Biological soil activity and its indicators - Ground science

Biological soil activity and its indicators

Biological soil activity is its ability to create relatively favorable conditions for the development and life of biota in them. It is expressed by the total manifestation of the activity of biochemical processes and characterizes the intensity and direction of the processes of the transformation of substances and energy in the soil that occur under the influence of living organisms. Biological activity of soils determines the danger of processes of destruction of soil organic materials and structural elements. The gradual decrease in the strength of soils at the base of structures, caused by the vital activity of micro- and macro-organisms, leads to a decrease in their bearing capacity, additional and often uneven precipitation, which can cause the structures to go into emergency and pre-emergency conditions. The main biological degradants of organics and building structures contained in the ground include representatives of the following biological groups: bacteria, fungi, including micromycetes, algae, lichens, mosses, self-sowing grasses and trees. The listed organisms are capable of damaging materials due to chemical and mechanical effects, participation in the electrochemical corrosion process. It is necessary to distinguish macro- and microbiological activity of the soil. The first reflects the ability of the soil to create conditions for the development of macroorganisms of Oribs, plants, animals), in the background - for the development of microorganisms. Accordingly, distinguish between micro- and macrobiodextures.

Mechanical impact on soils and materials of structures can have, both micro- and macroorganisms. Microorganisms (bacteria, micromycetes, microalgae), getting into cracks/microcracks in building materials, at the junction of various structures, under favorable conditions begin to develop, accumulating biomass. Mycelia of many fungi can penetrate into microcracks at any depth. Self-sowing grasses and trees that have settled on the foundations are capable of destroying the foundation, walling, etc., of its root system, etc. Biological damage to commercial wood, wooden buildings and building structures causes wood-destroying fungi and insects that use cellulose as a food source, lignin and other components.

Chemical impact on organic soils and building materials are mainly microorganisms: bacteria, actinomycetes, micromycetes, microalgae, lichens. As a rule, communities of microorganisms take part in the destruction. Moreover, some species destroy the protective layer, while others - the basic material of the structure. Communities can include microorganisms that do not directly participate in the destruction of materials, but play an important role in the life of the community and contribute to the accumulation of general biomass. In the course of their life microorganisms produce enzymes, ketones, alcohols and such aggressive metabolites as acids - organic (oxalic, glycolic, succinic, acetic, etc.) and inorganic (nitric, sulfuric, etc.), as well as ammonia, hydrogen sulphide, methane, carbon dioxide. The products of their vital activity can play the role of powerful catalysts of chemical processes, accelerating chemical reactions several times. Some microorganisms, for example thionic bacteria , can increase the reaction rate by hundreds of thousands and even millions of times. Many types of microorganisms are able to sorb moisture from the air, release water as a metabolite, which leads to excessive moistening of the material, dissolution of pollutants, and the development of other microorganisms. Some types of microorganisms (actinomycetes, molds and other fungi) that develop on building materials are related to pathogenic or conditionally pathogenic organisms and can have a negative impact on people's health when their spores or products of life enter their air environment.

Most microbes colonize materials in the presence of oxygen (aerobic organisms). However, many microorganisms are well adapted to existence in the absence of oxygen (anaerobes). Most of them play an important role in the destructive processes occurring in the underground space of the city.

The microorganisms are most active in organic and organic mineral soils, and in the near-surface layer ammonifying bacterium-aeorobes, spore bacteria, bacteria, digesting mineral forms of nitrogen with an organic carbon source, actinomycetes, nitrifying bacteria, oligonitrophils, mold fungi, denitrifying bacteria. Ammonifying bacteria predominate, which begin the decomposition process of organic nitrogen, oligonitrophilic and assimilate mineral nitrogen at an organic carbon source. The number of bacteria in these three groups under aerobic conditions is significantly increased. Neporobrazuyuschie ammonifying bacteria participate in the destruction of available forms of organic matter in peat, spore-forming enter the process at later stages. As for nitrifiers, whose activity is related to the oxidation of ammonia forms of nitrogen to nitrite and nitrate, their quantity determines the ammonification rate - the more nitrifiers, the less ammonifying. Nitrification in strongly decomposed peat is slower than in a poorly mineralized diet of weakly decomposed peat [68]. The number of different physiological groups of bacteria in peat and hacked sandy-argillaceous sediments can be estimated from the data of Table. 2.26. Approximate data of the study of bog biogeocenosis, given in Table. 2.27, indicate a very significant biomass in peat and a variety of different types of microorganisms.

Table 2.26

Number of bacteria in lowland bogs [118]

Forms of bacteria

Physiological groups

Number, cells/g



10 * ... 10









10 "


Nitrifying substances



10 ... 10 -



Table 2.27

The weight of microbial biomass and the ratio of its components in various peatlands [118]

Dry biomass weight, t/ha

Microbial biomass. %

Peat type

Peatland power, m








High ash














































Note. Recalculation of dry biomass: a) by 1.0 m; b) on the whole indicated thickness of peat.

Humus is formed in warm periods of the year, when the surface of soils or peat dries, the aeration is improved, the activity of microorganisms participating in the decomposition of plant remains is activated, while in the wet periods their activity is slowed down. This largely explains the incomplete decomposition of plant remains in conditions of high humidity of the substrate, as a result of which peat is formed. In humps and mochezhinah, where the surface does not dry out even in droughty years, humus accumulates slowly. Some researchers believe that under these conditions, humus is formed from the above-water parts of plants, and possibly also from the vegetation of neighboring ridges.

The activity of aerobic microorganisms is due to climatic features: in drier periods, their vital activity becomes more intense, they multiply faster, and as a result, peat of higher degree of decomposition is deposited; in wet periods, the activity of aerobic microorganisms decreases, then less decomposed peat is deposited. There are cases when the deepest layers of peat have a lower degree of decomposition than the higher layers, as a result of the water cut in the deposit at that stage of development. Thus, climate change causes uneven, spasmodic peat formation, which is typical of the upper marshes that receive the main food with atmospheric precipitation. In the low-lying deposits there is no spasmodic distribution of peats according to the degree of decomposition, which is explained by a more stable ground feeding. A weakly acidic and close to neutral reaction of the environment and a sufficient supply of mineral nutrition favor the development of a rich and diverse microflora and soil fauna. The maximum number of microorganisms is concentrated in the upper peat layer [51].

Biological activity of the soil is estimated by both direct and indirect indicators. A direct indicator of the biological activity of the soil is the amount (concentration) of biota of one type or another in the soil. The number of macroorganisms , including large animals, is estimated by the number of individuals (specimens) living on a unit area or per unit volume of soil (ind./ha, specimen/m, etc.). The number of microorganisms in the soil is estimated in thousands of copies per 1 g of solid ground phase; for other organisms, the relative content of living phyto- or zoomass of organisms per unit volume of soil (mg/cm, etc.) is determined. The main biodestructors are:

iron bacteria are bacteria that can oxidize reduced iron compounds, which can be divided into two groups. The first group includes iron bacteria, for which the oxidation of ferrous iron serves as a source of energy, and the only source of carbon is CO :. The second group consists of iron bacteria, which also oxidize ferrous iron, but this process serves as a detoxification method for H2O2 formed during respiration. There are several types of iron bacteria, which differ in the ability to deposit iron oxides on the surface of cells; some bacteria accumulate not only iron oxides, but also manganese;

nitrifying bacteria - aerobic bacteria, cause corrosion of metals and damage to porous building materials as a result of the formation of nitric acid in the oxidation of ammonia and/or ammonium;

thionic bacteria - oxidize various reduced sulfur compounds to sulfates, using the evolved energy for their development. Under aerobic conditions, they oxidize sulfur, metal sulfides, ferrous sulphate, sulfuric acid. Some sulfur bacteria convert ferrous sulphate to oxide, which is a more active oxidant than sulfuric acid;

sulfate-reducing (desulfating) bacteria - the main causative agents of anaerobic corrosion of steel, iron and aluminum. The mechanism of the corrosion of metals they cause is the stimulation of cathodic depolarization by solid iron sulfides as a result of the vital activity of these bacteria or because of their consumption of polarized hydrogen.

Bacteria - this small microorganisms (0,1 ... 10,0 microns), devoid of a formed nucleus; for nutrition use materials of both organic and inorganic nature; some groups decompose materials in an oxygen-free environment. When carrying out bacteriological analysis, two complementary methods should be used: quantitative and qualitative. This establishes the belonging of bacteria to certain groups, and also assess their content in 1 gram of the test material by direct sowing on a solid nutrient medium or by the the most probable numbers (NMR) when sowing into specific liquid storage media. The result is expressed in CFU/r for direct sowing and kl/g - for the NMH method.

Methods of conducting bacteriological analysis [118]. In accordance with the rules of aseptic, the sample in 1 g is crushed in a sterile mortar and transferred to a bottle with 10 ml of sterile saline. The bottle is shaken thoroughly for at least 15 minutes. 1 ml of the resulting suspension corresponds to 0.1 g of starting material. A number of consecutive tenfold dilutions from 10 to 10 are prepared from the suspension.

Determination of the total number of bacteria . The total number of bacteria is usually understood to mean the amount of mesophilic aerobic and facultative anaerobic bacteria that can grow when deep-sown on a ready commercial nutrient agar made from fish oil hydrolyzate.

Add 1 ml of the initial suspension and dilute it from 10 to 10 in empty sterile Petri dishes in duplicate. In each cup, 8 ... 12 ml of nutrient agar melted and cooled to 45 ° C are poured. Quickly mix the contents of the cups, evenly distributing the bacterial suspension in a nutrient medium. After solidification of the medium, the plates with crops are placed in a thermostat upside down and incubated at a temperature of 25 ... 28 ° C for 3-5 days. Count only the colonies of bacteria, not including the total number of colony mold fungi. The result is averaged and counted for 1 gram of the test material.

To determine nitrifying bacteria , use the Vinogradskoy medium of the following composition (g/l): (NH4) 2 S0 4 - 2.0; To 2 HP0 4 - 1.0; MgS0 4 7H 2 0 - 0.4; FeS0 4 -7H 2 0 - 0.4; NaCl - 2.0; sterile water - 1 liter. The medium is poured into 15 ml flasks. The thickness of the medium layer should not be more than 1.0 ... 1.5 cm. A small amount of chalk is introduced into each flask at the tip of the spatula. Sowing is carried out in a volume of 1 ml from the initial suspension and its dilutions 10 '; 10, 10 * in triplicate. Incubation of crops is carried out at 28 ... 30 ° C for three weeks. The presence of nitrifying bacteria is established by the appearance of nitrates. Detection of nitrates is carried out with diphenylamine. To do this, 2 g of diphenylamine are dissolved in 100 ml of concentrated sulfuric acid, then 20 ml of water are added. To 1 drop of culture, applied to a white ceramic plate, add a drop of reagent. The presence of nitrates causes the appearance of intense blue staining. The content of nitrifying bacteria is determined as the most probable number (kl/g of the material under study) according to the statistical tables of Mac-Credit.

Harisson's medium is used to determine the iron bacteria . Solution 1 (g/l): (NH 4 ) 2 S0 4 - 2.0; KC1 - 0.1; To 2 P0 4 - 0.25; MgS0 4 -7H 2 0 - 0.25; Ca (N0 3 ) 2 - 0.01; distilled water; pH 2.0 ... .4.0. Solution 2 (g/l): agarose - 8.0; distilled water. Solution 3 (g/l): FeS0 4 • H 2 0 - 40.0; distilled water. A mixture of molten agarose and solution 1 (1: 1) is prepared, cooled to 45 ° C, solution 3 is added at a final concentration of 1% FeS0 4 and the medium is poured into Petri dishes stored at 10 ° C . The inoculum (0.1 ml of the native suspension and dilutions thereof up to 10 ") is introduced into a 0.3% agarose solution (60 mg of agarose is added to 10 ml of water, sterilized and mixed with 10 ml of sterile solution 1, 0.5 ml of solution 3, preheated to 45 ° C) and poured into the cups with a second layer. The crops are incubated for 1-4 weeks. Count the colonies of iron bacteria bright orange or yellow. The result is expressed as the amount of CFU of iron bacteria in 1 g of starting material.

To determine thiobacilli use Beijerink's medium (g/l): Na 2 S0 4 - 5, 0; NH4CI = 0.1; NaHC0 3 - 1.0; Na 2 HP0 4 -2H 2 0 - 2.0; MgCl 2 -6H 2 0 - 0.1; FeS0 4 H 2 0 - traces; sterile water. Thiosulphate and bicarbonate are sterilized separately, dissolved in a small amount of water, and after cooling, they are added to the solution of the remaining salts together with FeS0 4 . The pH of the medium is 9.2-9.4. The initial suspension and its dilutions up to 10 are inoculated into a ready-made medium in a sin repetition. In the presence of thiobacteria in the inoculum, the medium becomes turbid after 2-4 days, and a molecular sulfur film appears on this surface, which is formed during the oxidation of thiosulphate. The content of thiobacilli is determined in the form of the most probable number (kl/g of the test material) according to the tables of Mac-Credit.

To determine the sulfate of reducing bacteria use the Postgate environment B with sediment, since the initial development of bacteria occurs in the sediment. Postgate Wednesday V (g/l): NaCl-1; To 2 НР0 4 - 0.5; NH 4 C1 - 1.0; CaS0 4 -2H 2 0 - 1.0; MgS0 4 -7H 2 0 - 2.0; sodium lactate (70%) - 3.5; yeast extract - 1.0; ascorbic acid 1.0; Thioglycolic acid 1.0; FeS0 4 -7H 2 0 - 0.5; distilled water. Ascorbic and thioglycolic acid 'in the form of 5% sterile solutions and ferric sulphate in 1% hydrochloric acid are added to the nutrient medium immediately before sowing. The reaction medium is adjusted to pi I 7.5 by neutralizing with a 5% solution of hydrochloric acid or sodium carbonate. The medium must have a low oxidation-reduction potential, which at the very beginning of cultivation is created by adding a reducing agent, for example sodium sulphide, at a concentration of 1 mM. The accumulation cultures are best mixed in 30 to 60 ml bottles with glass stoppers, which are lubricated before autoclaving with silicone grease. Infection produces 0.1 ... 1.0 g of material. The bottle is filled with medium so that after infection under the stopper there are no air bubbles left. The content of sulfate-reducing bacteria is determined in the form of the most probable number (kl/g of the test material) according to the tables of McCabe.

In some cases, when it is necessary to determine anaerobic organisms to a species, it is advisable to conduct a study of microorganisms on the surface of the material using the Scanning Electron Microscopy (SEM) method. Samples of damaged material, 0.5 ... 1.0 cm x 0.5 ... 1.0 cm in size, should be examined under a binocular magnifier. The criterion for selecting material for the SEM analysis is the presence of a variety of biological structures on its surface. The selected samples are suitably kept in a moist chamber for 24 hours in order to activate microorganisms, after which the material is fixed and analyzed in a scanning electron microscope in the magnification range from 100 to 10,000.

Accumulation of microorganisms and products of their vital activity most actively affects the physicochemical properties of sand deposits. In the zone of intensive and long-term contamination by sewage in anaerobic conditions due to colmatization of pore space by bacterial mass, low permeability of medium-grained and fine-grained sands is formed. The gradual increase of the total protein (SB) contributes to a significant decrease in the filtration coefficient (Xgf, m/day) of sand (Table 2.28). Removal of biomass during low-temperature calcination led to an increase in cph up to 4 ... 25 m/day, which fully corresponds to their granulometric composition.

Cells of microorganisms and their metabolic products are actively sorbed on mineral particles of dispersed rocks, forming biofilms. In this case, the intensity of the molecular interaction of mineral particles decreases due to the screening action of biofilms, which also play the role of a kind of lubricant, contributing to a decrease in the strength of the soils, their permeability and water loss. In sandy soils, in which active microbiological activity is noted, floating properties may appear. An increase in the content of gases in the pore water of the sands accelerates their transition to the "heavy gas-saturated liquid" state. Even insignificant accumulation of sparingly soluble gases in sandy-clay soils (СН 4 , N 2 , Н 2 ), formed as a result of biochemical generation, promotes decompression soil and change the stress-strain state, creating conditions for their transition to a mobile state. In microbiologically affected sands, the angle of internal friction is reduced to 12 ° or less.

Table 2.28

Dependence of the sand filtration coefficient on the amount of total protein [1 18]

With B. μg/g







kf, m/day


10 ^ _

2 • 10

8 10 -5

10 ~

5 • 10 _

Simultaneous effects of anaerobic reducing conditions and microbes significantly affect the composition and physico-mechanical properties of clay soils. The formation of reducing conditions in conjunction with microbial activity predetermines the destruction of cementation bonds due to the compounds of ferric iron, which serve as the main cementitious material. Trivalent iron has an aggregating effect, its reduction promotes the transition of its compounds into soluble forms of ferrous iron, as well as the dispersion of clay aggregates in soils and, accordingly, their hydrophilicity, the reduction in filtration capacity, strength and modulus of general deformation (Table 2.29) . In the formation of clays in an oxygen-free environment, these deposits show a pronounced tendency to develop plastic deformations. In clay soils under the marshes all the signs of gleying appear (the process of transformation of soils and soils under the influence of microorganisms under anaerobic conditions): dark gray, gray, bluish, greenish shades of soil due to the restoration of iron and other elements with variable valence, higher degree of dispersion , an abnormal microbiological affection, in some cases an increased content of biochemical gases.

Table 2.29

Indicators of the mechanical properties of clay moraine as a function of oxidation-reduction conditions and microbial damage [118]


Total deformation module MPa

Internal friction angle & lt; />. degrees.

Strength s. MPa

In an oxidizing environment, with the background content of the SB & lt; 30 μg/g

& gt; 25

& gt; 15

0.I5 ... 0.22

In a reducing environment with SB more than 80 μg/g


& lt; 10


Decomposition processes occur during storage of samples and in laboratory tests. If the compression experiments last 1-2 months at room temperature, the sample will have a different degree of decomposition and physical and mechanical properties than in natural conditions. M.P. Petrov and P.A. Kostychev [65] found that the optimal temperature for the vital activity of most bacteria is 32 ... 36 ° C and humidity 60 ... 80% of the total moisture capacity, and even at a temperature of -2 to -5 ° C the decomposition process continues. Apparently, the processes of decomposition of organic matter and cause a significant extent duration of the experiment. In the works of PA. Konovalov [65] special attention is paid to these processes and their effect on the self-compacting of ground soils. The author notes that the rate of decomposition is particularly high during the first three to six months, and the rate under aerobic conditions (both in sandy and clayey soils) was higher by 10 ... 20% than under anaerobic conditions. For 2 years in decayed clay and sandy soils, under aerobic conditions, 56 and 70% of organic substances were disintegrated, in anaerobic conditions -45 and 56%. Further, the rate of decomposition decreases because of the organic acids formed, which considerably slow down the process. P.A. Konovalov recommends taking into account the additional porosity formed during the decomposition, to predict the precipitation from humification.

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