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Geochemical, mineralogical and isotopic investigation of Inle Lake (Southern Shan State, Myanmar): preliminary results.
No full textThis paper reports some preliminary results obtained on waters and sediments from the Inle Lake. Carbonate equilibria dominate the lake water hydrochemistry. During the summer season, strong evaporation affects the water body, coupled to intense photosynthetic activity. These processes favour authigenic carbonate precipitation, as indicated by the high calcite content detected in the lake sediments. Isotopes of the water molecule indicate a residence time shorter than one year. The short residence time and calcite precipitation likely prevent the accumulation of anthropogenic contaminants and nutrients within the lake
Hydrological processes at Inle Lake (Southern Shan State, Myanmar) inferred from hydrochemical, mineralogical and isotopic data<sup>†</sup>
Get PDFA one-year hydrochemical and isotopic monitoring was conducted at the Inle Lake, the second largest lake in Myanmar, also considering sediment samples. Lake waters are characterised by low electrical conductivities (236–489 μS/cm), neutral to alkaline pH (7.36–9.26), oxidising Eh (329–457 mV) and Ca–Mg–HCO3 facies. Stable isotopes indicate that lake waters are only slightly affected by evaporation, are fully flushed yearly and are not stratified. Carbonate equilibria dominate the lake water hydrochemistry. In summer, photosynthetic activity and temperature increase induce calcite precipitation, as testified by its high content in the sediments, up to 97 %, and by its isotopic composition. The short residence time and endogenic calcite precipitation likely prevent the accumulation of contaminants and nutrients in lake waters. This study suggests a high resilience of the system to anthropogenic disturbances and demonstrates the sediment potential for the reconstruction of the environmental evolution in time and for the anthropogenic impact assessment.</p
Present status and future criticalities evidenced by an integrated assessment of water resources quality at catchment scale: The case of Inle Lake (southern Shan state, Myanmar)
Get PDFAssessing aquifer dynamics and groundwater interactions with surface waters are prerequisite for the correct management of water resources in the long-term, especially under the increasing pressure of climate change and the growing freshwater demand. This work presents the results of the first integrated assessment in the Inle Lake catchment aimed at understanding the surface and groundwater dynamics and the impact of agriculture and tourism on water quality. Results of an investigation performed in winter 2015, targeting the water chemical and isotopic (δ18OH2O and δ2HH2O) composition, and soil mineralogy, confirmed that Inle is an alkaline lake, where carbonate equilibria dominate its hydrochemistry. The high resilience of the lake to external perturbations is due to calcite precipitation, that represents an effective mechanism of P removal and, combined to the low residence time of water, prevents the accumulation of nutrients in lake waters. The investigation also permitted the first characterization of groundwater in the region, highlighting the dominance of Mg(Ca)-HCO3facies. Two deep groundwater circulations could be evidenced: one of high temperature, Na-HCO3 type (Khaung Daing Hot Spring) and one in equilibrium with the dolomitic rocks of the basement, upwelling along a fault zone oriented N-S in the Northern part of the basin. The latter groundwater contributes to Inle lake by mixing with local recharge in the aquifer and by feeding the network of artificial channels created for reclamation purposes. Evidencing recharge mechanisms of both surface and groundwater makes it possible to highlight the impact of seasonal fluctuations of the water levels, and the associated flooding of some sectors of the catchment, on the Inle Lake agroecosystems and to evaluate possible scenarios for the future sustainable development of the region
Geochemical and mineralogical composition of grab and core sediments from Inle Lake (Southern Shan State, Myanmar)
No full textLake sediments were sampled in March 2014 in 16 locations selected so as to cover the whole lake area. At each lake site, grab sediment samples were collected with a stainless-steel, Ponar type sampler; in addition, at 5 stations, sediment cores were collected with a sampler prototype (handmade), which ensures careful recovery of the sediment-water interface. Cores ranged from 55 to 85 cm in length and were cut into 5 cm slices on the same day of collection.
The mineralogical analyses were carried out by X-ray Powder Diffractometry (XRD) performed both on natural samples, and on treated samples to identify the clay minerals, using the standard procedure of ethylene-glycol saturation followed by heating at 550°C for the identification of the swelling clay minerals. Mineralogical results are expressed in %.
The chemical composition (major and trace elements) was analysed by "Near Total" Digestion ICP/MS (Code UT-4M) at the Activation Laboratory, Canada. Analysed elements include Ca, Mg, Na, K, Al, Fe, P, S, Ti (in %), and Sr, Ba, Rb, Li, Rb, Cs, Mn, Cd, Co, Cr, Cu, Ni, Pb, Mo, V, Zn, W, Tl, Bi, Sn, As, Sb, Ag, Au, Sc, Ti, Y, Zr, Nb, La, Ce, Hf, Ta, U, Th (in mg/kg).
The dataset includes 6 tables:
Grab samples (16 locations, approx. depth 0-10 cm)
Core 2 (UTM Long. 47Q 0283122 Lat. 2280515, depth 5-80 cm)
Core 3-1 (UTM Long. 47Q 0282707 Lat. 2276910, depth 5-55 cm)
Core 4-2 (UTM Long. 47Q 0281190 Lat. 2269152, depth 5-75 cm)
Core 4-3 (UTM Long. 47Q 0282356 Lat. 2268878, depth 5-60 cm)
Core 6 (UTM Long. 47Q 0282396 Lat. 2265350, depth 5-85 cm
Geochemical and mineralogical composition of sediment core 4-2 from Inle Lake (Southern Shan State, Myanmar)
No full textGeochemical and mineralogical composition of sediment core 2 from Inle Lake (Southern Shan State, Myanmar)
No full textGeochemical and mineralogical composition of grab samples from Inle Lake (Southern Shan State, Myanmar)
No full textGeochemical and mineralogical composition of sediment core 3-1 from Inle Lake (Southern Shan State, Myanmar)
No full textMineralogical and geochemical characterisation of alkaline lake sediments to trace origin, depositional processes, and anthropogenic impacts: Inle Lake (Southern Shan State, Myanmar)
Get PDFSoutheast Asia contains a major portion of wetland areas of international significance, but only 14% of these wetlands are under protection. Inle Lake is the second largest freshwater body in Myanmar and the most important for its environmental, economic, and agricultural values. However, the lake is seriously threatened by anthropic activities as they are dramatically decreasing its open water surface. While water-quality studies have assessed the presence of nutrients and contaminants, little is known about the sediment quality. Therefore, the overall objective of the present study was to analyse the natural sedimentation patterns and the anthropogenic disturbances in this lake. To this end, both grab and core sediments were investigated by combining mineralogical, morphological, and geochemical analyses, and their composition was compared to the composition of rocks and soil from the watershed. Mineralogical data indicate that sediment samples collected at or near the main inflow, and at the outflow show a lower abundance (about 43%) of calcite, which generally increases with depth in sediment cores, reaching more than 90% in the centre of the lake. Lower calcite contents correspond to higher percentages of other minerals. These findings allow us to clearly distinguish the allogenic (quartz, mica/illite, kaolinite, and detrital calcite) from the endogenic (mostly calcite) minerals, as confirmed by the soil and rock mineralogy. The origin of the mineral contents at the different sites is further supported by the observation of the grain morphology and composition. The most abundant metal in the lake sediments is Ca, in agreement with the high calcite content. Following in order of abundance are Al, Fe, and K, which are connected to the detrital input to the lake. In the rock and soil samples, the most abundant trace element is Mn, which is significantly correlated with many other trace elements (e.g., Co, Cr, Cu, Ni, V, Zn, and As), suggesting their common lithogenic origin. Similarly, in the lake sediments, the trace elements Co, Cr, Cu, Ni, Pb, V, Zn, and As display fairly homogenous concentration ranges, in the order of tens of ppm, and are strongly correlated with the detrital minerals (mica, kaolinite, and quartz) and negatively correlated with the calcite content. The mineralogical and elemental distribution in the lakebed area and with depth in the sediment cores allowed us to identify the increased soil and bedrock erosion as a major anthropogenic impact to the lake. The sedimentation disturbance is especially evident at the main inflow, the Nanlit stream, which has caused the development of a large alluvial fan, visible in satellite images. This large sediment
input is likely to have accelerated the decrease in open water surface and in depth of this shallow lake. Additionally, when the measured concentrations of Potentially Toxic Elements were compared to consensus-based Sediment Quality Guidelines (SQGs), it was shown that As, Cr, Cu, Ni, Pb, and Zn often exceeded the threshold effect concentration (TEC), and that Cr, Ni, and Pb sometimes exceeded the probable effect concentration (PEC). On the other hand, Enrichment Factors (EFs), calculated with respect to soils of the watershed, showed minimal enrichment and indicated that the potential toxicity effect was primarily a result of detrital sedimentation outpacing carbonate sedimentation. Sediment characterisation allowed us to obtain a better understanding of lake dynamics and environmental impacts, which is fundamental in achieving effective management and maintenance of the ecological character of Inle Lake, in line with the objective set by the Ramsar Convention.
for wetlands of international relevance
Hydrochemical and isotopic features of the Khaung Daing hot spring (Inle lake, Southern Shan State, Myanmar)
Get PDFThe Inle lake watershed develops along a right-lateral strike-slip fault running parallel to the Sangaing fault, a major continental transform fault between the India and Sunda Plates. Located on the northwestern border of the Inle lake basin, the Khaung Daing hot spring outflows at a temperature of about 70̊C. This contribution represents a reconnaissance study of the spring and describes its main hydrochemical and isotopic features, compared to surface and ground waters in the watershed. The water pH is slightly acidic, and, compared to the other water samples from the watershed, shows an EC in the high range (57-1284μS/cm), the lowest pH and Eh values, and is Na-HCO3, whereas surface and ground waters are Ca(Mg)-HCO3 type. The hot spring isotopic composition falls close to the Yangon Meteoric Water Line, indicating that, despite its temperature, it is not strongly modified by water-rock interaction processes. Preliminary results suggest that this hydrothermal water is likely related to deep meteoric and ground water circulation within a fault zone, in a region characterized by an elevated geothermal gradient
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