Gunnar G. Raddum

A critical limit for acid neutralizing capacity in Norwegian surface waters, based on new analyses of fish and invertebrate responses

Abstract 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.

Developing Conceptual Frameworks for the Recovery of Aquatic Biota from Acidification

Abstract Surface water acidity is decreasing in large areas of Europe and North America in response to reductions in atmospheric S deposition, but the ecological responses to these water-quality improvements are uncertain. Biota are recovering in some lakes and rivers, as water quality improves, but they are not yet recovering in others. To make sense of these different responses, and to foster effective management of the acid rain problem, we need to understand 2 things: i) the sequence of ecological steps needed for biotic communities to recover; and ii) where and how to intervene in this process should recovery stall. Here our purpose is to develop conceptual frameworks to serve these 2 needs. In the first framework, the primarily ecological one, a decision tree highlights the sequence of processes necessary for ecological recovery, linking them with management tools and responses to bottlenecks in the process. These bottlenecks are inadequate water quality, an inadequate supply of colonists to permit establishment, and community-level impediments to recovery dynamics. A second, more management-oriented framework identifies where we can intervene to overcome these bottlenecks, and what research is needed to build the models to operationalize the framework. Our ability to assess the benefits of S emission reduction would be simplified if we had models to predict the rate and extent of ecological recovery from acidification. To build such models we must identify the ecological steps in the recovery process. The frameworks we present will advance us towards this goal.

Recovery from Acidification in European Surface Waters: A View to the Future

Abstract There is now overwhelming documentation of large-scale chemical recovery from surface water acidification in Europe, but to date there has been little documentation of biological recovery. Modelling studies based on current emission reduction plans in Europe indicate that there will be further chemical recovery. The uncertainties in these scenarios mainly relate to the future behavior of nitrogen in the ecosystem and the effects of climate change. Four major climate-related confounding factors that may influence the chemical and biological recovery process are: i) increased frequency and severity of sea-salt episodes; ii) increased frequency and severity of drought; iii) in-creased turnover of organic carbon; iv) increased mineralization of nitrogen. International cooperative work to abate acidification has so far been very successful, but there is still a long way to go, and many potential setbacks. It is essential that future development of water chemistry and aquatic biota in acidified waterbodies continue to be monitored in relation to further emission reductions of S and N and future effects of climate change.

Acid precipitation : biological monitoring of streams and lakes

Abstract 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.

Quantitative relationships of invertebrates to pH in Norwegian river systems

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.

Liming of River Audna, Southern Norway: A Large-scale Experiment of Benthic Invertebrate Recovery

Abstract 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 µg 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 dispersal 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 the 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 main factors determining the fauna composition in River Audna independent of the reason for the change in water quality.

Improvements in Water Quality and Aquatic Ecosystems Due to Reduction in Sulphur Deposition in Norway

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.

Recovery of acid-sensitive species of Ephemeroptera, Plecoptera and Trichoptera in River Audna after liming

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.

Growth and feeding of Fredericella sultana (bryozoa) in the outlet of a humic acid lake

AbstractMonthly observations on the bryozoa Fredericella sultana have been carried out in the outlet of a humic acid lake for more than two years. The growth of the colonies were rapid during algal bloom and in fall the colonies almost covered the free underside of nearly all stones on the bottom.In winter most of the colonies died out, but scattered individuals were also observed alive during this period. Statoblasts produced in summer were ‘hatching’ in March–April next year. F. sultana seems to feed on all particles that can pass through the mouth opening. A special study regarding this was made on the diatoms, by analysis of fecal pellets. It was found that young colonies of F. sultana filtrated most efficiently the smallest particles (<20 µm) while older individuals in addition were able to elevate the filtration of bigger particles (40–100 µm). The feeding takes place both by filtration by the cilia and by an active use of the tentacles themselves on the lophophore.

Distribution of benthic invertebrates in relation to environmental factors. A study of European remote alpine lake ecosystems

Alpine lake ecosystems are, despite their remoteness, vulnerable to long-range transported air pollutants due to their normally low capacity to neurralize acidic deposition. The soi! and vegetation cover in their catchments are thin and pollutants are not effectively prevented from reaching rhe surface waters. Further, high mountain ecosystems are very sensitive to climate change as temperature limits for many species and processes are exceeded. Pollutants accumulate more easily in cold, low-alkaline waters and future climatic warming in Europe is predicted to be greatest in the arctic and alpine regions (WATHNE et al. 1997). With this background a multi-national project, AL:PE (Acidification of mountain Lakes: Palaeolimnology and Ecology), funded by the European Commission, was started in 1991. lt represents the first comprehensive study of remote lakes at a European scale. The sensitivity of invertebrate species to airborne acid pollution is frequendy used as a too! in monitoring freshwater ecosystems (RADDUM et al. 1988, FJELLHEIM & RADDUM 1990, HAMALAINEN & HUTTUNEN 1990). Invertebrates are also a valuable group in detecting changes in the nutrient levels of lakes (S.t:THER 1979, WIEDERHOLM 1984). Such changes may also be connected to early stages of pollution (ScHNELL & RADDUM 1993). The main objective of the invertebrate studies of the AL:PE programme was to increase our understanding of high altitude freshwater ecosystems and their response to environmental changes. This paper presents an overview of the results obtained in the AL:PE 2 programme (1993-1995, WATHNE et al. 1997).