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At least 973 records · Page 54Linked to original sources
USGS2010

Using Selective Drainage Methods to Extract Continuous Surface Flow from 1-Meter Lidar-Derived Digital Elevation Data

Digital elevation data commonly are used to extract surface flow features. One source for high-resolution elevation data is light detection and ranging (lidar). Lidar can capture a vast amount of topographic detail because of its fine-scale ability to digitally capture the surface of the earth. Because elevation is a key factor in extracting surface flow features, high-resolution lidar-derived digital elevation models (DEMs) provide the detail needed to consistently integrate hydrography with elevation, land cover, structures, and other geospatial features. The U.S. Geological Survey has developed selective drainage methods to extract continuous surface flow from high-resolution lidar-derived digital elevation data. The lidar-derived continuous surface flow network contains valuable information for water resource management involving flood hazard mapping, flood inundation, and coastal erosion. DEMs used in hydrologic applications typically are processed to remove depressions by filling them. High-resolution DEMs derived from lidar can capture much more detail of the land surface than courser elevation data. Therefore, high-resolution DEMs contain more depressions because of obstructions such as roads, railroads, and other elevated structures. The filling of these depressions can significantly affect the DEM-derived surface flow routing and terrain characteristics in an adverse way. In this report, selective draining methods that modify the elevation surface to drain a depression through an obstruction are presented. If such obstructions are not removed from the elevation data, the filling of depressions to create continuous surface flow can cause the flow to spill over an obstruction in the wrong location. Using this modified elevation surface improves the quality of derived surface flow and retains more of the true surface characteristics by correcting large filled depressions. A reliable flow surface is necessary for deriving a consistently connected drainage network, which is important in understanding surface water movement and developing applications for surface water runoff, flood inundation, and erosion. Improved methods are needed to extract continuous surface flow features from high-resolution elevation data based on lidar.

Scientific Investigations Report↗
USGS2022

Advances in the study and understanding of groundwater discharge to surface water

Groundwater discharge is vitally important for maintaining or restoring valuable ecosystems in surface water and at the underlying groundwater-surface-water ecotone . Detecting and quantifying groundwater discharge is challenging because rates of flow can be very small and difficult to measure, exchange is commonly highly heterogeneous both in space and time, and surface-water hydrodynamics can influence the exchange and hinder measurements . Fortunately, a growing number of methods developed during the last several decades has led to advancements in our capabilities to identify and quantify groundwater discharge to surface water, including better use of seepage meters , application of tracers such as heat or isotopes , and improved groundwater-modeling capabilities . This progress has led to coalescence in characterizing the complex mix of hydrological, biological, and chemical processes that occur at the groundwater-surface water interface , along with relevant societal effects . Still, many uncertainties and assumptions show an incomplete knowledge of these processes, including the lack of studies in many regions of the world, insufficient sharing of practical methodologies between scientific disciplines , incomplete understanding of processes and parameters specific to the sediment-water interface , and challenges associated with measuring exchange at multiple scales of time and space.

Water↗
USGS2010

Paleoclimates: Understanding climate change past and present

The field of paleoclimatology relies on physical, chemical, and biological proxies of past climate changes that have been preserved in natural archives such as glacial ice, tree rings, sediments, corals, and speleothems. Paleoclimate archives obtained through field investigations, ocean sediment coring expeditions, ice sheet coring programs, and other projects allow scientists to reconstruct climate change over much of earth's history. When combined with computer model simulations, paleoclimatic reconstructions are used to test hypotheses about the causes of climatic change, such as greenhouse gases, solar variability, earth's orbital variations, and hydrological, oceanic, and tectonic processes. This book is a comprehensive, state-of-the art synthesis of paleoclimate research covering all geological timescales, emphasizing topics that shed light on modern trends in the earth's climate. Thomas M. Cronin discusses recent discoveries about past periods of global warmth, changes in atmospheric greenhouse gas concentrations, abrupt climate and sea-level change, natural temperature variability, and other topics directly relevant to controversies over the causes and impacts of climate change. This text is geared toward advanced undergraduate and graduate students and researchers in geology, geography, biology, glaciology, oceanography, atmospheric sciences, and climate modeling, fields that contribute to paleoclimatology. This volume can also serve as a reference for those requiring a general background on natural climate variability.

Book↗
USGS2019

Modeling connectivity of non‐floodplain wetlands: Insights, approaches, and recommendations

Representing hydrologic connectivity of non‐floodplain wetlands (NFWs) to downstream waters in process‐based models is an emerging challenge relevant to many research, regulatory, and management activities. We review four case studies that utilize process‐based models developed to simulate NFW hydrology. Models range from a simple, lumped parameter model to a highly complex, fully distributed model. Across case studies, we highlight appropriate application of each model, emphasizing spatial scale, computational demands, process representation, and model limitations. We end with a synthesis of recommended “best modeling practices” to guide model application. These recommendations include: (1) clearly articulate modeling objectives, and revisit and adjust those objectives regularly; (2) develop a conceptualization of NFW connectivity using qualitative observations, empirical data, and process‐based modeling; (3) select a model to represent NFW connectivity by balancing both modeling objectives and available resources; (4) use innovative techniques and data sources to validate and calibrate NFW connectivity simulations; and (5) clearly articulate the limits of the resulting NFW connectivity representation. Our review and synthesis of these case studies highlights modeling approaches that incorporate NFW connectivity, demonstrates tradeoffs in model selection, and ultimately provides actionable guidance for future model application and development.

Journal of the American Water Resources Associatio↗
USGS1996

Effect of snow and firn hydrology on the physical and chemical characteristics of glacial runoff

Near-surface processes on glaciers, including water flow over bare ice and through seasonal snow and firn, have a significant effect on the speed, volume and chemistry of water flow through the glacier. The transient nature of the seasonal snow profoundly affects the water discharge and chemistry. Water flow through snow is fairly slow compared with flow over bare ice and a thinning snowpack on a glacier decreases the delay between peak meltwater input and peak stream discharge. Furthermore, early spring melt flushes the snowpack of solutes and by mid-summer the melt water flowing into the glacier is fairly clean by comparison. The firn, a relatively constant feature of glaciers, attenuates variations in water drainage into the glacier by temporarily storing water in saturated layer. Bare ice exerts opposite influences by accentuating variations in runoff by water flowing over the ice surface. The melt of firn and ice contributes relatively clean (solute-free) water to the glacier water system.

Hydrological Processes↗
USGS2008

Application of a geomorphic and temporal perspective to wetland management in North America

The failure of managed wetlands to provide a broad suite of ecosystem services (e.g., carbon storage, wildlife habitat, ground-water recharge, storm-water retention) valuable to society is primarily the result of a lack of consideration of ecosystem processes that maintain productive wetland ecosystems or physical and social forces that restrict a manager's ability to apply actions that allow those processes to occur. Therefore, we outline a course of action that considers restoration of ecosystem processes in those systems where off-site land use or physical alterations restrict local management. Upon considering a wetland system, or examining a particular management regime, there are several factors that will allow successful restoration of wetland services. An initial step is examination of the political/social factors that have structured the current ecological condition and whether those realities can be addressed. Most successful restorations of wetland ecosystem services involve cooperation among multiple agencies, acquisition of funds from non-traditional sources, seeking of scientific advice on ecosystem processes, and cultivation of good working relationships among biologists, managers, and maintenance staff. Beyond that, in on-site wetland situations, management should examine the existing hydrogeomorphic situation and processes (e.g., climatic variation, tides, riverine flood-pulse events) responsible for maintenance of ecosystem services within a given temporal framework appropriate for that wetland's hydrologic pattern. We discuss these processes for five major wetland types (depressional, lacustrine, estuarine, riverine, and man-made impoundments) and then provide two case histories in which this approach was applied: Seney National Wildlife Refuge with a restored fen system and Bosque del Apache National Wildlife Refuge where riverine processes have been simulated to restore native habitat. With adequate partnerships and administrative and political support, managers faced with degraded and/or disconnected wetland processes will be able to restore ecosystem services for society in our highly altered landscape by considering wetlands in their given hydrogeomorphic setting and temporal stage. ?? 2008 The Society of Wetland Scientists.

Wetlands↗
USGS2025

ARCHI: A new R package for automated imputation of regionally correlated hydrologic records

Missing data in hydrological records can limit resource assessment, process understanding, and predictive modeling. Here, we present ARCHI (Automated Regional Correlation Analysis for Hydrologic Record Imputation), a new, open-source software package in R designed to aggregate, impute, cluster, and visualize regionally correlated hydrologic records. ARCHI imputes missing data in “target” records by linear regression using more complete “reference” records as predictors. Automated imputation is implemented using a novel, iterative algorithm that allows each site to be considered a target or reference for regression, growing the pool of complete references with each imputed record until viable gap-filling ceases. Users can limit artifacts from spurious correlations by specifying model-acceptance criteria and applying geospatial, correlation, and group-based filters to control reference selection. ARCHI provides additional functions for visualizing results, clustering records with similar correlation structures, evaluating holdout data, and interactive parameterization with an accessible and intuitive graphical user interface (GUI). This methods brief provides an overview of the ARCHI package, modeling guidelines, and benchmarking on two regional groundwater-level datasets from the Central Valley, CA and Long Island, NY. We evaluate ARCHI alongside widely used multivariate imputation software to highlight and contextualize its computational efficiency, imputation accuracy, and model transparency when applied to large, groundwater-level datasets.

California, New York↗
USGS2011

Effects of conservation practices on wetland ecosystem services in the Mississippi Alluvial Valley

Restoration of wetland ecosystems is an important priority for many state and federal agencies, as well as nongovernmental conservation organizations. The historic conversion of wetlands in the Mississippi Alluvial Valley (MAV) has resulted in large‐scale implementation of a variety of conservation practices designed to restore and enhance wetland ecosystem services. As a consequence, the effectiveness of multiple approaches in achieving desired conservation goals varies depending on site conditions, practices employed, and specific ecosystem services. We reviewed government agency programs and the scientific literature to evaluate the effects of conservation practices on wetlands in the MAV. There were 68 different conservation practices applied to a combined total of 1.27 million ha in the MAV between 2000 and 2006. These practices fell into two categories: Wetland Conservation Practices and Upland Conservation Practices. Sixteen different practices accounted for nearly 92% of the total area, and only three of these are directly related to wetlands: Wetland Wildlife Habitat Management, Wetland Restoration, and Riparian Forest Buffer. All three of these practices involve reforestation, primarily planting hard‐mast species such as Quercus sp. and Carya sp. These plantings are likely to develop into even‐aged stands of low tree diversity with little structural heterogeneity, which will impact future wildlife habitat. Since hydrology is a critical driver of wetland processes, the ability of a given conservation practice to restore wetland hydrology is a key determinant of how well it can restore ecosystem services. However, there is little to no follow‐up monitoring of projects, so it is difficult to know how much variability exists for any given practice or the efficacy of specific practices. Conservation practices that only plant trees without reconnecting the wetland to the hydrologic and nutrient fluxes in the watershed may restore some wildlife habitat but will do little for regulating services such as nitrogen retention. While conservation practices have overall beneficial effects on many ecosystem services in the MAV, the most effective are those with a direct link between the actions associated with a given practice and controls over ecosystem processes and services.

Arkansas, Kentucky, Louisiana, Mississippi, Missou↗
USGS2021

Reconstruction of an extreme flood hydrograph and morphodynamics of a meander bend in a high-peak discharge variability river (Powder River, USA)

Understanding of morphodynamic processes associated with large-scale floods has recently improved following significant advances of modern technologies. Nevertheless, a clear link between flood discharge and in-channel sedimentation processes remains to be resolved. The hydrological and geomorphological data available for the meandering Powder River (Montana, USA) since 1977 makes it a perfect laboratory to investigate connections between flood discharge and point-bar sedimentation processes. This study focuses on a point-bar that accreted laterally ca 70 m during a 50-year recurrence flood, which lasted about 14 days in May 1978. In September 2018, a trench ca 2 m deep and 70 m long was excavated through the axial point-bar deposits, and the 1978 flood deposits were delineated based on georeferenced pre-flood and post-flood cross-section surveys. Sedimentological data show that point-bar deposits accumulated at the early and late flood stages, when the flow was confined to the channel, and have similarities with classical facies models in terms of palaeocurrent patterns and vertical grain-size trend. However, during high-stage flood conditions, when the flow overtopped the bar, cross-cutting of the bar and armouring were typical processes. Integration of sedimentological and palaeo-hydrological data highlight that the relation between channel cross-sectional area and flood discharge play a key role in preserving bar deposits. The integrated approach adopted here provides a basis for advancing palaeoflood hydrology beyond the stage of estimating peak discharges to the next stage of estimating palaeoflood hydrographs.

Montana↗
USGS2012

P2S--Coupled simulation with the Precipitation-Runoff Modeling System (PRMS) and the Stream Temperature Network (SNTemp) Models

A software program, called P2S, has been developed which couples the daily stream temperature simulation capabilities of the U.S. Geological Survey Stream Network Temperature model with the watershed hydrology simulation capabilities of the U.S. Geological Survey Precipitation-Runoff Modeling System. The Precipitation-Runoff Modeling System is a modular, deterministic, distributed-parameter, physical-process watershed model that simulates hydrologic response to various combinations of climate and land use. Stream Network Temperature was developed to help aquatic biologists and engineers predict the effects of changes that hydrology and energy have on water temperatures. P2S will allow scientists and watershed managers to evaluate the effects of historical climate and projected climate change, landscape evolution, and resource management scenarios on watershed hydrology and in-stream water temperature.

Open-File Report↗
USGS2000

Stable isotope systematics of sulfate minerals

Stable isotope studies of sulfate minerals are especially useful for unraveling the geochemical history of geological systems. All sulfate minerals can yield sulfur and oxygen isotope data. Hydrous sulfate minerals, such as gypsum, also yield oxygen and hydrogen isotope data for the water of hydration, and more complex sulfate minerals, such as alunite and jarosite also yield oxygen and hydrogen isotope data from hydroxyl sites. Applications of stable isotope data can be divided into two broad categories: geothermometry and tracer studies. The equilibrium partitioning of stable isotopes between two substances, such as the isotopes of sulfur between barite and pyrite, is a function of temperature. Studies can also use stable isotopes as a tracer to fingerprint various sources of hydrogen, oxygen, and sulfur, and to identify physical and chemical processes such as evaporation of water, mixing of waters, and reduction of sulfate to sulfide. Studies of sulfate minerals range from low-temperature surficial processes associated with the evaporation of seawater to form evaporite deposits to high-temperature magmatic-hydrothermal processes associated with the formation of base-and precious-metal deposits. Studies have been conducted on scales from submicroscopic chemical processes associated with the weathering of pyrite to global processes affecting the sulfur budget of the oceans. Sulfate isotope studies provide important information to investigations of energy and mineral resources, environmental geochemistry, paleoclimates, oceanography (past and present), sedimentary, igneous, and metamorphic processes, Earth systems, geomicrobiology, and hydrology. One of the most important aspects of understanding and interpreting the stable isotope characteristics of sulfate minerals is the complex interplay between equilibrium and kinetic chemical and isotopic processes. With few exceptions, sulfate minerals are precipitated from water or have extensively interacted with water at some time in their history. Because of this nearly ubiquitous association with water, the kinetics of isotopic exchange reactions among dissolved species and solids are fundamental in dictating the isotopic composition of sulfate minerals. In general, the heavier isotope of sulfur is enriched in the higher oxidation state, such that under equilibrium conditions, sulfate minerals (e.g. barite, anhydrite) are expected to be enriched in the heavy isotope relative to disulfide minerals (e.g. pyrite, marcasite), which in turn are expected to be enriched relative to monosulfide minerals (e.g. pyrrhotite, sphalerite, galena) ( Sakai 1968 , Bachinski 1969 ). The kinetics of isotopic exchange among minerals with sulfur at the same oxidation state, such as sphalerite, and galena, are such that equilibrium is commonly observed. In contrast, isotopic equilibrium for exchange reactions between minerals of different oxidation states depends on factors such as the pH, time and temperature of reaction, the direction of reaction, fluid composition, and the presence or absence of catalysts ( Ohmoto and Lasaga 1982 ). The kinetics of oxygen isotope exchange between dissolved sulfate and water are extremely sluggish. Extrapolation of the high-temperature (100 to 300°C) isotopic exchange kinetic data of Chiba and Sakai (1985) to ambient temperatures suggests that it would take several billions of years for dissolved sulfate and seawater to reach oxygen isotopic equilibrium. In contrast, the residence time of sulfate in the oceans is only 7.9 million years ( Holland 1978 ). However, at higher temperatures (>200°C), oxygen isotopic exchange is sufficiently rapid to permit application of sulfate isotope geothermometry to geothermal systems and hydrothermal mineral deposits. In general, equilibrium prevails at low pH and high temperatures, whereas kinetic factors preclude equilibrium at low temperatures even at low pH. Thus, the sluggish kinetics of sulfur and oxygen isotope exchange reaction at low temperatures impair the use of these isotopes to understand the conditions of formation of sulfate minerals in these environments. However, because of these slow kinetics, the oxygen and sulfur isotopic compositions of sulfate minerals may preserve a record of the sources and processes that initially produced the dissolved sulfate, because the isotope ratios may not re-equilibrate during fluid transport and mineral precipitation. The first part of this chapter is designed to provide the reader with a basic understanding of the principles that form the foundations of stable isotope geochemistry. Next, an overview of analytical methods used to determine the stable isotope composition of sulfate minerals is presented. This overview is followed by a discussion of geochemical processes that determine the stable isotope characteristics of sulfate minerals and related compounds. The chapter then concludes with an examination of the stable isotope systematics of sulfate minerals in a variety of geochemical environments.

Reviews in Mineralogy and Geochemistry↗
USGS1965

Hydrology of subsurface waste disposal, National Reactor Testing Station, Idaho: Annual progress report for 1964

The principal purpose of the past research program on geohydrology at the NRTS has been to acquire information on the physical and geochemical environment of the station. This requires a knowledge of the composition and structure of the earth materials underlying the plain, the inventory of the water resources, the dynamics of natural and man-produced changes in the hydrologic regimen, details of the hydrologic cycle, and relevant geochemical processes. The Geological Survey in the course of its early studies by Nace and others (IDO 22033-34-USGS) obtained, compiled, and analyzed a considerable amount of basic geologic and hydrologic information on these subjects. These basic goals were expanded and carried forward to guide the continuing research work. Jones (IDO 22042-USGS) emphasized the use of borehole geophysics and specialized down-hole techniques. Olmsted (IDO 22043-USGS) made a preliminary appraisal of the nature and distribution of the quality of ground water beneath the Station. Their work has been continued and elaborated upon by Morris and others (IDO 22044-USGS, 46-USGS) and the present report with greater emphasis on the regional geology and hydrology. This involved some procurement of needed information but, for the most part, involved a continued evaluation and refinement of data and results that had been acquired in the past. The Geological Survey also encouraged a more comprehensive study of the regional geologic structure including the use of aeromagnetic, gravity, and seismic geophysical techniques and cosponsored a seminar on it in 1964. Along with this investigation and study of the regional geology and of hydrologic principles operative in the basalt environment, and made possible because of it, research continues on the-hydrologic aspects of the disposal of low-level aqueous waste to the environment.

Idaho↗
USGS1990

Multidisciplinary hydrologic investigations at Yucca Mountain, Nevada

Future climatic conditions and tectonic processes have the potential to cause significant changes of the hydrologic system in the southern Great Basin, where a nuclear-waste repository is proposed for construction above the water table at Yucca Mountain, Nevada. Geothermal anomalies in the vicinity of Yucca Mountain probably result from the local and regional transport of heat by ground-water flow. Regionally and locally irregular patterns of hydraulic potential, local marsh and pond deposits, and calcite veins in faults and fractures probably are related principally to climatically imposed hydrologic conditions within the geologic and topographic framework. However, tectonic effects on the hydrologic system have also been proposed as the causes of these features, and existing data limitations preclude a full evaluation of these competing hypotheses. A broad program that integrates many disciplines of earth science is required in order to understand the relation of hydrology to past, present and future climates and tectonism.

Conference Paper↗
USGS2016

Insights into plant water uptake from xylem-water isotope measurements in two tropical catchments with contrasting moisture conditions

Water transpired by trees has long been assumed to be sourced from the same subsurface water stocks that contribute to groundwater recharge and streamflow. However, recent investigations using dual water stable isotopes have shown an apparent ecohydrological separation between tree-transpired water and stream water. Here we present evidence for such ecohydrological separation in two tropical environments in Puerto Rico where precipitation seasonality is relatively low and where precipitation is positively correlated with primary productivity. We determined the stable isotope signature of xylem water of 30 mahogany ( Swietenia spp.) trees sampled during two periods with contrasting moisture status. Our results suggest that the separation between transpiration water and groundwater recharge/streamflow water might be related less to the temporal phasing of hydrologic inputs and primary productivity, and more to the fundamental processes that drive evaporative isotopic enrichment of residual soil water within the soil matrix. The lack of an evaporative signature of both groundwater and streams in the study area suggests that these water balance components have a water source that is transported quickly to deeper subsurface storage compared to waters that trees use. A Bayesian mixing model used to partition source water proportions of xylem water showed that groundwater contribution was greater for valley-bottom, riparian trees than for ridge-top trees. Groundwater contribution was also greater at the xeric site than at the mesic–hydric site. These model results (1) underline the utility of a simple linear mixing model, implemented in a Bayesian inference framework, in quantifying source water contributions at sites with contrasting physiographic characteristics, and (2) highlight the informed judgement that should be made in interpreting mixing model results, of import particularly in surveying groundwater use patterns by vegetation from regional to global scales.

Hydrological Processes↗
USGS2012

Cyclic biogeochemical processes and nitrogen fate beneath a subtropical stormwater infiltration basin

A stormwater infiltration basin in north–central Florida, USA, was monitored from 2007 through 2008 to identify subsurface biogeochemical processes, with emphasis on N cycling, under the highly variable hydrologic conditions common in humid, subtropical climates. Cyclic variations in biogeochemical processes generally coincided with wet and dry hydrologic conditions. Oxidizing conditions in the subsurface persisted for about one month or less at the beginning of wet periods with dissolved O 2 and NO 3 - showing similar temporal patterns. Reducing conditions in the subsurface evolved during prolonged flooding of the basin. At about the same time O 2 and NO 3 - reduction concluded, Mn, Fe and SO 4 2 - reduction began, with the onset of methanogenesis one month later. Reducing conditions persisted up to six months, continuing into subsequent dry periods until the next major oxidizing infiltration event. Evidence of denitrification in shallow groundwater at the site is supported by median NO 3 -–N less than 0.016 mg L -1 , excess N 2 up to 3 mg L -1 progressively enriched in δ 15 N during prolonged basin flooding, and isotopically heavy δ 15 N and δ 18 O of NO 3 - (up to 25‰ and 15‰, respectively). Isotopic enrichment of newly infiltrated stormwater suggests denitrification was partially completed within two days. Soil and water chemistry data suggest that a biogeochemically active zone exists in the upper 1.4 m of soil, where organic carbon was the likely electron donor supplied by organic matter in soil solids or dissolved in infiltrating stormwater. The cyclic nature of reducing conditions effectively controlled the N cycle, switching N fate beneath the basin from NO 3 - leaching to reduction in the shallow saturated zone. Results can inform design of functionalized soil amendments that could replace the native soil in a stormwater infiltration basin and mitigate potential NO 3 - leaching to groundwater by replicating the biogeochemical conditions under the observed basin.

Florida↗
USGS2012

Linking river management to species conservation using dynamic landscape scale models

Efforts to conserve stream and river biota could benefit from tools that allow managers to evaluate landscape-scale changes in species distributions in response to water management decisions. We present a framework and methods for integrating hydrology, geographic context and metapopulation processes to simulate effects of changes in streamflow on fish occupancy dynamics across a landscape of interconnected stream segments. We illustrate this approach using a 482 km 2 catchment in the southeastern US supporting 50 or more stream fish species. A spatially distributed, deterministic and physically based hydrologic model is used to simulate daily streamflow for sub-basins composing the catchment. We use geographic data to characterize stream segments with respect to channel size, confinement, position and connectedness within the stream network. Simulated streamflow dynamics are then applied to model fish metapopulation dynamics in stream segments, using hypothesized effects of streamflow magnitude and variability on population processes, conditioned by channel characteristics. The resulting time series simulate spatially explicit, annual changes in species occurrences or assemblage metrics (e.g. species richness) across the catchment as outcomes of management scenarios. Sensitivity analyses using alternative, plausible links between streamflow components and metapopulation processes, or allowing for alternative modes of fish dispersal, demonstrate large effects of ecological uncertainty on model outcomes and highlight needed research and monitoring. Nonetheless, with uncertainties explicitly acknowledged, dynamic, landscape-scale simulations may prove useful for quantitatively comparing river management alternatives with respect to species conservation.

Georgia↗
USGS2014

Deposit model for heavy-mineral sands in coastal environments

This report provides a descriptive model of heavy-mineral sands, which are sedimentary deposits of dense minerals that accumulate with sand, silt, and clay in coastal environments, locally forming economic concentrations of the heavy minerals. This deposit type is the main source of titanium feedstock for the titanium dioxide (TiO 2 ) pigments industry, through recovery of the minerals ilmenite (Fe 2+ TiO 3 ), rutile (TiO 2 ), and leucoxene (an alteration product of ilmenite). Heavy-mineral sands are also the principal source of zircon (ZrSiO 4 ) and its zirconium oxide; zircon is often recovered as a coproduct. Other heavy minerals produced as coproducts from some deposits are sillimanite/kyanite, staurolite, monazite, and garnet. Monazite [(Ce,La,Nd,Th)PO 4 ] is a source of rare earth elements as well as thorium, which is used in thorium-based nuclear power under development in India and elsewhere. The processes that form coastal deposits of heavy-mineral sands begin inland. High-grade metamorphic and igneous rocks that contain heavy minerals weather and erode, contributing detritus composed of sand, silt, clay, and heavy minerals to fluvial systems. Streams and rivers carry the detritus to the coast, where they are deposited in a variety of coastal environments, such as deltas, the beach face (foreshore), the nearshore, barrier islands or dunes, and tidal lagoons, as well as the channels and floodplains of streams and rivers in the coastal plain. The sediments are reworked by waves, tides, longshore currents, and wind, which are effective mechanisms for sorting the mineral grains on the basis of differences in their size and density. The finest-grained, most dense heavy minerals are the most effectively sorted. The result is that heavy minerals accumulate together, forming laminated or lens-shaped, heavy-mineral-rich sedimentary packages that can be several meters and even as much as tens of meters thick. Most economic deposits of heavy-mineral sands are Paleogene, Neogene, and Quaternary in age; some are modern coastal deposits. Superimposed on these basic processes of ore formation are a multitude of contributing and modifying factors, such as the following: Strong, sustained wave action moves sand from offshore to the shore, where the sand and heavy minerals are sorted by size and density. Mineral sorting occurs mainly on the upper part of the hightide swash (wave) zone. Fine-grained sands and heavy minerals on the foreshore can be remobilized by winds, forming heavy mineral-rich sand dunes behind the beach. Longshore drift combined with the geomorphology of the coast exert strong influence on the location of the heavy-mineral sands deposits. Sea level changes are a function of climatic changes, such as ice ages. Rises in regional sea level (transgression) and lowering of sea level (regression) strongly influence the deposition and preservation of heavy-mineral sands. The majority of heavy-mineral sands accumulation appears related to seaward progradation of the shore during regression events. Local faulting may affect the geomorphology of the coast, which controls the distribution of heavy mineral deposition in a coastal basin. Heavy mineral grains appear to weather primarily after their deposition in the coastal plain; this weathering is caused by groundwaters, humic acids, and other intrabasinal fluids. This weathering can enhance the TiO 2 content of ilmenite. Iron is leached from ilmenite during weathering, which thereby upgrades the TiO 2 content of the ilmenite, forming leucoxene. The resulting deposits of heavy-mineral sands can be voluminous. Individual bodies of heavy mineral-rich sands are typically about 1 kilometer wide and more than 5 kilometers long. Many heavy-mineral sands districts extend for more than 10 kilometers and contain several individual deposits that are spread along an ancient or modern strandline. Reported thicknesses of economic deposits range from 3 to 45 meters. Individual ore deposits typically comprise at least 10 megatonnes of ore (the total size of the individual sand-silt body), whose overall heavy-mineral content is 2 to greater than 10 percent. Heavy-mineral sands deposits are relatively easy to mine because they are weakly to poorly consolidated, and they are relatively easy to process. From a geoenvironmental standpoint, mining of heavy mineral-sands generates little or no acid or solubilized metals. However, environmental and human health concerns related to such mining include potential effects on indigenous flora and fauna, effects on local hydrology, and issues related to processing and storing thorium-bearing monazite, owing to its radioactivity. Regional exploration for deposits of heavy-mineral sands can utilize the analyses of stream sediment samples for Ti, Hf, the rare earth elements, Th, and U, and geophysical surveys, particularly radiometric (gamma-ray spectrometry for K, U, and Th) and magnetic methods. Geophysical anomalies may be small, and surveys are generally more successful when conducted close to sources of interest.

Scientific Investigations Report↗
USGS1997

Geochemistry of the processes that attenuate acid mine drainage in wetlands

Because conventional treatment of acid-mine drainage (AMD) involves installation and maintenance of water treatment plants, regulators and mine operators have sought lower cost and lower maintenance technologies. One ecological engineering technology that has received increasing research attention is the use of natural and constructed wetlands for remediation of some of the water-quality problems associated with AMD. As surface water flows through a wetland, several processes can occur to decrease the elevated concentrations of sulfate, trace metals, arsenic, and hydrogen ions that characterize AMD. These processes range from precipitation of mineral phases to the active uptake of solutes by vegetation. The relative importance of these processes between different wetlands depends on the hydrologic and geochemical characteristics of the wetlands. This paper describes the geochemistry of the processes that contribute to AMD attenuation in wetlands and presents some of the case studies that have identified these processes. The attenuation of AMD in wetlands has been studied in natural and in man- made (constructed) wetlands. In this paper, case studies of both are presented. A discussion of some of the general characteristics of wetlands is followed by more detailed discussions of the processes and geochemistry that contribute to the treatment of AMD in wetlands, relevant case studies, and a brief discussion of constructed wetland design. The physical, chemical, and hydrologic characteristics of a wetland that affect its potential for supporting specific types of reactions are also emphasized.

Book chapter↗