A promising direction for improving the environmental situation at the Aral Sea

. The Aral Sea, which was unique, beautiful and one of the largest closed water bodies in the world, almost within the life of one generation was on the verge of complete extinction, which turned into an unprecedented disaster and irreparable damage to the livelihoods of the population living here, the ecosystem and biodiversity of the Aral Sea region. The article presents the results of many years of experiments on the cultivation of aquatic plants (Azolla caroliniana) in environmentally unfavorable conditions of drainage systems. The results of the analysis of drainage water before and after the cultivation of the above plants are presented. The possibility of using the program "Google Earth Pro" for such studies is considered.


The scale of the Aral Sea ecological catastrophe
One of the largest global environmental disasters in recent history, experienced by the countries and the 62 million population of Central Asia, is the Aral Sea tragedy, which, due to its environmental, climatic, socio-economic and humanitarian consequences, poses a direct threat to the sustainable development of the region, health, gene pool and the future of the people living there.Until 1960, the Aral Sea was one of the largest enclosed water bodies in the world with an area of 68.9 thousand square meters.km and a water volume of 1083 cubic meters.km, its length was 426 km, width -284 km, maximum depth -68 m [1].Over the past 50 years, the total flow of rivers into the Aral Sea has decreased to an average of 12.7 cubic meters.km, or almost 4.5 times.The area of the water surface of the sea has decreased by 8 times, the volume of the water mass has decreased by more than 13 times.For comparison, the mineralization of the World Ocean water is 18-24 g/l, the Aral Sea 120-280 g/l.The increase in the area of the dried bottom of the Aral Sea has led to an increase in the number of storms in the region [2].
Powerful salt storms in the Aral Sea region began to be recorded on satellite images from the mid-1970s.The center of their occurrence was the dried coastal strip of the previously shallow northeastern and eastern coasts of the sea.For the period from 1975 to 1982.35 storms were found here, the dust drifts of which reached a length of 200-400 km.[3,4].The salts released into the atmosphere fell on the underlying surface with atmospheric precipitation and in dry form.Salt dust has an adverse effect on the vegetation of Ustyurt pastures, as well as oases located in the delta of the Amudarya and Syrdarya.The last of which was recorded on May 26-27, 2018.The second indicator of the negative impact is the river waters that irrigate the lands near the Aral Sea.The water resources of the Aral Sea region consist of replenished surface and ground waters, as well as return waters from anthropogenic use (waste and drainage waters).There are two large river basins in the Aral Sea basin: the Syr Darya in the north and the Amu Darya in the south.Long-term observations of changes in the mineralization of river water show their increase over the past 3 decades.If 30-35 years ago the mineralization of water in the Nukus section was 0.7-0.9g/l in terms of solid residue, then in recent years their value has reached 1.6-2.0g/l.The main reason for this is, on the one hand, the general decrease in the water content of the river, and, on the other hand, the discharge of a large amount of drainage water into the riverbed from the middle and lower reaches (up to 10 km 3 per year).
Locally, although in small areas, there are high values up to 14-15 g/l.In some places it is possible to observe slightly mineralized 1.3 g/l.This information can be used to support water management.In low salinity areas, reuse can be seen as a promising option to conserve water.Areas of high salinity may help identify areas requiring further water management activities or may help identify marginal areas.Especially harmful can be the use of mineralized waters for irrigation during periods of strong accumulation of salts in the upper layers of the soil, due to the lack of a flushing effect.In 2008, the potential allocation for reuse of water from the collector and drainage network was in the amount of 275 million m 3 .The amount of water for reuse was set for the period from the 2nd decade of May to September 2008 [5].
Natural and anthropogenic salinization of soils.The area of saline soils in Kazakhstan (including alkaline, alkaline soils and combinations with other soils) is 111.55 million hectares, or 41% of the entire territory of the country.In Kyrgyzstan, 21.3% of all agricultural land.Up to 68% of the total area of irrigated soils in Turkmenistan is affected by excessive salinization.The area of saline soils in Uzbekistan is 51% of irrigated lands, and suffer from excessive soil salinization [6].It should be noted that the construction of drainage systems in Central Asia was widely developed in 1960-1990, when intensive development of new and reconstruction of the reclamation network on old irrigated lands was carried out in all republics.As a result of these works, by the beginning of the 90s, 200.55 thousand km of the collector-drainage network were built here, of which 45 thousand km were inter-farm and main collectors, 155.5 thousand km were on-farm collectors (including 48.6 thousand km of drainage closed type, as well as 7,762 vertical drainage wells).The largest area covered by drainage falls on Uzbekistan, where the length of the inter-farm and on-farm collectordrainage network is 137,793.3km, including 31,353.6 km of the inter-farm one [7].

Consequences of salinization in the Aral Sea territories
The salinity value in the Aral Sea region has increased by 2.5% in the last decade, and the amount of oxygen in the inhaled air is constantly decreasing [8].The level of congenital anomalies, neoplasms, diseases of the respiratory and digestive organs increased 3 times, diseases of the hematopoietic and endocrine systems increased more than 2 times [9].The annual analysis of the incidence of bronchial asthma by researchers in Uzbekistan showed that the highest intensive rate is observed in the Khorezm region -113, and this is more than 3 times higher than the national average, and in Karakalpakstan it is almost 2 times higher than the national average [10].The works [11] studied the negative impact on the functional activity of the liver in collective farmers of an ecologically unfavorable region on the territory of Turkmenistan.
The impact of the Aral Sea catastrophe is now observed all over the world.According to international experts, poisonous salts from the Aral Sea region have been found on the coast of Antarctica, on the glaciers of Greenland, in the forests of Norway, and in many other parts of the world [12].To our great regret, today it has become obvious that it is no longer possible to fully restore the Aral Sea.The most important task of the present time is to reduce the detrimental impact of the Aral Sea crisis on the environment and the livelihoods of millions of people living in the Aral Sea region.
Since the 1990s, all countries experiencing the devastating consequences of the Aral catastrophe, from the rostrum of the United Nations and other international and regional organizations, have been constantly drawing the attention of the world community to the Aral problem and its close relationship with issues of regional and global security.Even at the 48th session of the UN General Assembly on September 28, 1993 and at its 50th session on October 24, 1995, representatives of the countries of the Central Asian region appealed to the world community to assist in saving the Aral Sea and the Aral Sea region, drawing the attention of the UN to the fact that without support and assistance from international financial institutions and developed countries, without the organizing role of the UN, it is impossible to solve this problem.
During the Summit on Sustainable Development in September 2015 in New York, the Uzbek side took the initiative to create under the auspices of the UN a special Trust Fund for the Aral Sea and the Aral Sea zone, the main task of which will be to coordinate efforts and implement targeted programs and projects in the following key directions:  protecting the health and preserving the gene pool of the population, developing a system of effective incentives for the socio-economic development of the Aral Sea zone and creating the necessary conditions to ensure a decent life for the population living in this region;  maintaining the ecological balance of the Aral Sea region, taking consistent measures to combat desertification, introducing rational water use;  restoration of the biodiversity of the animal and plant world, the preservation of the unique flora and fauna, which is currently on the verge of extinction;  use of the region's limited water resources, primarily transboundary water arteries -the Amudarya and Syrdarya, in the interests of all countries in the region and in strict accordance with international law.The lake systems of the Amudarya River delta are small local reservoirs under the South Aral Sea.As a result of the project "Creation of small local water bodies in the Amudarya river delta", Phase-I, implemented by the Government of the Republic of Uzbekistan, 180 thousand hectares of land were watered and local water bodies were created, which contributes to restoration of flora and fauna.At present, the implementation of Phase-II of the project continues, under which it is planned to create reservoirs with a total area of 208.69 thousand hectares [13].

Distribution and use of the aquatic plant Azolla caroliniana
Azolla carolinianaa plant of the genus Azolla native to the warm temperate and tropical regions of the Americas, as well as Asia and Australia.It is a floating water fern with very rapid growth, capable of spreading across the surface of lakes, and can provide complete coverage of the water surface in just a few months.Each plant is 1-2 cm wide, is colored pink, orange or red at the edges, branches freely and breaks into smaller patches as it grows.It does not tolerate low temperatures, and in a temperate climate in winter it mostly dies, surviving due to buds located under water.
Optimal growth conditions for Azolla were studied by Sheriff and James (1994), according to their research the favorable water temperature for rapid reproduction of Azolla usually occurs at 18 to 26 ºC.The optimum relative humidity for Azolla growth is 85 to 90 percent.Azolla becomes dry and brittle at relative humidity below 60 percent [14].
According to Ferentinos et al. (2002) the nitrogen fixation capacity of Azolla was found to vary from 53-1 000 kg/ha with a dry matter production of 39-390 tonnes/ha, in crop cycles of 40-365 days.The linear growth phase is usually between 6 and 21 days and is characterized by low lignin and cell wall fractions.Due to its high lignin content (20 percent), nitrogen is released slowly from the plant initially, with about two-thirds released on the first 6 weeks after application.Under flooded conditions, 40-60 percent of the available N is released after 20 days and 55-90 percent within 40 days [15].
The symbiotic Azolla-Anabaena system has been the subject of research.because of its value as a nitrogen-fixing greenhouse crop for rice crops [16,17,18,19].In several studies by scientists [20][21][22] Azolla spp.are capable of achieving high growth rates through asexual reproduction and are very strong accumulators of phosphorus (P) and nitrogen (N)3, making them very suitable for phytoremediation, biogas production, animal feed and crop fertilization.Recently, azolla has been increasingly used as a feed and/or fertilizer in studies of rice and fish farming systems in many other Asian countries.the authors [23] reported that the manure schedule can be reduced by 30-35 percent by bio-fertilizer Anabaena azollae -Azolla in aquaculture ponds.A cage culture study [24] used fresh whole A. pinnata as supplemental feed for cage culture of Nile tilapia in Laguna de Bay, Philippines.Azolla were propagated in fine-mesh aviaries in the lake and harvested for caged tilapia feeding.Biofuel production has been proposed by scientists [25,26], which can be produced from any biomass containing biological carbon, and the most common sources of carbon are photosynthetic plants [27].
It is known that overpopulation is increasingly causing serious concerns for surface waters such as rivers, lakes and other bodies of water due to improper disposal of sewage and pollution.And aquatic macrophytes have high potential to phytoextract or absorb organic matter, salts, solids and metals in their tissues and clean up polluted water bodies.Research work on cleaning polluted water bodies has been done by the following scientists [28][29][30][31][32][33].Many properties have been studied by scientists in wastewater treatment as an aquatic plant with high potential for phytoremediation programs due to its ability to scavenge toxic metals [34][35][36][37][38] such as cadmium, chromium, nickel and zinc [39], arsenic [40].
Methods of mass cultivation of Azolla caroliniana under introduction conditions in the North of Uzbekistan on large ecologically unfavorable areas have not been developed yet.Only some experimental data on cultivation under laboratory conditions are available.
Thus, the development of methods for mass cultivation of Azolla caroliniana under Aral Sea conditions is one of the topical tasks of applied sciences.The aim of this work is to develop methods of mass cultivation of Azolla caroliniana under the conditions of introduction to the North of Uzbekistan.

Experimental procedures
pH of water samples was controlled using a pH meter (pH meter, model PXSJ-216F, USA) and a glass electrode, and water hardness was determined by the mechanism.Hidrometers model: Densitometer (Liaoning Huake Petroleum Apparatus Science & Technology Co., Ltd.China.Titration of Water Sample 1. Dilute 25 ml of sample water (or such volume that <15 ml of titrant is required) to approx.50 ml with dd water in a 125 ml Erlenmeyer flask.Samples were prepared in triplicate [Official method recommends the following: For water of low hardness (<5 mg/L), use 100-1000 mL specimen, proportionately larger amounts of reagents, microburet, and blank of distilled water equal to specimen volume.]2. Adjusted pH to 10 ± 0.05.3. Slowly titrate each sample with EDTA (Ethylenediaminetetraacetic acid) standard solution.4. Record the volume of EDTA solution used for each titration.The processing was evaluated by measuring the parameters of the collected samples immediately after delivery to the laboratory.Thus, the characteristics of water samples were determined before and after the end of the experiment, and the rate of decrease or increase in any of them was recorded during the experiment lasting one week.

Results
In the spring of 2016, by our actions in the collector-drainage canal of the city of Urgench (Khorezm region.Uzbekistan.The climate is sharply continental, average humidity 20-24%) planted one plant (Azolla caroliniana) of 1 cm square with geographical indicators latitude 41°32'54.71"C, longitude 60°40'8.88"B and at present the area is 30640 meters square i.e. the length of Azolla channel colonization was 7.66 kilometers (it should be considered that drainage collectors freeze in winter) with average width of 4 meters.All of this can be seen from the space image made by the program "Google Earth Pro" where the roughness of the earth's surface was taken into account.It was revealed that the yield of Azolla caroliniana in the drainage system of Urgench city of Khorezm province depends on many factors first of all on the intensity of water movement.Positive indices were got from 1,26 kilometers till 2,45 kilometers yield of Azolla per m2 using method of weighing of its raw biomass was on average 16427 gram/m2, maximum indices were got between 5,67 and 6,26 kilometers where average yield was 21078 gram/m2 it is connected with the fact that there are small enterprises of agroindustrial complex.The lowest yields of Azolla were found at 0,382., 2,75., 3,38 and 5,2 kilometers of the drainage system and ranged from 100-250 grams/m2.A formula for increasing the area of distribution of Azolla in a given interval is derived, taking into account the temperature effect.Considering the maximum winter 2018 of -18 degrees Celsius, the growth of Azolla has not yet been studied at such temperature intervals.An example of scientists' works on optimal growth conditions for the plant [14].
The pH value of water acidity in the drainage canal up to the growing area of Azolla was on average pH= 6.11 and when leaving the growing area it was pH= 7.11-7.21.The density of water before Azolla is 1000 kg/m 3 and after 999 kg/m 3 .
Water hardness was measured according to AOAC Method 920.196 before Azolla growing area water hardness was 25 0 after passing 10 0 .Azolla's capture of territory over the years can be seen using the program "Google Earth Pro".

Fig. 2 .
Fig. 2. Photo from space showing the area of Azolla distribution in the drainage system

Fig. 3 .
Fig. 3. Curved line of increase in the area of distribution of Azolla

Fig. 5 .
Fig. 5. Photo from space showing the distribution of the plant over the years