Western North American Naturalist 60(3), © 2000, pp. 255–272 A COMPARISON OF RIPARIAN CONDITION AND AQUATIC INVERTEBRATE COMMUNITY INDICES IN CENTRAL NEVADA Tom B. Kennedy1,3, Adina M. Merenlender2,4, and Gary L. Vinyard1,5 [Authors are listed alphabetically] ABSTRACT.—The importance of maintaining healthy riparian communities to sustain natural stream processes and function is well documented. Land management agencies in the West are currently developing methods to assess and monitor riparian community condition to adapt land use practices that would better protect rangeland ecosystems. To determine whether these methods also provide an indication of abiotic and biotic stream condition, we compared the classification system of riparian communities developed by the U.S. Forest Service (USFS) to physical parameters of stream condition and to aquatic invertebrate community assemblages. Thirty-three sites in 19 different streams of the Toiyabe Range in central Nevada were measured for water quality, substrate characteristics, and fish abundance and diversity. We sampled aquatic invertebrates and calculated community indices based on environmental tolerance levels, taxonomic diversity, and abundance of sensitive taxa. USFS personnel classified these sites by dominant riparian plant community type (meadow, willow, or aspen) and ecological status (low, moderate, or high) using plant abundance data, rooting depth, and soil infiltration to determine similarities to potential natural communities. Riparian condition indices as well as community diversity were significantly correlated to proportions of fine and small-diameter substrate in streambeds. Accumulation of silt was significantly related to plant community type, with meadow sites expressing highest proportions. Further examinations indicated that 2 of 6 invertebrate community indices were significantly related to ecological status, with highest diversity levels occurring mainly in willow- and aspen-domi- nated sites in moderate ecological condition. Nevertheless, we show that several other environmental variables, including substrate characteristics, dissolved oxygen, water temperature, and species richness of fish communities, were more strongly and consistently related to invertebrate assemblage patterns. Our results demonstrate that information on aquatic invertebrates and stream condition could augment the existing riparian classification system and provide useful monitoring tools to more thoroughly examine ecosystem health in rangelands. Key words: Toiyabe, Great Basin, rangeland, aquatic invertebrates, biotic indicators, riparian condition, ecological status, diversity measures. Healthy riparian plant communities are peak velocities of high flows, thereby reducing essential components for proper stream eco- energies that could otherwise erode banks, system processes and function (Karr and elevate sediment loads, and widen channels Schlosser 1978, Gregory et al. 1991, Elmore (Schumm and Meyer 1979). By stabilizing soils, 1992, Edwards and Huryn 1996, Friberg robust vegetation also helps reduce potential 1997). Riparian zones in rangelands provide damage that could result from land manage- critical sources of diversity and biomass pro- ment activities such as livestock grazing (Platts ductivity for both plant and animal species 1981, Swanson et al. 1982). (Thomas et al. 1979). Stream bank vegetation The U.S. Forest Service (USFS) has esti- also produces essential organic matter for head- mated that 22% of riparian habitat under its water communities (Cummins 1974, Cummins jurisdiction is not meeting their natural resource and Spengler 1978) as well as processed mate- objectives (USDI Bureau of Land Manage- rial for downstream catchments (Kennedy 1977). ment and USDA Forest Service 1994). One Moreover, riparian habitat condition exerts a recently developed method used to improve strong influence on stream channel morphol- rangeland condition assessment is the Ecolog- ogy. Riparian plant root systems increase bank ical Status Riparian Determination scorecard stability, and streamside vegetation attenuates developed by the USFS Humboldt-Toiyabe 1Biological Resources Research Center, University of Nevada–Reno, Reno, NV 89557-0015. 2Center for Conservation Biology, Stanford University, Stanford, CA 94305 3Present address: Sierra Nevada Aquatic Research Lab, Star Route 1, Box 198, Mammoth Lakes, CA 93546. 4Present address: Environmental Science, Policy, and Management, University of California–Berkeley, Berkeley, CA 94720-3110. 5Deceased. 255 256 WESTERN NORTH AMERICAN NATURALIST [Volume 60 National Forest Ecology Team (Weixelman et al. Table 1). Soil condition ratings based on color 1996, 1997, 1999). Managers using this method of surface layers, depth of fine roots, and infil- measure impacts of disturbance to riparian tration tests of water absorption were used to corridors by comparing existing soil and plant adjust these classifications. Eight low-, 12 mod- communities to presumed potential natural erate-, and 13 high-condition sites were sam- communities (PNC) at selected reference sites. pled, with meadow riparian bank vegetation These scorecards classify soil and vegetation occurring at 12 sites, willow species dominat- communities into low, moderate, or high eco- ing at 11 sites, and aspen at 10 (Fig. 2). logical status ratings. Soil and plant community We collected 5 invertebrate samples using ratings are based on color and permeability of an upper-frame Winget-modified Surber net soil surface layers, plant species composition (Winget and Mangum 1979) in June 1994 at and abundance, litter cover, and rooting depths. each site from similar microhabitats reflecting Managers use this evaluation system to identify dominant substrate conditions and flow regimes habitat that may require rest from livestock (Hauer and Resh 1996). All samples were pre- grazing, presumably before damage becomes served in 95% isopropyl alcohol. Invertebrates irreparable. Although this evaluation may pro- were identified in the lab using Usinger (1956), vide a useful indication of riparian condition, Edmondson (1959), Thorp and Covich (1991), it may not address aspects of stream condition, and Merritt and Cummins (1996). Difficult which is of primary importance to the mainte- taxonomic identifications were sent to the nance of healthy rangeland ecosystems (National USDA Aquatic Ecosystem Laboratory at Brig- Research Council 1994). ham Young University in Provo, Utah, for veri- Stream invertebrate communities have been fication. routinely used and recommended as biological At 17 sites where fish were present, we indicators of habitat degradation from land use completed population estimates using 3-pass practices (Plafkin et al. 1989, Rosenberg and depletion sampling with an electrofisher. Cap- Resh 1993, Barbour et al. 1995, Resh et al. tured fish were identified, weighed, measured, 1995), including impacts from livestock graz- and released. Total reach lengths surveyed ing (Bauer and Burton 1993). Aquatic inverte- (combined upstream and downstream sections brate communities are useful monitors because from the invertebrate sampling point) varied they integrate ecological conditions both tem- from 20 to 66 m, depending on stream order. porally and spatially. Our research explores We measured section widths at the upstream whether the USFS riparian classification sys- seine net, middle of the reach, and downstream tem reflects abiotic and biotic components of net, and then averaged them. Estimated den- associated streams. To address this, we com- sities (fish ⋅ m–2) extrapolated to zero-effort pared condition ratings of riparian communi- were calculated using regression equations for ties derived from the USFS Ecological Status each of the 2 sections and averaged. Cumula- Riparian Determination methodology to abi- tive species captured from the 2 reaches were otic measures and community assemblages of recorded with no adjustments made. aquatic invertebrates in streams of central We also measured water quality parameters Nevada. that affect habitat conditions for aquatic organisms. Mean daily water temperature (°C) METHODS was recorded at 2-h intervals for the month using Hobo digital data loggers. Replicate Fieldwork water samples were collected with sterilized Thirty-three sampling sites were located in Nalgene containers and analyzed that same 19 different drainages (Fig. 1). Region 4 staff day under laboratory conditions. Ammonia of the USFS surveyed plant and soil commu- (NH3–N), nitrite (NO2–N), nitrate (NO3–N), nities at each of these sites using the Ecologi- and orthophosphate phosphorus (PO4–P) con- cal Condition scorecard methodology (Weixel- centrations (µg L–1) were measured using a man et al. 1996). Dominant plant communities portable spectrophotometer. Alkalinity (µeq were typed and rated for percent similarity to L–1) was measured using titration with a phe- PNC and grouped into 3 ecological status cat- nolphthalein indicator (Wetzel and Likens egories based on litter cover and abundance of 1991). Total dissolved residues (mg L–1) were vegetative species (low, moderate, and high; quantified by filtering 200-mL samples onto 2000] RIPARIAN AND AQUATIC COMMUNITY INDICES 257 Fig. 1. Study site locations in the Toiyabe Range, Nevada. pre-weighed 0.50-µm glass fiber filters that YSI meters. Primary production (chlorophyll were evaporated to dryness for 1 d, folded in a) was assessed by placing 10 glass microscope foil wraps, dried overnight in an oven set to slides into fitted plexiglas