On August 13, 2022, a large number of dead fish were caught in the Oder River on the border between Germany and Poland. In the days since, German volunteers have found the same in other channels of the river, and at least 10 tons of dead fish have been salvaged. Is the large number of dead fish in the river a natural disaster or a man-made disaster?
Natural or man-made?
Müller, an old man who lives in the small town of Leibbs in eastern Germany, was the first to discover the phenomenon of dead fish, and he was walking along the Oder River that day when he stumbled upon a white light looming in the curved channel under the cover of a reed bush.
Curious, Mueller slowly walked over to find out, but as he approached the river, the smell grew stronger. Looking at the reeds, there were countless dead fish with white bellies floating on the river. Some of these densely packed dead fish have grown to nearly half a meter long, while others are only the size of fingernails. A panicked Mueller immediately reported the situation to the local environmental department.
At the same time, near the other channels of the Oder River, a large number of dead fish were like a huge gray carpet, filling the open space on the riverbank. It is not known whether they were salvaged by volunteers or washed ashore by the river. After seeing this, local residents said that they had never seen such an appalling "ecological disaster", and even said that it was probably the worst disaster in local history.
Since the Oder River originates in the Czech Republic and most of the course runs along the border between Germany and Poland, after the incident, the German Environment Minister and the Polish Minister of Climate and Environment began to blame each other, and both explained that no toxic substances were found in the channels under their jurisdiction. For example, Poland's environment minister said that after a large number of fish deaths in the Oder River, the laboratory detected high salinity in the water, but there were no heavy metal pollutants such as mercury.
Even so, in fact, from the perspective of the river where a large number of fish die, the water quality of the river is not good, and there are many aquatic plants and duckweed inside, even abandoned glass bottles. Originally, these pollution problems were not particularly serious, and they had not yet reached the bottom of the fish that caused a large area of dead fish, but it unfortunately encountered abnormally hot weather this year.
The suitable growth temperature of aquatic grasses is about 26 °C, but this year's temperature can reach 40 °C. Aquatic weeds and fish are difficult to quickly adapt to such a large change in ambient temperature, and they will die and rot in large quantities, consuming a large amount of oxygen in the river water; At the same time, rising temperatures will reduce dissolved oxygen in the water, allowing less oxygen to breathe, and eventually cause more fish to suffocate.
Suzhou Creek also has a large number of dead fish?
In fact, since the summer of this year, there have been many anomalies like this that have occurred to fish. Since July, there have been 13 large-scale dead fish incidents in Suzhou Creek. In order to avoid the further spread of river pollution, the staff patrols and fishes the rivers every day, and at most several tons of dead fish can be salvaged in a day.
If the dead fish incident in Germany is a natural disaster, then the accident in Suzhou can be said to be a man-made disaster.
Because Germany has a temperate oceanic climate, which is generally mild and humid throughout the year, even in summer, it will not be very hot, so this year's sudden weather anomalies will lead to a large number of local fish deaths.
Pastures in temperate oceanic climates
In the southern part of the mainland, especially in the Jiangsu and Zhejiang regions, there are often droughts in summer, and the temperature reaches more than 35 ° C, so the fish in the nearby waters have basically adapted to such a climate in the long-term survival process, and it is not easy to heat death under natural conditions. So why is this happening in Suzhou Creek?
In fact, this is caused by many residents releasing a large number of fish. Due to the proximity of the college entrance examination, the middle school entrance examination and the time period for querying the scores, many residents have chosen the method of "release" in order to pray for their children. Logically, the release of a fish by household will not have much impact on the Suzhou Creek. But this year is different, according to Cai Haifeng, deputy director of the Suzhou Creek Management Station, "In the past, dozens of kilograms may have been put in, but now it is directly transported by truck, and the fish are unloaded from the car box by box, and hundreds of kilograms or even a ton of fish are released together." ”
Suzhou uses trucks to transport fish to the river for release
The number of released fish will inevitably lead to a significant increase in oxygen consumption, plus the released fish are generally transported from fish farms, their living environment has been very comfortable, and the water temperature is stable at 15-30 ° C all year round, just like the flowers in the greenhouse. As a result, this release into the Suzhou Creek, especially in special high temperatures such as this year, the fish will be heated to death, or suffocated due to lack of oxygen. If the force is not immediately organized to salvage, the dead fish will quickly stink and pollute the water environment of the Suzhou Creek.
Why are aquatic organisms so sensitive to high temperatures?
The strange things since August do not stop there.
On Aug. 11, in Fukui Prefecture, Japan, a dolphin attacked two adult males in the morning and afternoon of the same day, resulting in bites to their arms and fingers, respectively. This is the sixth time this year that this dolphin has "committed a crime".
On August 12, in Keelung Harbor in the northeast of Taiwan Province, tens of thousands of blue-scaled fish jumped out of the sea together, and a large number of small fish successfully landed.
In the summer, especially since August, the strange things that happen to "fish" frequently can't help but attribute these anomalies to abnormally hot weather. So why are these aquatic creatures so sensitive to high temperatures and behave so strangely?
First of all, dolphins, they are not fish, but a mammal. Dolphins behave very contradictoryly toward humans, sometimes they dare to stand up to drive sharks to protect humans, and sometimes they bite humans inconspicuously, making it difficult for us to distinguish whether they are friends or foes.
Scientists believe that dolphins that like to attack humans are often male dolphins in estrus. Because male dolphins are very grumpy, they often treat their mates almost abusively, and even launch a crazy "pursuit" of any creature of similar size in order to satisfy the desire of estrus.
In general, dolphins have a estrus period after spring, but some scientists believe that they can be in heat all year round like humans. Of course, the temperature will also affect the temper of dolphins, 15 ° C -25 ° C sea water is the most suitable for their survival, although in 40 ° C water can survive, but the high temperature will make these brains as complex as humans become restless, and then attack the creatures that approach it.
For fish, the effects of high temperatures are even greater. Ordinary fish can not withstand the water temperature of 40 ° C, even if there are fish can withstand the "cooking" of high temperature, but the reduction of oxygen content caused by high temperature will also make them suffocate. This is because oxygen molecules are not stable when dissolved in water, and they want to escape into the air at any time, and when the temperature rises, oxygen molecules will gradually expand and move vigorously, squeezing excess oxygen out of the water body, eventually leading to a decrease in the dissolved oxygen content in the water.
On cloudy summer days, due to the sweltering weather, schools of fish will swim to the surface of the water on a large scale to absorb oxygen, and even more oxygen-hungry fish such as goldfish will jump out of the water. Therefore, jumping out of the water to absorb oxygen has become a last resort for many fish, which explains why fish are so sensitive to temperature.
This year's high temperatures around the world have led to the death of countless fish, which has also produced many strange phenomena. We should be aware that human activities have posed a great threat to our own living environment and the survival of other creatures, and if we continue to destroy the planet unbridledly, a greater crisis could creep in like this year's heat.