Chapter 2 Bioindication of soil condition

Soil is the only component of the landscape that results from the interaction of all its other components: rocks, climate, natural waters, vegetation, microorganisms and animals. Being the main depositing medium, soils themselves can be considered as an integral indicator of pollution of the natural-territorial complex.

Contaminated soils are sources of secondary pollution of the surface layer of air, surface and ground waters; plants absorb minerals from the soil, involving them in the biological cycle. Thus, the soil cover determines the migration of chemical elements along the food chain, so the study of its state is an essential part of the work on assessing the impact of anthropogenic factors on the natural environment.

The main characteristics of soils that are the object of bioindication are acidity, mechanical composition, humidity, nutrient content. The degree of accumulation of certain toxic substances in plants (accumulative bioindication) is used to judge the degree of soil contamination by them.

Bioindication of the processes of acidification, neutralization or alkalization of soil solutions is carried out using phytoindicators of soil acidity, as well as changes in the species composition of the biocenosis and its dynamics over time. In relation to the pH of the environment, acidophiles are isolated – plants growing on acidic soils; basiphylls – plants growing on alkaline soils; neutrophils are soil plants with a neutral reaction.

Depending on the attitude to the abundance of nutrients in soils, plants are divided into oligotrophs – plants growing on poor soils; mesotrophs – plants growing on soils with an average level of nutrients; megatrophs – plants growing on rich soils.

Depending on the attitude to soil salinity, plants are divided into halophytes – plants of saline habitats and halophobes (glycophytes) – plant species that avoid saline soils. There are facultative and obligate halophytes, euryhaline and stenohaline species that can grow in conditions of a wide or narrow amplitude of salt concentration and tolerate salinity of different composition or adapted to a certain type of salinity.

Plants can serve as indicators of the increased content of various elements in the soil. Allocate plants calcephiles and silicophiles . In areas with a natural high content of heavy metals, metallophyte floras (copper-cobalt, etc.) appear, consisting of specific species. (Lyashenko O.A., 2012).

Soil animals are also used to indicate the conditions of the soil environment. Communities of large invertebrates are especially valuable and convenient: earthworms, insect larvae, centipedes, etc. Reproduction of earthworms largely depends on the presence of pesticides, heavy metals and other pollutants in the processed substrate.

There is no single method for accounting for all groups of animals living in the soil; the methods of work are determined by the goals of the expert study and the characteristics of the objects under study. (Baeva Yu.I. et al., 2016).

Usually, soil excavation is used to extract pedobionts from the soil. On the territory to be surveyed, at least four test sites 0.25 m 2 in size are laid (the length of each side is 0.5 m, the depth of the excavation depends on soil conditions and possibilities). The distance between the excavations can be different, but within 5-10 m. From the laid excavation, the soil is selected in layers or according to genetic horizons, carefully rubbed with fingers, the clods are kneaded and all animals found without exception are removed. Animals selected from the soil are placed in jars or test tubes with a fixative liquid. (Baeva Yu.I. et al., 2016).

One of the fastest methods of fixation is scalding the animals in boiling water and, after cooling, placing them in 96 ° alcohol. A few days later, the animals are transferred to alcohol of a lower strength (70 o ) for long-term storage. It fixes insect larvae well without preheating and protects them from darkening. The liquid of the following composition: concentrated formalin 5-6 parts, ethyl alcohol 96 about – 15 parts, glacial acetic acid – 2 parts, distilled water – 30 parts. After 10 days, animals from this liquid should be transferred to 70 % alcohol for storage.

To fix earthworms, the following technique is used: worms selected from the soil are placed in a jar of clean water and rinsed while holding with tweezers; in this way, the worms are washed from soil and mucus. Washed worms are placed 5-6 pieces in a bath with a weak solution of formalin (1-2%). When the worms stop moving, they are wiped with cotton wool and transferred to a 5% formalin solution. (Geltser Yu.G., 1986).

The test tubes are stored in a dark place, since when exposed to sunlight, the contents may become discolored or softened, thereby becoming unsuitable for further research.

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