Ecology of glacier-fed rivers: current status and concepts

1. This paper is an introduction to a special issue of Freshwater Biology containing papers dealing with various aspects of the ecology of glacier-fed rivers.
2. Using similar field protocols, a wide range of glacier-fed systems were studied across Europe from the French Pyrenees to Svalbard within the framework of the European Commission project, Arctic and Alpine Stream Ecosystem Research (AASER). Recent investigations from other parts of Europe together with New Zealand and Greenland are also reported. This work has advanced our knowledge of the functioning of these types of rivers and has led to the modification and quantification of the conceptual model of Milner & Petts (1994) .
3. Glacier-fed rivers, by virtue of the dominance of physical variables in shaping macroinvertebrate communities, are not only good indicators of climate change, but also may be suitable testing grounds for examining ecological concepts.     

Spatial population genetic structure and limited dispersal in a Rocky Mountain alpine stream insect

Using the mitochondrial cytochrome oxidase I (COI) gene, we assessed the phylogeographic structure of Prosimulium neomacropyga, a black fly (Simuliidae) whose distribution in the US Southern Rockies ecoregion is limited to alpine tundra streams. Given high habitat specificity, lack of hydrological connection between streams, and a terrestrial environment restrictive to insect flight, we hypothesized limited gene flow. A spatially nested sampling design showed that grouping populations according to high-elevation 'islands' of alpine tundra (which typically include headwater streams of > 1 watershed) explained a significant proportion of genetic variation while grouping streams according to major watershed (across islands) did not. Nested clade analysis and isolation-by-distance (IBD) relationships further implicated limited ongoing gene flow within but not among the isolated alpine islands. IBD was strong among five streams within an individual island using each of four alternative models of pairwise landscape connectivity for flying insects. Results of all landscape models were positively correlated, suggesting that straight-line distance is an acceptable surrogate for presumably more biologically meaningful connectivity measures in this system. IBD was significantly weaker across the entire study area, comprised of three separate islands. Overall, population structure was significant with F(ST) = 0.38, suggesting limited dispersal across a small spatial extent.     

Effects of snow cover on the benthic fauna in a glacier-fed stream

1. Alpine streams above the tree line are covered by snow for 6–9 months a year. However, winter dynamics in these streams are poorly known. The annual patterns of macroinvertebrate assemblages were studied in a glacial stream in the Austrian Alps, providing information on conditions under the snow.
2. Snow cover influenced water temperature, the content of benthic organic matter and insect development. Taxa richness and abundance of macroinvertebrates did not show a pronounced seasonal pattern. The duration of the autumn period with stable stream beds was important in determining the abundance and composition of the winter fauna.
3. There were significant differences in species composition between summer and winter. Two potential strategies in larval survival were evident: adaptation to the extreme abiotic conditions in summer (e.g. Diamesa spp.) or avoidance of these conditions and development during winter (e.g. Ephemeroptera and Plecoptera).
4. A comparison of a stream reach with continuous snow cover and a stream reach that remained open throughout winter showed that conditions under snow are suboptimal. At the open stream site, with higher water temperatures and greater food supply (benthic organic matter content), abundance and taxa richness was higher and larval growth was faster. Several taxa were found exclusively at this site.
5. Winter conditions did not provide an entirely homogeneous environment, abiotic conditions changed rapidly, especially at the onset of snowfall and at snowmelt. Continuous monitoring is necessary to recognize spatial and temporal heterogeneity in winter environments and the fauna of alpine streams.     

凉水、帽儿山低级溪流中水生昆虫的群落特征及水质生物评价

在东北林业大学凉水国家级自然保护区和帽儿山实验林场,对3种类型低级溪流中水生昆虫进行采集、鉴定,分析水生昆虫群落组成、季节优势集中性和取食功能群,并应用指示生物法、Shannon-Weiner多样性指数、群落相似性系数和BI指数对溪流水质进行生物评价。共采集到水生昆虫4907个,分别隶属于8目38科,其中,毛翅目、蜉蝣目、横翅目和双翅目为四大优势类群,个体数量占水生昆虫总数量的91．13％。原始林溪流中水生昆虫个体数量最多,占总数的58．98％,次生林溪流次之,农田溪流最少。次生林溪流水生昆虫物种多样性要高于原始林和农田溪流,且其各种取食功能群比例较均衡。齿角石蛾科、鳞石蛾科、新蜉科和黑横科昆虫可以作为溪流清洁水质的指示生物。水生昆虫季节优势集中性与Shannon-Weiner多样性指数水质评价结果之间具有相关性,即随溪流水质污染程度的加重,水生昆虫的物种多样性逐渐减少。群落相似性系数的分析表明,原始林溪流和次生林溪流水质对水生昆虫的群落组成没有影响,农田溪流则产生中等影响。生物指数（BI）评价结果显示除了农田溪流10月的水质为轻污染外,其余时间3种溪流的水质都能达到清洁标准以上。     

Seasonal relationships between planktonic microorganisms and dissolved organic material in an alpine stream

The relationships between the abundance and activity of planktonic, heterotrophic microorganisms and the quantity and characteristics of dissolved organic carbon (DOC) in a Rocky Mountain stream were evaluated. Peak values of glucose uptake, 2.1 nmol L⁻¹ hr⁻¹, and glucose concentration, 333 nM, occurred during spring snowmelt when the water temperature was 4.0°C and the DOC concentration was greatest. The turnover time of thein situ glucose pool ranged seasonally from 40–1110 hours, with a mean of 272 hr. Seasonal uptake of³H-glucose, particulate ATP concentrations, and direct counts of microbial biomass were independent of temperature, but were positively correlated with DOC concentrations and negatively correlated with stream discharge. Heterotrophic activity in melted snow was generally low, but patchy. In the summer, planktonic heterotrophic activity and microbial biomass exhibited small-scale diel cycles which did not appear to be related to fluctuations in discharge or DOC, but could be related to the activity of benthic invertebrates. Leaf-packs placed under the snow progressively lost weight and leachable organic material during the winter, indicating that the annual litterfall in the watershed may be one source of the spring flush of DOC. These results indicate that the availability of labile DOC to the stream ecosystem is the primary control on seasonal variation in heterotrophic activity of planktonic microbial populations.     

Does rapid glacial recession affect feeding habits of alpine stream insects?

1. Glacial retreat, accompanied by shifts in riparian vegetation and glacier meltwater inputs, alters the energy supply and trophic structure of alpine stream food webs. Our goal in this study was to enhance understanding of dietary niches of macroinvertebrates inhabiting different alpine streams with contrasting glacial and non‐glacial (groundwater, precipitation, snowmelt) water inputs in conjunction with seasonal and habitat‐specific variation in basal resource availability.
2. We measured a range of stream physico‐chemical attributes as well as carbon and nitrogen isotopes (δ¹³C, δ¹⁵N) of macroinvertebrates and primary food sources at seven sites across seasons within a Swiss glaciated catchment (Val Roseg) undergoing rapid glacial retreat (1–2 km between 1997 and 2014). Sampling sites corresponded to streams used in a previous (1997/1998) study within the same alpine catchment.
3. Physico‐chemical attributes showed wide variation in environmental conditions across streams and seasons. Significant correlation among physico‐chemical proxies of glacier meltwater (phosphate‐P, total inorganic carbon, conductivity, turbidity) and macroinvertebrate δ¹³C, δ¹⁵N, and size‐corrected standard ellipse area (a proxy for feeding niche width) values showed that the extent of glacial water input shapes the energy base among alpine streams. Feeding niche differences among common alpine stream insect taxa (Chironomidae, Baetidae, Heptageniidae) were not significant, indicating that these organisms probably are plastic in feeding behaviour, opportunistically relying on food resources available in a particular stream and season.
4. Seasonal trends in macroinvertebrate δ¹³C largely followed patterns in periphyton δ¹³C values, indicating that autochthonous resources were the main consumer energy source within the stream network, as shown previously. The overall range in macroinvertebrate δ¹³C (?33.5 to ?18.4‰) and δ¹⁵N (?6.9 to 6.7‰) values also corresponded to values measured in the previous study, suggesting that macroinvertebrates altered diets in line with changes in environmental conditions and food resources during a period of rapid glacial retreat. Our results suggest that environmental changes brought on by rapid glacial retreat have not yet caused a profound change in the trophic structure within these fluvial networks.

     

Climate‐induced glacier and snow loss imperils alpine stream insects

Climate warming is causing rapid loss of glaciers and snowpack in mountainous regions worldwide. These changes are predicted to negatively impact the habitats of many range‐restricted species, particularly endemic, mountaintop species dependent on the unique thermal and hydrologic conditions found only in glacier‐fed and snow melt‐driven alpine streams. Although progress has been made, existing understanding of the status, distribution, and ecology of alpine aquatic species, particularly in North America, is lacking, thereby hindering conservation and management programs. Two aquatic insects – the meltwater stonefly (Lednia tumana) and the glacier stonefly (Zapada glacier) – were recently proposed for listing under the U.S. Endangered Species Act due to climate‐change‐induced habitat loss. Using a large dataset (272 streams, 482 total sites) with high‐resolution climate and habitat information, we describe the distribution, status, and key environmental features that limit L. tumana and Z. glacier across the northern Rocky Mountains. Lednia tumana was detected in 113 streams (175 sites) within Glacier National Park (GNP) and surrounding areas. The probability of L. tumana occurrence increased with cold stream temperatures and close proximity to glaciers and permanent snowfields. Similarly, densities of L. tumana declined with increasing distance from stream source. Zapada glacier was only detected in 10 streams (24 sites), six in GNP and four in mountain ranges up to ~600 km southwest. Our results show that both L. tumana and Z. glacier inhabit an extremely narrow distribution, restricted to short sections of cold, alpine streams often below glaciers predicted to disappear over the next two decades. Climate warming‐induced glacier and snow loss clearly imperils the persistence of L. tumana and Z. glacier throughout their ranges, highlighting the role of mountaintop aquatic invertebrates as sentinels of climate change in mid‐latitude regions.     

Longitudinal distribution of macroinvertebrate assemblages in a glacially influenced stream system in the Italian Alps

1. The longitudinal distribution of macroinvertebrates was investigated in June, August and September 1996 and 1997 in the Conca glacial stream and its tributary (Italian Alps; 46°N, 10°E). The principal aim was to test the 22 model that predicts the succession of faunal groups downstream of the glacial snout in relation to water temperature and channel stability. The effect of a non‐glacial tributary on the taxonomic richness and density patterns occurring in the glacial stream was also considered. 2. Channel stability showed an atypical longitudinal trend in the Conca glacial stream, being high in the upper part with Pfankuch Index values between 30 and 33. Water temperature exceeded 6 °C at all stations, with average values below 2 °C occurring only within 700 m from the glacial snout. 3. Taxonomic richness and diversity increased downstream. Taxonomic richness in the glacial stream (at about 1.5 km from the glacier) was comparable with the tributary and the reach after the confluence. Abundance also increased downstream in the glacial stream, but not as greatly as the number of taxa. 4. At higher taxonomic levels, the community structure in the tributary stations appeared to be similar to the two stations in the glacial stream just upstream of the confluence. The effect of the tributary was evident mainly at the genus or species level of the Chironomidae community. Some taxa found in the non‐glacial stream (e.g. Cricotopus fuscus, Eukiefferiella coerulescens, Metriocnemus sp., Paratrichocladius rufiventris, P. skirwitensis, Rheocricotopus effusus and Smittia sp.) were found also in the Conca stream but only after the confluence. 5. The upper glacial reach (within 700 m from the glacier snout) was dominated by the chironomid Diamesa spp. Less than 400 m from the glacier other Diamesinae (Pseudokiefferiella parva) and a few Orthocladiinae, especially Orthocladius (Euorthocladius) rivicola gr., colonized the stream. Some Diamesinae maintained relatively dense populations at mean water temperature around 5 °C, while some Orthocladiinae colonized reaches with mean water temperature <3 °C. 6. Contrary to the 22 model, Dipteran families such as Empididae and Limoniidae were more abundant in the upper stations than Simuliidae; non‐insects such as Nematoda and Oligochaeta were also numerous at some sites. Leuctridae, Taeniopterygidae and Nemouridae were the first Plecoptera to appear upstream, while Chloroperlidae were restricted to the lower reaches. Among Ephemeroptera, Heptageniidae were more abundant than Baetidae in the glacial sites. 7. In this glacial system channel stability and maximum temperature did not show the expected longitudinal trend and thus a typical kryal community was confined within 700 m from the glacier snout where summer mean water temperature was below 4 °C.     

Modern assemblages of arctic and alpine Chironomidae as analogues for late-glacial communities

Surficial sediment data, illustrating the differences between arctic and temperate chironomid faunas, are presented and briefly discussed.     

Species richness of aquatic macrophyte communites in Central Canada

Aquatic macrophyte species richness (SR) was examined at 430 sites in the central Canadian region in relation to water body type, bottom substrate and 8 water chemistry parameters. SR was highest in rivers and lakes, intermediate in creeks, and lowest in ponds. The highest values occurred where granitic bedrock, highly organic substrates or sand predominated. SR was significantly inversely correlated in the study area as a whole with 7 of the water chemistry parameters; of these, total alkalinity was the most important. However, the relative importance of the respective parameters differed for various water body types. The relationship between SR and phosphorus was positive in ponds, but negative for all other water body types. Stepwise sultiple regression analysis identified phosphorus, total alkalinity and dissolved organic matter as important factors in ponds; sulphate, total alkalinity and chloride in lakes, and sulphate and phosphorus in lotic habitats. Log transformations improved the correlations for some variables. However, the water chemistry parameters examined accounted for less than half of the total variability in SR. Apparently SR depends on many different factors, including surface areaand bottom type, whose relative contributions vary with situation.     

The chironomid larvae of a small chalk stream in Berkshire, England

Abstract. 1. The longitudinal distributions of larval Chironomidae (Diptera) were examined for 1 year in the intermittent and perennial sections of the Winterbourne, a small chalk stream in Berkshire, England.
2. Forty-nine chironomid taxa were recorded at ten major sites which were sampled on six occasions and four additional taxa were recorded at sites sampled only once.
3. Cluster analyses using data from the major sampling sites identified three groups of sites. A pond in the stream channel which had a distinct chironomid fauna was distinguished from all other sites before the remaining intermittent sites were separated from all perennial sites on the basis of the chironomid fauna.
4. In the perennial stream, a site heavily shaded by trees had low species richness compared with partially and unshaded sites further downstream. The lowest site, which was near to the confluence with a larger chalk stream, the River Lambourn, had the highest number of taxa (thirty-five), including several which were frequent in the Lambourn.
5. By recording the occurrence of prepupae, an indication of emergence periods was obtained and many taxa were shown to have extended periods of emergence.     

Seasonality and distribution of epilithic diatoms,macroalgae and macrophytes in a spring-fed stream system in Ontario,Canada

A study of the epilithic diatom, macroalgal and macrophyte communities from a spring-fed stream in Ontario, Canada was undertaken from September 1996 to July 1997. The relative abundance of the epilithic diatom flora, percent cover of macroalgal and macrophyte taxa, and several physical and chemical stream conditions were monitored along a 20-m stretch at each of four sites, approximately every 2 months. Several stream conditions were relatively constant over the sampling period (pH, maximum width and maximum depth), while others exhibited a distinct seasonal pattern (water temperature, specific conductance and daylength) and some fluctuated strongly with no discernable seasonal pattern (turbidity, current velocity). A total of 124 taxa were identified from the four sites, including 79 epilithic diatoms, three macroalgal diatom species (large gelatinous masses), one cyanobacterium, two red algae, eight green algae, one chrysophyte alga, one tribophyte alga, three mosses, three horsetails and 23 angiosperm taxa. Species richness was positively correlated to stream channel maximum width and depth, indicating that the total number of species tends to increase in a downstream direction. Distribution of several diatom and macroalgal species was significantly correlated to stream conditions (e.g. Gomphonema parvulum and Phormidium subfuscum with current velocity); however, the vast majority of species did not display seasonal variation in abundance that could be explained by changes in stream conditions. Many of the taxa identified from Blue Springs Creek are common elsewhere in North America.     

Incidence of Wolbachia in aquatic insects

Wolbachia is a genus of intracellular bacteria typically found within the reproductive systems of insects that manipulates those systems of their hosts. While current estimates of Wolbachia incidence suggest that it infects approximately half of all arthropod species, these estimates are based almost entirely on terrestrial insects. No systematic survey of Wolbachia in aquatic insects has been performed. To estimate Wolbachia incidence among aquatic insect species, we combined field‐collected samples from the Missouri River (251 samples from 58 species) with a global database from previously published surveys. The final database contained 5,598 samples of 2,687 total species (228 aquatic and 2,459 terrestrial). We estimate that 52% (95% CrIs: 44%–60%) of aquatic insect species carry Wolbachia, compared to 60% (58%–63%) of terrestrial insects. Among aquatic insects, infected orders included Odonata, Coleoptera, Trichoptera, Ephemeroptera, Diptera, Hemiptera, and Plecoptera. Incidence was highest within aquatic Diptera and Hemiptera (69%), Odonata (50%), and Coleoptera (53%), and was lowest within Ephemeroptera (13%). These results indicate that Wolbachia is common among aquatic insects, but incidence varies widely across orders and is especially uncertain in those orders with low sample sizes such as Ephemeroptera, Plecoptera, and Trichoptera.     

The role of competition in invertebrate community development in a recently formed stream in Glacier Bay National Park,Alaska

New streams formed following ice recession in Glacier Bay National Park, southeastern Alaska allow insights into the role of abiotic and biotic interactions in the assemblage of benthic communities. Reductions in abundance of a pioneer chironomid colonizer, Diamesa alpina/lupus, in one new stream, Wolf Point Creek, is considered to be a result of competitive interactions with subsequent colonizers, as opposed to intolerance of warmer water temperature as previously suggested. Reduced densities of potential competitors (25–50 larvae per 500 cm²) in a cobble transplant experiment between streams, allowed persistence of D. alpina/lupus at low densities. In addition, significantly more D. alpina/lupus larvae emigrated from artificial stream channels containing other chironomid taxa than channels without potential competitors while there was no significant correlation of emigration with water temperature. A small number of D. alpina/lupus transplanted from a cold stream (4–6 °C) survived at water temperatures of 10–15 °C for 1 week. These results infer that interference competition is the causal mechanism in the decline of D. alpina/lupus. Complete exclusion of D. alpina/lupus from the stream has not occurred and water temperature may play a role in partitioning D. alpina/lupus from other taxa on a temporal or a spatial basis. This revised version was published online in August 2006 with corrections to the Cover Date.     

Emerging aquatic insects as predators in terrestrial systems across a gradient of stream temperature in North and South America

1. Empirical and theoretical research over the past decade has demonstrated the widespread importance of aquatic subsidies to terrestrial food webs. In particular, adult aquatic insects that emerge from streams and lakes are prey for terrestrial predators. While variation in the magnitude of this subsidy is clearly important, the potential top‐down effects of the predatory adults of some aquatic insects in terrestrial food webs are largely unknown. 2. I used published data on benthic insect density (as a proxy for emergence) in North and South America to explore how the proportion of benthic insects that are predatory as adults varies across a gradient of mean annual stream temperature. 3. The proportion of benthic insects that are predatory as adults varied widely across sites (0–12% by abundance; 0–86% by biomass). There was a positive relationship between mean annual stream temperature and the proportion of predatory adults across all sites, driven largely by the greater abundance/biomass of predatory taxa (e.g. odonates), relative to non‐predators (e.g. midges, mayflies, caddisflies), in tropical than in temperate streams. 4. The ‘trophic structure’ (i.e. the proportion of predators) of emerging adult aquatic insects is an understudied source of variation in aquatic–terrestrial interactions. Incorporation of trophic structure in future studies is needed to understand how future modification of fresh waters may affect adjacent terrestrial food webs through both bottom‐up and top‐down effects.     

Adult aquatic insects: Potential contributors to riparian food webs in Australia's wet–dry tropics

Abstract Changes in the abundance and biomass of aquatic and terrestrial aerial insects with distance (mid‐stream, 0, 10–15 and 160 m) from lowland streams were examined across the dry season landscape in Kakadu National Park, northern Australia. Malaise traps and sticky intercept traps were used to sample the insects at four streams, spaced over an area of 1650 km². Malaise and intercept catches were dominated by Diptera (flies and midges), both numerically and by biomass. Chironomid midges were the most abundant taxon, making up 43.4 and 51.0% of the malaise and intercept trap catches, respectively. However, most chironomids were small (less than 3 mm body length), contributing 34.9% to intercept trap biomass, but only 5.2% in malaise traps. Ceratopogonid midges and caddisflies (Trichoptera) accounted for most of the remaining adult aquatic insects. Major terrestrial components were Diptera and Hymenoptera in malaise traps and Coleoptera and Diptera in intercept traps. The total abundance and biomass of insects were much greater over streams and along the water's edge than in riparian (10–15 m) and savanna (160 m) habitats primarily because of the presence of large numbers of adult aquatic insects. The abundance and biomass of terrestrial insects in malaise traps showed no relationship with distance, but intercept trap catches suggested slightly greater abundances over the water and at the water's edge. The great abundance of aquatic insects relative to terrestrial insects close to streams suggests that they have the potential to be an important component of the diets of riparian insectivores, and predation may be an important pathway by which aquatic nutrients and energy are moved into terrestrial food webs.     

Seasonal and diel patterns of invertebrate drift in different alpine stream types

1. We examined the seasonal and diel patterns of invertebrate drift in relation to seston and various habitat characteristics in two each of four different kinds of alpine streams [rhithral (snow‐fed) lake outlets, rhithral streams, kryal (glacial‐fed) lake outlets and kryal streams]. Samples were collected at four times of the day (dawn, midday, dusk and midnight) during three seasons (spring, summer and autumn). 2. Habitat characteristics differed mainly between rhithral and kryal sites, with the latter having higher discharge and turbidity, lower water temperature, and higher concentrations of ammonium, and particulate and soluble reactive phosphorus. Seasonality in habitat characteristics was most pronounced for kryal streams with autumn samples being more similar to rhithral sites. 3. The concentration of seston was lowest in the glacial‐influenced lake outlets and slightly higher in the stream sites; no seasonal or diel patterns were evident. 4. The density of drifting invertebrates averaged less than 100 m^?3 and was lowest (<10 m^?3) at three of the four kryal sites. Taxon richness and diversity were lowest at rhithral lake outlets. Chironomidae dominated the drift as well as benthic communities and <30% of benthic taxa identified were found in the drift. 5. Drifting invertebrates showed no consistent seasonal pattern. However, density tended to be highest in spring at rhithral sites and in autumn at kryal sites. No diel periodicity in drift density was found at any site and the lack of diel pattern may be a general feature of high altitude streams. 6. Glacially influenced habitat parameters were a major factor affecting drift in these alpine streams, whereas no clear differences were observed between streams and lake outlets. Our findings indicate that invertebrate drift in alpine streams is primarily influenced by abiotic factors, and therefore, substantially differs from patterns observed at lower altitude.     

Movement of immature aquatic insects in a lotic habitat

The movement of immature insects up down and across Salem Creek, Ontario, was measured with traps and nets at two week intervals from January to December 1977. Drift of most taxa was more strongly correlated with water velocity from August to December than it was over the whole year. That of Baetis, however, was not correlated with water velocity and it was significantly greater at the side of the stream than at the centre from May to July. Upstream movement, as measured in three different ways, was small compared with drift, being only 2.1, 7.3 and 15.2 percent respectively.Upstream and across stream movements were not consistently different from one another, changes in their intensity apparently merely representing changes in numbers and behaviour of the animals. It is concluded therefore that upstream movement is only random movement.Colonization of empty sediment in trays on and above the substratum confirmed that most reoccupation of denuded areas is by drift. This supports the finding that drift is far geater than random wandering of the insects.     

The effect of long pools on the drift of macro-invertebrates in a mountain stream

Macro-invertebrate drift was measured entering and leaving two pools on the Middle Fork of the Cosumnes River, a third order California stream. Drift rates for Baetis spp., Chironomidae, Simulium spp., Capniidae and total drift were calculated. Significant differences in the numbers of organisms entering the two pools were found for Baetis, Chironomidae, and Capniidae. Comparisons of drift rates at the upstream and downstream ends of each pool showed that the abundance of Chironomidae, Simulium, Capniidae and total drift changed in different directions across the pools. The numbers of organisms leaving the two pools, however, were not significantly different for Baetis, Simulium, Capniidae and total drift. These findings lead us to hypothesize that long pools act as barriers, not filters, to stream macro-invertebrate drift. The composition of drift leaving the pools in this experiment appeared to be controlled by the composition of the benthic habitat at the tail of the pool and not by the composition of upstream drift entering the pools.