Drying reservoirs. Why do rivers dry up and bodies of water disappear? How lungfish served science
People with shovels and buckets walked along the bed of the dry lake. Every now and then they picked something in the sticky mud with a bayonet and, picking it up, threw it into a bucket. “Collecting water chestnuts! Looking for worms! They’re trying to find Napoleon’s sunken warehouse!” – nothing else came to mind, and in vain. Each one had about half a bucket of crucian carp: when the pond dried up, the crucian carp buried themselves in the mud in the hope of sitting out the drought there until the autumn rains, and they would have done so if greedy people, hungry for fried crucian carp in sour cream, had not started collecting them like manna from heaven.
Crucian carp is a fish that no poachers will catch and no industrial enterprises will destroy. In our army car park, in the car wash where the water was drained after washing the cars, a couple of dozen crucian carp lived for several years until demobilization and they were released in the spring for a snack. One can write and talk endlessly about the unpretentiousness and super-survivability of crucian carp. For example, there have been cases of crucian carp freezing into ice. One crucian carp, having spent the entire winter frozen in a small container (200 ml), successfully thawed in the spring and again drove the cat Paramon crazy, who had a grudge against him last fall. Here each of us will say that his crucian carp lived in a liter jar for two years, and he will be right. Well, how does he behave in his natural conditions?
Crucian carp loves simple reservoirs and feels great there. The more grass and dirt in the lake, the more luxurious his apartment. It is practically not found in very deep and cold lakes, and if it lives, it is of a different species: golden round and silver round, or, as it is also called, lake one. This, apparently, is a real crucian carp, and what usually gets caught on a hook or in poachers’ nets is who knows what! Just let’s not get confused in the terminology and leave everything as it is. Let this “who knows what” be crucian carp. I don’t have the opportunity to look into most of the Belarusian crucian carp lakes; they are terribly muddy even in autumn and winter. But where this can be done and where the water exceeds the visibility of one and a half meters, there I examine these crucian carp from the flight distance of a harpoon. Crucian carp behave the same way and adhere to the same rules in almost all bodies of water. If it is an artificial reservoir, then, as a rule, there are deeper places near dams, locks, dams, and embankments. Large individuals usually stay in these deep places, choosing vegetation, fragments of reinforcement, and uneven bottom relief as shelter. There they can be found in the cold season, when, having eaten enough during the warm season, they move to winter quarters.
In summer (I checked) these places are lifeless and covered in dirt and mud. Life in them begins with cold weather. During the warm season, try to find this crucian carp! Walks across the open spaces, rubs itself in the grass near the shore, busily rummages through dumps at a depth where there is enough grass. On one large lake one day in August I observed that crucian carp stayed only on islands of grass. There were thousands of them on a vast plateau overgrown with patches of grass. Curious crucian carp faces peeked out from every grass crack. In the rest of the territory, strewn with yellow sand, only individual individuals were found, hurrying about their business. It is characteristic that the fish did not move further than half a meter from their grass shelter, which, by the way, was so dense that you couldn’t even see the cruiser “Aurora” in it from two meters. I am sure that the bite of crucian carp in such grass would be simply crazy. In November, I visited my old acquaintances and discovered that their numbers had decreased slightly, and the crucian carp had switched from half-water to a bottom lifestyle. They no longer ran away from me, not seeing the road, but calmly and carefully squeezed through the roots of the vegetation, deeper and away from the uninvited guest.
I observed a different picture on a small wild forest lake, where, in addition to crucian carp (golden and silver), there were many tench and pike. At the height of summer, they are found quite often in shallow water in the grass. Since this lake is heavily overgrown with grass, we can assume that there are very, very many of them there. As a rule, they stand alone (which, by the way, distinguishes gold and silver crucian carp from their hybrid) in the coastal grass in maximum thickets at noon. Towards evening they can already be found on the move and in search of food. When a crucian carp feeds, it stands almost upside down and every now and then picks up something from the bottom. Visiting this reservoir in late autumn, you see that there are no crucian carp in this lake and, apparently, never have been. Looking at the stacks of pikes standing in ambush, you involuntarily think about their gluttony, and the next season history repeats itself: summer - the dominance of crucian carp, which have eaten all the pike caviar, and autumn - the absence of crucian carp, pike revenge for the eaten caviar. Crucian carp is interesting in late autumn, when nothing pleases him anymore and his optimism has completely faded. His sides are swollen with fat accumulated from fishing baits, and he, the fat man, hides under snags, buries himself in the mud - only his upper fins stick out.
Apparently, fish really have their own character. I observed crucian carp standing in a stupor, up to their ears in mud with their gills glued together, and literally ten meters away fresh crucian feeding holes were dug, in which the mud had not yet settled. A flock of walking crucian carp was busily sweeping up the remains of bait, apparently intended for roach, raising a cloud of turbidity, and the roach huddled forlornly on the sidelines. In early spring, after the ice melts, crucian carp can be found in their former winter quarters. The water has not yet warmed up, and it is practically not found in shallow water. At this time of year, it sits in the remnants of stunted vegetation, is quite inactive, and does not jump off the bat at the sight of a submariner. Sometimes he fussily tries to bury himself in the mud right in the place where he was taken by surprise. In this case, he, raising a cloud of turbidity, hides his head in the mud, and if it fits there, he freezes, believing that he is not visible. I noticed that crucian carp is quite curious: when it hears movement or unfamiliar sounds in the water, it comes to look. This is especially pronounced if there are a lot of crucian carp. Perhaps they feel stronger in a pack? One of the strong impressions from the trip to Astrakhan for spearfishing was the impression made by the crucian carp round dances.
When I was hunting for carp in ambush (dwelling place), the crucian carp always came first to look. Imagine clear water, a weak current flowing through the reeds, the sun standing at its zenith, a depth of two meters and among this beauty a line of swimming crucian carp. Schools of five to ten fish, each weighing at least 1-2 kg, surround you on all sides, and just like that, they’ll attack you, like predatory piranhas. Well, you lie there and use your gun to disperse them, saying, don’t get in the way.
Yes, crucian carp are curious! More than once I had the opportunity to observe how representatives of this indestructible tribe swam to the sound of a shot. Maybe fishermen should sometimes gurgle their floats harder on the water?
Like other bodies of water, the Aral experiences level fluctuations due to climatic, geomorphological, tectonic factors, and in recent millennia, human economic activity. In particular, such changes were associated with the destruction of irrigation structures in the 70-80s of the 14th century. during the conquest of Khorezm by Timur.Fluctuations in the level of the Aral Sea have also occurred recently, but their amplitude over the past 200 years has not exceeded 4 m, and in the first half of the last century 1 m. In the 50s of the twentieth century, the ecological situation in the region was quite stable.
Since the early 1960s. the flow of river flow to the Aral began to decline rapidly due to a number of reasons, the main one of which–withdrawal of Amu Darya and Syrdarya runoff for irrigation.
The area of irrigated land in the second half of the twentieth century increased almost 2 times and amounted to about 6 million hectares, and the intensity of irrigation itself also increased. Additional water losses due to evaporation from the surface of numerous reservoirs built in the Amu Darya and Syr Darya basins played an important role.
If in the period from 1911 to 1960, out of 120 cubic km of river waters formed in the feeding areas, an average of 56 cubic km per year reached the Aral Sea, then in the mid-70s, as a result of water withdrawal, the inflow into the Aral decreased to 7 -11 cubic km, and in the 80s, for a number of years, the influx of river water into the Aral was practically absent.
The reduction in flow has led to a significant reduction in the area of lakes in the deltas of the Amu Darya and Syr Darya. The level of the Aral Sea fell from 53 m in 1960 to 40.3 m in 1987, the area of the sea decreased from 67 to 41 thousand sq. km, and its volume - from 1064 to 404 cubic km. These changes are recorded on the above satellite image from 1975 and on the map compiled by the Kazakh Aerogeodetic Enterprise based on materials from space surveys of 1977, 1984, 1989. Over these years, the coastline has retreated on the eastern coast to 70-80 km, here the islands of the Akpetka archipelago have become attached to the land and the unique Aral type of coastline has disappeared; the northern part of the reservoir, the Small Sea, was separated; the configuration of the coastline of the southern coast has changed greatly, where Adzhibay Bay and the Tiger Tail Peninsula have disappeared, and Dzhiltyrbas Bay has turned into a lake; Vast shallows around the Renaissance Islands were exposed.
, made by the crew of the 5th ISS expedition in June 2002, shows a further reduction in the area of the sea, the connection of the former islands of Vozrozhdeniya, Lazarev and others, an increase in the area of the sandbank around them, and the dismemberment of a single body of water into parts.
In addition, one can notice the complete absence of flow into the sea from the Amu Darya during this period.
- an endorheic salt lake-sea in Uzbekistan (Karakalpakstan) and Kazakhstan.
Due to the uncontrolled withdrawal of water for irrigation in Central Asia and Kazakhstan, which began in the 50-60s of the twentieth century, the flow of water into the Aral decreased sharply, and sometimes (in the 1980s) stopped altogether. In 1961, the total area of the sea was 66 thousand square kilometers. Over the course of a year, the change in level due to the evaporation of water from the surface was about 1 meter; this change was no longer compensated by river flow.
Urmia is an endorheic salt lake in northwestern Iran. Located at an altitude of 1275 meters above sea level. It is located in a tectonic depression in the eastern foothills of the Kurdish Mountains. The banks are mostly low, salt marshes and swamps. The largest tributary is the Jagatu River.
The size of the lake is subject to large seasonal and interannual fluctuations. The area ranges from 5.2 to 6 thousand square kilometers. Length - about 140 kilometers, width - 40-55 kilometers. The maximum depth reaches 16 meters.
The material was prepared based on information from RIA Novosti and open sources
Drying rivers is a pressing issue for residents of many countries
The reasons for the complete shallowing of the river or a significant decrease in the water level in it are two main factors: human and climatic (seasonal).
CLIMATIC (SEASONAL) FACTOR
Dry years take “life” away from rivers. Lack of precipitation in the autumn-winter period and abnormally high temperatures in summer lead to drying up of rivers.
In countries with a dry, hot climate, due to a long absence of rain, river beds completely dry out in their lower parts. And they fill only during periods of long heavy rains and melting snow.
HUMAN
- Pollution
People actively use surface fresh water to meet industrial and domestic needs. In densely populated areas, wastewater and industrial discharges are highly
pollute nearby water bodies. As a result, water reuse occurs
impossible.
Nobody wants to take responsibility for cleaning the bottom and banks - springs (underground sources of river replenishment) are dying, and the riverbed is overgrown.
Irrigation
The construction of irrigation canals can improve the quality and quantity of crops, but at the same time threatens to significantly reduce water levels in rivers.
Some people build dams to divert water to their plots, without thinking about the damage they cause.
- Deforestation
Cutting down forest belts along river banks is a serious reason for their shallowing. A tree over 20 years old attracts water to the river like a pump. The construction of new “green spaces” will be a long stage in the restoration of dry riverbeds.
CONCLUSION
“Global warming” plays a role in the widespread drying up of rivers.
But human irresponsibility towards fresh water sources plays a major role in this vital problem. And even in rainy years, the water level in the rivers is not restored to its previous levels and shallowing continues.
