Fish kill in Oder river - it is what I have feared

Sunnuntai 14.8.2022 klo 15:23

As a background, I have studied temperature responses of fish since 1980 and have written the book “Introduction to Aquatic Toxicology”, which was published by Elsevier in 2014, so both temperature- and pollution-related problems are within my expertise.

This summer has been intolerably warm in Central and Southern Europe. Fish kills are frequent in small, shallow lakes during heat waves in Finland, because of both reduced oxygen levels and increased temperatures. Fish kills don’t usually occur in rivers, because they have higher oxygen levels and remain cooler than small lakes. The species composition of fishes in the rivers also differs from that in the small lakes: rivers have more species, which require cooler water and higher oxygen levels. Thus, in the case of the Oder fish kill, one would need to evaluate, if all species have died equally or if species with lowest thermal maxima are overrepresented among the dead fish. If the latter is the case, then it is likely that we are experiencing the first climate change-related mass mortality of fish in Central Europe.

As the reason for the Oder fish kill, one has almost unequivocally concentrated on chemical pollution, although there have not so far been definitive measurements showing that this would have been the case. This is by all means possible, as dredging has been done in the river, which usually liberates contaminants which have been hidden in the sediment. However, even in this case an equally worrisome problem is that drought has caused the flow of the river to decrease markedly: any liberated pollutants have much higher concentrations than would be the case without drought. Also, virtually all pollutants are more toxic to fish at high than at low temperature. This being the case, even if pollutants are the cause of fish deaths, their level need not have increased. Because of the temperature increase, the toxicant level is lethal, even though it would not have been that at a lower temperature. This could be the case even if contaminant concentrations have increased.

In conclusion, the Oder fish kill is either directly caused by climate change, or temperature increase has contributed to the pollutant-induced fish kill. If serious climate actions are not done soon, I am afraid that similar events are observed regularly throughout the globe.

Kommentoi kirjoitusta. Avainsanat: climate change, biodiversity loss, aquatic pollution

Deoxygenation of oceans is an increasing problem with effets on sealife

Perjantai 13.12.2019 klo 18:01 - Mikko Nikinmaa

The deoxygenation of the seas has increased markedly during the last 100 years. The areas with reduced oxygen have increased ten times between 1900 and 2000. There have always been oxygen-minimum zones in oceans, but their volume has increased markedly in the recent past, because of decreased ocean circulation and as a result of increased respiration following elevated temperature. In addition to the climate change-caused increase in hypoxic seas, the eutrophication of coastal areas because of human actions have caused pronounced low-oxygen areas especially in the traditionally industrialized western countries.


Spreading hypoxia is a major problem, as it decreases the populations of fish and other organisms. It further affects the species distributions with more preferred species decreasing and decreases biodiversity. The effects of reduced oxygen level as such are aggravated by an increased water temperature, i.e. climate change,  because the oxygen consumption of fish and other poikilothermic animals increases with temperature increase. Simultaneously, the oxygen solubility in water decreases. Even this isn’t enough, but the oxygen binding by haemoglobin is reduced at a given oxygen tension with increased temperature. This reduces the capability of fish and other animals to survive in hypoxic conditions. This makes it more difficult of animals to tolerate increased temperature.

So, climate change and the pollution of the seas together cause deoxygenation. The pollution further decreases  the capability of microscopic algae to produce oxygen by photosynthesis. To combat the deoxygenation problem we need to stop eutrophication, and sea pollution by wastewater cleaning. Further, we need to combat climate change much more effectively than we have hitherto done. We need healthy seas to be able to feed the world, and the current increase in ocean deoxygenation is not doing that.

The ocean deoxygenation problem is the subject of an IUCN report, downloadable from (p.s. I have been studying hypoxia responses in fish from1980).

Kommentoi kirjoitusta. Avainsanat: climate change, aquatic pollution, hypoxia, oxygen transport

Tipping Points to Vicious Circles, When We Cannot Control Temperature Rise

Torstai 5.12.2019 klo 15:23 - Mikko Nikinmaa

In the Eocene period about 50 million years ago, the mean temperature of the Earth was about 14oC higher than presently, and there was practically no ice anywhere. Further, the temperature gradient between poles and the tropics was small. This is taken by “climate deniers” to mean that human actions have little to do with temperature increase; “temperature increases as a result of natural causes”. Further, “climate deniers” maintain that human-like creatures were able to exist in Eocene conditions. Undoubtedly true, but at that time the number of human-like creatures was maximally a few million, and not more than seven billion. Close to half of the present human population lives in an area, which would be under the sea in ice-free world.

So, as a conclusion, there has been a markedly higher temperature on the earth because of natural causes, and some human-like creatures have survived it. However, this does not mean that mankind does not affect climate today, there is ample evidence on the contrary. At the worst, human actions can serve as trigger, causing a small temperature increase, which leads to tipping points with resulting vicious circles causing marked increases in temperature without any human role. Originally it was thought that the temperature rise before tipping points were likely to occur would be more than 5oC, then it decreased to 3-4 oC and the latest suggestion is that the probability for the occurrence of tipping points increases markedly, if the temperature increases 1.5-2 oC. The temperature has already increased by 1 oC from the preindustrial average, and the present promised actions to combat climate change would limit the temperature increase to approximately 3 oC. This is clearly larger temperature increase than what would be required for an increased probability for the tipping points and consecutive vicious circles of temperature increase to occur. Because of this, we have the CLIMATE EMERGENCY. Human actions matter now, but if enough of the tipping points have been reached, temperature increases no matter what we do. Below I list a couple of the tipping points with vicious circle properties, which may have been reached already.

Melting of Arctic sea ice. Recent years have seen open water in large areas of the Arctic sea. Virtually all the reports about it have been positive. Politicians have, e.g., rejoiced over the possibility of commercial shipping from Europe to Asia via the northeastern route. However, with melting sea ice one easily forgets that the white ice reflects virtually all the heat back to the sky, whereas the dark water absorbs the heat. This leads to marked acceleration of temperature increase.

Thawing of permafrost. Virtually all climate models have started with the outset that the thawing is gradual, and any effects reach significant level only a couple of hundred years from now. However, it has proven that the permafrost ice is a significant structural component of close to 20 % of the land area. Where this is the case, thawing permafrost is seen as huge craters etc. Where they occur, release of carbon (and methane) is much larger than estimated in the models. The carbon release can be double to what has been estimated.

Forest fires. The importance of forests as carbon dioxide sinks has repeatedly been emphasized. Whenever a forest burns, all the carbon it has accumulated is returned to atmosphere. Because of the hot and dry weather, the area affected by forest fires has increased markedly during recent years. In addition to forest fires, deforestation to gain agricultural land, and disease and harmul insect outbreaks especially in boreal forest decrease their carbon dioxide sink properties.

Aquatic pollution. For most of us it is unknown that about half of the Earth’s photosynthesis, i.e. carbon dioxide removal, is carried out by (mainly microscopic) algae. During recent years, the algal photosynthesis has been reduced by 10-20 % globally as the pollution of oceans has decreased the photosynthesis by algae.

Nitrous oxide production. The nitrogen fertilization, which is on the increase, increases the conversion of the fertilizers to nitrous oxide. This gas is the third most important greenhouse gas after carbon dioxide and methane. The need for nitrogen-containing fertilizers is on the increase as the fertility of agricultural land is decreasing.

Two articles in Nature have aspects of what I have written above (Lenton et al. Nature 575: 592-595, 2019; Turetsky et al. Nature 569: 32-34, 2019).

Kommentoi kirjoitusta. Avainsanat: climate change, permafrost, deforestatio, aquatic pollution

Sustainable aquaculture

Sunnuntai 25.3.2018 klo 20:24

To be sustainable and ecological, food production should take place near the place of consumption. So, in the best possible case fish and vegetables are produced in towns next to where they are consumed. This is nowadays possible. The news have carried items showing vegetable production in city buildings using irrigated individual boxes. Similarly, it is nowadays possible to recirculate water for aquaculture so that fish production is possible in an establishment next door fish restaurant.

It is actually quite incredible how recirculation has improved water quality in several cases. In 1970's paper and pulp mill industry was polluting Finnish and Swedish waters so that even recently some persistent organic pollutants have occurred in the Baltic Sea at concentrations, which have exceeded EU norms for food. And this has been the case, even though the levels are 1/5-1/10th of values in 1970's-80's. Since then the industry has started to recirculate water (and stopped the use of the toxic compounds), so that nowadays the mills are almost closed systems, and the water quality, e.g., in Saimaa and near Äänekoski has improved immensely. Also, traditional aquaculture causes significant eutrophication. It can be completely avoided in the recirculating aquaculture systems, where bacteria in biofilters use up all the eutrophying material - in fact acting as small water cleaning units.

So, future aquaculture can be sustainable and ecological, if it is based on recirculation. 

Kommentoi kirjoitusta. Avainsanat: aquatic pollution, ecological food production, recirculation