F. Richard Hauer

Biotic and Abiotic Controls in River and Stream Communities

Lotic ecologists share a major goal of explaining the distribution and abundance of biota in the worlds rivers and streams, and of predicting how this biota will respond to change in fluvial ecosystems. We discuss five areas of research that would contribute to our pursuit of this goal. For mechanistic understanding of lotic community dynamics, we need more information on: 1. Physical conditions impinging on lotic biota, measured on temporal and spatial scales relevant to the organisms. 2. Responses of lotic biota to discharge fluctuations, including the processes that mediate community recovery following resets caused by spates or droughts. 3. Movements of lotic organisms that mediate gene flow, resource tracking, and multilevel species interactions. 4. Life history patterns, with special emphasis on ontogenetic bottlenecks that determine the vulnerability of populations confronting environmental perturbation. 5. Consequences of species interactions for community- and ecosystem-level processes in rivers and streams. Without attempting to be comprehensive in our review, we discuss limits and limitations of our knowledge in these areas. We also suggest types of data and technological development that would advance our understanding. While we appreciate the value and need for empirical and comparative information, we advocate search for key mechanisms underlying community interactions as the crucial step toward developing general predictions of responses to environmental change. These mechanisms are likely to be complex, and elucidation of interacting bilateral, or multilateral, biotic and abiotic controls will progress only with the continuing synthesis of community- and ecosystem-level approaches in lotic ecology.

ASSESSMENT OF CLIMATE CHANGE AND FRESHWATER ECOSYSTEMS OF THE ROCKY MOUNTAINS, USA AND CANADA

The Rocky Mountains in the USA and Canada encompass the interior cordillera of western North America, from the southern Yukon to northern New Mexico. Annual weather patterns are cold in winter and mild in summer. Precipitation has high seasonal and interannual variation and may differ by an order of magnitude between geographically close locales, depending on slope, aspect and local climatic and orographic conditions. The regions hydrology is characterized by the accumulation of winter snow, spring snowmelt and autumnal baseflows. During the 2-3-month spring runoff period, rivers frequently discharge > 70% of their annual water budget and have instantaneous discharges 10-100 times mean low flow. Complex weather patterns characterized by high spatial and temporal variability make predictions of future conditions tenuous. However, general patterns are identifiable; northern and western portions of the region are dominated by maritime weather patterns from the North Pacific, central areas and eastern slopes are dominated by continental air masses and southern portions receive seasonally variable atmospheric circulation from the Pacific and the Gulf of Mexico. Significant interannual variations occur in these general patterns, possibly related to ENSO (El Nino-Southern Oscillation) forcing. Changes in precipitation and temperature regimes or patterns have significant potential effects on the distribution and abundance of plants and animals. For example, elevation of the timber-line is principally a function of temperature. Palaeolimnological investigations have shown significant shifts in phyto- and zoo-plankton populations as alpine lakes shift between being above or below the timber-line. Likewise, streamside vegetation has a significant effect on stream ecosystem structure and function. Changes in stream temperature regimes result in significant changes in community composition as a consequence of bioenergetic factors. Stenothermic species could be extirpated as appropriate thermal criteria disappear. Warming temperatures may geographically isolate cole water stream fishes in increasingly confined headwaters. The heat budgets of large lakes may be affected resulting in a change of state between dimictic and warm monomictic character. Uncertainties associated with prediction are increased by the planting of fish in historically fishless, high mountain lakes and the introduction of non-native species of fishes and invertebrates into often previously simple food-webs of large valley bottom lakes and streams. Many of the streams and rivers suffer from the anthropogenic effects of abstraction and regulation. Likewise, many of the large lakes receive nutrient loads from a growing human population. We concluded that: (1) regional climate models are required to resolve adequately the complexities of the high gradient landscapes; (2) extensive wilderness preserves and national park lands, so prevalent in the Rocky Mountain Region, provide sensitive areas for differentiation of anthropogenic effects from climate effects; and (3) future research should encompass both short-term intensive studies and long-term monitoring studies developed within comprehensive experimental arrays of streams and lakes specifically designed to address the issue of anthropogenic versus climatic effects.

Measuring Groundwater–Stream Water Exchange: New Techniques for Installing Minipiezometers and Estimating Hydraulic Conductivity

Abstract Measurements of groundwater–stream water interactions are increasingly recognized as important to understanding the ecology of fishes and other organisms in stream and riparian ecosystems. However, standard measurement techniques are often feasible only at small spatial scales, in areas with easy access, or in systems with relatively fine substrata. We developed simple new techniques for installing minipiezometers and obtaining estimates of vertical hydraulic gradient, hydraulic conductivity, and specific discharge in gravel and cobble streambeds that allowed for large numbers of measurements to be obtained in remote locations. Our approach yielded values comparable to those obtained through more traditional methods. Consequently, these techniques may provide a labor cost-efficient way for detecting groundwater−stream water interaction patterns that are critical labor-attributes of stream and riparian systems at multiple scales.

Wildfire effects on stream food webs and nutrient dynamics in Glacier National Park, USA

We documented immediate and mid-term (5 years) impacts on streams from a large (15,500 ha) wildfire in northwestern Montana. Fire-related impacts were ecosystem-wide, extending from water chemistry to fish. During the initial firestorm, phosphorus and nitrogen levels increased 5- to 60-fold above background levels resulting from aerial deposition from smoke and ash. Nutrients returned to background concentrations within several weeks after the fire. During subsequent years, nutrient concentrations periodically increased in fire-impacted sites compared to reference sites, especially during spring run-off. Evidence of post-fire changes was also documented in the aquatic food web via stable isotope analyses. Macroinvertebrates and fish from fire-impacted sites were significantly more enriched in 15 N and depleted in 13 C than consumers from forested reference sites (P < 0:001). The post-fire isotopic shift in consumers was consistent with increased utilization of algae and/or other autochthonous food sources together with decreased reliance on terrestrial leaf litter and other allochthonous food sources. Such a post-fire shift from a detritus based on a periphyton-based food web fits predictions of the river continuum concept following canopy removal and nutrient enrichment. Following decades of active fire suppression, forest managers are now contemplating aggressive efforts to reduce the fuel build-up noted in forests throughout the western US. Such efforts could involve increased use of fire and mechanical thinning and harvest. Results from our work and others suggest that expanded fire activity could mobilize substantial quantities of highly available nutrients to lakes and streams. With significant nutrient delivery mechanisms involving water, as well as airborne transport via smoke and ash, the potential for increased nutrient loadings to surface waters could extend well beyond the catchment of any particular fire. As natural resource managers contemplate expanding the use of fire as a forest restoration tool, they face the dilemma that such efforts could run counter to a decades-long effort to reduce nutrient loadings to lakes and other surface waters threatened by eutrophication. # 2003 Elsevier Science B.V. All rights reserved.

CLIMATE, HYDROLOGIC DISTURBANCE, AND SUCCESSION: DRIVERS OF FLOODPLAIN PATTERN

Floodplains are among the worlds most threatened ecosystems due to the pervasiveness of dams, levee systems, and other modifications to rivers. Few unaltered floodplains remain where we may examine their dynamics over decadal time scales. Our study provides a detailed examination of landscape change over a 60-year period (1945-2004) on the Nyack floodplain of the Middle Fork of the Flathead River, a free-flowing, gravel-bed river in northwest Montana, USA. We used historical aerial photographs and airborne and satellite imagery to delineate habitats (i.e., mature forest, regenerative forest, water, cobble) within the floodplain. We related changes in the distribution and size of these habitats to hydrologic disturbance and regional climate. Results show a relationship between changes in floodplain habitats and annual flood magnitude, as well as between hydrology and the cooling and warming phases of the Pacific Decadal Oscillation (PDO). Large magnitude floods and greater frequency of moderate floods were associated with the cooling phases of the PDO, resulting in a floodplain environment dominated by extensive restructuring and regeneration of floodplain habitats. Conversely, warming phases of the PDO corresponded with decreases in magnitude, duration, and frequency of critical flows, creating a floodplain environment dominated by late successional vegetation and low levels of physical restructuring. Over the 60-year time series, habitat change was widespread throughout the floodplain, though the relative abundances of the habitats did not change greatly. We conclude that the long- and short-term interactions of climate, floods, and plant succession produce a shifting habitat mosaic that is a fundamental attribute of natural floodplain ecosystems.

Geomorphology, Logging Roads, and the Distribution of Bull Trout Spawning in a Forested River Basin: Implications for Management and Conservation

Abstract The Swan Basin in Montana is considered a stronghold of regional significance for the bull trout Salvelinus confluentus, a native char whose populations are fragmented and declining throughout its range. We used correlation analysis to examine spatial and temporal variation of bull trout redd count data (1982–1995) relative to geomorphic and land-use factors among nine principal spawning tributaries of the Swan River. Bull trout redd numbers were positively correlated with the extent of alluvial valley segments bounded by knickpoints and negatively correlated with the density of logging roads in spawning tributary catchments. The density of logging roads in spawning tributary catchments was not significantly correlated with geomorphic factors. Temporal trends among the principal spawning streams were variable. In four of the nine principal spawning streams, redd numbers increased significantly during the survey period, and in the remaining streams, redd numbers showed no significant change. Chang...

Rapid growth of snag-dwelling chironomids in a blackwater river : the influence of temperature and discharge

Growth rates were measured for chironomid larvae throughout the year in chambers simulating natural conditions at a field site on the bank of the Ogeechee River, a blackwater river in the Georgia Coastal Plain. Growth rates were among the highest ever reported for chironomids in laboratory or field studies, averaging 0.60, 0.43, and 0.44 mg mg-1 d-1 for Chironomini, Tanytarsini, and Orthocladiinae, respectively. The relationship of growth with temperature was best described with second-order polynomial curves for Chironomini, Tanytarsini, and total Chironomidae. Most curves suggest an x-axis intercept (zero growth) at 4-7°C and a growth maximum at 21-24°C. Growth rates were significantly lower and the relationship of growth with temperature was no longer significant when river discharge was well below the mean. Growth equations were applied to natural environmental conditions, predicting maximum growth during spring and fall, with an annual growth rate (an approximation of annual P/B ratio) ranging from 222 for Chironomini to 182 for Tanytarsini. Predicted growth rates were high throughout all seasons, indicating that the bioenergetic role of chironomids in invertebrate communities is substantially greater than can be assumed based on their standing stock biomass alone.

The Effects of Postfire Salvage Logging on Aquatic Ecosystems in the American West

Abstract Recent changes in the forest policies, regulations, and laws affecting public lands encourage postfire salvage logging, an activity that all too often delays or prevents recovery. In contrast, the 10 recommendations proposed here can improve the condition of watersheds and aquatic ecosystems.

Phosphorus and nitrogen dynamics in streams during a wildfire

Various studies report changes in phosphorus and nitrogen concentrations in surface waters after wildfires; however, we have found no reports which include nutrient data collected during actual wildfire activity. We had an opportunity to collect water chemistry data from several streams as a large (15,500 ha) intense firestorm passed through their watersheds. Phosphorus and nitrogen concentrations increased from 5 to 60 fold over background levels within the first two days of the fire with maximum recorded concentrations for dissolved nutrients reaching as high as 135 μg/L soluble reactive phosphorus, 261 μg/L ammonium, and 61 μg/L nitrate + nitrite. Total phosphorus and total nitrogen levels increased up to 206 μg/L and 349 μg/L respectively. Nutrient concentrations declined to background levels typically <5-10 μg/L within several days to several weeks. Experimental evidence suggests that the primary source of phosphorus was from leaching of ash deposited directly into the streams during the firestorm while the primary source of nitrogen appeared to be from diffusion of smoke gases into the stream waters.

Influence of Temperature and River Hydrograph on Black Fly Growth Rates in a Subtropical Blackwater River

Black fly larvae (Simulium spp.) were grown in 1.8-L circulating airlift chambers on the bank of the Ogeechee River, Georgia. Larvae were collected from the river, divided into size classes, and introduced into the stream chambers for growth trials whenever they were abundant during the year. Stream chambers were maintained at natural or experimental temperatures by immersing them in large tanks either supplied with a flow-through of river water or controlled by a heater or refrigeration unit. Daily mean river temperatures ranged from 11° to 30°C. Stream chamber water was exchanged twice daily with river water to closely resemble naturally occurring seston quantity and quality. Although instantaneous growth rate (g) of black flies was correlated with temperature, we found considerable variation. A positive growth rate was measurable at temperatures as low as 6.5°C and growth was not inhibited at ambient temperatures as high as 30°C. Growth rates at natural temperatures varied throughout the year from 0.09 to 0.43 mg mg-1 d-1. However, black flies grew more rapidly during the initial stages of high river discharge. Two predictive equations were developed relating growth to temperature; one for use during early stages of flooding, the other during late flood and low flow conditions. River flooding may increase seston quantity and quality and was associated with high larval densities of natural black fly populations. At the growth rates reported here, black flies are capable of completing larval development in less than 2 wk throughout much of the year. Such growth rates mean that annual production/biomass ratios will be several times greater than most values reported for temperate regions.