Sriroop Chaudhuri

Long-term (1930–2010) trends in groundwater levels in Texas: Influences of soils, landcover and water use

Rapid groundwater depletion has raised grave concerns about sustainable development in many parts of Texas, as well as in other parts of the world. Previous hydrologic investigations on groundwater levels in Texas were conducted mostly on aquifer-specific basis, and hence lacked state-wide panoramic view. The aim of this study was to present a qualitative overview of long-term (1930-2010) trends in groundwater levels in Texas and identify spatial patterns by applying different statistical (boxplots, correlation-regression, hierarchical cluster analysis) and geospatial techniques (Morans I, Local Indicators of Spatial Association) on 136,930 groundwater level observations from Texas Water Development Boards database. State-wide decadal median water-levels declined from about 14 m from land surface in the 1930s to about 36 m in the 2000s. Number of counties with deeper median water-levels (water-level depth>100 m) increased from 2 to 13 between 1930s and 2000s, accompanied by a decrease in number of counties having shallower median water-levels (water-level depth<25 m) from 134 to 113. Water-level declines across Texas, however, mostly followed logarithmic trends marked by leveling-off phenomena in recent times. Assessment of water-levels by Groundwater Management Areas (GMA), management units created to address groundwater depletion issues, indicated hotspots of deep water-levels in Texas Panhandle and GMA 8 since the 1960s. Contrasting patterns in water use, landcover, geology and soil properties distinguished Texas Panhandle from GMA 8. Irrigated agriculture is the major cause of depletion in the Texas Panhandle as compared to increasing urbanization in GMA 8. Overall our study indicated that use of robust spatial and statistical methods can reveal important details about the trends in water-level changes and shed lights on the associated factors. Due to very generic nature, techniques used in this study can also be applied to other areas with similar eco-hydrologic issues to identify regions that warrant future management actions.

Characterization of groundwater resources in the Trinity and Woodbine aquifers in Texas

A vast region in north-central Texas, centering on Dallas-Fort Worth metroplex, suffers from intense groundwater drawdown and water quality degradation, which led to inclusion of 18 counties of this region into Priority Groundwater Management Areas. We combined aquifer-based and county-based hydrologic analyses to (1) assess spatio-temporal changes in groundwater level and quality between 1960 and 2010 in the Trinity and Woodbine aquifers underlying the study region, (2) delve into major hydrochemical facies with reference to aquifer hydrostratigraphy, and (3) identify county-based spatial zones to aid in future groundwater management initiatives. Water-level and quality data was obtained from the Texas Water Development Board (TWDB) and analyzed on a decadal scale. Progressive water-level decline was the major concern in the Trinity aquifer with >50% of observations occurring at depths >100 m since the 1980s, an observation becoming apparent only in the 2000s in the Woodbine aquifer. Water quality degradation was the major issue in the Woodbine aquifer with substantially higher percentage of observations exceeding the secondary maximum contaminant levels (SMCL; a non-enforceable threshold set by the United State Environmental Protection Agency (USEPA)) and/or maximum contaminant level (MCL, a legally enforceable drinking water standard set by the USEPA) for sulfate (SO4(2-)), chloride (Cl(-)), and fluoride (F(-)) in each decade. In both aquifers, however, >70% of observations exceeded the SMCL for total dissolved solids indicating high groundwater salinization. Water-level changes in Trinity aquifer also had significant negative impact on water quality. Hydrochemical facies in this region sequentially evolved from Ca-Mg-HCO3 and Ca-HCO3 in the fluvial sediments of the west to Na-SO4-Cl in the deltaic sediments to the east. Sequentially evolving hydrogeochemical facies and increasing salinization closely resembled regional groundwater flow pattern. Distinct spatial zones based on homogenous hydrologic characteristics have become increasingly apparent over time indicating necessity of zone-specific groundwater management strategies.

Spatio-temporal variability of groundwater nitrate concentration in Texas: 1960 to 2010.

Nitrate (NO) is a major contaminant and threat to groundwater quality in Texas. High-NO groundwater used for irrigation and domestic purposes has serious environmental and health implications. The objective of this study was to evaluate spatio-temporal trends in groundwater NO concentrations in Texas on a county basis from 1960 to 2010 with special emphasis on the Texas Rolling Plains (TRP) using the Texas Water Development Boards groundwater quality database. Results indicated that groundwater NO concentrations have significantly increased in several counties since the 1960s. In 25 counties, >30% of the observations exceeded the maximum contamination level (MCL) for NO (44 mg L NO) in the 2000s as compared with eight counties in the 1960s. In Haskell and Knox Counties of the TRP, all observations exceeded the NO MCL in the 2000s. A distinct spatial clustering of high-NO counties has become increasingly apparent with time in the TRP, as indicated by different spatial indices. County median NO concentrations in the TRP region were positively correlated with county-based area estimates of crop lands, fertilized croplands, and irrigated croplands, suggesting a negative impact of agricultural practices on groundwater NO concentrations. The highly transmissive geologic and soil media in the TRP have likely facilitated NO movement and groundwater contamination in this region. A major hindrance in evaluating groundwater NO concentrations was the lack of adequate recent observations. Overall, the results indicated a substantial deterioration of groundwater quality by NO across the state due to agricultural activities, emphasizing the need for a more frequent and spatially intensive groundwater sampling.

Temporal evolution of depth-stratified groundwater salinity in municipal wells in the major aquifers in Texas, USA.

We assessed spatial distribution of total dissolved solids (TDS) in shallow (<50 m), intermediate (50-150 m), and deep (>150 m) municipal (domestic and public supply) wells in nine major aquifers in Texas for the 1960s-1970s and 1990s-2000s periods using geochemical data obtained from the Texas Water Development Board. For both time periods, the highest median groundwater TDS concentrations in shallow wells were found in the Ogallala and Pecos Valley aquifers and that in the deep wells were found in the Trinity aquifer. In the Ogallala, Pecos Valley, Seymour and Gulf Coast aquifers, >60% of observations from shallow wells exceeded the secondary maximum contaminant level (SMCL) for TDS (500 mg L(-1)) in both time periods. In the Trinity aquifer, 72% of deep water quality observations exceeded the SMCL in the 1990s-2000s as compared to 64% observations in the 1960s-1970s. In the Ogallala, Edwards-Trinity (plateau), and Edwards (Balcones Fault Zone) aquifers, extent of salinization decreased significantly (p<0.05) with well depth, indicating surficial salinity sources. Geochemical ratios revealed strong adverse effects of chloride (Cl(-)) and sulfate (SO4(2-)) on groundwater salinization throughout the state. Persistent salinity hotspots were identified in west (southern Ogallala, north-west Edwards-Trinity (plateau) and Pecos Valley aquifers), north central (Trinity-downdip aquifer) and south (southern Gulf Coast aquifer) Texas. In west Texas, mixed cation SO4-Cl facies led to groundwater salinization, as compared to Na-Cl facies in the southern Gulf Coast, and Ca-Na-HCO3 and Na-HCO3 facies transitioning to Na-Cl facies in the Trinity-downdip regions. Groundwater mixing ensuing from cross-formational flow, seepage from saline plumes and playas, evaporative enrichment, and irrigation return flow had led to progressive groundwater salinization in west Texas, as compared to ion-exchange processes in the north-central Texas, and seawater intrusion coupled with salt dissolution and irrigation return flow in the southern Gulf Coast regions.

Early C Sequestration Rate Changes for Reclaimed Minesoils

Abstract Reclaimed minesoils have well-defined ages (time since reclamation), making them suitable for studying temporal changes in terrestrial carbon sequestration. The objective of this research was to assess the effect of time since reclamation on soil organic carbon (SOC) sequestration and related soil properties such as texture, bulk density, and cation exchange capacity in three West Virginia minesoils along a chronosequence. The minesoils’ surface 750 Mg ha−1 (0–6 cm) was sampled at 1, 4, and 21 years and again at 2, 5, and 22 years postreclamation, giving a total of 6 site-years of information. Average SOC stocks (Mg C ha−1) were highest in the oldest minesoils. Soil bulk density was highest and unrelated to SOC concentration in the youngest minesoil, reflecting recent compressive reclamation techniques. The cation exchange capacity of older minesoils was influenced more by SOC than by clay, whereas the opposite was observed in younger minesoils. The relationship of SOC stock to time since reclamation was best described by a logarithmic diminishing returns model. Short-term (1 year) SOC sequestration rates (Mg C ha−1 y−1) were not appropriate to describing the change in SOC sequestration rate occurring along the chronosequence. When taken as the first derivative of the diminishing returns model, long-term SOC sequestration rates were shown to decline precipitously (80%) in the first 5 years after reclamation. The model predicts that the surface 750 Mg ha−1 of minesoil will contain about 13.3 Mg SOC ha−1 at 50 years after reclamation. About 75% of that SOC storage is predicted to be achieved in the first decade after reclamation.

Land Use Effects on Sample Size Requirements for Soil Organic Carbon Stock Estimations

Soil organic carbon (SOC) stock (in metric tons of carbon per hectare) is calculated from SOC concentration (in grams per kilogram) and soil bulk density (&rgr;b; in grams per cubic centimeter). Temporal changes in SOC stock are used to calculate terrestrial carbon sequestration rates used in global climate change models. The inherent variability in soil properties like SOC and &rgr;b means that larger sample sizes may be needed to accurately determine SOC stocks. Our objective was to calculate the minimum sample size required to detect changes in &rgr;b, SOC, and SOC stock for two land uses. Surface soils (0-5 cm) from two reclaimed mine soils and two managed hay fields in northern West Virginia were intensively sampled (60-74 samples each). Mean SOC and SOC stock values were larger in the hay fields (40 g/kg, 29 Mg ha−1) than in the mine soils (20 g/kg, 20 Mg ha−1), but &rgr;b was larger in reclaimed mine soils (1.4 g cm−3) than in hay field soils (1.2 g cm−3). The &rgr;b variance was larger in mine soils than that in hay field soils, but field variances for a given land use were similar (0.09 and 0.11 [g cm−3]2 in mine soils; 0.02 and 0.03 [g cm−3]2 in hay field soils). The variances in SOC concentration and SOC stock were not related to land use and were not similar within a land use. As a result, the minimum number of samples required to detect a change in &rgr;b, SOC, and SOC stock was a site-specific property and cannot be assumed a priori.

Detection of two intermixed invasive woody species using color infrared aerial imagery and the support vector machine classifier

Abstract Both the evergreen redberry juniper (Juniperus pinchotii Sudw.) and deciduous honey mesquite (Prosopis glandulosa Torr.) are destructive and aggressive invaders that affect rangelands and grasslands of the southern Great Plains of the United States. However, their current spatial extent and future expansion trends are unknown. This study was aimed at: (1) exploring the utility of aerial imagery for detecting and mapping intermixed redberry juniper and honey mesquite while both are in full foliage using the support vector machine classifier at two sites in north central Texas and, (2) assessing and comparing the mapping accuracies between sites. Accuracy assessments revealed that the overall accuracies were 90% with the associated kappa coefficient of 0.86% and 89% with the associated kappa coefficient of 0.85 for sites 1 and 2, respectively. Z -statistics ( 0.102 < 1.96 ) used to compare the classification results for both sites indicated an insignificant difference between classifications at 95% probability level. In most instances, juniper and mesquite were identified correctly with < 7 % being mistaken for the other woody species. These results indicated that assessment of the current infestation extent and severity of these two woody species in a spatial context is possible using aerial remote sensing imagery.

Overview of rural water supply sector in West Bengal, India: challenges and concerns

ABSTRACT:Objective of this study was to reconnoitre existing rural water supply infrastructure in West Bengal between 2009 and 2014, which is indispensable for laying out the strategies for sustainable water management and human development but currently is lacking. Results indicated that West Bengal ranked 21 in India in 2014 in terms of receiving ‘full coverage’ (FC: 40 litres of piped water supply per capita per day; lpcd) as compared to 11 in 2009. In districts of Bardhaman, Birbhum, Cooch Bihar, Hoogli, Puruliya, Dinajpurs, over three-fourth of blocks lacked FC in over 50% of rural habitations. Additionally, in 14 districts water supply services have ‘slipped-back’ between 2012 and 2014: dropping from 40 lpcd (FC) to <40 lpcd, which challenges well-being of a vast cross-section of populace. Overall, the study indicated growing concerns that need to be addressed with region-specific knowledge of natural and human-induced factors. Such studies should also be performed in other parts of India, threatened by similar ‘inadequacies’.