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At least 1,315 records · Page 73Linked to original sources
USGS2009

Relations between sinkhole density and anthropogenic contaminants in selected carbonate aquifers in the eastern United States

The relation between sinkhole density and water quality was investigated in seven selected carbonate aquifers in the eastern United States. Sinkhole density for these aquifers was grouped into high (>25 sinkholes/100 km 2 ), medium (1–25 sinkholes/100 km 2 ), or low (<1 sinkhole/100 km 2 ) categories using a geographical information system that included four independent databases covering parts of Alabama, Florida, Missouri, Pennsylvania, and Tennessee. Field measurements and concentrations of major ions, nitrate, and selected pesticides in samples from 451 wells and 70 springs were included in the water-quality database. Data were collected as a part of the US Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program. Areas with high and medium sinkhole density had the greatest well depths and depths to water, the lowest concentrations of total dissolved solids and bicarbonate, the highest concentrations of dissolved oxygen, and the lowest partial pressure of CO 2 compared to areas with low sinkhole density. These chemical indicators are consistent conceptually with a conduit-flow-dominated system in areas with a high density of sinkholes and a diffuse-flow-dominated system in areas with a low density of sinkholes. Higher cave density and spring discharge in Pennsylvania also support the concept that the high sinkhole density areas are dominated by conduit-flow systems. Concentrations of nitrate-N were significantly higher ( p < 0.05) in areas with high and medium sinkhole density than in low sinkhole-density areas; when accounting for the variations in land use near the sampling sites, the high sinkhole-density area still had higher concentrations of nitrate-N than the low sinkhole-density area. Detection frequencies of atrazine, simazine, metolachlor, prometon, and the atrazine degradate deethylatrazine indicated a pattern similar to nitrate; highest pesticide detections were associated with high sinkhole-density areas. These patterns generally persisted when analyzing the detection frequency by land-use groups, particularly for agricultural land-use areas where pesticide use would be expected to be higher and more uniform areally compared to urban and forested areas. Although areas with agricultural land use and a high sinkhole density were most vulnerable (median nitrate-N concentration was 3.7 mg/L, 11% of samples exceeded 10 mg/L, and had the highest frequencies of pesticide detection), areas with agricultural land use and low sinkhole density still were vulnerable to contamination (median nitrate-N concentration was 1.5 mg/L, 8% of samples exceeded 10 mg/L, and had some of the highest frequencies of detections of pesticides). This may be due in part to incomplete or missing data regarding karst features (such as buried sinkholes, low-permeability material in bottom of sinkholes) that do not show up at the scales used for regional mapping and to inconsistent methods among states in karst feature delineation.

Missouri↗
USGS2009

A shallow subsurface controlled release facility in Bozeman, Montana, USA, for testing near surface CO2 detection techniques and transport models

A controlled field pilot has been developed in Bozeman, Montana, USA, to study near surface CO2 transport and detection technologies. A slotted horizontal well divided into six zones was installed in the shallow subsurface. The scale and CO2 release rates were chosen to be relevant to developing monitoring strategies for geological carbon storage. The field site was characterized before injection, and CO2 transport and concentrations in saturated soil and the vadose zone were modeled. Controlled releases of CO2 from the horizontal well were performed in the summers of 2007 and 2008, and collaborators from six national labs, three universities, and the U.S. Geological Survey investigated movement of CO2 through the soil, water, plants, and air with a wide range of near surface detection techniques. An overview of these results will be presented.

Montana↗
USGS2009

Changes in the chemistry of shallow groundwater related to the 2008 injection of CO2 at the ZERT field site, Bozeman, Montana

Approximately 300 kg/day of food-grade CO 2 was injected through a perforated pipe placed horizontally 2–2.3 m deep during July 9–August 7, 2008 at the MSU-ZERT field test to evaluate atmospheric and near-surface monitoring and detection techniques applicable to the subsurface storage and potential leakage of CO 2 . As part of this multidisciplinary research project, 80 samples of water were collected from 10 shallow monitoring wells (1.5 or 3.0 m deep) installed 1–6 m from the injection pipe, at the southwestern end of the slotted section (zone VI), and from two distant monitoring wells. The samples were collected before, during, and following CO 2 injection. The main objective of study was to investigate changes in the concentrations of major, minor, and trace inorganic and organic compounds during and following CO 2 injection. The ultimate goals were (1) to better understand the potential of groundwater quality impacts related to CO 2 leakage from deep storage operations, (2) to develop geochemical tools that could provide early detection of CO 2 intrusion into underground sources of drinking water (USDW), and (3) to test the predictive capabilities of geochemical codes against field data. Field determinations showed rapid and systematic changes in pH (7.0–5.6), alkalinity (400–1,330 mg/l as HCO 3 ), and electrical conductance (600–1,800 μS/cm) following CO 2 injection in samples collected from the 1.5 m-deep wells. Laboratory results show major increases in the concentrations of Ca (90–240 mg/l), Mg (25–70 mg/l), Fe (5–1,200 ppb), and Mn (5–1,400 ppb) following CO 2 injection. These chemical changes could provide early detection of CO 2 leakage into shallow groundwater from deep storage operations. Dissolution of observed carbonate minerals and desorption-ion exchange resulting from lowered pH values following CO 2 injection are the likely geochemical processes responsible for the observed increases in the concentrations of solutes; concentrations generally decreased temporarily following four significant precipitation events. The DOC values obtained are 5 ± 2 mg/l, and the variations do not correlate with CO 2 injection. CO 2 injection, however, is responsible for detection of BTEX (e.g. benzene, 0–0.8 ppb), mobilization of metals, the lowered pH values, and increases in the concentrations of other solutes in groundwater. The trace metal and BTEX concentrations are all significantly below the maximum contaminant levels (MCLs). Sequential leaching of core samples is being carried out to investigate the source of metals and other solutes.

Montana↗
USGS2010

Landslide-dammed lake at Tangjiashan, Sichuan province, China (triggered by the Wenchuan Earthquake, May 12, 2008): Risk assessment, mitigation strategy, and lessons learned

Landslides and rock avalanches triggered by the 2008 Wenchuan Earthquake produced 257 landslide dams, mainly situated along the eastern boundary of the Qinghai-Tibet Plateau where rivers descend approximately 3,000 m into the Sichuan Basin. The largest of these dams blocked the Tongkou River (a tributary of the Fujiang River) at Tangjiashan. The blockage, consisting of 2.04 × 10 7 m 3 of landslide debris, impounded a lake with a projected maximum volume of 3.15 × 10 8 m 3 , potentially inundating 8.92 km 2 of terrain. Its creation during the rainy season and the possibility of an uncontrolled release posed a serious, impending threat to at least 1.3 million people downstream that could add substantially to the total of 69,200 individuals directly killed by the earthquake. Risk assessment of the blockage indicated that it was unlikely to collapse suddenly, and that eventual overtopping could be mitigated by notching the structure in order to create an engineered breach and achieve safe drainage of the lake. In addition to the installation of monitoring and warning instrumentation, for emergency planning we estimated several outburst scenarios equivalent to 20, 25, 33, and 50% of the dam failing suddenly, creating, respectively, 3.35, 3.84, 4.22, and 4.65 km 2 of flooded area, and overbank water depths of 4.6, 5.1, 5.7, and 6.2 m, respectively, in Mianyang, the second largest city in Sichuan Province, 48 km downstream from the blockage. Based on these scenarios, recommendations and plans for excavating a sluiceway, draining the lake, and downstream evacuation were proposed and later were implemented successfully, with the blockage breached by overtopping on June 10, less than a month after dam emplacement. The peak discharge of the release only slightly exceeded the flood of record at Mianyang City. No lives were lost, and significant property damage was avoided. Post-breaching evaluation reveals how future similar mitigation can be improved. Although initial breach erosion was slow, later erosion was judged uncontrollably rapid; increased slope of the engineered channel and adoption of a compound, trapezoid–triangular cross-section can be considered, as can other measures to control the rate of breach incision. Evacuees from Mianyang City spent an unnecessarily long time (12 days) in temporary settlements; more precise risk management planning can reduce this time in the future.

Sichuan Province↗
USGS2010

The dispersion of fibrous amphiboles by glacial processes in the area surrounding Libby, Montana, USA

Mining operations began at a world-class vermiculite deposit at Vermiculite Mountain near Libby, Montana, circa 1920 and ended in 1990. Fibrous and asbestiform amphiboles intergrown with vermiculite ore are suspected to be a causative factor in an abnormally high number of cases of respiratory diseases in former mine and mill workers, and in residents of Libby. The question addressed in this report is whether some of the amphibole from Vermiculite Mountain could have been dispersed by Pleistocene glacial processes rather than by human activity after vermiculite mining began. The history of Pinedale glaciation in the Libby area provides a framework for estimating the presence and distribution of asbestiform amphiboles derived from Vermiculite Mountain and found in naturally occurring sediments of Glacial Lake Kootenai that underlie the Libby Valley area. There were two situations where sediments derived from Vermiculite Mountain were deposited into Glacial Lake Kootenai: (1) as lake-bottom sediments derived from meltwater flowing down Rainy Creek when the valley south of Vermiculite Mountain was free of ice but active ice still covered Vermiculite Mountain; and (2) as lake-bottom sediments eroded from the Rainy Creek outwash and re-deposited during a re-advance of the Purcell Trench Glacier lobe near Moyie Springs, Idaho.

Montana↗
USGS2011

Arsenic associations in sediments from shallow aquifers of northwestern Hetao Basin, Inner Mongolia

Understanding the mechanism of arsenic mobilization from sediments to groundwater is important for water quality management in areas of endemic arsenic poisoning, such as the Hetao Basin in Inner Mongolia, northern China. Aquifer geochemistry was characterized at three field sites (SH, HF, TYS) in Hangjinhouqi County of northwestern Hetao Basin. The results of bulk geochemistry analysis of sediment samples indicated that total As concentrations have a range of 6. 8-58. 5 mg/kg, with a median of 14. 4 mg/kg. The highest As concentrations were found at 15-25 m depth. In the meanwhile, the range of As concentration in the sediments from background borehole is 3-21. 8 mg/kg, with a median value of 9 mg/kg. The As sediments concentrations with depth from the SH borehole were correlated with the contents of Fe, Sb, B, V, total C and total S. Generally, the abundance of elements varied with grain size, with higher concentrations in finer fractions of the sediments. Distinct lithology profile and different geochemical characteristics of aquifer sediments indicate the sediments are associated with different sources and diverse sedimentary environments. Up to one third of arsenic in the sediments could be extracted by ammonium oxalate, suggesting that Fe oxyhydroxides may be the major sink of As in the aquifer. Sequential extraction results indicate that arsenic occurs as strongly adsorbed on and/or co-precipitated with amorphous Fe oxyhydroxides in sediments accounting for 35 and 20%, respectively, of the total contents of arsenic. The release of As into groundwater may occur by desorption from the mineral surface driven by reductive dissolution of the Fe oxide minerals. Furthermore, small proportions of As associated with iron sulfides occur in the reductive sediments. ?? 2011 Springer-Verlag.

Environmental Earth Sciences↗
USGS2011

Transient electromagnetic study of basin fill sediments in the Upper San Pedro Basin, Mexico

The Upper San Pedro River Basin in Mexico and the United States is an important riparian corridor that is coming under increasing pressure from growing populations and the associated increase in groundwater withdrawal. Several studies have produced three-dimensional maps of the basin fill sediments in the US portion of the basin but little work has been done in the Mexican portion of the basin. Here, the results of a ground-based transient electromagnetic (TEM) survey in the Upper San Pedro Basin, Mexico are presented. These basin fill sediments are characterized by a 10–40 m deep unsaturated surficial zone which is composed primarily of sands and gravels. In the central portion of the basin this unsaturated zone is usually underlain by a shallow clay layer 20–50 m thick. Beneath this may be more clay, as is usually the case near the San Pedro River, or interbedded sand, silt, and clay to a depth of 200–250 m. As you move away from the river, the upper clay layer disappears and the amount of sand in the sediments increases. At 1–2 km away from the river, sands can occupy up to 50% of the upper 200–250 m of the sediment fill. Below this, clays are always present except where bedrock highs are observed. This lower clay layer begins at a depth of about 200 m in the central portion of the basin (250 m or more at distances greater than 1–2 km from the river) and extends to the bottom of most profiles to depths of 400 m. While the depth of the top of this lower clay layer is probably accurate, its thickness observed in the models may be overestimated due to the relatively low magnetic moment of the TEM system used in this study. The inversion routine used for interpretation is based on a one-dimensional geologic model. This is a layer based model that is isotropic in both the x and y directions. Several survey soundings did not meet this requirement which invalidates the inversion process and the resulting interpretation at these locations. The results from these locations were rejected.

Arizona↗
USGS2011

Processes affecting geochemistry and contaminant movement in the middle Claiborne aquifer of the Mississippi embayment aquifer system

Groundwater chemistry and tracer-based age data were used to assess contaminant movement and geochemical processes in the middle Claiborne aquifer (MCA) of the Mississippi embayment aquifer system. Water samples were collected from 30 drinking-water wells (mostly domestic and public supply) and analyzed for nutrients, major ions, pesticides, volatile organic compounds (VOCs), and transient age tracers (chlorofluorocarbons, tritium and helium-3, and sulfur hexafluoride). Redox conditions are highly variable throughout the MCA. However, mostly oxic groundwater with low dissolved solids is more vulnerable to nitrate contamination in the outcrop areas east of the Mississippi River in Mississippi and west Tennessee than in mostly anoxic groundwater in downgradient areas in western parts of the study area. Groundwater in the outcrop area was relatively young (apparent age of less than 40 years) with significantly ( p < 0.05) higher dissolved oxygen and nitrate&ndash;N concentrations and higher detections of pesticides and VOCs compared to water samples from wells in downgradient areas. Oxygen reduction and denitrification rates were low compared to other aquifers in the United States (zero order rate constants for oxygen reduction and denitrification were 4.7 and 5&ndash;10 &mu;mol/L/year, respectively). Elevated concentrations of nitrate&ndash;N, and detections of pesticides and VOCs in some deep public supply wells (>50 m depth) indicated contaminant movement from shallow parts of the aquifer into deeper oxic zones. Given the persistence of nitrate in young oxic groundwater that was recharged several decades ago, and the lack of a confining unit, the downward movement of young contaminated water may result in higher nitrate concentrations over time in deeper parts of the aquifer containing older oxic water.

Claiborne Aquifer;Mississippi Embayment↗
USGS2012

Using hydrogeology to identify the source of groundwater to Montezuma Well, a natural spring in central Arizona: part 1

Montezuma Well is a natural spring located within a “sinkhole” in the desert environment of the Verde Valley in Central Arizona. It is managed by the National Park Service as part of Montezuma Castle National Monument. Because of increasing development of groundwater in the area, this research was undertaken to better understand the sources of groundwater to Montezuma Well. The use of well logs and geophysics provides details on the geology in the area around Montezuma Well. This includes characterizing the extent and position of a basalt dike that intruded a deep fracture zone. This low permeability barrier forces groundwater to the surface at the Montezuma Well “pool” with sufficient velocity to entrain sand-sized particles from underlying bedrock. Permeable fractures along and above the basalt dike provide conduits that carry deep sourced carbon dioxide to the surface, which can dissolve carbonate minerals along the transport path in response to the added carbon dioxide. At the ground surface, CO 2 degasses, depositing travertine. Geologic cross sections, rock geochemistry, and semi-quantitative groundwater flow modeling provide a hydrogeologic framework that indicates groundwater flow through a karstic limestone at depth (Redwall Limestone) as the most significant source of groundwater to Montezuma Well. Additional groundwater flow from the overlying formations (Verde Formation and Permian Sandstones) is a possibility, but significant flow from these units is not indicated.

Arizona↗
USGS2012

Using geochemistry to identify the source of groundwater to Montezuma Well, a natural spring in Central Arizona, USA: Part 2

Montezuma Well is a unique natural spring located in a sinkhole surrounded by travertine. Montezuma Well is managed by the National Park Service, and groundwater development in the area is a potential threat to the water source for Montezuma Well. This research was undertaken to better understand the sources of groundwater to Montezuma Well. Strontium isotopes ( 87 Sr/ 86 Sr) indicate that groundwater in the recharge area has flowed through surficial basalts with subsequent contact with the underlying Permian aged sandstones and the deeper, karstic, Mississippian Redwall Limestone. The distinctive geochemistry in Montezuma Well and nearby Soda Springs (higher concentrations of alkalinity, As, B, Cl, and Li) is coincident with added carbon dioxide and mantle-sourced He. The geochemistry and isotopic data from Montezuma Well and Soda Springs allow for the separation of groundwater samples into four categories: (1) upgradient, (2) deep groundwater with carbon dioxide, (3) shallow Verde Formation, and (4) mixing zone. δ 18 O and δD values, along with noble gas recharge elevation data, indicate that the higher elevation areas to the north and east of Montezuma Well are the groundwater recharge zones for Montezuma Well and most of the groundwater in this portion of the Verde Valley. Adjusted groundwater age dating using likely 14 C and δ 13 C sources indicate an age for Montezuma Well and Soda Springs groundwaters at 5,400–13,300 years, while shallow groundwater in the Verde Formation appears to be older (18,900). Based on water chemistry and isotopic evidence, groundwater flow to Montezuma Well is consistent with a hydrogeologic framework that indicates groundwater flow by (1) recharge in higher elevation basalts to the north and east of Montezuma Well, (2) movement through the upgradient Permian and Mississippian units, especially the Redwall Limestone, and (3) contact with a basalt dike/fracture system that provides a mechanism for groundwater to flow to the surface. While the exact nature of the groundwater flow connections is still uncertain, the available data indicate that flow to Montezuma Well may be more susceptible to future groundwater development in the Redwall Limestone than from any other geologic unit. Overall, the shallow groundwater in the surrounding Verde Formation appears to be largely disconnected from deeper groundwater flowing to Montezuma Well.

Arizona↗
USGS2012

Development and application of a soil organic matter-based soil quality index in mineralized terrane of the Western US

Soil quality indices provide a means of distilling large amounts of data into a single metric that evaluates the soil’s ability to carry out key ecosystem functions. Primarily developed in agroecosytems, then forested ecosystems, an index using the relation between soil organic matter and other key soil properties in more semi-arid systems of the Western US impacted by different geologic mineralization was developed. Three different sites in two different mineralization types, acid sulfate and Cu/Mo porphyry in California and Nevada, were studied. Soil samples were collected from undisturbed soils in both mineralized and nearby unmineralized terrane as well as waste rock and tailings. Eight different microbial parameters (carbon substrate utilization, microbial biomass-C, mineralized-C, mineralized-N and enzyme activities of acid phosphatase, alkaline phosphatase, arylsulfatase, and fluorescein diacetate) along with a number of physicochemical parameters were measured. Multiple linear regression models between these parameters and both total organic carbon and total nitrogen were developed, using the ratio of predicted to measured values as the soil quality index. In most instances, pooling unmineralized and mineralized soil data within a given study site resulted in lower model correlations. Enzyme activity was a consistent explanatory variable in the models across the study sites. Though similar indicators were significant in models across different mineralization types, pooling data across sites inhibited model differentiation of undisturbed and disturbed sites. This procedure could be used to monitor recovery of disturbed systems in mineralized terrane and help link scientific and management disciplines.

Environmental Earth Sciences↗
USGS2012

Assessment of regional change in nitrate concentrations in groundwater in the Central Valley, California, USA, 1950s-2000s

A regional assessment of multi-decadal changes in nitrate concentrations was done using historical data and a spatially stratified non-biased approach. Data were stratified into physiographic subregions on the basis of geomorphology and soils data to represent zones of historical recharge and discharge patterns in the basin. Data were also stratified by depth to represent a shallow zone generally representing domestic drinking-water supplies and a deep zone generally representing public drinking-water supplies. These stratifications were designed to characterize the regional extent of groundwater with common redox and age characteristics, two factors expected to influence changes in nitrate concentrations over time. Overall, increasing trends in nitrate concentrations and the proportion of nitrate concentrations above 5 mg/L were observed in the east fans subregion of the Central Valley. Whereas the west fans subregion has elevated nitrate concentrations, temporal trends were not detected, likely due to the heterogeneous nature of the water quality in this area and geologic sources of nitrate, combined with sparse and uneven data coverage. Generally low nitrate concentrations in the basin subregion are consistent with reduced geochemical conditions resulting from low permeability soils and higher organic content, reflecting the distal portions of alluvial fans and historical groundwater discharge areas. Very small increases in the shallow aquifer in the basin subregion may reflect downgradient movement of high nitrate groundwater from adjacent areas or overlying intensive agricultural inputs. Because of the general lack of regionally extensive long-term monitoring networks, the results from this study highlight the importance of placing studies of trends in water quality into regional context. Earlier work concluded that nitrate concentrations were steadily increasing over time in the eastern San Joaquin Valley, but clearly those trends do not apply to other physiographic subregions within the Central Valley, even where land use and climate are similar.

California↗
USGS2013

A GIS and statistical approach to identify variables that control water quality in hydrothermally altered and mineralized watersheds, Silverton, Colorado, USA

Hydrothermally altered bedrock in the Silverton mining area, southwest Colorado, USA, contains sulfide minerals that weather to produce acidic and metal-rich leachate that is toxic to aquatic life. This study utilized a geographic information system (GIS) and statistical approach to identify watershed-scale geologic variables in the Silverton area that influence water quality. GIS analysis of mineral maps produced using remote sensing datasets including Landsat Thematic Mapper, advanced spaceborne thermal emission and reflection radiometer, and a hybrid airborne visible infrared imaging spectrometer and field-based product enabled areas of alteration to be quantified. Correlations between water quality signatures determined at watershed outlets, and alteration types intersecting both total watershed areas and GIS-buffered areas along streams were tested using linear regression analysis. Despite remote sensing datasets having varying watershed area coverage due to vegetation cover and differing mineral mapping capabilities, each dataset was useful for delineating acid-generating bedrock. Areas of quartz–sericite–pyrite mapped by AVIRIS have the highest correlations with acidic surface water and elevated iron and aluminum concentrations. Alkalinity was only correlated with area of acid neutralizing, propylitically altered bedrock containing calcite and chlorite mapped by AVIRIS. Total watershed area of acid-generating bedrock is more significantly correlated with acidic and metal-rich surface water when compared with acid-generating bedrock intersected by GIS-buffered areas along streams. This methodology could be useful in assessing the possible effects that alteration type area has in either generating or neutralizing acidity in unmined watersheds and in areas where new mining is planned.

Colorado↗
USGS2013

Factors affecting the movement and persistence of nitrate and pesticides in the surficial and upper Floridan aquifers in two agricultural areas in the southeastern United States

Differences in the degree of confinement, redox conditions, and dissolved organic carbon (DOC) are the main factors that control the persistence of nitrate and pesticides in the Upper Floridan aquifer (UFA) and overlying surficial aquifer beneath two agricultural areas in the southeastern US. Groundwater samples were collected multiple times from 66 wells during 1993–2007 in a study area in southwestern Georgia (ACFB) and from 48 wells in 1997–98 and 2007–08 in a study area in South Carolina (SANT) as part of the US Geological Survey National Water-Quality Assessment Program. In the ACFB study area, where karst features are prevalent, elevated nitrate-N concentrations in the oxic unconfined UFA (median 2.5 mg/L) were significantly (p = 0.03) higher than those in the overlying oxic surficial aquifer (median 1.5 mg/L). Concentrations of atrazine and deethylatrazine (DEA; the most frequently detected pesticide and degradate) were higher in more recent groundwater samples from the ACFB study area than in samples collected prior to 2000. Conversely, in the SANT study area, nitrate-N concentrations in the UFA were mostly <0.06 mg/L, resulting from anoxic conditions and elevated DOC concentrations that favored denitrification. Although most parts of the partially confined UFA in the SANT study area were anoxic or had mixed redox conditions, water from 28 % of the sampled wells was oxic and had low DOC concentrations. Based on the groundwater age information, nitrate concentrations reflect historic fertilizer N usage in both the study areas, but with a lag time of about 15–20 years. Simulated responses to future management scenarios of fertilizer N inputs indicated that elevated nitrate-N concentrations would likely persist in oxic parts of the surficial aquifer and UFA for decades even with substantial decreases in fertilizer N inputs over the next 40 years.

Florida;Georgia;South Carolina↗
USGS2014

The long-term trends (1982-2006) in vegetation greenness of the alpine ecosystem in the Qinghai-Tibetan Plateau

The increased rate of annual temperature in the Qinghai-Tibetan Plateau exceeded all other areas of the same latitude in recent decades. The influence of the warming climate on the alpine ecosystem of the plateau was distinct. An analysis of alpine vegetation under changes in climatic conditions was conducted in this study. This was done through an examination of vegetation greenness and its relationship with climate variability using the Advanced Very High Resolution Radiometer satellite imagery and climate datasets. Vegetation in the plateau experienced a positive trend in greenness, with 18.0 % of the vegetated areas exhibiting significantly positive trends, which were primarily located in the eastern and southwestern parts of the plateau. In grasslands, 25.8 % of meadows and 14.1 % of steppes exhibited significant upward trends. In contrast, the broadleaf forests experienced a trend of degradation. Temperature, particularly summer temperature, was the primary factor promoting the vegetation growth in the plateau. The wetter and warmer climate in the east contributed to the favorable conditions for vegetation. The alpine meadow was mostly sensitive to temperature, while the steppes were sensitive to both temperature and precipitation. Although a warming climate was expected to be beneficial to vegetation growth in the alpine region, the rising temperature coupled with reduced precipitation in the south did not favor vegetation growth due to low humidity and poor soil moisture conditions.

Qinghai-tibetan Plateau↗
USGS2015

Geochemical evolution of groundwater in the Mud Lake area, eastern Idaho, USA

Groundwater with elevated dissolved-solids concentrations&mdash;containing large concentrations of chloride, sodium, sulfate, and calcium&mdash;is present in the Mud Lake area of Eastern Idaho. The source of these solutes is unknown; however, an understanding of the geochemical sources and processes controlling their presence in groundwater in the Mud Lake area is needed to better understand the geochemical sources and processes controlling the water quality of groundwater at the Idaho National Laboratory. The geochemical sources and processes controlling the water quality of groundwater in the Mud Lake area were determined by investigating the geology, hydrology, land use, and groundwater geochemistry in the Mud Lake area, proposing sources for solutes, and testing the proposed sources through geochemical modeling with PHREEQC. Modeling indicated that sources of water to the eastern Snake River Plain aquifer were groundwater from the Beaverhead Mountains and the Camas Creek drainage basin; surface water from Medicine Lodge and Camas Creeks, Mud Lake, and irrigation water; and upward flow of geothermal water from beneath the aquifer. Mixing of groundwater with surface water or other groundwater occurred throughout the aquifer. Carbonate reactions, silicate weathering, and dissolution of evaporite minerals and fertilizer explain most of the changes in chemistry in the aquifer. Redox reactions, cation exchange, and evaporation were locally important. The source of large concentrations of chloride, sodium, sulfate, and calcium was evaporite deposits in the unsaturated zone associated with Pleistocene Lake Terreton. Large amounts of chloride, sodium, sulfate, and calcium are added to groundwater from irrigation water infiltrating through lake bed sediments containing evaporite deposits and the resultant dissolution of gypsum, halite, sylvite, and bischofite.

Idaho↗
USGS2016

Effect of phytoremediation on concentrations of benzene, toluene, naphthalene, and dissolved oxygen in groundwater at a former manufactured gas plant site, Charleston, South Carolina, USA, 1998–2014

Concentrations of benzene, toluene, naphthalene, and dissolved oxygen in groundwater at a former manufactured gas plant site near Charleston, South Carolina, USA, have been monitored since the installation of a phytoremediation system of hybrid poplar trees in 1998. Between 2000 and 2014, the concentrations of benzene, toluene, and naphthalene (BT&N) in groundwater in the planted area have decreased. For example, in the monitoring well containing the highest concentrations of BT&N, benzene concentrations decreased from 10,200 &micro;g/L to less than 4000 &micro;g/L, toluene concentrations decreased from 2420 &micro;g/L to less than 20 &micro;g/L, and naphthalene concentrations decreased from 6840 &micro;g/L to less than 3000 &micro;g/L. Concentrations of BT&N in groundwater in all wells were observed to be lower during the summer months relative to the winter months of a particular year during the first few years after installing the phytoremediation system, most likely due to increased transpiration and contaminant uptake by the hybrid poplar trees during the warm summer months; this pathway of uptake by trees was confirmed by the detection of benzene, toluene, and naphthalene in trees during sampling events in 2002, and later in the study in 2012. These data suggest that the phytoremediation system affects the groundwater contaminants on a seasonal basis and, over multiple years, has resulted in a cumulative decrease in dissolved-phase contaminant concentrations in groundwater. The removal of dissolved organic contaminants from the aquifer has resulted in a lower demand on dissolved oxygen supplied by recharge and, as a result, the redox status of the groundwater has changed from anoxic to oxic conditions. This study provides much needed information for water managers and other scientists on the viability of the long-term effectiveness of phytoremediation in decreasing groundwater contaminants and increasing dissolved oxygen at sites contaminated by benzene, toluene, and naphthalene.

South Carolina↗