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At least 811 records · Page 45Linked to original sources

Development of perennial thaw zones in boreal hillslopes enhances potential mobilization of permafrost carbon

Permafrost thaw alters subsurface flow in boreal regions that in turn influences the magnitude, seasonality, and chemical composition of streamflow. Prediction of these changes is challenged by incomplete knowledge of timing, flowpath depth, and amount of groundwater discharge to streams in response to thaw. One important phenomenon that may affect flow and transport through boreal hillslopes is development of lateral perennial thaw zones (PTZs), the existence of which is here supported by geophysical observations and cryohydrogeologic modeling. Model results link thaw to enhanced and seasonally-extended baseflow, which have implications for mobilization of soluble constituents. Results demonstrate the sensitivity of PTZ development to organic layer thickness and near-surface factors that mediate heat exchange at the atmosphere/ground-surface interface. Study findings suggest that PTZs serve as a detectable precursor to accelerated permafrost degradation. This study provides important contextual insight on a fundamental thermo-hydrologic process that can enhance terrestrial-to-aquatic transfer of permafrost carbon, nitrogen, and mercury previously sequestered in thawing watersheds.

Alaska↗

Invasive species management and research using GIS

Geographical Information Systems (GIS) are powerful tools in the field of invasive species management. GIS can be used to create potential distribution maps for all manner of taxa, including plants, animals, and diseases. GIS also performs well in the early detection and rapid assessment of invasive species. Here, we used GIS applications to investigate species richness and invasion patterns in fish in the United States (US) at the 6-digit Hydrologic Unit Code (HUC) level. We also created maps of potential spread of the cane toad (Bufo marinus) in the southeastern US at the 8-digit HUC level using regression and environmental envelope techniques. Equipped with this potential map, resource managers can target their field surveys to areas most vulnerable to invasion. Advances in GIS technology, maps, data, and many of these techniques can be found on websites such as the National Institute of Invasive Species Science (www.NIISS.org). Such websites provide a forum for data sharing and analysis that is an invaluable service to the invasive species community.

Conference Paper↗

Resource subsidies between stream and terrestrial ecosystems under global change

Streams and adjacent terrestrial ecosystems are characterized by permeable boundaries that are crossed by resource subsidies. Although the importance of these subsidies for riverine ecosystems is increasingly recognized, little is known about how they may be influenced by global environmental change. Drawing from available evidence, in this review we propose a conceptual framework to evaluate the effects of global change on the quality and spatiotemporal dynamics of stream–terrestrial subsidies. We illustrate how changes to hydrological and temperature regimes, atmospheric CO 2 concentration, land use and the distribution of nonindigenous species can influence subsidy fluxes by affecting the biology and ecology of donor and recipient systems and the physical characteristics of stream–riparian boundaries. Climate-driven changes in the physiology and phenology of organisms with complex life cycles will influence their development time, body size and emergence patterns, with consequences for adjacent terrestrial consumers. Also, novel species interactions can modify subsidy dynamics via complex bottom-up and top-down effects. Given the seasonality and pulsed nature of subsidies, alterations of the temporal and spatial synchrony of resource availability to consumers across ecosystems are likely to result in ecological mismatches that can scale up from individual responses, to communities, to ecosystems. Similarly, altered hydrology, temperature, CO 2 concentration and land use will modify the recruitment and quality of riparian vegetation, the timing of leaf abscission and the establishment of invasive riparian species. Along with morphological changes to stream–terrestrial boundaries, these will alter the use and fluxes of allochthonous subsidies associated with stream ecosystems. Future research should aim to understand how subsidy dynamics will be affected by key drivers of global change, including agricultural intensification, increasing water use and biotic homogenization. Our conceptual framework based on the match–mismatch between donor and recipient organisms may facilitate understanding of the multiple effects of global change and aid in the development of future research questions.

Global Change Biology↗

Panola Mountain, Georgia: A Water, Energy, and Biogeochemical Budgets Program Site

The Panola Mountain Research Watershed (PMRW) is a 41-hectare forested watershed in the southern Piedmont physiographic province near Atlanta, Georgia. The watershed contains a naturally regenerated second-growth forest on abandoned agricultural land, typical of the Piedmont. Research at PMRW has focused on how streamflow is generated, and in particular, on how water and solutes move from hillslopes to the stream. The research shows that streamflow and solute concentrations of precipitation, throughfall, soil water and streamwater change rapidly during rainstorms. Furthermore, these variations are strongly associated with the soil-moisture conditions, the soil type and thickness, and the rainfall intensity, all of which effect the chemical interactions and mixing of water traveling along hydrological pathways over and through the bedrock and soils.

Georgia↗

A conceptual workflow for projecting future riverine and coastal flood hazards to support the federal flood risk management standard

In 2021, the reinstatement of the Federal Flood Risk Management Standard (FFRMS) required federally funded projects to recognize potential increases in flood hazards over their service lives due to climate change or local anthropogenic perturbations. Recognizing that the state of the science had advanced since the implementation guidelines for this standard were published in 2015 (WRC, 2015, Appendix H), an interagency state-of-the-science review committee conceptualized a workflow to guide the mapping and risk communication of projected future flood hazards in both riverine and coastal settings. This five-element workflow connects climate, hydrologic, and hydraulic models, incorporates land and water management impacts and ongoing geomorphic changes, and can be tailored to the unique nature of different agency needs and resources. These conceptual workflows also provide a basis for a Climate-Informed Science Approach (CISA) implementation roadmap that identifies incremental steps for addressing the research and data gaps elucidated in our review. Many of these incremental steps present opportunities for interagency collaboration that would facilitate the rollout of the FFRMS in diverse riverine and coastal settings of the United States. We conduct case-study thought experiments to evaluate the implementation of the riverine and coastal workflows at three different locations in the United States: central Indiana, Galveston, Texas, and a small coastal community in western Alaska (Shaktoolik). Our thought experiments consider different project horizons, data availability, failure consequences, technical training requirements, and computational resources.

Conference Paper↗

Examining Submarine Ground-Water Discharge into Florida Bay by using 222Rn and Continuous Resistivity Profiling

Estimates of submarine ground-water discharge (SGD) into Florida Bay remain one of the least understood components of a regional water balance. To quantify the magnitude and seasonality of SGD into upper Florida Bay, research activities included the use of the natural geochemical tracer, 222Rn, to examine potential SGD hotspots (222Rn surveys) and to quantify the total (saline + fresh water component) SGD rates at select sites (222Rn time-series). To obtain a synoptic map of the 222Rn distribution within our study site in Florida Bay, we set up a flow-through system on a small boat that consisted of a Differential Global Positioning System, a calibrated YSI, Inc CTD sensor with a sampling rate of 0.5 min, and a submersible pump (z = 0.5 m) that continuously fed water into an air/water exchanger that was plumbed simultaneously into four RAD7 222Rn air monitors. To obtain local advective ground-water flux estimates, 222Rn time-series experiments were deployed at strategic positions across hydrologic and geologic gradients within our study site. These time-series stations consisted of a submersible pump, a Solinist DIVER (to record continuous CTD parameters) and two RAD7 222Rn air monitors plumbed into an air/water exchanger. Repeat time-series 222Rn measurements were conducted for 3-4 days across several tidal excursions. Radon was also measured in the air during each sampling campaign by a dedicated RAD7. We obtained ground-water discharge information by calculating a 222Rn mass balance that accounted for lateral and horizontal exchange, as well as an appropriate ground-water 222Rn end member activity. Another research component utilized marine continuous resistivity profiling (CRP) surveys to examine the subsurface salinity structure within Florida Bay sediments. This system consisted of an AGI SuperSting 8 channel receiver attached to a streamer cable that had two current (A,B) electrodes and nine potential electrodes that were spaced 10 m apart. A separate DGPS continuously sent position information to the SuperSting. Results indicate that the 222Rn maps provide a useful gauge of relative ground-water discharge into upper Florida Bay. The 222Rn time-series measurements provide a reasonable estimate of site- specific total (saline and fresh) ground-water discharge (mean = 12.5+-11.8 cm d-1), while the saline nature of the shallow ground-water at our study site, as evidenced by CPR results, indicates that most of this discharge must be recycled sea water. The CRP data show some interesting trends that appear to be consistent with subsurface geologic and hydrologic characterization. For example, some of the highest resistivity (electrical conductivity-1) values were recorded where one would expect a slight subsurface freshening (for example bayside Key Largo, or below the C111 canal).

Open-File Report↗

Sand deposition in shoreline eddies along five Wild and Scenic Rivers, Idaho

Sand bars deposited along the lateral margin of a river channel are frequently a focus of recreational activities. Sand bars are appealing sites on which to camp, picnic, fish and relax because they are relatively flat, soft, non-cohesive sand, free of vegetation and near the water's edge. The lack of vegetation and cohesion make sand bars easily erodible. Without appreciable deposition of new material, number and size of bars through a given reach of river will decline substantially over a period of years. We studied 63 beaches and their associated eddies located throughout 10 selected reaches within the designated Wild and Scenic River sections of the Lochsa, Selway, Middle Fork Clearwater, Middle Fork Salmon and Salmon Rivers in Idaho to determine the relation of beaches to the frequency and magnitude of streamflows that deposit appreciable quantities of sand. At present, these rivers have been altered little, if at all, by flow regulation, and only the Salmon River has substantial diversion upstream of a study reach. The river reaches studied have an abundance of sand bar beaches of appreciable size, in spite of suspended sand concentrations that rarely exceeded a few hundred milligrams per litre even during the largest floods. Calculated mean annual rates of deposition in an eddy vary from 5.8 to more than 100 cm depending primarily on: (1) the duration of streamflows that inundate the eddy sand bar depositions; (2) the rate of the flow exchange between the channel and an eddy and (3) the concentrations of suspended sand in the primary channel. The annual thickness of sand deposition in an eddy varies greatly from year to year depending on the duration of relatively large streamflows. Maximum annual sand depositions in an eddy are three to nine times the estimated long-term mean values. Relatively large, sustained floods deposit an appreciable portion of total deposition over a period of years. For the period of record, 1930-2002, the seven largest annual depositions, which represent more than 40% of all material deposited over the Lochsa River 21.9 km eddy, occurred in the years with the seven largest instantaneous annual peak floods. Beach area and volume for most beaches, however, are less variable year-to-year than the variation in annual deposition would indicate. Accumulative 10-year weighed deposition rate was computed to estimate the effective variability of beach deposition. Although less variable than the annual deposition, the cumulative 10-year deposition calculated for the longest hydrologic records, 71 years, existing on the Idaho Wild and Scenic Rivers varied by more than an order of magnitude from less than 20 cm to more than 220 cm.

River Research and Applications↗

Connecting tributary mercury loads to nearshore and offshore sediments in Lake Superior

Lake Superior has a vast and largely undeveloped watershed in comparison to the other Great Lakes, which makes it challenging to study mercury (Hg) sources and cycling. To examine Hg inputs to Lake Superior, we conducted an expansive binational assessment in 40 watersheds from a diverse range of landcover types. We further paired tributary Hg data to sediment source portfolios in the nearshore and offshore zones of Lake Superior through partnership with the Great Lakes Sediment Surveillance Program. We observed that total Hg loads were highest in the spring driven by the combination of elevated Hg concentrations and increased water discharge from snowmelt. In addition, total Hg concentrations in tributaries from remote, heavily forested regions, such as Pukaskwa National Park and the Minnesota Northshore, were higher than the Southshore and Thunder Bay regions. Methylmercury concentrations and loads were more spatially dependent, often corresponding to regions with more wetlands (e.g., Michigan Upper Peninsula). We estimated that the total Hg tributary load to Lake Superior in 2021 was 126 kg per year. To further examine the fate of watershed Hg sources, we examined sediments from 28 sites in Lake Superior using Hg stable isotopes. At open water sites, precipitation was the primary Hg source to sediments, but within nearshore sites Hg originated predominantly from watershed runoff. This work further defines the sources and fate of Hg within Lake Superior and highlights how Hg delivery is intrinsically tied to varying hydrologic regimes.

Michigan, Minnesota, Ontario, Wisconsin↗

Interseismic ground deformation and fault slip rates in the greater San Francisco Bay Area from two decades of space geodetic data

The detailed spatial variations of strain accumulation and creep on major faults in the northern San Francisco Bay Area (North Bay), which are important for seismic potential and evaluation of natural hazards, remain poorly understood. Here we combine interferometric synthetic aperture radar data from the ERS‐1/2 and Envisat satellites between 1992 and 2010 with continuous and campaign GPS data to obtain a high spatial and temporal coverage of ground deformation of the North Bay. The SAR data from both ascending and descending orbits are combined to separate horizontal and vertical components of the deformation. We jointly invert the horizontal component of the mean velocities derived from these data to infer the deep strike‐slip rates on major locked faults. We use the estimated deep rates to simulate the long‐wavelength deformation due to interseismic elastic strain accumulation along these locked faults. After removing the long‐wavelength signal from the InSAR horizontal mean velocity field, we estimate fault‐parallel surface creep rates of up to 2 mm/year along the central section of the Rodgers Creek fault and surface creep rates ranging between 2 and 4 mm/year along the Concord fault. No surface creep is geodetically resolved along the West Napa and Green Valley fault zones. We identified characteristically repeating earthquakes on the Rodgers Creek fault, the West Napa fault, the Green Valley fault, and the Concord fault. Nontectonic deformation in the Geysers geothermal field and in Late Cenozoic basins (Rohnert Park and Sonoma basins) are also observed, likely due to hydrological and sediment‐compaction processes, respectively.

Journal of Geophysical Research B: Solid Earth↗

Mississippi’s resiliency and changing environmental conditions

Mississippi is experiencing shifts in environmental conditions, many of which are expected to intensify in the coming decades, and will have important implications for ecosystems, species, and natural resource management across the state. Historical climate analyses and downscaled projections summarized for the state’s Environmental Protection Agency (EPA) level III Ecoregions show that Mississippi will likely face increases in extremely hot days, more intense heatwaves, greater evapotranspiration, and reductions in cold-season extremes. Temperature trends indicate that while Mississippi has warmed relatively little over the last century, recent years have been among the warmest on record. Projections suggest substantial increases in the number of days with maximum temperatures at or above 95°F across all Ecoregions, particularly under higher warming scenarios. Correspondingly, the number of freezing nights is expected to decline, with statewide decreases of 7–21 days depending on the global warming level and timeframe. These combined patterns are likely to reshape habitat conditions, influence species’ thermal stress, and alter ecological processes such as soil moisture retention and stream temperature regimes. Mississippi’s hydrological systems are also expected to be significantly affected. Extreme rainfall events, particularly the most intense 1% of precipitation days, are projected to increase across the state, raising risks of flooding, erosion, and altered stream flow. Coastal Mississippi faces additional stress from sea‑level rise, which is already contributing to more frequent high‑tide flooding; projections show continued increases in inundation risk throughout the century. These flooding patterns, combined with stronger hurricane rainfall rates and the potential for landfalling storms to stall, pose ongoing threats to coastal ecosystems and communities. The state is also vulnerable to extreme weather hazards such as tornadoes. Recent research shows a geographic shift in tornado activity toward the Southeast, with Mississippi experiencing some of the nation’s greatest increases in favorable tornado days and nighttime tornado frequency—hazards that have direct implications for wildlife, habitat stability, and human safety. Drought conditions may intensify as well: higher temperatures and increased evapotranspiration during dry spells could worsen water stress regardless of uncertainty in average annual precipitation. These changing environmental conditions have important consequences for Mississippi’s Species of Greatest Conservation Need (SGCN). Vulnerability assessments and ecological niche models indicate that several fish, mussel, crayfish, plant, amphibian, bird, and mammal species may face heightened stress due to warming temperatures, shifting hydrology, habitat loss, and increases in extreme events. For example, many cold‑water and moisture‑dependent species in the state’s rivers and wetlands are already near their thermal limits, and further warming could reduce suitable habitat. Birds breeding in bottomland hardwood forests, such as the Prothonotary Warbler, are increasingly susceptible to nest loss from flooding. Similarly, species like the Louisiana Black Bear may encounter higher risks from habitat inundation and shifting food availability. The “A Closer Look” section underscores the vulnerability of the Mississippi Alluvial Plain—one of the state’s most ecologically rich yet heavily altered Ecoregions. Its bottomland hardwood forests, wetlands, and floodplain habitats support diverse wildlife but are increasingly threatened by rising temperatures, hydrological changes, development pressures, and compounded disturbances. These habitats provide critical ecosystem services such as water filtration, flood attenuation, and biodiversity support, making their conservation particularly urgent under future conditions. Collectively, these findings indicate that Mississippi’s ongoing and projected environmental changes present both challenges and opportunities for natural resource management. Incorporating adaptation strategies into the State Wildlife Action Plan will be essential for sustaining habitats, mitigating risks, and supporting the long‑term resilience of Mississippi’s wildlife and ecosystems.

Mississippi↗

Interactive effects of climate change with nutrients, mercury, and freshwater acidification on key taxa in the North Atlantic Landscape Conservation Cooperative region

The North Atlantic Landscape Conservation Cooperative LCC (NA LCC) is a public–private partnership that provides information to support conservation decisions that may be affected by global climate change (GCC) and other threats. The NA LCC region extends from southeast Virginia to the Canadian Maritime Provinces. Within this region, the US National Climate Assessment documented increases in air temperature, total precipitation, frequency of heavy precipitation events, and rising sea level, and predicted more drastic changes. Here, we synthesize literature on the effects of GCC interacting with selected contaminant, nutrient, and environmental processes to adversely affect natural resources within this region. Using a case study approach, we focused on 3 stressors with sufficient NA LCC region-specific information for an informed discussion. We describe GCC interactions with a contaminant (Hg) and 2 complex environmental phenomena—freshwater acidification and eutrophication. We also prepared taxa case studies on GCC- and GCC-contaminant/nutrient/process effects on amphibians and freshwater mussels. Several avian species of high conservation concern have blood Hg concentrations that have been associated with reduced nesting success. Freshwater acidification has adversely affected terrestrial and aquatic ecosystems in the Adirondacks and other areas of the region that are slowly recovering due to decreased emissions of N and sulfur oxides. Eutrophication in many estuaries within the region is projected to increase from greater storm runoff and less denitrification in riparian wetlands. Estuarine hypoxia may be exacerbated by increased stratification. Elevated water temperature favors algal species that produce harmful algal blooms (HABs). In several of the region's estuaries, HABs have been associated with bird die-offs. In the NA LCC region, amphibian populations appear to be declining. Some species may be adversely affected by GCC through higher temperatures and more frequent droughts. GCC may affect freshwater mussel populations via altered stream temperatures and increased sediment loading during heavy storms. Freshwater mussels are sensitive to un-ionized ammonia that more toxic at higher temperatures. We recommend studying the interactive effects of GCC on generation and bioavailability of methylmercury and how GCC-driven shifts in bird species distributions will affect avian exposure to methylmercury. Research is needed on how decreases in acid deposition concurrent with GCC will alter the structure and function of sensitive watersheds and surface waters. Studies are needed to determine how GCC will affect HABs and avian disease, and how more severe and extensive hypoxia will affect fish and shellfish populations. Regarding amphibians, we suggest research on 1) thermal tolerance and moisture requirements of species of concern, 2) effects of multiple stressors (temperature, desiccation, contaminants, nutrients), and 3) approaches to mitigate impacts of increased temperature and seasonal drought. We recommend studies to assess which mussel species and populations are vulnerable and which are resilient to rising stream temperatures, hydrological shifts, and ionic pollutants, all of which are influenced by GCC.

Chesapeake Bay↗

Aeolian sediments in paleowetland deposits of the Las Vegas Formation

The Las Vegas Formation (LVF) is a well-characterized sequence of groundwater discharge (GWD) deposits exposed in and around the Las Vegas Valley in southern Nevada. Nearly monolithologic bedrock surrounds the valley, which provides an excellent opportunity to test the hypothesis that GWD deposits include an aeolian component. Mineralogical data indicate that the LVF sediments are dominated by carbonate minerals, similar to the local bedrock, but silicate minerals are also present. The median particle size is ~35 μm, consistent with modern dust in the region, and magnetic properties contrast strongly with local bedrock, implying an extralocal origin. By combining geochemical data from the LVF sediments and modern dust, we found that an average of ~25% of the LVF deposits were introduced by aeolian processes. The remainder consists primarily of authigenic groundwater carbonate as well as minor amounts of alluvial material and soil carbonate. Our data also show that the aeolian sediments accumulated in spring ecosystems in the Las Vegas Valley in a manner that was independent of both time and the specific hydrologic environment. These results have broad implications for investigations of GWD deposits located elsewhere in the southwestern U.S. and worldwide.

Nevada↗

Identification of seasonal streamflow regimes and streamflow drivers for daily and peak flows in Alaska

Alaska is among northern high‐latitude regions where accelerated climate change is expected to impact streamflow properties, including seasonality and primary flow drivers. Evaluating changes to streamflow, including flood characteristics, across this large and diverse environment can be improved by identifying the distribution and influence of flow drivers. Using metrics of mean monthly streamflow data from 253 streamgages, seasonal flow regimes were clustered to guide identification of seasonal‐flow drivers and form hydrologic groups for identification of peak‐flow populations. Nine seasonally distinct subclasses described variability within three classes dominated by (mostly fall) rainfall, (spring) snowmelt, and (summer) high‐elevation melt. The most glacierized basins exclusively grouped into high‐elevation melt subclasses, and less glacierized basins sometimes exhibited seasonal patterns aligned with rainfall‐ and snowmelt‐dominated regimes. Peak‐flow populations varied by subclass from dominant rainfall or dominant snowmelt to mixed rainfall‐snowmelt or mixed rainfall, snowmelt, and high‐elevation melt. Within subclasses, rainfall generated higher mean peak flows (relative to mean annual flow) than snowmelt or high‐elevation melt. Seasonal flow regimes showed clear but complex associations with basin characteristics, primarily elevation and winter temperature, and with geographic location. These dependencies provided elevation‐based analogies for changes associated with warming and insights for seasonal flow regime prediction and hydrologic region delineation. These results provide a spatially comprehensive perspective on seasonal streamflow drivers across Alaska from historical data and serve as an important historical basis for analysis.

Alaska↗

Will it rise or will it fall? Managing the complex effects of urbanization on base flow

Sustaining natural levels of base flow is critical to maintaining ecological function as stream catchments are urbanized. Research shows a variable response of stream base flow to urbanization, with base flow or water tables rising in some locations, falling in others, or elsewhere remaining constant. The variable baseflow response is due to the array of natural (e.g., physiographic setting and climate) and anthropogenic (e.g., urban development and infrastructure) factors that influence hydrology. Perhaps as a consequence of this complexity, few simple tools exist to assist managers to predict baseflow change in their local urban area. This paper addresses this management need by presenting a decision support tool. The tool considers the natural vulnerability of the landscape, together with aspects of urban development in predicting the likelihood and direction of baseflow change. Where the tool identifies a likely increase or decrease it guides managers toward strategies that can reduce or increase groundwater recharge, respectively. Where the tool finds an equivocal result, it suggests a detailed water balance be performed. The decision support tool is embedded within an adaptive-management framework that encourages managers to define their ecological objectives, assess the vulnerability of their ecological objectives to changes in water table height, and monitor baseflow responses to urbanization. We trial our framework using two very different case studies: Perth, Western Australia, and Baltimore, Maryland, USA. Together, these studies show how pre-development water table height, climate and geology together with aspects of urban infrastructure (e.g., stormwater practices, leaky pipes) interact such that urbanization has overall led to rising base flow (Perth) and falling base flow (Baltimore). Greater consideration of subsurface components of the water cycle will help to protect and restore the ecology of urban freshwaters.

Maryland, Western Australia↗

Global GIS database. Digital atlas of Central and South America

This CD-ROM contains a digital atlas of the countries of Central and South America. This atlas is part of a global database compiled from USGS and other data sources at the nominal scale of 1:1 million and is intended to be used as a regional-scale reference and analytical tool by government officials, researchers, the private sector, and the general public. The atlas includes free GIS software or may also be used with ESRI's ArcView software. Customized ArcView tools, specifically designed to make the atlas easier to use, are also included. The atlas contains the following datasets: country political boundaries, digital shaded relief map, elevation, slope, hydrology, locations of cities and towns, airfields, roads, railroads, utility lines, population density, geology, ecological regions, historical seismicity, volcanoes, ore deposits, oil and gas fields, climate data, landcover, vegetation index, and lights at night.

Data Series↗

The tides and inflows in the mangroves of the Everglades (TIME) interdisciplinary project of the South Florida Ecosystem Program

The U. S. Geological Survey (USGS) has a prominent role in the Federal Government's comprehensive restoration plan for the south Florida ecosystem encompassing the Everglades-the largest remaining subtropical wilderness in the continental United States. USGS scientists, in collaboration with researchers from the National Park Service (NPS), other governmental agencies, and academia, are providing scientific information to land and resource managers for planning, executing, and evaluating restoration actions. One major thrust of the restoration effort is to restore the natural functioning of the ecosystem to predrainage conditions, an objective that requires knowledge of the hydrologic and hydraulic factors that affect the flow of water. A vast network of interlaced canals, rimmed with levees and fitted with hydraulic control structures, and highways, built on elevated embankments lined by borrow ditches and undercut by culverts, now act to control and direct the flow of water through the shallow low-gradient wetlands. As water flows south from Lake Okeechobee past the city of Miami and through Everglades National Park (ENP), it is diminished by canal diversions, augmented by seasonably variable precipitation, and depleted through evapotranspiration. Along its path, the shallow flowing water, referred to as sheet flow, interacts with surficial aquifers and is subject to the resistance effects of variably dense vegetation and forcing effects of winds. New scientific investigations are providing additional insight into the hydrologic and hydraulic processes governing the flow, and recent data-collection efforts are supplying more comprehensive data describing the flow behavior, both of which are benefiting development of improved numerical models to evaluate and restore the natural functioning of the ecosystem.

Florida↗

Application of drilling, coring, and sampling techniques to test holes and wells

The purpose of this manual is to provide ground-water hydrologists with a working knowledge of the techniques of test drilling, auger drilling, coring and sampling, and the related drilling and sampling equipment. For the most part, the techniques discussed deal with drilling, sampling, and completion of test holes in unconsolidated sediments because a hydrologist is interested primarily in shallow-aquifer data in this type of lithology. Successful drilling and coring of these materials usually is difficult, and published research information on the subject is not readily available. The authors emphasize in-situ sampling of unconsolidated sediments to obtain virtually undisturbed samples. Particular attention is given to auger drilling and hydraulic-rotary methods of drilling because these are the principal means of test drilling performed by the U.S. Geological Survey during hydrologic studies. Techniques for sampling areas contaminated by solid or liquid waste are discussed. Basic concepts of well development and a detailed discussion of drilling muds, as related to hole conditioning, also are included in the report. The information contained in this manual is intended to help ground-water hydrologists obtain useful subsurface data and samples from their drilling programs.

Techniques of Water-Resources Investigations↗

Potential warming-induced changes in stream water sources between proglacial and non-glacial streams, south-central Alaska

Snow and ice-melt are essential for global water resources. Rising air temperatures are causing vegetation encroachment and shrubification of previously snow- and ice-covered landscapes, and precipitation regimes are changing. Collectively, these changes will likely affect the hydrology of mountain environments, although the exact ways in which the hydrology will change are poorly understood. Changing source waters (i.e., the proportion of ice-melt, snowmelt, rain and groundwater) affect the timing and magnitude of streamflow and affect stream temperature, sediment, solute and nutrient fluxes. We investigate spatial and seasonal source water contributions across sub-watersheds of the Nellie Juan River watershed on Alaska's Kenai Peninsula, which differ in glacier cover, elevation and land cover, using a space-for-time approach. To do so, we use a three-endmember mixing model to quantify the contribution of rain, snow/ice-melt and deep groundwater. We show that snow/ice-melt peak later in proglacial streams compared to non-glacial streams. Endmember contributions in non-glacial streams generally vary with elevation and season. We also found that groundwater is a major contributor to streamflow across the study area, contributing between 12% and 47% seasonally, and may become increasingly important as snowpack and ice-melt decrease. This research characterises the shift from a glacierised to a deglaciating landscape through the lens of source water contribution. Broadly, these findings could help improve understanding of how water resources in glacierised watersheds are affected by warming air temperatures.

Alaska↗