Bioassessment I: Lotic Studies
Presiding: J A Latimore, Huron River Watershed Council; M Moeykens, US Environmental Protection Agency
NB23A-01 13:30h
Basin Scale Evaluation of Stream Invertebrate Community Functional Organization
Invertebrate community functional organization was studied at the basin scale in the Freshwater Creek catchment in northern California in August and September, 2004. Timed, D-frame net samples were taken in six tributaries (study reaches 0.5 - 2.7 km) and two sections of the mainstem (3.4 and 4.5 km) of Freshwater Creek. The 317 samples from 106 sites were collected by habitat (cobble, 167; riparian litter, 82; fine sediments, 36; large woody debris, 32). The sample sites matched randomly selected locations within a sample frame of a concomitant juvenile salmonid survey. Juvenile salmonid stomach samples were also taken at each invertebrate survey site. Shredders and total collectors each dominated one tributary and one mainstem reach and scrapers dominated four tributaries. Using the invertebrate ecosystem surrogate method developed by Cummins and Merritt, half of the tributaries/mainstem reaches were characterized as heterotrophic, the other half as autotrophic. The invertebrate functional group community organization was strongly correlated with habitat type but, in general, the relationship with salmonid abundance was indirect. Initial analysis of juvenile salmonid stomachs from one stream (Cloney Gulch) indicated that food availability was good for drift-feeding fish.
NB23A-02 13:45h
Evaluation of Arctopsyche grandis (Hydropsychidae) as a Biological Monitoring Tool in Rocky Mountain Streams
Trace metal loading has been shown to cause marked disturbance in benthic invertebrate communities of Rocky Mountain streams. Metal concentrations in invertebrate tissues are commonly measured in biological monitoring studies as an indicator of metals contamination in the stream. Comparisons of metal body burdens across sampling sites and occasions carry the assumption that burdens reflect metal bioavailability in the field. Laboratory experiments were conducted with indigenous, larval, net-spinning caddisflies (Arctopsyche grandis) to evaluate this important assumption. Caddisfly larvae were exposed to a range of zinc (50 to 1000 ppb) and copper (10 to 360 ppb) concentrations for 96 hours. Water hardness (50, 100 ppm) and dissolved organic carbon (3, 6 ppm) concentrations were systematically varied in order to estimate differences in metal burdens due to changes in aqueous chemistry. Whole individual larvae were analyzed for trace metal concentrations. Results suggest that larval A. grandis are capable of regulating internal zinc concentrations. Surprisingly, maximum zinc burdens were observed where hardness and DOC were highest. Conversely, copper accumulation was reduced by 30 percent where DOC (3 ppm) was added to the exposure medium. Results will be discussed with respect to their significance for future biomonitoring efforts.
NB23A-03 14:00h
Resilience as a Component of Ecological Health: Lessons From Stream Ecosystems
Ecological health may be described as a product of system function, structure, and resilience to disturbance. Measures of ecological function, including abundance, productivity, and biomass, are relatively simple to obtain in the field, as are measures of structure, such as species richness and diversity. However, determination of resilience is less than straightforward because of its dependence on the nature of the disturbance and on the choice of endpoints for recovery. We experimentally investigated the recovery process in temperate warmwater stream fish assemblages subject to controlled biotic disturbance. We measured resilience in a number of ways, including level of and time to recovery of assemblage density, richness, and structure. While there was no relationship between the pre-disturbance structure of the fish assemblage and its resilience to disturbance, certain functional and habitat attributes appeared to encourage recovery. We formed a conceptual model of resilience by combining our results with published studies of disturbance in streams. We suggest that an understanding of the recovery process has relevance to theoretical investigations of system structure and function as well as predictive utility for the management of disturbed systems, and therefore warrants further research.
NB23A-04 14:15h
Increased Use of No-till Cropping Systems Improves Stream Ecosystem Quality
Release of sediments to streams from tilled lands has been a significant stressor to streams in agro-ecosystems for decades and has been shown to impact aquatic biota in a variety of ways. To limit soil erosion from cultivated lands, conservation tillage techniques, including the use of no-till systems, have been developed and widely adopted throughout the region. However, there haves been no tests of the effects of no-till systems on stream quality at a watershed scale. We measured habitat and water quality and sampled the benthic macroinvertebrate (BMI) and fish communities in 32 small (100-1400 ha) subwatersheds along a gradient of the proportion of land under no-till cropping systems to determine relationships between the use of no-till and stream quality. Our results demonstrate that with increasing proportions of no-till, habitat scores improve, the quantities of sediment and sediment associated stressors in the water decline, the BMI community exhibits reduced dominance by Oligocheata and Sphaeriidae, as well as improved Family Biotic Index (FBI) scores, and fish species richness increases. We concluded that increased use of no-till cropping systems by farmers does contribute to improved quality of streams in agro-ecosystems.
NB23A-05 14:30h
Broad-scale, Repeatable Response Patterns of Invertebrates and Fish Exposed to Pulp and Paper Mill Effluent
Since 1992, pulp mill effects on aquatic biota have been measured over a broad geographic scale by the National Environmental Effects Monitoring Program in Canada. The standardized sampling and reporting methodology, extensive database, and subsequent analyses have provided a fairly robust picture of the effects of these effluents on receiving waters across the country. Over the last decade, the national average response pattern measured for benthic invertebrate communities has been one typically associated with eutrophication, ranging from mild to more pronounced, partly depending on habitat type. More specifically, invertebrate communities exposed to pulp mill effluent have commonly exhibited increases in abundance, together with some combination of increases, decreases or no change in taxon richness, depending on the degree of eutrophication. Over the same time period, the national average response for fish has been one of nutrient enrichment overlaid by metabolic disruption. That is, exposed fish have consistently shown evidence of increased food availability (fatter, faster growing, larger livers) together with disruption of allocation to reproduction (smaller gonads). Thus, although sublethal toxicity testing demonstrated large improvements in effluent quality during the mid 1990's, measurable effects remain in the field. Efforts are currently underway to better understand and ameliorate these remaining effects.
NB23A-06 14:45h
Ecoregional and State Differences in the Effects of Nonnative Fish on Fish Assemblage Structure
Nonnative aquatic vertebrates have been widely introduced across the western U.S. We analyzed data from 1039 site visits sampled during 2000 -2003 by the U.S. EPA's Environmental Monitoring and Assessment Program's (EMAP) Western Pilot to determine occurrence and proportion of stream length occupied by nonnative fish and aquatic amphibians in streams and rivers of 12 conterminous western states and three ecoregions (Western Forest, Plains, Xeric). An estimated 41% (±5%) of the stream length in the region, where vertebrates were collected, contained nonnative vertebrates. Nonnatives represented greater than 50% of the individuals in 18% of the stream length and were present in over 80% of the length of 5th order or larger rivers. The Plains contained the greatest number of nonnative species versus other ecoregions. Trout (rainbow, brown, brook) are the most common nonnatives found in the western states. California contained the most nonnative taxa collected (27) while 7 of 12 predominant fish in Arizona are nonnatives. Nonnatives are usually gamefish or fish supporting game fish including baitfish such as minnows.