Assessing the changes in river water quality across a land-use change (forest to oil palm plantation) in peninsular Malaysia using the stable isotopes of water and nitrate.

Land conversion from natural forests to plantations (e.g., oil palm) in Southeast Asia is one of the most intensive land-use changes occurring worldwide. To clarify the effects of oil palm plantations on water quality, we conducted multipoint river and stream water sampling in peninsular Malaysia at the end of the rainy season over a 3-year period (2013-2015). We measured the major dissolved ions and stable isotope ratios of water (δ2H-H2O and δ18O-H2O) and nitrate (δ15N-NO3- and δ18O-NO3-) in water from the upper streams in mountainous forests to the midstream areas of two major rivers in peninsular Malaysia. The electrical conductivity increased, and the d-excess value (as an index of the degree of evaporation) decreased with increasing distance from the headwaters, suggesting the effect of evaporative enrichment and the addition of pollutants. We separated the sampling points into four groups (G1-G4) through cluster analysis of the water quality data. From the land use/land cover (LULC) classification maps developed from satellite images and local information, we found that G1 and G2 mainly consisted of sampling points in forested areas, while G3 and G4 were located in oil-palm-affected areas. The concentrations of major ions were higher in the oil palm areas, indicating the effects of fertilizer and limestone (i.e., pH adjustment) applications. The dissolved inorganic nitrogen concentration did not differ among the groups, but the dissolved organic carbon, total dissolved nitrogen, and δ15N-NO3- were higher in the oil palm area than in the forested area. Although the nitrogen concentration was low, even in the oil palm area, the significantly higher δ15N-NO3- in the oil palm area indicated substantial denitrification. This implies that denitrification contributed to the lowering of the NO3- concentration in rivers in the oil palm area, in addition to nutrient uptake by oil palm trees.

Effect of body lipid content is linked to nutritional adaptation in the acclimation responses of mesic-adapted Paederus to seasonal variations in desiccation stress.

Desiccation stress causes mesic-adapted arthropods to lose their body water content. However, mesic-adapted Paederus beetles can survive over prolonged periods under dry field conditions, suggesting that these beetles adopt an array of water conservation mechanisms. We investigated the water balance mechanisms of field-collected Paederus adults over a 14-month sampling period. We also assessed their nutritional adaptations by performing a stable isotope analysis to examine their diet. The water loss rate (WLR) of the beetles was significantly associated with the rice crop cycle and saturation deficit. The cuticular permeability (CP) of adult beetles was maintained at < 30 µg cm-2h-1 mmHg-1; however, CP increased significantly with the WLR. This result indicates that CP might play a minor role in reducing excessive water loss in beetles. The beetles' body water content and percentage total body water content increased when the WLR was high. Trehalose, glucose, and glycogen did not appear to play a central role in enhancing the water reserves in the insects. The body lipid content ranged from 0.22 ± 0.06 to 0.87 ± 0.07 mg and was negatively associated with the WLR. This association indicates that the increase in internal metabolic water was mediated by lipid catabolism. Stable isotope analysis results revealed that the Paederus beetles shifted their diet to carbohydrate-rich plants when the saturation deficit increased and the associated WLR reached its peak; otherwise, they consumed a high amount of staple carbohydrate-poor herbivore prey. The accumulation of energy reserves in the form of lipids through seasonal dietary shifts may exert major effects on the survival and population success of mesic-adapted Paederus beetles.

Polarity-Dependent Chemical Characteristics of Water-Soluble Organic Matter from Laboratory-Generated Biomass-Burning Revealed by 1-Octanol-Water Partitioning.

Polarity distribution of water-soluble organic matter (WSOM) is an important factor in determining the hygroscopic and cloud nucleation abilities of organic aerosol particles. We applied a novel framework to quantitatively classify WSOM based on the 1-octanol-water partition coefficient (KOW), which often serves as a proxy of polarity. In this study, WSOM was generated in a laboratory biomass-burning experiment by smoldering of Indonesian peat and vegetation samples. The fractionated WSOM was analyzed using a UV-visible spectrophotometer, spectrofluorometer, and time-of-flight aerosol chemical speciation monitor. Several deconvolution methods, including positive matrix factorization, parallel factor analysis, and least-squares analysis, were applied to the measured spectra, resulting in three classes of WSOM. The highly polar fraction of WSOM, which predominantly exists in the range of log KOW < 0, is highly oxygenated and exhibits similar optical properties as those of light-absorbing humic-like substances (HULIS, termed after the humic substances due to the similarity in chemical characteristics). WSOM in the least-polar fraction, which mainly distributes in log KOW > 1, mostly consists of hydrocarbon-like and high molecular weight species. In between the most- and least-polar fraction, WSOM in the marginally polar fraction likely contains aromatic compounds. The analyses have also suggested the existence of HULIS with different polarities. Comparison with previous studies indicates that only WSOM in the highly polar fraction (log KOW < 0) likely contributes to water uptake.