The response of Chironomidae (Diptera) to a long-term exclusion of terrestrial organic matter

We examined the effects of a seven-year detrital exclusion on chironomid assemblages in an Appalachian headwater stream. We hypothesized that litter exclusion would lead to a reduction in all chironomids at both the subfamily and generic levels because organic matter serves as both food and habitat in these headwater streams. Tanytarsini total abundance and biomass significantly declined after litter exclusion. Before litter exclusion, Tanytarsini average abundance was 4271 ± 1135 S.E. m⁻² and 625 ± 98 after litter exclusion. Biomass was 3.57 ± 0.96 mg AFDM m⁻² before litter exclusion and 1.03 ± 0.9 after exclusion. In contrast, Orthocladiinae abundance and biomass did not change because a psammanophilic chironomid, Lopescladius sp., and other Orthocladiinae genera did not decline significantly. Overall chironomid taxa richness and diversity did not change as a result of litter exclusion. However, Canonical Correspondence Analysis (CCA) of genus-level biomass did show a clear separation between the litter exclusion stream and a reference stream. Separation of taxa between the two streams was due to differences in fine (r ² = 0.39) and coarse (r ² = 0.36) organic matter standing stocks and the proportion of small inorganic substrates (r ² = 0.39) present within a sample. As organic matter declined in the litter exclusion stream, overall chironomid biomass declined and the chironomid community assemblage changed. Tanytarsini were replaced by Orthocladiinae in the litter exclusion stream because they were better able to live and feed on biofilm associated with inorganic substrates. Handling editor: K. Martens     

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.     

THE SEASONAL DISTRIBUTION,ABUNDANCE AND DIVERSITY OF DESMIDS (CHLOROPHYTA) IN A SOFTWATER,NORTH TEMPERATE STREAM1

Suspended and benthic algal communities from a mildly acidic, third-order Rhode Island stream were examined to determine the seasonal distribution, abundance and diversity of the lotic desmids. Within a one-year sampling period, 148 species and 202 subspecific taxa of desmids were identified, representing 23 genera. Species of Cosmarium and Closterium accounted for approximately 70% of the desmids present, and were the most diverse and abundant taxa during all seasons except spring, when Hyalotheca dissiliens was the dominant desmid species. Average abundance and species richness generally were greatest during summer for both suspended and benthic desmids. Most desmids occurred in benthic habitats, and were randomly distributed among substrata. Average seasonal abundance was 7.4 × 10⁴ cells·g^?1 dry wt substratum, among 13 types of substrata. Highest desmid abundance was measured among substrata with intricate morphologies, such as Fontinalis spp., which was associated with 1.2 × 10⁶ desmid cells·g^?1 dry wt substratum, or 1.7 × 10³ cells·cm^?2 substratum. Cell division was observed for 70 desmid taxa, and average seasonal reproduction (based on cell numbers) among all substrata ranged from 4% in winter to 20% during summer. In addition, sexually produced zygospores were found occasionally for H. dissiliens. Desmids were distributed among most substrata examined in this stream, with abundance comparable to reported estimates from softwater lakes and acid bogs. In contrast to established dogma, lotic desmids are not incidental drift organisms, but rather comprise a viable and persistent component of the stream periphyton.     

Diel drift of Chironomidae larvae in a pristine Idaho mountain stream

Simultaneous hourly net collections in a meadow and canyon reach of a mountain stream determined diel and spatial abundances of drifting Chironomidae larvae. Sixty-one taxa were identified to the lowest practical level, 52 in the meadow and 41 in the canyon. Orthocladiinae was the most abundant subfamily with 32 taxa and a 24 h mean density of 294 individuals 100 m⁻³ (meadow) and 26 taxa and a mean of 648 individuals 100 m⁻³ (canyon). Chironominae was the second most abundant subfamily. Nonchironomid invertebrates at both sites and total Chironomidae larvae (meadow) were predominantly night-drifting. Parakiefferiella and Psectrocladius were day-drifting (meadow) whereas 8 other chironomid taxa (meadow) and 2 taxa (canyon) were night-drifting. All others were aperiodic or too rare to test periodicity, Stempellinella cf brevis Edwards exhibited catastrophic drift in the canyon only. The different drift patterns between sites is attributed to greater loss of streambed habitat in the canyon compared to the meadow as streamflow decreased. Consequent crowding of chironomid larvae in the canyon caused catastrophic drift or interfered with drift periodicty. This study adds to knowledge of Chironomidae drift and shows influences on drift of hydrologic and geomorphic conditions.     

Ecology of a cyanobacterial mat community in a Korean thermal wastewater stream

Cyanobacterial mats along a small stream receiving thermal wastewater from an artificial hot spring in the mid-upper part of the Mankyeong River system, Korea, were studied during the winter of 1995-1996. In the cyanobacterium, Oscillatoria terebriformiscomprised >95% of total biomass. Ash-free dry-weight (AFDW) and chlorophyll a in the cyanobacterial mats decreased significantly (r²= 0.78 and 0.83, respectively) with distance downstream from the thermal water outlet, while primary productivity increased slightly. The concentrations of the majority of ions sharply decreased with distance downstream, although they were not markedly related with spatial changes in AFDW, Chl a and primary productivity. O. terebriformis appeared to have a tremendous potential in wastewater treatment because of its marked ability to glean ions.     

Phenology and bathymetric distribution of the profundal chironomid fauna in Starnberger See (F.R. Germany)

Results of the first long-term investigation of the profundal chironomid fauna of Starnberger See, a prealpine lake are reported. Data are presented on the qualitative and quantitative composition of the chironomid fauna in the profundal of Starnberger See, on the spatial variation, and on the phenology of the dominant species, based on pupal occurrence and the seasonal distribution of larval instars. Twenty-five distinct chironomid taxa could be recorded in the profundal zone. Typical inhabitants of the profundal zone of Starnberger See are the larvae of the genus Micropsectra. The maximum abundance of Micropsectra larvae were found at 60 m with 5644 Ind.m⁻². Abundance, distribution and phenology of the dominant chironomid species are discussed in comparison with other lakes.     

Bryophytes as invertebrate habitat in two New Zealand alpine streams

SUMMARY. 1. Quantitative samples of lotic benthic invertebrates and associated organic material were taken monthly for 18 months from bryophyte and gravel habitats in two New Zealand alpine streams in Arthur's Pass National Park, South Island; an unshaded site above the tree-line and a shaded stream flowing through mountain beech forest. This was to assess the ecological role of bryophytes in these habitats and to determine the relative effects on the fauna of algal and detrital resources. 2. Bryophytes were confined to stable bedrock substrata in shallow (mean depth of 4.5 and 10.5 cm), fast water (mean velocity of 0.21 ms^?1 and 0.30ms^?1) at the unshaded and shaded sites. Mean ash-free dry weight (AFDW) of organic material from bryophyte areas was similar at the unshaded and shaded sites (335.6 and 272.4 gm^?2). Low stream-bed stability of the gravel areas resulted in poor retention of organic matter, with average AFDW of 59.1 and 77.9 gm^?2 at the unshaded and shaded sites, respectively. Periphyton biomass, however, was much higher at the unshaded site. 3. Within bryophytes, water velocity is reduced and large quantities of periphyton and detritus accumulate. This explains the greatly enhanced invertebrate densities within bryophytes (218400 and 53500 individuals m^?2), compared with gravel areas (20900 and 7400 individuals m^?2) in the unshaded and shaded sites, respectively. The higher invertebrate densities at the unshaded site reflect greater periphyton biomass there. 4. Invertebrate densities followed clear seasonal patterns, attributable to changes in chironomid densities. These reflected larval chironomid hatching following adult oviposition. This illustrates the importance of these plants as oviposition sites, and as protective nurseries for small larvae where they can obtain shelter during floods and consume the abundant food sources available to them. 5. DECORANA ordination revealed taxonomically distinct invertebrate communities in each stream, and in bryophytes and gravels. Several taxa appeared restricted to either the unshaded site (e.g. Acroperla spiniger and Hydrobiosis silvicola) or the shaded site (e.g. Zelolessica     

Spatial and temporal fluctuations in presence and use of chironomid prey by shorebirds in the Odiel saltpans, south-west Spain

We studied the seasonal variation in abundance and distribution of shorebirds and chironomid Chironomus salinarius larvae in both traditional and industrial salines in the Odiel marshes, south-west Spain, in 2001. We selected 12 ponds that were representative of the different phases of the salt production process. The benthic chironomids were sampled in each pond every 2 months, and the birds were counted weekly. Chironomid larvae were most abundant in spring and autumn, and in the ponds of lower salinity. The density of larvae averaged 7023 ± 392 m⁻² (±SE) over the six sampling events. Shorebirds were always more abundant at high tide than at low tide, and were especially abundant during the spring and autumn migration periods when up to 20,775 birds were counted. A total of 24 species were recorded, six of which were present in internationally important numbers. The salines were especially important as foraging and roosting habitat during migration. The percentage of birds that were feeding in the ponds was positively correlated with the abundance of chironomid larvae at accessible depths. The number of feeding birds was also higher in ponds with more chironomid larvae available. Despite more intensive management, industrial salines held higher densities of birds and a similar abundance of chironomids when compared with traditional salines.     

The ecology of algae in the Moruya river,Australia

The standing crop of benthic and planktonic algae in the Moruya River, Australia, was, in general, low compared with values given for northern hemisphere rivers. Diatoms always accounted for more than 90% of the algae on the sediments with the most common species being typical of holarctic flora. The relative abundance of each of six predominant taxa was similar at the three sampling localities and did not show marked seasonal variation. However, Gomphonema spp. contributed a relatively greater number in the downstream area whereas Cocconeis placentula Ehr. was comparatively more abundant upstream. The highest standing crop (1.47 × 10⁶ cells/cm²) was found downstream and in the calmest part of the river between January and March, coincident with maximum water temperatures. A true phytoplankton succession comprising filamentous chlorophytes, Scenedesmus, Melosira varians Ag., Dactylococcopsis, Eudorina and Merismopedia was observed at the most downstream site during the spring and summer, with a maximum standing crop of 126.7 × 10³ cells/litre being attained in December. The gut of larval lampreys > 100 mm contained large numbers (44,000–525,000 cells) of algae. Scenedesmus and Dactylococcopsis occurred much more frequently in the gut than in either the sediment or water, but the reverse was true for filamentous algae.     

Distribution,abundance and diversity of macrozoobenthos in Aiba Reservoir,Iwo, Nigeria

Spatial and seasonal variation in macrozoobenthic composition, abundance and diversity in Aiba Reservoir were investigated bimonthy between June 2004 and April 2005 using a van Veen grab. A depauperate fauna of nine taxa was recorded. Generally, larger numbers of taxa were recorded during the dry season than in the wet season. Melanoides tuberculata and chironomid larvae dominated the macrozoobenthos and showed wide spatial distribution. Diversity and evenness were lower during the wet season than in the dry season, when densities of the major species were low. Melanoides tuberculata and chironomid larvae were recorded from maximum depths of 3.9 m and 2.6 m, respectively. Both taxa were also recorded from all substrate texture types, regardless of the amount of macrophyte material present. The benthic fauna is characterised as being poor in terms of density, taxonomic richness and diversity     

Leaf-pack dynamics in a southern African mountain stream

SUMMARY 1. The occurrence, composition and invertebrate fauna of naturally-occurring leaf packs were studied over 24 months in Langrivier, a second-order mountain stream in the south-western Cape, South Africa. Langrivier is shallow and fast-flowing and stores very low levels of allochthonous detritus, although natural leaf packs form an obvious part of the energy base in the stream throughout the year. 2. The occurrence and size of the packs were influenced mainly by stream discharge and by the timing and character of leaf fall from riparian trees. Packs were smallest (minimum dry mass 17 g, minimum volume 1.7–10^?5 m³) in winter when discharge was high, and largest (maximum dry mass 191 g, maximum volume 4.2–10^?3 m³) in spring when discharge decreased and leaf fall from the evergreen riparian trees began. Through the year the packs covered a mean 0.41 % of the stream bed and had a mean abundance of 0.46 packs m^?2 of stream bed. They were ephemeral, lasting on average <1.7 months and yet accounted for 29% of the stored detritus in the system. Wood was the dominant component of packs, and leaves at ali stages of decomposition were present throughout the year. 3. The ratio of numbers of invertebrates in packs: numbers of individuals in the benthos was very low (0.002–0.030), presumably because of the rarity and small size of the packs. Nevertheless, the density of invertebrates per unit area covered by leaf packs was consistently much higher than the density in an equivalent area of the benthos, except during peak leaf fall (October to December). 4. Experiments were undertaken with artificial leaf packs in order to determine the extent to which these simulated natural packs. Although both natural and artificial leaf packs contained a high proportion of Plecoptera (46% and 29% respectively), the natural packs contained high numbers of simuliid larvae (33% of total), whereas artificial packs had a high percentage of chironomid larvae (62%), Several other taxa regularly occurred in both types of pack but in very low numbers. In addition,     

Pelagic food web interactions among benthic invertebrates and trout in mountain lakes

1. Benthic chironomid larvae and the amphipod Gammarus lacustris have been observed in the pelagic habitats of many mountain lakes. The main goal of this study was to determine if chironomid larvae and gammarids potentially affect predator–prey and nutrient dynamics in pelagic food webs of mountain lakes. 2. Eighty‐six mountain lakes were surveyed in Alberta and eastern British Columbia during the years 1965–1984, 1991–2004 and 2005–2007. Pelagic chironomid larvae were found in 86% of these lakes, and pelagic gammarids were found in 29% of lakes. Densities of pelagic chironomid larvae were 92% lower in lakes with pelagic gammarids and 76% lower in lakes with trout (P < 0.05). Intraguild predation of trout on gammarids appeared to reduce predation pressure on chironomid larvae. Gammarids consumed in vitro about 1 chironomid per gammarid per day or about 20% of their body mass in chironomid biomass per day. 3. Concentrations of total dissolved P and N, particulate C, and chlorophyll‐a increased with increasing densities of pelagic gammarids and chironomid larvae in situ (R² = 0.14 ± 0.19 SD, P < 0.1) and in vitro (P < 0.001). 4. Our findings suggest that gammarids and chironomid larvae are linked as predators and prey in pelagic food webs, possibly stimulating phytoplankton abundance via nutrient release.     

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.     

Ecological influences on larval chironomid communities in shallow lakes: implications for palaeolimnological interpretations

1. To correctly interpret chironomid faunas for palaeoenvironmental reconstruction, it is essential that we improve our understanding of the relative influence of ecosystem variables, biotic as well as physicochemical, on chironomid larvae. To address this, we analysed the surface sediments from 39 shallow lakes (29 Norfolk, U.K., 10 Denmark) for chironomid head capsules, and 70 chironomid taxa (including Chaoborus) were identified. 2. The shallow lakes were selected over large environmental gradients of aquatic macrophytes, total phosphorus (TP) and fish communities. Redundancy analysis (RDA) identified two significant variables that explained chironomid distribution: macrophyte species richness (P < 0.001) and TP (P < 0.005). Generalised linear models (GLM) identified specific taxa that had significant relationships with both these variables. Macrophyte percentage volume infested (PVI) and species richness were significant in classifying the lake types based on chironomid communities under twinspan analysis, although other factors, notably nutrient concentrations and fish communities, were also important, illustrating the complexities of classifying shallow lake ecosystems. Lakes with plant species richness >10 all had relatively diverse (Hill’s N2) chironomid assemblages, and lakes with Hill’s N2 >10 all had TP <250 μg L⁻¹ and total fish densities <2 fish per m². 3. Plant density (PVI), and perhaps more importantly species richness, were primary controls on the distribution of chironomid communities within these lakes. This clearly has implications for palaeoenvironmental reconstructions using zoobenthos remains (i.e. chironomids) and suggests that they could be used to track changes in benthic/pelagic production and could be used as indicators of changing macrophyte habitat. 4. Measuring key biological gradients, in addition to physicochemical gradients, allowed the major controls on chironomid distribution to be assessed more directly, in terms of plant substrate, food availability, competition and predation pressure, rather than implying indirect mechanisms through relationships with nutrients. Many of these variables, notably macrophyte abundance and species richness, are not routinely measured in such studies, despite their importance in determining zoobenthos in temperate shallow lakes. 5. When physical, chemical and ecological gradients are considered, as is often the case with palaeo‐reconstructions rather than training sets chosen to maximise one gradient, complex relationships exist, and attempting to reconstruct a single trophic variable quantitatively may not be appropriate or reliable.     

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.     

Vertical microdistribution of benthic chironomid larvae within a section of the littoral zone of a lake

A study of the vertical distribution of all instars of chironomid larvae was carried out in the littoral zone of a lake in southwest England over a period of 14 months. Samples were collected every month by using a 44 mm (i.d.) piston core sampler. Each core sample was sectioned at 1 cm intervals and preserved immediately after collection. The density of larvae in the study area varied from a low of 16,368 larvae m^–2 in August 1989 to maximum values of 106,249 and 129,954 larvae m^–2 in June 1989 and May 1990, respectively. During spring and early summer, first instar larvae comprised approximately half of the larval population. No significant differences were found in seasonal vertical distribution of the chironomid larvae. Over 85% of the larval population inhabited the top 6 cm of the sediment, with the first and second instar larvae of all taxa most abundant in the top 1 cm section.     

Quantification of submerged wood in a lowland Australian stream system

1. The importance of submerged wood (snags) as macroinvertebrate habitat was evaluated in the Pranjip-Creightons Creek system, a lowland stream system in northern Victoria. Snag surface area and biomass were measured at ten sites along the system. The first four upstream sites, located in the foothills of the Strathbogie Ranges, and the next three sites, on the northern Victorian riverine plain, were affected by streambank erosion and high sediment loads and contained little instream wood. A further three sites (Sites 8, 9 and 10) downstream on the riverine plain were not as affected by erosion and possessed extensive stands of riparian river redgum, Eucalyptus camaldulensis, which contributed large amounts of wood to the stream channel. 2. Wood quantities at Site 8 were less than at Sites 9 and 10 downstream where the density of riparian redgum was greater. At Sites 9 and 10, snag surface area per m² of stream bed was 0.57–0.92m² and 0.38–0.71m² depending on discharge. Total snag biomass in the stream channel at the same sites was 26 and 41kg m^?2, respectively. Redgum was important to macroinvertebrates as habitat, at one site contributing 25% of total macroinvertebrate densities and over 30% of total macroinvertebrate biomass m^?2 of stream bed. 3. Estimations of nitrogen content and C:N ratios of decayed redgum were carried out to provide information on its putative nutritional quality to xylophagous macroinvertebrates. Decayed redgum wood has a comparatively high N content and therefore a low C:N ratio, but appeared to be unpalatable to most macroinvertebrates. Only two macroinvertebrate species, the chironomid larvae Stenochironomus sp. and Dicrotendipes sp., were found to consume decayed redgum.     

Macroinvertebrate communities in Wheeler Reservoir (Alabama) tributaries after prolonged exposure to DDT contamination

Quarterly measurements were conducted of the structure, abundance, and diversity of macroinvertebrates comprising two distinct, but overlapping zoobenthic communities in backwaters to Wheeler Reservoir Alabama. The study area included portions of Huntsville Spring Branch (HSB) and Indian Creek (IC) which contain massive quantities of DDT residues (DDTR = DDT, DDD, DDE). Additionally, sewage effluents entering HSB just upstream from the study area have resulted in nutrient enrichment, especially at the two uppermost stations. Herpobenthos (burrowed in bottom sediments) and haptobenthos (attached to substrates) were collected at seven stations along an east-west gradient including a control site above the DDT contamination, and sites with mean sediment residues ranging from 2,730 ppm DDTR in HSB down to 12 ppm DDTR at the mouth of IC.Fifty taxa were collected from dredge samples of the herpobenthos; Tubificid oligochaetes and chironomid larvae comprised 97% of the herpobenthos. At the two uppermost stations in HSB, the control site and the site with the highest sediment DDTR, oligochaete density averaged twice that of chironomids. Downstream, densities of both groups were similar. Mean density at the upper two stations was 9431 and 10 644 organisms m^–2, respectively, significantly (P < 0.05) higher than downstream stations. Herpobenthos was dominated by detrital-algal feeders in HSB while in IC, predaceous chironomids were more numerous. Taxa diversity was also lowest (P < 0.05) at the two upper sites.Forty-five taxa were collected from artificial substrate (Hester-Dendy multiplate samplers) samples of the haptobenthos. Naidid oligochaetes and chironomids dominated the haptobenthos, although nematodes were occasionaly abundant. Chironomids were more abundant than oligochaetes at all sites except the control station, which received the greatest nutrient enrichment from sewage effluents. Mean haptobenthic density in the middle portion of the study area ranged from 31 163 to 37 310 organisms m^–2 and was diferent (P < 0.05) from upper and lower stations. Taxa diversity was lowest at the upper-most station, but no trends were evident among stations.Nutrient enrichment from sewage effluents apparently had greater impact on zoobenthic communities in the HSB-IC System than did DDT contamination. However, the presence of DDTR undoubtedly contributed, in part, to the few Ephemeroptera, Plecoptera, and Trichoptera collected at contaminated stations. Based on the density of oligochaetes and chironomid larvae at station 2 (highest DDTR), macroinvertebrates in this system are resistant to DDTR.     

Macroinvertebrate stream communities along regional and physico-chemical gradients in Western Greenland

1. Macroinvertebrates were collected and physico‐chemical variables measured at 16 stream sites in Western Greenland during July 1999. Eight sites were located on Disko Island in an arctic oceanic climate and eight sites in the Kangerlussuaq area close to the icecap where the climate is arctic continental. The streams had different water sources (glacial, groundwater, snowmelt and lake water). 2. The streams showed pronounced differences in water temperature (2.2–17.3 °C), concentrations of suspended solids (0–2400 mg L^?1), and conductivity (10–109 μS cm^?1). Principal component analysis (PCA) analysis of the physico‐chemical variables separated the Disko Island sites into a distinct group, whereas the sites in the Kangerlussuaq area were more dispersed. 3. A total of 56 macroinvertebrate species were found, including 31 species of Chironomidae, the most abundant of which was Orthocladius thienemanni. Diamesa sp. was only the sixth most abundant chironomid taxon. Species composition varied between sites, and abundance varied from about 20 individuals m^?2 in a glacier fed stream to more than 16 000 m^?2 in a lake outlet. 4. The macroinvertebrate communities of the 16 streams were separated into five TWINSPAN groups reflecting water source, irrespective of region. Lake outlets and ground‐water‐fed streams had the highest species richness and abundance, temperature and bed stability, while glacier‐fed streams were characterized by low species richness, abundance, temperature, bed stability and high concentrations of suspended solids. Macroinvertebrate species richness was positively correlated with water temperature and negatively with bed stability. Conductivity was positively correlated with invertebrate abundance. 5. The results of this study suggest that the source of stream water can be used to predict invertebrate community composition in Greenlandic streams and thus the effects of changes in water balance and flow regime, and to identify sites of special conservation interest.     

Night — day drift patterns and the size of larvae of two aquatic insects

A test of Allan's (1978) hypothesis about differential drift abundance of mayflies of the genus Baetis between night and day, and the size of larvae was performed at a mountain stream in Idaho. Palisades Creek, Idaho, contains a different species of mayfly, B. tricaudatus, and vertebrate predator, Salmo clarki, than Cement Creek, Colorado (B. bicaudatus, and brook trout, Salvelinus fontinalis). Consequently it was not known if B. tricaudatus would exhibit a similar pattern as its congener in Cement Creek, with large instars tending to avoid daylight drift, as found by Allan (1978). However, similar results were observed in the present study. It appears that the earlier hypothesis may have generality for geographically distinct streams with a different vertebrate predator and mayfly prey. The existence of a similar pattern for chironomid larvae was also tested, however, no such pattern existed. This discrepency between taxa may be due to differential predation, or to inherent differences in drift abilities.