protect the Clark Fork from nuisance algae. Nitrogen to phosphorus ratios suggest that benthic algae are nitrogen limited in Lolo Creek. No significant sources of nutrient enrichment were observed along the length of Lolo Creek. During the study, Lolo Creek supplied from 1-5% of the TP, TKN & NOx loads to the Bitterroot River and from 1-30% of the SRP load. Given nutrient and benthic algae levels observed during the study, Lolo Creek is not currently impaired by algae or nutrients.
5) Analysis of aquatic macroinvertebrate communities and their habitat suggests that Lolo Creek’s aquatic habitat is moderately impaired downstream of the Lee Creek site to the mouth of the creek. Macroinvertebrate community composition suggests that no extreme thermal or chemical events have negatively affected the instream biota.
6) The physical and biological assessments agree that the 4 sites below the Lee Creek Campground site were moderately impaired, suggesting that the creek only partially supports aquatic life and a cold water fishery. The Lee Creek Campground site was not impaired and may have some usefulness as a reference site for the creek.
7) Causes of impairment appear to be land use practices such, as logging and road building and maintenance (especially Highway 12) in the upper watershed. In the lower watershed, additional impacts include dewatering, recreational use and encroaching development.
This study provided evidence that habitat conditions such as stream bank instability, channel alteration and narrow riparian zones negatively affect the ability of Lolo Creek to support aquatic life. Hence the following recommendations are made for actions to improve habitat conditions.
Re-vegetation of unstable stream banks (found at all sites except Ft Fizzle) would likely improve instream habitat conditions for aquatic life. At sites disturbed by Highway 12 ( Lee and Lolo Creek Campgrounds), new riprap should be avoided, and revegetation should be especially aggressive. At Traveler’s Rest and Bantam Acres, rehabilitation could include restricting access to the creek by foot, thus limiting compaction and erosion potential.
Aggressive restoration efforts that make dramatic changes in creek morphology or hydrologic function at some sites could cause undesired changes at other sites as well as causing short term water quality degradation. Hence small restorative steps coupled with continued assessment are recommended to improve overall conditions on Lolo Creek.
Future Monitoring and Studies
This study was conducted primarily on public lands and could misrepresent the creek’s overall condition. If there is sufficient interest, assessments could be conducted on private lands to provide a more complete picture of the creek.
Repeating this study’s assessments about every 5 years could serve as a long term monitoring program that would help detect future changes and establish a long term record of the creek’s habitat condition.
Photodocumentation is a particularly effective long term monitoring tool. Photos collected in this study and their locations are provided in a separate CD and could form the basis for a long term photo record.
Algae and nutrient levels in Lolo Creek indicate that algae is currently limited below nuisance levels by low N levels. However, with increasing development and disturbance in the watershed, N levels are likely to rise, and algae could become a problem. Hence it would be helpful to enlist citizens in visual monitoring of algae levels (the UM Watershed Health Clinic can provide training to interested citizens). In addition, every 5 years, nutrient levels could be reassessed, especially in winter or early spring before nutrients are depleted by algal uptake, to see if levels are rising. Future nutrient levels could be compared to nutrient levels measured in this study and in Boer’s study (2002) of septic-derived nutrients in the Lolo area.