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Qvenild T, Hesthagen T and Fjellheim A. 2020. The freshwater shrimp Gammarus lacustris (Malacostraca, Amphipoda) in lakes on the Hardangervidda mountain plateau, southern Norway: distribution and environmental requirements. Fauna norvegica 40: 1–21. The distribution of the amphipod Gammarus lacustris on the Hardangervidda mountain plateau was mapped by screening published data from 245 lakes in 11 and 16 catchments in western and central/eastern areas, respectively. These data are primarily based on stomach analyses of brown trout Salmo trutta. In central/eastern areas, G. lacustris was recorded in 79% of all the lakes examined, while there are only two former records (4%) in the western area. The distribution pattern of G. lacustris on Hardangervidda appears to be related to environmental conditions. The apparent absence of G. lacustris in the western area may be explained by a combined effect of cold water due to higher deposits of snow and water with low ionic strength as a consequence of its bedrock of Precambrian gneisses and granites with little or no moraine cover. However, lakes in central/eastern areas sustain G. lacustris in spite of dilute water, as G. lacustris has been recorded in 89 lakes of which 28% had calcium concentration

On the Norwegian mainland, the Arctic tadpole shrimp Lepidurus arcticus is a typically alpine species mainly co-occurring with fish. The Hardangervidda mountain plateau is the main area of the southernmost L. arcticus populations. Here L. arcticus is widely distributed, especially in the central and eastern parts of the plateau. Lepidurus arcticus has a univoltine life cycle emerging from resting eggs at ice break-up and fulfil development during the short mountain summer, before they reproduce and die. The main goal in this study was to investigate the thermal thresholds for L. arcticus. Timing of ice break-up and the proceeding water temperature are hypothesized to constitute the primary drivers of L. arcticus's development and growth. Stomach analyses of brown trout is the most sensitive method for sampling L. arcticus, especially at low densities. Analyses of 4 460 brown trout stomachs revealed that at least 400 degree-days are needed for development and growth from hatching in to adults. It is a significant gradient in climatic conditions on Hardangervidda with a coastal impact in the western part of the plateau with a three - to fourfold winter deposition compared to a dryer inland region in the east. The snow deposits have increased since the 1980s and snow rich winters have been more frequent. An additional increase is projected. This may give lower water temperature and shorter ice-free seasons. Thus, the cold western lakes could be even more hostile habitats for L. arcticus. During the same period, an abrupt increase in spring-summer temperatures was detected. This has improved the conditions for L. arcticus in many lakes. However, as a cold stenotherm species a further increase in temperature may be detrimental. Especially in shallow lakes in the central and eastern parts this may be a problem even without reaching critical levels by inducing life cycle mismatches.

The WHAM-FTOX model uses chemical speciation to describe the bioavailability and toxicity of proton and metal mixtures (including Al) to aquatic organisms. Here, we apply the previously parameterised model to 45 UK and Norwegian upland surface waters recovering from acidification, to compare its predictions of the maximum species richness of the macroinvertebrate Orders Ephemeroptera, Plecoptera and Trichoptera (SR-EPT) with time-series observations. This work uses data from two national scale survey programmes, the Acid Waters Monitoring Network in the UK and a lakes survey in Norway. We also investigate data from a long-studied catchment, Llyn Brianne in Wales. For the national surveys, model results relate well with actual trends, with Regional Kendall analysis indicating biological recovery rates for both actual and predicted species richness that are generally consistent (1.2–2.0 species per decade). However, actual recovery rates in AWMN lakes were less than in the rivers (0.6 vs. 2.0 species per decade), whilst predicted rates were similar (1.7 vs. 2.0). Several sites give a very good fit between model predictions and observations; at these sites chemistry is apparently the principal factor controlling limits of species richness. At other sites where there is poorer agreement between model predictions and observations, chemistry can still explain some of the reduction in species richness. However, for these sites, additional (un-modelled) factors further suppress species richness. The model gives a good indication of the extent of these un-modelled factors and the degree to which chemistry may suppress species richness at a given site.

Invertebrates inhabiting alpine water bodies are sensitive to environmental variability and lake faunal communities can therefore be important indicators of long-range airborne pollution, climate change and other human impacts. Information about the trophic structure and species composition of alpine lake ecosystems over space and time should therefore give important insights into environmental change effects.To explore the sensitivity of the faunal communities to environmental variability at local and regional scales we sampled biological and environmental variables from alpine lakes in seven dif- ferent alpine lake districts in six European mountain regions. The fauna of the lakes was mainly com

The water temperature and discharge of the Vassbygdelvi River, Aurland watershed, was altered after regulation due to transfer of cold water from the higher parts of the catchment. The lower part of the river receives a considerable amount of groundwater, which affected the water temperature due to reduced discharge. Compared to a closely situated reference station, the temperature increased by 9% on a yearly basis. The temperature differences were most pronounced during the winter when average January water temperature at the reference and the stretch influenced by groundwater was 0.8 and 3.3°C, respectively. Studies of benthic insects in the two habitats showed that the temperature differences had little effect on the length of the life cycle. Although some species show significant differences in growth pattern during parts of the year, with more rapid development in the winter-warm locality, there was a trend for synchronous growth at both localities. Compared to the situation before regulation, two species of stoneflies became extinct and one mayfly species colonized the area, probably as a result of the increased number of annual degree-days.

The Aurland watershed has been regulated for hydropower since the establishment of a series of power plants during the period 1970–1983. This resulted in a strong reduction of the flow in the river Vassbygdelvi, the inlet river to lake Vassbygdvatn. In the downstream river Aurland, the flow has varied, but from 2000 the intention has been to simulate pre-regulation winter flow as far as possible. The temperature in the river Vassbygdelvi has increased from about 1500 degree-days per year before regulation to above 2000 degree-days after regulation. In the river Aurland the thermal regime, expressed as degree-days per year, was more or less unchanged, but a small reduction in the summer temperature and a corresponding increase during other periods was observed. The mayfly Ephemerella aurivillii (Bengtsson) was not recorded in Vassbygdelvi prior to regulation, but became abundant in the river after. Full-grown larvae were recorded 1–2 months earlier in the river Vassbygdelvi than in the river Aurland after regulation. E. aurivillii has a 1-year life cycle with imagos present in June–August. Young larvae occurred from June to early September. It is concluded that larvae of E. aurivillii could not complete their life cycle within 1 year before regulation in the river Vassbygdelvi, due to low temperature. The study demonstrates how temperature can regulate the distribution of a species with a strict 1-year life cycle. Copyright © 2008 John Wiley & Sons, Ltd.

High mortality rates due to predation from fish may reduce densities of preferred prey animals. Predation may also depress the rate of recovery from environmental stress. In an alpine ecosystem damaged by acidification, we compared three different techniques of monitoring the recovery of two large species of crustaceans, the amphipod Gammarus lacustris and the notostrachan Lepidurus arcticus. The methods used were: (1): benthic littoral kick samples, (2): artificial substrate in the form of jute bags, (3): examination of brown trout stomachs. The monitoring took place in two limed lakes at the Hardangervidda mountain plateau in Central Norway, L. Svartavatn and L. Svartavasstjorni. Brown trout, Salmo trutta, is the only fish species in the lakes. Liming as a water quality improvement measure was started in 1994. All stomach samples were negative with respect to Gammarus and Lepidurus during the period 1987–1998. In 1999, the first records of both species were done in trout stomachs collected from Lake Svartavatnet. In Lake Svartavasstjorni, Lepidurus and Gammarus reappeared in fish stomachs in 2001 and 2002, respectively. During the period of monitoring, no records of these crustaceans were done in benthic samples and on artificial substrate in any of the two lakes. In an unacidified reference site, Lake Skiftesjoen, both benthic samples and the jute bags indicated a dense population of Gammarus. Our results strongly indicate that studies of fish stomachs are the best method for monitoring low-density populations of attractive fish food animals.

A novel method, redundancy analysis (RDA), has been used to examine whether chemical recovery from acidification in the western Norwegian Nausta watershed produces detectable recovery within the community structure of the macro-zoobenthos. The RDA results have been compared with measures of recovery based on the changes detected using highly specialized and regionally defined biological acidity indices. We found that the beginning of biological recovery in the Nausta watershed was recognizable during the period 1989–1998. Recovery occurred in the upper reaches and in the tributaries. The multivariate approach proved to complement the acidity indices approach, and much biological information can be gained by their combined use. The RDA method is conservative, i.e. does not overestimate biological recovery, and it is not geographically constrained as are the acidity indices. We also found that seasonal climatic factors strongly influence the benthic community, and may confound the detection of the biological recovery process. publishedVersion

The composition of benthic invertebrates was investigated in three Norwegian alpine watersheds during the period 1991–1997. The watersheds represented an environmental gradient in chemical factors. The Kvenna watershed was relatively well buffered, Lake Ovre Neadalsvatn was poorly buffered, but receives low inputs of atmospheric pollution while Lake Stavsvatn has low buffering capacity and receives larger inputs of acidifying components. Qualitative samples were taken in the inlet rivers, lake littoral zone, lake outlet and in the outlet rivers of the lakes for analyses of species composition. In O. Neadalsvatn the water chemical data showed strong seasonal variations with waters of low ionic content during snowmelt and summer, while increased ion concentrations build up during winter. The time of ice break and/or water temperature rise during the growing season affected the life cycle of Siphlonurus lacustris and Parameletus chelifer. Even small changes in pH or ANC seemed to have a strong effect on Baetis rhodani. In the Kvenna watershed eight very sensitive species were found at sites with pH ≥ 6.5, Ca ≥ 1.2 mg L-1 and LAl < 10 μeq L-1. Only two highly sensitive species, B. rhodani and Capnia sp. were recorded when pH was ≈6, concentration of calcium ≤ 0.8 mg L-1 and low labile aluminium < 10 μeq L-1. None of the highly sensitive species occurred in Stavsvatn, a formerly acidified area, where LAl concentrations ranged between 25–40 μeq L-1. Low ionic content and elevated concentrations of labile aluminium are suggested to exclude sensitive invertebrates in alpine lakes. Synergistic effects of dilute water and harsh climate are assumed to increase sensitivity of invertebrates to acid water. Global warming will result in higher precipitation and more snow in the west Norwegian alpine area. This will shorten the growing season, increase the amount of dilute water and consequently threaten invertebrate species living close to their tolerance limits.

A program for monitoring acidification in Norway was developed in 1980. The program included water chemistry, fish and invertebrates. The monitoring have been performed in areas with strong as well as low acidification. Information about the status of the fauna is regularly obtained from sites covering both affected and unaffected areas. Tolerance limits for different species have been established and used for the evaluation of changes in acidification since the early eighties. A significant improvement in water chemistry was recorded in accordance with a 45 to 70 % reduction in sulphur deposition. The invertebrate monitoring shows recovery of sensitive species, and watersheds with earlier low damage have probably returned to an unaffected status. In the most acidified areas also significant improvements are noted, especially during the last ten years. However, acidic episodes connected with sea-salt deposition and spring snowmelt are found to confound the recovery process in these naturally low buffered systems.

(1998). Life cycle and drift of Glossosoma intermedia (Trichoptera: Glossosomatidae) in western Norway. SIL Proceedings, 1922-2010: Vol. 26, No. 4, pp. 2048-2052.

The invertebrate fauna has been surveyed for twenty one unlimed generally acidic river systems in Norway. The data consist of 180 samples and 127 invertebrate taxa and associated water chemistry data (pH, calcium, acid neutralizing capacity, total aluminium, and conductivity). Multivariate numerical methods are used to quantify the relationships between aquatic invertebrates and water chemistry. Detrended canonical correspondence analysis (DCCA) shows one dominant axis of variation with high correlations for pH and aluminium. DCCA axis 2 is significantly correlated with calcium. The predictive abilities of invertebrates to pH are explored by means of weighted averaging (WA) regression and calibration and weighted averaging partial-least-squares regression (WA-PLS). The performance of the methods is reported in terms of the root mean square error of prediction (RMSEP) of (observed pH-inferred pH). Bootstrapping and leave-one-out jackknifing are used as cross-validation procedures. The predictive abilities of invertebrates are good (RMSEPboot for WA = 0.309 pH units). Comparison of the invertebrates with diatom studies shows that invertebrates are as good predictors of modern pH as diatoms are. RMSEPjack shows that WA-PLS improves the predictive abilities. Indicator taxa for pH are found by Gaussian regression. Anisoptera, Agrypnia obsoleta, Leptophlebia marginata, Sialis lutaria, and Zygoptera have significant sigmoidal curves where abundances increase with decreasing pH. Cyrnus flavidus shows a significant unimodal response and has an estimated optimum in the acid part of the gradient. Isoperla spp. and Ostracoda show significant sigmoidal responses where abundances increase with increasing pH. Amphinemura borealis, Diura nanseni, Isoperla grammatica, I. obscura, and Siphonoperla burmeisteri show significant unimodal responses and have high pH optima. Many taxa do not have statistically significant unimodal or sigmoidal curves, but are found by WA to be characteristic of either high pH or low pH. These results suggest that a combined use of Gaussian regression and direct gradient analysis is needed to get a full overview of potential indicator taxa.

In the period 1975–1990 long-term studies of succession and dynamics of invertebrates and fish were conducted in a weir basin area in the strongly regulated River Ekso. During the years of the study, the invertebrate community in the basin was subjected to great changes. In the first years after weir building, biomass was greatest in the riffles due to a higher abundance of lotic species like the mayfly, Baetis, blackflies and many stonefly larvae. The biomass of oligochaetes and chironomids was similar both in the riffles and in the deeper and more lentic weir basin. In the following years the biomass of lentic chironomid species increased dramatically in the basin. In 1984 the fauna was dominated by Stictochironomus pictulus. In 1988 another species, Chironomus melanotus, also became very abundant. At this time net benthic animal production in the basin had increased 10-fold compared with 1975–1976. A high flow situation during the summer of 1989 altered the weir basin community dramatically. The mean autumnal biomass decreased 4.5 times compared with 1988, dominant lentic species disappeared and lotic/semi-lotic species like the stoneflies Amphinemura sulcicollis, Leuctra fuscaand Capnia pygmaea increased in density. Prior to regulation the density of brown trout in the riffle, which later constituted the weir basin area, was 2.5 individuals 100 m−2. During the first years after regulation and weir building, fish density increased to 11.1. In 1983 a density of 23.0 trout 100 m−2 was achieved. The trout were stunted and showed marked tendencies towards food depletion. During 1984–1985 most of the brown trout population of the basin were removed and used as stock material in the reservoirs of the hydropower station. This resulted in a higher growth rate in the remaining weir basin population. The strong reduction in trout density was followed by major immigration of small ( 2+ and 3+) trout from the surrounding riffles to the basin. The trout population was now harvested, while a small population of adult spawners was retained. Weir basins increase the area of pool habitats in strongly regulated rivers, and are of major benefit for trout populations, especially by segregating size classes and increasing winter survival. The presence of intermittent riffle sections is also very important, both as spawning and nursery areas and for fish food production.

The distribution of benthic invertebrates was studied under different flow regimes in an unregulated West Norwegian river. A total of 150 quantitative benthic samples was taken from fixed transects at three different stations in the river. Hydrophysical characteristics were recorded at each sampling spot. The depth and flow preferences of the different species varied. According to the distribution, two of the species, the caddisflies Polycentropus flavomaculatus and Oxyethira spp., were closely associated with shallow, slow-flowing areas, differing significantly from nearly all the other species tested. Rhyacophila nubila, Baetis rhodani and Glossosoma intermedia were all classified as rheophilic, not differing significantly in preferences of water velocity and depth. Diura nanseni was most abundant in water velocities above 30 cm s−1. This species preferred shallow areas, in contrast with Leuctra hippopus and G. intermedia. Three of the species, Amphinemura sulcicollis, A. borealis and L. hippopus were classified as indifferent with respect to water velocities. Gaussian logit and linear logit regression showed that only one of the species tested, A. borealis, had a significant response curve to the depth of the water column. The density of this species decreased sigmoidally with an increase in depth. D. nanseni was the only species showing a significant response to the water velocity.

The status of fish and invertebrate populations was analysed in the context of surface water acidification and loss of acid neutralizing capacity in Norwegian lakes and streams. The invertebrate data came from 165 sites, and the fish data included populations in 1095 lakes, plus the Atlantic salmon populations in 30 rivers. The status of both fish and invertebrates was strongly related to both acid neutralization capacity ANC (Σ base cations - Σ strong acid anions) and the concentration of labile aluminium. Ca 2+ and TOC mederated the toxicity of both low pH and high aluminium. The critical level of ANC varied among fish species, with Atlantic salmon being the most sensitive, followed by brown trout. Perch were the most tolerant of low pH/high Al n+ . Atlantic salmon status appears to be a good indicator of acidification of rivers, and trout is a useful indicator for lakes. Based on an evaluation of fish and invertebrate populations, a critical lower limit of ANC = 20 μequiv./l is suggested as the tolerance level in Norwegian surface waters.

Fertilized eggs of Atlantic salmon (Salmo salar) were artificially deposited in the regulated River Ekso, western Norway. This was done by placing 320–2400 eggs in perforated platic baskets, together with small stones and gravel, buried in the river. To evaluate development of the eggs, some baskets were removed and examined with respect to fertilization and mortality at the eye-roe stage. After swim-up of alevins, all baskets were examined for the number of dead eggs. The hatching of eggs was between 55 and 98% in the baskets. There was no correlation between the egg number in the basket and survival. The alevins were restricted to their hatching area for the first month; after the first season they migrated 50 m upstream and 175 m downstream of their birthplace. One year later they occupied the whole area (375 m) between the two weir basins. Mortality was 80% in the first season and 87% in the second (regarded as normal and high, respectively). High mortality was probably due to acid episodes, independent of regulation. Growth was fast and salmon became smolt at age 2+, explained by favourable temperature and low fish density. Competition between salmon and native brown trout (Salmo trutta) seemed to be low as they occupied different habitats.

The acidified Lake Hovvatn have been limed in 1981, 1987, 1989 and 1991. After the first liming the lake reacidified close to the prelimed condition. The reliming, which started in 1987, was planned to maintain the pH at a relatively high level for the lake. A detailed monitoring of pH and temperature was performed at depth 0.5, 1, 1,5 and 5 m since spring 1993. Quantitative samples of benthic invertebrates were taken in spring and fall in 1977 and regularly at the same seasons from 1981 at depth 0.5, 2, 5 and 10 m. A reference lake, Lille Hovvatn have been sampled with the same procedure since 1988. The acid tolerant mayfly Leptophlebia vespertina responded quickly to the first liming with a 20 times increase in density after a few months. However, the densities rapidly decreased during the first years of reacidification. The lime treatments in 1987 and 1989, resulted in a second peak in density in 1990. After this, the densities have been reduced in spite of generally good water quality in Hovvatn. During fall the density increase was significant at 0.5 m depth in 1990, at 2 m depth in 1989, 1990 and 1992 and at 5 m depth in 1988 to 1990. No significant increase was observed in the limed localities during spring. It is concluded that acid surface water, prior to ice break, affect the food resources to L. vespenina and reduce the population at all depths during spring and in the littoral zone in fall.

Studies of benthic animal communities in three limed Norwegian rivers showed different progress in the recovery response of sensitive animals. In River Vikedal highly sensitive species established populations in the limed part of the river after a few months. The response was slower in River Audna. Longer distances to parental populations was probably the main reason for this. The benthic community of the main River Ogna was unstable, while continuous liming of a highly acidified tributary did not result in improvement of the fauna. In River Vikedal, the bivoltine mayfly Baetis rhodani was more numerous in the autumn samples indicating critical water quality during spring. An adjustment of the pH of the limed water resulted in an increase of this species. The relative abundance of sensitive animals increased downstreams from the point of liming. This may partly be explained by clogging of powdered limestone in the areas closest to the lime doser. A better and more stable water chemistry in the downstream reaches is probably also important. Contrary, the suspended lime did not influence the abundance of filter-feeders.

The Norwegian monitoring programme of acidification include studies of invertebrates, which started in 1981. The invertebrate programme is based on kick samples from a fixed station net in 8 river systems. The stations include tributaries as well as stations in the main river. This paper deals with three rivers located in a gradient covering the range of acidic deposition in West Norway. The invertebrates are identified to species level and sorted with respect to acid sensitive and acid tolerant species, used for stating an acidification index. The spring samples generally show the highest acidification due to release of acids during snow smelt. In fall the acidity was lower and the index was less variable. A significant increase in the acidification index (reduced acidity) was recorded during fall in the period 1989 – 94 in two of the watersheds. In the third watershed no significant trend was recorded. During the years 1982 – 1988 a significant increase in the index occurred in spring in the watershed with lowest acidic deposition. The increases observed in the index is probably a result of the reductions in acid deposition in Norway.

In this paper, we describe a development methodology for building real-time knowledge-based systems (RTKBS) using the REAKT toolkit. In RAM (REAKT Application Methodology), we attempt to combine elements from three separate streams of ideas: Knowledge based systems (KBS), real-time systems (RT), and object-orientation (OO). The concept of application frameworks for building and reusing real-time knowledge-based systems is proposed. The methodology is illustrated with examples from an alarm handling application at an oil refinery.

The benthic invertebrate fauna in River Aurland was investigated during 1966/67, before regulation, and during 1988/89, after regulation. The regulation strongly reduced the water flow in the inlet river to Lake Vassbygdvatn, whereas the reduction in the outlet river was lower, minimum flows of 30 m3 s-1 in summer and 3 m3 s-1 in winter. After regulation the temperature increased in the inlet river, while a small decrease was measured in the outlet river. A high increase in density of mayflies, stoneflies and chironomids was recorded, whereas the number of blackfly larvae was strongly reduced after regulation. Measurements of biomass showed small changes compared with the high increase in density. The reduction of large stonefly species and the almost extinction of blackfly larvae were the main reasons for the low response in biomass. Alternations in species dominance and changes in the life cycle of some mayflies and stoneflies were found.

The benthic invertebrate fauna of the lowland part of the Aurland River was investigated in 1966–7 over a full year cycle. The watershed was built out for hydropower production during 1979–83. In this study the life cycle and production of Baetis rhodani from pre-regulated conditions (1966–7) was compared with two types of post-regulation streams (1988–9). Before regulation the water flow was high during May-June and in autumn, combined with heavy rainfall. The lowest flow was in winter and early spring. The pre-regulated temperature was low in winter, increasing from April to a maximum in August (10–14°). After regulation one part of the river received reduced flow and increased summer temperatures (upper part) and one received hypolimnion release and reduced summer temperatures (lower part). In the upper part the density of B. rhodani increased between 10 and 20 times. The reason for this seems to be increased temperature, reduced accidental drift of larvae and increased amount of stored organic material on the bottom. In the lower part the density increase was two to five times and the production two times higher after regulation. The lower increase in production than density was due to a much higher proportion of small larvae. B. rhodani had mainly an univoltine life cycle before regulation, but a small part of the population was bivoltine. After regulation the species was univoltine in the lower part. In the upper part the life cycle was about one month faster, but no clear indication of bivoltinism was seen. The absence of the second generation is due to low temperatures and probably a lack of signals connected with temperature.

Benthic animal densities, biomass and production were studied in a weir basin and the upstream adjacent riffle area in a regulated west Norwegian river in 1988 and 1989. In years of normal discharge, such as 1988, water from a large part of the catchment area is transferred to a hydroelectric power station in another watershed, and the discharge at the study site is low. In 1989 heavy precipitation and a mild winter climate caused surplus production of hydroelectric power. Consequently large amounts of stored water had to be released as overflow at the dam. On a yearly basis the discharge at the study site was 4.8 times higher in 1989 than 1988, whereas peak values were 12.0 and 54.0 m3 s−1 in 1988 and 1989, respectively. The change in flow regime resulted in reduced biomass and faunal changes. Biomass was high during 1988 and the first months of 1989. Corresponding to the flow increase in June 1989 the biomass in the weir basin was reduced from 7.1 to 2.2 g dw m 2 and from 8.0 to 0.8 g dw m−2 at the two studied transects. The mean biomass in the autumn period was 270 and 800% higher at the two transects in 1988 compared to 1989. A great part of the biomass reduction was caused by reduced densities of the chironomids Stictochironomus pictulus and Chironomus melanotus. The mean autumnal densities of these two species were reduced from 4400 to 170 ind. m2 and from 876 to 2 ind. m2, respectively. An increase in the biomass was recorded for rheophilic insect larvae, such as the stoneflies Leuctra fusca and Capnia pygmaea. On the other hand lentic caddis larvae such as Apatania spp. and Oxyethira spp. were reduced. Mean benthic animal production of the weir basin was reduced from 22.3 g dw m−2 yr−1 in 1988 to 12.5 g dw m −2 yr−1 in 1989. In a riffle upstream of the weir basin the production was reduced from 9.1 to 3.9 g dw m−2 yr −1 in the same period. The faunal change is explained by an altered physical environment and destruction of lentic habitats.

We studied acid-sensitive organisms in Lake Saudlandsvatn in southernmost Norway in relation to acidification: brown trout (Salmo trutta), the caddisfly Hydropsyche siltalai and the zooplankter Daphnia longispina. The study lake was highly acidified with episodic pH depressions5.0 in the 1970s and 1980s, and sulphur (S) deposition five times greater than the critical load. Chemical recovery following reduced deposition of S became evident in the late 1990s, when the pH increased to 5.5-6.0. By 2000, S deposition had decreased to the critical load. The lake sustained a good brown trout population until the early 1980s, but then it started to decline and nearly went extinct ten years later. Severe recruitment failures were found in most years prior to 1995, both in the inlet and outlet stream. However, since 2003 a marked recovery of the brown trout population has occurred in the lake. During the 1980s, the H. siltalai disappeared from the lake tributaries. In 1996, the species reappeared, and increased highly in abundance from 2000 and onwards. The first post-acidification record of D. longispina from net hauls in Lake Saudlandsvatn was in 2002. Palaeolimnological data confirmed their presence prior to acidification. Any significant recovery in all three organism groups coincided with an acid-neutralizing capacity (ANC) of20 μeq L⁻¹ and toxic inorganic aluminium of30 μg L⁻¹. Projections made with the MAGIC model indicate that unless further reductions in deposition of S are made, the ANC will fluctuate around the ANC survival threshold for the biological elements described. Thus, full biological recovery will not occur in the near future.

River Audna has been continuously limed on a full scale basis since 1985. Monitoring of benthic invertebrates of the river showed that the fauna was dominated by acid-tolerant species before liming and during the first year after the start of the treatment. Moderately acid-sensitive species, like Diura nanseni, Isoperla grammatica and Hydropsyche siltalia were found only in small numbers in a few localities in this period. In autumn 1987, the first appearance of the highly acid-sensitive mayfly Baetis rhodani was recorded at two stations in the main river. During the following years, this species colonized other localities and several other sensitive invertebrates, such as Heptagenia sulphurea, Caenis horaria, Hydropsyche pellucidula and Lepidostoma hirtum were also recorded. The change in faunal composition was highly significant compared to unlimed reference stations.

This article summarizes the activities and results from the Norwegian invertebrate acidification monitoring program. The program was started in 1981 and includes at present five watersheds. A key tool in the invertebrate monitoring program is a model which calculates an acidification index based on acid-sensitive invertebrates. The model is briefly presented, together with the acidification tolerance limits for different invertebrates. The degree of damage due to acidification differed both between watersheds and over time. Generally, the watersheds in the southernmost parts of Norway were most acidified. In watersheds on the west coast, maximum acidification was measured in 1983–1984. This was correlated with episodic kills of young Atlantic salmon. During recent years, acidification has decreased in most rivers with the exception of those found in the southernmost regions. The rivers are, however, still vulnerable due to poor buffer capacity.

This study describes the recovery of sensitive invertebrates after liming of the anadromous part of River Audna in 1985. The river lost its salmon population during 1960-1970. The aim of the liming was to produce a water quality with pH > 6.0 and ANC > 20 microg L(-1) and to reduce the content of labile aluminum. Highly sensitive invertebrates like the mayfly Baetis rhodani were not found in the river before liming. Two years after liming, several sensitive invertebrate species showed a positive response. B. rhodani was then recorded at 2 sites in the lower part of the river. In the following 5 years several species of sensitive invertebrates recolonized the whole limed reach of the river and became numerous. Ten years after liming the snail Lymnaea peregra was recorded in the river. The dispersa of this species was also very fast and after 5 years it was found at all investigated sites in the limed main river covering a reach of 40 km. Reduced sulfur deposition in the area also resulted in water-quality improvements in th unlimed stretches of River Audna. Comparisons between limed and unlimed localities indicated that the water quality and the critical limits of sensitive species are the ma factors determining the fauna composition in River Audna independent of the reason for the change in water quality.

The amphipod Gammarus lacustris was earlier a main food item of brown trout in Lake Svartavatnet at the Hardangervidda mountain plateau in South Norway. In the middle of the 1980’s, G. lacustris disappeared from the trout diet due to increased acidification. In order to preserve a unique genetic variant of brown trout living in the area, a liming programme was initiated in 1994. During the first years after liming, G. lacustris was absent both in fish stomachs and in lake littoral samples. In 1999, it reappeared in brown trout stomach samples together with two other strongly sensitive species, the tadpole shrimp Lepidurus arcticus and the freshwater gastropod Lymnaea peregra. Data from monitoring indicate that the water chemical conditions of L. Svartavatnet are still close to the critical limits of these animals. They have probably survived in small refuges of acceptable water quality, either in areas of inflowing groundwater or in the littoral, below the more acidic surface layer. The fact that these sensitive animals have not yet been found in benthic samples emphasise fish diet as an important tool in early registration of the presence/absence of invertebrates with low abundance or patchy distribution.

On a large scale, the acidified River Bjerkreim, southwestern Norway, has been treated with lime since the autumn 1996. During the Atlantic salmon (Salmon salar) smolting period pH has been above 6.2 and LAI concentrations below 10 μg L-l. Before 1996, only the western part of the watercourse harboured acid-sensitive species, such as the Atlantic salmon, snails, mayflies, daphnids and Gammarus lacustris. Prior to liming in 1996, Atlantic salmon fry (0+) and parr (≥1+)were found in 4 of 20 sampling sites, contrary to 17 (fry) and 12 (parr) in 1999. Atlantic salmon catches have increased from about 0.8 tons in 1994 to about 10 tons in 1998 and 1999. Acid-sensitive invertebrates have invaded the limed parts of the river.

This paper deals with benthic invertebrate population responses to acidification and liming in the lower part of River Vikedal. In 1979 the river showed signs of increasing acidification. Highly sensitive invertebrates like the mayfly Baetis rhodani were present in the river in low abundance, but disappeared in the subsequent years. In order to re-establish a nontoxic water quality for fish, liming of the spring snowmelt to a minimum of pH 5.7 was started in 1987. During the later years liming has been successively increased. The invertebrate fauna showed a slow, but positive, response during the first years after liming, especially during autumn. B. rhodani recolonized the river in low density, but the spring cohort was still weak. Since 1994 the lime dosage was increased to secure a minimum pH of 6.3 during spring snowmelt. This has resulted in an overall increased biodiversity in the limed section of the river. Several acid-sensitive species, like both cohorts of B. rhodani and freshwater snails have colonized this part of the river. Simultaneously biodiversity in the unlimed reference sites has slightly improved during the last years. This is correlated with decreased sulphur deposition and improved surface water chemical conditions.

In this paper, we describe a development methodology for building real-time knowledge-based systems (RTKBS) using the REAKT toolkit. In RAM (REAKT Application Methodology), we attempt to combine elements from three separate streams of ideas: Knowledge based systems (KBS), real-time systems (RT), and object-orientation (OO). The concept of application frameworks for building and reusing real-time knowledge-based systems is proposed. The methodology is illustrated with examples from an alarm handling application at an oil refinery.

The effects of transferring glacier-fed water to a clear-water river on production and food organisms of brown trout (Salmo trutta L.) were investigated in a mountain river, in southern Norway. Production in unregulated fluvial habitat was 271.5 g 100 m−2 yr−1 compared with 103.1 g 100 m−2 yr−1 in a glacier-fed reach of the river. This difference was due to low fish density and recruitment rate. The growth rate, at least for younger fish (2+ to 4+ age groups), was significantly higher in the regulated reach of the river. The main difference in food composition was the low abundance of crustaceans Eurycercus lamellatus and Gammarus lacustris in the regulated reach. Trichopterans were the main diet component in both sites.

Benthic animal production was studied in a weir basin area of western Norway in 1984, eleven years after construction of the basin and eight years after the first benthic study. Compared to estimates from 1976, a marked change in production and species composition had occurred. Benthic animal production at two stations inside the basin was 199 and 169 KJ m−2 yr−1, an increase of 440 and 270 per cent respectively compared to 1976. In a riffle upstream of the basin, the production estimate was 50 KJ m−2 yr−1, a decrease of 40 per cent since 1976. Chironomids formed the main contribution to the increased production in the weir basin, mainly through increased abundance of larger species like Stictochironomus pictulus and Micropsectra spp. Also other species more adapted to lentic water, like the ephemeropterans Siphlonurus aestivalis and Ameletus inopinatus, showed increased density. The fauna succession and increased production in the weir basin was mainly due to improved habitats and food conditions, as the amount of organic sediments had increased since the first production study.

During 1981 to 1986 fish and invertebrates have been monitored in connection with acidification problems in western Norway. Based on tolerance limits of acid sensitive invertebrates, a model has be...

Larval drift of the trichopteran Rhyacophila nubila (Zett.) was studied in a West Norwegian river. The frequency distribution of different instars in the drift samples was significantly different compared with the benthic samples. The drift, measured as the number which passed a transect of the river, rised markedly in periods of high water discharge. Different instars can be arranged according to the extent in which they are drifting: 2>3>4>1>5. Instar 1 and 2 shared a neutral phototaxis. From the 2nd instar and on, the larvae became increasingly night-active with a culmination in the last instar which was highly night active, also confined by laboratory studies. It is suggested that changes in activity patterns is associated with a shift towards a more carnivorous way of life.

The trout population in a 10.6 ha weir basin in western Norway has been studied over thirteen years. Baseline investigations were carried out during 1974–78, three to five years after construction of the weir. Studies in 1983 showed dominance of the 1977 and 1978 year-classes. This dominance lasted until 1985. Removal of 75 per cent of the population for stocking in reservoirs reduced the fish biomass from 1.43 to 0.28 kg 100 m−2. This increased the growth rate and condition factor of the remaining fish in subsequent years. The trout enter the basin mainly at age 2+ and 3+. No increase in the number of immigrants was observed during the first two years after removal of fish. In the third year, however, a five-fold increase was measured. Most of these fish belonged to the 1985 year-class, which had little contact with the strong classes of 1977 and 1978. We conclude that density-dependent factors control immigration to the basin, whereas a combination of density-dependent and independent factors act on the recruitment in the riffle areas. We suggest that the highest recruitment of fish is obtained by reducing the density-dependent effect through removing a very high proportion of the young fish, 2+ and 3+, every year.