The abundance of aquatic vegetation is increasing in rivers and lakes worldwide. The aim of this study was to find how the macrophyte
Juncus bulbosus
Linnaeus affects salmonids and benthic ...macroinvertebrates in Norwegian rivers. The proliferation of
J. bulbosus
in the study rivers commenced after the development of hydropower in the 1960s and 1970s.
J. bulbosus
is now considered a nuisance for humans in many areas of the rivers. We found a higher density of juvenile fish and higher density, weight and species richness of invertebrates in areas with
J. bulbosus
than in areas with gravel, suggesting that the vegetation is not limiting fish and invertebrates. This may be because macrophytes increase the surface area and provide shelter, food and a variety of ecological niches. Adult salmonid fish can be negatively affected when their spawning grounds are covered by vegetation. However, overgrowth is not common and may take years since fish clear the river bed of macrophytes during redd digging, indicating competition between macrophytes and fish for riverbed habitat. Our results suggest that one should not assume that outgrowths of macrophytes have negative impacts on the ecosystem. It is important to map all impacts and distinguish nuisance to humans from effects on the ecosystem.
Total dissolved gas (TDG) supersaturation downstream of hydropower plants may cause gas bubble disease (GBD) and harmful effects in fish. Little is known about tolerance levels of TDG supersaturation ...on Atlantic salmon (
Salmo salar
Linnaeus, 1758) in natural rivers. The present study investigated the effects of TDG supersaturation on the survival of Atlantic salmon smolts at two field sites in Norway. Here, we kept smolts in cages at increasing distances from hydropower plants known to cause TDG supersaturation and at control sites. We recorded fish mortality and examined for GBD using a stereo microscope. Mortality and symptoms of GBD commenced in fish exposed to an average of 108.3% TDG (maximum 111.0%, water depth 0.55 m) for 2 days. Significant differences in time before mortality at the control sites and test sites commenced at 110.2% TDG (maximum 111.8%) for 3 days. The study indicates that Atlantic salmon may be more vulnerable to TDG supersaturation than Pacific salmonids, which are considered at risk when the TDG is above 110%. In addition, the study provides important data to link effects caused by TDG in the laboratory and in the field.
•Acidification in aquatic ecosystems is still a driver of biodiversity loss.•Few metrics to assess acidification impact are calibrated for lentic-lotic waters.•Few metrics assess impacts of ...acidification across large geographic regions.•We developed an invertebrate-based index to assess acidity impacts and recovery.•Our index enables standardized assessment in lentic-lotic water in Nordic countries.
1)Emissions of acidifying compounds have decreased over several decades, nevertheless acidification impacts on aquatic ecosystems remains as a regionally important environmental driver resulting in biodiversity loss and impaired function in many lakes and streams.2)Many metrics based on macroinvertebrates are currently used to assess the biological impacts of acidification. However, few include measures of community composition, abundance, diversity, and the presence/absence of tolerant/sensitive taxa, and fewer still are calibrated simultaneously for both lentic and lotic waters and across large geographic regions.3)Data on water chemistry and benthic macroinvertebrates was extracted from a database compiled by representatives from Norway, Sweden and Finland. Using lake- and stream data on water chemistry and macroinvertebrates from Norway and Sweden, we developed a Nordic macroinvertebrate-based multimetric index (MMI) for acidity (NAMI) to assess impacts of and recovery from acidity using information on measures of community structure and traits.4)Lake and stream datasets were explored together and independently for correlation between measures of community structure and traits to acid neutralizing capacity (ANC), modified ANC regarding 1/3 of the organic acids as strong (ANCo1) and pH. Significantly correlated candidate metrics with highest correlations were chosen using forward stepwise linear regression models against ANC, ANCo1 and pH. Results showed that the combined lake and stream MMI had the highest correlation (r-squared) with ANCo1.5)Seven metrics were included in NAMI: one measure of composition (sum of the combined relative abundance of Gastropoda, Bivalvia and Crustacea), two measures of diversity (the number of Ephemeroptera taxa excluding leptophlebiids and the number of Bivalvia taxa), one effect trait (taxa with life cycle duration > 1 year), two response traits (taxa with resistance forms: eggs and plastron respiration) and one tolerance trait (preference > 5 pH < 5.5).6)The NAMI is a promising metric to standardize lake and stream macroinvertebrate assessments of acidity impacts and recovery across the Nordic countries, and to harmonize chemical and biological classifications of water quality, including progress towards achieving international objectives.
River regulation alters flow and sediment regime, habitat availability, and ultimately the ecological functioning of rivers. Various restoration and mitigation measures have been developed to improve ...ecological function, and among them is the addition of gravel to enhance the reproduction of gravel bed spawning fishes. However, information on long-term efficiency, costs, and maintenance needs of gravel additions are scarce. Here, we study the functioning of gravel additions at eight sites in three rivers in western Norway for up to 18 years. Gravel was added between 2002 and 2010 to enhance spawning of Atlantic salmon and anadromous Brown trout. We monitored changes in the size of the gravel-covered areas, sediment composition, interstitial oxygen, egg survival, and juvenile fish densities. Additionally, we report monetary costs, identify potential maintenance needs, and calculate a cost-benefit ratio. Juvenile densities of Atlantic salmon and Brown trout increased significantly after the gravel augmentations. After 10–18 years, the median egg survival was still high (> 90%) and sediment conditions were still suitable for salmonid fish reproduction. The areas were, however, shrinking across time (median area reduction 26%), mostly caused by scouring of gravel in the steep, supply-limited, and partly regulated rivers. The average construction costs of spawning gravel augmentations were 11.2 NOK (1.12 €) m
−2
year
−1
. Compared to similar measures elsewhere, the measures have had a long life span (up to 18 years) at relatively low costs. Gravel augmentation was concluded to be a successful management measure that contributed to significantly increased Atlantic salmon and Brown trout reproduction.
Abstract
Many Norwegian rivers and lakes are regulated for hydropower, which affects freshwater ecosystems and anadromous fish species, such as sea trout (
Salmo trutta
). Lakes are an important ...feature of many anadromous river systems. However, there is limited knowledge on the importance of lakes as habitat for sea trout and how hydropower affects the behaviour of sea trout in lakes. To investigate this, we conducted an acoustic telemetry study. A total of 31 adult sea trout (532 ± 93 mm total length) were captured by angling in river Aurlandselva, Norway, and tagged between July 20 and August 12, 2021. The tags were instrumented with accelerometer, temperature, and depth sensors, which provided information on the sea trout’s presence and behaviour in lake Vassbygdevatnet. Our results indicate that there was a large prevalence of sea trout in the lake during the spawning migration, and that the sea trout were less active in the lake compared to the riverine habitats. An increase in activity of sea trout in the lake during autumn might indicate that sea trout spawn in the lake. However, the discharge from the high-head storage plant into the lake did not affect the depth use or activity of sea trout in the lake. Furthermore, the large prevalence of spawners in the lake during autumn will likely cause an underestimation of the size of the sea trout population in rivers with lakes during annual stock assessment. In conclusion, our results could not find evidence of a large impact of the discharge on the behaviour of sea trout in the lake.
The Norwegian Coastal Current transports natural debris and plastic waste along the Norwegian coastline. Deposition occurs in so-called wreck-bays and includes floating debris, such as seaweed, ...driftwood and volcanic pumice, and increasing amounts of plastics during the last decades. Deposition in these bays is controlled by ocean currents, tidal movements, prevailing winds and coastal morphology. We have compared soil profiles, analyzed the vegetation and inspected aerial photos back to 1950 in wreck-bays and defined three zones in the wreck-bays, where accumulation follows distinct physical processes. Zone 1 includes the foreshore deposition and consists of recent deposits that are frequently reworked by high tides and wave erosion. Thus, there is no accumulation in Zone 1. Zone 2 is situated above the high tide mark and includes storm embankments. Here, there is an archive of accumulated debris potentially deposited decades ago. Zone 3 starts above the storm embankments. The debris of Zone 3 is transported by wind from Zone 1 and Zone 2, and the zone continues onshore until the debris meets natural obstacles. Plastic accumulation seems to escalate soil formation as plastic is entangled within the organic debris Mapping and characterizing the soil layers indicates that deep soils have been formed by 50 or more years’ accumulation, while the pre-plastic soil layers are thin. The plastic soil forms dams in rivers and wetlands, changing the shape and properties of the coastal landscape, also altering the microhabitat for plants. This case-study describes an ongoing landscape and vegetation change, evidently co-occurring with the onset of plastic accumulation. Such processes are not limited to the Norwegian coastline but are likely to occur wherever there is accumulation of plastic and organic materials. If this is allowed to continue, we may witness a continued and escalating change in the shape and function of coastal landscapes and ecosystems globally.
Education within higher education is often divided into discipline-oriented and professional programs. Professional programs prepare students for a specific profession and include relevant ...theoretical- and practical knowledge. Discipline-oriented programs emphasize theoretical knowledge and research within a specific discipline or field. Except for a career within research and higher education, discipline-oriented programs provide less obvious links to future careers. The transition from student life to working life may therefore be challenging. In this paper, we present and discuss the development and implementation of a work placement course as part of the disciplinary programs in biology at the University of Bergen. The course was developed to provide students with practical- and work- related skills and competences, inform about future careers and to foster motivation and learning. We have revised the course according to feedback from students, workplace hosts and our experience during the six semesters the course has been running. The work placement course is at the bachelor (BSc) level and consists of two main components; the work placement itself and the student’s own reporting of placement outcomes. For the placement, the students work 140 hours at a workplace as a biologist. The reporting consists of four open blog-posts, one written reflective essay and a final oral presentation. The course teachers also meet with the students and convey information on the roles of biology and biologists in today’s society through a Facebook group. Feedback from the students, hosts and course teachers point to a range of benefits from work practice courses in discipline- oriented study programs. Based on our experience, we provide guidance for developing such courses as part of discipline-oriented curricula.
During the monitoring of total dissolved gas (TDG) saturation in the Vetlefjordelva River in western Norway in 2014–2015, characteristic waves of supersaturated water were discovered. These waves ...were significantly correlated with hydropower operation, which was run by hydropeaking (R2=0.82, p<0.001). The TDG saturation varied between 99% and 108%, with a median of 105%.
The term “saturopeaking” is introduced for these waves, defined as the artificial, rapid, periodic and frequent fluctuation of gas saturation caused by hydropeaking. Hydropeaking is recognized as hydropower operation that rapidly fluctuates according to the electricity market demand. Though the observed TDG saturation levels were moderate and not likely to cause acute effects on biota, we expect that the observed saturopeaking may have significant ecological impacts in general, especially in cases with TDG saturation levels >110^% which is considered as potentially lethal for fish in rivers.
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•Characteristic waves of gas supersaturation were discovered which were linked to hydropeaking•The term “saturopeaking” is introduced for these waves.•Saturopeaking may have significant ecological impacts.
Biological invasions are regarded as one of the largest threats to native biodiversity. The eradication of alien invasive fish or parasites by culling of hosts is a controversial conservation ...strategy, particularly when using indiscriminate methods involving whole ecosystem collateral damage. While short‐term effects are abundantly documented, long‐term surveys needed to detect potential wider ecosystem effects are scarce. Here, we report a five‐year study on effects of the piscicide rotenone on invertebrate communities from a Norwegian watercourse using a Before‐After‐Control‐Impact design. Kick‐net samples of benthic invertebrates were collected from three lentic sampling stations and two lotic stations two to four times per year in both a treated and nearby control catchment. In general, only relatively minor short‐term effects, measured as temporal beta‐diversity of benthic invertebrates, were observed in lentic and lotic locations following rotenone treatment. However, the lotic fauna was severely negatively affected following a period of long‐term rotenone exposure from a late autumn treated upstream lake where rotenone degradation was slow, likely due to low temperatures. Species turnover co‐varied markedly between control and treatment locations, indicating that natural environmental variation override effects of rotenone treatment. Likewise, the abundance of invertebrate taxa varied considerably both over time and between control and treatment locations. Our study indicates minor short‐term (i.e., <1 month) or long‐term (i.e., 4 years) effects of rotenone treatment on benthic invertebrates, but severe effects on the lotic fauna 8 months after treatment following long‐term low‐dose exposure. This suggests that exposure time is of high importance. The findings from the current study therefore highlight both the importance of long‐term monitoring including control sites for the study of rotenone treatment effects on benthic invertebrates as well as the importance of minimizing exposure time.
The return of the Eurasian otter (Lutra lutra) to western Norway has sparked human–predator conflicts because otters prey on vulnerable Atlantic salmon (Salmo salar) populations. Although predation ...may not be the ultimate cause of salmon population declines, otters that kill adult salmon in rivers before they spawn impact the salmon spawning stock, with potential consequences for stock recruitment and ecosystem services (especially fisheries).
To gain insight into impacts of otter predation on salmon populations, we quantified the predation by otters on adult salmon in two rivers in western Norway using a combination of radiotelemetry and temperature loggers. We tagged 30 salmon in Aureelva and 30 salmon in Søre Vartdalselva, and tracked the salmon until they died or left the river.
This method identified the fates of 95% of tagged salmon. Estimated predation rates on adult salmon were 32% in Aureelva and 95% in Søre Vartdalselva. The salmon stock in Søre Vartdalselva was well below the spawning target, partly attributable to putatively additive mortality from predation by otters. Notwithstanding, we found no evidence that otters selectively killed salmon based on sex, length, health status, or activity level.
Salmon in Søre Vartdalselva had greater predation risk compared to salmon in Aureelva, possibly due to differences in habitat types such as availability of holding pools. The presence of more holding area in Aureelva probably provided predation refuges for adult salmon that buffered the effectiveness of otter predation.
Our findings emphasise that management decisions should be guided by river‐specific evaluations of impacts of predation on salmon. Otters are a very visible predator operating at the final phase of the life cycle before spawning, so predation is liable to be controversial given that salmon are now Red Listed in Norway.
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