R and streams, by their very nature long ribbons of aquatic habitat, are inherently difficult to study. Approaching the banks of a flowing-water (lotic) system, one can see only a short fragment of the entire stream, from one bend to another, and can gain little appreciation for important features that lie beyond view. Moreover, materials transported downstream by the flow, and organisms traveling up or down the hydraulic highway, are soon gone from the reach and the opportunity to study them is often lost. Lakes present their own challenges for study, but by contrast to streams, one can usually see large expanses from shore that encompass all major habitats needed for aquatic organisms to complete their life history, such as gravel shoals, beds of aquatic vegetation, and open water habitats. Much of our knowledge of the ecology of rivers and streams is based on observations and experiments on organisms and habitat in the short fragments we can view or quickly traverse on foot, and this limited understanding underpins our efforts at conservation of stream fishes. Here, we argue that this understanding is incomplete, like viewing only disjunct parts of a landscape painting through small holes in a curtain draping it. We propose that a continuous view of rivers is essential for effective research and conservation of their fishes and other aquatic biota—a view not just of disjunct reaches but of the entire spatially heterogeneous scene of the river environment, the riverscape, unfolding through time. One symptom of our incomplete understanding is the alarming rate of decline over the last 50 years of fishes that inhabit rivers and streams of North America. The public is aware that salmon are disappearing from the Pacific Northwest, with about a quarter of the 214 stocks of anadromous salmon and trout imperiled a decade ago (Nehlsen et al. 1991). Even little-known small fishes native to Great Plains and southwestern desert streams have suffered drastic declines (Minckley and Douglas 1991, Fausch and Bestgen 1997), and many are now either protected by federal or state listing as endangered or threatened species or are being considered for such protection. North America harbored the greatest diversity worldwide of temperate freshwater fishes (Warren and Burr 1994), crayfishes (Taylor et al. 1996), and mussels (Williams et al. 1993), but about 30% to 75% of the taxa in each group are at increased risk of extinction (i.e., categorized as rare, threatened, or endangered species). Fishes are also the most imperiled vertebrates worldwide (Allan and Flecker 1993, Leidy and Moyle 1998) and a large proportion spend at least part of their lives in streams.

https://www.jstor.org/stable/10.1641/0006-3568(2002)052%5B0483%3ALTRBTG%5D2.0.CO%3B2

Landscapes to Riverscapes: Bridging the Gap between Research and Conservation of Stream Fishes

/ Although sedimentation is a naturally occurring phenomenon inrivers, land-use changes have resulted in an increase in anthropogenicallyinduced fine sediment deposition. Poorly managed agricultural practices,mineral extraction, and construction can result in an increase in suspendedsolids and sedimentation in rivers and streams, leading to a decline inhabitat quality. The nature and origins of fine sediments in the loticenvironment are reviewed in relation to channel and nonchannel sources andthe impact of human activity. Fine sediment transport and deposition areoutlined in relation to variations in streamflow and particle sizecharacteristics. A holistic approach to the problems associated with finesediment is outlined to aid in the identification of sediment sources,transport, and deposition processes in the river catchment. The multiplecauses and deleterious impacts associated with fine sediments on riverinehabitats, primary producers, macroinvertebrates, and fisheries are identifiedand reviewed to provide river managers with a guide to source material. Therestoration of rivers with fine sediment problems are discussed in relationto a holistic management framework to aid in the planning and undertaking ofmitigation measures within both the river channel and surrounding catchmentarea.KEY WORDS: Sedimentation; Fine sediment; Holistic approach; Ecologicalimpact; River restoration

http://deq.idaho.gov/media/525755-Biological_Effects_Fine_Sediment_lotic_Environment_Wood_Armitage_1997.pdf

Biological Effects of Fine Sediment in the Lotic Environment

Long-term discharge records (17–81 yr) of 78 streams from across the continental United States were analyzed to develop a general quantitative characterization of streamflow variability and predict...

Implications of Streamflow Variability and Predictability for Lotic Community Structure: A Regional Analysis of Streamflow Patterns

Summary
1. Stream ecosystems are increasingly impacted by multiple stressors that lead to a loss of sensitive species and an overall reduction in diversity. A dominant paradigm in ecological restoration is that increasing habitat heterogeneity (HH) promotes restoration of biodiversity. This paradigm is reflected in stream restoration projects through the common practice of re-configuring channels to add meanders and adding physical structures such as boulders and artificial riffles to restore biodiversity by enhancing structural heterogeneity.

2. To evaluate the validity of this paradigm, we completed an extensive evaluation of published studies that have quantitatively examined the reach-scale response of invertebrate species richness to restoration actions that increased channel complexity/HH. We also evaluated studies that used manipulative or correlative approaches to test for a relationship between physical heterogeneity and invertebrate diversity in streams that were not in need of restoration.

3. We found habitat and macroinvertebrate data for 78 independent stream or river restoration projects described by 18 different author groups in which invertebrate taxa richness data in response to the restoration treatment were available. Most projects were successful in enhancing physical HH; however, only two showed statistically significant increases in biodiversity rendering them more similar to reference reaches or sites.

4. Studies manipulating structural complexity in otherwise healthy streams were generally small in scale and less than half showed a significant positive relationship with invertebrate diversity. Only one-third of the studies that attempted to correlate biodiversity to existing levels of in-stream heterogeneity found a positive relationship.

5. Across all the studies we evaluated, there is no evidence that HH was the primary factor controlling stream invertebrate diversity, particularly in a restoration context. The findings indicate that physical heterogeneity should not be the driving force in selecting restoration approaches for most degraded waterways. Evidence suggests that much more must be done to restore streams impacted by multiple stressors than simply re-configuring channels and enhancing structural complexity with meanders, boulders, wood, or other structures.

6. Thematic implications: as integrators of all activities on the land, streams are sensitive to a host of stressors including impacts from urbanisation, agriculture, deforestation, invasive species, flow regulation, water extractions and mining. The impacts of these individually or in combination typically lead to a decrease in biodiversity because of reduced water quality, biologically unsuitable flow regimes, dispersal barriers, altered inputs of organic matter or sunlight, degraded habitat, etc. Despite the complexity of these stressors, a large number of stream restoration projects focus primarily on physical channel characteristics. We show that this is not a wise investment if ecological recovery is the goal. Managers should critically diagnose the stressors impacting an impaired stream and invest resources first in repairing those problems most likely to limit restoration.

/pdf/river-restoration-habitat-heterogeneity-and-biodiversity-a-112ceeyv5h.pdf

River restoration, habitat heterogeneity and biodiversity: a failure of theory or practice?

The diversity of life in headwater streams (intermittent, first and second order) contributes to the biodiversity of a river system and its riparian network. Small streams differ widely in physical, chemical, and biotic attributes, thus providing habitats for a range of unique species. Headwater species include permanent residents as well as migrants that travel to headwaters at particular seasons or life stages. Movement by migrants links headwaters with downstream and terrestrial ecosystems, as do exports such as emerging and drifting insects.

/pdf/the-contribution-of-headwater-streams-to-biodiversity-in-55aehboa1f.pdf

The contribution of headwater streams to biodiversity in river networks

Manipulations of substrate size and components of heterogeneity were designed to test their independent effects and interactions on the abundance and species richness of stream macroinvertebrates. Two components of substrate heterogeneity, variation in size class proportions and number of size classes, had no independent effect on abundance or richness; and in general did not interact with median particle size. Median particle size, stream current, and detritus accounted for most of the significant variation in macroinvertebrates colonizing the experimental substrates. Rocks with high surface heterogeneity (roughness) were colonized by more individuals (but not taxa) than rocks with low surface heterogeneity.

The response of stream macroinvertebrates to substrate size and heterogeneity

Native freshwater faunas in North America are declining, principally due to the combined effects of habitat degradation and introduced species. Relatively little attention has been directed to the decline of freshwater invertebrates, which may be even more threatened than fishes. This paper chronicles recent changes in the distribution and abundance of the Shasta crayfish (Pacifastacus fortis Faxon), a state and federally endangered species endemic to the midreaches of the Pit River system in northeastern California. We made snorkeling and SCUBA surveys for crayfish in 1990 and 1991 and examined various records for historic distributions. Shasta crayfish have been extirpated from much of their historic range by water impoundment and diversion, and they are further threatened by two introduced crayfish species (Pacifastacus leniusculus Dana and Orconectes virilis Hagen). By 1990 Shasta crayfish were restricted to seven isolated populations, mostly in the headwaters of spring-fed tributaries to the Pit river. P. leniusculus had become established throughout much of the study area in about 12 years. In one site P. leniusculus probably contributed to the precipitous decline of Shasta crayfish, from 2000–3000 in 1980 to about 370 (± 135) in 1991. O. virilis, which occurred in only the most disturbed parts of the system, showed little range expansion in 30 years and had been replaced in a large stretch of the Pit River by P. leniusculus. P. leniusculus occupied sites with a broad range of habitat variables (temperature, pH, turbidity, substrate size) partly or wholly overlapping measures of sites with the other two species. The decline of the Shasta crayfish, like the extinction of its closest relative P. nigrescens in the San Francisco Bay area earlier this century, reflects the decline of its habitat and probably pressure from the aggressive exotic P. leniusculus.

Decline of the Shasta Crayfish (Pacifastacus fortis Faxon) of Northeastern California

Adult rainbow trout Oncorhynchus mykiss were observed in a 20-m reach of river to determine habitat use (at four flow levels) and preference (at two flow levels) under daily fluctuations in discharge from a hydropower peaking operation. Maximum increase in discharge was threefold (from 1.6 to 5.1 m3/s), which is small compared with that of some hydropower peaking operations. Available habitat (based on velocity and depth) was different under low and high flows. At the low discharge level, nearly twice as much of the lowest velocity-class (0.00–0.15 m/s) and eight times more of the shallowest depth-class (0.0–0.2 m) were available. Distributions of adult habitat use revealed that fish focal point and water column velocities increased with increasing discharge. At the highest discharge levels, more fish were found in the deepest water, and the fish assumed positions closer to the streambed, than at the three lower discharges. Fish were usually associated with boulders at all discharges. Habitat pre...

Habitat Use by Adult Rainbow Trout under Moderate Artificial Fluctuations in Flow

From 1972 to 1975, an estimated 39–47% of the adult rainbow trout (Salmo gairdneri) in Sagehen Creek spawned in an intermittent stream—Kiln Meadow Tributary—while several permanently flowing tributaries attracted only 10–15% of the run The balance of the fish presumably spawn in the upper reaches of the main stream Kiln Meadow Tributary drains a south-facing slope, and peak runoff from snow melt occurs early This may be one factor that attracts spawning fish The absence of competition from brook trout, which cannot spawn in Kiln Meadow Tributary in the fall, may enhance the value of this watercourse for rearing young rainbow trout The number of spawning rainbows in Kiln Meadow Tributary declined from 707 in 1972 to 254 in 1975 Two large year classes were present in 1972 and 1973 following winter floods in preceding winters Males matured a year earlier than females Males outnumbered females in every year: the sex ratio in mature fish varied from 24:1 to 49:1 Repeat spawners to Kiln Mead

The Quantitative Importance of an Intermittent Stream in the Spawning of Rainbow Trout

Fish populations were compared before (1952–1961) and after (1970–1972) construction of Stampede Reservoir in a mile of Sagehen Creek above the reservoir. Relative abundance and species composition were quite different after reservoir construction. Suckers (Catostomus platyrhynchus and C. tahoensis) are now numerically dominant (79% of all fish); whereas, formerly they made up 18% (by numbers) of the fish composition. Rainbow trout have increased, but brown trout and whitefish have decreased; and brook trout have not been collected since impoundment. Reservoir construction is the only major change in the Sagehen Creek watershed.

Upstream Changes in Fish Populations following Impoundment of Sagehen Creek, California

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