Distribution of Heavy Metals and Rare Earth Elements in the Surface Sediments of Penang River Estuary, Malaysia

Geochemical sediment of the tropical Pinang River, Malaysia was carried out with the aim at documenting elemental concentrations and pollution level assessment. Concentration of selected heavy metals (Cu, Cd, Cr, Pb, Zn and Mn), rare earth elements, TOC and grain size distribution of sediments were determined at 100 m sampling interval along the river. Sediment size showed a positive correlation with ∑REE and Mn and medium correlations with TOC, Zn, Cu, Cr and Pb contents showing enrichment in the clay size fraction. Results of enrichment factor and geoaccumulation index showed that most of the elemental sources were natural (especially REE) and mostly likely represented background values. However, pollution load index revealed the higher levels of Cr, Cd, Zn and Pb, and, therefore, indicating to the anthropogenic sources (i.e. fishing activities) especially in the downstream locations. Thus, the Pinang River is classified as moderately to highly polluted.

Evaluation of mercury methylation in fresh and pre dried sediments using ^(203)Hg radioisotope

Mercury methylation rates in fresh and pre dried river sediments were determined in sediment water systems spiked with 203 HgCl 2 at a level of 0.75—0.95 ppm as Hg. At the end of the incubation period (21—38 days), methylmercury production in the fresh sediments was in the order of 3.0% to 13.75%, whereas in the pre dried sediments the methylation was much lower, at 0.6% to 3.9%. The highest methylation levels were generally recorded in the uppermost, 1 cm layer of the sediment column. Total mercury concentration in water in equilibrium with the 203 Hg spiked fresh sediments was in the range of 44.7 to 634 ng/L, whereas in equilibrium with the pre dried sediments the concentration was in the range of 19.5 to 34.5 ng/L. The proportion of methylmercury to total mercury in the water varied from 9.4% to 66.6% over the fresh sediments, and from 7.1% to 10.8% over the pre dried sediments. In the system consisting of water, sediment and sediment inverterbrates the concentrations of methylmercury were 8.61 to 15.69 ng/g in the sediment, 0.011 ng/ml in the water, and 9.22 to 40.69 ng/g in the inverterbrates. Methylmercury bioaccumualtion factors (BAFs) were in the order of 274 to 8087 relative to the water, and 0.25 to 7.31 relative to the sediment. These results provide further evidence for the tendency of methylmercury to accumulate in high concentrations in aquatic organisms, even at very low total mercury concentration in water.

Preliminary data of life history traits of Mormyridae(Actinopterygii:Teleostei)in the Upper Sanaga River,Central Region of Cameroon

The present study on some biological aspects of the Mormyridae fishes,was conducted between May and August 2015 in the Upper Sanaga at L´eki´e Department(Monat´el´e Town),Center Cameroon.For this purpose,125 specimens collected by local fishermen were used.Fishes were identified and measured,and their feeding and reproductive parameters were obtained after dissection.The catch composition of 4 species(Campylomormyrus phantasticus,Mormyrops anguilloides,Mormyrus macrophtalamus,Mormyrus tapirus)of Mormyridae identified in the region was very low(17%–30%).The mean±standard deviation of total weight and total length were 103.14±37.83 g and 27.47±4.84 cm,respectively.The minimum and maximum size(of 21.1 cm and 43 cm)were recorded from C.phantasticus and M.anguilloides,respectively.The mean±standard deviation of the relative length and mass of the digestive tract were 0.35%±0.20%and 5.27%±23.20%,respectively confirming that Mormyridae fish species have a strict carnivorous diet and consume prey that are difficult to digest.The size frequency distribution of the Mormyridae fishes showed that the majority of the fish caught are small sizes in classes 23–26 cm and 26–29 cm in C.phantasticus,M.macrophthalamus and M.tapirus.M.anguilloides did not record small specimens,however,it recorded larger sized specimens(41–44 cm)compared to the rest.The sex ratio ranged from 1M:1.14F(M.anguilloides)to 1M:4F(M.tapirus),mean 1M:2.04F has been generally in favour of females.The gonadosomatic index(GSI)was generally low in all species.However,it was higher in females of C.phantasticus and M.anguilloides compared to other species.The hepatosomatic index(HSI)was weakly correlated with the GSI in these species.

Nutrient variability and its influence on nitrogen processes in a highly turbid tropical estuary(Bangpakong, Gulf of Thailand)

Estuarine ecosystems in SE Asia have been poorly studied when compared to other tropical environments. Important gaps exist particularly in the understanding of their biogeochemical function and contribution to global change. In this work we looked into N-turnover in the water column and sediments of the Bangpakong estuary（13°N）. A seasonal sampling program was performed along the salinity gradient covering different stretches of the estuary（68 km）.Key physical and chemical characteristics were also monitored in order to unravel possible environmental controls. Results showed the occurrence of active denitrification in sediments（5.7–50.9 nmol N-N2/（cm3·hr））, and water column（3.5–1044 pmol N-N2/（cm3·hr））. No seasonal or spatial variability was detected for denitrification potential in sediment samples. However, in the water column, the denitrification activity peaked during the transition season in the downstream sites coinciding with high turbidity levels. Therefore, in that period of the year, the water column compartment may be an important contributor to nitrate reduction within the estuary. The rather low nitrification rates detected were not always measurable, probably due to the reduced oxygen content and high siltation. This study is one of the few dealing simultaneously with sediments and water column processes in a highly turbid tropical estuary.Therefore, it emerges as a valuable contribution for the understanding of the dynamics of the nitrogen cycle in tropical environments by exploring the role of estuarine N microbial activity in reducing the effects of increased nitrogen loads.

Indexing the relationship between polar motion and water mass change in a giant river basin

Previous studies on the relationship between polar motion and water mass change have mainly concentrated on the excitation of polar motion via global terrestrial water storage changes(TWSC). In view of the uneven distribution of global terrestrial water storage, the relationship between regional water mass change and polar motion needs to be further explored owing to the lack of documented results. In addition, given the uncertainty in the estimation of TWSC, it is required to develop appropriate indices to describe water mass change from different perspectives. The Amazon River basin(referred to Amazon hereafter), containing the world's largest river, located at around the 90°W longitude, is selected as the study area. Water vapor flux, precipitation, runoff and TWSC are selected as the indices of water mass changes to reveal the relationship between polar motion and water mass change in this giant basin. The Mann-Kendall(M-K) method, the accumulated anomaly analysis method and the curvature method are used to identify the abrupt change points; the least squares method is used to estimate the trends,and the Fast Fourier Transform(FFT) and the Ensemble Empirical Mode Decomposition(EEMD) are used to perform a periodic analysis, for all the above indices. It is shown that, of all the indices from 1948 to 2011, water vapor flux is the most closely related index to polar motion. In detail, precipitation and water vapor flux contain beat periods of polar motion; water vapor flux,precipitation and polar motion have a common M-K test abrupt change point(occurring in ca. 1968) at the 0.05 significance level; water vapor flux has a similar accumulated anomaly curve with that of polar motion; and water vapor flux is more highly correlated with polar motion than most other indexes. It is found, just like global TWSC, the χ2 component of the excitation via water vapor flux and water storage change in the Amazon follows that of observed polar motion; χ1 does not follow. However, the pattern in the Amazon that the χ2 component of the excitation by water follows that of observed polar motion is at a more significant level than in global. Finally, the new index termed Location of Vapor-based Inter Tropical Convergence Zone(LVITCZ) we proposed to describe the annual mean latitudinal location of water mass change shows a more close and visual relationship between water mass change and polar motion than other chosen indices do.

Achieving fish passage outcomes at irrigation infrastructure;a case study from the Lower Mekong Basin

Irrigation infrastructure expansion threatens the diversity of freshwater fish worldwide.Irrigation infrastructure creates migration barriers which can block access to important nursery,feeding and spawning habitat.Lao PDR is a landlocked country situated within the Lower Mekong River Basin where there is a substantial dependency on rice and fish for food,income and livelihoods.The country is experiencing an unprecedented boom in irrigation infrastructure investment,with modernisation programs being implemented in every province.Despite significant investment in infrastructure upgrades,and the potential impact on freshwater fish,little consideration has been given to fish passage solutions.In 2008,we commenced a fish passage program in Lao PDR.The intent of this case study is to outline the pivotal elements of the program of knowledge development and transfer,in the context of river connectivity and fisheries management in Lao PDR.We also highlight challenges in international research in development and lessons learned.