Variant – 24

1. Normalization of the harmful substances, disposal with sewage.

Before disposal in a pond sewage should be cleaned up to the highest degree because under effect of natural factors the secondary products of decomposition may be formed, negatively influencing quality of water.

To carry out process it is necessary, firstly, after sewage disposal, the presence in the pond of the soluble oxygen. Chemical or bacterial oxidation of the organic substances contained in the sewage, results in decrease in concentration of oxygen, dissolved in water. (1 liter of H2O contains 8-9 sm3 of O2. Organic substances interacting with dissolved O2 are oxidized to СО2 and Н2О. Therefore, the parameter was entered allowing estimating the total quantity of pollution in water according to absorption of О2. Such parameter is biochemical demand of oxygen (BOD). BOD is equaled to quantity of O2. Depending on time there are BOD5 (five-day), BOD20 (twenty-day), BOD (full), in this case the oxidation is finished.

According to « Rules of surface waters protection from pollution » the water quality of a reservoir after sewage disposal should meet to the following basic requirements: quantity of dissolved О2 should be not less than 4 mg / l; BOD (full) at 20 С is not higher than 3 mg/l. The contents of weighed substances in water after sewage discharge should not be increased more than in 0,25 and 0,75 mg /l for reservoirs I and II correspondently, a mineral sediment is no more than 100 mg /l; including chlorides is 350, sulfates is 500 mg / l; odour and smacks of water should absent; a surface of water should not contain the floating impurities, films, spots, oils, oil products, poisonous substances.

2. Biocenosis

A group of organisms in a self-sufficient community naturally occupying a small area with a uniform environment throughout. In the field of paleontology, it is one of three types of fossil communities, which depends on the condition and completeness of the community when found. Biocenosis is the most complete type, able to offer the most information about what the community was like when it was alive.

(biocoenose, biocenose, biotic community, biological community, ecological community), coined by Karl Möbius in 1877, describes the interacting organisms living together in a habitat. This term is rarely used in English, as this concept has not been popularized in Anglophone countries. Instead, English-speaking scientists normally use the terms ecosystems or communities.

Descriptors in an ecosystem are:

• Zoocoenosis for the faunal community,

• Phytocoenosis for the floral community,

• Microbiocoenosis for the microbial community.

Ecosystems

An ecosystem, as originally defined by Tansley (1935), is a biotic community (or biocoenosis) along with its physical environment (or biotope). In ecological studies, biocoenosis is the emphasis on relationships between species in an area. These relationships are an additional consideration to the interaction of each species with its physical environment.

Leading component in the biocoenosis is phytocoenosis. It defines what there will be zoocoenosis and microbiocoenosis.

3. Death rate

Dynamic parameters of community reflect the processes proceeding in the community for certain time interval. The basic parameters from them: birth rate, death rate, growth rate of the community.

Death rate (velocity of the death rate) is a number of the species who have lost in the community for a time unit (from predators, illnesses, an old age and other reasons). Death rate is a size return to the birth rate.

There are the minimal and actual death rates. The minimal death rate is a minimally possible size of the death rate. Actual death rate is a real size of the death rate.

There are absolute and specific death rates. The absolute (general) death rate or death rate is defined by the attitude: dN / dt.

Where dN is a species number, who have lost for a time interval dt.

Specific death rate (d) is a relation of death rate to initial number (Ndt):

D = dN / (Ndt).