Search

Estuaries have strong physicochemical gradients that lead to complex variability and often high rates of biogeochemical processes, and they are also often impacted by humans. Yet, our understanding of estuarine biogeochemistry remains skewed towards temperate latitudes. We examined seasonal and spatial variability in dissolved organic matter (DOM) and nutrients along a partly eutrophic, agricultural–urban estuary system in Southeast Asia: the Johor River and the East Johor Strait. Dissolved organic carbon (DOC) and coloured DOM (CDOM) showed non-conservative mixing, indicating significant DOM inputs along the estuary. The CDOM spectral slopes and CDOM : DOC ratios suggest that terrigenous, soil-derived DOM dominates along the Johor River, while phytoplankton production and microbial recycling are important DOM sources in the Johor Strait. CDOM properties were not unambiguous source indicators in the eutrophic Johor Strait, which is likely due to heterotrophic CDOM production. Nitrate concentrations showed conservative mixing, while nitrite concentrations peaked at intermediate salinities of 10–25. Ammonium concentrations decreased with salinity in the Johor River but increased up to 50 µ mol L -1 in the Johor Strait, often dominating the dissolved inorganic nitrogen (DIN) pool. Phosphate concentrations were low (<0.5 µ mol L -1) throughout the Johor River but increased in the Johor Strait, where DIN : phosphate ratios were typically ≥ 16 : 1. This suggests that the Johor Strait may experience phosphorus limitation and that internal recycling is likely important for maintaining high nutrient concentrations in the Johor Strait. Overall, our results indicate that the Johor River and Johor Strait are clearly not part of the same estuarine mixing continuum and that nutrient recycling processes must be quantified to understand nutrient dynamics in the Johor Strait. Moreover, our results highlight the need for better techniques for DOM source tracing in eutrophic estuaries. [ABSTRACT FROM AUTHOR]

Estuaries have strong physicochemical gradients that lead to complex variability and often high rates of biogeochemical processes. The biogeochemistry of many estuaries is also increasingly impacted by human activities. Yet our understanding of estuarine biogeochemistry remains skewed towards temperate systems in the northern hemisphere, with far less research from tropical estuaries. This study examined seasonal and spatial variability in dissolved organic matter (DOM) and nutrient biogeochemistry along a partly eutrophic, mixed agricultural/urban estuary system in Southeast Asia, the Johor River and the East Johor Strait. Dissolved organic carbon (DOC) and chromophoric DOM (CDOM) properties showed non-conservative mixing, indicating significant DOM inputs along the estuary. The CDOM spectral slopes and CDOM:DOC ratios suggest that these inputs are dominated by terrigenous, soil-derived DOM along the Johor River, but that phytoplankton production and microbial recycling are more important DOM sources in the Johor Strait. Nitrate consistently showed conservative mixing, while nitrite concentrations peaked at intermediate salinities of 10–25. Ammonia decreased with salinity in the Johor River. In the Johor Strait, however, ammonia increased up to 50 µmol l-1, often dominating the dissolved inorganic nitrogen (DIN) pool. Phosphate was low (<0.5 µmol l-1) throughout the Johor River, but increased in the Johor Strait, where DIN:phosphate ratios were typically at or above 16:1. This suggests that phytoplankton in the Johor Strait may sometimes experience phosphorus limitation. Moreover, internal recycling is likely important for maintaining high nutrient concentrations in the Johor Strait. [ABSTRACT FROM AUTHOR]

Material fluxes at the land--ocean interface impact seawater composition and global cycling of elements. However, most attention has been focused on the fluvial dissolved fluxes. For elements like lead (Pb), whose fluvial particulate flux into the ocean is two orders of magnitude higher than the dissolved counterpart, the role of particulates in elemental cycling is potentially important but currently less appreciated. Using both chemical analyses on samples collected from around equatorial Southeast Asia and model simulations, we show that particulate-dissolved exchange is an important mechanism controlling the concentration and isotopic composition of dissolved Pb in the ocean. Our model indicates that Pb contributed from particulate-dissolved exchange at ocean boundaries is larger than, or at least comparable to, other major Pb sources to the seawater before the Anthropocene, when the anthropogenic Pb was absent. Our work highlights the importance of boundary exchange in understanding marine element cycling and weathering-climate feedback. [ABSTRACT FROM AUTHOR]

Agriculture in Malaysia makes up to twelve percent of the nation’s GDP and is supplying one-third of the world rubber export. Ambitious agriculture demand increases the intensity of forest conversion which is driven to the soil erosion. Thus, this study is to measure and analyse the impact of forest conversion on soil erosion relate to some manipulated variables such as slope, bulk density, soil moisture, canopy openness and ground cover, where rainfall and soil type are constant within the sites. Two different land-uses of High Conservation Value Forest (HCVF) and Mature Rubber Plantation of Timber Latex Clone (MRP) were selected around Kelantan state, due to the high land conversion compared to the other states of West Malaysia. Ground height change was monitored by using Modified Laser Erosion Bridge (MLEB) in between 17 to 48 transects. The result found that the annual soil erosion rate was 76.12 t.ha-1.yr-1 for HCVF is higher compared to the MRP was 6.37 t.ha-1.yr-1. Terrace soil conservation technique is practiced for MRP helps in reducing soil movement resulted significant low erosion rate compared to the HCVF. The results indicate that even a relatively limited forest conversion can be assumed to have a significant effect on regional soil erosion rate.

Most of the causes of river pollution are due to the impact of human activities through the development of new construction projects, agriculture, industry and others. As an alternative to deal with this problem, macro-composite has been used as a pretreatment process to treat wastewater before discharge into the river. Therefore, this study aims to characterize the water quality of the effluent and to investigate the treatment efficiency of different hydraulic retention times (HRTs) using macro-composite technology in treating the effluent from Flat Taman Jaya. The parameters tested were chemical oxygen demand (COD), biochemical oxygen demand, ammonia nitrogen (NH3-N), pH, total suspended solid (TSS), turbidity and total phosphate (TP). The efficacy of the macro-composites was tested by immersing 70% of the macro-composites into the 750 mL wastewater sample for five different periods. The results of each wastewater sample were measured after 2 d of treatment. The results showed that the most efficient treatment was achieved with the macro-composite at 3 d HRT with COD, NH3-N, TSS, turbidity and TP removal of 80%, 97%, 60%, 49% and 89%, respectively, at pH 7.33. [ABSTRACT FROM AUTHOR]