James R. Karr

The Natural Flow Regime

H umans have long been fascinated by the dynamism of free-flowing waters. Yet we have expended great effort to tame rivers for transportation, water supply, flood control, agriculture, and power generation. It is now recognized that harnessing of streams and rivers comes at great cost: Many rivers no longer support socially valued native species or sustain healthy ecosystems that provide important goods and services (Naiman et al. 1995, NRC 1992).

Assessment of Biotic Integrity Using Fish Communities

Abstract Mans activities have had profound, and usually negative, influences on freshwater fishes from the smallest streams to the largest rivers. Some negative effects are due to contaminants, while others are associated with changes in watershed hydrology, habitat modifications, and alteration of energy sources upon which the aquatic biota depends. Regrettably, past efforts to evaluate effects of mans activities on fishes have attempted to use water quality as a surrogate for more comprehensive biotic assessment. A more refined biotic assessment program is required for effective protection of freshwater fish resources. An assessment system proposed here uses a series of fish community attributes related to species composition and ecological structure to evaluate the quality of an aquatic biota. In preliminary trials this system accurately reflected the status of fish communities and the environment supporting them.

Habitat Structure and Stream Fish Communities

Stream habitat complexity is correlated with fish species diversity in selected Indiana and Panama streams. Habitat diversity was measured along 3 dimensions judged important to a wide range of fish groups and applicable to many stream conditions: stream depth, bottom type, and current. Increasing community and habitat diversity followed stream-order gradients. Natural streams supported fish communities of high species diversity which were seasonally more stable than the lower-diversity communities of modified streams. After disturbances such as channelization, seasonal peaks in species diversity attain levels typical of undisturbed streams. Because seasonal changes in stream quality are high, the stability of the fish community is lower in modified than in natural streams. The general correlation between habitat characteristics and presence and absence of fish species sug- gests that most fishes of small streams are habitat specialists.

Patch dynamics in lotic systems: the stream as a mosaic*

This paper applies concepts of landscape ecology and patch dynamics to lotic systems. We present a framework for the investigation of pattern and process in lotic ecosystems that considers how specific patch characteristics determine biotic and abiotic processes over various scales. Patch characteristics include: size, size distribution within the landscape, juxtaposition, diversity, duration, and mechanisms affecting patch formation. Several topics of current interest in lotic ecology are examined from a patch-dynamics perspective: (1) response of periphyton communities to nutrient patches; (2) effects of patch dynamics on nutrient spiralling; (3) riparian patch dynamics and effects of leaf litter characteristics on lotic food webs; (4) beaver-induced patch dynamics; and (5) patch dynamics of river floodplains. We conclude that a patch-dynamics perspective coupled with a strong experimental approach can enhance the utility and predictive power of unifying concepts in lotic ecology, such as the river continuum hypothesis and nutrient spiralling, through its focus on organismal and process-specific building blocks of lotic systems. The effectiveness of a patch-dynamics approach as a framework for the study of lotic systems lies in the strength of the linkage between reductionist and whole-stream perspectives.

A Benthic Index of Biotic Integrity (B‐IBI) for Rivers of the Tennessee Valley

Invertebrate data from rivers in the Tennessee Valley were used to: (1) evaluate the utility of 18 characteristics of invertebrate assemblages (attributes) to assess the biological condition of streams and (2) develop a comprehensive benthic invertebrate index that reflects important aspects stream biology and responds to the effects of human society in detectable ways. We used data from the Tennessee Valley Authoritys (TVA) fixed—station monitoring program established in 1986 to evaluate water resources in the Tennessee Valley. The streams covered sites with various types and levels of human disturbance. TVA biologists sampled riffles and pools using quantitative methods. To evaluate attributes we determined (1) the ability of each attribute to distinguish among sites (analyses of variance), (2) the associations among attributes (correlation coefficients), (3) the concordance of assessments of sites using each attribute with two independent site assessments (water quality and analysis of fish assemblages based on the index of biotic integrity), and (4) the variability of each attribute across habitats (riffles and pools) and ecoregions. Thirteen attributes (total taxa richness and taxa richnesses of intolerant snails and mussels, mayflies, caddisflies, and stoneflies; relative abundances of Corbicula, oligochaetes, omnivores, filterers, grazers, and predators; dominance; total abundance) were valuable in discriminating sites, exhibited concordance with other methods of assessment, and were relatively uncorrelated among themselves. Five attributes (sediment—surface taxa richness; relative abundances of shredders, gatherers, detritivores, and chironomids) were not acceptable for inclusion in the index because they either were not in concordance with other methods of assessment or were strongly correlated with other attributes. Based on the results of this evaluation, 13 attributes were included in a benthic index of biotic integrity (B—IBI). The B—IBI was evaluated using a more extensive fixed—station data set and was tested using an independent data set where samples were taken above and below the release of an industrial effluent to the North Fork Holston River. The fixed—station sites were correctly ranked, although rankings were not always consistent for pool and riffle habitats. B—IBI also distinguished the industrial impact. The B—IBI has potential as an assessment tool for streams, although more testing and evaluation of both the attributes and the index are warranted.

Relationships between Woody Debris and Fish Habitat in a Small Warmwater Stream

Abstract Abundance of woody debris was manipulated in a small Illinois stream to determine the importance of this material to fish. When a stream reach was divided along midchannel, and debris was added to one side, but removed from the other, fish and benthic invertebrates were usually more abundant on the side with woody debris than on the cleared side. In further experiments during a low-flow year (1980), debris removal was followed by rapid decreases in water depth and occurrence of benthic organic litter, and increases in current velocity and proportion of sand bottom. These changes were less apparent in unaltered reaches during 1980, and in all reaches during 1981, which was a high-flow year. Artificial debris was colonized by many invertebrates, including chironomids, trichopterans, and ephemeropterans. Most large fish (age 2+) avoided reaches without debris, whereas some smaller fish (such as johnny darter) preferred them; preferences for reach treatments were stronger in 1980 than in 1981. The ad...

Regional application of an index of biotic integrity based on stream fish communities

Abstract The recently proposed index of biotic integrity (IBI) was evaluated for several watersheds throughout the midwestern United States. Five of the community metrics comprising the IBI depend on the number of fish species present and must be adjusted for changes in expected species richness with stream size or zoogeography. We use basic relationships of fish species richness versus stream size, calculated from historical fish community data for seven watersheds, to define lines of maximum species richness. These lines are used to predict attributes of “excellent” fish communities, the basis of comparison for assigning scores to 5 of 12 IBI metrics. When zoogeographic and stream-size factors were accounted for in assigning scores, the IBI accurately reflected watershed and stream conditions. As partial tests of the IBI, we found that the index conforms to knowledge of biologists familiar with several watersheds, is independent of stream order in homogeneous watersheds, and is not biased upwards in gen...

Biological Integrity versus Biological Diversity as Policy Directives

Two phrases — biological integrity and biological diversity—have joined the lexicon of biologists and natural resource managers during the past two decades. The importance of these phrases is demonstrated by their influence on environmental research, regulatory, and policy agendas. The concepts behind the phrases are central to strategies being developed to sustain global resources (Lubchenco et al. 1991). Unfortunately, the phrases are widely used by the media, citizens, policy makers, and some biologists without adequate attention to the concepts they embody. Precise use of the terms integrity and diversity can help set and achieve societal goals for sustaining global resources; imprecise or inappropriate use may exacerbate biotic impoverishment—the systematic decline in biological resources (Woodwell 1990).

Assessing invertebrate responses to human activities: evaluating alternative approaches

The goal of biological monitoring is to evaluate the effect of human activities on biological resources. In this study, we linked human activities across landscapes to specific changes in assemblages of benthic macroinvertebrates in streams that drain those landscapes. We used data from 2nd- to 4th-order streams in southwestern Oregon to test approximately 30 hypotheses about how macroinvertebrates respond to several common human actions, especially logging and associated road construction. We found 10 attributes of macroinvertebrate assemblages to be reliable indicators of disturbance. Data from a subsequent year confirmed those results. We used simple graphical methods to evaluate land-use data and to relate the data to observed responses of invertebrates. We constructed a multimetric index (benthic index of biological integrity, or B-IBI) from component metrics that distinguished disturbed stream sites from minimally disturbed sites. Using an independent data set, we found that B-IBI scores were significantly lower for streams whose watersheds were more degraded by human activities. We also tested rapid bioassessment protocol (RBP) III as modified by Oregon Department of Environmental Quality. RBP III failed to detect differences among sites that B-IBI did detect Because biologists continue to debate the relative merits of a multimetric vs. a multivariate approach for interpreting biomonitoring data, we also used principal components analysis (PCA) to explore patterns in our multidimensional data. We chose PCA based on species abundance because it has been the most common technique used by state and federal agency biologists to interpret biomonitoring data. PCA failed to detect clear differences in our data set (e.g., between most and least disturbed sites). We suggest that multivariate statistical analyses are most appropriate for exploratory analysis when the investigator has limited knowledge of an ecological system and wants to generate testable hypotheses. We demonstrate that sufficient information about the natural history of stream invertebrates is available to support more direct tests of how invertebrates respond to human disturbance. The components of a good multimetric index are founded on tested hypotheses and thus provide a sound scientific assessment of a stream site. We argue that a method that incorporates ecological information is more suitable for biomonitoring than one relying on statistical algorithms.

Fish communities along environmental gradients in a system of tropical streams

SynopsisFish community structure was examined in 9 forested streams (1–6 m wide) in central Panama during dry seasons over a 3 year period. Study regions varied in annual rainfall, degree of canopy shading, and topographical relief. Benthic invertebrates were more abundant in riffles than in pools and more abundant in early (January) than late (March) dry season. In addition, benthos abundances were negatively correlated with canopy shading among study regions. Terrestrial invertebrate abundances were greater in January than March and were correlated with stream width. Fishes were assigned to 7 feeding guilds (algivores, aquatic insectivores, general insectivores, piscivores, scale-eaters, terrestrial herbivores, omnivores) on the basis of similarity of gut contents. Four species exhibited marked dietary shifts with increasing size. Distributions of feeding guilds (biomass) among habitats and streams were not generally correlated with availabilities of their major food resources. All feeding guilds except aquatic insectivores were most concentrated (biomass per area) into deep pools. Densities of algivores and terrestrial herbivores increased with stream size, but the density of aquatic insectivores declined. Species richness of feeding guilds increased with stream size and canopy openness. The proportion of fish biomass supported by algae and terrestrial plant material increased with stream size, while that supported by aquatic and terrestrial invertebrates declined. Small fishes (<40 mm TL) were most abundant in pools of small streams. Terrestrial predators appeared to be more important than food availability in determining distributions of fish among habitats. However, trophic diversity of fish communities may be related to the reliability of available food resources.