Actuality of the topic. Hydrosphere is a habitat of numerous creatures, which need a number of parameters of physico-chemical state of a water environment for their normal habitability. One of the most important among them is the concentration of the dissolved oxygen. Sufficient amount of the dissolved oxygen is a necessary condition of the existence of hydrobionts. Because of the extremely minor solubility of oxygen its amount in water is limited and besides it reduces with pollution or heating, which causes mass death of hydrobionts. Concentration of the dissolved oxygen in water depends on many factors and first of all on biotic and anthropogenic influence.
Basically the main initiator of the changes in a pool (in a number of cases considered in the work - in a lake) is anthropogenic influence, especially in our period of increasing influence of human activity on the environment: biogenic elements go to a lake from the territory of its water-gathering often used in agriculture. They cause intensive growth of a biomass, which leads to a reduction of the level of dissolved oxygen and rapid eutrophy of a lake.
The comparative analysis of natural processes in a pool and processes initiated by the anthropogenic load is so actual because the last quickly lead to a death of a pool as an ecosystem.
Object of investigation. Lakes Krasnoye, Borisovskoye, Sjar'ba, river Svir' and a number of pools relating to its basin.
Subject of investigation. Hydrochemical regime and trophic status of the pools.
Aim of investigation. Detection of the dynamics of the developing of listed pools, detection of the character of dominating influences on directivity of processes in these pools, comparative analysis of hydrochemical regime of pools developing naturally and developing under essential influence of the anthropogenic load.
1). Analysis of morphometric characteristics, structure of water balance, natural features of water-gathering in particular, of the investigated pools.
2). Investigation of water assays on pH, the amount of hydrocarbonat ion, sulfate ion, nitrate ion, nitrite ion, ion of ammonium, phosphate ion and cations of calcium and magnesium and also the amount of the dissolved oxygen as one of the most important parameters of hydrochemical regime of a pool which characterizes its vitality and is a peculiar indicator of its trophic state. The amount of the dissolved oxygen was determined with the method of Winkler in field conditions by means of the portable laboratory.
3). The comparative analysis of the obtained data.
Hypothesis. Change of abiotic environment may be caused both by the activity of creatures inhabiting it and under the influence of the anthropogenic load. But in the first case there's a natural process typical for biosphere as a dynamic system, and in the second case changes are large-scale, are developing intensively and have pernicious character quickly leading to the death of the ecosystem.
Sources. During the realization of the work results of complex investigations of several years by the Club of Young Travellers-Ecologists were used, in particular, which enabled to observe the dynamics of developing of pools of different types, especially lakes, of Leningrad region. Besides the theoretical informational basis in the field of the hydrology of the rivers and lakes of Leningrad region and hydrochemistry was used.
Logic of deployment of the topic.
The first part of the work is devoted to the investigation of the hydrochemical regime of pools where the anthropogenic load is small or where there isn't any anthropogenic load. Lakes Krasnoye and Sjar'ba, pools of the basin of the river Svir' in her low flow (the right tributary of Svir', the river Segezha in her middle and low flow, bay Lakhta etc).
In the second part of the work the stream, the tributary of Segezha was investigated. Its hydrochemical regime was changed by means of biotic influence, i. e. the activity of beavers, which inhabit the stream.
The third part of the work is devoted to the investigation of the lake Borisovskoye. It's the pool where the anthropogenic influence is brightly expressed.
1). Analysis of the water of the river Segezha showed the increasing of the concentration of the dissolved oxygen from the source to the mouth.
2). On the basis of the analysis of the water of the lake Krasnoye its mesotrophic character was detected. Mineralization of the water is low (summary concentration of substances dissolved in water, which we were able to indicate is 30 mg/l) and it's the reason of its supersaturation with the dissolved oxygen (12,9 mg/l). Because of the minor anthropogenic load the amount of biogenic elements, both nitrogen and phosphorous, is low. It enables to suppose the high vitality of the pool.
3). On the basis of the analysis of the water of the eutrophic lake Sjar'ba the natural character of its eutrophy was proved. Because of the mainly marshy feeding of the lake, shift of pH to the acidic side (5,7), low concentration of HCO3- ions, high concentration of SO42- ions are typical for its water. Mineralization of the lake is low (summary concentration of substances dissolved in water, which we were able to indicate is 12 mg/l). On the basis of the data about reduction of the dissolved oxygen on 0,74 mg/l and increase of ion of ammonium on 0,06 mg/l the during two years, slow development of the eutrophy was detected. In spite of the fact that we ought to value the dynamics of the eutrophy of a pool by its main parameter - the amount of primary production - we don't have means to indicate it and we make an attempt of ecological simulation on the basis of a very limited range of parameters. High amount of NH4- ions is connected with the processes of biochemical decomposing of organic residues. Absence of the anthropogenic influence on the lake shows in low amount of phosphorous in its water.
4). Investigation of the water of the beavers' stream showed extremely low amount of the dissolved oxygen (3,6 mg/l) because of the intensive accumulation of the ooze and its oxidation, bogging of the pool. This process is initiated by the secondary ecological succession caused by the activity of beavers. Change of a liquid water content causes the change of a hydrochemical regime. In this case the change of biocenosis causes essential changes of biotope. Biogeocenose changes.
5). Analysis of the water of the eutrophic lake Borisovskoye detected the essential role of the anthropogenic load in its eutrophy. The high amount of nitrogen in water by way of nitrite ion, nitrate ion and ion of ammonium and high amount of phosphorous is typical for the water of the lake because of the depositing of fertilizings on agricultural areas which make the principle part of its water-gathering. Because of the high concentration of biogens, the intensive escalating of the biomass in the lake is detected which accelerates the eutrophy.
1). The increasing of the concentration of the dissolved oxygen in water of the flowing pool from a source to a mouth, in terrain with a flat relief, in a summer period of time (the beavers' stream 3,6 mg/l - the middle flow of the riv. Segezha 9 mg/l - the low flow of the riv. Segezha 12 mg/l - riv. Svir' 13,5 mg/l), and corresponding improvement of the life conditions for hydrobionts, was practically proved. It's explained by the increasing of an average depth and reduction of temperature, increasing of the influence of the underground tributary.
2). On the basis of the data of the reduction of the amount of the dissolved oxygen and the increase of the ion of ammonium in the water of the lake Sjar'ba during 2 years, the development of its eutrophy was detected. It has however an extremely low intensity because of the absence of anthropogenic load.
3). On the basis of the comparative analysis of the lakes Sjar'ba and Borisovskoye and also Krasnoye, the considerable role of the anthropogenic load and of the increasing of the intensity of the eutrophy of the lake was detected (high amount of phosphates, nitrates and nitrites in the water of the lake Borisovskoye and, as a consequence, considerably more fast process of its eutrophy).
4). During the investigation of the beavers' stream the example of the change of the abiotic environment under the influence of the activity of the creatures was considered. It's a natural process for the biosphere as a dynamic system, unlike the intensive and large-scale changes in the environment caused by the influence of the human activity (lake Borisovskoye).
Thus, it was proved that processes, natural for a pool, differ from ones caused by the anthropogenic load, the influence of the human activity essentially changes an ecosystem of a pool, quite often leading to its death, which emphasizes the necessity of its protection.
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