The assessment of water-extractable organic matter using an autoclave can provide useful information on physical, chemical, and biological changes within the soil. The present study used virgin forest soils from Chini Forest Reserve, Langkawi Island, and Kenyir Forest Reserve (Malaysia), extracted using different extraction methods. The dissolved organic carbon (DOC), total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and ammonium-nitrate content were higher in the autoclave treatments, up to 3.0, 1.3, 1.2, and 1.4 times more than by natural extraction (extracted for 24 h at room temperature). Overall, the highest extractable DOC, TDN, TDP, ammonium and nitrate could be seen under autoclaved conditions 121 °C 2×, up to 146.74 mg C/L, 8.97 mg N/L, 0.23 mg P/L, 5.43 mg N mg/L and 3.47 N mg/L, respectively. The soil extracts became slightly acidic with a higher temperature and longer duration. Similar trends were observed in the humic and nonhumic substances, where different types of soil extract treatments influenced the concentrations of the fractions. Different soil extraction methods can provide further details, thus widening the application of soil extracts, especially in microbes.

Microalgae are widely utilized in commercial industries. The addition of a modified artificial medium (soil extract) could enhance their growth. Soil extract collected from the Raja Musa peat swamp and mineral soil from the Ayer Hitam Forest Reserve (AHFR), Selangor, Malaysia, were treated using various extraction methods. Carteria radiosa PHG2-A01, Neochloris conjuncta, and Nephrochlamys subsolitaria were grown in microplates at 25 °C, light intensity 33.75 µmol photons m⁻²s⁻¹ for 9 days. N. conjuncta dominated the growth in 121 °C twice extraction method AFHR samples, with 47.17% increment. The highest concentrations of ammonia and nitrate were detected in the medium with soil extract treated with 121 °C twice extraction method, yielding the concentrations of 2 mg NL⁻¹ and 35 mg NL⁻¹ for ammonia and nitrate of RM soil and 2 mg NL⁻¹ and 2.85 mg NL⁻¹ for the AH soil. These extracts are proved successful as a microalgal growth stimulant, increasing revenue and the need for enriched medium. The high rate of nutrient recovery has the potential to serve as a growth promoter for microalgae.

The study of organic matter characterisation in coastal sediment is useful for understanding how dissolved organic matter (DOM) reactivity influences the fate of pollutants in the aquatic environment. However, there is little information available on the structural properties of DOM in coastal sediment. Chemical analysis, UV-Visible (UV-Vis) absorbance, fluorescence, and Fourier-transform infrared (FTIR) spectroscopy were used in this work to characterise and compare the components of water-extractable organic matter (WEOM) fractions from sediment from an estuary, a coastal area, and a port in Peninsular Malaysia, Malaysia. The elemental analysis (H/C and C/N ratios) of the three samples differed, which coincided with the findings of optical indices estimated from UV-Visible and fluorescent spectroscopy analyses. WEOM had an average output of 7.05 to 8.47 mg/L and was very dominating with heavy fraction organic carbon (HFOC). In DOM-KS and DOM-K sediments, the allochthonous component with a high degree of condensation and the aromatic compound was the dominating composition. Meanwhile, the DOM-KT possessed a high autochthonous composition as well as carboxylic and phenolic content. Correlation analysis indicates that the aromaticity index SUVA₂₅₄ and humification index (HIX) have positive correlations. The combined results of the chemical and spectroscopic analyses indicate that different coastal ecosystems, with the integration of various human and land activities, produce variations in DOM in the coastal area.