Burrowing benthic organisms promote water and solute fluxes across the sediment–water interface. Water and solutes penetrate the burrow walls and are transported into/out of the sediment when organisms flush their burrows with overlying water. Few studies have been done to investigate bioirrigation under shifting environmental conditions. We experimentally quantified bioirrigation by Chironomus plumosus larvae in the laboratory at 3 ranges of O₂ saturation (low, medium, and high O₂ concentrations), 2 temperatures (10 and 20°C), and over different seasons. We measured ventilation activities with O₂ and flow-velocity microsensors, flow velocities during pumping periods with color tracers, pumping rates with conductivity exchange experiments, and rates of advective and diffusive water influx into the sediment by influx assays (NaCl was the tracer in both latter experiments). O₂ saturations <12% extended pumping durations/h, whereas saturations <3% decreased pumping durations to ∼0. Flow velocities were 2× higher when O₂ saturation was >50% than when it was <10%. Rising temperatures altered larval pumping (higher pumping frequency, lower pumping length) and increased flow velocity. Hence, pumping rate and rates of water influx were significantly higher at 20 than at 10°C. Seasonal variations in bioirrigation occurred despite constant laboratory conditions, i.e., the rate of water influx was significantly higher in spring/summer than in autumn. Our study shows that temporally varying environmental conditions should be considered when evaluating bioirrigation-mediated benthic fluxes across the sediment–water interface.

Knickpoints are dynamic geomorphic formations in the longitudinal stream profile that have long been a subject of interest for geomorphologists, but have been largely unstudied in stream ecology. We measured discharge, bed sediment, and macroinvertebrate communities around knickpoints in forested and urban catchments. Knickpoints introduced microscale heterogeneity in discharge. This heterogeneity may be important in providing refugia for benthic biota during low-flow conditions, depending on the condition of the bed sediment below the knickpoint, which was highly variable. In addition, knickpoints supported a unique filterer-dominated community of macroinvertebrates not found elsewhere in the stream reach. The knickpoint itself also may maintain a higher overall density of macroinvertebrates in comparison to other habitats in the stream reach, but this prediction was only weakly supported. Instead, the largest differences in macroinvertebrate community metrics were consistently between urban and forested knickpoints. Decreases in density, species richness, and diversity from forested to urban knickpoints greatly outweighed any longitudinal differences in the macroinvertebrate community within individual knickpoint sites. Thus, we conclude that knickpoints may serve as hotspots of biodiversity and provide substantial habitat heterogeneity over a small area, but the valley-scale influence of catchment land use far outweighs the effect of these microscale geomorphic features in influencing benthic communities.

Displacement of riparian vegetation by exotic species is a global phenomenon with the potential to affect leaf breakdown rates by shredders. We predicted that exotic riparian vegetation would have a greater effect on leaf breakdown by temperate than by tropical shredders because temperate shredders usually feed on a limited range of generally palatable leaves, whereas tropical shredders are naturally exposed to a higher variety of leaves, many of them unpalatable. We tested 3 hypotheses with common shredder assemblages from tropical Queensland and temperate Tasmania (Australia): 1) tropical shredders are equally efficient at breaking down native and exotic vegetation, whereas temperate shredders are less efficient at breaking down exotic vegetation; 2) tropical shredders are more generalist in their leaf choices than temperate shredders; and 3) shredders are more generalist in their leaf choices among exotic than among native vegetation. Hypothesis 1 was not supported. Caddisflies (tropical or temperate) were able to consume both native and exotic leaves, whereas non-caddisfly shredders fed only on native leaves, a result suggesting that shredding capacity depends on the identity of the shredder species or their phylogenetic position rather than on their origin. Hypothesis 2 was supported. Tropical shredders fed on various leaf types, whereas most temperate shredders chose one leaf type and fed on it for the duration of the experiment. Hypothesis 3 was not supported. Specificity of shredder choices did not differ between native and exotic leaves, a result suggesting that shredding behavior is not flexible, regardless of the leaf litter available. Thus, invasive riparian plants may affect leaf breakdown by shredders, particularly in temperate streams, but effects may vary depending on assemblage composition, the nature and timing of litterfall, and interactions with climate.

Anthropogenic activities increase rates of N input to the environment, and loss of this N is controlled by several factors, including denitrification. Streams are the initial receptors of terrestrial N, but the extent to which variability in stream denitrification rates are related to differences in microbial community structure are largely unexplored. In our study, the rate of denitrification and taxonomic and functional gene diversity and abundance were examined in 3 Indiana (USA) streams with differing amounts of watershed agriculture. Taxonomic and functional gene diversity were measured using terminal restriction length polymorphisms of the 16S ribosomal ribonucleic acid (rRNA) and nitrous oxide reductase (nosZ) genes, and abundance was examined using quantitative polymerase chain reaction (Q-PCR) and total direct cell counts. As expected, streams with highest amounts of watershed agriculture had highest NO₃⁻ concentrations and highest sediment organic matter (OM) content leading to higher denitrification rates. Overall, denitrification rates were controlled primarily by sediment OM content and secondarily by nosZ abundance and nosZ terminal restriction fragment (T-RF) number. However, total bacterial numbers were not related to peaks in denitrification rate. The 2 sites with the most substantial differences in watershed agriculture, NO₃⁻ concentrations, and sediment OM content also had the largest differences in both nosZ abundance and nosZ gene profiles. Overall, our results suggest that denitrification rates in agricultural streams are influenced by a combination of environmental variables (primarily benthic OM and NO₃⁻ concentrations) and microbial community composition.

State water-quality professionals developing new biological assessment methods often have difficulty relating assessment results to narrative criteria in water-quality standards. An alternative to selecting index thresholds arbitrarily is to include the Biological Condition Gradient (BCG) in the development of the assessment method. The BCG describes tiers of biological community condition to help identify and communicate the position of a water body along a gradient of water quality ranging from natural to degraded. Although originally developed for fish and macroinvertebrate communities of streams and rivers, the BCG is easily adapted to other habitats and taxonomic groups. We developed a discriminant analysis model with stream algal data to predict attainment of tiered aquatic-life uses in Maine's water-quality standards. We modified the BCG framework for Maine stream algae, related the BCG tiers to Maine's tiered aquatic-life uses, and identified appropriate algal metrics for describing BCG tiers. Using a modified Delphi method, 5 aquatic biologists independently evaluated algal community metrics for 230 samples from streams and rivers across the state and assigned a BCG tier (1–6) and Maine water quality class (AA/A, B, C, nonattainment of any class) to each sample. We used minimally disturbed reference sites to approximate natural conditions (Tier 1). Biologist class assignments were unanimous for 53% of samples, and 42% of samples differed by 1 class. The biologists debated and developed consensus class assignments. A linear discriminant model built to replicate a priori class assignments correctly classified 95% of 150 samples in the model training set and 91% of 80 samples in the model validation set. Locally derived metrics based on BCG taxon tolerance groupings (e.g., sensitive, intermediate, tolerant) were more effective than were metrics developed in other regions. Adding the algal discriminant model to Maine's existing macroinvertebrate discriminant model will broaden detection of biological impairment and further diagnose sources of impairment. The algal discriminant model is specific to Maine, but our approach of explicitly tying an assessment tool to tiered aquatic-life goals is widely transferrable to other regions, taxonomic groups, and waterbody types.

Conservation and management of headwater streams amid rapid global change require an understanding of the spatial and environmental factors that drive species distributions and associated ecosystem processes. We used a hierarchical analytical framework to model effects of catchment-scale topography and wetland geomorphic classes on stream physical habitat, chemistry, and macroinvertebrate and fish communities in 30 headwater streams across the Kenai Lowlands, southcentral Alaska, USA. We identified 135 macroinvertebrate taxa, 122 of which were aquatic insects, of which 79 were dipterans. We collected only 6 species of fish, but juvenile coho salmon and Dolly Varden were collected in 17 and 25 of the 30 streams and reached densities >500 and 1300/km, respectively. Flow-weighted slope, an indicator of water residence time and gradient, was the best catchment-scale correlate of macroinvertebrate and fish community structure, and its effect was mediated by wetland geomorphic classes and numerous water chemistry, substrate composition, and channel geomorphology variables measured at the reach scale. Many macroinvertebrate taxa showed high fidelity to different levels of the topographic gradient, resulting in high β diversity but relatively similar levels of α diversity across the gradient. Juvenile salmonids were segregated among streams by both species and age classes. Coho salmon fry and parr (<10 cm total length [TL]) had significant unimodal distributions that peaked in streams with intermediate slopes and gravel substrate, whereas presmolts (≥10 cm) were found only in lowest-sloping streams with mostly peat substrate and deep, slow channels. Large Dolly Varden (≥8 cm) were found across the entire gradient but were most abundant in high-sloping catchments, whereas small Dolly Varden (<8 cm) followed a similar distribution but were absent from the lowest-gradient sites with low flow velocity, dissolved O₂, and gravel substrate. Predictive modeling indicated that all of the 547 km of headwater streams in the study area might serve as potential habitat for ≥1 species and age class of salmonids. Our study should assist in development of catchment management tools for identifying and prioritizing conservation efforts in the region and may serve as a framework for other studies concerning biodiversity and focal species conservation in headwater streams.

Most foodweb research in lentic systems has focused on pelagic primary (phytoplankton) and secondary (zooplankton) production as the primary energy sources for higher trophic-level production. Recent research has demonstrated that secondary production of benthic primary consumers can affect pelagic fish production and foodweb structure in lakes. We used the instantaneous growth method to calculate secondary production of chironomids in Lake Winnebago, Wisconsin (USA), where previous research has shown that lake sturgeon (Acipenser fulvescens) rely heavily on the benthos (chironomids) as a food source. We also used literature-derived data and the instantaneous growth method to calculate annual production of lake sturgeon to test whether chironomid production is sufficient to support the current lake sturgeon population in Lake Winnebago. We collected benthic samples with an Ekman grab at 4 profundal sites during ice-free conditions on 11 dates from spring 2008 through spring 2009. We measured instantaneous growth rates for 7 chironomid length classes at 5 thermal regimes in the laboratory. Mean annual density of Chironomidae was 2714 individuals/m², mean biomass was 2.75 g dry mass (DM)/m², and mean annual production of Chironomidae was 7.59 g DM m⁻² y⁻¹. Estimated annual production of lake sturgeon was 0.02 g DM m⁻² y⁻¹ in 2007. We concluded that in 2008–2009 chironomid secondary production was sufficient to support the lake sturgeon population in Lake Winnebago. The annual production rates for chironomids in Lake Winnebago are higher than rates in many other lakes in North America, presumably because of the eutrophic condition of Lake Winnebago.

Many pharmaceutical compounds have been detected in surface waters, but their effects on stream ecosystem function are not currently understood. Concentrations of cimetidine, a widely used antihistamine, have increased in streams and rivers. Invertebrates may be affected by exposure to cimetidine because they use histamines to regulate olfactory and stomatogastric function. Primary producers, such as algal biofilms, also may be affected by cimetidine, which may in turn, alter metabolism and ultimately invertebrate population dynamics. We conducted a long-term (83 d) experiment in artificial streams to measure the chronic effects of cimetidine on benthic biofilm function and stream invertebrate growth and population dynamics. We exposed 2 common invertebrate species, Gammarus fasciatus and Psephenus herricki, and biofilm to concentrations of cimetidine similar to what is found in USA surface waters (0.07–70.0 µg/L). We found no consistent effect of cimetidine on biofilm chlorophyll a or function (gross primary production, respiration). Growth and final biomass of reproducing G. fasciatus was reduced across all cimetidine treatments compared to the control. In addition, no individuals of the smallest size class occurred at lower concentrations of cimetidine suggesting that cimetidine may either more strongly affect invertebrates of smaller size classes or may suppress adult reproduction. We also found that higher concentrations of cimetidine significantly reduced survivorship of P. herricki. Low concentrations of cimetidine appear to have no effect on primary producers, but our observations indicate there are indirect negative effects on invertebrate growth and population dynamics.

The Platte River caddisfly (Ironoquia plattensis) is a semiterrestrial limnephilid that inhabits sloughs along the Platte River in central Nebraska (USA). The species was discovered in 1997, and little is known about what controls its limited distribution or threatens its existence. We investigated effects of grazing by cattle (Bos taurus) on caddisfly abundance in a grassland slough. In April 2010, we established exclosures to isolate cattle from areas with caddisflies. We measured aquatic larval densities in April 2010 and 2011. We estimated grazing intensity from the normalized difference vegetation index (NDVI) values extracted from aerial images made in autumn 2010. Grazing intensity varied among plots, but ungrazed plots had more vegetation (higher NDVI values) than grazed plots. In April 2011, larval densities were greater in ungrazed than in grazed plots. Larval densities and NDVI values were strongly positively correlated, a result suggesting that reduction in vegetative cover from grazing was associated with decreased densities of caddisflies. Increased vegetative cover may have provided structure needed for adult courtship and inputs of organic matter to support larval feeding. Repeated, season-long grazing may have long-term negative consequences for the Platte River caddisfly in grassland sloughs when vegetation does not recover and other effects of cattle persist year after year. Resting pastures from grazing to permit vegetation to rebound appears to allow cattle and Platte River caddisflies to coexist in sloughs along the Platte River.

The concept of nutrient spiraling combines the geological, hydrological, and biological processes that influence nutrient cycling in streams. Spiraling studies have demonstrated connections between metabolic and nutrient cycles, organic matter (OM) dynamics, and hydrologic controls. Most spiraling studies have addressed the dynamics of a single element. However, nutrients do not move through ecosystems in isolation. Recent models have used ecological stoichiometric theory to couple N and P cycles, but empirical data to support these conceptual frameworks are generally lacking. We investigated the relationship between N and P uptake and the extent to which OM stoichiometry was related to the relative uptake of N and P in a headwater stream across 2 seasons. In addition, we explored whether our results were consistent with theoretical predictions derived from ecological stoichiometry and consumer–resource imbalances. We found that higher respiration led to higher NH₄ and P uptake rates. NH₄ and P uptake were strongly correlated, but the nature of this relationship shifted with a seasonal change in the dominant OM to fresh leaf litter in autumn. OM stoichiometry was a strong predictor of relative nutrient uptake (NH₄∶SRP uptake ratios). Seasonal input of low N∶P leaf litter led to relatively higher NH₄ uptake from the water column, which caused a shift in relative nutrient uptake but did not alter the strength of the coupling. Our results indicate that stoichiometric imbalances between nutrient consumers and resources have a strong influence on nutrient uptake in streams. Moreover, stoichiometric models of consumer–resource imbalances between microbes and dominant OM substrates accurately captured N and P uptake dynamics in our study system. Integrating stoichiometry with metabolic controls provides insights into nutrient dynamics and acts as a framework to link N and P cycles.

Pronounced stoichiometric imbalances (C∶N∶P) between consumers and resources reported from nutrient-poor systems potentially constrain key ecological processes, but such imbalances should be less marked when more nutrients are available. In a headwater stream rich in nutrients (total P  =  208 µg/L; total oxidizable N  =  7 mg/L), we determined the elemental composition and standing stock of the consumer species and basal resources in relation to taxonomic identity, feeding mode, and season (spring and autumn). Compared with previous studies, basal resources had low elemental ratios (C∶N and C∶P), reflecting the high concentrations of inorganic nutrients in the water. Nevertheless, elemental imbalances were still evident between consumers and these basal resources, particularly for organisms feeding on detritus. Some of the variation in elemental ratios among consumers could be attributed to taxonomic identity. Furthermore, detritivores typically were depleted in N and P compared to taxonomically related species with different feeding modes. Elemental ratios of primary consumers differed between the 2 sampling occasions. Collector-gatherers and scrapers had lower C∶P and N∶P and shredders had higher C∶N in October than in May. Basal resources (fine and coarse particulate organic matter and periphyton) made up most of the standing stock of organic N and P, but quantities varied between May and October. The elemental composition of consumers of basal resources appeared to track changes in resource availability. Even with a plentiful supply of inorganic N and P available to primary producers, the availability of elements from food (a combination of quality and quantity) may influence the elemental composition of consumers.

Natural temporal variation in biological assemblages is generally acknowledged, but rarely controlled for in existing bioassessment approaches. Many bioassessment methods ignore the variation of assemblage structure through time and, thus, lack a process to evaluate the effects of natural temporal variation on their outcomes. We used an 11-y data set from 24 near-pristine reference streams (validation sites) and a 5-y data set from 10 streams exposed to human disturbance (test sites) in northern Finland to examine: 1) the amount of interannual variation in macroinvertebrate communities in both types of streams measured as variation in taxonomic completeness (i.e., ratio of observed/expected taxa; O/E ratio), and 2) how temporal variability affects bioassessment outcomes. Most of the variation in O/E values was explained by stream type (validation or test). Interannual variation in O/E was low at both validation and test sites, a result supporting the assumption of high constancy of biological assemblages through time. Temporal variation in O/E at validation sites was related to climatic factors (regional precipitation) and to some local environmental variables, e.g., substratum heterogeneity. Communities in validation and test sites responded differentially to climatic variation. The low interannual variation in O/E suggests that 1-y data from reference sites can be extrapolated across years relatively safely, but climatically extreme years may be problematic. Temporal variability in O/E was low at both types of sites, but it was still high enough to result in variable ecological status assessments across years, mainly at test sites with lower O/E ratios. Thus, at test sites, use of only 1-y data may cause erroneous management decisions, and accurate assessment of the biological quality of test sites might require repeated sampling over several years.

Adults and larvae of a new species of Contulma Flint (Trichoptera:Anomalopsychidae) are described from Ecuador. The new species is similar to Contulma papallacta Holzenthal and Flint, but differs in having shorter, less spatulate dorsolateral processes and shorter setose lateral processes of segment IX in the male genitalia. Monthly Hess, sticky trap, and emergence-trap collections indicated that the new species is uncommon, probably univoltine, but with continuous larval growth and extended adult emergence, and has algivorous larvae.

Excessive nutrient inputs and grazers can influence biomass and elemental composition of primary producers in freshwater ecosystems. How interactions between nutrient enrichment and grazing fish alter benthic habitats through effects on periphyton autotrophy, biomass, and elemental composition has been studied rarely. We compared the effects of grazing by central stonerollers (Campostoma anomalum) on autotrophic and total periphyton biomass, sediment mass, and C, N, and P stoichiometry of periphyton in 12 flow-through stream mesocosms randomly assigned to 1 of 3 different PO₄-P concentrations (control: 8 µg/L, low: 20 µg/L, high: 100 µg/L). Fish grazing suppressed periphyton ash-free dry mass (AFDM) and sediment accumulation, regardless of P treatment. However, grazing also increased the proportion of algal biomass in the periphyton, evidenced by a reduction in benthic C:chlorophyll a on grazed substrates. The response of periphyton stoichiometry to experimental P enrichment was stronger on grazed substrates because central stonerollers maintained a higher proportion of algae in the periphyton matrix. Grazing enhanced the response of P standing stocks to enrichment, reduced C∶P and C∶N in high-P streams, and increased N∶P in control and low-P streams. Shifts from detritus- and sediment-bound nutrients to algal resources probably increase the palatability of benthic food resources and nutrient availability for other grazing organisms. Grazing fish may play a stronger role in benthic processes, such as nutrient cycling, than is currently recognized. Our results suggest that fish drive periphyton toward autotrophy, enhance sequestration of excess nutrients in periphyton and, thus, may relax stoichiometric constraints on fast growing organisms in stream communities.

Springs are unique aquatic habitats that contribute significantly to local and regional biodiversity because of their high habitat complexity and the large number of different spring types. Many springs are small, but they are numerous and often of high water quality, and thus, provide habitats for species that are rare elsewhere because of their sensitivity to anthropogenic impacts (least-impaired habitat relicts). Springs are often species-rich and contain a larger number of Red List taxa than other aquatic habitats. Hydrological factors, particularly flow permanence, water chemistry, and temperature are important ecological factors determining species distribution and community composition. Despite their importance for biodiversity and water quality, springs are much less studied than other aquatic ecosystems. They also are insufficiently covered by protective legislation, often resulting in the destruction of their natural habitat. The authors of papers in this special issue describe specific spring biota, including multitaxon studies, and discuss the role of environmental factors, habitat variability at different spatial and temporal scales, and the importance of natural and anthropogenic disturbance in spring habitats. They suggest directions for future research, including defining reference conditions for springs and their role in long-term ecological research, the development of quality-assessment methods, and their more sustainable use as freshwater resources.

Benthic algae were used to identify reference conditions of springs for bioassessment purposes. Benthic algae and environmental factors were quantified in 70 springs (nonthermal and mostly near-natural) in the southeastern Alps. Spring types were identified by fuzzy clustering of nondiatom, benthic algal assemblages. Canonical Correspondence Analysis (CCA) and indicator species analysis (IndVal) were used to identify the most relevant environmental determinants of taxonomic composition in springs and to characterize the ecological traits of key taxa. A total of 120 macro- and microscopic benthic pro- and eukaryotic algae (excluding diatoms) were identified. Cyanobacteria (especially Chroococcales and Oscillatoriales) were strongly prevalent. Seven spring types were identified by fuzzy clustering of nondiatom, benthic algal assemblages. IndVal identified 22 taxa that were significant indicators of spring type, and fuzzy clustering based on environmental preferences identified 18 other important taxa associated with spring type. Spring types differed in environmental features, species richness, and diversity. Mid-to-high altitude, oligotrophic, carbonate flowing springs (rheocrenes) with medium conductivity were the most common spring type and were characterized by shade-tolerant (Chroococcales) or rheophilic (Tapinothrix varians) cyanobacteria. Low-altitude, shaded, and slightly NO₃-N-enriched carbonate rheocrenes with medium-to-high conductivity supported rheophilic or eutraphentic cyanobacteria and red algae. Siliceous rheocrenes had benthic algal assemblages dominated by soft-water, rheophilic cyanobacteria and by the rheobiontic chrysophyte, Hydrurus foetidus. Mostly siliceous seepages and pool springs supported predominantly chlorophytes, especially filamentous Zygnematales. Xerotolerant cyanobacteria were common on carbonate rock-face seepages. Tufa springs were characterized by cyanobacteria and by the desmid, Oocardium stratum. In iron springs, benthic algae (mainly filamentous green algae and xanthophytes) were poorly developed, whereas iron bacteria were common. The most influential factors were pH and conductivity, shading, NO₃-N, temperature, current velocity, and substratum particle size. The spring types identified may prove useful as references for assessments of ecological integrity naturalness value, at least for the Alps ecoregion.

Spring habitats are highly diverse and have a mosaic microhabitat structure. They are endangered by diffuse exploitation as drinking-water resources, an impact likely to increase with climate change. Diatoms were sampled from stones and bryophytes in 110 nonthermal, near-natural springs in the southeastern Alps (Trentino) and 16 carbonate springs in the Dolomiti Bellunesi National Park. Fuzzy clustering identified 6 assemblages in the main types of springs. Carbonate rheocrenes hosted Achnanthidium spp., Gomphonema elegantissimum, and Nitzschia fonticola. Several of these species are rheophilic. This group was divided into 4 subassemblages defined by decreasing A. lineare and increasing A. pyrenaicum with increasing flow. Carbonate rheocrenes with shading or moderate NO₃⁻ enrichment contained a majority of sciaphilic and NO₃-tolerant taxa: Cocconeis taxa, Amphora spp., Caloneis fontinalis, Reimeria spp., and Eunotia arcubus. Well-buffered siliceous rheocrenes supported Diatoma spp., Eunotia minor, Encyonema minutum, Navicula exilis, and Planothidium lanceolatum. Many of these species are heliophilic and rheophilic. Carbonate rheocrenes with lower conductivities or seasonal desiccation contained typical taxa of unstable environments: Diadesmis spp., Planothidium frequentissimum, Meridion circulare, and Achnanthidium dolomiticum. Carbonate rock-face seepages and some tufa springs supported xerotolerant diatom species with a preference for higher conductivities: Encyonopsis spp., Delicata spp., Gomphonema lateripunctatum, Denticula spp., and Cymbopleura spp. Siliceous seepages and pool springs, some very-low alkalinity rheocrenes, and 1 iron spring were characterized by acidophilous mire taxa, such as Eunotia spp., Frustulia crassinervia, and Tabellaria flocculosa, and very-low-alkalinity indicators, such as Psammothidium acidoclinatum. The other iron springs harbored species-poor assemblages with low numbers of cells. Many diatom species showed a significant preference for stones or bryophytes. Epibryon had higher richness and diversity than epilithon, and mean diversity did not differ among the most frequent bryophyte species. Bryophytes are quick and easy to sample and are proposed as the target substratum for diatom-based assessments of springs.

We analyzed responses of chironomid (Diptera:Chironomidae) communities to environmental factors in 124 natural, moderately, and highly disturbed springs in the Italian Prealps and Alps to investigate environmental factors influencing species distribution in springs and to evaluate chironomids as bioindicators of spring water quality. Self-Organizing Map analysis found differences among spring types and effects of anthropogenic pressures. Natural or little-disturbed springs at high altitude with low temperature, low conductivity, and high current velocity differed from lowland springs, including highly disturbed ones, with low current velocity and higher temperature, conductivity, and nutrient concentrations. Cold stenothermal intolerant species were clustered in the 1^st group, tolerant and euriecious species in the 2^nd group. Indicator value analysis detected species characterizing springs with different degrees of disturbance and of different types. Most species' distributions were related to water temperature and conductivity. Coinertia Analysis (CoA) detected relationships among species structure and environmental variables. CoA axis 1 represented a gradient of water temperature, altitude, alkalinity, and conductivity and separated cold stenothermal species (Pseudokiefferiella parva, Pseudodiamesa branickii, Diamesa spp.) from species tolerant of high temperatures (Polypedilum nubeculosum, Phaenopsectra flavipes, Paratrissocladius excerptus). Axis 2 represented a hydrologic (rheocrene–limnocrene) and anthropogenic disturbance (total disturbance, agriculture, organic debris) gradient and separated species by preference for water velocity and spring type (rheocrenes: Eukiefferiella spp.; limnocrenes: Prodiamesa olivacea, Natarsia sp.), and pollution tolerance (P. nubeculosum, Macropelopia spp.). Water temperature and chemical composition affected chironomid distribution. Some species were associated with degraded (P. nubeculosum) or pristine conditions (Diamesa spp., Stilocladius montanus).

Creation of spring typologies for different regions is essential for evaluating spring degradation and for restoration of headwaters. We present a regional spring typology for the German federal state Schleswig-Holstein in the Northern European Lowlands. We used a standardized physicochemical and hydromorphological protocol to map 174 near-natural springs distributed area-wide. Principal component analysis distinguished types of springs (rheocrenes, helocrenes, limnocrenes, and an intermediate type, rheohelocrenes) on the basis of water chemistry and substratum composition. The spatial distribution of the types corresponded with the regional fluvioglacial landscapes of Schleswig-Holstein (hill country, Baltic Sea margin, the high Geest, and the low Geest). The most important discriminating factors were related to water hardness and conductivity. We sampled macroinvertebrates in 60 springs (twice in 40, once in 20) selected based on type and distribution among fluvioglacial landscapes. We detected 121 taxa, most of them Hydrachnidia (25 species), Trichoptera (19), Coleoptera (19), and Gastropoda (12). Many of the species are considered rare for Schleswig-Holstein (regional red-list species). Forty-two species were restricted mainly to springs (crenobiont or crenophilous species). Average taxon richness was similar for helocrenes (23 species), rheohelocrenes (22), and rheocrenes (25), but markedly lower for limnocrenes (11). Species composition differed between rheocrenes and helocrenes and between limnocrenes and all other spring types. Faunal distinctness of rheohelocrenes was less pronounced. We were able to produce a validated spring typology founded on substratum composition, physicochemical factors, and taxon composition. This typology can serve as a guide for restoration of severely degraded springs and headwaters in Schleswig-Holstein and in similar areas of Central Europe.

The traditional and widely used ecomorphological spring classification—pool springs (limnocrenes), seepages (helocrenes), and flowing springs (rheocrenes)—is based mainly on the flow regime at the spring mouth. This clear distinction is based purely on environmental conditions, but how and to what extent these spring typologies are reflected by biological assemblages consisting of different taxonomic groups remains largely untested. Classification of habitats typically is based on one or few taxonomic groups. However, groups are likely to differ in their response to the environment, so different, equally valid classifications might result with different groups. We evaluated the responses and their congruence of a wide range of taxonomic groups to different spring types. Eighty-six springs in the Italian Alps were first classified based on environmental factors only. The consistency of this classification was tested using diatoms, bryophytes, vascular plants, nematodes, mollusks, oligochaetes, water mites, copepods, ostracods, chironomids, stoneflies, and caddisflies. When only environmental variables were used, 7 spring types were distinguished: limnocrenes and helocrenes, low- and high-altitude rheocrenes on carbonate rocks, rheocrenes on siliceous rocks, rheocrenes with high discharge, and hygropetric rheocrenes. This classification was reflected by most taxonomic groups, and many species were characteristic for ≥1 spring type. However, the predictive power of the environment for determining species distribution was generally low, a result suggesting that other factors may play an important role in structuring spring assemblages. Concordance among taxonomic groups was found for 2 macrogroups of organisms: autotrophs (diatoms, bryophytes, and vascular plants) and heterotrophs. This result shows that achieving a general classification of springs relevant across all taxonomic groups would be difficult.

I assessed effects of the widest range of temperatures ever examined on maximal food-chain length (L) and macroinvertebrate species richness (S) by a worldwide comparison of spring ecosystems with mean water temperatures (T) ranging from 4.5 to 93°C. Eukaryotic L averaged ∼3.2 and varied independently of T between 4.5 and 31°C. However, over the relatively narrow T range of 35 to 50°C, L dropped abruptly to 0 and remained so up to 91°C. The negatively nonlinear relationships of L vs T and macroinvertebrate S vs T both deviated from predictions based upon metabolic theory, and the negative effect of T on S contrasted with positive relationships observed at larger regional scales. Thermal tolerance limits apparently play a major role in causing these relationships, but other factors also may be involved (e.g., availability of colonists adapted to different temperatures and temperature-dependent rates of resource use and species interactions that affect population establishment and persistence).

An increasing number of recent investigations of a wide range of species have considerably changed perspectives in spring ecology. However, relatively little is known about the differences between the eucrenon and assemblages in downstream habitats. We studied changes in environmental conditions and in 4 taxonomic groups along a downstream continuum. Assemblages of diatoms, other benthic macroalgae including cyanobacteria, macroinvertebrates, and bryophytes were compared among eucrenal, hypocrenal, and epirhithral stations in 2 spring-fed streams of the southeastern Italian Alps. Environmental factors were less variable at the eucrenal station than at downstream stations, but this pattern was not reflected by an equivalent response of biotic assemblages. The eucrenon clearly differed from assemblages at downstream stations in ways that varied between taxonomic groups and time. Diatom and macroinvertebrate assemblage compositions were more variable at the eucrenal station than at downstream stations. Space was a more important factor than time for diatoms and benthic macroalgae, whereas space and time were almost equally important for macroinvertebrates. Downstream changes were inconsistent between taxonomic groups, and a larger number of spring-fed streams must be studied to detect more generally valid patterns in downstream variation of different taxonomic groups.

The structure (biomass, species or Operational Taxonomic Unit [OUT] composition) and function (photosynthetic performance) of autotrophic and heterotrophic biofilm communities were investigated along a chemical gradient created downstream of a small Fe spring (Llémena watershed, Girona, northeastern Spain). Diatom species composition, diatom abundance, and algal biomass (measured as basal fluorescence [Fo]) followed the chemical gradient. Site ordination scores based on the photosynthetic performance of biofilms (measured as effective quantum yield [Yeff] and photosynthesis–irradiance curve parameters) and on bacterial densities and denaturing gradient gel electrophoresis (DGGE) data (OTUs for Fungi and Bacteria) were not linearly related to the chemical gradient. The extreme chemical environment selected for low-productivity, stress-tolerant community characterized by low algal biomass, absence of cyanobacteria, and dominance of the diatom taxon Navicula cincta. The unimodal pattern of response of heterotrophs to the chemical gradient and the observed coincidence with the pattern of photosynthetic performance indicate that interspecies competition within a trophic level may be obscured by biotic interactions between primary producers and decomposers. We hypothesize that these biotic interactions may be important under extreme chemical conditions because of differences in sensitivity between autotrophic and heterotrophic components of the biofilm to chemical stress or limiting resources.

Habitat conditions and spring-associated limestones (SALs) formed by ambient precipitation with the biotic contribution of the desmid Oocardium stratum Nägeli 1843 (Zygnematophyceae) were studied in 5 springs along a north–south transect across the central Eastern European Alps. Spring waters were characterized by permanent flow and temporally almost stable physicochemical conditions, but variable relationships among major ions (especially HCO₃⁻:SO₄²⁻ and Ca² :Mg² ) among sites. In most cases, CO₂ supersaturation (0.2–1.8 µM/L) caused in situ depression of pH from near equilibrium (8.3) to <8, with a minimum pH of 7.1. SAL areas dominated by Oocardium growth were greatest some distance downstream of the spring origin where degassing of excess CO₂ had occurred and pH had risen to >8.1. The calcified segments of spring streams were limited to areas <300 m from the spring mouth. Within the uppermost segment of larger rheocrenes (CO₂ supersaturated areas), extensive weakly calcified bryophyte crops (Eucladium verticillatum, Palustriella commutata) were replaced further downstream by Oocardium-spiked calcified coatings. The various morphologies of Oocardium cells (assessed with light microscopy [LM], scanning electron microscopy [SEM], and petrographic thin sections) revealed different types of calcification, from micritic (<1–4 µm) to sparitic calcites (>100–1000 µm) whose ultrastructural features were best seen with SEM. The distribution of SAL types within and among sites was evaluated in relation to water-chemistry and additional environmental variables. The findings were compared with earlier records from the Alps and other mountain areas of Europe (in particular, Croatia and UK) to facilitate recognition and delimitation of Oocardium niches in the environment and to foster protection of these rare habitats.

Springs are characterized by consistent thermal and hydrologic conditions, which enable use of spring-inhabiting organisms as sensitive indicators of biogeochemical changes in their catchments. We hypothesized that bryophytes would show a stronger response than vascular plants to changes in spring water quality because submerged bryophytes do not take up compounds from the soil. We analyzed species responses to interannual changes in spring water quality (discharge, water temperature, electrical conductivity, and pH) in 57 forest springs over 4 consecutive years. We calculated interannual turnover in species composition for bryophytes and vascular plants with the Bray–Curtis dissimilarity index. We applied regression analysis to test interannual changes in species composition of the taxonomic groups over time, and we used 2-sided t-tests to compare year-to-year changes in species composition between bryophytes and vascular plants. We used boosted regression tree (BRT) models to quantify the relative importance of different physicochemical variables and Pearson linear correlation to quantify short-term changes in vegetation relative to changes in spring-water pH. For both groups, interannual changes in species composition were significantly positively related to time scale. Bryophytes did not show a significantly stronger response than vascular plants to interannual changes in the environment. Alterations in pH and conductivity explained most of the observed interannual changes in species composition of both groups, whereas changes in water temperature and discharge were less important. However, responses of single species to environmental change may be delayed, resulting in inertia at the community and ecosystem scales. Hence, longer time periods need to be considered for a better understanding of response times of the vegetation of European forest springs to changes in spring water quality.

Despite extensive research on the link between disturbance and diversity in ecology and several eloquent models to describe the relationship, a universally applicable model remains elusive. However, most investigations of the diversity–disturbance relationship have been limited in spatial coverage. Recent theoretical and conceptual advances in macroecology suggest that such spatially constrained studies may limit interpretation. To explore the effect of geographic location on the disturbance–diversity relationship, we examined invertebrate assemblages in streams of northern Spain and New Zealand (NZ) and in multiple regions within NZ. Habitat characteristics were similar across all sites and locations, except that undisturbed sites (springbrooks) differed from disturbed sites (rhithral streams) by having constant thermal and hydrologic regimes. The resource base and the density of invertebrates were greater in the more-stable habitats in all regions. However, patterns of invertebrate species richness differed markedly between locations in the Northern and Southern Hemispheres. Springbrooks in all regions within NZ had greater richness than rhithral streams. In contrast, springbrooks in Spain had considerably lower species richness than rhithral streams. Thus, low hydrological disturbance in Spain yielded low diversity, whereas in NZ it yielded high diversity. Amphipoda dominated the springbrook faunas in Spain, whereas insects dominated in NZ. Thus, differences in the diversity patterns between Spain and NZ are potentially related to phylogenetic differences or environmental constraints on life-history cues. A universal model to link disturbance and diversity is more likely to be successful if it incorporates life-history traits rather than morphological traits.

Discharge variability is an important disturbance factor, and its effect on macroinvertebrate assemblages has been widely studied in river ecosystems. In comparison, few researchers have investigated discharge variability in springs because they are thought to be relatively stable ecosystems and because discharge is not easy to measure in springs. We used the gypsum-dissolution method to assess the discharge regime of 5 natural perennial springs during a 1-y study. We calculated discharge from the mass loss of gypsum spheres at a given temperature after calibration of the method in the laboratory. We also collected seasonal macroinvertebrate samples during the study period to assess the effect of discharge variability on the composition of macroinvertebrate assemblages in the springs. The calibration experiments revealed significant linear relationships between mass loss and discharge. In the field experiments, we were able to differentiate springs with high discharge variability from springs with low discharge variability. Species richness was highest in springs with highest maximum discharge. Seasonal variability in macroinvertebrate assemblages was higher in these springs than in springs with low discharge variability. Discharge variability (disturbance intensity) did not influence the diversity and number of spring specialists. We found no evidence for highest diversity at an intermediate level of disturbance as predicted by the intermediate disturbance hypothesis. The gypsum dissolution method is an appropriate method for assessing short- and medium-term discharge variability in springs. The importance of discharge variability as flow-associated disturbance is expected to increase in the context of the predicted effects of changes in global climate and land use, i.e., increasing drought periods and flood events.

Like all headwater systems, springs have been increasingly modified by multiple land uses, but the effects of these modifications on species diversity and community composition are poorly understood. We assessed the consequences of forestry-related disturbance (mainly draining) on benthic macroinvertebrate and bryophyte diversity and community composition in boreal springs. We used predictive modeling (BEnthic Assessment of SedimenT [BEAST]), indicator species analysis, and descriptive statistics on data from 55 near-pristine reference springs and 20 modified (test) springs spanning 3 ecoregions (hemiboreal to middle boreal) in Finland. Invertebrate and bryophyte communities were relatively similar between the reference and test springs. BEAST identified deviation from the reference condition in 9 and 10 sites based on benthic macroinvertebrates and bryophytes, respectively. These sites were identified mostly as possibly different from reference, with the exception of a few seriously degraded springs with low levels of groundwater flow. Indicator species for both reference-condition and test springs included spring-preferring and ubiquitous taxa. Bryophyte richness was lower in test than in reference springs, but no significant differences were detected for macroinvertebrate richness. Red-listed species were more common in reference than in test springs. Our results suggest that, despite only moderate effects on community composition, anthropogenic disturbance impoverishes spring fauna and flora and causes a decline of spring-preferring red-listed species. Restoration will be necessary to preserve biodiversity in springs, but benign methods should be used to avoid further disturbance to biota, particularly red-listed spring specialists.

We analyzed the composition of spring fauna in relation to the mesoscale variability in environmental conditions in 77 permanent springs in a geologically homogenous area. We hypothesized that the species would occur in definite patterns reflecting the differences in factors that operate at the spring-level scale. We focused on the differences resulting from spring morphology, substrate composition, shading, and water chemistry. Our goal was to identify the abiotic variables that control the character of interspecies associations. The spring assemblages comprised species of 9 higher taxonomic groups (Plecoptera, Trichoptera, Coleoptera, Diptera, Turbellaria, Crustacea, Mollusca, Oligochaeta, Hydracarina). We used binomial regression successfully to construct single-species environmental models for several of the most abundant taxa. The most important factors explaining the species' occurrence were hydromorphological and substrate characteristics. Results of nonmetric multidimensional scaling ordination on species composition indicated 3 groups of springs. However, the analysis did not provide evidence for strong interspecies associations. Group 1 separated springs with running water, high substrate heterogeneity, and high taxonomic richness. Groups 2 and 3 included mostly helocrene-like springs differing in slope and substrate composition. The assemblages of these 2 groups comprised the same dominant species. However, the springs from group 3 had lower species abundances. Our study demonstrates the importance of mesoscale differences in habitat conditions for structuring the spring-associated benthic assemblages.