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At least 271 records · Page 15Linked to original sources
USGS1997

Seismic reflection images beneath Puget Sound, western Washington State: The Puget Lowland thrust sheet hypothesis

Seismic reflection data show that the densely populated Puget Lowland of western Washington state is underlain by subhorizontal Paleogene and Neogene sedimentary rocks deformed by west and northwest trending faults and folds. From south to north beneath the Lowland, features seen on the seismic data include: the horizontally-stratified, 3.5 km thick Tacoma sedimentary basin; the Seattle uplift with south dipping (∼20°) strata on its south flank and steeply (50° to 90°) north dipping strata and the west-trending Seattle fault on its north flank; the 7.5 km thick, northward-thinning Seattle sedimentary basin; the antiformal Kingston arch; and the northwest trending, transpressional Southern Whidbey Island fault zone (SWIF). Interpreting the uplifts as fault-bend and fault-propagation folds leads to the hypothesis that the Puget Lowland lies on a north directed thrust sheet. The base of the thrust sheet may lie at 14 to 20 km depth within or at the base of a thick block of basaltic Crescent Formation; its edges may be right-lateral strike-slip faults along the base of the Cascade Range on the east and the Olympic Mountains on the west. Our model suggests that the Seattle fault has a long-term slip rate of about 0.25 mm/year and is large enough to generate a M 7.6 to 7.7 earthquake.

Washington↗
USGS2012

Simulation of climate change in San Francisco Bay Basins, California: Case studies in the Russian River Valley and Santa Cruz Mountains

As a result of ongoing changes in climate, hydrologic and ecologic effects are being seen across the western United States. A regional study of how climate change affects water resources and habitats in the San Francisco Bay area relied on historical climate data and future projections of climate, which were downscaled to fine spatial scales for application to a regional water-balance model. Changes in climate, potential evapotranspiration, recharge, runoff, and climatic water deficit were modeled for the Bay Area. In addition, detailed studies in the Russian River Valley and Santa Cruz Mountains, which are on the northern and southern extremes of the Bay Area, respectively, were carried out in collaboration with local water agencies. Resource managers depend on science-based projections to inform planning exercises that result in competent adaptation to ongoing and future changes in water supply and environmental conditions. Results indicated large spatial variability in climate change and the hydrologic response across the region; although there is warming under all projections, potential change in precipitation by the end of the 21st century differed according to model. Hydrologic models predicted reduced early and late wet season runoff for the end of the century for both wetter and drier future climate projections, which could result in an extended dry season. In fact, summers are projected to be longer and drier in the future than in the past regardless of precipitation trends. While water supply could be subject to increased variability (that is, reduced reliability) due to greater variability in precipitation, water demand is likely to steadily increase because of increased evapotranspiration rates and climatic water deficit during the extended summers. Extended dry season conditions and the potential for drought, combined with unprecedented increases in precipitation, could serve as additional stressors on water quality and habitat. By focusing on the relationship between soil moisture storage and evapotranspiration pressures, climatic water deficit integrates the effects of increasing temperature and varying precipitation on basin conditions. At the fine-scale used for these analyses, this variable is an effective indicator of the areas in the landscape that are the most resilient or vulnerable to projected changes. These analyses have shown that regardless of the direction of precipitation change, climatic water deficit is projected to increase, which implies greater water demand to maintain current agricultural resources or land cover. Fine-scale modeling provides a spatially distributed view of locations in the landscape that could prove to be resilient to climatic changes in contrast to locations where vegetation is currently living on the edge of its present-day bioclimatic distribution and, therefore, is more likely to perish or shift to other dominant species under future warming. This type of modeling and the associated analyses provide a useful means for greater understanding of water and land resources, which can lead to better resource management and planning.

California↗
USGS2017

Sparse targets in hydroacoustic surveys: Balancing quantity and quality of in situ target strength data

Hydroacoustic sampling of low-density fish in shallow water can lead to low sample sizes of naturally variable target strength (TS) estimates, resulting in both sparse and variable data. Increasing maximum beam compensation (BC) beyond conventional values (i.e., 3 dB beam width) can recover more targets during data analysis; however, data quality decreases near the acoustic beam edges. We identified the optimal balance between data quantity and quality with increasing BC using a standard sphere calibration, and we quantified the effect of BC on fish track variability, size structure, and density estimates of Lake Erie walleye ( Sander vitreus ). Standard sphere mean TS estimates were consistent with theoretical values (−39.6 dB) up to 18-dB BC, while estimates decreased at greater BC values. Natural sources (i.e., residual and mean TS) dominated total fish track variation, while contributions from measurement related error (i.e., number of single echo detections (SEDs) and BC) were proportionally low. Increasing BC led to more fish encounters and SEDs per fish, while stability in size structure and density were observed at intermediate values (e.g., 18 dB). Detection of medium to large fish (i.e., age-2+ walleye) benefited most from increasing BC, as proportional changes in size structure and density were greatest in these size categories. Therefore, when TS data are sparse and variable, increasing BC to an optimal value (here 18 dB) will maximize the TS data quantity while limiting lower-quality data near the beam edges.

Ohio↗
USGS2023

Monitoring of wave, current, and sediment dynamics along the Chincoteague living shoreline, Virginia

Nature-based features, also called living shorelines, are increasingly applied in coastal protection and restoration. However, the processes and mechanisms (feedbacks and interactions) of wave attenuation, current velocity change, and sediment deposition and erosion along the living shoreline remain unclear, thus limiting the adaptive management of living shoreline restoration projects for coastal shoreline resilience under future storm conditions. In this study, wave, current, and sediment dynamics along the Little Toms Cove living shoreline, Chincoteague National Wildlife Refuge, Virginia, a low wave energy environment, were investigated during a 2-month winter period in 2019 to examine the effects of living shoreline structures on shoreline protection and oyster habitat enhancement. It was found that wave attenuation by the living shoreline structures (oyster castles or constructed oyster reefs) is dependent on water depth, wind speed, wind direction, and local bathymetry. Analysis of observed data indicate that the oyster castles along the Little Toms Cove living shoreline play a limited role in wave attenuation in this low wave energy environment. During the 2-month winter period, wave energy was attenuated by 39.7 percent when oyster castles were emergent or slightly submerged with southwest winds. In contrast, when the oyster castles were fully submerged, wave energy behind the oyster castles increased by 38.6 percent. The construction of oyster castles affected circulation patterns with increase or decrease in velocity at nearshore waters protected by the castles depending on locations of measurements in relation to the oyster castles. Bottom shear stress analysis indicates that tidal currents play a larger role than waves on shoreline and marsh edge erosion along the Little Toms Cove shoreline during the 2 months of field monitoring. The oyster castles protecting the marsh edge and tidal flat from erosion resulted in higher fine sediment concentration in the water column landward of the castles because more sediment was retained in the lee side of the castles. It is important to maximize sediment within the wetlands and adjacent mudflats behind the oyster castles. Erosion from the marsh edge and interior serves as the major source of sediment for this wetland system due to the limited sediment supply in Assateague Channel. Furthermore, it was found that the oyster castles along the Little Toms Cove living shoreline were inundated more than 60 percent of the time, leading to the enhanced oyster habitat as evidenced by suitable velocity (less than 10 centimeters per second) and mean grain size (less than 0.08 millimeters) for oyster feeding and the increased oyster shell density and growth in the intertidal zone protected by the castles than in the control area. More field data (for example, concurrent monitoring of sediment concentration and salinity) over other seasons (for example, summer) could help examine the long term and combined engineering and ecological benefits of living shoreline restoration projects under seasonal and enhanced future storm conditions.

Virginia↗
USGS2024

Asymmetric mate preference and reproductive interference mediate climate-induced changes in mate availability in a small mammal hybrid zone

Range expansion and contraction are among the most common biotic responses to changing environmental conditions, yet much is to be learned about the mechanisms that underlie range-edge population dynamics, especially when those areas are points of secondary contact between closely related species. Here, we present field-measured parentage data that document the reproductive outcomes of changes in mate availability at a secondary contact zone between two species of woodrat in the genus Neotoma . Changes in mate availability resulted from drought-driven differential survival between the species and their hybrids. As the availability of conspecifc mates declined, rates of hybridization increased, leading to the accumulation of admixed individuals in the zone of contact. Patterns of reproductive success in the wild appear to be the result of a combination of both pre-mating isolation and post-zygotic selection resulting from genomic incompatibilities between the parental lineages. Evidence of asymmetric mate preference between the parental lineages came from both skewed reproductive output in the field and laboratory preference trials. Moreover, partial genomic incompatibility was evident from the near-zero reproductive success of F1 males and because nearly all surviving hybrids had one pure parent. Nonetheless, the high reproductive success of F1 females and backcrossing in both parental directions allow for introgression between the parental species. These findings reveal how climate change may alter evolutionary outcomes for species at the edge of their ranges through an interplay of behavioral, demographic, and genetic mechanisms.

California↗
USGS2025

Evaluating and enhancing nest survival of an insular passerine threatened by an invasive snake

Predatory Boiga irregularis (brown treesnakes) have decimated Guam’s avifauna since their introduction to the island. Aplonis opaca (Såli, Micronesian Starling) is one of two native forest bird species that have survived, though it remains poorly understood how its population has persisted. We compared nest survival and causes of nest failure between snake-resistant nestboxes and natural nesting locations and tested hypotheses to identify drivers of variation in nest survival as well as the efficacy of snake-resistant nestboxes. We monitored 340 nest attempts by 40 A. opaca pairs nesting in nestboxes and 53 attempts by 32 pairs nesting in natural nests (outside of nestboxes). Overall nest survival in nestboxes (62%) was double that in natural nest sites (31%). Nest failure was equally divided between the egg and nestling stage in natural nests, whereas 82% of failures occurred at the egg stage for attempts in nestboxes. Hatch rates per nesting attempt in natural and nestbox nests were similar and generally low (overall mean ± SE = 71.2 ± 2.1%), possibly due to inbreeding depression; hatching failure was the leading cause of failure during the egg stage. We found no evidence of nest predation in nestboxes, while several nest failures during the nestling stage in natural nests were consistent with B . irregularis predation. Nest survival was positively correlated with use of nestboxes, clutch size, and distance from forest edge. Our nestbox placement strategy was highly effective at reducing predation of A. opaca nests, demonstrating its importance as a conservation tool for cavity-nesting birds on Guam. Protected nestboxes combined with a yearly mean of 4.3 successful nests per breeding pair produced a high mean annual fecundity (4.01 ± 0.34 female offspring per female), suggesting nestboxes could help offset low hatch rates and contribute to A. opaca population persistence and expansion on Guam.

Guam↗
USGS2019

Marshes are the new beaches: Integrating sediment transport into restoration planning

Recent coastal storms and associated recovery efforts have led to increased investment in nature-based coastal protection, including restoration of salt marshes and construction of living shorelines. In particular, many of these efforts focus on increasing vertical elevation through sediment nourishment, where sediment is removed from the tidal channel and placed on the marsh plain, or preventing lateral erosion through shoreline protection. In the USA alone, millions of dollars have been allocated or spent on these coastal protection solutions over the last few decades because of their perceived sustainability and ecologically positive co-benefits including habitat provision and carbon sequestration. These projects would benefit from integration of sediment transport pathways, budgets, and metrics during planning and modeling of restoration outcomes, in order to evaluate sustainability before investment. This is analogous to the decades of experience with coastal management and engineering on the open coast. Salt marshes are geomorphic features that rely partially on external sediment supply to maintain their network of tidal channels, intertidal flats, and marsh plain. Removing sediment from one component of the overall system to nourish another component may be counterproductive, given that the net sediment budget is unchanged. For example, dredging a tidal channel beyond its equilibrium condition will cause it to fill with sediment from the tidal flat or elsewhere in the system. This may cause slumping of the marsh edge, or over-deepening of other sections of the channel to compensate. Similarly, shoreline protection that prevents edge erosion hampers the marsh plain’s ability to accrete on the levee and naturally transgress landward or it starves other components of the system of regularly supplied sediment. A limited vertical or lateral-only perspective, instead of a three-dimensional perspective, during project planning and evaluation may lead to suboptimal decision-making regarding restoration priorities, approaches, and outcomes. I contend that before significant investments are made in marsh restoration through sediment nourishment or shoreline protection, sediment transport measurements and models that consider sediment dynamics should be integrated into the early phases of restoration planning. This will help identify where and under what conditions marsh restoration will most likely be successful and economically justified. Triaging and prioritizing is then possible, which is a sustainable approach for restoration, given the persistent vulnerability of marshes to sea-level rise, storms, and sediment deficits.

Estuaries and Coasts↗
USGS1982

Examination of woodcock nest sites in central Pennsylvania

Evidence is given to support Iow selectivity in choice of nest sites by woodcock (Philohela minor). Habitat characteristics measured at 30 woodcock nest sites were compared with non-nest control sites in Huntingdon County, central Pennsylvania. Mean nest density per year was 1/4.8 ha within the 54-ha study area. Of 14 characteristics measured, higher shrub-stem density at nests was the only variable significantly different (P < 0.05) from controls by univariate t-test. A multivariate t-test showed no significant difference (P > 0.05) between habitat characteristics at nests and controls. A computed discriminant function also indicated little distinction between nests and controls. Spatial distribution of nests for each of the three years did not depart significantly (P :> 0.05) from a random distribution. Although evidence is given for little overall selectivity, greater shrub-stem density at nests and associations related in part to 'edge' habitat may be important in the location of substantial numbers of woodcock nests. The mean distance from nest site to nearest tree (1.0 ? 1.1 m) and to nearest shrub (22.8 ? 17.8 cm) was significantly less (P < 0.01) than for control areas. Additional research on woodcock nest-site selection may lead to enhanced woodcock production in a variety of habitats.

Wildlife Research Report↗
USGS1972

Mineral reconnaissance of the southern part of the Wadi Qaraqir quadrangle, Saudi Arabia

Introduction At the end of a field trip to the Wadi as Surr quadrangle (Johnson and Trent, 1967) a few days were spent in the southern part of the adjoinning Wadi Qaraqir quadrangle in order to extend our mineral reconnaissance as far east as the Arabian Plateau. The area examine is shown by the distribution of sample localities on the accompanying map. No mineral deposits of economic interest were seen. The terrain is one of broad plains and low hills that extend westward from the base of a prominent erosional scarp which forms the western edge of the Arabian Plateau. Streams cutting headward into the low-dipping massive sandstone of the Plateau have carved deep canyongs with vertical walls, and outliers of the sandstone are preserved as buttes and erosional forms of varied shapes. There are no permanent settlements in the mapped areas. The one road leads up a tributary of Wadi Qaraqir to some date gardens at the base of the sandstone cliffs. A well-travelled caravan route crosses the passes at Al Khuraytah to reach the Plateau H. St. John Philby strongly recommended that a road be constructed through these passes to provide direct access from Tabuk to the Red Sea coast. Burton (1878) was probably the first European to visit the area. He was searching for mineral deposits and he also located some Nabatcan ruins. Philby in company with R. G. Bogue, U. S. Geological Survey, explored the scarp in the Wadi Qaraqir valley and drove northwestward to Al Khuraytah pass. The geology of the Wadi Qaraqir quadrangle shown on the geologic map of the Northwestern Hijaz (Brown and others, 1963) was compiled from Bogue's work. Our work consisted of making traverses around the hilly area and up accessible wadis. We examined the rocks along the traverse routes and visited target areas that had been selected by examination of aerial photographs. Samples of wadi sediment were collected from fault zones, granite contacts, and areas that showed some evidence of hydrothermal alteration. The work was made possible by the cooperation fo the officials of the Directorate General of Mineral Resources, Ministry of Petroleum and Mineral Resources, who arranged for vehicles and accompanying personnel. We did not have a counterpart Saudi geologist for this portion of our trip.

Open-File Report↗
USGS2016

Complementary approaches to diagnosing marine diseases: a union of the modern and the classic

Linking marine epizootics to a specific aetiology is notoriously difficult. Recent diagnostic successes show that marine disease diagnosis requires both modern, cutting-edge technology (e.g. metagenomics, quantitative real-time PCR) and more classic methods (e.g. transect surveys, histopathology and cell culture). Here, we discuss how this combination of traditional and modern approaches is necessary for rapid and accurate identification of marine diseases, and emphasize how sole reliance on any one technology or technique may lead disease investigations astray. We present diagnostic approaches at different scales, from the macro (environment, community, population and organismal scales) to the micro (tissue, organ, cell and genomic scales). We use disease case studies from a broad range of taxa to illustrate diagnostic successes from combining traditional and modern diagnostic methods. Finally, we recognize the need for increased capacity of centralized databases, networks, data repositories and contingency plans for diagnosis and management of marine disease.

Philosophical Transactions of the Royal Society B:↗
USGS2024

Evaluation and refinement of chlorophyll-a algorithms for high-biomass blooms in San Francisco Bay (USA)

A massive bloom of the raphidophyte Heterosigma akashiwo occurred in summer 2022 in San Francisco Bay, causing widespread ecological impacts including events of low dissolved oxygen and mass fish kills. The rapidly evolving bloom required equally rapid management response, leading to the use of near-real-time image analysis of chlorophyll from the Ocean and Land Colour Instrument (OLCI) aboard Sentinel-3. Standard algorithms failed to adequately capture the bloom, signifying a need to refine a two-band algorithm developed for coastal and inland waters that relates the red-edge part of the remote sensing reflectance spectrum to chlorophyll. While the bloom was the initial motivation for optimizing this algorithm, an extensive dataset of in-water validation measurements from both bloom and non-bloom periods was used to evaluate performance over a range of concentrations and community composition. The modified red-edge algorithm with a simplified atmospheric correction scheme outperformed existing standard products across diverse conditions, and given the modest computational requirements, was found suitable for operational use and near-real-time product generation. The final version of the algorithm successfully minimizes error for non-bloom periods when chlorophyll a is typically <30 mg m −3 , while also capturing bloom periods of >100 mg m −3 chlorophyll a .

California↗
USGS1987

Modes of development of slope canyons and their relation to channel and levee features on the Ebro sediment apron, off-shore northeastern Spain

Six submarine slope canyons in an area of the northwestern Mediterranean, offshore from the Ebro River and Delta, were surveyed with bathymetric swathmapping (SeaBeam) and mid-range side-looking sonar (SeaMARC I). All of the canyons have slightly winding paths with concave-upwards gradients that are relatively steep shallower than 1,200 m. Two major types of canyons are identified on the basis of their morphologic character at the base of the slope; Type-I canyons lead to an unchannelled base-of-slope deposit and Type-II canyons are continuous with channel-levee systems that cross the rise. Four Type-I canyons were surveyed in the area. Two of these are broad, U-shaped, steep (average gradients of 1:14), do not indent the shelf, and terminate downslope at debris-flow deposits. These two canyons, the most northern in the area, have rounded heads with extensive gullies separated by knife-edge ridges. Relief of the canyon walls is about equal on both sides of the canyons, although the right-hand walls (looking downslope) are generally steeper. The other two Type-I canyons in the area are similar in that they do not indent the shelf, but they are much smaller and shallower and coalesce before terminating in the base-of-slope region. The two Type-II canyons that feed leveed-channels are U-shaped with flatter floors, longer profiles and gentler gradients than Type-I canyons. They are closer to the Valencia Valley and have relatively small cross-sectional areas. We propose a four-stage evolutionary sequence to explain the development of the canyons observed in this section on the prograding Ebro margin. During the initial stage, slumping and erosion on the slope creates a network of small gullies. During the next stage, headward growth of one (or more) gully leads to a major indentation of the shelf. This is the critical factor for developing a channel that will incise the slope and provide a major conduit for moving sediment to the basin. Stage 3 is characterized by the development of a continuous channel accompanied by levee growth across the lobe. In the final stage, the channel-levee system becomes inactive either through destruction by mass wasting, infilling of the channel, or loss of the major sediment source. ?? 1987.

Marine and Petroleum Geology↗
USGS1995

Geologic/geomorphologic map of the Chryse Planitia region of Mars

Since the 1970’s, when the Mariner 9 spacecraft revealed the geologic diversity of Mars, the Chryse Planitia region has been noted for its immense outflow channels and chaotic terrain (McCauley and others, 1972; Sharp and Malin , 1975; Baker, 1982, chap. 3; Mars Channel Working Group , 1983). Various proposals for the origin of these features have been offered; most workers have favored a mechanism in which ground water or water-rich debris was expelled from beneath a frozen crust, leading to catastrophic debris flows o r floods that may have contained significant amounts of ice (Baker and Milton, 1974; Carr , 19 79; Nummedal and Prior, 1981; Lucchitta , 1982 ; MacKinnon and Tanaka, 1989). The channels originated on or near the flanks of the volcanotectonic rises of Tharsis (whose east margin is in the west edge of the map region) and Valles Marineris , which suggests that tectonics and igneous activity led to the conditions for discharge. Estimated discharge rates for some channels exceed thos of prehistoric floods on Earth ( Carr , 1979; Komar , 1979; Robinson and Tanaka, 1990) . Some workers think that the discharges may have led to the development of temporary oceans that filled the northern lowlands (Parker and others, 1989; Baker and others, 1991). The Chryse basin ( Chryse and southern Acid alia Planitiae ), which is part of those lowlands, apparently has been the site of lava and sediment deposition (Greeley and others, 1977; Scot and T anaka, 1986).

IMAP↗
USGS2024

Home range size and resource use by eastern spotted skunks in Virginia

Throughout much of the eastern U.S., many forested ecosystems have lost large amounts of core forest areas due to land-use change, isolating wildlife in forest fragments. The eastern spotted skunk ( Spilogale putorius ) is considered a species of conservation concern in Virginia, where populations are restricted to spatially disjunct forest patches in the central Appalachian Mountains. We caught and radio-tagged eastern spotted skunks in the Appalachian Mountains of Virginia to assess whether current habitat fragmentation restricts skunk movements and hence distribution, potentially leading to isolation among habitat patches. Denning home range size (approximately 3.7 km 2 ) in our study was smaller than those in other studies of eastern spotted skunks and excursive movements were primarily limited to core forested areas (>2 km 2 ). Core forested areas were used more than non-forested and forest-edge areas. We conclude core forest area fragmentation limits eastern spotted skunk movement between mountain ridges. Increased forest patch connectivity may help prevent genetic and demographic isolation, reduce the likelihood of local extinctions, and facilitate colonization of suitable unoccupied areas.

Virginia↗
USGS2024

Beyond the wedge: Impact of tidal streams on salinization of groundwater in a coastal aquifer stressed by pumping and sea-level rise

Saltwater intrusion (SWI) is a well-studied phenomenon that threatens the freshwater supplies of coastal communities around the world. The development and advancement of numerical models has led to improved assessment of the risk of salinization. However, these studies often fail to include the impact of surface waters as potential sources of aquifer salinity and how they may impact SWI. Based on field-collected data, we developed a regional, variable-density groundwater model using SEAWAT for east Dover, Delaware. In this location, major users of groundwater from the surficial aquifer are the City of Dover and irrigation for agriculture. Our model includes salinized marshland and tidal streams, along with irrigation and municipal pumping wells. Model scenarios were run for 100 years and included changes in pumping rates and sea-level rise (SLR). We examined how these drivers of SWI affect the extent and location of salinization in the surficial aquifer by evaluating differences in chloride concentration near surface waters and the subsurface freshwater-saltwater interface. We found the presence of the marsh inverts the typical freshwater-saltwater wedge interface and that the edge of the interface did not migrate farther inland. Additionally, we found that tidal streams are the dominant pathways of SWI at our site with salinization from streams being exacerbated by SLR. Our results also show that spatial distribution of pumping affects both the magnitude and extent of salinization, with an increase in concentrated pumping leading to more intensive salinization than a more widely distributed increase of the same total pumping volume.

Delaware↗
USGS2008

Effect of imbalanced nutrients and immigration on Prymnesium parvum community dominance and toxicity: Results from in-lake microcosm experiments

Prymnesium parvum, a haptophyte species, forms harmful blooms, including those that have caused severe fish kills in Texas, USA, over the past 6 yr. We studied P. parvum dynamics using in situ microcosm experiments at Lake Possum Kingdom, Texas, during 3 seasons (fall 2004, winter and spring 2005). Experimental treatments included full and partial nutrient enrichment (encompassing nitrogen [N] and phosphorus [P] deficient treatments), P. parvum immigration and combinations of these factors. In the control and N and P deficient treatments, P. parvum populations dominated the community, but only in the N deficient treatments did P. parvum experience a significant growth in the population. In contrast, when nutrients were not limiting, P. parvum tended to lose its competitive edge to other taxa such as chlorophytes, euglenophytes and diatoms, which then dominated the community. Population growth of P. parvum was also stimulated through immigration, but only during the winter experiment, a period of the year when bloom initiation is common. This finding suggests that movement into the water column may be an important process leading to P. parvum bloom initiation. Toxicity of P. parvum to fish was also affected by the nutrient changes: during conditions of no nutrient addition P. parvum was most toxic; intermediate toxicity was observed under N and P deficient conditions, and full nutrient enrichments resulted in nearly non-toxic conditions. ?? Inter-Research 2008.

Aquatic Microbial Ecology↗
USGS1990

Interaction of cold-water aquifers with exploited reservoirs of the Cerro Prieto geothermal system

Cerro Prieto geothermal reservoirs tend to exhibit good hydraulic communication with adjacent cool groundwater aquifers. Under natural state conditions the hot fluids mix with the surrounding colder waters along the margins of the geothermal system, or discharge to shallow levels by flowing up fault L. In response to exploitation reservoir pressures decrease, leading to changes in the fluid flow pattern in the system and to groundwater influx. The various Cerro Prieto reservoirs have responded differently to production, showing localized near-well or generalized boiling, depending on their access to cool-water recharge. Significant cooling by dilution with groundwater has only been observed in wells located near the edges of the field. In general, entry of cool water at Cerro Prieto is beneficial because it tends to maintain reservoir pressures, restrict boiling, and lengthen the life and productivity of wells.

Conference Paper↗
USGS2005

Relationships between gap makers and gap fillers in an Arkansas floodplain forest

Question: In floodplain forests, does frequent flooding allow for self-replacement of shade-intolerant tree species or do small canopy gap openings lead to replacement by shade-tolerant tree species? Location: Cache River, Arkansas, US; 55 m a.s.l. Methods: The species, diameter-at-breast height, and elevation of primary gap-maker trees were determined for new gaps from 1995–1998. The size and species of gap-filler trees were identified and placed into three classes: definitive, edge, or interior. Transition probabilities were determined. Results: The dominant shade-intolerant species Quercus texana is being replaced primarily by the more shade-tolerant A. rubrum var. drummondii, Fraxinus spp. and Ulmus americana. Only 20 of 2767 gap fillers were Q. texana. Replacement probabilities are not constant across elevations, however, as the least shade-tolerant of the three most common species of definitive gap fillers, Fraxinus spp., occurred at lower elevations than A. rubrum var. drummondii , and U. americana. Conclusions: The contention that frequent flooding would allow for self-replacement of shade-intolerant species was only partially supported. The small canopy gaps undoubtedly influenced canopy replacement processes.

Arkansas↗