National Centre for Earth Science Studies

Instrumentation

NCESS-CAMECA SXFive-Tactis is equipped with five wave length dispersive spectrometers, BSE detectors, SE detectors, cathodoluminescence and sophisticated visible light optics. The self-biased electron gun of the instrument has the provision for both W and LaB6 filaments. The instrument is configured in such a way so that operation as well as basic imaging and data processing are made easy for having intuitive touch screen interface. In expert mode, the interface is designed to have benefit from a full complement of different tool parameters and software options. The system involves a high degree of automation with the capacity of prolonged unattended analytical schedules with high analytical precision, accuracy and reproducibility with minimum down-time, high quality imaging at high spatial resolution including multi-element x-ray mapping. Vertical WDSs are compatible to have suitable combinations in high sensitivity diffracting crystals (e.g. LTAP, LPC1, LLIF and LPET) as well as six diffracting crystals such as TAP, LIF, PET, PC0, PC3 and PC2. Another advantage of this instrument is that it is equipped with a fully integrated Electron Dispersive Spectrometer hypermapping module making data processing and analysis faster and easier. SX- Five with LaB6 Column: Accelerating Voltage: 15KV and 20 KV; Beam Current: 20 uA onwards; Beam Stability: +-0.5% per hour @ 20kV, 20nA.

Capabilities

Qualitative analysis: WDS Spectrum-to find out the elements present. Wavelength Dispersive Spectrometry is acknowledged as the method of choice for high precision quantitative microanalysis. The SXFive-Tactis spectrometers have the highest resolution and, as a result high peak to background ratios, thereby providing high sensitivities. The absolute spectral positioning is provided by optical encoders attached to the system. Only one peak measurement is needed to calibrate the entire spectrometer range.

Quantitative analysis: Accurate quantification of chemical composition of any solid material. SXFive-Tactis delivers the true quantitative analysis. The quantitative data can be displayed such as wt%, oxide wt%, cations. See the table below for our precision:

BSE Imaging: Backscattered electrons are high energy primary electrons scattered in such a direction (>90°) that they leave the target entirely. Most BSE have energies slightly lower than that of the primary electron beam. By using these emissions as video BSE images are produced and used for phase identification and mineral identification.

Cathodoluminescence (CL) Imaging: Cathodoluminescence is non-metal valence shell phenomenon leading to light emission. By using these emission as a video signal we can produce CL images that can be used to reveal the defects and impurities in materials.

X-Ray Mapping: With the help of X-Ray Mapping one can see the distribution the particular element in desired area of interest and segregation of impurities in metal alloy samples.

U-Th-Total Pb Chemical dating: Calibration Set up: 20 kV–20 nA, Quantification Set Up: 20 kV–200 nA. Following X-ray lines are used for major, trace and REE concentration as well as age determination for Monazite, viz., P–Ka, Ca–Ka, Si–Ka, Fe–Ka, Al–Ka, Y–La, La–La, Ce–La, Pr–Lb, Nd–Lb, Sm–Lb, Gd–Lb, Er–La, Eu–La, Dy–Lb, Ho–Lb, Pb–Ma, Th–Ma and U–Mb. Detailed analytical protocol is given in “Chemical dating of monazite: Testing of analytical protocol for U–Th–total Pb using CAMECA SXFive tactis EPMA at the National Centre for Earth Science Studies, Thiruvananthapuram, India,” by Sorcar et al., J. Earth Syst. Sci. (2021)130:234 (https://doi.org/10.1007/s12040-021-01738-4)

NCESS is setting up Critical Zone Observatories (CZOs) in South Peninsular India under the theme TERRAIN (Tropical Ecosystem Research Observatories in Peninsular India with an objective to understand the relative influence of natural perturbations (climate variability) and anthropogenic activities on the hydrological and biogeochemical cycles in different agroclimatic regions of India which will be elevated to the standards of global test bed for Critical Zone studies. In the first phase, CZOs has been set up in the Attappadi (Sub-Humid to Semi-Arid transition zone), Munnar (Humid - High altitude mountainous terrain) and Aduthurai (Tropical wet and dry deltaic region) representing different agroclimatic zones. These CZOs are being instrumented to monitor instantaneous and continuous soil moisture (surface and profile), groundwater level, streamflow, canopy characteristics (Leaf Area Index, Vegetation Water Content, Biomass), porewater geochemistry, hydrochemistry of surface and groundwater, soil properties (physical and hydraulic properties), meteorological variables, evaporation, soil water balance (Lysimeter) etc. These variables are monitored at different spatio-temporal scales and the data generated from these observatories will enable to understand the Critical Zone dynamics and its resilience in the context of natural and forced changes.

Attappadi Critical Zone Observatory

The Attappadi CZO lies in the transition zone between the humid areas of Silent Valley National Park to sub-humid areas in the Nilgiri Plateau and extends to semi-arid region. The CZO is situated between E longitudes 76°25’to 76°50’and N latitudes 11°0” to 11°30’ and covers an area of 1225km2. Monitoring stations has been setup in the Palur watershed (8.5 km2 area). The river Bhavani, which is the tributary of east flowing Cauvery river, originates from the Nilgiri mountain ranges of southern Western Ghats. The river drains nearly 8% of the total area of the Cauvery Basin. The important tributaries of the Bhavani are the Siruvani, the Kundah, the Conoor and the Moyar. The river has a catchment area of 6,200 km2 which is spread essentially over Tamil Nadu (87%) and partly in Kerala (9%) and Karnataka (4%) states. The Bhavani basin is characterized by a considerable amount of tribal population and is predominantly an agricultural watershed. Characterization of soil physical, chemical and hydraulic properties is ongoing in the Attappadi CZO. Surface and groundwater hydrochemical characterization of the Attappadi CZO is progressing through continuous sampling.

Munnar Critical Zone Observatory

Munnar CZO is a tropical high altitude mountainous observatory, characterized by a highly heterogeneous terrain. The CZO encompasses the watersheds of Mutirapuzha, Idamalayar and Amaravati rivers. Monitoring stations has been setup in Matupetty and Vattavada regions of the Munnar CZO. Geologically the area forms a part of the Madurai granulite block (MGB) of the southern granulite terrain (SGT) and comprised essentially of charnockites, hornblende gneiss, granite etc. Geomorphologically the area forms a part of Munnar plateau whose elevation varies between 1460 and 1620 m above msl. The slope is generally steep (>30°) and the soil is mainly of lateritic type with appreciably high content of clay and organic matter. The hills of Munnar are home to different cash crops. Tea gardens and settlement with mixed cultivation are the major land use of this area. Eucalyptus and acacia, planted under the government’s social forestry scheme, occupy a major part of the forest plantation, whereas the upslope portions are occupied by degraded forests and shola grasslands. On the other hand, the Amaravati watershed are generally occupied by cold climate driven vegetation. The contrasting climatic conditions and agricultural activities makes the CZO unique in many aspects.

Aduthurai Critical Zone Observatory

Aduthurai CZO is located in the Cauvery delta in the eastern part of Tamil Nadu and experiences a tropical wet and dry climate. This CZO is predominantly an agricultural watershed with rice as the principal crop. The region experiences an average annual rainfall, of about 1000 mm with North East monsoon being the major contributor (550 mm) of the annual rainfall. The Cauvery delta region is generally known as the Rice Bowl of Tamil Nadu and is also the largest coconut producer in Tamil Nadu. The upper part of the Cauvery Delta is bordered by Cuddalore lateritic sandstones of pilo-miocene age and majority of the delta is covered by alluvium. The south eastern part of the delta constitutes the coastal lands. Aduthurai CZO will be augmented with monitoring stations shortly.

Critical Zone Laboratory at NCESS

Critical Zone Laboratory has been setup at NCESS for carrying out laboratory scale experiments on soil, water and vegetation. The laboratory is equipped with

• Soil Hydraulic Property Estimation setup – HYPROP, KSAT
• Dual Head Infiltrometer, Mini Disk Infiltrometer
• Automatic Soil Particle Size Analyzer – PARIO
• Hydrometer, Sieve Shaker, Pore Water Sampler
• Plant Canopy Analyzer, NDVI Meter