Microbial Abundance and Nutrient Concentration in Riverine and Coastal Waters of North-East Langkawi

Abstract

We measured both biotic and abiotic variables at 19 stations along the three river systems and also off the Langgun Island in the North-East (NE) Langkawi region. Temperature ranged between 29.8-31.3°C whereas salinity ranged between 22-32. pH was between 7.4 and 8.2 whereas redox potential ranged between -82 to -32. Dissolved oxygen (DO) concentration ranged between 120-280 µM. Both pH and DO concentration were lower upstream of the rivers. For inorganic nutrient concentrations; ammonium (NHâ‚„) ranged between 0.56-4.30 µM, nitrate (NO₃) between 0.31-1.46 µM, nitrite (NOâ‚‚) between 0.04-0.38 µM and silicate (SiOâ‚„) between 1.36-15.23 µM. Of the nitrogen species, NHâ‚„ was dominant, making up to 79% of total dissolved inorganic nitrogen (mean=57%). Total suspended solids (TSS) in the water samples were high, ranging between 270 to 330 mg L⻹ whereas particulate organic matter (POM) constituted a very small component of TSS (<5%, 3.6-14.4 mg L⻹). For biotic variables, chlorophyll a (Chl a) concentration that represented the photoautotrophs present in the water, with the range of 1.49-8.24 µg L⻹. Bacteria ranged between 1.5-5.3×10ⶠcells mL⻹ whereas phototrophic picoplankton and protists ranged between 1.7-4.3×10âµ cells mL⻹ and 0.8-1.6×10â´ cells mL⻹, respectively. Marine bacteria cultured ranged from 4×10² to 1.2×10âµ cfu mL⻹. Although our limited sampling was inadequate to detect controlling factors for bacterial abundance, our study showed that bacteria could have caused the lower DO concentration in the rivers in NE Langkawi