Jack W. Feminella

The urban stream syndrome: current knowledge and the search for a cure

Abstract The term “urban stream syndrome” describes the consistently observed ecological degradation of streams draining urban land. This paper reviews recent literature to describe symptoms of the syndrome, explores mechanisms driving the syndrome, and identifies appropriate goals and methods for ecological restoration of urban streams. Symptoms of the urban stream syndrome include a flashier hydrograph, elevated concentrations of nutrients and contaminants, altered channel morphology, and reduced biotic richness, with increased dominance of tolerant species. More research is needed before generalizations can be made about urban effects on stream ecosystem processes, but reduced nutrient uptake has been consistently reported. The mechanisms driving the syndrome are complex and interactive, but most impacts can be ascribed to a few major large-scale sources, primarily urban stormwater runoff delivered to streams by hydraulically efficient drainage systems. Other stressors, such as combined or sanitary sewer overflows, wastewater treatment plant effluents, and legacy pollutants (long-lived pollutants from earlier land uses) can obscure the effects of stormwater runoff. Most research on urban impacts to streams has concentrated on correlations between instream ecological metrics and total catchment imperviousness. Recent research shows that some of the variance in such relationships can be explained by the distance between the stream reach and urban land, or by the hydraulic efficiency of stormwater drainage. The mechanisms behind such patterns require experimentation at the catchment scale to identify the best management approaches to conservation and restoration of streams in urban catchments. Remediation of stormwater impacts is most likely to be achieved through widespread application of innovative approaches to drainage design. Because humans dominate urban ecosystems, research on urban stream ecology will require a broadening of stream ecological research to integrate with social, behavioral, and economic research.

DEVELOPMENT AND EVALUATION OF PREDICTIVE MODELS FOR MEASURING THE BIOLOGICAL INTEGRITY OF STREAMS

The ratio of the number of observed taxa to that expected to occur in the absence of human-caused stress (OIE) is an intuitive and ecologically meaningful measure of biological integrity. We examined how OIE ratios derived from stream invertebrate data varied among 234 unimpaired reference sites and 254 test sites potentially impaired by past logging. Data were collected from streams in three montane ecoregions in California. Two sets of River Invertebrate Prediction and Classification System (RIVPACS) predictive mod- els were built: one set of models was based on near-species taxonomic resolution; the other was based on family identifications. Two models were built for each level of taxonomic resolution: one calculated 0 and E based on all taxa with probabilities of capture (Pj) > 0; the other calculated 0 and E based on only those taxa with Pc ? 0.5. Evaluations of the performance of each model were based on three criteria: (1) how well models predicted the taxa found at unimpaired sites, (2) the degree to which OIE values differed among unimpaired reference sites and potentially impaired test sites, and (3) the degree to which test site OIE values were correlated with independent measures of watershed alteration. Predictions of species models were more accurate than those of family models, and pre- dictions of the PC ? 0.5 species model were more robust than predictions of the PC > 0 model. OIE values derived from both species models were related to land use variables, but only assessments based on the Pc > 0.5 model were insensitive to naturally occurring differences among streams, ecoregions, and years.

Interactions between Stream Herbivores and Periphyton: A Quantitative Analysis of past Experiments

This review summarizes the state of knowledge regarding herbivory in stream ecosystems by quantitatively analyzing the results of 89 experimental studies published between 1972 and 1993. Our primary objective was to determine if general patterns exist among stream ecosystems in the type and strength of interactions occurring between herbivores (grazers) and their primary food source, periphyton. We conducted two types of meta-analyses of the published literature: (1) analyses of the proportion of studies showing significant effects for three types of interactions (effects of grazers on periphyton, effects of periphyton on grazers, and effects of grazers on other grazers and benthic animals) and (2) analyses of factors influencing the magnitude of effect that grazers had on periphyton. For effects of grazers on periphyton, we also determined (1) if the likelihood of observing significant effects varied with the spatial and temporal scale at which experiments were done and (2) if the magnitude of effect by grazers on periphyton abundance varied with spatial and temporal scale, grazer taxon, grazer abundance, and periphyton accrual based on the difference in treatments with and without grazers. Grazers held at ambient densities usually reduced periphyton biomass (70% of experiments) and altered algal taxonomic or physiognomic structure (81%) relative to grazer removal treatments, whereas grazers had slightly lower effects on periphyton productivity (usually <70% of experiments, depending on productivity measure). Experiments conducted in laboratory streams and at two spatial scales in the field (few or single habitat units and stream reaches or basins) were equally likely to report significant effects of grazers. Both short-term (≤4 wk) and longterm (>4 wk) experiments also were equally likely to report significant effects of grazers on periphyton. However, the magnitude of effect grazers had on periphyton biomass varied with the amount of periphyton accrual, grazer taxon, and grazer population biomass. Grazer effects also were higher for longer studies conducted under laboratory conditions than for shorter studies conducted in the field. A high proportion of the experiments that manipulated periphyton abundance significantly affected grazer densities and growth. Reduction in periphyton abundance usually reduced grazer density and growth. Experimental manipulations of dominant grazers typically had strong and usually negative effects on densities and growth of other species of benthic animals, either from direct (e.g., interference) or indirect (e.g., resource exploitation) mechanisms. Results of these analyses suggest that stream herbivores regulate their food resources as or more frequently than herbivores in other ecosystems, and strongly contradict the view held by many ecologists that stream communities are regulated primarily by abiotic factors. Although publication bias (i.e., the tendency for journals to publish positive results) appears minimal, we cannot yet generalize from these results to the entire universe of stream ecosystems because (1) most studies were conducted during summer base flow conditions and (2) results do not adequately represent interactions during the more physically stressful conditions that occur during periods of flooding, drought, or extreme cold. If rapid progress in the development of general stream ecosystem theory is to occur, we believe (1) future studies should be explicitly designed within the context of general ecological questions, (2) as much background information as possible describing environmental conditions should be collected, and (3) journals should permit and urge inclusion of tabular data describing both experimental conditions and treatment means and variances.

Channel morphology, water temperature, and assemblage structure of stream insects

Temperature is known to be an important mechanism affecting the growth and distribution 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 analyses 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 assemblage structure among streams was significantly related to temperature, although assemblage structure 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.

Comparison of Benthic Macroinvertebrate Assemblages in Small Streams along a Gradient of Flow Permanence

Benthic invertebrates were quantified in 6 small upland streams in Alabama for 2 y to examine the degree to which variation in assemblage structure was related to the hydrologic permanence of riffle habitats. Streams differed along a gradient of flow permanence: 2 were normally intermittent (i.e., riffles ceased flowing in normal rainfall years) in summer, 1 was rarely intermittent (i.e., normally perennial), and 3 streams were occasionally intermittent (i.e., riffles ceased flowing during dry years). Despite large differences in flow permanence among streams, invertebrate assemblages differed only slightly. Presence-absence data revealed that 75% of the species (171 total taxa, predominantly aquatic insects) were ubiquitous across the 6 streams or displayed no pattern with respect to permanence; 7% of the total species were found exclusively in the normally intermittent streams. Although somewhat variable, many of the community richness and diversity measures were positively correlated with stream permanence. Year-to-year differences in assemblages within single streams appeared as great as differences between streams of contrasting permanence within a given year. Faunal similarity among streams was higher in 1995, a year with normal summer rainfall that followed a wet year (1994), than in 1994, a wet year that followed a dry year. Between-year differences in density and richness were lowest in spring and winter and greatest in summer, the season when communities were directly exposed to drying of riffles in intermittent streams. Several populations of common invertebrates during summer displayed non-random distributions along the permanence gradient. These data in general support the hypotheses that 1) benthic invertebrate assemblages show predictable, albeit subtle, relationships with stream permanence, and 2) antecedent hydrologic conditions associated with riffle permanence, perhaps because of their effects on survival and recruitment of subsequent generations, can influence the structure of benthic assemblages in streams.

Hydrologic Influences, Disturbance, and Intraspecific Competition in a Stream Caddisfly Population

In an earlier study, exploitative intraspecific competition was demonstrated for middle instars of the caddisfly Helicopsyche borealis in Big Sulphur Creek, a stream in northern coastal California. This population is univoltine with early instars first appearing in June, growing into late instars the following spring, and emerging as adults in May. Competition occurs during the summer dry season (June-September), a period of low-flow conditions without storms or increases in stream discharge. Beginning in autumn, however, larval densities decline because of wet-season storms and high discharge. Using multiple regression, we found a strong relationship between spring (i.e., post wet season) density of late-instar H. borealis and various hydrologic parameters of the preceding wet season over a 4-yr period, 1985-1988. Of eight hydrologic parameters used as indices of disturbance, total wet-season rainfall and peak discharge together accounted for 42% (P < .0001) of the variation in H. borealis density. In contrast, densities of middle instars of the next generation in summer were unrelated either to the preceding wet-season hydrologic regime or late- instar densities of the previous generation. Field experiments conducted in enclosures using larval densities of H. borealis that corresponded to harsh, moderate, and mild wet-season hydrologic regimes (low, inter- mediate, and high densities, respectively) indicated that: (1) increases in larval density had a strong negative effect on algal biomass (as chlorophyll a); (2) larval density was negatively correlated with the proportion of larvae that pupated, and with pupal size; and (3) the high density (mild hydrologic regime) treatment produced smaller adult males and females, and lower fecundities than intermediate and low densities (moderate and harsh regimes, re- spectively). In most years, storms and associated disturbance reduce late-instar H. borealis density below levels of larval competition; this counteracts earlier competition among middle instars that occurs during low-flow conditions. In drought years, however, densities may not be reduced as severely by wet-season storms and competition may continue until emergence. In this case, competition can reduce individual fitness, but because of high adult densities during these mild-disturbance conditions the reproductive capacity of the population is unaffected.

Herbivory and intraspecific competition in a stream caddisfly population

SummaryField experiments were conducted to assess the effects of different population densities of the herbivorous caddisfly Helicopsyche borealis on periphyton biomass and on its own growth rate in Big Sulphur Creek, a third-order stream in northern California, USA. Stream enclosures were used to vary grazer density from one-eighth to twice natural density (1/8X–2X) in two experiments (35 d and 60 d), which spanned the period of most rapid larval growth. Periphyton biomass and chlorophyll a were inversely related to grazer density. Grazer densities of 1/8X–1/2X moderately reduced periphyton when compared to an ungrazed control, whereas densities of 1X–2X greatly depleted periphyton. The growth rate of H. borealis larvae declined with increasing larval density. Growth rate was highest at densities of 1/8X–1/2X; larvae grew more slowly at 1X and showed no growth at 2X. Weekly supplementation of periphyton to 1/4X, 1X, and 2X densities significantly increased the final body mass of larvae at 1X and 2X (by 26% and 50%, respectively, compared to unsupplemented larvae) but did not change the body mass of larvae at 1/4X. These results suggest that periphyton is a limiting resource in Big Sulphur Creek and that H. borealis larvae compete exploitatively for that resource. Intraspecific competition may be an important, but often overlooked, feature of many herbivore populations in streams.

Herbivorous caddisflies macroalgae and epilithic microalgae dynamic interactions in a stream grazing system

Summary1. During the low-flow period (April–October) in sunlit pools of Big Sulphur Creek (northern coastal California), the attached algal community predictably changes from an assemblage dominated by lush, upright Cladophora glomerata filaments in spring and early summer to one dominated by epilithic diatoms and blue-green algae (together=microalgae) in late summer through early autumn. Previous studies in this stream indicated that grazing by the caddisflies Helicopsyche borealis and Gumaga nigricula maintain low algal biomass during the latter part of this period. We used a combination of in situ exclusion/enclosure experiments to examine (1) the separate and combined effects of these grazers on Cladophora and microalgal assemblages, and (2) food preferences, growth, and microdistribution patterns of grazers when offered these different algal foods. 2. Grazers exerted strong but divergent effects on algal assemblages. Selective grazing on Cladophora by G. nigricula greatly accelerated the transition from upright Cladophora to epilithic microalgae, whereas selective grazing on microalgae by H. borealis dramatically reduced biomass of these forms. Grazers were largely ineffective at reducing the non-preferred algal food source (i.e. Cladophora by H. borealis, microalgae by G. nigricula). In the case of each grazer, growth was highest on the preferred algal food. Together, the activity of these grazers produced a low-biomass assemblage dominated by microalgal cells. 3. Removal of the Cladophora overstory by G. nigricula resulted in a three-fold increase in the abundance of epilithic microalgae, the preferred food of H. borealis. Elimination of Cladophora by G. nigricula can increase food availability for H. borealis and, in so doing, can indirectly facilitate the growth of this grazer during food-limited conditions. However, microdistribution of G. nigricula shifts from high overlap with H. borealis in spring and early summer when Cladophora is abundant to low overlap in late summer after Cladophora has been eliminated. This may indicate intense competition between these species for limited epilithic algae, and a concomitant movement by G. nigricula to areas in the stream where food resources are more available.

Correspondence between stream macroinvertebrate assemblages and 4 ecoregions of the southeastern USA

Benthic invertebrates were quantified at summer baseflow from 30 streams draining largely forested watersheds within 7 river catchments (Coosa, Tallapoosa, Tennessee, Black Warrior, Conecuh, Altamaha, Chattahoochee) of 4 Level III ecoregions (Blue Ridge, Southwestern [SW] Appalachians, Piedmont, Southeastern [SE] Plains) of the southeastern USA. The study 1) compared invertebrate distributions classified by large-scale ecoregions against those of small-scale river catchments, and 2) assessed if taxonomic resolution of invertebrate identification (family vs genus/morphospecies) influenced relative classification strength of ecoregions and catchments. Principal components analysis indicated that environmental differences across catchments and ecoregions were associated more with variation in baseflow water chemistry (e.g., total alkalinity, conductivity) than with geomorphic or geographic variables. Using simple community presence/absence measures, richness of Ephemeroptera, Plecoptera, and Trichoptera (EPT richness) followed the pattern Blue Ridge > SW Appalachians = Piedmont = SE Plains. When grouped by catchment, total and EPT richness tended to be lower in lowland than in upland regions. However, Bray–Curtis presence/absence similarities coupled with flexible UPGMA (unweighted pair-group method using arithmetic averages) analyses revealed that invertebrate assemblages were distinctive among ecoregions both at the genus/morphospecies and family levels. Differences in overall similarity among ecoregions were highly significant, with upland Blue Ridge and lowland SE Plains streams displaying the lowest interecoregional similarity, and Piedmont and SW Appalachians streams displaying the highest similarity. Faunal similarity within a given ecoregion approximated that observed within individual catchments. Family-level groupings were almost as robust at discriminating catchments and ecoregions as were classifications derived from genus/morphospecies. The ecoregion concept appears to be as useful a classification scheme as that derived from smaller river catchments in the delineation of stream invertebrate distributions in the southeastern USA.

Detection of biotic responses to urbanization using fish assemblages from small streams of western Georgia, USA

We examined relationships between stream fish assemblages and land use alteration associated with urbanization in 15 lower Piedmont watersheds along an urbanization gradient north of Columbus, western Georgia. Based on land cover data from 2002 Landsat 7 TM imagery aerial photos, streams drained watersheds that were largely urban, developing (suburban), agricultural (pasture), managed pine forest, and unmanaged mixed-forest. We quantified fish seasonally from 3 run-pool segments in each stream, and used a variety of metrics as response variables in analyses of relationships between fish assemblage structure and land use and natural basin variation. In general, Georgia-Index of Biotic Integrity (GA-IBI) values, Bray-Curtis faunal similarity of streams to mean conditions within reference streams, proportions of fish as lithophilic spawners, and fish lacking eroded fins, lesions, tumors decreased with increasing urbanization. Multiple regression indicated that assemblages were explained by a combination of land use and natural basin variables (basin size, average discharge, nearest distance to a larger downstream tributary [colonization source]), with land use variables being important predictors of summer assemblages and natural basin variables being more important in winter and spring assemblages. Non-metric multidimensional scaling (NMDS) ordinations revealed strong separation between assemblages in urban watersheds and forested watersheds, whereas assemblages in agricultural and developing watersheds were intermediate between those in urban and forested watersheds. Our data suggest that fish are reliable indicators of anthropogenic disturbance at the landscape scale, at least seasonally, and may be used to forecast the magnitude of landscape-level changes in stream structure and function associated with the conversion of forests to urban/suburban land in the Southeast.