Chapter 2: The effects of oil contamination on growth of Avicennia marina,
2.2 Materials and methods
Glasshouse study
2.2.1. Growth conditions
Propagules of A. marina and B. gymnorrhiza, were collected from the Beachwood Mangroves Nature Reserve (29° 48ʹ S, 31° 02ʹ E) and those of R. mucronata from the Isipingo estuary (29° 59ʹ S, 30° 56ʹ E) in March 2010. After collection, A. marina propagules were placed in water and pericarps allowed to shed naturally (24 hours).
Propagules of A. marina were planted in 17 cm diameter x 15 cm height and those of B. gymnorrhiza and R. mucronata in 24 cm x 21 cm plastic pots. All pots contained a mixture of sand, potting soil and compost (1:2:1). Pots were watered daily with tap water and once monthly with 10% seawater. All pots were maintained in a glasshouse for 13 months. The temperature in the glasshouse during the experimental period was 25 °C (day) and 18 °C (night).
In this study, propagules of A. marina, with or without pericarps were subjected to one of five treatments:
i. control (C) – propagules with pericarps were planted in the sediment.
ii. SO – propagules without pericarps were planted in sediment to which 50 ml of oil were carefully poured onto the soil surface.
iii. PO1 – propagules with pericarps were completely dipped in oil and planted in sediment.
iv. PO2 – propagules without pericarps were completely dipped in oil and planted in sediment.
v. ½PO – ½ of the propagule without a pericarp was dipped in oil using a pair of forceps.
Propagules of B. gymnorrhiza (about 12.5 ± 0.5 cm in height), and R. mucronata (about 22 ± 2 cm in height) were subjected to one of three treatments:
i. control (C) – untreated propagules were planted in the sediment.
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ii. SO – propagules were planted in sediment to which 50 ml of oil were carefully poured onto the soil surface.
iii. ⅔PO – ⅔ of the propagule from the base/radical end was dipped in oil using a pair of forceps.
There were four replications per treatment for all species. The bunker fuel oil used was obtained from FFS Refineries (Pty) Ltd, Durban. The properties of this oil are indicated in Table 2.1.
2.2.2 Plant growth measurements
Measurements were made of plant height and number of leaves monthly.
2.2.3 Chlorophyll content
Measurements of leaf chlorophyll content (five per replicate) began four months after commencement of treatments, and monthly thereafter. Chlorophyll content was determined with a hand-held chlorophyll absorbance meter (CCM-200, Opti Sciences, Tyngsboro, MA, USA). The CCM-200 is a cost-effective instrument that provides a non- destructive and reliable estimate of leaf chlorophyll content (Naidoo et al., 2010;
Khaleghi et al., 2012; Flores-de-Santiago et al., 2013).
Table 2.1
Specifications of bunker fuel 150 (FFS Refiners, 2002)
Unit Value
Energy content (gross) kJ kgˉ¹ 43,400
Viscosity @ 50 °C cSt 140
Total sulphur as S mass% 3.2
Pour point °C -10
Flashpoint (PMCC) °C 95
Water content mass% 0.45
Density @ 20 °C kg lˉ¹ 0.98
Ash mass% 0.05
20 Field study
Field investigations were undertaken in the Beachwood Mangroves Nature Reserve and Isipingo estuary. The average daily maximum and minimum temperatures for Beachwood were 26 °C and 17 °C and for Isipingo, 27 °C and 16 °C, respectively. The mean annual rainfall is 1228 mm for Beachwood and 1040 mm for Isipingo. Soil characteristics for Beachwood and Isipingo are indicated in Table 2.2. Selected plants were tagged for identification with plastic tape.
2.2.4 Leaf and internode oiling experiment
Healthy, young, naturally occurring, one year old seedlings of A. marina (about 46.5 ± 7 cm in height), B. gymnorrhiza (about 48.5 ± 8 cm in height) and R. mucronata (about 66.5 ± 9 cm in height) were selected for oiling experiments. Two study sites were used, Beachwood and Isipingo, based on the abundance of seedlings present for each species. A. marina (Fig. 2.12A) and B. gymnorrhiza (Fig. 2.13A) seedlings from Beachwood and R. mucronata seedlings from Isipingo (Fig. 2.14) were subjected to one of three treatments:
i. control (C) – plants were untreated.
ii. IO – the second internode from the base of the stem of A. marina (the first internode was too short for oil application) and the first internode from the base of the stem of B.
gymnorrhiza and R. mucronata were oiled.
iii. LO – both surfaces of the last pair of mature leaves directly below the shoot tip of each plant were oiled.
Oil was applied with a paintbrush.
Internodes and leaves of A. marina and B. gymnorrhiza were oiled at the commencement of the experiment in October 2010 and again after 7, 15, 19, 27, 32, and 48 weeks. Initially, leaves were oiled on the adaxial surface at the commencement of the experiment and again after seven weeks. At 15 weeks until the end of the experiment, leaves were oiled on both the adaxial and abaxial surfaces. Internodes and leaves of R. mucronata were oiled at the commencement of the experiment in November 2010 and again after 5, 14, 18, 25, 30 and 48 weeks. Leaves were oiled on the adaxial surface at the commencement of the experiment and again after five
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weeks. At 14 weeks until 48 weeks, leaves were oiled on both the adaxial and abaxial surfaces. There were seven replications per treatment for each species. Measurements of plant height and number of leaves were taken on the same days as the oiling.
2.2.5 Sediment oiling experiment
This investigation was undertaken in the Isipingo estuary. Healthy young, one to two year old seedlings of A. marina (about 110 ± 50 cm in height), B. gymnorrhiza (about 65 ± 6 cm in height) and R. mucronata (about 76 ± 8 cm in height) were selected for oiling experiments. Groups of seedlings of each species were enclosed by 0.5 m radius x 0.5 m height circular perspex sheets (Figs. 2.18 - 2.20). The sheets were pushed into the soil to a depth of 5 cm to prevent loss of oil as the tide receded. The height of the enclosures was adequate to prevent the escape of oil with the rising tide. Control plants were also enclosed like the treatment plots, but no oil was applied. There were nine replications per treatment for A. marina (because of the abundance of A. marina plants in the stand) and four for B. gymnorrhiza and R. mucronata, respectively. Dosage rate was 5 Lmˉ² for all plots. Oil treatments were applied once in June 2011 and monitoring continued until June 2012. Measurements of plant height and number of leaves were taken at 16, 26, 38, 46 and 53 weeks after treatment.
2.2.6 Soil analysis
Soil samples were collected from the experimental sites in Beachwood and Isipingo, placed onto plastic sheets and left to air dry in the glasshouse. After one week, the samples were crushed using a wooden mallet and thereafter passed through a 1 mm sieve. Coarse materials (>1 mm) were discarded. Clay content was analyzed by near- infrared reflectance. Soil pH was measured using a gel-filled combination glass electrode placed in a potassium chloride solution (Manson and Roberts, 2000).
Concentrations of ions were determined by atomic absorption using mid-infrared spectroscopy (Bruker Tensor 27, FTIR Spectrometer with HTS/XT). The instrument detects light (2500 – 15000 nm) reflected by the sample. Carbon and nitrogen contents were analyzed by the Automated Dumas dry combustion method using a LECO CNS 2000 (Leco Corporation, Michigan, USA; Matejovic, 1996). The results of the soil analyses for Beachwood and Isipingo are indicated in Table 2.2
22 2.2.7 Data analyses
Means and standard errors were calculated for all measurements. Resulting data were tested for normality using the Kolmogorov-Smirnov test and subjected to one-way analysis of variance (ANOVA) and Tukey-Kramer multiple comparisons test (P ≤ 0.05) using MINITAB version 16 (Minitab Statistical Software, MINITAB Inc. USA). Other data were subjected to unpaired t-tests to detect for differences between control and oiled treatments.