Why doesn’t the water in reservoirs freeze to the very bottom in winter? Water temperature and ice phenomena Temperature of sea water under ice in winter.
Temperature under the ice 0.1-0.3° above zero, in the spring during ice drift it does not exceed 1 °. During periods without ice, the water temperature depends mainly on the air temperature. The average daily water temperature before mid-summer is usually lower than air temperature, at the end of summer and autumn it is higher.
Below the reservoirs, the temperature of the river water in summer is significantly lower than usual, and higher in winter, which leads to the appearance of many kilometers of ice-free sections of the river. Abundant underground feeding of the river cools its water in the summer, in winter it leads to a decrease in ice cover, and sometimes to the formation of polynyas.
Daily maximum water temperatures are 1-2 hours behind the air temperature.
On small and medium-sized rivers, the water temperature practically does not change in depth; on large rivers it may decrease in summer in the lower layers by 1-2°.
Thermal sink(W m in J or kcal) - the amount of heat carried through a given river section over a time interval (∆ t):
W m = L melt ·ρ·T·V, Where V- volume of water flow over the same time interval, T - average water temperature, ρ - its density, L melt - specific heat capacity of water.
Large rivers flowing in a meridional direction - transzonal rivers- have a water temperature that is not typical for rivers in the area.
According to the nature of the ice regime, rivers are divided into three groups: freezing, with unstable ice cover and non-freezing.
On freezing rivers, three periods with characteristic ice phenomena are distinguished: 1) freezing, or autumn ice phenomena, 2) freeze-up, 3) opening, or spring ice phenomena.
Freezing of rivers. When the water temperature drops to zero, autumn ice phenomena begin in the river. Grease - floating spots of ice film, consisting of ice crystals in the form of thin needles. Around the same time, banks form - strips of motionless ice off the coast. When water is supercooled (to fractions of a degree below zero), intra-water ice can form in its thickness and at the bottom - an opaque, spongy, ice mass of chaotically fused ice crystals. The accumulation of intra-water ice on the surface or in the thickness of the flow forms slush. Its movement is called sludge. At the same time, ice floes consisting of crystalline ice form on the surface. Their movement is the autumn ice drift. Blockage of the riverbed by slush is called a jam, and by ice floes - a jam.
Freeze-up is the formation of a continuous, motionless ice cover. Small ice-free areas are polynyas. They are associated with groundwater outlets or rapid currents, sometimes with the discharge of warm water into the river by industrial and municipal enterprises. As the thickness of the ice cover increases, the cross-section of the channel decreases. Under the influence of the resulting pressure, water can flow onto the surface of the ice. When it freezes, ice forms.
Opening up of rivers. With the onset of positive air temperatures in the spring, snow and then ice begin to melt. Stripes of clean water form on the river near the banks - edges. The adhesion of the ice cover to the shore ceases, and cracks appear. Sometimes after this, small (several meters) displacement of the ice fields is observed - ice movements. Then the ice cover is divided into separate ice floes, the movement of which forms spring ice drift. More often than in autumn, congestion occurs, especially on large rivers flowing from south to north. On small rivers, the ice cover often melts in place without ice drift.
In central Russia, phenological (natural) winter usually begins in mid-November. By this time, the “off-season” period, so unloved by fishermen, ends with its changes in atmospheric pressure and temperature, alternating frosts and rains, and the vagaries of many species of fish. Fans of winter fishing consider winter to be the period from the formation of stable ice cover to the melting of the ice (from mid-November to the end of March). Sometimes ice cover on reservoirs appears a month to a month and a half later than the beginning of the calendar winter (somewhere in early to mid-January). More often this happens in the southern regions of Russia. In some regions of the CIS, there is no ice cover on rivers and lakes at all, and the difference between the prolonged autumn and the imperceptibly approaching winter is almost imperceptible.
With the onset of winter, significant changes occur in aquatic systems, affecting the behavior of underwater inhabitants.
Ice cover, lighting and fish behavior.
The importance of light in the life of animals cannot be overestimated. Light “dominates” over all other environmental factors. No environmental factor undergoes such changes as illumination: during the day its intensity changes tens of millions of times (from hundreds of lux to ten-thousandths of a lux). In terms of its intensity and duration, illumination plays the role of a signal for aquatic living organisms as a signal of the beginning of certain changes in the environment (the onset of morning, night, the beginning of warming up of water, etc.), which leads to a change in the behavior of fish.
Throughout autumn and early winter, there is a gradual decrease in the daylight period: in November, the length of daylight hours on average does not exceed 9 hours 10 minutes. The establishment of ice cover, snowfall, and the predominance of cloudy days further reduce the illumination of water bodies. For four long months, twilight reigns in the underwater kingdom...
The behavior of fish during the initial period of winter is interesting. Many species of heat-loving fish (carp, crucian carp, tench, grass carp) gather in huge schools in October-November and go to the so-called wintering pits. In a semi-stupor, practically not moving, they will spend about three months here (until the end of February). Carp stand very densely at depth, sometimes up to 15-20 individuals per 1 m3, nearby there are asps, ides, and tenches. During severe frosts, bream also coexist with them, but with a change in atmospheric pressure and when the frost weakens, schools of bream leave their wintering pits and “scatter” throughout the reservoir in search of food.
Refuting the generally accepted point of view about the location of the winter “bed” of catfish, river giants occupy places near wintering pits - at the exits from the depths, the boundaries of pits and bottom elevations. This placement of mustachioed predators is explained by the fact that in the pit itself, already a month after the formation of the ice cover, the oxygen regime changes sharply, which this fish, unlike the “thick-skinned” carp (carp), cannot easily tolerate.
Perch, pike, pike perch, after the autumn migration to deeper places (moving away from high water transparency and significant illumination), with the establishment of ice cover, return to their September hunting grounds. Moreover, roach, silver crucian carp, verkhovka and bleak, with rare exceptions, practically do not leave their habitats chosen in the summer.
In shallow and low-food reservoirs, silver crucian carp burrows under leaves or “dives” into the silt. True, only in the northern regions does it stay there for a long time; in more southern areas, the motor activity of crucian carp resumes when the water temperature increases by 3.5 ° C (February). Therefore, during not too cold winters in Ukraine, Kazakhstan and other regions, ice fishing for silver crucian carp is common.
The appearance of ice cover makes adjustments to the behavior of predatory fish. There is such a division of predators in relation to light: perch is considered a twilight-daytime predator, pike - crepuscular, pike perch - deep-twilight.
In autumn, perches and pike feed around the clock: during the day they hunt for prey from ambush, at dusk and dawn they go out into open water and pursue victims. “Twilight” feeding of predators occurs at illumination from hundreds to tenths of lux (in the evening) and vice versa (in the morning). Pike perch can use their vision in conditions where other fish cannot see. The retina of a predator's eye contains a highly reflective pigment - guanine, which increases its sensitivity. The hunt of pike perch for small schooling fish is most successful in deep twilight illumination - 0.001 and 0.0001 lux (almost complete darkness).
At dusk and in the early morning hours, perch and pike have daytime vision with maximum visual acuity and range, and dense defensive schools of prey fish begin to disintegrate, ensuring successful hunting for predators. With the onset of darkness, individual fish disperse throughout the water area; when the illumination drops below 0.01 lux, the top and bleak sink to the bottom and freeze. The hunting of predatory fish stops at this time.
At the beginning of winter, the situation under the ice changes. The twilight plays into the hands of the twilight predators, who in the first days of the establishment of ice cover organize a “St. Bartholomew’s Night” for their demoralized victims. Predatory fish no longer need to distribute their hunting time between early morning and evening hours. This is how the famous “first ice” predator’s gorging begins and continues (usually not for very long).
By the way, in winter, the reaction of prey fish to a threat sharply decreases; tops and bleaks react much weaker to the “smell of fear” emitted by their companions when they are grabbed by a predator.
When searching for a predator in large bodies of water, it is not at all necessary to look for it in holes and snags. Much more often it can be found near areas of ice free of snow: weak, diffused light penetrating into the depths throughout the winter attracts bleak and verkhovka, so beloved by pike perch.
Areas of ice cleared of snow also attract juvenile perches, which gather at a dimly lit area of the “hard surface” of the reservoir after 15-20 minutes. Underwater studies have shown that adult perches, which approach a little later than juveniles, are also attracted to weak light. Moreover, unlike the “minors,” humpback whales avoid the illuminated area and patrol around it in the dark.
Water temperature and fish behavior.
The temperature of the aquatic environment is the most significant natural factor that directly affects the level of metabolism of poikilothermic (somewhat unfortunate synonymous term - “cold-blooded”) animals, which include fish.
All fish, according to the temperature range at which their normal life activity is possible, are divided into heat-loving (roach, carp, crucian carp, tench, herbivorous species (silver carp, grass carp), sturgeon and others) and cold-loving (brook trout, whitefish, salmon , burbot, etc.).
The metabolism of the first representatives is most efficient at high temperatures. They feed most intensively and are active at a temperature of +17-28°C; when the water temperature drops to +17°C, their feeding activity weakens (and in winter for many species it stops altogether). They spend the pre-winter period and the entire winter in a sedentary state in the deep places of the reservoir.
For cold-loving fish, the optimal temperature is +8-16°C. In winter they feed actively, and their spawning occurs in the autumn-winter period.
It is known that fish “get used to cold weather and a decrease in water temperature”, rebuilding their metabolism in only 17-20 days. When the water temperature decreases from +12°C to +4°C for grayling, for example, energy consumption decreases by 20%.
As the water temperature decreases, the solubility of oxygen increases, so in winter the saturation of water with oxygen is quite high.
With a prolonged decrease in water temperature, fish must not only have a sufficient supply of fat as an energy material, but also maintain normal metabolism during this period.
Fishing strategy in winter.
There are sometimes more fans of winter fishing in certain regions of the CIS than summer fishing enthusiasts. Despite the unpredictable vagaries of the weather and the sometimes inexplicable lack of bite from underwater inhabitants, excellent fishing is possible in winter. You just need to clearly imagine and “calculate” the situation on a specific body of water. You need to know that throughout the winter, at least 20-35 species of fish (in different reservoirs in different ways) continue to feed intensively, sometimes even despite changes in atmospheric pressure.
Naturally, each specific species requires its own, special approach, which will certainly bring success to the experimental fisherman if he has some fishing experience, knowledge of the behavior of fish during this period of the year and, of course, a passionate desire to catch his trophy!..
POND IN WINTER
Date of: 12.1.10| Chapter: Reservoirs
With the onset of cold weather, everything in the garden freezes. However, it should be remembered that fish and other living creatures will spend the winter in frozen ponds. It is necessary to thoroughly prepare the pond for winter; this is especially important for reservoirs about 1 meter deep.
When the water temperature drops to 8 °C, the living creatures living in the pond go into a state of deep sleep. Depending on the water temperature, you need to gradually reduce the portion of food. During this period, the fish's sense of taste and smell are dulled; they react only to water movement, pressure changes and touch. They sink to the bottom, choosing the deepest and warmest places in the reservoir - there they spend the whole winter. At a depth of 1 meter, the water temperature is approximately 5 °C - this is quite enough for the fish to survive the winter. However, in places where living organisms accumulate, there is often a lack of oxygen. If the pond is under ice for a long time, the gases do not escape and the fish may die.
Before the first frost
You should think about the conditions for wintering fish in a reservoir before the onset of the first frost. In autumn it is not at all necessary to cut reeds and reeds. Thanks to the plants swaying in the wind, the water in the place where they grow will freeze at the very last moment.
To prevent the entire pond from becoming covered with ice, it is worth releasing a so-called foam float (sold in specialized gardening stores) into the water. This design consists of a ring and a lid (the lid should be removed if it is necessary to open the hole in the ice). The water under the ring will not freeze if the lower part is immersed to a depth of at least 10 cm. The ring contains special chambers into which sand or stones can be poured. When the temperature drops to -8 °C, the hole under the lid freezes. Then a special heater or compressor must be installed in the foam float. You can also place bunches of chopped reeds in the float, thanks to which the water in the holes will not freeze and the gas exchange process will resume.
On the icy surface
During severe frosts, the entire surface of the pond will be covered with ice. It is necessary to make holes in several places. For drilling holes in thick ice, the best option is a brace, or ice drill, which cuts holes with a diameter of about 1 5 cm even in the thickest ice. The larger the hole, the better. To prevent the ice holes from freezing, you can put bundles of reeds in the holes.
First winter
If the pond inhabited by fish was equipped only this season, then the first wintering can become a serious test from which the necessary lessons will need to be learned. For example, improper and excessive feeding of the inhabitants of your pond could lead to clogging of the country pond. Undoubtedly, this will complicate the wintering of your fish. They will also have to fight for survival if, when moving in, you violated the recommended standards: for each fish 10-15 cm long there should be at least 50 liters of water. When purchasing pets for your man-made pond, do not forget to find out what the maximum adult size is. One of the main conditions for a healthy winter is a sufficient amount of oxygen. Reservoirs with a larger surface have advantages, but they should not be shallow, otherwise there is a danger of complete freezing.
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A difficult problem in home fish farming is the overwintering of fish.
Amateur fish farmers use a variety of techniques to prevent winter death. Most often, after a reservoir freezes, when the ice is 1.5 - 2.5 cm thick, a hole is cut and water is pumped out through it. The resulting air cavity between the surface of the water and the ice, 15–20 cm high, saturates the water with oxygen. Hole in
The ice is covered and insulated so that the cold does not penetrate to the surface of the water and freeze it again. In this case, it is useful to insulate the ice with snow.
You can organize the wintering of fish differently. With the onset of autumn cooling, when the water temperature is below 8°, the fish stop feeding. The pond is cleared of water. I place some of the fish (decorative and intended for growing) in a wintering pit. This is a concrete well with a diameter of 70 cm and a depth of 2.5 m, where it remains until the spring snowmelt, that is, until the end of March next year. The water level in it during the winter decreases from 2.2 to 1.7 m. Dug in non-freezing swampy soil, covered on top with a wooden shield, and in winter with snow, the wintering pit-well maintains a positive temperature inside throughout the winter. The water in it does not freeze and oxygen from the surface air layer freely enriches the water, saving the fish from death. For a long time I searched and asked on the forums about various techniques for preventing winter death, and now I found how they used to be saved without electricity. This is where you can lower the water from under the ice, and the ice will be held back by shallow waters and mounds under the ice, and there will be voids filled with air.
Deep autumn. The days are getting shorter and shorter. The sun will peek out for a minute from behind the heavy clouds, slide across the ground with its oblique ray and disappear again. The cold wind walks freely through empty fields and bare forest, looking for somewhere else a surviving flower or a leaf clinging to a branch in order to pick it, lift it high and then throw it into a ditch, ditch or furrow. In the morning, the puddles are already covered with crispy pieces of ice. Only the deep pond still does not want to freeze, and the wind still ripples its gray surface. But now fluffy snowflakes began to flash. They spin in the air for a long time, as if not daring to fall on the cold, inhospitable ground. Winter is coming.
A thin crust of ice, which first formed near the shores of the pond, creeps into the middle to deeper places, and soon the entire surface is covered with clean transparent glass of ice. Frosts hit, and the ice became thick, almost a meter thick. However, the bottom is still far away. Water remains under the ice even in severe frosts. Why doesn't a deep pond freeze to the bottom? The inhabitants of reservoirs should be grateful for this one of the features of water. What is this feature?
It is known that the blacksmith first heats the iron tire and then puts it on the wooden rim of the wheel. As the tire cools, it will become shorter and fit tightly around the rim. The rails are never laid close to each other, otherwise, when heated in the sun, they will definitely bend. If you pour a full bottle of oil and place it in warm water, the oil will overflow.
From these examples it is clear that when heated, bodies expand; When cooled they contract. This is true for almost all bodies, but for water this cannot be stated unconditionally. Unlike other bodies, water behaves in a special way when heated. If, when heated, a body expands, it means that it becomes less dense, because the same amount of substance remains in this body, but its volume increases. When heating liquids in transparent vessels, one can observe how warmer and therefore less dense layers rise up from the bottom, and cold ones sink down. This is the basis, by the way, for a water heating device with natural circulation of water. As the water cools in the radiators, it becomes denser, falls down and enters the boiler, displacing upward the water already heated there and therefore less dense.
A similar movement occurs in a pond. Giving up its heat to the cold air, the water cools from the surface of the pond and, being more dense, tends to sink to the bottom, displacing the lower warm, less dense layers. However, such a movement will occur only until all the water has cooled to plus 4 degrees. The water collected at the bottom at a temperature of 4 degrees will no longer rise upward, even if its surface layers had a lower temperature. Why?
Water at 4 degrees has the highest density. At all other temperatures - above or below 4 degrees - water turns out to be less dense than at this temperature.
This is one of the deviations of water from the laws common to other liquids, one of its anomalies (an anomaly is a deviation from the norm). The density of all other liquids, as a rule, starting from the melting point, decreases when heated.
What will happen next when the pond cools down? The upper layers of water become less and less dense. Therefore, they remain on the surface and at zero degrees turn into ice. As it cools further, the ice crust grows, and underneath there is still liquid water with a temperature between zero and 4 degrees.
Here, probably, many people have a question: why doesn’t the lower edge of the ice melt if it is in contact with water? Because the layer of water that is in direct contact with the lower edge of the ice has a temperature of zero degrees. At this temperature, both ice and water exist simultaneously. In order for ice to turn into water, it is necessary, as we will see later, a significant amount of heat. But this warmth is not there. A light layer of water with a temperature of zero degrees separates deeper layers of warm water from the ice.
But now imagine that water behaves like most other liquids. A slight frost would be enough for all rivers, lakes, and perhaps even the northern seas to freeze to the bottom during the winter. Many of the living creatures of the underwater kingdom would be doomed to death.
True, if the winter is very long and severe, then many bodies of water that are not too deep can freeze to the bottom. But in our latitudes this is extremely rare. Ice itself prevents water from freezing to the bottom: it conducts heat poorly and protects the lower layers of water from cooling.
Nature surprises us with inexplicable phenomena. One of them is water crystallization. Many people are interested in such an unusual question as why, at sub-zero temperatures, ice forms on the surface of a reservoir, but under the ice the water remains liquid. How to explain this?
Why water under thick ice does not freeze: answers
At what temperature does it begin to harden? This process begins when the temperature drops to 0 degrees Celsius, provided that the normal level of atmospheric pressure is maintained.
The ice layer in this case performs a thermal insulation function. It protects the water underneath from exposure to low temperatures. The layer of liquid that is located directly under the ice crust has a temperature of only 0 degrees. But the lower layer has a higher temperature, which fluctuates within +4 degrees.
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If the air temperature continues to decrease, the ice becomes thicker. At the same time, the layer that is located directly under the ice is cooled. At the same time, all the water does not freeze, since it has an elevated temperature.
In addition, an important condition for the formation of an ice crust is that the low temperature must be maintained for a long time, otherwise the ice will not have time to form.
How is ice formed?
As the temperature decreases, the density of the liquid decreases. This is what explains the fact that warmer water is at the bottom and colder water is at the top. Exposure to cold causes expansion and decrease in density, resulting in the formation of an ice crust on the surface.
Thanks to these properties of water, the temperature in the lower layers is maintained at +4 degrees. This temperature regime is ideal for inhabitants of the depths of reservoirs (both fish and shellfish, plants). If the temperature drops, they will die.
It is interesting that in the warm season the opposite is true - the temperature of the reservoir on the surface is much higher than at depth. How quickly water freezes depends on how many salts are present in its composition. The higher the salt concentration, the worse it freezes.
The ice crust helps retain heat, so the water underneath is slightly warmer. Ice prevents the passage of air into the lower layer, which helps maintain a certain temperature regime.
If the ice crust is thick and the reservoir is of sufficient depth, the water in it will not freeze completely. If there is not much of it, there is a possibility that the entire reservoir will freeze when exposed to low temperatures.
