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Showing papers in "Journal of The North American Benthological Society in 1997"


Journal ArticleDOI
TL;DR: Multi-scale, mechanistic understanding of species-environment relations will likely contribute to better predictions about large scale problems, such as the establishment and spread of exotic species or alterations in community composition with changing land use or climate.
Abstract: A heuristic framework for understanding and predicting the distribution and categorical abundance of species in stream communities is presented. The framework requires that species be described in terms of their functional relationships to habitat selective forces or their surrogates, which constitute "filters" occurring at hierarchical landscape scales (ranging from microhabitats to watersheds or basins). Large-scale filters are viewed as causative or mechanistic agents that constrain expression of local selective forces or biotic potential at lower scales. To join a local community, species in a regional pool must possess appropriate functional attributes (species traits) to "pass" through the nested filters. Biotic interactions are also a potential filter on local community composition, and they are invoked at the lower hierarchical levels, after species have passed through the physicochemical habitat filters. Potential landscape filters and their associated selective properties are identified, as are ...

1,690 citations


Journal ArticleDOI
TL;DR: Comparing the procedures for establishing reference conditions, and assessing the strengths and deficiencies of multimetric and multivariate methods for establishing water-quality status, it is recommended that they be used together, and in conjunction with, multimetric studies.
Abstract: Traditional methods of establishing control sites in field-oriented biomonitoring studies of water quality are limited. The reference-condition approach offers a powerful alternative because sites serve as replicates rather than the multiple collections within sites that are the replicates in traditional designs using inferential statistics. With the reference-condition approach, an array of reference sites characterises the biological condition of a region; a test site is then compared to an appropriate subset of the reference sites, or to all the reference sites with probability weightings. This paper compares the procedures for establishing reference conditions, and assesses the strengths and deficiencies of multimetric (as used in the USA) and multivariate methods (as used in the UK, Can- ada, and Australia) for establishing water-quality status. A data set of environmental measurements and macroinvertebrate collections from the Fraser River, British Columbia, was used in the compar- ison. Precision and accuracy of the 2 multivariate methods tested (AUStralian RIVer Assessment Scheme: AusRivAS, BEnthic Assessment of SedimenT: BEAST) were consistently higher than for the multimetric assessment. Classification by ecoregion, stream order, and biotic group yielded precisions of 100% for the AusRivAS, 80-100% for the BEAST, and 40-80% for multimetrics; and accuracies of 100%, 100%, and 38-88%, respectively. Multimetrics are attractive because they produce a single score that is comparable to a target value and they include ecological information. However, not all infor- mation collected is used, metrics are often redundant in a combination index, errors can be com- pounded, and it is difficult to acquire current procedures. Multivariate methods are attractive because they require no prior assumptions either in creating groups out of reference sites or in comparing test sites with reference groups. However, potential users may be discouraged by the complexity of initial model construction. The complementary emphases in the multivariate methods examined (presence/absence in AusRivAS cf. abundance in BEAST) lead us to recommend that they be used together, and in conjunction with, multimetric studies.

661 citations



Journal ArticleDOI
TL;DR: A healthy stream is an ecosystem that is sustainable and resilient, maintaining its eco- logical structure and function over time while continuing to meet societal needs and expectations as discussed by the authors, which is a concept described in this paper explicitly incorporates both ecological integrity (maintaining structure and functions) and human values (what society values in the ecosystem).
Abstract: A healthy stream is an ecosystem that is sustainable and resilient, maintaining its eco- logical structure and function over time while continuing to meet societal needs and expectations. The concept described in this paper explicitly incorporates both ecological integrity (maintaining structure and function) and human values (what society values in the ecosystem). Stream ecologists who want their research to contribute to improving conditions in flowing waters require concepts like stream health, which will stimulate research in directions that will be more effective in restoring and preserving the unique organisms and ecosystems they study. Determining what is a healthy stream requires integration of stream ecology with disciplines such as economics and political science, because a concept of stream health must take into account the human attitudes and social institutions that are a part of the stream's societal watershed. New and fruitful directions for stream research lie in developing operational measures of stream health, which include the human dimension and move beyond identifying symptoms of ecological stress, and in elucidating the ecological processes and human actions that maintain stream health.

245 citations


Journal ArticleDOI
TL;DR: The results indicate that condensed tannin, N, C:N, and lignin are significantly correlated with processing rates, although the predictive power of these simple relationships is weak.
Abstract: Processing rates of autumn-shed leaves in aquatic habitats are highly variable. It has been hypothesized that these processing rates may, in part, be regulated by the concentrations of residual tannins in the leaves. Tests of this hypothesis have been inconclusive, and experimental designs may have been compromised by the use of both processing rates and tannin concentrations taken from a variety of sources using highly variable methods, sites, and experimental conditions. Here, processing rates of 48 species of deciduous leaves are measured using uniform conditions, and related to concentrations of leaf tannins, N, P, C:N, lignin, and toughness. The results indicate that condensed tannin, N, C:N, and lignin are significantly correlated with processing rates, although the predictive power of these simple relationships is weak. A multiple regression model using tannins, measured as total phenolics, N, and lignin explained almost 50% of the variation in processing rates, suggesting that the inhibition of pr...

239 citations


Journal ArticleDOI
TL;DR: It is proposed that dispersal capability and the stochastic effects of recruitment are key determinants of observed spatial and temporal variation in community structure in some streams.
Abstract: Analysis of genetic variation among populations of stream invertebrates provides a measure of the consequences of effective dispersal, and can be used to determine the extent of movement within and between streams and to infer the likely mechanisms involved. In our recent studies of rainforest stream invertebrates, we have found considerable genetic differentiation among populations of fully aquatic taxa, indicating limited in-stream movement on a very small scale. Adult flight appears to be the principal mechanism of dispersal for aquatic insects; however, analysis of the genetic structure of larval populations of some species also suggests that in-stream movement is limited to a small spatial scale. Furthermore, detailed analysis of the genetic structure of larval populations suggests that recruitment at the reach scale is the result of only a few adult matings and most likely from oviposition by only a few females. We propose that dispersal capability and the stochastic effects of recruitment are key d...

237 citations


Journal ArticleDOI
TL;DR: A more detailed analysis indicates that the most appropriate measure of disturbance may vary even among quite closely related taxa, and the painted-particle approach, described here, has the potential to permit such standarized comparative studies.
Abstract: Appropriate tests of disturbance theory require that disturbance is defined and measured in an organism-related sense. We quantified 7 measures of disturbance, 3 dealing with the pattern of disturbance of the stream bed (assessed using painted tracer particles), 3 dealing with aspects of discharge variation and 1 being a subjective composite measure of stream channel stability (Pfank- uch's index). Hypotheses relating to invertebrate taxon richness (maximal at intermediate levels of disturbance) and the representation of particular insect species traits (assemblages in more disturbed sites contain higher percentages of individuals possessing high adult mobility and streamlined-flat- tened larval morphology) were both supported when disturbance was measured in terms of bed movement but generally not when measured in terms of discharge variation. When disturbance was estimated by Pfankuch's index, species trait predictions were supported but the taxon richness pre- diction was not. A co-inertia analysis, searching for a co-structure between our environmental and faunistic data sets, allowed us to distinguish taxa that apparently are resistant to bed movement from taxa that appear to be resistant to flow variations; this more detailed analysis indicates that the most appropriate measure of disturbance may vary even among quite closely related taxa. The construction of a comprehensive theory of disturbance in streams requires that disturbance is quantified in a way that allows both multi-site and multi-study comparisons. The painted-particle approach, described here, has the potential to permit such standarized comparative studies.

228 citations


Journal ArticleDOI
TL;DR: In this article, a hierarchical framework of environmental factors affecting benthic algal spatial heterogeneity is presented with the ultimate determinants (climate, geology, land use, and biogeography) that are important constraints on Benthic assemblage structure at large spatial scales.
Abstract: The objectives of this paper were to introduce frameworks for predicting the determinants and consequences of the great heterogeneity in benthic algal assemblages. A hierarchical framework of environmental factors affecting benthic algal spatial heterogeneity is presented with the ultimate determinants (climate, geology, land use, and biogeography) that are important constraints on benthic algal assemblage structure at large spatial scales. These ultimate determinants constrain expression of intermediate and proximate determinants of benthic algal function and structure. A similar framework for temporal heterogeneity distinguishes how assemblages respond to short-term and long-term environmental changes, referred to as disturbances and stresses, respectively. Assemblages recover from punctuated (short-term) environmental change (disturbance) by immigration and reproduction of both persistent and recolonizing species. Assemblages adapt to permanent (longterm) environmental change (stress) by changing speci...

227 citations


Journal ArticleDOI
TL;DR: Examples of how alterations to streams and rivers in their lower reaches can produce biophysical legacies in upstream reaches on levels from genes to ecosystems are considered.
Abstract: Modifications of lower watersheds such as water abstraction, channel modification, land-use changes, nutrient enrichment, and toxic discharge can set off a cascade of events upstream that are often overlooked. This oversight is of particular concern since most rivers are altered by humans in their lower drainages and most published ecological investigations of lotic systems have focused on headwater streams. Factors contributing to ecological processes or biophysical legacies in upper watersheds often go unacknowledged because they occur at disparate geographic locations downstream (e.g., gravel mining, water abstraction, dams) with significant lag times. This paper considers examples of how alterations to streams and rivers in their lower reaches can produce biophysical legacies in upstream reaches on levels from genes to ecosystems. Examples include: 1) genetic- and species-level changes, such as reduced genetic flow and variation in isolated upstream populations; 2) population- and community-level chan...

226 citations


Journal ArticleDOI
TL;DR: At a global level, stream organic matter dynamics are driven primarily by climate through its effect on terrestrial vegetation.
Abstract: 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...

224 citations


Journal ArticleDOI
TL;DR: In this paper, the authors measured summer daytime temperature and the structure of riffle benthic insect assemblages from 45 montane streams in California and found that variation in assem- blage structure among streams was significantly related to temperature.
Abstract: Temperature is known to be an important mechanism affecting the growth and distri- bution of stream insects. However, little information exists that describes how variable temperatures are among streams of similar size, especially in physically heterogeneous landscapes. We measured summer daytime temperature and the structure of riffle benthic insect assemblages from 45 montane streams in California. Summer stream temperature was nearly randomly distributed across large-scale geographic gradients of latitude (6?) and elevation (2000 m). The lack of geographic trends in summertime stream temperature appeared to be caused by the strong relationship between local channel morphology and summer water temperature. Mean daytime water temperature was most strongly related to the % of the channel present as pools, which did not vary systematically with either latitude or elevation. We used multiple multivariate regression analysis, non-metric multidimensional scaling (NMDS), and graphical techniques to both quantify differences in insect assemblage structure among streams and to determine the degree to which assemblage structure was related to temperature. NMDS anal- yses were conducted on 3 similarity matrices based on: 1) presence and absence of all aquatic insect taxa encountered during the study, 2) densities of the 16 most numerically abundant taxa, and 3) population biomasses of the 16 most common taxa. All 3 analyses showed that variation in assem- blage structure among streams was significantly related to temperature, although assemblage struc- ture was most strongly related to sampling date-a consequence of sampling over a 98-d period. Temperature probably influenced assemblage structure in 2 ways: 1) by influencing developmental rates of individual taxa and overall assemblage phenology, thus affecting the relative abundances of taxa found on a specific sampling date, and 2) by excluding taxa unable to tolerate certain temperature ranges. Because of the strong dependency of assemblage structure on temperature and the lack of strong geographic trends in temperature among these streams, much of the measured variation in assemblage structure appeared to be unrelated to latitude or elevation. These results have important implications for both our understanding of natural biogeographic patterns of lotic organisms and our ability to detect and model the effects of climate change and other thermal alterations on stream ecosystems.

Journal ArticleDOI
TL;DR: Benthic algal community dynamics in a stream during and after a spate, including effects of grazers on freshwater benthic algae, is studied.
Abstract: in Rhode Island. III. Distribution of macrophytic vegetation in a small drainage basin. Hydrobiologia 140:183-191. STEINMAN, A. D. 1992. Does an increase in irradiance influence periphyton in a heavily-grazed woodland stream? Oecologia 91:163-170. STEINMAN, A. D. 1996. Effects of grazers on freshwater benthic algae. Pages 341-373 in R. J. Stevenson, M. L. Bothwell, and R. L. Lowe (editors). Algal ecology: freshwater benthic ecosystems. Academic Press, San Diego, California. STEVENSON, R. J. 1990. Benthic algal community dynamics in a stream during and after a spate. Journal of the North American Benthological Society 9:277-308.

Journal ArticleDOI
TL;DR: The hyporheic zone is assumed to be an important site for decomposition and nutrient turnover in many river ecosystems and the difference between whole-ecosystem respiration and respiration of the epilithic community was used for calculating the hypor heic contribution.
Abstract: The hyporheic zone is assumed to be an important site for decomposition and nutrient turnover in many river ecosystems. We determined ecosystem respiration, hyporheic community respiration, and respiration of the epilithic community at the sediment surface in the Necker, a gravel-bed river, during August 1994. Ecosystem respiration, assessed using single-station diel oxygen curves, varied between 4.6 and 7.0 g O 2 m -2 d -1 . To estimate the respiration of the epilithic community, stones were collected from the surface layer and enclosed in flow-through respiration chambers. The respiration of the epilithic community (mainly algae) ranged from 1.0 to 1.5 g O 2 m -2 d -1 , contributing 4-19% of the river ecosystem respiration. Two different methods were used for measuring hyporheic community respiration. First, chambers were incubated at 30 cm sediment depth for direct assessment of respiration rates. Respiration rates of the hyporheic sediment were...

Journal ArticleDOI
TL;DR: In this paper, the authors evaluated the inputs of coarse particulate organic matter (CPOM) to two headwater streams, one flowing through a mixed deciduous forest and one through a plantation of Eucalyptus globulus.
Abstract: To test whether afforestation with eucalyptus affects the amount, quality, and timing of litter inputs, we evaluated the inputs of coarse particulate organic matter (CPOM) to 2 headwater streams, one flowing through a mixed deciduous forest and one through a plantation of Eucalyptus globulus. Vertical and lateral traps were sampled at least monthly, and the material collected was sorted into 4 main categories: fallen leaves (several species), fruits and flowers, twigs and bark, and debris. The eucalyptus plantation resulted in a reduction of 32% of total litter inputs, and 73% of lateral inputs, compared to the mixed deciduous forest. It also had a less marked seasonal pattern of inputs, and different timing of peak litterfall, the peak in the deciduous forest occurring in autumn, whereas in the eucalyptus plantation the peak occurred in summer. Similarly, leaf diversity was greatly reduced under the eucalyptus, with 98% of the leaf litter mass from 1 species, resulting in broad changes in litter quality....

Journal ArticleDOI
TL;DR: In this article, a review of statistical techniques for quantitatively describing aspects of heterogeneity in spatial data, emphasizing the decomposition of heterogeneity into different scales of variation (trends, overall variability and spatial dependence or autocorrelation).
Abstract: Although theoretical and empirical studies show that spatial heterogeneity has important effects on the dynamics of populations and the structure of communities, there has been little rigorous quantification of terms like ''patchiness'' or ''spatial heterogeneity'' in studies of lotic systems. In order to compare the spatial heterogeneity of different systems and understand the causes and consequences of that heterogeneity, we must first be able to quantitatively measure it. Spatial heterogeneity has many aspects that change with the scale of our observations, so we need a battery of descriptive measures that explicitly consider the scale-dependence of ecological pattern Response variables exhibiting similar frequency distributions (i.e., similar overall variability) can have very different spatial distributions; consequently, descriptions of spatial heterogeneity require spatial data, i.e., data related to geographic locations (maps). We review statistical techniques for quantitatively describing aspects of heterogeneity in spatial data, emphasizing the decomposition of heterogeneity into different scales of variation (trends, overall variability and spatial dependence or autocorrelation). Gradients in spatial data can be evaluated using trend analyses (e.g., regressions), whereas the spatial structure of variation around trends can be evaluated using geostatistical methods. The central concept of geostatistics is spatial dependence, which is the degree to which values of a response variable differ as a function of the distance (lag) between sampling locations. Semivariograms plot variation among samples separated by a common lag Versus lag, and can be objectively decomposed by piece-wise regression techniques to estimate the strength and scales of spatial dependence. A variety of other methods can be used to quantify spatial heterogeneity from categorical and numerical maps depending on the question of interest and the underlying structure of the spatial data (e.g., methods derived from fractal geometry and information theory, nearest neighbor analysis, spectral analysis, Mantel's test). Spatial heterogeneity in stream organisms is driven by local variation in environmental conditions, by interactions between individuals of the same or different species, and by the effects of organisms on their abiotic environment. By applying geostatistical methods to spatial data collected from field experiments, stream ecologists can evaluate the effects of biotic and abiotic factors on the spatial arrangement of organisms in streams. We present examples of data obtained from experiments examining how consumers affect, and respond to, spatial heterogeneity in their resources. The results indicate that consumer-resource feedbacks should be considered when modeling the causes and consequences of spatial heterogeneity in streams.

Journal ArticleDOI
TL;DR: In this paper, the influence of heterogeneity on pattern and processes in streams describes why we need to examine heterogeneity, and outlines major themes that need to be considered, including the spatial distribution and persistence of biota, predator-prey interactions, and flux of materials among ecosystem compartments.
Abstract: This introduction to 9 articles on the influence of heterogeneity on pattern and processes in streams describes why we need to examine heterogeneity and outlines major themes we need to consider. Contributors show that a wide range of lotic patterns and processes may be influenced by physical and biological heterogeneity, including the spatial distribution and persistence of biota, predator-prey interactions, and flux of materials among ecosystem compartments. Authors have relied on both theoretical approaches (e.g., numerical simulation models) and empirical approaches (e.g., manipulative experiments) to garner insights into the causes and consequences of spatial and temporal variability in streams. We outline 6 major themes that emerged from this collection of papers and from the symposium on ecological heterogeneity held at the 1995 meeting of the North American Benthological Society in Keystone, Colorado. These themes encompass much of the nature of heterogeneity, and they have important implications ...

Journal ArticleDOI
TL;DR: The authors showed that precipitation was highly correlated with their 1st principle component but didn't come into their analysis until the 3rd principle component, which was probably due to the more limited latitudinal extent of their sites.
Abstract: Temperature fluctuation and nitrate were highly correlated with their 2nd principle component. One difference between their analysis and ours was that precipitation was highly correlated with their 1st principle component but didn't come into our analysis until the 3rd principle component. The lack of a temperature effect and the greater importance of precipitation in the study by Cushing et al. were probably results of the more limited latitudinal extent of their sites.

Journal ArticleDOI
TL;DR: The sampling characteristics of 8 invertebrate samplers in vegetated habitats by employing them side-by-side in the Florida Everglades suggested the use of 3: the funnel trap, the D-frame sweep net, and the 1-m2 throw trap, for studies of aquatic invertebrates in heavily vegetated wetlands such as the Everglade.
Abstract: Designing an effective sampling program and accurately interpreting the results requires a knowledge of the sampling characteristics of the various devices which might be used, but such knowledge is lacking for invertebrate samplers that can be used in heavily vegetated wetlands. We evaluated the sampling characteristics of 8 invertebrate samplers in vegetated habitats by employing them side-by-side in the Florida Everglades. The samplers differed in the number of individuals captured, number of species captured, and the equitability of species abundances. A funnel trap, a D-frame sweep net, and a stovepipe collected more individuals, more taxa, and a more even distri- bution of individuals among taxa, than did a 1-m2 throw trap and Hester-Dendy artificial substrates. Three other samplers, a minnow trap, a benthic corer, and a plankton net, captured very few indi- viduals. Most importantly, samplers differed consistently in the taxonomic composition of the inver- tebrates each captured. These differences argue for the use of several complementary methods in order to gain a complete representation of the invertebrate assemblage. We discuss issues involved in choosing samplers and recommend the use of 3: the funnel trap, the D-frame sweep net, and the 1-m2 throw trap, for studies of aquatic invertebrates in heavily vegetated wetlands such as the Ev- erglades.

Journal ArticleDOI
TL;DR: Simulations of population changes over a series of disturbance events showed that each of 4 mechanisms could maintain a viable population under certain conditions, and empirical evidence supports the efficacy of these mechanisms.
Abstract: We outline a hierarchical framework of classes of mechanisms, operating at different spatial and temporal scales, by which populations may exploit environmental heterogeneity to ensure persistence in environments subject to physical disturbance. Examples are provided for stream systems subject to high flow disturbances. Genotypic heterogeneity, encompassing morphological and physiological adaptations, operates at evolutionary and biogeographic scales, and ultimately constrains mechanisms at smaller scales. On ecological scales, organisms may exploit temporal or spatial heterogeneity, or both, to maintain population sizes larger than possible by morphological adaptations alone. For 2 classes of mechanism operating at large scales (>1 generation and >1 habitat patch), individuals do not survive disturbances and population persistence depends on recruitment from external sources. Where generations overlap and populations exploit temporal refugia in complex life cycles, dispersal occurs between habitat patche...

Journal ArticleDOI
TL;DR: In this paper, the authors compared Sonoran Desert streams with other streams in terms of retention efficiency of nitrate and examined the effects of a flood on nitrate retention and to determine which factors control the retention in the surface stream subsystem in Sycamore Creek, Arizona.
Abstract: The objectives of this study were 1) to compare Sonoran Desert streams with other streams in terms of retention efficiency of nitrate; 2) to examine the effects of a flood on nitrate retention and to determine which factors control nitrate retention in the surface stream subsystem in Sycamore Creek, Arizona; and 3) to compare the short-term nutrient addition technique with computations based upon natural nutrient gradients. From June to September 1995, we did 8 short-term nitrate and chloride additions (4 additions before and 4 after a flood) in a 240-m reach to measure nitrate uptake length as an index of surface stream retention efficiency of nitrate. We also calculated nitrate uptake lengths based on a natural downstream decline in nitrate concentration, using data from the addition dates and from previous studies. Nitrate uptake lengths measured in Sycamore Creek were short (<120 m) compared to published values from other streams, indicating a high retention efficiency of nitrate in this nitrogen-limi...

Journal ArticleDOI
TL;DR: In this article, the authors employ an inter-basin comparison of headwater streams to assess the influence of ecosystem hydrology on the structure and functioning of GW-SW ecotones.
Abstract: The groundwater-surface water (GW-SW) ecotone, or hyporheic zone, is an active component of stream ecosystems that influences whole-system metabolism and nutrient retention. Because hydrologic fluxes affect the supply of carbon, nutrients, and oxygen to the GW-SW ecotone, the biogeochemical structure of the ecotone (i.e., nutrient content) and the role of the ecotone in nutrient retention are expected to vary under differing hydrologic conditions. In this paper, we employ an inter-basin comparison of headwater streams to assess the influence of ecosystem hydrology on the structure and functioning of GW-SW ecotones. Specifically, we address how differing rate and extent of GW-SW interaction influences heterogeneity in interstitial nutrient content and how variation in GW-SW interaction alters the role of the ecotone in whole-system nutrient retention. A multiple regression model derived from 6 solute-injection experiments identified the extent and rate of hydrologic exchange between the stream and its aqui...

Journal ArticleDOI
TL;DR: The results suggest that nutrients added to the water column were quickly converted into benthic biomass, likely reducing pelagic responses to enrichment.
Abstract: Although the responses of pelagic algae and invertebrates to gradients of nutrient enrichment are well known, less is known about the responses of benthos to such gradients or how benthic and pelagic responses may interact. We performed a 9-wk experiment in 2000-L mesocosms in the field to test for the effect of water-column nutrient enrichment on phytoplankton, algae on sediments (epipelon) and hard surfaces (plastic strips), as well as pelagic and benthic primary consumers. The experimental design consisted of 4 nutrient enrichment rates (0, 0.5, 1.0 and 2.0 μg P L -1 d -1 , together with N to yield an N:P ratio of 20:1 by weight). Nutrient enrichment induced significant increases in chlorophyll a in phytoplankton and attached algae, but not epipelon. Zooplankton biomass was significantly higher in enriched mesocosms than in controls over the initial 4 wk of enrichment, but the effect was not sustained over the course of the experiment. Densities of sediment-dwelling, and hard-substra...

Journal ArticleDOI
TL;DR: In this article, the authors focus on the variation in annual average dissolved organic matter (DOM) concentrations and flux in streams and identify what factors might be most responsible for this variation.
Abstract: Dissolved organic matter (DOM) in streams is important as an energy resource for food webs (Bott et al. 1984, Meyer 1990a), a regulator of nutrient uptake and cycling by heterotrophic microbes (Lock 1981, Meyer et al. 1988), a complexing agent for metals (McKnight and Bencala 1990, Mierle and Ingram 1991), and a determinant of pH and alkalinity (Oliver et al. 1983). DOM has been shown to be an important metabolic substrate in some streams, with DOM use contributing significantly to total stream metabolism (Naiman et al. 1987, Meyer and Edwards 1990). Sources of DOM are both the terrestrial watershed (McDowell and Likens 1988, Hornberger et al. 1994) and instream processes, such as leaching and decomposition of allochthonous particulate organic matter and release by stream algae (Kaplan and Bott 1982, Meyer 1990b). For small streams, the primary site of DOM use is the stream bottom, including the interstitial waters of streambed sediments (Dahm 1981, Hynes 1983, Ford and Naiman 1989, Fiebig and Lock 1991). In larger rivers, the water column may also be an important site for DOM use (Vannote et al. 1980). Stream DOM is an important indicator of watershed-scale hydrologic and biogeochemical processes. Large water-soluble pools of DOM are present in the upper soil horizons of forests and grasslands (litter, 0, and A horizons) and are sources of DOM to drainage waters; however, lower soil horizons (B and C horizons) often contain materials (e.g., iron and aluminum oxides) that effectively sorb and immobilize DOM (McDowell and Wood 1984, Cronan 1990). Hydrologic pathways involving lateral flow of water through or over surface soil layers often have relatively high concentrations of DOM, whereas water flowpaths that pass slowly through lower soil layers usually have low DOM concentrations (Moore and Jackson 1989, Kaplan and Newbold 1993). The commonly observed increase in DOM concentrations during periods of high discharge is at least partly due to shifts in dominant flowpaths from deeper routes to shallow subsurface or surface pathways (Tate and Meyer 1983, Mulholland et al. 1990, Hornberger et al 1994). Wetlands are also an important source of DOM to streams, and several analyses have shown that differences in baseflow DOM concentrations among streams are strongly related to the amount of wetland drainage contributing to streams (Mulholland and Kuenzler 1979, Eckhardt and Moore 1990). Saturated riparian soils and wetlands appear to be particularly important contributors to stream DOM, especially during storms (Fiebig et al. 1990, Hemond 1990). In this paper I focus on the concentrations and flux of DOM in streams whose organic matter budgets are presented in the preceding chapters. My objective is to define the variation in annual average DOM concentrations and flux and to identify what factors might be most responsible for this variation.

Journal ArticleDOI
TL;DR: Future directions for the use of variance in stream ecology should attempt to couple scale-dependent physical patterns with biological patterns or processes, develop experimental frameworks to determine if species interactions or other biotic processes vary with scale, embrace statistical methods for determining the relative importance of variance-generating processes, and develop methods for the quantification of Variability in biologically meaningful ways.
Abstract: Variability in the spatial and temporal patterns of stream biota has been well documented, yet the causes and consequences of this variability are poorly understood. Most early work focused on how changes in mean environmental parameters over space or time influence the abundance or distribution patterns of biota. We argue for an increased focus on the study of variability in these parameters. To date, only a few lotic studies have used variance as a dependent variable i.e., showing that changes in the variance in some parameter can be related to changes in the mean of that or another parameter. These studies have suggested interesting links between ecological patterns and processes at a variety of scales. The use of variance as an independent variable and its experimental manipulation (i.e., hold the mean of some parameter constant while altering its variance) may also lead to new understandings of how pattern and process are linked. We begin by outlining when and why the study of variance may be importa...

Journal ArticleDOI
TL;DR: The data suggest that diatom species differ in their tolerance to resource-limiting conditions in developing periphyton mats, and these differences affect autecological characteristics.
Abstract: We followed periphyton succession for 120 d in an artificial stream system to: 1) document an increase in cell densities and associated decrease in irradiance to the base of developing periphyton mats; 2) determine the vertical location of motile and nonmotile diatom species within the mat associated with these changes; and 3) determine the viability of diatom cells at the base of the mat compared with those of the same species at different vertical locations within the mat. We developed a novel method for producing thin cross-sections of intact periphyton mats to document the vertical distribution of algal species in horizontal 0.1-mm strata from the base of the mat to the canopy. Results demonstrated that the adnate nonmotile diatom Achnanthidium minutissimum exploited the substratum during early succession when the mat was relatively thin and without a canopy, and the population retained live cells at the base of the mat throughout the 120-d experiment, demonstrating a high tolerance to low light level...

Journal ArticleDOI
TL;DR: This exploration of ideas about stream shape and its functional consequences suggests several opportunities for stream ecology to contribute to general ecological theory and suggests that the process of idea generation is straightforward, accessible, and beneficial for both science and scientist.
Abstract: Stream research has contributed only modestly to general ecological theory. Moreover, the rate of generation of new ideas in stream ecology may have slowed recently. These shortcomings might be remedied by a more deliberate effort to generate new, creative ideas about streams that will enhance their use in developing general theory. The creative process has been thoroughly studied by psychologists and, while the field is still in flux, most cognitive psychologists agree that juxtaposition of disparate concepts or observations can stimulate new ideas. How this technique might enhance stream ecology is illustrated with an analogy between functional morphology and stream ecology. Definition of form and function in streams is required to develop this analogy and a hierarchical, scale-dependent approach is essential. The effect of structure and configuration of stream channels on their functioning is a promising research area that can be applied at several scales. Parallels with landscape ecology are strong. E...

Journal ArticleDOI
TL;DR: P predictive models using 2 macroinvertebrate data sets from bankside habitats at 49 undisturbed reference sites from 6 Victorian river basins showed that the fauna conformed with expectation, and the O/E ratio could thus be considered a sensitive measure of disturbance.
Abstract: We constructed predictive models using 2 macroinvertebrate data sets (for both species and family) from bankside habitats at 49 undisturbed reference sites from 6 Victorian river basins; data were accumulated over 4 to 6 sampling occasions. Classification (by unweighted pair-group arithmetic averaging with the Bray-Curtis association measure) showed 3 site groups were evident at the species level and 4 at the family level. A subset of 5 of 22 environmental variables provided maximum discrimination (using stepwise discriminant analysis) between the 3 species site groups; these variables were: conductivity, altitude, substrate heterogeneity, distance of a site from source, and longitude. Four variables discriminated between the 4 family site groups: conductivity, catchment area upstream of site, mean annual discharge, and latitude. From the discriminant analysis, it was possible to predict the group into which an unknown site (specified only by measurements on the 4 or 5 variables just noted) would be placed and thus the probabilities of occurrence of taxa at this site. To test predictive ability, 4 sites were removed at random from the 2 data sets and the classification and discriminant models were recalculated. This process was repeated 5 times. The identity and number of taxa observed at each of these sites were compared with those predicted with a probability of occurrence >50% and the results expressed as a ratio of numbers observed to numbers expected (O/E). This ratio varied from 0.75 to 1.05 at the species level and from 0.83 to 1.12 at the family level, indicating that the fauna conformed with expectation (O/E near 1.0). To test such predictive models on independent data, O/E ratios were also calculated for family data collected in spring at 18 sites from a basin not used in the original models. Two new discriminant models based on single sets of samples from the reference sites taken in spring were constructed for this purpose. O/E ratios varied from 0.09 to 1.01 for the 18 sites and were inversely correlated (r = -0.4 to -0.8) with a range of water quality variables, the values of which increased as water quality deteriorated. The O/E ratio could thus be considered a sensitive measure of disturbance.

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TL;DR: Their ability to extrapolate from individual behaviors to populations and communities in streams will improve when the authors consider the repercussions of individual behaviors and environmental factors over broader spatial and temporal scales.
Abstract: Biological processes, such as predator-prey or competitive interactions, occur at multiple spatial and temporal scales, but their impacts on the distribution, abundance, and fitness of organisms may only be detectable at some scales. This is because 1) small scale (local) processes may be constrained by large-scale (regional) processes, 2) the influence of organism movement changes with spatial scale, and 3) multiple small-scale processes may interact and produce variation that obscures large-scale patterns. Most ecologists would like to know the relevance of small-scale observations and experiments for large-scale patterns and processes acting over long time periods. In this paper we consider whether patterns of individual behavior translate in a straightforward way to patterns in population dynamics, community structure, or individual fitness at larger spatial and longer temporal scales. We illustrate our discussion with data from communities living in high altitude streams in western Colorado, coastal ...

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TL;DR: In lotic ecosystems, BOM tends to decrease downstream as channels become larger and riparian influences decline, and benthic detrital storage is one of the most poorly understood components of stream organic matter budgets.
Abstract: In lotic ecosystems, BOM is a major energy source for secondary production (Minshall 1967, Benke et al. 1984), influences nutrient cycles (Mulholland et al. 1985), and affects export of DOM and POM (Bilby and Likens 1980, Bilby 1981, Smock et al. 1989). Benthic detritus also influences channel stability and retention characteristics (Keller and Swanson 1979, Mosley 1981, Webster et al. 1994) and provides habitat for stream microorganisms, macroinvertebrates (Benke et al. 1984, Huryn and Wallace 1987), and fish (Angermeirer and Karr 1984, Elliott 1986). However, in spite of the great importance of BOM to stream ecosystem function, benthic detrital storage is one of the most poorly understood components of stream organic matter budgets (Cummins et al. 1983). Storage of BOM is governed by a broad spectrum of processes. At the scale of the river continuum, BOM tends to decrease downstream as channels become larger and riparian influences decline (Naiman and Sedell 1979, Minshall et al. 1983, Conners and Naiman 1984, Naiman et al. 1987). Individual reaches, however, are influenced not only by their position along a river continuum but also by local variations such as the character of riparian vegetation (Minshall et al. 1983, Gurtz et al. 1988) and floodplain size. Within reaches, BOM distribution is further affected by retention mechanisms, including debris dams and pools (Huryn and Wallace 1987, Smock et al. 1989, Trotter 1990, Jones and Smock 1991), channel characteristics like gradient, and interactions between main-channels and flood-