Eva Bergman

Biomanipulation as an Application of Food-Chain Theory: Constraints, Synthesis, and Recommendations for Temperate Lakes

ABSTRACT The aim of this review is to identify problems, find general patterns, and extract recommendations for successful biomanipulation. An important conclusion is that the pelagic food chain from fish to algae may not be the only process affected by a biomanipulation. Instead, this process should be viewed as the “trigger” for secondary processes, such as establishment of submerged macrophytes, reduced internal loading of nutrients, and reduced resuspension of particles from the sediment. However, fish reduction also leads to a high recruitment of young-of-the-year (YOY) fish, which feed extensively on zooplankton. This expansion of YOY the first years after fish reduction is probably a major reason for less successful biomanipulations. Recent, large-scale biomanipulations have made it possible to update earlier recommendations regarding when, where, and how biomanipulation should be performed. More applicable recommendations include (1) the reduction in the biomass of planktivorous fish should be 75% or more; (2) the fish reduction should be performed efficiently and rapidly (within 1–3 years); (3) efforts should be made to reduce the number of benthic feeding fish; (4) the recruitment of YOY fish should be reduced; (5) the conditions for establishment of submerged macrophytes should be improved; and (6) the external input of nutrients (phosphorus and nitrogen) should be reduced as much as possible before the biomanipulation. Recent biomanipulations have shown that, correctly performed, the method also achieves results in large, relatively deep and eutrophic lakes, at least in a 5-year perspective. Although repeated measures may be necessary, the general conclusion is that biomanipulation is not only possible, but also a relatively inexpensive and attractive method for management of eutrophic lakes, and in particular as a follow-up measure to reduced nutrient load.

COMPETITION BETWEEN A PLANKTIVORE, A BENTHIVORE, AND A SPECIES WITH ONTOGENETIC DIET SHIFTS'

Competition between a planktivore, a benthivore, and a species with ontogenetic niche shifts

Foraging abilities and niche breadths of two percids, Perca fluviatilis and Gymnocephalus cernua, under different environmental conditions

Foraging abilities and niche breadths of two percids, Perca fluviatilis and Gymnocephalus cernua, under different environmental conditions

Temperature-dependent differences in foraging ability of two percids, Perca fluviatilis and Gymnocephalus cernuus

SynopsisThe effects of temperature on capture rate, handling time, capture probability and routine swimming performance were studied in two fish species, perch Perca fluviatilis and ruffe Gymnocephalus cernuus. In addition, the reaction distance (RD) of both species was measured. Handling time decreased and capture rate increased with increasing temperature for both perch and ruffe. The response of handling time and capture rate to temperature was more pronounced for perch than for ruffe. Routine swimming performance increased with increasing temperature for perch but not significantly so for ruffe. The laboratory study showed that the foraging ability of ruffe was less sensitive to temperature than it was for perch. These results were consistent with the vertical distributions of both species in thermally stratified lakes; ruffe, which occurred at all depths, utilized a wider temperature range than perch.

Effects of Roach Rutilus rutilus on Two Percids, Perca fluviatilis and Gymnocephalus cernua: Importance of Species Interactions for Diet Shifts

Effects of roach Rutilus rutilus on two percids, Perca fluviatilis and Gymnocephalus cernuus: importance of species interactions for diet shifts

The barriers encountered by teachers implementing education for sustainable development: discipline bound differences and teaching traditions

Background : According to the Swedish curriculum teachers in all subjects have a responsibility to integrate a holistic perspective of sustainable development (SD) and teach according to an education for sustainable development (ESD) approach. However previous research has shown that teachers from different subjects perceive SD differently. Purpose : The study aimed at investigating if and how teachers’ subject area influences their ability to implement a holistic perspective of ESD; we investigated both the impact of teaching traditions and the barriers that teachers experienced. Sample : A stratified sample of 224 Swedish upper secondary schools participated. An online questionnaire was sent and answered by a total of 3229 teachers at these schools. In total, there were 669 science teachers, 373 social science teachers, 483 language teachers, 713 vocational and esthetical–practical teachers, and 739 teachers from other disciplines who participated in the survey. Design and methods : The questionnaire consisted of questions requiring Likert-scale responses and multiple-choice questions. The data from the questionnaire were analyzed using Pearson’s Chi-square test and one-way ANOVA. The significance level accepted was p < 0.05. Results : Teachers were influenced by their own subject traditions. Science teachers in our study were grounded in the fact-based tradition and lectures were the most common teaching method used. The teaching tradition of the social science teachers seemed to be most in line to an ESD approach. Many language teachers (41%) stated they did not include SD issues in their teaching at all. Among the barriers identified, the most common obstacles were that the teachers lacked inspiring examples of how to include SD in their teaching and that they lacked the necessary expertise about SD. Conclusion : This study highlights the need for the management within schools to create opportunities for teachers to work collaboratively when teaching ESD. It is also important to provide further training that is adjusted to the needs of different disciplines.

Impact of cyprinid reduction on the benthic macroinvertebrate community and implications for increased nitrogen retention

The benthic macroinvertebrate community in a severely eutrophicated South Swedish lake, Lake Ringsjon, was found to re-establish after the lake was subjected to a substantial reduction of cyprinids (mainly bream and roach). Being totally dominated by chironomids and oligochaetes during the 1980s, the lake became repopulated by groups like Amphipoda, Ephemeroptera, Coleoptera and Mollusca after the fish reduction in 1988–1992. These groups appeared in numbers similar to that found in 1969, before the lake entered its worst stage of eutrophication. The re-establishment of the invertebrates mainly occurred in the littoral parts of the lake. The profundal community was still dominated by chironomids and oligochaetes after the fish reduction. The increase in numbers of benthic macroinvertebrates in the littoral zone of the lake was likely an effect of lowered predation pressure from fish. The potential role of an increased macroinvertebrate abundance due to fish removal and its effects on recirculation of nutrients over the sedimentiawater interface is discussed. It was observed that average total nitrogen retention in Lake Ringsjon before and after the reduction was 59±5% and 82±15%, respectively.

Subject- and experience-bound differences in teachers’ conceptual understanding of sustainable development

This article describes the results of a nationwide questionnaire study of 3229 Swedish upper secondary school teachers’ conceptual understanding of sustainable development in relation to their subject discipline and teaching experience. Previous research has shown that teachers have difficulties understanding the complex concept of sustainable development. According to the Swedish curriculum, all teachers in all subjects should integrate a holistic perspective of sustainable development including economic, ecological, and social dimensions. This study shows that teachers differ in their understanding of the concept mostly according to their subject traditions. Social science teachers emphasize social dimensions and science teachers’ ecological dimensions, respectively. Teachers are aware of the relevance of the three dimensions to various degrees, but do not generally have a holistic understanding. The greatest uncertainty in teachers’ understanding is related to the economic dimension. Science and social science teachers are critical of incorporating economic growth into the concept of sustainable development while language, vocational, and esthetical–practical teachers are not. No experience-bound differences of the teachers’ understanding could be found, but recently qualified teachers consider their understanding of sustainable development to be poorer in comparison with more experienced teachers’ self-evaluation. The study highlights the need for further training in sustainable development since more than 70% of the questioned teachers stated that they need such training.

Forest-Stream Linkages: Effects of Terrestrial Invertebrate Input and Light on Diet and Growth of Brown Trout (Salmo trutta) in a Boreal Forest Stream

Subsidies of energy and material from the riparian zone have large impacts on recipient stream habitats. Human-induced changes, such as deforestation, may profoundly affect these pathways. However, the strength of individual factors on stream ecosystems is poorly understood since the factors involved often interact in complex ways. We isolated two of these factors, manipulating the flux of terrestrial input and the intensity of light in a 2×2 factorial design, where we followed the growth and diet of two size-classes of brown trout (Salmo trutta) and the development of periphyton, grazer macroinvertebrates, terrestrial invertebrate inputs, and drift in twelve 20 m long enclosed stream reaches in a five-month-long experiment in a boreal coniferous forest stream. We found that light intensity, which was artificially increased 2.5 times above ambient levels, had an effect on grazer density, but no detectable effect on chlorophyll a biomass. We also found a seasonal effect on the amount of drift and that the reduction of terrestrial prey input, accomplished by covering enclosures with transparent plastic, had a negative impact on the amount of terrestrial invertebrates in the drift. Further, trout growth was strongly seasonal and followed the same pattern as drift biomass, and the reduction of terrestrial prey input had a negative effect on trout growth. Diet analysis was consistent with growth differences, showing that trout in open enclosures consumed relatively more terrestrial prey in summer than trout living in covered enclosures. We also predicted ontogenetic differences in the diet and growth of old and young trout, where we expected old fish to be more affected by the terrestrial prey reduction, but we found little evidence of ontogenetic differences. Overall, our results showed that reduced terrestrial prey inputs, as would be expected from forest harvesting, shaped differences in the growth and diet of the top predator, brown trout.

Synthesis of theoretical and empirical experiences from nutrient and cyprinid reductions in Lake Ringsjön

The reduction in external phosphorus load to Lake Ringsjön during the 1980s, did not result in improved water transparency during the following ten-year period. Furthermore, a fish-kill in the Eastern Basin of the lake, in addition to a cyprinid reduction programme (biomanipulation; 1988–1992), in contrast to theory, did not lead to any increase in zooplankton biomass or size. This absence of response in the pelagic food chain may have been attributed to the increase in abundance of YOY (0+) fish, following the fish reduction programme. Despite the lack of effect on zooplankton, there was a decrease in phytoplankton biomass, a change in species composition and an increase in water transparency following biomanipulation. In 1989, one year after the fish-kill in Eastern Basin, the Secchi depth (summer mean) increased from 60 cm to 110 cm. In the following years, water transparency increased further, despite an increase in phosphorus loading. An unexpected effect of the biomanipulation was an increase in benthic invertebrate and staging waterfowl abundances, which occurred 2–4 years after fish reduction. Hence, the response in the benthic community following biomanipulation was considerably stronger than in the pelagic community. A likely explanation is that reduction in abundance of the benthic feeding fish species bream (Abramis brama), strongly affected the benthic invertebrate fauna. In this paper, we present what we believe happened in Lake Ringsjön, and which processes are likely to have been important at various stages of the restoration process.