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At least 271 records · Page 15Linked to original sources
USGS2017

Spatial and temporal variability in the effects of wildfire and drought on thermal habitat for a desert trout

We studied how drought and an associated stressor, wildfire, influenced stream flow permanence and thermal regimes in a Great Basin stream network. We quantified these responses by collecting information with a spatially extensive network of data loggers. To understand the effects of wildfire specifically, we used data from 4 additional sites that were installed prior to a 2012 fire that burned nearly the entire watershed. Within the sampled network 73 reaches were classified as perennial, yet only 51 contained surface water during logger installation in 2014. Among the sites with pre-fire temperature data, we observed 2–4 °C increases in maximum daily stream temperature relative to an unburned control in the month following the fire; effects (elevated up to 6.6 °C) appeared to persist for at least one year. When observed August mean temperatures in 2015 (the peak of regionally severe drought) were compared to those predicted by a regional stream temperature model, we observed deviations of −2.1°-3.5°. The model under-predicted and over-predicted August mean by > 1 °C in 54% and 10% of sites, respectively, and deviance from predicted was negatively associated with elevation. Combined drought and post-fire conditions appeared to greatly restrict thermally-suitable habitat for Lahontan cutthroat trout ( Oncorhynchus clarkii henshawi ).

Oregon↗
USGS2020

Utilization of multiple microbial tools to evaluate efficacy of restoration strategies to improve recreational water quality at a Lake Michigan Beach (Racine, WI)

Hydro-meteorological conditions facilitate transport of fecal indicator bacteria (FIB) to the nearshore environment, affecting recreational water quality. North Beach (Racine, Wisconsin, United States), is an exemplar public beach site along Lake Michigan, where precipitation-mediated surface runoff, wave encroachment, stormwater and tributary outflow were demonstrated to contribute to beach advisories. Multiple restoration actions, including installation of a stormwater retention wetland, were successfully deployed to improve recreational water quality. Implementation of molecular methods (e.g. human microbial source tracking markers and Escherichia coli ( E. coli ) qPCR) assisted in identifying potential pollution sources and improving public health response time. However, periodic water quality failures still occur. As local beach managers reassess restoration measures in response to climatic changes, use of expanded microbial methods (including bacterial community profiling) may contribute to a better understanding of these dynamic environments. In this 2-year study (2015 and 2019), nearshore/offshore Lake Michigan, stormwater, and tributary samples were collected to determine if, 1) the constructed wetland (~50 m from the shoreline) continued to provide stormwater separation/retention and 2) mixing between onshore sources, Root River and Lake Michigan, was increasing due to rising precipitation/lake levels. Monthly rainfall totals were 1.5× higher in 2019 than 2015, coinciding with a 0.63 m lake-level rise. The prevalence of more intense, onshore winds also increased, facilitating interaction between potential reservoirs of FIB with nearshore water through wind driven waves and lake intrusion, e.g. beach sands and the adjacent Root River. While a strong relationship existed between wet weather wetland and North Beach nearshore E. coli concentrations (all sites), bacterial communities were strikingly different. Conversely, bacterial community overlap existed between the Root River mouth and nearshore/offshore sites. These results suggest the constructed wetland can accommodate the climate-related changes observed in this study. Future restoration activities could be directed towards upstream tributary sources in order to minimize microbial contaminants entering Lake Michigan.

Wisconsin↗
USGS2022

Critical thermal maximum of stream fishes including distinct populations of Smallmouth Bass

Understanding the thermal tolerances of stream fishes, including sport fishes, is important for assessing thermal stressors that are common across the landscape. Our study objectives were to determine the thermal tolerances of 17 stream fishes (15 species and 2 genetically distinct populations of juvenile Smallmouth Bass Micropterus dolomieu : the Neosho subspecies M. dolomieu velox and the Ouachita strain M . sp. cf. dolomieu velox ). Fish were collected from the field and acclimated to laboratory conditions at 20°C or 25°C, with dissolved oxygen maintained above 6 mg/L. We determined the critical thermal maximum (CTM) using an incomplete block design with 9–11 replications for each species. During trials, we increased the water temperature at a rate of 2°C per hour until fish experienced loss of equilibrium. The estimated CTM ranged from 32.43°C to 38.26°C among species. The CTM values differed significantly between taxonomic groups and species, including the genetically distinct populations of Smallmouth Bass. The Neosho subspecies of Smallmouth Bass had a significantly lower thermal tolerance than the Ouachita strain at both acclimation temperatures; however, the magnitude of the difference was about 0.5°C greater at the higher acclimation temperature. Closely related species, including the Bigeye Shiner Notropis boops and Kiamichi Shiner N . ortenburgeri , had significantly different thermal tolerances despite occupying similar riverine locations. Our results suggest that our perceptions of a species’ thermal tolerance based on that of closely related species or that of species using similar habitat may be incorrect. Moreover, the differences in thermal tolerances among populations may be an important consideration for conservation and management actions, such as stocking decisions. Laboratory data such as those provided in this study can be integrated with field data to better assess thermal responses of fishes in a changing environment.

Oklahoma↗
USGS1993

Coupled effects of vertical mixing and benthic grazing on phytoplankton populations in shallow, turbid estuaries

Coastal ocean waters tend to have very different patterns of phytoplankton biomass variability from the open ocean, and the connections between physical variability and phytoplankton bloom dynamics are less well established for these shallow systems. Predictions of biological responses to physical variability in these environments is inherently difficult because the recurrent seasonal patterns of mixing are complicated by aperiodic fluctuations in river discharge and the high-frequency components of tidal variability. We might expect, then, less predictable and more complex bloom dynamics in these shallow coastal systems compared with the open ocean. Given this complex and dynamic physical environment, can we develop a quantitative framework to define the physical regimes necessary for bloom inception, and can we identify the important mechanisms of physical-biological coupling that lead to the initiation and termination of blooms in estuaries and shallow coastal waters? Numerical modeling provides one approach to address these questions. Here we present results of simulation experiments with a refined version of Cloern's (1991) model in which mixing processes are treated more realistically to reflect the dynamic nature of turbulence generation in estuaries. We investigated several simple models for the turbulent mixing coefficient. We found that the addition of diurnal tidal variation to Cloern's model greatly reduces biomass growth indicating that variations of mixing on the time scale of hours are crucial. Furthermore, we found that for conditions representative of South San Francisco Bay, numerical simulations only allowed for bloom development when the water column was stratified and when minimal mixing was prescribed in the upper layer. Stratification, however, itself is not sufficient to ensure that a bloom will develop: minimal wind stirring is a further prerequisite to bloom development in shallow turbid estuaries with abundant populations of benthic suspension feeders.

Journal of Marine Research↗
USGS2000

Geochemical effects of rapid sedimentation in aquatic systems: Minimal diagenesis and the preservation of historical metal signatures

Rapid sedimentation exerts a pronounced influence on early sedimentary diagenesis in that there is insufficient time for a sediment particle to equilibrate in any one sediment layer before that layer may be displaced vertically by another layer. These sedimentation patterns are common in surface-water reservoirs whose sedimentation rates (1-10 cm yr-1) are several orders of magnitude greater than those for natural lakes (0.01-0.5 cm yr-1). Two examples of the effects of rapid sedimentation on geochemical metal signatures are presented here. Interstitial-water data (Fe) from two sites in the Cheyenne River Embayment of Lake Oahe on the Missouri River illustrate the effects of changing sedimentation rates on dissolved species. Rapid burial during high-flow yrs appears to limit early sedimentary diagenesis to aerobic respiration. Solid-phase metal data (Pb) from a site in Pueblo Reservoir on the upper Arkansas River in Colorado appear to record historical releases by flooding of abandoned mine sites upstream in Leadville, Colorado. Interstitial-water ammonia and ferrous Fe data indicate that at least one interval at depth in the sediment where solid metal concentrations peak is a zone of minimal diagenesis. The principal diagenetic reactions that occur in these sediments are aerobic respiration and the reduction of Mn and Fe oxides. Under slower sedimentation conditions, there is sufficient time for particulate organic matter to decompose and create a diagenetic environment where metal oxides may not be stable. The quasi-steady-state interstitial Fe profiles from Tidal Potomac River sediments are an example of such a situation. This occurs primarily because the residence time of particles in the surficial sediment column is long enough to allow benthic organisms and bacteria to perform their metabolic functions. When faster sedimentation prevails, there is less time for these metabolic reactions to occur since the organisms do not occupy a sediment layer for any length of time. Also, the quantity and quality of the organic matter input to the sediment layer is important in that reservoirs often receive more terrestrial organic matter than natural lakes and this terrestrial organic matter is generally more refractory than autochthonous aquatic organic matter.

Journal of Paleolimnology↗
USGS2005

Identification of amoebae implicated in the life cycle of Pfiesteria and Pfiesteria-like dinoflagellates

This study was undertaken to assess whether amoebae commonly found in mesohaline environments are in fact stages in the life cycles of Pfiesteria and Pfiesteria-like dinoflagellates. Primary isolations of amoebae and dinoflagellates were made from water and sediment samples from five tributaries of the Chesapeake Bay. Additional amoebae were also cloned from bioassay aquaria where fish mortality was attributed to Pfiesteria . Electron microscopy and small subunit (SSU) rRNA gene sequence analysis of these isolates clearly demonstrated that the commonly depicted amoeboid form of Pfiesteria is very likely a species of Korotnevella and is unrelated to Pfiesteria or Pfiesteria -like dinoflagellates. We have determined that the Pfiesteria and Pfiesteria -like dinoflagellates examined in this study undergo a typical homothallic life cycle without amoeboid stages. Furthermore, we have demonstrated that cloned amoebae sharing morphological characteristics described for stages in the life cycle of Pfiesteria do not transform into dinozoites. The strict clonal isolation and cultivation techniques used in this study substantially support the conclusion that the amoebae and some of the flagellates depicted in the life cycle of Pfiesteria are environmental contaminants of the Pfiesteria culture system and that the Ambush Predator Hypothesis needs to be rigorously reevaluated.

Maryland, Virginia↗
USGS2007

Methane gas hydrate effect on sediment acoustic and strength properties

To improve our understanding of the interaction of methane gas hydrate with host sediment, we studied: (1) the effects of gas hydrate and ice on acoustic velocity in different sediment types, (2) effect of different hydrate formation mechanisms on measured acoustic properties (3) dependence of shear strength on pore space contents, and (4) pore pressure effects during undrained shear. A wide range in acoustic p-wave velocities (V p ) were measured in coarse-grained sediment for different pore space occupants. V p ranged from less than 1 km/s for gas-charged sediment to 1.77–1.94 km/s for water-saturated sediment, 2.91–4.00 km/s for sediment with varying degrees of hydrate saturation, and 3.88–4.33 km/s for frozen sediment. V p measured in fine-grained sediment containing gas hydrate was substantially lower (1.97 km/s). Acoustic models based on measured V p indicate that hydrate which formed in high gas flux environments can cement coarse-grained sediment, whereas hydrate formed from methane dissolved in the pore fluid may not. The presence of gas hydrate and other solid pore-filling material, such as ice, increased the sediment shear strength. The magnitude of that increase is related to the amount of hydrate in the pore space and cementation characteristics between the hydrate and sediment grains. We have found, that for consolidation stresses associated with the upper several hundred meters of sub-bottom depth, pore pressures decreased during shear in coarse-grained sediment containing gas hydrate, whereas pore pressure in fine-grained sediment typically increased during shear. The presence of free gas in pore spaces damped pore pressure response during shear and reduced the strengthening effect of gas hydrate in sands.

Journal of Petroleum Science and Engineering↗
USGS2026

Deep subsurface organic-rich shale supports abundant, diverse, and novel fungi

As Earth’s principal reservoir of organic carbon and microbial biomass, the deep subsurface hosts microorganisms capable of mobilizing this once-sequestered carbon. Contrary to standard assumptions of eukaryotic scarcity, this study documents abundant fungal communities, ranging from 4.2 × 10 3 to 6.8 × 10 3 fungal cells mL −1 , across a methane-producing organic-rich shale 247–556 meters below the surface. Although fungal:bacterial cell ratios ranged from 1:7028 to 1:713, application of biomass conversion factors developed for oceanic systems yielded a median fungal:bacterial biomass ratio of 1:4.7. 16S rRNA gene amplicons revealed bacterial and archaeal communities mirroring those found in well-characterized extremophilic, carbon-degrading environments, while sequencing of 18S rRNA gene and ITS rRNA spacer amplicons collectively identified a eukaryotic hotspot with 689 fungal OTUs across six phyla. The dominant fungal classes, Agaricomycetes and Dothideomycetes, are well-established degraders of recalcitrant carbon compounds at the surface, suggesting they may similarly contribute to organic matter degradation and ecosystem maintenance in the subsurface. Cultivation and isolation efforts yielded 205 fungal strains, including 13 candidate novel taxa, underscoring the deep subsurface as an underexplored eukaryotic habitat. Stable carbon isotopes indicate methane is predominantly generated via microbial conversion of the fossil carbon, while water isotopes suggest in situ geochemical conditions have been relatively stable since the Late Pleistocene, with subglacial recharge as a plausible mechanism for microbial introduction. Collectively, these findings suggest that fungi are underrecognized contributors to organic matter transformation and functional diversity in the deep biosphere, revealing a critical gap in our understanding of deep subsurface ecosystem processes.

Indiana, Michigan, Ohio↗
USGS2006

Persistence of Pasteurella multocida in wetlands following avian cholera outbreaks

Avian cholera, caused by Pasteurella multocida, affects waterbirds across North America and occurs worldwide among various avian species. Once an epizootic begins, contamination of the wetland environment likely facilitates the transmission of P. multocida to susceptible birds. To evaluate the ability of P. multocida serotype-1, the most common serotype associated with avian cholera in waterfowl in western and central North America, to persist in wetlands and to identify environmental factors associated with its persistence, we collected water and sediment samples from 23 wetlands during winters and springs of 1996a??99. These samples were collected during avian cholera outbreaks and for up to 13 wk following initial sampling. We recovered P. multocida from six wetlands that were sampled following the initial outbreaks, but no P. multocida was isolated later than 7 wk after the initial outbreak sampling. We found no significant relationship between the probability of recovery of P. multocida during resampling and the abundance of the bacterium recovered during initial sampling, the substrate from which isolates were collected, isolate virulence, or water quality conditions previously suggested to be related to the abundance or survival of P. multocida. Our results indicate that wetlands are unlikely to serve as a long-term reservoir for P. multocida because the bacterium does not persist in wetlands for long time periods following avian cholera outbreaks.

Journal of Wildlife Diseases↗
USGS2018

Late Holocene paleoceanography in the Chukchi and Beaufort Seas, Arctic Ocean, based on benthic foraminifera and ostracodes

Calcareous microfossil assemblages in late Holocene sediments from the western Arctic continental shelf provide an important baseline for evaluating the impacts of today’s changing Arctic oceanography. This study compares 14 C-dated late Holocene microfaunal assemblages of sediment cores SWERUS-L2-2-PC1, 2-MC4 and 2-KL1 (57 mwd), which record the last 4200 years in the Herald Canyon (Chukchi Sea shelf), and HLY1302-JPC-32, GGC-30, MC-29 (60 mwd), which record the last 3000 years in the Beaufort Sea shelf off the coast of Canada. Foraminiferal and ostracode assemblages are typical of Arctic continental shelf environments with annual sea-ice cover and show relatively small changes in terms of variability of dominant species. Important microfaunal changes in the Beaufort site include a spike in Spiroplectammina biformis coinciding with a decrease in Cassidulina reniforme in the last few centuries suggesting an increase of Pacific Water influence and decreased sea-ice. There is low-amplitude centennial-scale variability in proportions of benthic foraminiferal species, such as C. reniforme . In addition to these species, Cassidulina teretis s.l., Elphidium excavatum clavatum and Stainforthia feylingi are also common at this site. At the Herald Canyon site in the last few centuries, C. reniforme peaks around 150 years BP and then decreases while Spiroplectammina earlandi spikes and Acanthocythereis dunelmensis decreases also suggesting an increase in Pacific Water influence and decreased sea-ice at this site. This site also includes Buccella spp. and Elphidium excavatum clavatum . Differences in benthic foraminifera and ostracode species dominance between the two sites may be due to a greater influence of Pacific Water in the Chukchi shelf, compared to the more distal Beaufort shelf, which is also affected by the Beaufort Gyre and the Mackenzie River.

Arctic Ocean, Beaufort Sea, Chukchi Sea↗
USGS2009

Monitoring suspended sediments and associated chemical constituents in urban environments: Lessons from the city of Atlanta, Georgia, USA Water Quality Monitoring Program

Background, aim, and scope The City of Atlanta, Georgia (COA) is part of the ninth largest metropolitan area in the USA and one of the fastest growing (e.g., >24% between 2000 and 2007). Since 2003, the US Geological Survey has been operating an extensive long-term water-quantity and water-quality monitoring network for the COA. The experience gained in operating this network has provided insights into the challenges as well as some solutions associated with determining urban effects on water quality, especially in terms of estimating the annual fluxes of suspended sediment, trace/major elements, and nutrients. Discussion and findings The majority (>90%) of the annual fluxes of suspended sediment and discharge (>60%) from the COA occur in conjunction with stormflow. Typically, stormflow averages ≤20% of the year. Normally, annual flux calculations employ a daily time-step; however, due to the “flashy” nature of the COA’s streams, this approach can produce substantial underestimates (from 25% to 64%). Greater accuracy requires time-steps as short as every 2 to 3 h. The annual fluxes of ≥75% of trace elements (e.g., Cu, Pb, Zn), major elements (e.g., Fe, Al), and total P occur in association with suspended sediment; in turn, ≥90% of the transport of these constituents occurs in conjunction with stormflow. With the possible exception of nitrogen, baseflow sediment-associated and both baseflow and stormflow dissolved contributions represent relatively insignificant portions of the total annual load; hence, nonpoint (diffuse) sources are the dominant contributors to the fluxes of almost all of these constituents.

Georgia↗
USGS2019

Understanding conservation decisions of agriculture producers

Most land in the United States (US) is privately owned and used for agriculture. To address the effect of agriculture on wildlife, conservation professionals and organizations need to understand the land use decisions made by farmers and ranchers. We developed a tool for categorizing farmers and ranchers by their conservation land use values (LUVs) to understand how those values affect their land use motivations and resultant decisions. We defined land as the whole natural environment including soil, water, plants, fish, and wildlife. We used principal axis factoring and reliability analysis to identify statements representing human-centered values and nature-centered values of farmers and ranchers. We tested the validity of the combined statements with a survey of South Dakota’s private landowners (N = 4,000, [Jan through May 2016]) resulting in the LUV scale. Crossing the average scores on the human-centered and nature-centered statements identified 4 LUV types: humans first (20%), nature first (29%), interconnected (29%), and disconnected (22%). Analysis of variance and chi-square tests showed that, compared to the humans first and disconnected LUV types, the nature first and interconnected LUV types reported significantly greater importance of the following: most categories of types of wildlife in their land use decisions; conservation-related motivations for participating in a United States Farm Bill Conservation Program; conservation-related motivations for land use decisions; and participation in conservation-related behaviors. Conservation professionals and organizations may use the LUV scale to better understand landowners’ land use decisions to evaluate and inform conservation policy, programs, messaging, and improve conservation outcomes.

Journal of Wildlife Management↗
USGS2021

The influence of legacy contamination on the transport and bioaccumulation of mercury within the Mobile River Basin

Past industrial use and subsequent release of mercury (Hg) into the environment have resulted in severe cases of legacy contamination that still influence contemporary Hg levels in biota. While the bioaccumulation of legacy Hg is commonly assessed via concentration measurements within fish tissue, this practice becomes difficult in regions of high productivity and methylmercury (MeHg) production, like the Mobile River Basin, Alabama in the southeastern United States. This study applied Hg stable isotope tracers to distinguish legacy Hg from regional deposition sources in sediments, waters, and fish within the Mobile River. Sediments and waters displayed differences in δ 202 Hg between industrial and background sites, which corresponded to drastic differences in Hg concentration. Sites that were affected by legacy Hg, as defined by δ 202 Hg, produced largemouth bass with lower MeHg content (59–70%) than those captured in the main rivers (>85%). Direct measurements of Hg isotopes and mathematical estimates of MeHg isotope pools in fish displayed similar distinctions between legacy and watershed sources as observed in other matrices. These results indicate that legacy Hg can accumulate directly into fish tissue as the inorganic species and may also be available for methylation within contaminated zones decades after the initial release.

Alabama↗
USGS2012

An exploratory investigation of the landscape-lake interface: Land cover controls over consumer N and C isotopic composition in Lake Michigan rivermouths

Rivermouth ecosystems are areas where tributary waters mix with lentic near-shore waters and provide habitat for many Laurentian Great Lakes fish and wildlife species. Rivermouths are the interface between terrestrial activities that influence rivers and the ecologically important nearshore. Stable isotopes of nitrogen (N) and carbon (C) in consumers were measured from a range of rivermouths systems to address two questions: 1) What is the effect of rivermouth ecosystems and land cover on the isotopic composition of N available to rivermouth consumers? 2) Are rivermouth consumers composed of lake-like or river-like C? For question 1, data suggest that strong relationships between watershed agriculture and consumer N are weakened or eliminated at the rivermouth, in favor of stronger relationships between consumer N and depositional areas that may favor denitrification. For question 2, despite apparently large riverine inputs, consumers only occasionally appear river-like. More often consumers seem to incorporate large amounts of C from either the nearshore or primary production within the rivermouth itself. Rivermouths appear to be active C and N processing environments, thus necessitating their explicit incorporation into models estimating nearshore loading and possibly contributing to their importance to Great Lakes biota.

Lake Michigan↗
USGS2014

Potential environmental effects of pack stock on meadow ecosystems of the Sierra Nevada, USA

Pack and saddle stock, including, but not limited to domesticated horses, mules, and burros, are used to support commercial, private and administrative activities in the Sierra Nevada. The use of pack stock has become a contentious and litigious issue for land management agencies in the region inter alia due to concerns over effects on the environment. The potential environmental effects of pack stock on Sierra Nevada meadow ecosystems are reviewed and it is concluded that the use of pack stock has the potential to influence the following: (1) water nutrient dynamics, sedimentation, temperature, and microbial pathogen content; (2) soil chemistry, nutrient cycling, soil compaction and hydrology; (3) plant individuals, populations and community dynamics, non-native invasive species, and encroachment of woody species; and (4) wildlife individuals, populations and communities. It is considered from currently available information that management objectives of pack stock should include the following: minimise bare ground, maximise plant cover, maintain species composition of native plants, minimise trampling, especially on wet soils and stream banks, and minimise direct urination and defecation by pack stock into water. However, incomplete documentation of patterns of pack stock use and limited past research limits current understanding of the effects of pack stock, especially their effects on water, soils and wildlife. To improve management of pack stock in this region, research is needed on linking measurable monitoring variables (e.g. plant cover) with environmental relevancy (e.g. soil erosion processes, wildlife habitat use), and identifying specific environmental thresholds of degradation along gradients of pack stock use in Sierra Nevada meadows.

Rangeland Journal↗
USGS2014

Latitudinal and photic effects on diel foraging and predation risk in freshwater pelagic ecosystems

1. Clark & Levy ( American Naturalist , 131 , 1988, 271–290) described an antipredation window for smaller planktivorous fish during crepuscular periods when light permits feeding on zooplankton, but limits visual detection by piscivores. Yet, how the window is influenced by the interaction between light regime, turbidity and cloud cover over a broad latitudinal gradi- ent remains unexplored. 2. We evaluated how latitudinal and seasonal shifts in diel light regimes alter the foraging- risk environment for visually feeding planktivores and piscivores across a natural range of turbidities and cloud covers. Pairing a model of aquatic visual feeding with a model of sun and moon illuminance, we estimated foraging rates of an idealized planktivore and piscivore over depth and time across factorial combinations of latitude (0 – 70 ° ), turbidity (0  1 – 5 NTU) and cloud cover (clear to overcast skies) during the summer solstice and autumnal equinox. We evaluated the foraging-risk environment based on changes in the magnitude, duration and peak timing of the antipredation window. 3. The model scenarios generated up to 10-fold shifts in magnitude, 24-fold shifts in duration and 5  5-h shifts in timing of the peak antipredation window. The size of the window increased with latitude. This pattern was strongest during the solstice. In clear water at low turbidity (0  1 – 0  5 NTU), peaks in the magnitude and duration of the window formed at 57 – 60 ° latitude, before falling to near zero as surface waters became saturated with light under a midnight sun and clear skies at latitudes near 70 ° . Overcast dampened the midnight sun enough to allow larger windows to form in clear water at high latitudes. Conversely, at turbidities ≥ 2 NTU, greater reductions in the visual range of piscivores than planktivores created a window for long periods at high latitudes. Latitudinal dependencies were essentially lost during the equinox, indicating a progressive compression of the window from early summer into autumn. 4. Model results show that diel-seasonal foraging and predation risk in freshwater pelagic ecosystems changes considerably with latitude, turbidity and cloud cover. These changes alter the structure of pelagic predator – prey interactions, and in turn, the broader role of pelagic consumers in habitat coupling in lakes.

Journal of Animal Ecology↗
USGS2018

Groundwater modeling

The state of the science and practice in groundwater modeling brings to mind highly sophisticated computer models that are running in parallel on many multi-processor machines. These models are expected to incorporate many different processes of both saturated and unsaturated groundwater flow and transport and possibly the media to which it connects, like surface waters and the atmosphere. We are increasingly aware we cannot study groundwater flow in isolation if we are to make useful predictions of, for instance, the impacts of climate change on the groundwater regime. We have come a long way. Today we are no longer limited to equations for flow toward a well, perhaps near an infinitely long straight canal (method of images), to sandbox models in the laboratory, or to simple steady state models of flow in a single aquifer. We now have computer models that solve groundwater flow and transport in multi-aquifer settings under transient conditions and with a user-friendly graphical user interface that allows widespread use. Additionally, multi-media models are now leaving the research environment and becoming available to mainstream consultants. So in that sense the science of groundwater modeling has matured. The practice of groundwater modeling, however, has also matured. We have come to realize that model output, being a necessary simplification of an unknowably complex natural world, has inherent limitations. That is, a model of reality is not reality itself. There is uncertainty associated with all facets of our model—parameterization, aquifer geometry and discretization, boundary conditions, and future hydrologic drivers such as future pumping regimes and climates. Today a model is now more appropriately seen as a tool that provides a quantitative framework to make supportable forecasts rather than an oracle that gives us all the answers. In this chapter we set out to briefly review the state of the science and practice in modeling. In doing so, we augment existing assessments from the journal Groundwater (e.g., Hunt and Zheng 2012; Langevin and Panday 2012; Molz 2017a,b; White 2017), specifically in terms of modeling approach. An effective modeling approach is critical. If a modeler does not decompose the societal problem correctly, the model will not be fit-for-purpose, no matter how sophisticated the code’s capabilities. Moreover, capabilities of codes will be ever improving; good modeling practices have a timelessness that is more robust. How best to decompose the problem and provide models that are accepted? We lay out here some approaches for today’s applied groundwater modeling. Specifically, we suggest: (1) a step-wise modeling process; (2) including a two-dimensional areal model within this process; (3) keeping abreast of industry standards; and (4) ways to increase acceptance of the models we produce.

Book chapter↗
USGS2024

Photogrammetry of the deep seafloor from archived unmanned submersible exploration dives

Large amounts of video images have been collected for decades by scientific and governmental organizations in deep (>1000 m) water using manned and unmanned submersibles and towed cameras. The collected images were analyzed individually or were mosaiced in small areas with great effort. Here, we provide a workflow for utilizing modern photogrammetry to construct virtual geological outcrops hundreds or thousands of meters in length from these archived video images. The photogrammetry further allows quantitative measurements of these outcrops, which were previously unavailable. Although photogrammetry had been carried out in recent years in the deep sea, it had been limited to small areas with pre-defined overlapping dive paths. Here, we propose a workflow for constructing virtual outcrops from archived exploration dives, which addresses the complicating factors posed by single non-linear and variable-speed vehicle paths. These factors include poor navigation, variable lighting, differential color attenuation due to variable distance from the seafloor, and variable camera orientation with respect to the vehicle. In particular, the lack of accurate navigation necessitates reliance on image quality and the establishment of pseudo-ground-control points to build the photogrammetry model. Our workflow offers an inexpensive method for analyzing deep-sea geological environments from existing video images, particularly when coupled with rock samples.

Journal of Marine Science and Engineering↗