LAND USE AND AQUATIC BIOINTEGRITY IN THE BLACKFOOT RWER WATERSHED, MONTANA¹

Abstract

Benthic macroinvertebrate samples representing 151 taxa were collected in August 1995 to examine the linkage between land use, water quality, and aquatic biointegrity in seven tributaries of the Blackfoot River watershed, Montana. The tributaries represent silvicultural (timber harvesting), agricultural (irrigated alfalfa and hay and livestock grazing), and wilderness land uses. A 2.4 km (1.5 mile) reach of a recently restored tributary also was sampled for comparison with the other six sites. A geographic information system (GIS) was used to characterize the seven subwatersheds and estimate soil erosion, using the Modified Universal Soil Loss Equation, and sediment delivery. The wilderness stream had the highest aquatic biointegrity. Two agricultural streams had the largest estimated soil erosion and sediment delivery rates, the greatest habitat impairment from nonpoint source pollution, and the most impoverished macroinvertebrate communities. The silvicultural subwatersheds had greater rates of estimated soil erosion and sediment delivery and lower aquatic biointegrity than the wilderness reference site but evinced better conditions than the agricultural sites. A multiple-use (forestry, grazing, and wildlife management) watershed and the restored site ranked between the silvicultural and agricultural sites. This spectrum of land use and aquatic biointegrity illustrates both the challenges and opportunities that define watershed management. (KEY TERMS: macroinvertebrates; aquatic ecosystems; land use; GIS; biomonitoring; nonpoint source pollution; sediment delivery; soil erosion; watershed management.)1Paper No.

Effects of Adjacent Agricultural Activities and Watershed Characteristics on Stream Macroinvertebrate Communities

“…aquatic macrophytes was greater at the cow sites than the corn sites and most of the locations of the reference sites (the exception being the downstream locations of Reference Site 2), as has been reported in other studies of agriculturally impacted streams (Dance and Hynes, 1980;Delong and Brusven, 1998;Rothrock et al, 1998;Harding et al, 1999).…”

“…Plecoptera richness and the relative percent composition of shredders and stoneflies are predicted to decrease with increasing human disturbance (Kerans and Karr, 1994;Barbour et al, 1999), with shredders becoming rare in some agricultural streams (Dance and Hynes, 1980;Lenat and Crawford, 1994;Delong and Brusven, 1998;Rothrock et al, 1998;Harding et al, 1999). These patterns were evident in this study.…”

Changes in agricultural intensity and river health along a river continuum

“…It is widely accepted that agricultural activities result in a wide array of negative effects on river systems (Schlosser & Karr, 1981;Hughes et al, 1986;Carpenter et al, 1998;Rothrock, Barten & Ingman, 1998); however, several attempts to demonstrate changes in ecosystem health have led to conflicting results. Middle-aged farmers remarked on their ability to swim in the lower reaches of the river during their childhood (today they would not let their children swim there), and being able to clearly see fish and crayfish on the bottom of the riverbed in the lower reaches, something which is not possible today.…”

Headwater stream response to grassland agricultural development in New Zealand

“…Alterations to nutrient loading (Cooper & Thomsen 1988;Biggs & Close 1989;Allan et al 1997), solar energy flux and organic matter inputs (Hicks 1997), hydrology (Davies-Colley 1997), and sediment inputs (Rothrock et al 1998;Nerbonne & Vondracek 2001;Zweig & Rabeni 2001) have been implicated as factors that influence community and ecosystem parameters such as biodiversity, nutrient cycling, energy flux, and food-web characteristics. Identification of the suite of changes to inputs to stream systems and how systems respond to these changes is important if we are to make further progress in mitigating the effects of land use practices on aquatic systems.…”