Delineation of potential groundwater zones based on multicriteria decision making technique

Groundwater is the most prioritized water source in India and plays an indispensable role in India's economy. The groundwater potential mapping is key to the sustainable groundwater development and management. A hybrid methodology is applied to delineate potential groundwater zones based on remote sensing, geographical information systems(GIS) and analytic hierarchy process(AHP) as on multicriteria decision making. For the purpose of demonstrating field application, Chittar watershed, Tamilnadu, India is studied as an example. The important morphological characteristics considered in the study are lithology, geomorphology, lineament density, drainage density, slope, and Soil Conservation Service–Curve Number(SCS-CN). These six thematic layers are generated in a GIS platform. Based on intersecting the layers, AHP method, the values for adopting the pairwise comparison normalized weight and normalized subclasses weightage were given. The normalized subclass weightage is input into each layer subclass. Then, weighted linear combination method is used to add the data layers in GIS platform to generate groundwater potential Index(GWPI) map. The GWPI map is validated based on the net recharge computed from the differences of measured groundwater levels between the pre-monsoon and post-monsoon in the year 2018. The kappa statistics are used to measure level spatial consistency between the GWPI and net recharge map. The overall average spatial matching accuracy between the two data sets is 0.86, while the kappa coefficient for GWPI with net recharge, 0.78. The results show that in Chittar watershed about 870 km~2 area is divided into high potential zone(i.e. sum of very high and high potential zone), 667 km~2 area, as the moderate one and the rest 105 km~2 area, as the poor zone(i.e. sum of very poor and poor potential zone).     

Contrasting phytoplankton community structure and associated light absorption characteristics of the western Bay of Bengal

Absorption spectra, particulate pigments, and hydrochemical constituents were measured in the western Bay of Bengal (BoB) during July-August 2010 when influence of river discharge is at peak. Chromophoric dissolved organic matter (CDOM) absorption coefficient (a_CDOM(440)) displayed a significant inverse linear relationship with salinity in the surface waters implying conservative mixing of marine and terrestrial end members. The northern part of the study area is influenced by discharge from the river Ganga and a dominant terrestrial CDOM signal is seen. The southern part receives discharge from peninsular rivers with corresponding signals of higher CDOM than the linear model would indicate and higher UV-specific absorption coefficient (SUVA) indicating more aged and humified DOM. Lower contribution of CDOM to total non-water absorption and higher phytoplankton biomass (chlorophyll a absorption coefficient, a_ph(440)) but lower chlorophyll a specific phytoplankton absorption coefficient (a _ph ^* (440)) characterize the northern part, compared to the southern part. Chlorophyll b had a distinct linear relationship with chlorophyll a in the latter. The size index (SI) indicated dominance of microphytoplankton in the northern and nano and picophytoplankton in the southern parts. Chlorophyll a is significantly related to a _ph ^* (440) by an inverse power model in the northern part but by an inverse linear model in the southern part. Our study suggests that knowledge of the phytoplankton community structure is essential to improve chlorophyll a algorithm in the coastal Bay of Bengal.     

Definition of subsoil structure and preliminary ground response in Aigion city (Greece) using microtremor and earthquakes

An extensive campaign—including detailed geologic and geotechnical surveys both existing and news as well as noise measurements—was conducted along a cross-section in order to define both geometry and soil properties (mainly the shear wave velocity) of the main formations in Aigion city. Aigion city is located in the Gulf of Corinth, Greece, a highly seismic region of the Aegean Sea. The main objective of the accurate 2D soil model is its use in site response modeling and in the interpretation of observations from a vertical down-hole accelerograph array. This model revealed a complex geologic structure with a multi-faulted shear zone related to the Aigion fault. The defined subsurface structure offered the possibility for its correlation with estimated site effects, in terms of spectral ratios. Two different data sets, earthquakes recorded at down-hole accelerograph network and noise measurements at 17 sites, were used. To translate the empirical transfer functions with the geologic structure, the 1D estimates were also computed. All these results are consistent, indicating a satisfactory correlation between the soil model and preliminary site response.     

Hydrodynamic control of microphytoplankton bloom in a coastal sea

The influence of hydrodynamics on phytoplankton bloom occurrence/formation has not been adequately reported. Here, we document diurnal observations in the tropical Bay of Bengal’s mid-western shelf region which reveal microphytoplankton cell density maxima in association with neap tide many times more than what could be accounted for by solar insolation and nutrient levels. When in summer, phytoplankton cells were abundant and the cell density of Guinardia delicatula reached critical value by tide caused zonation, aggregation happened to an intense bloom. Mucilaginous exudates from the alga due to heat and silicate stress likely promoted and stable water column and weak winds left undisturbed, the transient bloom. The phytoplankton aggregates have implication as food resource in the benthic region implying higher fishery potential, in carbon dioxide sequestration (carbon burial) and in efforts towards improving remote sensing algorithms for chlorophyll in the coastal region.     

High resolution spatiotemporal analysis of erosion risk per land cover category in Korçe region,Albania

Some recent land use changes in Albania, such as deforestation, cropland abandonment, and urban sprawl, have caused serious increase of erosion risk. The main objective of this study was to map erosion risk in Korçe region and assess the degree at which every land use is concerned. The G2 erosion model was applied, which can provide erosion maps and statistical figures at month-time intervals using input from free European and global geodatabases. The mapping results in Korçe region were derived at a 30-m cell size, which is an innovation for G2. Autumn-winter months were found to be the most erosive, with average erosion rates reaching the maximum in November and December, i.e. 2.62 and 2.36 t/ha, respectively, while the annual rate was estimated at 10.25 t/ha/yr. Natural grasslands, shurblands, mixed forests, and vineyards showed to exhibit the highest mean erosion rates, while shrublands, broad-leaved forests and natural grasslands were found to be the most extended land covers risky for non-sustainable erosion rates (i.e. >10 t/ha/yr). A detailed examination of the detected hot spots is now necessary by the competent authorities, in order to apply appropriate, site-specific conservation measures. Notably, use of SPOT VGT data did not prevent the maps from having extended gaps due to cloudiness. Sentinel-2 time series, freely available by the European Space Agency (ESA), have the potential to improve spatiotemporal coverage of V-factor, thus further empowering the G2 model, in the near future.