TAMANOS POBLACIONES SUBREGIONALES (ESTIMADOS)

In 2016, field monitoring was only undertaken in winter, spring and summer. The year- round field monitoring covering the four seasons (winter, spring, summer and autumn) was completed in 2017 with a total of three hundred and sixty samples collected. At each monitoring season/period, ninety composite soil samples were collected within 0–15 cm and 15–30 cm depths across grazing, non-grazing and reed bed land uses/land covers located at the lowlands of the estuarine floodplain (that is, 3 replicates from 5 sampling points within the two depths respectively). The whole plants (shoot and root) within 1 m2 _{around the auger}

hole were collected for determination of biomass (see Figure 5.1). Three mini pits (45 cm x 45 cm x 70 cm) were sunk, one at each land use/land cover, and the morphological properties

101

were described under moist field conditions using Munsell colour chart. The mini pits samples were collected using a knife based on the genetic horizon, starting from the lower horizon to the top. This is to avoid contamination of soil from different horizons, and a soil auger was used to collect an additional 30 cm depths. Soil samples for measurement of bulk density were collected using core samplers. The empty cores had the volume of 106.043 cm3 _and

were driven into the soil until the tubes were level in the ground and bulk samples were collected with the help of a knife without disturbing the soil inside the cores and were transferred into labelled bags and then taken to the laboratory. Plant biomass was collected within the B area (see Figure 5.2) packed into sampling bags and was taken to the University of Salford laboratory.

Figure 5. 2 Sampling techniques for soil and plant biomass (A= soil auger, B= length of quadrat in a 1 m2 _{area, Cs= 5 sampling points bulked to have a composite sample that is} representative and the point where the plant biomass was collected).

5.2.2 Sample preparation

Soil samples were sorted out in the laboratory into labelled envelopes and were oven dried at 40 °C until a constant weight was obtained. Soil samples were crushed and sieved and were passed through a 2 mm sieve for laboratory analyses. Plants samples collected in

102

m2 _{quadrats were weighed fresh (W1) before being oven dried at a maximum temperature of}

70 °Cusing labelled envelopes. The oven dried weight was also recorded (W2) and the water content of the vegetation was calculated as W1 - W2 to get dry weight of the plant W3 in grams (g). The dry weight was presented in kilograms, the area in square metres was converted into hectares and the results were presented in kg/ha. The dry weight value is then used to convert recorded fresh weights from the field to dry weights for the calculation of the plant biomass according to Coombs, Hall, & Long (2014).

5.2.3 Laboratory analysis

Laboratory analyses for physical and chemical properties was carried out using different laboratory protocols, as listed below.

5.2.3.1

Bulk density

The bulk density of the soil was determined using a combination of Gywnne (2004) and Smith (2013) procedures. The core samples from the field were weighed fresh and recorded and then put into the oven at 105 °C and the dried weight was recorded until a constant weight was obtained. The bulk density was calculated as the dry weight of the core samples in grams/the volume of the core samples used in centimetres cubed. The bulk density values were used to calculate the soil carbon stock or pool within the study area by multiplying the bulk density values by the carbon distribution within the study site. The porosity of the study area was also calculated from the bulk density using 1-bulk density/particle density. Particle density is the weight of an individual soil particle per unit volume (g/cm3_{). The particle density of the soil in the temperate region is constant (2.65}

g/cm3_).

5.2.3.2

Particle size distribution

The particle size distribution was determined by the hydrometer method (Bouyoucos, 1951). Fifty grams of air-dried soil samples which passed through a 2 mm sieve were poured into a 250 ml conical flask which served as a dispersion cup, 10 ml of 5% calgon solution was added. The calgon used helps to disperse the soil particles into different sizes or fractions. One hundred millilitres of deionised water were poured into the conical flask and mixed using a mechanical stirrer for 5 minutes. The mixture was then transferred into a 1,000 mL cylinder with all soil particles rinsed into the cylinder with deionised water until the volume in the

103

cylinder was made up to the 1,000 ml mark (see Figure 5.3). The cylinder was sealed using a stopper and then thoroughly mixed. A hydrometer was inserted gently into the mixture in the cylinder and the first hydrometer reading (H1) was recorded at 40 seconds along with the

corresponding temperature reading (T1). The second hydrometer reading (H2) was recorded

with corresponding temperature reading (T2), using a thermometer, after standing for two

hours. H1 gives the weight of the silt plus the clay fractions in the suspension while H2 gives

the clay fraction in the mixture only. The hydrometer was calibrated at 20 °C so any temperature above or below this requires a temperature correction factor. The correction factor is ± 0.3 x t °C (where t= temperature in degrees Celsius). For temperatures above 20 °C, the values will be corrected using + 0.3 x t °C, while temperatures below 20 °C will be corrected with -0.3 x t °C. The textural class of the soil was determined using a textural triangle according to FAO, 2011 guidelines.

Figure 5. 3 Different soil horizon samples used for particle size analysis

5.2.3.3

Soil pH, Eh and EC

Meters were used to measure soil pH, Eh and EC. pH and Eh were measured using an HI-2020 edge meter and EC was measured with a Mettler Toledo EC meter. The procedure involves the weighing of 5 g of 2 mm sieved soil into 150 mL bottles. Twenty-five millilitres of

104

deionised water were added and shaken with a mechanical stirrer for 5 minutes before inserting the pH, Eh and EC probes.

5.2.3.4

Soil organic carbon determination

The soil organic carbon content was determined using the loss on ignition and Walkley-Black methods. The loss on ignition method was carried out in the University of Salford laboratory, the procedures involved have been detailed in Chapter 4. The Walkley & Black (1934) wet oxidation method using 20 mL conc. Sulphuric acid (H2SO4) and 10 ml

potassium dichromate (KCr2O7), later titrated with standard ferrous sulphate solution

according to Nelson and Sommers (1982) was conducted using the external resource of the University of Ibadan laboratory. This method destroyed the carbonates and silicate bound to organic carbon. The data from the two methods were correlated across the sampling locations (GSM, GSM-N and RB) and were positively correlated (R² = 0.9681, R² = 0.7687 and R² = 0.6503 respectively). This is to know how reliable the loss on ignition method is to the Walkley-Black method