Judith L. Li

Cumulative Effects of Riparian Disturbances along High Desert Trout Streams of the John Day Basin, Oregon

Abstract In a study of cumulative effects of riparian disturbance by grazing on the trophic structure of high desert trout streams, watersheds with greater riparian canopy had higher standing crops of rainbow trout Oncorhynchus mykiss, lower daily maximum temperatures (range, 16–23°C compared with 26–31°C), and perennial flow. Watershed aspect influenced the response of trophic structure to grazing influences. Standing crops of rainbow trout were negatively correlated with solar radiation and maximum temperature in watersheds flowing northward. A different relationship was observed for a set of watersheds with a southern aspect, perhaps due to the presence of spring seeps and stream desiccation in the heavily grazed stream. Trout biomass was negatively correlated with solar radiation, whereas positive relationships were found for discharge and depth. Algal biomass was positively correlated with solar insolation (r = 0.9 1), total invertebrate biomass (r = 0.77), and herbivorous invertebrate biomass (r = 0...

PROJECTING THE BIOLOGICAL CONDITION OF STREAMS UNDER ALTERNATIVE SCENARIOS OF HUMAN LAND USE

We present regression models for estimating the status of fish and aquatic invertebrate communities in all second to fourth-order streams (1:100 000 scale; total stream length 5 6476 km) throughout the Willamette River Basin, Oregon (USA). The models project fish and invertebrate status as a function of physiographic, land-use/land-cover, and stream flow variables, with the latter two sets of variables subject to change under historical and alternative future scenarios of human development. Models are developed using sample data collected between 1993 and 1997 from 149 wadeable streams in the basin. Model uncertainties are propagated through model projections and into aggregated estimates of regional status. The projections show no significant change in basin-wide status in year 2050, relative to Circa 1990, for scenarios either of increased human development or continuation of current development trends, because landscape change under these scenarios is dominated by conversion of agricultural land to rural residential and urban uses, and because these changes affect only a small percentage of the basin. However, under a scenario of increased conservation, regional medians of biotic status indicators are projected to improve by 9-24% by year 2050. None of the changes projected between Circa 1990 and year 2050 is as large in magnitude as the decline in status projected to have occurred between the time of pre-European settlement and Circa 1990.

Relationships between riparian cover and the community structure of high desert streams

Many studies on cool, forested streams have shown that removal of riparian canopy leads to higher incident radiation, blooms in algal and macroinvertebrate populations, and concomitant increases in salmonid abundance. In warm, high-elevation desert streams, however, an open canopy may not increase salmonid density. Our seven study reaches on 3rd-order tributaries of the John Day River in eastern Oregon included riparian areas ranging from denuded, heavily grazed streambanks to intact conifer forest. Average summer solar inputs to these sites varied from 165 to 2230 megajoules/m2, and stream temperatures were influenced by the density and extent of canopy. Densities of steelhead trout (Oncorhynchus mykiss) and sculpin (Cottus supp.) decreased significantly with greater incident radiation and higher stream temperatures, although many warm-water cyprinids increased in abundance in unshaded sites. Periphyton standing crops (g ash-free dry mass/m2) closely tracked solar inputs and was, in turn, strongly positively correlated with biomasses of total invertebrates and of grazers. Collector, shredder, and predator biomasses, and numerical abundances of all invertebrate groups, did not change with canopy density. The abundances of chironomids and baetids were unrelated to increases in light or algal resources, in contrast to studies in Cascades and Coast Range streams where irruptions of these taxa occurred in canopy openings. In our streams the large-bodied caddisfly Dicosmoecus accounted for the higher total invertebrate biomass observed in exposed sites. These insects composed 55-96% of the total biomass in open reaches but only 0-1.4% in the three most shaded sites. Increases in total invertebrate biomass with increasing light levels or periphyton were not observed when Dicosmoecus were removed from the analysis. Dicosmoecus are consumed infrequently by juvenile trout or other small fish species common in John Day tributaries; consequently, extensive openings in the canopy appear to produce few advantages to upper trophic levels in these streams.

Effect of Bull Trout and Brook Trout Interactions on Foraging Habitat, Feeding Behavior, and Growth

Abstract Observations of free-ranging sympatric bull trout Salvelinus confluentus and nonnative brook trout S. fontinalis in two eastern Oregon headwater streams provided little evidence of habitat partitioning. Both species held focal feeding points in similar microhabitats and fed primarily from the water column rather than from the surface or benthos. In an instream experiment, 20 enclosures were assigned one of three treatments: two bull trout, four bull trout, or a mix of two bull trout and two brook trout. In the enclosures, macroinvertebrate drift was restricted and trout densities were elevated, creating an environment of reduced food and habitat resources. Under these conditions, there was no indication of a niche shift by bull trout; feeding behavior and habitat use by bull trout did not differ depending on the presence or absence of brook trout. Brook trout in the mixed-species treatment were the most aggressive, maintained dominance in 75% of the enclosures, and exhibited significantly higher ...

Influence of grazer type and abundance on plant-herbivore interactions in streams

Grazer-periphyton interactions were investigated in 11 laboratory streams holding a range of densities of three herbivore taxa during a 32-d experiment. Effects of grazers on algae were strongest with Dicosmoecus gilvipes caddisflies, intermediate with Juga silicula snails, and weakest with Baetis spp. mayflies. Algal standing crop, export, and gross primary production declined logarithmically with increasing grazer density. Algal turnover rate, however, increased with grazer abundance. At high densities of all grazers, responses in most algal parameters converged, suggesting that high grazing pressure, regardless of taxon, will similarly affect periphyton. Growth of both Dicosmoecus caddisflies and Juga snails was density-dependent, with the highest growth rates occurring at the lowest densities. Caddisflies displayed high growth rates but low efficiency in resource use. Snails had lower growth rates but were more efficient in resource use. The coexistence of Dicosmoecus and Juga, or other competing herbivores, in natural streams may be related to these fundamental differences in life history strategies.

Restricted hyporheic exchange in an alluvial river system: implications for theory and management

Abstract Large-scale patterns of hyporheic exchange are predictable within some river systems, but our understanding of the factors driving hyporheic processes and the magnitude of hyporheic exchange needed to influence biophysical patterns at larger scales remains limited. We investigated the patterns, magnitude, and potential effects on biota of reach-scale hyporheic exchange in an alluvial river of the Pacific Northwest. The river was topographically similar to and in the same geographic region as other systems where large-scale hyporheic exchange and associated biological responses have been observed. We hypothesized that predictable reach-scale patterns of hyporheic exchange would occur in alluvial valley segments of the river and that hyporheic upwelling would be associated with reach-scale patterns of physical and biological characteristics. We used in-channel piezometers and synoptic stream flow measurements to quantify hyporheic exchange. We measured temperature, dissolved O2, pH, specific conductivity, chlorophyll a biomass, primary production, and benthic macroinvertebrates as indicators of physical and biological responses. Contrary to our expectations, we found no evidence, physical or biological, of reach-scale hyporheic exchange. Hyporheic connectivity in this river system probably is constrained by geologic and geomorphic characters as well as the legacy of human land use in the basin. Thus, our results illustrate the variability of hyporheic processes that can occur among alluvial river systems and may have implications for watershed management.

Influence of clearcut logging, flow duration, and season on emergent aquatic insects in headwater streams of the Central Oregon Coast Range

Abstract We measured the effects of timber-harvest condition (clearcut and forested) and flow duration (perennial and intermittent) on emergent aquatic insect assemblages at 20 headwater streams in the Central Oregon Coast Range. Clearcut streams had been logged to the stream banks within 2 y prior to the start of our study. Adult aquatic insects were sampled from a 40-m reach at each study stream in 3 seasons: summer, autumn, and spring. Emergent insects were strong indicators of harvest condition and, regardless of flow duration or season, more aquatic insects emerged from streams in clearcut catchments than in forested catchments. Plecoptera had higher emergence rates from intermittent streams than from perennial streams in spring. Functional feeding group composition was not apparently affected by harvest condition or flow duration. Taxon richness was slightly higher at clearcut than at forested streams, primarily because of the occurrence of rare taxa at clearcut streams. Nonmetric multidimensional scaling (NMS) ordination of emergent aquatic insect assemblages showed community patterns that varied by season and harvest condition, but little by flow duration. Stream canopy % cover, stand age, logging debris (% slash), and substrate composition differed between clearcut and forested streams and were strongly correlated with NMS axes. Taxa that responded to conditions created by logging, such as % slash or canopy opening, contributed to differences in assemblages between headwater streams flowing through clearcut and forested catchments.

Three responses to small changes in stream temperature by autumn-emerging aquatic insects

Abstract In this experimental study, conducted in coastal Oregon USA, we examined how small increases in summer water temperatures affected aquatic insect growth and autumn emergence. We maintained naturally fluctuating temperatures from 2 nearby streams and a 3rd regime, naturally fluctuating temperatures warmed by 3–5°C, in flow-through troughs from mid-summer until autumn. We added selected abundant Ephemeroptera, Plecoptera, and Trichoptera species to the 3 treatments in late July and observed emergence until early December. We described the taxon-specific responses of the caddisfly Psychoglypha bella and the mayfly Paraleptophlebia bicornuta, both of which survived well in the troughs (67–86%), and the stonefly Mesocapnia projecta, which we did not collect in mid-summer but had colonized all experimental troughs by October. We observed primarily phenological rather than morphological responses to higher water temperatures. The most synchronous emergence of male and female P. bella and P. bicornuta occurred in the trough with the coolest temperatures. Only P. bella emerged asynchronously from the trough with the warmest temperatures. The decreases in synchrony were largely the result of earlier emergence of males. Paraleptophlebia bicornuta were larger and tended towards asynchrony in the trough with water (and temperatures) from their natal stream. Individuals in the trough with the warmest temperature were smaller than individuals in other troughs, but did not emerge earlier. Mesocapnia projecta showed greater synchrony in emergence, which occurred over a shorter interval, than the other species. When exposed to increased water temperatures, autumn-emergent taxa may be most vulnerable to trade-offs between asynchronous emergence and the probabilities for finding mates in unpredictable weather conditions.

Fish Use of Intermittent Watercourses Draining Agricultural Lands in the Upper Willamette River Valley, Oregon

Historically, the upper Willamette River valley in western Oregon was characterized by seasonal floods and large expansions of its stream network. During the past century, human activities have altered or eliminated many intermittent stream and floodplain habitats in the valley. As a result, the remaining intermittent streams and ditches, referred to as watercourses, may still provide habitat that is critical for native fish. Our objectives were to determine (1) fish presence, (2) the spatial gradients of fish distribution (including species identity, native versus nonnative status, and numbers), (3) fish use of the intermittent streams as spawning and nursery habitats, and (4) the main factors that influence the numbers of fish and fish species. In the winter and spring of 2002-2003, we examined the distributions of fish species in five subbasins within the Willamette River valley. The sampling sites were in intermittent watercourses that drained grass seed- producing fields. We collected water samples and sampled fish from December to May with minnow traps and an electrofishing unit and collected data on the standard fish habitat variables at all sites in spring. Thirteen fish species were found and only three of them were exotic. The presence of recently hatched and juvenile fish shows that intermittent watercourses offer conditions suitable for spawning and juvenile rearing. The two watershed-scale variables with the most influence on fish species richness were the percentage of the watershed covered by forest and the distance to perennial water, the first of which had a direct relationship to species diversity and the second an inverse relationship. In turn, fish abundance had a negative, albeit modest, relationship with the distance to perennial water. Among local-scale variables, water velocity and conductivity were inversely related to species richness and fish numbers. Our results highlight the relevance of intermittent agricultural watercourses for native fish species in the Willamette River valley and call for the promotion of agricultural conservation practices that benefit farmers while maintaining aquatic biodiversity in floodplain habitats.

Behavioral changes in the herbivorous caddisfly Dicosmoecus gilvipes (Limnephilidae)

Behavioral patterns differ among third-, fourth-, and fifth-instar Dicosmoecus gilvipes larvae. Feeding, crawling, resting, case building, and interactions were observed among all instars, but time spent in each category varied according to larval instar, hunger, and type of algae available. Larvae fed one-third of the time. Third-instar larvae fed longer on diatoms, whereas fourth and fifth instars fed longer on filamentous assemblages. Third-instar larvae crawled faster than other instars, fourth instars spent the most time case building, and fifth instars rested more than others. Resting and case building were often associated activities. Interactions among individuals were infrequent; neither aggression nor cannibalism were observed. The variety and changes in behavior exhibited by D. gilvipes may affect grazing levels on algal resources and influence possible competitive interactions. Behavioral studies that encompass developmental patterns of organisms provide critical contexts for studies of ecological processes in streams.