Studies of aquatic insects in the Atna River 1987–2002

Hydrobiologia 521: 87–105, 2004. O.T. Sandlund & K. Aagaard (eds), The Atna River: Studies in an Alpine–Boreal Watershed. © 2004 Kluwer Academic Publishers. Printed in the Netherlands. 87 Studies of aquatic insects in the Atna River 1987–2002 Kaare Aagaard1,2 , John O. Solem2 , Terje Bongard1 & Oddvar Hanssen1 1 Norwegian Institute for Nature Research (NINA) Tungasletta 2, NO-7485 Trondheim, Norway E-mail: [email protected] 2 Norwegian University of Science and Technology (NTNU), Museum of Natural History and Archaeology, NO-7491 Trondheim, Norway Key words: zoobenthos, RCC, bio-monitoring, long term studies, altitudinal zonation Abstract River Atna is situated in south-eastern Norway and stretches from approx. 1400 m a.s.l. in the Rondane Mountains, through Lake Atnsjøen, at 701 m a.s.l.; to the confluence with River Glomma at 338 m a.s.l. The catchment area is 1323 km2 , oligotrophic and very susceptible to acid precipitation. The river water is very poor in nutrients and ions, and pH varies from 5.0 to 7.2. Samples were taken each year from 1987 to 2002 at three to five localities from 1280 to 380 m a.s.l. Insect larvae were collected by Surber sampling and by kick sampling. Malaise traps were used to collect adults of Plecoptera, Trichoptera, Chironomidae and Limoniidae. A total of 16 taxa of Ephemeroptera, 24 taxa of Plecoptera, 39 taxa of Trichoptera, 125 taxa of Chironomidae and 52 taxa of Limoniidae, were identified. Our results from Atna provide some support for a zonation of the river based on zoobenthos. The occurrence and abundance of functional groups among the Plecoptera, Trichoptera, and Chironomidae are discussed in relation to the River Continuum Concept (RCC). Our conclusion is that grazers dominate in the zoobenthos in streams in the treeless alpine region in Norway. Natural lakes, which occur in most watercourses in Norway, appear to cause a disturbance in relation to the original RCC concept, as the zoobenthos community in and below the lake outlet is dominated by collectors (filter feeders). The pattern found in the Atna watercourse is probably a general pattern for a northern watercourse in the Holarctic, where the glacial periods created lakes in most watercourses. The results of the long term sampling in Atna are discussed in relation to the practicalities and the cost-benefit of zoobenthos in efficient bio-monitoring in rivers. Introduction Longitudinal distribution and community structure of invertebrates in rivers have been discussed in several papers over the last 40 to 50 years. The earliest papers were descriptive and focused mainly on the distribution of benthic communities (Müller, 1953; Illies, 1956, 1961; Illies & Botosaneanu, 1963). However, Webster (1975) pointed out that nutrients in a stream do not cycle in place, but are transported downstream as they complete a cycle; this coupling of transport and energy cycling was described as a ‘spiralling’ effect. This idea was further developed by Vannote et al. (1980) who introduced the River Continuum Concept (RCC). RCC takes into consideration not only the species composition, but also the production, respiration and feeding habits of the species, providing a more holistic and dynamic view of the running water ecosystem. The RCC classifies the zoobenthos in functional groups based on their feeding habits, i.e. grazers, shredders, collectors (filter feeders), and predators. Vannote et al. (1980) postulated a gradual change in community structure from the source of the river to its end in the ocean. In their study, the river source was in forest, i.e. heavily shaded, and they demonstrated a gradual change in the production/respiration ratio along the river. At the source, respiration was larger than production. Some distance downstream, production increased to become larger than respiration, while even further downstream res- 88 piration again became larger than production. Other authors, e.g., Statzner & Higler (1986) and Statzner (1987) focused on the stream hydraulics as an important factor governing the distribution of species. Townsend (1989) introduced the patch dynamics concept of stream community organization, stressing the importance of competition, succession, predation, grazing and disturbance. Norway (and Scandinavia) has been classified into several biotic zones based on terrestrial vegetation (Moen, 1999). Subsequently, the vertical zonation of Plecoptera and Trichoptera in rivers in relation to the zonation in adjacent terrestrial ecosystems was discussed by Lillehammer (1974) and Solem (1985). In this study we have collected zoobenthos from the river Atna, which runs through several vegetation zones (Table 1), in order to analyse the spatial and temporal changes in the community structure of Ephemeroptera, Plecoptera and Trichoptera. We have also included data on the species composition of Diptera families Chironomidae and Limoniidae. The objectives of the study were: (1) to document the species inhabiting the river; (2) to describe the longitudinal zonation in the aquatic insect communities and relate the aquatic fauna to the terrestrial biotic zonation; (3) to discuss the occurrence and dominance of functional groups in the different biotic zones in relation to the RCC concept; and (4) to evaluate the monitoring value of a low effort long term study. Methods Insect larvae were collected by Surber sampling and by kick sampling. The net meshes in the 0.1 m2 Surber sampler and kick sampling net were 0.5 mm. Caddis larvae (Trichoptera) were also handpicked, mostly in the upper parts of the river system. Mayflies (Ephemeroptera) are best caught with the kick sample method (Engblom, 1996). The use of the Surber sampler is probably one of the reasons for a relatively low specimen number in the samples. A careful use of the Surber method has nevertheless been shown to increase the number of rare taxa collected on heterogeneous substrates, while the number of specimens is lower in Surber samples compared to kick samples (Storey et al., 1991). Malaise traps were used to collect adults of stoneflies (Plecoptera), caddis flies, limonids and chiro- nomids. This adds information on species occurrence to facilitate community analyses and to reveal distribution patterns. One argument against sampling with Malaise traps for community analyses, is that species may fly in from other habitats than the one targeted by the sampling. However, Solem (1985) tested the validity of the Trichoptera collections in Malaise traps against emergence traps in the stream Raubekken, Dovrefjell, and concluded that Malaise trap collections are adequate for community analyses. Although the Malaise trap will always capture a few specimens of species that do not belong to the nearby community, these specimens are so few that they will not seriously disturb the general community analyses. An obvious advantage of Malaise traps is that they may sample continuously during the whole flying season, from late June, through July, August and September. During our sampling programme, the traps were emptied every week and the animals were conserved in ethanol. Study area and sampling sites River Atna is situated in southeastern Norway and originates in the Rondane Mountains well above the tree line, which is at 1100 m a.s.l. The river is 97 km long, and Lake Atnsjøen, at 701 m a.s.l., is situated in the middle of the water course. Atna joins River Glomma at 338 m a.s.l. Our sampling sites are situated between approximately 62◦ N, 9◦ 45′ E and 61◦ 45′ N, 10◦ 45′ E (Fig. 1). Surber samples were taken each year from 1987 to 2002 at three localities; Dørålseter, Vollen, and Solbakken, and covered a nearly 80 km stretch of the river. Surber samples have also been taken in some of the later years at Skranglehaugan (Table 1). The material of benthic insect larvae from these samples has been identified mostly to the species or genera level for the groups Plecoptera, Ephemeroptera and Trichoptera. Material of adult insects was collected with Malaise traps at Vidjedalsbekken Skranglehaugan, Dørålseter, Vollen, the outlet of Lake Atnsjøen and Solbakken (Table 1). Imagines of Trichoptera and Plecoptera were identified from all these localities, while imagines of Ephemeroptera and males of Chironomidae and Limoniidae were identified from Vidjedalsbekken, Skranglehaugan, Dørålseter, Vollen and Solbakken. The water in the river is very poor in nutrients and ions, and pH varies from 5.0 to 7.2 (cf. Lindstrøm et al., 2004). The catchment area is 1323 km2 , oli- 89 Figure 1. Map of the Atna watershed with sampling localities (cf. Table 1). Figure 2. Number of Chironomid larvae in the Surber samples during the period 1992 to 2002. 90 Table 1. Sampling sites with altitude, vegetation type, vegetation zone and -section according to Moen (1999), and zoobenthos sampling program. Station Altitude (m a.s.l) Vegetation type Vegetation zones Vegetation sections Surber samples Malaise traps Vidjedals-bekken Skrangle-haugan Dørålseter Vollen Atnsjøen Solbakken 1280 1120 1060 710 700 380 Treeless area Birch woodland belt Birch woodland belt Coniferous area Coniferous area Coniferous area Alpine Northern boreal Northern boreal Northern boreal Northern boreal Middle boreal Continental to oceanic Continental to oceanic Continental to oceanic Slightly continental Slightly continental Slightly continental – 1997–2002 1987–2002∗ 1987–2002∗ – 1987–2002∗ 1986 and 1987 1986 and 1987 1986 and 1987 1986 1986 1986 ∗ The material from 1996 was lost in an accident. Figure 3. Number of missing taxa in the Surber samples at Solbakken for each year and running periods for the last 2, 3 and 4 years. gotrophic and very susceptible to acid precipitation (Blakar et al., 1997). The water temperature in the lower part of the river, below the lake, may reach 20 ◦ C during summer, with mean temperatures in June to August at 10–12 ◦ C. Upstream of Lake Atnsjøen, the water temperature may reach 10 ◦ C only for short periods during summer. At Vidjedalsbekken, in the subalpine birch woodland belt, maximum water temperature may reach 7–8 ◦ C during summer, with mean temperatures during July and August of 4–6 ◦ C. At Dørålseter a little further downstream, maximum summer temperatures may reach 10–11 ◦ C. The increase in water temperatures during spring occurs nearly two months later at Vidjedalsbekken than at Solbakken, and there is a corresponding difference in summer temperature of 6 ◦ C (Tvede, 2004). River Atna and its tributaries, including Vidjedalsbekken, is unregulated, and only to a very limited extent influenced by human activities. No part of the tributary or river is significantly shaded by terrestrial vegetation. Consequently, the light conditions are very good for periphyton growth on the substratum. Results Distribution and abundance of Ephemeroptera A total of 16 taxa of mayflies were identified in the material collected during the years 1986–2002 (Table 2). This includes an unidentified Leptophlebidae collected at Solbakken. Baetis rhodani is by far the most common species in the river. In fact 30 000 individuals out of a total of 36 000 collected mayfly nymphs belonged to this species, which is by far Norway’s most common running water mayfly species. B. rhodani 91 Table 2. Distribution of Ephemeroptera species in the river Atna. Species records at each of the localties quantified as very abundant or abundant (xxxx or xxx), less abundant (xx) or rare (x). An i indicates that the species are identified from imago. Locality Skranglehaugan Dørålseter Baetis lapponicus Baetis rhodani Ephemerella aurivillii Heptagenia joernensis Baetis muticus Baetis fuscatus/scambus Ameletus inopinatus Siphlonurus lacustris Baetis subalpinus Heptagenia dalecarlica Siphlonurus aestivalis Baetis scambus Ephemerella mucronata Heptagenia sulphurea Leptophlebiidae Parameletus chelifer * Number of species x xx x xxxx x x x x x i Vollen xxxx xxx xx x x xx i xx x x Solbakken x xxxx xxxx xxx xxx xxxx xx i xxx xxx xx xx x x 2 8 10 14 ∗ Imago found in a Malaise trap at the outlet of Lake Atnasjøen. is a collector-gatherer and grazer (scraper) (Bækken, 1981; Elliott et al., 1988). At the site Skranglehaugan, 1120 m a.s.l., only nymphs of B. rhodani and B. lapponicus were recorded in the Surber and kick samples. At this elevation mayflies are at their extreme altitudinal limit in Norway. The third species of this genus known from high altitudes, B. subalpinus, was not found at the two high altitude sites (Vidjedalsbekken, Skranglehaugan) in Atna. This is somewhat surprising, since this species is characterised as a northern, high altitude species in Norway (Nøst et al., 1986). Eight species of Ephemeroptera were found at Dørålseter, which is situated in the birch woodland belt (1060 m a.s.l.) (Table 2). The site with most mayfly species was Solbakken in the middle boreal zone, where 14 species were recorded. At this site, Baetis fuscatus/scambus were caught in considerable numbers. Nymphs of the two species may not be easily separated (Elliott et al., 1988). However, as no B. fuscatus imagines has yet been recorded in Atna, it appears reasonable that the nymphs collected mainly were B. scambus The two species Heptagenia dalecarlica and H. joernensis were present in large numbers at Solbakken, while only one specimen of H. sulphurea was caught during all the sampling years. All mayfly species recorded in Atna during our sampling period (1986–2002) are common in Norway, except the species Parameletus chelifer that was found in a Malaise trap at the outlet of Atnsjøen. This species is missing in large parts of western and northern Norway, although it is not formally listed as rare or uncommon. Ameletus inopinatus has not previously been recorded from the area (Brittain et al., 1996). Distribution and abundance of Plecoptera The stonefly fauna must be considered well documented through this investigation. In our material we identified 24 of the 28 species previously recorded in the region (Table 3; Aagaard et al., 2002). Stoneflies generally prefer cold, clean, running waters, and a few species occur at all altitudes in all parts of Norway. The four species not recorded in this study is either a lake dweller (Diura bicaudata), or they are species with a distribution mainly restricted to lowland areas. (Dinocras cephalotes occurs in brooks and large rivers, Isoperla difformis has a wide, but sparse distribution, and Isogenus nubecula has a southern and eastern distribution in Scandinavia and is therefore rare in Norway). A total of 7048 stonefly nymphs were recorded in the Surber samples. Capnia atra was the most abundant species with a maximum at Dørålseter, while 92 Table 3. Distribution of Plecoptera species in the river Atna. Species records at each of the localties quantified as very abundant or abundant (xxxx or xxx), less abundant (xx) or rare (x). An i indicates that the species are identified from imago. Locality Skranglehaugan Capnia bifrons Arcynopteryx compacta Brachyptera risi Nemoura cinerea Capnia atra Protonemura meyeri Nemurella pictetii Amphinemura borealis Diura nanseni Isoperla obscura Isoperla grammatica Leuctra fusca Capnia pygmaea Amphinemura standfussi Leuctra digitata Leuctra nigra Leuctra hippopus Taeniopteryx nebulosa Nemoura avicularis Capnopsis schilleri Siphonoperla burmeisteri Amphinemura sulcicollis Nemoura flexuosa Xanthoperla apicalis i xx x x xx xx xx x x x x i i Number of species 13 Dørålseter xx xxx xx xxxx xxx xx x x x i x i i xx x x x 17 Vollen xx i xxx xx x xx xxx xxx xxx x i i x xx xx xxx x x x xx 20 Solbakken i x x x xxx xxx x x xx i xx x x xx i xx x i i 19 Figure 4. Number of species with different frequency of occurrence in the annual Surber samples at the three localities Dørålseter, Vollen and Solbakken in Atna, 1986–1998. 93 Diura nanseni dominated the samples from Vollen and Solbakken. No species were recorded in Malaise traps at Vidjedalsbekken, 1290 m a.s.l. in the midalpine zone. In the birch woodland belt (Skranglehaugan and Dørålseter) 17 species were found, and the fauna was dominated by Capnia atra, Brachyptera risi and Protonemura meyeri. B. risi is a grazer (scraper) on periphyton in streams. P. meyeri is a grazer and shredder. All the 24 species, except Arcynopteryx compacta, were collected in the boreal zone. A. compacta is an alpine species, and was only found at the two uppermost sites, Dørålseter and Skranglehaugan. Capnia species dominated at high altitudes. This genus includes three species in Atna, C. atra, C. bifrons and C. pygmaea. C. atra is the dominating species, according to our Malaise trap catches along the river. Other species caught in large numbers are Amphinemura borealis, Leuctra fusca, Isoperla obscura and Taeniopteryx nebulosa, all common species in Norway. Distribution and abundance of Trichoptera A total of 39 species of caddis flies were identified in our material from Vidjedalsbekken and the river Atna. One species was collected in the alpine zone, 14 species in the birch woodland belt, and 38 species in the boreal zone (Table 4). At the high altitude site Vidjedalsbekken, 1280 m a.s.l., the parthenogenetic Apatania zonella was the only caddis fly caught in the Malaise traps. At Skranglehaugan, the collecting site in the upper part of the birch woodland belt, the Scandinavian endemic, Apatania hispida, was the dominant species with more than 90% of the total number of individuals. In the lower part of the birch woodland belt at Dørålseter, 14 species were collected, with three species fairly equally represented. A. hispida, Potamophylax cingulatus and Ecclisopteryx dalecarlica each made up between 20 and 31% of the catches. There are no conspicuous changes in the caddis fauna at the collecting sites from Dørålseter, at 1060 m a.s.l., and downstream to Vollen, at 710 m (Table 4). However, an obvious change in the caddis fly community was found at the outlet of Lake Atnsjøen, where the collector or filter feeder (i.e. netspinning caddis) Polycentropus flavomaculatus constituted more than 70% of the total number of individuals. The highest number of caddis fly species, 34, was recorded at the site Solbakken in the mid-boreal zone, at 380 m elevation. Distribution and abundance of Limoniidae We captured 52 taxa of Limoniidae during this study (Table 5). This family includes both aquatic and terrestrial species. Six species were recorded in the alpine zone, 21 in the birch woodland belt, and 41 species in the boreal zone (Solem & Mendel, 1989). At Vidjedalsbekken, in the birch woodland belt, the dominant species in the Malaise traps, Phyllolabis macrura, is a terrestrial species, but the Orimarga and Ormosia species are aquatic. They are probably shredders and collectors/gatherers, respectively. Dicranota guerini is a predator, and dominates (about 64%) the Limoniidae fauna in the birch woodland belt. Ormosia fascipennis, Rhaphidolabis exclusa and Molophilus flavus are subdominant here. Distribution and abundance of Chironomidae A total of 125 species of Chironomidae were found in the Malaise trap samples from the five localities. Twentyeight species were recorded at Vidjedalsbekken, 54 at Skranglehaugan, 62 at Dørålseter, 54 at Vollen, and 52 species at Solbakken. Due to the traps’ positions at the different sampling sites, the samples are more representative for the stream fauna at the alpine sites than at Vollen and Solbakken. At the boreal sites, a larger number of the species caught are most probably ‘tourists’ from other habitats. However, the impression of a clear zonation of the species composition is not seriously effected by this problem. The chironomids are always an important component of the fauna in alpine streams. Although Vidjedalsbekken is not glacier feed, it shares many similarities with such brooks, which is reflected in the chironomid fauna. A chironomid community of ten Diamesa species and several species of Pseudodiamesa, Tokunagaia, Tvetenia, Eukiefferiella and Chaetocladius characterizes the three uppermost alpine localities. A total of 33 species were only captured in this region (Table 6). While only five species were found at both Vidjedalsbekken and Solbakken, 39 other species occurred both in the alpine and boreal part of the river (Table 7). A surprisingly high number of species, 48 in all, where captured only in the lower part of the river at Vollen or Solbakken (Table 8). The common occurrence of ‘tourist species’ originating from other habitats is most probably the main reason for this. The material of Chironomidae larvae taken in the Surber samples was not identified below the family level in this study. The number of individuals in five Surber samples was mostly found to be between 100 and 94 Table 4. Distribution of Trichoptera species in the river Atna. Species records at each of the localties quantified as very abundant or abundant (xxxx or xxx), less abundant (xx) or rare (x). An i indicates that the species are identified from imago. Locality Skranglehaugan Dørålseter Vollen Potamophylax cingulatus Chaetopteryx villosa Halesus digitatus Apatania hispida Apatania zonella Apatania muliebris Limnephilus coenosus Oxyethira flavicornis Ecclisopteryx dalecarlica Potamophylax latipennis Lepidostoma hirtum Apatania stigmatella Glossosoma spp.(intermedia) Rhyacophila nubila Arctopsyche ladogensis Philopotamus montanus Polycentropus flavomaculatus Micropterna sequax Annitella obscurata Halesus radiatus Ceratopsyche nevae Micrasema nigrum Micrasema gelidum Hydroptila simulans Hydroptila forciptata Sericostoma personatum Hydropsyche pellucidula Hydroptila tineoides Ceraclea spp. Psychomyia pusilla Athripsodes commutatus Hydropsyche siltalai Hydropsyche silfvenii Apatania wallengreni Phacopteryx brevipennis Ithythricia lamellaris Glossosoma conformis Agapetus ochripes Silo pallipes Number of species x x xx x x xx xxx xx x x xx x xx xx x x x xx xx xx x x xx xx xx x x xx x xx xx x xxx x xx xx xxx x x x xx x 13 14 15 Solbakken xx xx x x x x xxx xx xx xxx xxx x xxx x x xx i i i i xx x x x x x x x x x x x x x 34 95 Table 5. Distribution of Limonidae species found only at the localities in the river Atna. Species recorded at each of the localities quantified as very abundant (xxxx or xxx), less abundant (xx) or rare (x). Locality Vidjedalsbekken Skranglehaugan Dørålseter Vollen Solbakken Phyllolabis macroura Ormosia fascipennis Limonia macrostigma Dicranota guerini Orimarga attenuata Melanolimonia caledonica Rhaphidolabris exclusa Trichyphona immaculata Dicranota bimaculata Rhiphidia duplicata Brachylimnophila nemoralis Rhabdomastrix parva Symplecta hybrida Gonomyia sp. Paradicranota subtilis Paradicranota gracilipes Molophilus flavus Euphylidorea phaeostigma Dicranomyia incisurata Dicranomyia distendens Erinocopa trivialis Ormosia ruficauda Idioptera macropteryx Molophilus propinquus Parilisia vicina Neolimnophila (placida?) Dicranomyia halterata Limonia sylvicola Metalimnobia zetterstedti Dicranomyia terranovae Paradicranota robusta Erioptera lutea Phylidorea squalens Erioconopa diaturna Dicranomyia modesta Metalimnobia 4-notata Dicranomyia frontalis Metalimnobia bifasciata Limonia flavipes Ula sylvatica Limonia tripunctata Empeda cinerascens Euphylidorea fulvonervosa Archilimnophila unica Melanolimonia morio Ula mollisima Ormosia staegeriana Melanolimonia rufiventris Dicranomyia zernyi Dicranomyia sp. Number of species xxx xx x x x x x xx x xxx x x xx xxx x xxx x x x xx x x x x x x x x x xx x x x x x x x x xx x x x x x x x x x 14 18 x x x x x xxx x x x x x x x x x 6 xx xx 20 xx x x x x x xx xx xx x x x x x x x x x x x x x 29 96 Table 6. Distribution of Chironomidae species found only at the upper tree localities in the river Atna.Species recorded at each of the localties quantified as very abundant (xxxx or xxx), less abundant (xx) or rare (x). Vidjedalsbekken Bryophaenocladius inconstans (Brundin, 1947) Tokunagaia rectangularis (Goetghebuer, 1940) Pseudodiamesa nivosa (Goetghebuer, 1928) Chaetocladius laminatus Brundin, 1947 Diamesa incallida (Walker, 1856) Diamesa gregsoni Edwards, 1933 Eukiefferiella spp. Chaetocladius dissipatus (Edwards, 1929) Limnophyes brachytomus (Kieffer, 1922) Parametriocnemus sp. Tokunagaia scutellata (Brundin, 1956) Eukiefferiella dittmari Lehmann, 1972 Tvetenia bavarica (Goetghebuer, 1934) Thienemanniella indet. Chaetocladius piger (Goetghebuer, 1913) Rheocricotopus effusus (Walker, 1856) Krenosmittia camptophleps (Edwards, 1929) Tokunagaia parexcellens Tuiskunen, 1986 Parochlus kiefferi (Garrett, 1925) Pseudodiamesa branickii (Nowicki, 1873) Corynoneura lobata Edwards, 1924 Smittia edwardsi Goetghebuer, 1932 Rheocricotopus chapmani (Edwards, 1935) Limnophyes aagaardi Sæther, 1990 Natarsia punctata (Meigen, 1804) Prodiamesa olivacea (Meigen, 1818) Chaetocladius grandilobus Brundin, 1956 Corynoneura indet. Micropsectra boralis (Kieffer, 1922) Protanypus caudatus Edwards, 1924 Chaetocladius gracilis Brundin, 1956 Chaetocladius acuminatus Brundin, 1956 Tvetenia calvescens (Edwards, 1929) Number of taxa 1000 at all three localities, and the annual variation is synchronic with a maximum abundance in spring. In 1995, the extreme flood in spring (Tvede, 2004) clearly influenced the samples taken in August at the lower sampling sites (Fig. 2). At this date, the abundance at Dørålseter was normal, while the results from Solbakken showed the lowest number of chironomid larvae recorded during the ten year period. The effect of the flood was also seen in the low number of other insect groups this year. x x xx x x xx x xx x Skranglehaugan xx xx xx x xx x x x xx xxx xx xx xx xxx xx xx x x x 9 19 Dørålseter xx x x x xx x xxxx xxxx xx xx xx xx x x x x x x x x x x x x xx xx 26 Discussion Zonation of the benthic communities Because most Norwegian rivers run through a considerable altitudinal gradient over a relatively short distance, the question of biological zonation have been extensively discussed for several groups of organisms. Lillehammer’s (1974) studies of Plecoptera included a variety of localities with different environmental conditions and species composition. He did not, however, find it feasible to establish a Plecoptera-based classi- 97 Table 7. Distribution of Chironomidae species found at five or four localities in the river Atna. Species recorded at each of the localities quantified as very abundant (xxxx or xxx), less abundant (xx) or rare (x). Locality Vidjedalsbekken Skranglehaugan Dørålseter Vollen Solbakken Eukiefferiella claripennis (Lundbeck, 1898) Diamesa bertrami Edwards, 1935 Orthocladius (Euorthocladius) saxosus (Tokunaga, 1939) Eukiefferiella brevicalcar (Kieffer, 1911) Diamesa hyperborea Holmgren, 1869 Eukiefferiella devonica (Edwards, 1929) Chaetocladius suecicus (Kieffer, 1916) Diamesa lindrothi Goetghebuer, 1931 Diamesa latitarsis (Goetghebuer, 1921) Eukiefferiella minor (Edwards, 1929) Orthocladius (Eudactylocladius) mixtus (Holmgren, 1869) Diamesa bohemani Goetghebuer, 1932 Limnophyes bidumus Sæther, 1990 Limnophyes minimus (Meigen, 1818) Pseudosmittia recta (Edwards, 1929) Chironomus (Chironomus) longistylus Goetghebuer, 1921 Limnophyes natalensis (Kieffer, 1914) Limnophyes pumilio (Holmgren, 1869) Paratrichocladius skirwithensis (Edwards, 1929) Trichotanypus posticalis (Lundbeck, 1898) Diamesa serratosioi Willassen, 1985 Diamesa tonsa (Walker, 1856) Bryophaenocladius nitidicollis (Goetghebuer, 1913) Diamesa aberrata Lundbeck, 1889 Gymnometriocnemus volitans (Goetghebuer, 1940) Orthocladius (Euorthocladius) thienemanni Kieffer, 1906 Micropsectra groenlandica Andersen, 1937 Micropsectra lacustris Säwedal, 1975 Metriocnemus indet. Orthocladius (Orthocladius) frigidus (Zetterstedt, 1838) Limnophyes asquamatus Andersen, 1935 Bryophaenocladius indet. Parametriocnemus stylatus (Kieffer, 1924) Limnophyes edwardsi Sæther, 1990 Psectrocladius (Psectrocladius) indet. Cricotopus (Isocladius) indet. Parapsectra nana (Meigen, 1818) Heterotrissocladius marcidus (Walker, 1856) Micropsectra radialis Goetghebuer, 1939 Diplocladius cultriger Kieffer, 1908 Heterotanytarsus apicalis (Kieffer, 1921) Rheocricotopus fuscipes (Kieffer, 1909) Micropsectra atrofasciata (Kieffer, 1911) Smittia sp. Number of taxa x xx x x xx x x xxx xx xx xx xx x x x x x xx xx 19 xxx xxx xxx x xxx xx xx xxx xxx x xx xx x x x x x x x xxxx xxx xxx xx xxx xxx xx xx xx xx x x x x x x 35 xxxx xxxx x x xx x xxxx xx xxxx xxx x xx x x xx x xxxx xx xx x x xx x x xx x x x x x x x xx xx x x 36 xx xx xx x x x x x x x x x x x x xx x xx x x xxx xx x x x x x x x x xx x 32 x x x x x x x x x x x x x x x xx x x x x x x 22 98 Table 8. Distribution of Chironomidae species found only at the lower two localities in the river Atna.Species recorded at each of the localities quantified as very abundant (xxxx or xxx), less abundant (xx) or rare (x). Locality Vollen Thienemannimyia fusciceps (Edwards, 1929) Eukiefferiella ilkleyensis (Edwards, 1929) Tokunagaia excellens (Brundin, 1956) Parametriocnemus boreoalpinus Gouin, 1942 Micropsectra notescens (Walker, 1856) Tanytarsus gregarius Kieffer, 1909 Tanytarsus lestagei Goetghebuer, 1922 Ablabesmyia monilis (Linnaeus, 1758) Orthocladius (Orthocladius) indet. Corynoneura edwardsi Brundin, 1949 Saetheria reissi Jackson, 1977 Ablabesmyia phatta (Egger, 1863) Odontomesa fulva (Kieffer, 1919) Endochironomus indet. Stictochironomus maculipennis (Meigen, 1818) Einfeldia longipes (Stæger, 1839) Thienemanniella majuscula (Edwards, 1924) Limnophyes schnelli Sæther, 1990 Chironomus riparius Meigen, 1804 Paraphaenocladius impensus impensus (Walker, 1856) Procladius (Holotanypus) indet. Smittia aterrima (Meigen, 1818) Krenopelopia binotata (Wiedemann, 1817) Macropelopia nebulosa (Meigen, 1804) Nilotanypus dubius (Meigen, 1804) Orthocladius decoratus (Holmgren, 1869) Heleniella ornaticollis (Edwards, 1929) Dicrotendipes tritomus (Kieffer, 1916) Paracladopelma laminata (Kieffer, 1921) Constempellina brevicosta (Edwards, 1937) Micropsectra lindebergi Säwedal, 1976 Micropsectra recurvata Goetghebuer, 1928 Paratanytarsus penicillatus (Goetghebuer, 1928) Rheotanytarsus muscicola Thienemann, 1929 Tanytarsus fimbriatus Reiss & Fittkau, 1971 Potthastia longimana (Kieffer, 1922) Pseudosmittia indet. Demicryptochironomus vulneratus (Zetterstedt, 1838) Rheotanytarsus ringei Lehmann, 1970 Chaetocladius perennis (Meigen, 1830) Polypedilum albicorne (Meigen, 1838) Metriocnemus hygropetricus (Kieffer, 1912) Virgatanytarsus arduennensis (Goetghebuer, 1922) Cardiocladius capucinus (Zetterstedt, 1850) Rheopelopia maculipennis (Zetterstedt, 1838) Polypedilum convictum (Walker, 1856) Stempellinella brevis (Edwards, 1929) Limnophyes pentaplastus (Kieffer, 1921) Number of taxa x x x x x x x x x x x x x x x x x x xx x x x 22 Solbakken x x x x x x x x x x x x x x x x x x x x x x x x x x xx xx xx x 30 99 fication or zonation for Norwegian rivers similar to that developed by Illies & Botosaneanu (1963) for Central Europe. Our results from Atna provide some support for a zonation based on zoobenthos. Both the Trichoptera genus Apatania, and several species of the chironomid genera Diamesa, Pseudodiamesa, Tokunagaia, Tvetenia, Eukiefferiella and Chaetocladius, are restricted to localities in or above the birch woodland belt. However, there were no typical alpine species of Ephemeroptera, and only one high mountain species of Plecoptera; Arcynopteryx compacta. In total, there is a zonation shift in benthic communities from the alpine and birch woodland belt area to the lower boreal zone, coinciding with the vegetation regions. The shift from the north boreal zone at Vollen to the middle boreal zone at Solbakken is more obscure. This may partly be due to the difference in dominating mesohabitats between these two localities. However, both localities belong to the boreal zone, and it should perhaps be expected that the finer classification based on terrestrial vegetation is not well reflected in the aquatic fauna. The aquatic environment is, after all, more continuous in temperature and nutrient level. Trophic relationships and the RCC concept The trophic relationship among the zoobenthos can be discussed based on taxa shifts of Plecoptera, Trichoptera, and Chironomidae along the watercourse. The Ephemeroptera do not provide useful data in this context because Baetis rhodani was the dominant species at all sampling localities. In Atna, the grazers (the stoneflies Brachyptera risi, Protonemura meyeri, and the caddis flies Apatania hispida and A. zonella) dominated in the birch woodland belt. The reason is most probably the unshaded river channel together with low water temperature. Protonemura meyeri may also partly be a shredder, feeding on detritus. The Chironomidae species that inhabit the alpine zone and the birch woodland belt are either grazers or collectors. A similar pattern in the alpine zone and the birch woodland belt was found for Trichoptera also at Dovrefjell, further west in the Norwegian mountains (Table 9). In the boreal zone, shredders, represented by the stoneflies Amphinemura sulcicollis and Ecclisopteryx dalecarlica and the caddis fly Annitella obscurata, was the dominant functional group. In this zone, however, Lake Atnsjøen has a great influence on the occurrence of the various functional groups. At the outlet of the lake, the trichopteran collector or filter feeder, Polycentropus flavomaculatus, dominates the community. The River Continuum Concept (RCC) (Vannote et al., 1980) states that the shredders should dominate among the functional feeding groups when the source of the river is within a shaded area, e.g. in a forest. The RCC was further developed by Minshall et al. (1985), who included a treeless area (desert) at the source of the river. In this case, the different functional feeding groups (grazers, shredders, collectors, predators) constituted approximately one fourth of the community each. Our results from Atna, as well as the results reported from Dovrefjell (Solem 1985) (cfr. Table 9) differ from the pattern described both by Vannote et al. (1980) and Minshall et al. (1985). Our conclusion is that grazers dominate in the zoobenthos in streams in the treeless alpine region in Norway. The reason is most probably that the supply of dead organic material (detritus) from the heather-like riparian vegetation is restricted, while the light conditions provide a good environment for periphyton production (cf. Lindstrøm et al., 2004). Natural lakes, which are found in most water courses in Norway, may be considered a disturbance in relation to the original RCC concept. The lake causes a shift in the stream ecosystem structure and function. The export of particulate organic matter (phyto- and zooplankton) from the lake (Sandlund 1982) changes the relationships between the functional feeding groups, as the filter feeders (i.e. the caddis fly Polycentropus flavomaculatus) come to dominate the aquatic insect community. The RCC concept was intended as an universal model, but local topography must be taken into consideration when applying the concept. Lakes obviously constitute important elements in this. In Atna, there is a gradual change in the caddis fly community structure from the alpine to the boreal zone, but at the lake outlet there is a sudden and pronounced change in community dominance (Table 9). Therefore there is no obvious connection between the functional groups in the zoobenthos and the zonation in terrestrial vegetation given by Moen (1999). Still, the trophic relationships in the caddis fly communities are different in the alpine and boreal zones. The pattern found in the Atna water course is probably a general pattern for a northern water course in the Holarctic, where the glacial periods created lakes in most water courses. 100 Table 9. Proportion of functional groups (in per cent) of Trichoptera in vegetation zones along Atna River and rivers in the Dovre mountains (from Solem 1999). Functional group Grazers Shredders Predators Collectors Atna Alpine zone Birch woodland belt Lower boreal zone Outlet of Lake Atnsjøen 95 70 25 7 5 24 38 8 + 5 21 10 0 1 15 74 Dovre Alpine zone Birch belt 90 10 10 40 0 40 0 10 The monitoring value of a low effort long term study The aim of an efficient bio-monitoring is to detect possible impacts of human activities on a natural system with the lowest possible level of effort. However, as ecological systems are heterogeneous and variable at all spatial and temporal scales (Brown, 2003), the problem of all monitoring inventories is to distinguish between natural and human induced variation. In addition, nearly all sampling procedures introduce additional methodological uncertainties. The composition of the zoobenthos in a stream varies in time on a seasonal as well as on an annual scale, and in space from the scale of bioregions to that of mesohabitats (Beisel et al., 1998). This long time study of benthic animals covers bioregional differences from the alpine to the boreal region. Mesohabitat variation was not considered a recordable parameter when the studies started in 1986, and such information is consequently not available. The intention was to cover seasonal variation through a sampling program of two or three sampling periods during the ice-free season. However, in some years the budget allowed only one sampling period. The quality of this long-term study is therefore strongly influenced by the project economy. The information gained on the number of species recorded in a single year (Appendices A, B, C) is of limited value. However, if the material is seen as information data covering longer time periods, a fundamental question of a biodiversity monitoring survey might be answered: Did species disappear or did the dominant species composition change during the monitoring period? The Plecoptera and Ephemeroptera of this region are well known and it is therefore feasible to use these two groups in a methodological analysis. Few or no additional species are expected to be found in this watercourse in the future, unless there is a considerable change in the environmental factors. The sampling program during 15 years in the lower and middle parts of the river, at Solbakken and Vollen, and 13 years in the upper part at Dørålseter, gave a total of 28, 27 and 23 known taxa, respectively, as most of the nymphs were identified to species. The uncertainty of the species identity of some small nymphs leaves us with some uncertainty considering the exact number of species recorded in each sample or year. The following considerations are therefore based on the number of missing taxa, i.e., species that have been recorded in the total material, but which in a particular year were not identified among larvae or present as a possible member of an unidentified larva group (Appendices A, B, C). Several questions of relevance for monitoring programme designs could now be answered: – What is the mean number of missing taxa for each year? – If two, three or four years are seen together, what is then the mean number of missing taxa? – How does the number of sampling periods in each year affect the number of missing taxa? Number of missing taxa The mean numbers of taxa not included in the samples for any one year were 13.7 at Solbakken, 13.9 at Vollen and 14.3 at Dørålseter. This is nearly 50% of the total recorded number of species at Vollen and Solbakken, and 62% at Dørålseter. Combining samples from two, three, and four years, results in a substantial decrease in the number of 101 Figure 5. Number of sampling series and missing taxa at Dørålseter (d), Vollen (v) and Solbakken (s) for each year and locality. missing taxa. At Solbakken, two, three and four years running intervals result in mean numbers of 9.5, 7.3, and 5.9 missing taxa respectively (cf. Fig. 3). The actual results from each period show that fouryear periods unveiled most of the taxa in the years before 1995. For the last 6 years, i.e. the period after 1995, the four-year running interval resulted in the relatively stable number of 7 to 9 missing taxa for each sampling period. The most dominant or abundant species where found nearly every year while more than 60% of the species at Dørålseter and about 30% of the species at Vollen and Solbakken were present in only 25% of the years (Fig. 4). Rare species constitute a general problem in monitoring programmes. Species which occur only in a few samples are often supposed to be ‘tourists’ in the sense that they do not have a complete life cycle at the locality. Species with a low abundance that do not occur every year in the samples due to sampling error and/or annual variation of the population, are ‘real’ rare species. These species are often of great interest from a biodiversity conservation aspect. Beisel et al. (1998) found that more than 46% of the species at a given locality had both low abundance and were present in only one or a few mesohabitats on the river bed. They recommended that the sampling program was designed to include a sufficient number of mesohabitats. However, as this study indicates, species with low abundance may even then not be detected unless the sampling effort is increased beyond all practical means. When the results are evaluated in this way, there is no evidence for a shift in dominance or a real disappearance or extinction of any species in Atna. The most extreme results are from the year 1995 when the low number of individuals collected also resulted a high number of missing taxa at all localities. The low number of individuals was most likely a result of the extreme spring flood in this year. Seasonal sampling and number of missing taxa Sampling was done one to five times per year. One sampling series per year always results in a high number of missing taxa. While two sampling series per year results in a lower number of missing taxa, there is no clear difference between two and tree series per year. Four or five sampling series most often results in a low number of missing taxa, but not in all years (Fig. 5). Monitoring of human-induced disturbance In addition to a species by species analysis of changes in the Plecoptera and Ephemeroptera communities, there are several other methods available for describing or testing changes in community structure. Diserud & Aagaard (2002) found that the results were affected by the way the community structure was measured and that the conclusion depended heavily on the estimate 102 of the environmental variation. Even with a moderate expectation of environmental variation, the results could vary a great deal and still be within the limits of the expected range. In general, monitoring a large number of rare species will always be an expensive and difficult task. Monitoring environmental changes or pollution effects, on the other hand, could be done with much lower effort through methods based on models of community structure or diversity indices. Most methods for monitoring freshwater insects are best suited for detection of pollution impacts on community structure or species composition. So far, no index of rare species, or predictive models for the occurrence of rare species, have been suggested. The methods for rare species monitoring are all based on observation of the actual species in samples, which renders these methods expensive and cumbersome. Acknowledgements Thanks are due to Terje Hoffstad for assistance during field work. Funding was provided by the Norwegian Research Board for Science and Technology (NTNF), the Directorate for Nature Management (DN), NTNU and NINA. References Aagaard, K., T. Bækken, S.-E. Sloreid & T. Bongard, 2002. Det er andre arter I Finnmark enn på Sørlandet. NINA Temahefte 19: 18–21 (in Norwegian). Bækken, T., 1981. Growth patterns and food habits of Baetis rhodani, Capnia pygmaea and Diura nanseni in a West Norwegian river. Holarctic Ecology 4: 139–144. Beisel, J.-N., P. Usseglio-Polatera, S. Thomas & J.-C. Moretau, 1998. Effects of mesohabitat sampling on assessment of stream quality with benthic invertebrate assemblages. Archiv für Hydrobiologie 142: 493–510. Blakar, I. A., C. Espedalen & C. Wammer, 1997. Vannkvalitet i Atna og regionalt i nedbørfeltet til Atnsjøen i 1995. In Fagerlund, K. H. & Ø. Grundt (eds) Samlerapport for Atnavassdraget i perioden 1985–1995. FORSKREF Rapport nr. 02-1997: 205–213 (in Norwegian). Brittain, J., T. Nøst & J. V. Arnekleiv, 1996. Ephemeroptera Døgnfluer. In Aagaard, K. & D. Dolmen (eds), Limnofauna norvegica. Tapir forlag, Trondheim, 130–135 (in Norwegian). Brown, B. L., 2003. Spatial heterogeneity reduces temporal variability in stream insect communities. Ecology Letters 6: 316–325. Diserud, O. H. & K. Aagaard, 2002. Testing for changes in community structure based on repeated sampling. Ecology 83: 2271–2277. Elliott, J. M., U. H. Humpesch & T. T. Macan, 1988. Larvae of the British Ephemeroptera: a key with ecological notes. Scientific Publication of the Freshwater Biological Association 49: 1–145. Illies, J., 1956. Seeausfluss-Biozönosen lappländischer Waldbäche. Entomologisk Tidsskrift 77: 138–153. Illies, J., 1961. Versuch einer allgemeinen biozönotischen Gliederung der Fliesswässer. Internationale Revue der Hydrobiologie 46: 205–213. Illies, J. & L. Botosaneanu, 1963. Problèmes et méthodes de la classification et de la zonation écologique des eaus courantes, considérées surtout du point de vue faunistique. Mitteilungen der internationale Vereinigung für theoretische und angewandte Limnologie 12: 1–57. Lillehammer, A, 1974. Norwegian stoneflies. II. Distribution and relationship to the environment. Norsk entomologisk tidsskrift 21: 195–250. Lindstrøm, E.-A., S. W. Johansen & T. Saloranta, 2004. Periphyton in running waters – long-term studies of natural variation. Hydrobiologia 251: 63–86. Minshall, G. W., K. W. Cummins, R. C. Petersen, C. E. Cushing, A. Bruns, J. R. Sedell & R. L. Vannote, 1985. Developments in stream ecosystem dynamics. Ecological Monographs 53: 1–25. Moen, A., 1999. National Atlas of Norway: Vegetation. Norwegian Mapping Authority, Hønefoss. Müller, K., 1953. Investigations on the organic drift in north Swedish streams. Report, Institute of Freshwater Research, Drottningholm 35: 133–148. Nøst, T, K. Aagaard J. V. Arnekleiv, J. W. Jensen, J. I. Koksvik & J. O. Solem, 1986. Vassdragsreguleringer og invertebrater. En oversikt over kunnskapsnivået. Økoforsk Utredning 1986: 1, 80. Sandlund, O. T., 1982. The drift of zooplankton and microzoobenthos in the river Strandaelva, western Norway. Hydrobiologia 94: 33–48. Solem, J. O., 1985. Distribution and biology of caddisflies (Trichoptera) in Dovrefjell mountains, Central Norway. Fauna norvegica Serie B. 32: 62–79. Solem, J. O. & H. Mendel, 1989. Limonidae communities in alpine and boreal zones along the Atna River, South Norway (Diptera, Nematocera). Fauna norvegica Serie B 36: 107–114. Stazner, B., 1987. Characteristics of lotic ecosystems and consequenses for future research directions. In Schulze, E.-D. & H. Zwölfer (eds), Ecological Studies 61: 365–390. Statzner, B. & B. Higler, 1986. Stream hydraulics as a major determinant of benthic invertebrate zonation patterns. Freshwater Biology 16: 127–139. Storey, A. W., D. H. D. Edward & P. Gazey, 1991. Surber and kick sampling – a comparison for assessment of macroinvertebrate community structure in streams of South-western Australia. Hydrobiologia 211: 111–121. Townsend, C. R., 1989. The patch dynamics concept of stream ecology. Journal of the North American Benthological Society 8: 36–50. Tvede, A. M., 2004. Hydrology of Lake Atnsjøen and River Atna. Hydrobiologia 521: 21–34. Vannote, R. L., G. W. Minshall, K. W. Cummins, J. R. Sedell & C. E. Cushing, 1980. The river continuum concept. Canadian Journal of Fisheries and Aquatic Sciences 37: 130–137. Webster, J. R., 1975. Analysis of potassium and calcium dynamics in stream ecosystems on three southern Appalachian watersheds of contrasting vegetation. Ph.D. thesis, University of Georgia, Athens GA, 232 pp. Annex A. Plecoptera and Ephemeroptera larvae in Surber samples from Dørålseter. Species not identified but possibly present as a component of an unidentified taxon are marked by
. Species not present in the samples are indicated as missing taxa (m.t.). Year # sampling series per year Baetis rhodani Capnia atra Protonemura meyeri Brachyptera risi Arcynopteryx compacta Nemoura cinerea Nemurella pictetii Leuctra digitata Diura nanseni Leuctra nigra Heptagenia joernensis Ephemerella aurivillii Baetis muticus Amphinemura borealis Leuctra fusca Ameletus inopinatus Baetis lapponicus Leuctra hippopus Isoperla obscura Taeniopteryx nebulosa Baetis fuscatus Baetis scambus Siphlonurus aestivalis Identified individuals Siphlonurus sp Perlidae Isoperla sp. Nemoura sp Capnias sp Leuctra sp. Total number of individuals Number of missing taxa 1989 1990 1991 1992 1993 1994 1995 1997 1998 1999 2000 2001 2002 Total % 1 1 3 2 1 4 1 3 3 3 2 2 2 28 1
m.t. 12 m.t.
m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. 13 19 15 1 m.t. 6 2 m.t. m.t. m.t. m.t. m.t. 2 m.t. m.t. m.t. 1 m.t. m.t. m.t. m.t. m.t. m.t. m.t. 46 24 151 19 17 16 8 4 m.t. 1 m.t. 2 m.t. 1 1 m.t. m.t. m.t. 1 m.t. m.t.


245 22 8 2 m.t. 4 m.t. m.t. m.t. m.t. m.t. 2 1 2 1 m.t. 1 m.t. m.t.
m.t. m.t. m.t. m.t. 43 3 77 9 6 m.t.
4 m.t. 3 1 m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t.
m.t.

m.t. 103 14
6 7 5 m.t. 3 2 m.t. m.t. m.t. 1 m.t. m.t.
m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. 38 m.t.
14 m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. 14 m.t.
15 5 2
m.t. 1 m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. 23 m.t.
4 m.t. 3
2 3 m.t. m.t. m.t. m.t. m.t. m.t.
m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. 12 30 507 24 m.t. 9
10 8 m.t. m.t. m.t. m.t. m.t. m.t. 1 m.t. 2 m.t. m.t. m.t. m.t. m.t. m.t. 591 10 226 24 38 3 3 3
m.t. m.t. m.t. m.t. m.t. m.t. 1 m.t. m.t. m.t. 1 1 m.t. m.t. m.t. 310 4 110 21 14 m.t. 6 3 m.t. 3 3 m.t. m.t. m.t. m.t. m.t. m.t. m.t. 1 m.t. m.t. m.t. m.t. m.t. 165 1319 31 34 2 6 20 m.t. 6 m.t. 1 m.t. m.t. m.t. 1 m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. 1420 1446 1125 173 101 54 39 29 20 7 5 4 4 3 3 2 2 2 2 1 1 0 0 0 3023 36,88 28,69 4,41 2,58 1,38 0,99 0,74 0,51 0,18 0,13 0,10 0,10 0,08 0,08 0,05 0,05 0,05 0,05 0,03 0,03 0,00 0,00 0,00 77,10 0 1 0 1 2 0 17 19 0 0 0 0 63 0 109 16 1 0 0 0 69 0 315 8 0 0 6 0 21 0 70 12 0 1 5 6 0 0 115 12 0 0 0 0 127 1 166 14 0 0 0 0 18 0 32 21 0 0 0 5 300 0 328 16 0 3 0 6 223 2 246 15 0 0 0 8 0 0 599 13 0 0 0 16 0 3 329 12 0 0 0 1 9 0 175 14 0 0 0 0 0 0 1420 14 1 5 11 43 832 6 3921 14,3 0,03 0,13 0,28 1,10 21,22 0,15 100,00 103 Year # sampling series per year Baetis rhodani Diura nanseni Capnia atra Isoperla obscura Ephemerella aurivillii Taeniopteryx nebulosa Isoperla grammatica Protonemura meyeri Amphinemura borealis Ameletus inopinatus Brachyptera risi Baetis subalpinus Leuctra nigra Amphinemura sulcicollis Leuctra hippopus Heptagenia joernensis Leuctra fusca Capnopsis schilleri Heptagenia dalecarlica Leuctra digitata Siphonoperla burmeisteri Baetis muticus Nemurella pictetii Siphlonurus aestivalis Nemoura avicularis Baetis fuscatus/scambus Nemoura cinerea Identified individuals Diura sp. Amphinemura sp. Isoperla sp. Nemoura sp. Capnia sp. Leuctra digitat/fusca Siphlonurus sp. Baetis sp. Total number of individuals Number of missing taxa 1987 1988 1989 1990 1991 1992 1993 1994 1995 1997 1998 1999 2000 2001 2002 Total % 4 5 1 2 4 3 2 4 1 3 3 3 2 2 2 41 2,73 1255 59 1 m.t. 42 28 m.t. 1
3 m.t. 2 3
m.t. m.t. 1 m.t. m.t. 1 m.t. m.t. m.t.
m.t. m.t. m.t. 1396 17 3 0 0 15 2 9 0 1442 13 637 14

6 6
1
1 m.t. m.t. 8
m.t. m.t.
m.t. m.t.
m.t. m.t. 1

m.t.
674 2 6 5 2 13 5 22 0 729 9 98 3
m.t. 1 m.t. m.t. m.t. m.t. m.t. 1 m.t. m.t. m.t. m.t. m.t.
m.t. m.t.
m.t. m.t. m.t.
1 m.t. m.t. 104 0 0 0 0 4 1 1 0 110 18 474 25 4
2 25
2 6 m.t. 1 m.t. m.t. 1 m.t. m.t.
1 m.t. 2 1 m.t. m.t.
1 m.t. m.t. 545 0 0 25 0 37 13 1 0 621 10 4415 32 51 1 20 11 27 25 18 26 14 27 m.t. 8 m.t. 1 1 m.t. m.t.
m.t. m.t. m.t. m.t.
m.t.
4677 0 2 134 91 53 26 0 0 4983 9 1556 31 24 2 43 18 2 14 26 13 2 2 m.t. 1 m.t. 10 1 7 m.t.
m.t. 4 m.t. m.t. m.t. 1 m.t. 1757 0 0 137 0 0 9 0 0 1903 8 2586 11 2 45 6 m.t. 2 10 2 m.t. 10 m.t. 16 6 m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. 1 2 m.t. m.t. m.t. 2699 0 0 41 0 0 0 0 0 2740 14 728 36
10 5 7
2 1 m.t. m.t. m.t. m.t. m.t. m.t. 1 m.t. m.t. 7 m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. 797 0 0 9 0 5 0 0 0 811 16 18 6 m.t.
m.t. m.t.
m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. 24 0 0 4 0 0 0 0 0 28 23 1390 19
16 2 2
m.t. 1 m.t. 2 1 m.t. 1 m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. 1434 0 0 14 0 24 0 0 0 1472 16 1249 128
5 m.t. 1
1 1 m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t.
3 m.t. m.t. m.t. m.t. m.t. m.t. 1388 2 0 24 0 8 1 0 0 1423 17 2411 83 115
1 1 7 2 m.t. m.t. 5 5 m.t. 1 m.t. m.t. 5 m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. 2636 0 0 172 0 0 0 0 0 2808 15 1726 47 16 14 1 10 72 5 2 1 1 m.t. m.t. m.t. m.t. m.t. 1 m.t. 1
m.t. m.t. m.t. m.t. m.t. m.t. m.t. 1897 44 0 0 0 0 2 0 0 1943 13 1814 22 46 48 4 1 3 m.t. 1 2 4 m.t. m.t. 3 m.t. m.t. m.t. m.t. m.t. 1 m.t. m.t. m.t. m.t.
m.t.
1949 0 1 13 3 0 0 0 0 1966 12 1699 27
68 15 17 m.t. 2 4 m.t. 2 m.t. m.t. m.t. 18 m.t. m.t. m.t. m.t. 2 m.t. m.t. m.t. m.t. m.t. m.t. m.t. 1854 0 0 0 0 110 0 0 0 1964 16 22056 543 259 209 148 127 113 65 62 46 42 37 27 21 18 12 9 8 8 6 4 4 2 2 2 1 0 23831 65 12 578 96 269 59 33 0 24943 13,9 88,43 2,18 1,04 0,84 0,59 0,51 0,45 0,26 0,25 0,18 0,17 0,15 0,11 0,08 0,07 0,05 0,04 0,03 0,03 0,02 0,02 0,02 0,01 0,01 0,01 0,00 0,00 95,54 0,26 0,05 2,32 0,38 1,08 0,24 0,13 0,00 100,00 0,06 104 Annex B. Plecoptera and Ephemeroptera larvae in Surber samples from Vollen. Species not identified but possibly present as a component of an unidentified taxon are marked by
. Species is not present in the samples are indicated as missing taxa (m.t.). Annex C. Plecoptera and Ephemeroptera larvae in Surber samples from Solbakken. Species not identified but possibly present as a component of an unidentified taxon are marked by
. Species not present in the samples are indicated as missing taxa (m.t.). Year Sampling series pro year 1988 4 1989 1 1990 1 1991 4 1992 2 1993 2 1994 4 1995 1 1997 3 1998 3 1999 3 2000 2 2001 2 2002 2 Total 38 % 138 128 50 46 111 68 2 19
m.t. m.t. 2 1
1 m.t.
m.t. m.t. 4 m.t. m.t. m.t.

m.t. m.t. m.t. 570 0 0 4 2 13 0 17 606 11 118 38 393 15 22 19 8 15 4 m.t. m.t. 5 1
2 m.t.
m.t. m.t. m.t. m.t.
m.t. m.t. 1 1 m.t. m.t. 642 1 9 12 0 0 0 3 667 11 16 24 47 2 26 32 26 2 1 m.t. m.t.
m.t.
m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. 176 0 0 0 0 0 0 6 182 17 109 14 m.t. 2 13
m.t. 4 16 m.t. m.t. 3 m.t.
m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t.
m.t. m.t. m.t. m.t. 161 0 0 0 0 3 0 74 238 18 788 25 70 17 58 44 11 13 74 28 m.t.
8 1 m.t. 7 2 m.t. 5 1 4 1 1
m.t. m.t. m.t. m.t. 1158 122 0 0 0 8 0 78 1366 7 121 1 m.t. 9 1 1 m.t. 8 14 11 m.t. 2 1
m.t. m.t. 1 m.t. m.t. m.t. m.t. 1 m.t.
m.t. m.t. 1 m.t. 172 11 0 0 0 2 0 2 187 13 91 47 89 6 16 31 3 5 1 30

m.t. 3 1 m.t. m.t. 7 1 m.t. 1 2 1 m.t.
m.t. m.t. 1 336 0 2 0 1 0 2 2 343 7 480 26 95 63 68 39 63 83 4 9 m.t.
m.t.
m.t. m.t.
m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. 930 0 0 0 0 0 0 10 940 15 4 3 4 m.t. 7 14 1 m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t. m.t.
m.t. m.t. m.t. 33 0 0 0 2 0 0 0 35 21 166 11 182 47 57 72 53 22 12 9 1 4 m.t.
1 m.t. m.t. m.t. m.t. m.t. m.t. m.t. 1
m.t. m.t. m.t. m.t. 638 0 25 0 0 15 0 24 702 12 203 71 124 122 65 16 65 50 m.t. 1 16 7 2 1 m.t. m.t. m.t. m.t. m.t. m.t. m.t.
m.t. m.t. m.t. m.t. m.t. m.t. 743 2 0 0 0 0 0 12 757 14 1120 31 83 110 72 22 16 6 m.t. m.t. 18 9 6 m.t. m.t. m.t. 2 m.t. m.t. m.t. m.t. m.t. m.t. 3 1 m.t. m.t. m.t. 1499 0 0 0 0 0 0 0 1499 14 757 732 m.t. 86 27 m.t. 11 21 17 m.t. 1
2
m.t. m.t. m.t. m.t. m.t. m.t. m.t.
m.t. m.t. m.t. m.t. m.t. m.t. 1654 5 84 0 0 0 525 14 2282 16 830 52 m.t. 33 19 1 5 11 25 3 m.t. m.t. 2 m.t. 4 2 4 m.t. m.t. m.t. m.t. m.t. m.t. m.t. 1 m.t. m.t. m.t. 992 0 0 0 0 0 0 0 992 14 123 116 61 66 15 m.t. 52 m.t. m.t. m.t. m.t. 2 2 5 1 m.t.
m.t. m.t. m.t. m.t.
1 m.t. m.t. m.t. m.t. m.t. 444 3 0 0 0 0 0 0 447 15 5064 1319 1198 624 577 359 316 259 168 91 36 34 25 10 10 9 9 7 6 5 5 4 4 3 3 1 1 1 10148 144 120 16 5 41 527 242 11243 13,7 45,04 11,73 10,66 5,55 5,13 3,19 2,81 2,30 1,49 0,81 0,32 0,30 0,22 0,09 0,09 0,08 0,08 0,06 0,05 0,04 0,04 0,04 0,04 0,03 0,03 0,01 0,01 0,01 90,26 1,28 1,07 0,14 0,04 0,36 4,69 2,15 100 105 Baetis rhodani Ephemerella aurivillii Baetis fuscatus/scambus Heptagenia dalecarlica Diura nanseni Heptagenia joernensis Baetis subalpinus Baetis muticus Amphinemura borealis Ameletus inopinatus Ephemerella mucronata Leuctra fusca Taeniopteryx nebulosa Leuctra digitata Siphonoperla burmeisteri Amphinemura sulcicollis Capnia atra Leuctra nigra Protonemura meyeri Leuctra hippopus Nemoura sp. Isoperla grammatica Isoperla obscura Heptagenia sulphurea Baetis lapponicus Siphlonurus sp. Nemurella pictetii Leptophlebiidae Identified individuals Isoperla sp. Perlodidae(=nanseni?) Amphinemura sp Baetis sp. Heptagenia sp. Ephemerella sp. Leuctra fusca/digiata Total number of individuals Number of missing taxa 1987 4