Low-gradient Streams Research Articles

Development and Evaluation of a Habitat Rating System for Low-Gradient Wisconsin Streams

Abstract Most existing habitat indices and models have been developed for medium- to high-gradient streams and, therefore, tend to undervalue low-gradient streams. We analyzed physical habitat and fish community biotic integrity data from 50 low-gradient stream stations to develop a habitat rating index for the assessment of low-gradient streams in Wisconsin. Low-gradient stations were defined as having gradients of 3 m/km or lower and less than 5% of their length as riffles. Of 43 habitat variables considered, we selected 7 for use in the index: percent channelization, channelization age, percent instream cover, percent bank erosion, sinuosity, standard deviation of thalweg depth, and percent buffer vegetation. Based on a multiple-regression analysis, channelization age and percent instream cover were given greater weight in the index than the other five variables. Habitat index values explained 58% of the variation in index of biotic integrity (IBI) scores among the 50 stations used to develop the index...

REAERATION OF A LOW-GRADIENT TROPICAL RAINFOREST STREAM IN THE AMAZON BASIN OF PERU

Stream water quality data and atmospheric data were collected in a sub-basin of the Rio Napo in the Amazon rainforest of Peru. Previous investigations of a low-gradient stream indicated a diurnal dissolved oxygen curve that shows deoxygenation during daylight hours and reaeration during night hours. Data were collected to determine possible and most-probable causes of this unexpected pattern. Results of the investigation indicate that deoxygenation occurs during daylight hours because of the increase in stream temperature. Three agents of nighttime reaeration were found. The first and most significant was reaeration during rain events. Subsequent to the rain event, flow from a groundwater seep provided reaerated water to the site. In the absence of sufficient ground-water flow, nighttime condensate from the humid subcanopy atmosphere with nighttime drop in air temperature provided a source of well aerated water to the system. [Key words: water quality, dissolved oxygen, rainforest, Amazon, Peru.]

Drift ecology of western catostomid larvae with emphasis on Warner suckers, Catostomus warnerensis (Teleostei)

We studied drift ecology of Warner sucker, Catostomus warnerensis, larvae in streams of Warner Valley, Oregon in 1992 and 1993 in part to determine whether downstream transport of larvae limits juvenile recruitment. Variation in runoff for the two years was extreme, where peak discharge in 1992 was two orders of magnitude lower than peak discharge in 1993. We deployed drift nets in low-gradient stream sections that are modified by diversions. Low catches of drifting sucker larvae (zero in 1992 and two in 1993) indicate that losses into diversions were probably minimal. In 1992, we conducted in situ experiments to determine how sucker larvae behaved when exposed to high velocity current by placing individuals of various sizes in mid-channel and tracking drift responses by snorkeling. Even the smallest larvae used did not drift far (2.6 m) or for very long (0.97 min), as they resisted downstream transport by exploiting cover provided by aquatic plants and debris. We also recorded locations of larvae during a 24-hour cycle to determine whether positions occupied during the day changed at night. We found that groups were positioned closer to shore at night in 1993 than in 1992, suggesting that larvae reduced the likelihood of becoming entrained into swift current by moving away from mid-channel at night when visual orientation is impaired. These patterns of drift avoidance are different from behaviors of other western catostomid larvae, potentially because terminal lake habitat in Pleistocene basins such as the Warner Valley has been unreliable.

Effects of large woody debris placement on stream channels and benthic macroinvertebrates

Large woody debris (LWD) was added as an experimental stream restoration technique in two streams in southwest Virginia. Additions were designed to compare human judgement in log placements against a randomized design and an unmanipulated reach, and also to compare effectiveness in a low- and a high-gradient stream. Pool area increased 146% in the systematic placement and 32% in the random placement sections of the low-gradient stream, lending support to the notion that human judgement can be more effective than placing logs at random in low-gradient streams. Conversely, the high-gradient stream changed very little after LWD additions, suggesting that other hydraulic controls such as boulders and bedrock override LWD influences in high-gradient streams. Logs oriented as dams were responsible for all pools created by additions regardless of stream or method of placement. Multiple log combinations created only two pools, while the other seven pools were created by single LWD pieces. Total benthic macroinvertebrate abundance did not change as a result of LWD additions in either stream, but net abundances of Plecoptera, Coleoptera, Trichoptera, and Oligochaeta decreased, while Ephemeroptera increased significantly with the proportional increase in pool area in the low-gradient stream.

Stream Organic Matter Budgets: An Introduction

This analysis of organic matter dynamics in streams has 3 objectives: 1) to explore the relationships between physical characteristics of streams and their watersheds (climate, geomorphology) and stream organic matter dynamics using data from a broad geographic area; 2) to compare stream organic matter dynamics in a diverse array of streams in order to suggest determinants of observed patterns; and 3) to reveal deficiencies in currently available data on organic matter dynamics in streams. Streams were included in this analysis not to represent the global diversity of stream types but because organic matter data were available. In the introductory chapter we describe the kinds of data included for each stream and provide brief descriptions of previously published organic matter data for streams included in the comparative analysis but not described in individual chapters. The next 16 chapters present organic matter data for streams from North America, Europe, Australia, and Antarctica. Most of the streams represented are in the temperate zone of North America. Data presented include climate and geomorphic variables and organic matter inputs, exports, and standing crops. The chapters on individual streams are followed by 7 chapters analyzing physical features of these streams and specific components of the organic matter budgets. Stream size, water temperature, and precipitation were the most important variables setting the physical template for organic matter processes occurring in the streams. Watershed area was the best predictor of gross primary productivity (GPP), which increased with increasing watershed area. Watershed area, discharge, and soluble reactive phosphorus concentration explained 71% of the variation in GPP. Climate (latitude) and vegetation type were more important than stream order in predicting litter inputs across a broad geographic range of streams, although, within a river basin, litterfall decreased with increasing stream order. Regression of benthic organic matter (BOM) and latitude and precipitation proved useful in predicting BOM standing crop in streams at a continental scale, although BOM was also related to channel characteristics such as gradient and woody debris. Benthic respiration increased dramatically with increasing temperature (Q₁₀=7.6), suggesting a response related not only to metabolism but also to changes in BOM quality in response to latitudinal shifts in vegetation. Terrestrial and riparian vegetation was found to play an important role in regulating suspended particulate organic matter (POM) concentration and export, with higher values observed in forested streams and in lower gradient streams with extensive floodplains. Channel slope was the best predictor of dissolved organic matter (DOM) concentration and export, probably because of its relationship with riparian wetlands and hydrologic flowpaths. In the final chapter, a synthesis of the organic matter budgets, we reached two conclusions: 1) At a global level, stream organic matter dynamics are driven primarily by climate through its effect on terrestrial vegetation. 2) Despite significant progress in understanding organic matter processes in streams, many of the differences we found among streams reflect omissions of important components of the budget, especially accurate measures of streambed area, heterotrophic respiration, standing stock of fine BOM, and groundwater inputs of DOM.

Organic Matter Budgets for Streams: A Synthesis

Organic Matter Budgets for Streams: A Synthesis

Interreplicate Variance and Statistical Power of Electrofishing Data from Low-Gradient Streams in the Southeastern United States

I assessed the relationship between interreplicate variance and the mean for electrofishing catch per unit effort (defined as number of fish per 100 m2 of stream surface area) from 56 sites in 22 first- through fourth-order streams on the coastal plain of South Carolina. Variance and mean were strongly and positively related. This relationship was unaffected by type and quantity of instream structure and was similar among schooling and nonschooling species. Interreplicate variance was unaffected by replicate reach lengths ranging from 60 to 130 m. Replicate lengths near the lower end of this range required less total effort (number of replicates times replicate length) than longer replicates for comparable precision. Statistical power computations indicated that large numbers of samples (>25) were required to detect small (<20%) differences among means, and that the required number of samples was greater when catch per unit effort was low, indicating that power can be increased if multiple passes are used to increase the catch. However, it required less total time to use a relatively large number of single-pass replicates than a smaller number of multiple-pass replicates to achieve a given level of precision. Investigation of several types of data transformations indicated that the log transformation was most efficient at reducing the correlation between the variance and the mean, as required for parametric statistical analysis.

Impacts of River Regulation on the Terminal Lakes and Mouth of the River Murray, South Australia

The River Murray is a highly regulated, low gradient stream. Prior to barrage construction near the Murray Mouth saline water was present sporadically far upstream. Barrage completion by 1940 has had geo‐morphic and ecological impacts. Estuarine Lakes Albert and Alexandrina became permanent freshwater bodies with elevated water levels. Exposed lake margins have eroded by up to 10 m yr', whereas along sheltered shorelines, sedimentation has accompanied reed growth. Upstream weirs have inhibited coarse sediment from reaching the lakes. In the Goolwa Channel, sedimentation changed from bioclas‐tic sands to muds, accumulating at up to 4.5 mm yr' over the past 50 years. Regulation has also transformed a migrating flood tidal delta at the Murray Mouth into a permanently vegetated island.

Path analysis of collective properties and habitat relationships of fish assemblages in coastal plain streams

Collective properties of fish assemblages at 44 sites in low-gradient streams (orders 1–3) on the upper coastal plain of South Carolina, U.S.A., were highly variable among sites: richness, 2–17 species per site; density, 0.2–9.5 individuals∙m−2; mean individual mass, 0.4–22.2 g per individual; and biomass, 0.1–42.1 g∙m−2. Principal components analysis reduced 15 habitat parameters to four interpretable components that were used as orthogonal predictive variables in path analysis. Path analysis, with a directional model containing intermediate steps and multiple dependent variables, was used as an alternative to multiple regression. Two principal components, associated with velocity (and its covariates) and depth (and its covariates), were the primary correlates of biomass (R2 = 49%), richness (44%), mean size (36%), and density (20%), with cover variables contributing relatively little to any R2value. Velocity effects were negative and depth effects positive for all collective properties. Habitat effects on biomass were mediated by effects on individual fish size rather than numbers. Correlations of collective properties at sites sampled in 2 years were similar to those from the single year, habitat-based path model, implying that the path model was adequate and inclusive, and accurately reflected collective properties of these communities.

Cause of tectonic reactivation and subtle uplifts in the Rocky Mountain region and its effect on the stratigraphic record

Stratigraphic studies show that widespread, albeit subtle, topographic uplifts have occurred throughout the U.S. Rocky Mountain region during middle and late Mesozoic time. Individual paleotopographic highs generally have wavelengths on the order of tens of kilometres and amplitudes on the scale of metres. In places, these features correspond to sites of previous or later deformation and so suggest the possibility of tectonic reactivation along pre-existing zones of structural weakness in the crust. Observations of modern features and modeling studies indicate that uplifts of small magnitude are both a common and expected result of changes in intraplate stress levels. Finite-element modeling suggests that broad-wavelength, low-amplitude topography can develop in a heterogeneous elastic plate under high-stress magnitudes along preexisting faults and under low-stress magnitudes where zones of high and low strength are juxtaposed. Although these features are small, they have sufficient topography to bring about large changes in paleocurrent patterns for low-gradient streams and significantly affect isopach patterns. Although subtle uplifts from this cause are difficult to predict, they are likely a common occurrence and may be the most dramatic features in an area that is otherwise tectonically quiescent. Thus, subtle uplift may be a background noise rather than a harbinger of regional orogenesis.

Lotic Macroinvertebrate Production in Three Dimensions: Channel Surface, Hyporheic, and Floodplain Environments

A three—dimensional spatial perspective was used to determine annual macroinvertebrate production in two low—gradient, first—order stream systems on the Coastal Plain physiographic province of Virginia. Production in predominant habitats was weighted by the proportional areal abundance of each habitat to determine production in the channel surface, hyporheic zone, and floodplains of both blackwater streams. Highest production as dry mass in Buzzards Branch, a sand—bottomed stream, was in debris dams (27.4 g/m2); production on the sand sediment was lower (4.9 g/m2) and decreased with depth into the hyporheic zone, primarily as a function of decreasing oxygen concentration. Production on the floodplain varied with elevation, and hence period of inundation; it was 1.1 and 4.3 g/m2 at high and low elevations, respectively. Production, weighted for habitat abundance, was 1.7 g/m2 on the floodplain and 15.8 g/m2 in the channel (10.2 g/m2 in the hyporheic zone; 5.6 g/m2 on the channel surface). Production in the Buzzards Branch stream system, incorporating the channel and floodplain, was 2.4 g/m,2, 67% of which was on the floodplain, 21% in the hyporheic zone, and 12% on the channel surface. Production in the Colliers Creek system, with a clay and detritus sediment and no hyporheic zone, was only 2.8 g/m2 in debris dams but was 6.1—6.6 g/m2 on channel sediments and floodplain soils. Production in the stream system was 6.1 g/m2, 95% of which was on the floodplain. Primary consumers composed 72—74% of production in the channels and 80—85% on the floodplains. The predominant functional feeding groups differed between habitats, suggesting a spatial mosaic of functioning within the stream systems. The majority of production in debris dams and on the sediment was by shredders (30—46%) and predators (31—48%). Collector—gatherers composed 58% of production in the Buzzards Branch hyportheic zone and 56—61% on the floodplains of both streams. This study further emphasizes the patchy nature of lotic systems and that habitat—specific sampling is required to adequately determine invertebrate production and function in streams. It also shows the need to view streams with a three—dimensional spatial perspective. Both the hyporheic zone and floodplains can contribute a significant proportion of invertebrate production in low—gradient stream systems.

Incidence and Causes of Physical Failure of Artificial Habitat Structures in Streams of Western Oregon and Washington

Abstract In recent years an increasing share of fishery management resources has been committed to alteration offish habitat with artificial stream structures. We evaluated rates and causes of physical impairment or failure for 161 fish habitat structures in 15 streams in southwest Oregon and southwest Washington, following a flood of a magnitude that recurs every 2–10 years. The incidence of functional impairment and outright failure varied widely among streams; the median failure rate was 18.5% and the median damage rate (impairment plus failure) was 60%. Modes of failure were diverse and bore no simple relationship to structure design. Damage was frequent in low-gradient stream segments and widespread in streams with signs of recent watershed disturbance, high sediment loads, and unstable channels. Comparison of estimated 5–10-year damage rates from 46 projects throughout western Oregon and southwest Washington showed high but variable rates (median, 14%; range, 0–100%) in regions where peak discharge ...

Life History of the Least Darter Etheostoma microperca at the Northwestern Limits of Its Range

-From May 1984 to October 1985, we studied the life history of the least darter in a small low-gradient stream at the northwestern limit of the species' range. During the spawning and growing seasons, least darters occupied shallow, heavily weeded water in and immediately downstream of pools. In late autumn, they moved to the deep water of pools where they overwintered. Adults spawned between late May and late July on the leaves of Vallisneria, Potamogeton and Carex located at stream margins near pools. Larvae hatched in June and July, at 3.5-3.8 mm total length, absorbed the yolk at 4.0-4.5 mm and completed fin ray development at ca. 10 mm. Males and females grew to similar lengths in the 1st 2 yr (29 mm and 34 mm total length, respectively), but females attained greater total body mass (0.22 g vs. 0.20 g the 1st yr and 0.38 g vs. 0.33 g the 2nd yr). On average, females lived longer than males and reached a longer ultimate total length (38 mm vs. 35 mm). Of the 432 fish aged, 78.0% were young-of-the-year and 1-year-olds, 21.1% were 3-year-olds and 0.9% were 3-year-olds (3 females, 1 male). Both sexes reached maturity at age 1. Spawning potential in females was associated with gonadosomatic indices of 10-35%, but a similar association could not be determined for males. We believe that females developed a minimum of three egg clutches during the spawning season, with an average of 88 eggs for each of the first two clutches. Total fecundity averaged at least 226-264 eggs per female and increased as a function of body size. The diet of adult least darters consisted primarily of copepods and cladocerans in May (94%) and October (63%), and midge larvae in June (73%) and July (62%). When compared to a centrally located population, our population exhibited a slower growth rate, smaller size at maturity, and greater longevity, which translated into repeated reproduction. These life history differences may represent an adaptive response to reproductive uncertainty as predicted by bet-hedging theory.

Characteristics of Coarse Woody Debris for Several Coastal Streams of Southeast Alaska, USA

Coarse woody debris (&gt; 0.2 m in diameter and 1.5 m long) was measured along five undisturbed low-gradient stream reaches; volume, decay class, and horizontal orientation in relation to channel flow of first-, second-, third-, and fourth-order coastal streams were determined. Debris was also classified into four influence zones based on stream hydraulics and fish habitat. Average debris length, diameter, and volume per piece increased with stream size. Eighty percent of debris volume of the first-order and the smaller second-order streams was suspended above or lying outside the bankfull channel, while less than 40% was similarly positioned in the fourth-order stream. Approximately one-third of all debris was oriented perpendicular to stream flow, regardless of stream size. First-, second-, and third-order streams had a higher proportion of recent debris in the channel than the fourth-order stream ([Formula: see text]19 vs. 8%), most new debris being attributable to a major 1984 windstorm. Tree blowdown had a major influence on debris distribution along the smaller stream reaches. Debris jams and accumulations in the largest stream were formed from floated debris. These characterizations are useful for evaluating the distribution and amount of woody debris associated with land-management activities.

Effect of Nutrient Content on Leaf Decomposition in a Coastal Plain Stream: A Comparison of Green and Senescent Leaves

Abstract The decomposition of fresh-green and autumn-shed (senescent) red maple leaves (Acer rubrum) were compared in a low-gradient blackwater stream. When the two types of leaves were incubated in the stream during the fall, there was no significant difference in processing rate. The invertebrate fauna was similar on the two leaf types and did not appear to affect decomposition. However, higher densities of invertebrates were found on green leaves during the final stage of decomposition. Bacterial densities were higher on senescent leaves than on green leaves during the initial phase of decomposition, although green leaves were richer in nutrients. Toxic or inhibitory compounds in the green leaves may override effects of nutrient enhancement on bacterial growth and leaf decomposition.

Logging in Western Oregon: Responses of headwater habitats and stream amphibians

We compared occurrence and abundance of four species of aquatic amphibians in 23 streams flowing through uncut forests to 20 streams flowing through forests logged between 14 and 40 years prior to the study. Species richness was highest in streams in uncut forests. Eleven streams in uncut forests contained all four species, and only two of these streams had fewer than three species present. Eleven streams in logged stands had one or no species present, and only one contained all four species. Density and biomass of all four species were significantly greater (2–7 X) in streams in uncut forests. Physical comparisons between types of streams were similar, except that streams in logged stands had generally smaller substrata, resulting from increased sedimentation. Densities of Pacific giant salamanders ( Dicamptodon ensatus) and Olympic salamanders ( Rhyacotriton olymoicus) were positively correlated with stream gradient in logged stands, but not in uncut forests, suggesting that the disruptive effects of increased sedimentation are greatest in low-gradient streams. Tailed frogs ( Ascaphus truei) and Dunn's salamanders ( Plethodon dunni) occurred more often in strems in logged stands when uncut timber was present upstream, but neither density nor biomass of any species were related to either presence of uncut timber upstrem or years since logging. Logging upstream from uncut forests also had no effect on the presence, density or biomass of any species. Tailed frogs and Olympic salamanders may be extirpated from headwaters traversing clearcuts; these streams should be afforded some protection in plans for managed forests.

Correction: Two Simple Models for Estimating Daily Mean Water Temperatures and Diel Variations in a Danish Low Gradient Stream

Correction: Two Simple Models for Estimating Daily Mean Water Temperatures and Diel Variations in a Danish Low Gradient Stream

Two Simple Models for Estimating Daily Mean Water Temperatures and Diel Variations in a Danish Low Gradient Stream

The Danish River Sus'a is at the studied reaches a third-fourth order low gradient stream with a large summer biomass of macrophytes. In a simple model daily mean water temperature was described as a function of daily mean air temperature at the two localities studied. A linear regression analysis showed that the slopes of the two regression lines were significantly different, which could be explained by the relative proportion of incoming groundwater. A simple model for estimating the diel variations in stream water temperature was established from submodels of incoming and outgoing radiation and of the exchange of heat, mainly with the atmosphere. The only input to the model is air temperature and photosynthetic active radiation, PAR. Two parameters, Aso, and Acon were calibrated. The parameter Aso, expresses the proportion of PAR used to heat the water. At the upstream locality Aso, varied with season due to shading from the herbaceous bank vegetation, whereas Asol at the downstream locality was constant. ACon expresses the rate of heat exchange between air and water, and Acon was found to be linearly related to the reaeration coefficient, which was estimated independently. The model simulated the diel variations in water temperatures quite accurately. Even on days when air temperature and PAR showed large fluctuations did simulated water temperatures deviate less than 1°C from actual measurements during 90% of the time. Using the model at the downstream reach, with an average Asoi and A¢on as estimated from the reaeration coefficient simulated temperatures did never deviate more than 2°C from actual measurements and less than 1°C in 84% of the time. It is concluded that the establishment of such simple temperature models would be very useful in a wide range of ecological studies in streams.

The exopterygote insect community of a mountain stream in North Carolina, USA: Life histories, production, and functional structure

Life histories and production of the Exopterygota inhabiting a first to second order mountain stream in North Carolina, USA, were studied by replicated monthly sampling of three different habitats (BO = boulder‐outcrop, R = riffle, PL = pool). Life histories were diverse, ranging from multi‐voltine (e.g. Baetis) to semi‐voltine (e.g. Leuctra ferruginea, Sweltsa lateralis). Habitat‐weighted annual production was 1862 mg (ash‐free dry weight)/m2 with > 50% being based on four taxa (of 21 considered): Serratella sp. (16%), Peltoperlidae (16%), Leuctra spp. (13%), and Beloneuria spp. (8%). The Odonata, Ephemeroptera, and Plecoptera contributed 36, 760, and 1066 mg/m2 to annual production, respectively. Production was distributed evenly among four functional groups with collector‐gatherers, shredders, scrapers, and engulfing‐predators contributing 21%, 33%, 23%, and 23%, respectively. Production by functional groups followed broad taxonomic categories with the Ephemeroptera, euholognathous Plecoptera, and systellognathous Plecoptera contributing 93%, 90%, and 92% of the scraper, shredder, and engulfing‐predator production, respectively. Serratella sp. contributed 77% of the collector‐gatherer production. Annual production by the Exopterygota was greatest in the BO habitat (2056 mg) > R (1981 mg) > PL (951 mg). Production in the BO was attributable to a unique combination of taxa compared with R and PL. Sixty‐five percent of the BO production was based on Serratella sp., a collector‐gatherer. Collector‐gatherers constituted only 2% and 8% of PL and R production, respectively. The remainder of the PL and R production was generally distributed evenly among scrapers, shredders, and engulfing‐predators. Comparison of the functional structure of the exopterygote communities of headwaters with higher order streams indicated a shift from a dominance of detritivory to predation. In higher order, low gradient streams characterized by limited stable substrate, the majority of the Exopterygota are unable to use entrained food resources directly, and predation upon the filter‐feeding Endopterygota (e.g. Chironomidae) may be the predominant method of feeding.

Limitations on the Use of Gabions to Improve Fish Passage

Abstract Gabions are used frequently to improve aquatic habitat and rehabilitate damaged fish habitat in low-gradient streams. However, gabions should not be installed perpendicular to the stream flow if water velocities are expected to exceed 5 ft/s. This recommendation would preclude the use of gabions to improve fish passage at waterfalls. Also, gabions installed below culverts should be placed well downstream of the culvert. Weirs constructed of reinforced concrete and/or large boulders could be used as alternatives to gabions to provide for fish passage.