BIOLOGY Volume 2 - A Guide to General Biology - 2004

11. QUANTITATIVE ECOLOGY

The ecological principles discussed in the previous chapter are based on Qualitative and quantitative data obtained from studies of animals, plants, microorganisms, and abiotic factors. This chapter focuses on the qualitative and Quantitative Aspects of ecological research proper, outlining the Methods and techniques used to collect, present, and analyze information regarding the biotic and abiotic Components of the environment.

Before embarking on any study—not strictly an ecological one—it is essential to clearly define its Goals and Objectives, as well as the required level of precision for the resulting data. These factors will determine the choice of methods and The Nature of the data collected, which must be adequate to support the anticipated Conclusions. In many cases, such preliminary planning streamlines the work and saves time, money, resources, and effort. However, It is important to emphasize that research designs frequently change as the investigation progresses due to unexpected challenges or the accumulation of new data.

11.1. Methods for Measuring Environmental Factors

The principal environmental factors that must be examined to Complement the Analysis of the biotic component include soil characteristics, hydrology, topography, and climate (humidity, Temperature, light intensity, and wind). Many of the methods used to measure these factors are detailed in the sections below, which describe student-friendly experiments. Others will be discussed only in general terms.

11.1.1. Soil Factors

Soils vary considerably in Structure and Chemical composition. To obtain a General Overview of the soil profile, a vertical trench with smooth walls is excavated. The thickness of various soil particle fractions and the color of the layers (horizons) can be measured directly in the profile, while samples can be simultaneously collected from them for subsequent analysis.

Soil augers and core samplers can also be used (Fig. 11.1). This corkscrew-like tool is screwed into the ground to the desired depth and then withdrawn. Sometimes a single sampling operation yields cores from multiple horizons simultaneously. Soil from the various levels of the cutting HEAD is packed into separate bags for further analysis, each properly labeled with the time, Location, and sampling depth.

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Fig. 11.1. A — simple screw (auger) drill; B — cylindrical drill; C — "Dutch" auger.

Notes

1. Soil samples should not be stored in plastic bags for extended periods, as they may become moldy. Fluctuations in temperature and humidity will affect the soil microflora, which in turn influences soil pH and the chemical forms of available nutrients.

2. The screw (auger) drill (Fig. 11.1, A) is the most convenient tool for a preliminary Determination of the soil profile and, consequently, the soil type. It yields sufficient material for field analysis of pH and textural horizons; however, for more precise determinations of moisture content, organic matter, microflora, and the like, samples collected with "Dutch" or cylindrical augers (Fig. 11.1, B, C) are preferable. Obtaining a sufficient quantity of uncontaminated material from a strictly defined depth using a screw auger is particularly difficult when dealing with coarse-textured soils.

Experiment 11.1. Determination of Water content in a soil sample

Materials and Equipment

Approximately 80 g of soil

Aluminum foil dish

Balance with a readability of 0.1 g

Thermostatically controlled oven

Thermometer graduated up to 150 °С

Desiccator

Tongs

Procedure

1. Weigh the empty foil dish. Record its mass (a).

2. Place the crushed soil sample on it and weigh it. Record the mass (b).

3. Place the dish containing the soil in an oven set to 110 °C for 24 h.

4. Remove the sample from the oven and allow it to cool in a desiccator.

5. Weigh the cooled sample and record its mass.

6. Return the sample to the oven at 110 °C for another 24 h.

7. Repeat steps 4 and 5 until successive weighings yield identical results (constant mass). Record this mass (c).

8. Calculate the percentage of water content in the soil using the formula:

9. Store the soil sample in the desiccator for Experiment 11.2.

Note

The value obtained in this experiment indicates the total water content of the soil (absolute water content). It depends on recent precipitation levels. Other water-related soil properties include field capacity and available soil water (moisture). Field capacity is The amount of water retained in the soil after excess water has drained away due to gravity. To measure this, the soil in an area is watered until standing water remains On the surface for a few minutes. After 48 h, a sample is taken for determination and processed as described above. Available water is the moisture that plant roots are able to absorb. It can be determined by drying a weighed sample to a constant mass at room temperature. The difference between the moist and dry masses represents the amount of available water.

Experiment 11.2. Determination of organic matter (humus) content in a soil sample

Materials and Equipment

Dried soil sample from Experiment 11.1 stored in a desiccator

Crucible with lid

Tripod, Bunsen burner, asbestos mat, clay triangle

Desiccator

Crucible tongs

Procedure

1. Strongly heat the covered crucible over a burner to ensure it is completely dry. After letting it cool in a desiccator, weigh it and record its mass (a).

2. Place the dried soil sample (obtained from Experiment 11.1 and stored in the desiccator) into the crucible and weigh them together. Record the mass (b).

3. Ignite the soil sample in the covered crucible for 1 h (the crucible should become red-hot) to burn off all organic matter. Allow it to cool for 10 min and place it in the desiccator.

4. Weigh the cooled crucible containing the sample.

5. Repeat steps 3 and 4 until a constant mass is reached. Record this mass (c).

6. Calculate the percentage of organic matter using the formula:

7. Repeat this experiment with soil samples taken from different locations to demonstrate that varying soils contain unequal amounts of organic matter.

Note

The organic matter content determined in this experiment refers to dry soil rather than moist (fresh) soil. Using the data from Experiment 11.1, this value can also be recalculated for fresh soil.

11.1. When analyzing a fresh soil sample weighing 60 g, the following results were obtained. After repeated heating at 110 C and cooling in a desiccator, its constant dry mass was 45 g. Then, after repeated ignition in a crucible and cooling in a desiccator, its new mass was 30 g. Calculate the absolute moisture content of the initial sample and its organic matter content (i.e., in the fresh soil).

Experiment 11.3. Determining the air content in a soil sample

Materials and equipment

Tin can with a volume of approximately 200 ml

Beaker with a volume of approximately 500 ml

Water

100 ml graduated cylinder

Marker

Drill bit

Metal probe

Procedure

1. Place the tin can, open end up, into the beaker and fill the beaker with water until the level is above the rim of the can. Mark the water level in the beaker using the marker.

2. Carefully remove the can containing water and measure the volume of this water using the graduated cylinder. Record the result (a). The water level in the beaker will naturally drop.

3. Use a drill bit to make approximately 8 small holes in the bottom of the can.

4. Clear a patch of soil of vegetation and press the can into it, open end first, until earth appears through the holes in the bottom. Carefully dig out the can, turn it over, and remove any excess soil protruding above the rim of the can.

5. Place the soil-filled can back into the beaker of water, open end up, and loosen the soil to allow trapped air to escape more rapidly.

6. The water level in the beaker will decrease as water penetrates the can, displacing the air from the soil inside.

7. Add water from the graduated cylinder back into the beaker until it reaches the original level marked with the marker. Record the volume of water added (b).

8. Calculate the percentage of air (by volume) in the soil sample using the formula:

(b/а) х 100%

9. Repeat this experiment using soil from different locations.

Experiment 11.4. Determining the approximate proportion of various solid particles in a soil sample (i.e., determining its mechanical composition)

Materials and equipment

500 ml graduated cylinder

100 ml soil sample

300 ml water

Procedure

1. Pour the soil into the graduated cylinder and add water.

2. Shake the cylinder vigorously.

3. Allow the mixture to settle for 48 h. Once the soil has settled, different fractions differing in particle density and surface area will be clearly visible.

4. Determine the volume of the various particle-size fractions of the sample using the graduation marks on the cylinder.

Results

A clear distinction between the soil components will be noticeable. Organic matter will remain floating on the surface, some of the clay will remain suspended, larger clay particles will settle on top of the sand layer, and pebbles will be at the very bottom.

Experiment 11.5. Determining the pH of a soil sample

Materials and equipment

Long test tube (145 mm) with a stopper

Test tube rack

Barium sulfate

BDH universal indicator solution and accompanying color chart

Soil sample

Spatula

Distilled water

10 ml pipette

Procedure

1. Add soil to the test tube to a depth of approximately 1 cm and add an equal amount of barium sulfate, which will cause the suspended clay particles to flocculate.

2. Add 10 ml of distilled water and 5 ml of BDH universal indicator solution. Stopper the tube, shake vigorously, and allow the contents to settle for 5 min.

3. Compare the color of the liquid in the test tube with the BDH color chart and determine the corresponding pH value.

4. Repeat this experiment using soil samples from different locations.

Note

When analyzing soil, pH is one of the most critical parameters. Despite its straightforward measurement, the pH value depends on a multitude of interacting factors and provides insight into the soil's nutrient content; furthermore, it indicates which plant species (and consequently animals) can thrive in such soils. Acidic soils tend to be less nutrient-rich due to their lower cation-retention capacity.