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USGS2004

A tree-ring based reconstruction of the Atlantic Multidecadal Oscillation since 1567 A.D

We present a tree-ring based reconstruction of the Atlantic Multidecadal Oscillation (AMO) which demonstrates that strong, low-frequency (60-100 yr) variability in basin-wide (0-70??N) sea surface temperatures (SSTs) has been a consistent feature of North Atlantic climate for the past five centuries. Intervention analysis of reconstructed AMO indicates that 20th century modes were similar to those in the preceding ???350 yr, and wavelet spectra show robust multidecadal oscillations throughout the reconstruction. Though the exact relationships between low-frequency SST modes, higher frequency (???7-25 yr) atmospheric modes (e.g., North Atlantic Oscillation/Arctic Oscillation), and terrestrial climates must still be resolved, our results confirm that the AMO should be considered in assessments of past and future Northern Hemisphere climates. Copyright 2004 by the American Geophysical Union.

Geophysical Research Letters↗

USGS2009

Microseismicity at the North Anatolian Fault in the Sea of Marmara offshore Istanbul, NW Turkey

The North Anatolian Fault Zone (NAFZ) below the Sea of Marmara forms a “seismic gap” where a major earthquake is expected to occur in the near future. This segment of the fault lies between the 1912 Ganos and 1999 İzmit ruptures and is the only NAFZ segment that has not ruptured since 1766. To monitor the microseismic activity at the main fault branch offshore of Istanbul below the Çınarcık Basin, a permanent seismic array (PIRES) was installed on the two outermost Prince Islands, Yassiada and Sivriada, at a few kilometers distance to the fault. In addition, a temporary network of ocean bottom seismometers was deployed throughout the Çınarcık Basin. Slowness vectors are determined combining waveform cross correlation and P wave polarization. We jointly invert azimuth and traveltime observations for hypocenter determination and apply a bootstrap resampling technique to quantify the location precision. We observe seismicity rates of 20 events per month for M < 2.5 along the basin. The spatial distribution of hypocenters suggests that the two major fault branches bounding the depocenter below the Çınarcık Basin merge to one single master fault below ∼17 km depth. On the basis of a cross-correlation technique we group closely spaced earthquakes and determine composite focal mechanisms implementing recordings of surrounding permanent land stations. Fault plane solutions have a predominant right-lateral strike-slip mechanism, indicating that normal faulting along this part of the NAFZ plays a minor role. Toward the west we observe increasing components of thrust faulting. This supports the model of NW trending, dextral strike-slip motion along the northern and main branch of the NAFZ below the eastern Sea of Marmara.

Istanbul↗

USGS2012

Seismicity and detection/location threshold in the southern Great Basin seismic network

A spatially varying model of the detection/location capabilities of the Southern Great Basin seismic network (SGBSN) has been derived that is based on simple empirical relations and statistics. This permits use of almost all the catalog data gathered; instead of ignoring data that are below the threshold of completeness, a spatially varying threshold model is developed so that subregions having lower completeness levels than the network as a whole can be outlined and the completeness level of each sub-region determined. Such a model is required to unambiguously identify regions that are aseismic due to natural processes rather than to limited detection and/or location capabilities. Accounting for spatial variations in detection/location threshold is also important for studies in which magnitude-frequency distributions are interpreted in terms of source scaling properties. The characteristics of the spatial distribution of earthquakes, where earthquake clusters and aseismic regions locate, appear to be stable at all magnitude levels so that inferences about where strain is being accommodated will be the same whether numbers of earthquakes or strain estimated from seismic moments are examined. For the southern Great Basin region these principal characteristics include clusters at the northern end of the Furnace Creek fault and in the Pahranagat Shear Zone, and a relatively large number of earthquakes in the northern and southeastern portions of the Nevada Test Site. These clusters cover regions much larger than the surface projections of any of the mapped faults. The extent to which seismicity is induced by nuclear testing is unclear. The predominantly aseismic regions include the area west of the Death Valley/Furnace Creek fault system and an almost complete absence of events at Yucca Mountain. Finally, a considerable number of isolated events in the SGBSN catalog cannot be correlated with mapped faults.

Journal of Geophysical Research↗

USGS2008

Assessment of the instantaneous unit hydrograph derived from the theory of topologically random networks

An instantaneous unit hydrograph (iuh) based on the theory of topologically random networks (topological iuh) is evaluated in terms of sets of basin characteristics and hydraulic parameters. Hydrographs were computed using two linear routing methods for each of two drainage basins in the southeastern United States and are the basis of comparison for the topological iuh's. Elements in the sets of basin characteristics for the topological iuh's are the number of first-order streams only, ( N ), or the nuber of sources together with the number of channel links in the topological diameter ( N, D ); the hydraulic parameters are values of the celerity and diffusivity constant. Sensitivity analyses indicate that the mean celerity of the internal links in the network is the critical hydraulic parameter for determining the shape of the topological iuh, while the diffusivity constant has minimal effect on the topological iuh. Asymptotic results (source-only) indicate the number of sources need not be large to approximate the topological iuh with the Weibull probability density function.

Water Resources Research↗

USGS1995

Magnitude and frequency of peak discharges for Mississippi River Basin Flood of 1993

The magnitude and frequency of the 1993 peak discharges in the upper Mississippi River Basin are characterized by applying Bulletin 17B and L-moment methods to annual peak discharges at 115 unregulated watersheds in the basin. The analysis indicated that the 1993 flood was primarily a 50-year or less event on unregulated watersheds less than about 50,000 km 2 (20,000 mi 2 ). Of the 115 stations analyzed, the Bulletin 17B and L-moment methods were used to identify 89 and 84 stations, respectively, having recurrence intervals of 50 years or less, and 31 and 26 stations, respectively, having recurrence intervals greater than 50 years for the 1993 peak discharges. The 1993 flood in the upper Mississippi River Basin was significant in terms of (a) peak discharges with recurrence intervals greater than 50 years at approximately 25 percent of the stations analyzed, (b) peak discharges of record at 33 of the 115 stations analyzed, (c) extreme magnitude, duration, and areal extent of precipitation, (d) flood volumes with recurrence intervals greater than 100 years at many stations, and (e) extreme flood damage and loss of lives. Furthermore, peak discharges on several larger, regulated watersheds also exceeded the 100-year recurrence interval. However, for about 75 percent of the 115 unregulated stations in the analysis, the frequency of the 1993 peak discharges was less than a 50-year event.

Transportation Research Record↗

USGS2016

New perspectives on a 140-year legacy of mining and abandoned mine cleanup in the San Juan Mountains, Colorado

The Gold King mine water release that occurred on 5 August 2015 near the historical mining community of Silverton, Colorado, highlights the environmental legacy that abandoned mines have on the environment. During reclamation efforts, a breach of collapsed workings at the Gold King mine sent 3 million gallons of acidic and metal-rich mine water into the upper Animas River, a tributary to the Colorado River basin. The Gold King mine is located in the scenic, western San Juan Mountains, a region renowned for its volcano-tectonic and gold-silver-base metal mineralization history. Prior to mining, acidic drainage from hydrothermally altered areas was a major source of metals and acidity to streams, and it continues to be so. In addition to abandoned hard rock metal mines, uranium mine waste poses a long-term storage and immobilization challenge in this area. Uranium resources are mined in the Colorado Plateau, which borders the San Juan Mountains on the west. Uranium processing and repository sites along the Animas River near Durango, Colorado, are a prime example of how the legacy of mining must be managed for the health and well-being of future generations. The San Juan Mountains are part of a geoenvironmental nexus where geology, mining, agriculture, recreation, and community issues converge. This trip will explore the geology, mining, and mine cleanup history in which a community-driven, watershed-based stakeholder process is an integral part. Research tools and historical data useful for understanding complex watersheds impacted by natural sources of metals and acidity overprinted by mining will also be discussed.

Colorado↗

USGS2008

Specific conductance in the Colorado River between Glen Canyon Dam and Diamond Creek, Northern Arizona, 1988-2007

The construction of Glen Canyon Dam, completed in 1963, resulted in substantial physical and biological changes to downstream Colorado River environments between Lake Powell and Lake Mead - an area almost entirely within Grand Canyon National Park, Ariz. In an effort to understand these changes, data have been collected to assess the condition of a number of downstream resources. In terms of measuring water quality, the collection of specific-conductance data is a cost-effective method for estimating salinity. Data-collection activities were initially undertaken by the Bureau of Reclamation's Glen Canyon Environmental Studies (1982-96); these efforts were subsequently transferred to the U.S. Geological Survey's Grand Canyon Monitoring and Research Center (1996 to the present). This report describes the specific-conductance dataset collected for the Colorado River between Glen Canyon Dam and Diamond Creek from 1988 to 2007. Data-collection and processing methods used during the study period are described, and time-series plots of the data are presented. The report also includes plots showing the relation between specific conductance and total dissolved solids. Examples of the use of specific conductance as a natural tracer of parcels of water are presented. Analysis of the data indicates that short-duration spikes and troughs in specific-conductance values lasting from hours to days are primarily the result of flooding in the Paria and Little Colorado Rivers, Colorado River tributaries below Glen Canyon Dam. Specific conductance also exhibits seasonal variations owing to changes in the position of density layers within the reservoir; these changes are driven by inflow hydrology, meteorological conditions, and background stratification. Longer term trends in Colorado River specific conductance are reflective of climatological conditions in the upper Colorado River Basin. For example, drought conditions generally result in an increase in specific conductance in Lake Powell. Therefore, the average annual specific conductance below Glen Canyon Dam is inversely related to the volume of water in Lake Powell.

Arizona↗

USGS2001

Geologic map and digital database of the Conejo Well 7.5 minute quadrangle, Riverside County, southern California

This data set maps and describes the geology of the Conejo Well 7.5 minute quadrangle, Riverside County, southern California. The quadrangle, situated in Joshua Tree National Park in the eastern Transverse Ranges physiographic and structural province, encompasses part of the northern Eagle Mountains and part of the south flank of Pinto Basin. It is underlain by a basement terrane comprising Proterozoic metamorphic rocks, Mesozoic plutonic rocks, and Mesozoic and Mesozoic or Cenozoic hypabyssal dikes. The basement terrane is capped by a widespread Tertiary erosion surface preserved in remnants in the Eagle Mountains and buried beneath Cenozoic deposits in Pinto Basin. Locally, Miocene basalt overlies the erosion surface. A sequence of at least three Quaternary pediments is planed into the north piedmont of the Eagle Mountains, each in turn overlain by successively younger residual and alluvial deposits. The Tertiary erosion surface is deformed and broken by north-northwest-trending, high-angle, dip-slip faults in the Eagle Mountains and an east-west trending system of high-angle dip- and left-slip faults. In and adjacent to the Conejo Well quadrangle, faults of the northwest-trending set displace Miocene sedimentary rocks and basalt deposited on the Tertiary erosion surface and Pliocene and (or) Pleistocene deposits that accumulated on the oldest pediment. Faults of this system appear to be overlain by Pleistocene deposits that accumulated on younger pediments. East-west trending faults are younger than and perhaps in part coeval with faults of the northwest-trending set. The Conejo Well database was created using ARCVIEW and ARC/INFO, which are geographical information system (GIS) software products of Envronmental Systems Research Institute (ESRI). The database consists of the following items: (1) a map coverage showing faults and geologic contacts and units, (2) a separate coverage showing dikes, (3) a coverage showing structural data, (4) a point coverage containing line ornamentation, and (5) a scanned topographic base at a scale of 1:24,000. The coverages include attribute tables for geologic units (polygons and regions), contacts (arcs), and site-specific data (points). The database, accompanied by a pamphlet file and this metadata file, also includes the following graphic and text products: (1) A portable document file (.pdf) containing a navigable graphic of the geologic map on a 1:24,000 topographic base. The map is accompanied by a marginal explanation consisting of a Description of Map and Database Units (DMU), a Correlation of Map and Database Units (CMU), and a key to point-and line-symbols. (2) Separate .pdf files of the DMU and CMU, individually. (3) A PostScript graphic-file containing the geologic map on a 1:24,000 topographic base accompanied by the marginal explanation. (4) A pamphlet that describes the database and how to access it. Within the database, geologic contacts , faults, and dikes are represented as lines (arcs), geologic units as polygons and regions, and site-specific data as points. Polygon, arc, and point attribute tables (.pat, .aat, and .pat, respectively) uniquely identify each geologic datum and link it to other tables (.rel) that provide more detailed geologic information.

California↗

USGS2015

Land use structures fish assemblages in reservoirs of the Tennessee River

Inputs of nutrients, sediments and detritus from catchments can promote selected components of reservoir fish assemblages, while hindering others. However, investigations linking these catchment subsidies to fish assemblages have generally focussed on one or a handful of species. Considering this paucity of community-level awareness, we sought to explore the association between land use and fish assemblage composition in reservoirs. To this end, we compared fish assemblages in reservoirs of two sub-basins of the Tennessee River representing differing intensities of agricultural development, and hypothesised that fish assemblage structure indicated by species percentage composition would differ among reservoirs in the two sub-basins. Using multivariate statistical analysis, we documented inter-basin differences in land use, reservoir productivity and fish assemblages, but no differences in reservoir morphometry or water regime. Basins were separated along a gradient of forested and non-forested catchment land cover, which was directly related to total nitrogen, total phosphorous and chlorophyll- a concentrations. Considering the extensive body of knowledge linking land use to aquatic systems, it is reasonable to postulate a hierarchical model in which productivity has direct links to terrestrial inputs, and fish assemblages have direct links to both land use and productivity. We observed a shift from an invertivore-based fish assemblage in forested catchments to a detritivore-based fish assemblage in agricultural catchments that may be a widespread pattern among reservoirs and other aquatic ecosystems.

Tennessee River↗

USGS1978

Late Miocene mollusks from the Queen Charlotte Islands, British Columbia, Canada

A fauna of bivalve mollusks, scattered gastropods, and an echinoid from exposures of the Skonun Formation in the northeastern part of Graham Island is indicative of an early late Miocene age and correlation with the provincial Wishkahan Stage. The molluscan assemblages are from the upper 600 of the 1800-m-thick marine and nonmarine formation, which appears to be entirely of late Miocene age. The Skonun Formation is the strandline fa.cies of marginal marine and nonmarine deposits of the northwestern part of the Queen Charlotte basin, a Nieogene embayment paralleling the modern mainland coast. The molluscan fauna and associated lignite beds are known from a few widely scattered outcrops; they are indicative of alternating marine and nonmarine to brackish-water environments in the upper part of the formation. The Skonun fauna occurs near the northern boundary of the Pacific Northwest Neogene molluscan province. It is the only marine Neogene molluscan fauna known from the British Columbia coast. The fauna has strong taxonomic ties with the fauna of the Empire Formation of southwestern Oregon and has several species in common with the upper Miocene of the Lituya district, southeastern Alaska, implying that these three faunas are coeval.

Queen Charlotte Islands, Graham Island↗

USGS2024

Evolution of a lake margin recorded in the Sutton Island member of the Murray formation, Gale crater, Mars

This study uses data from the Mars Science Laboratory Curiosity rover to document the facies of the Sutton Island member of the Murray formation, interpret paleoenvironments, and establish key stratigraphic transitions at Gale crater. Two facies associations were identified: Facies Association 1 (FA1) and Facies Association 2 (FA2). Individual facies in FA1 include planar-laminated mudstone with minor intervals of planar sandstone, ripple cross-laminated sandstone, cross-stratified sandstone, and alternating laminated sandstone and mudstone. Meter-thick packages of planar-laminated mudstone in FA1 are interpreted to represent deposition in low-energy ponded environments along the lake margin. Straight- and curve-crested ripple cross-laminated facies are interpreted to represent current-influenced deposition. Cross-stratified sandstone facies consist of dm-thick sets that represent deposition in distal channels. Intercalated mm-scale mudstone and sandstone laminae represent waning flow conditions and possible channel abandonment. Facies in FA1 collectively represent deposition in a distal delta plain. FA2 is comprised of planar-laminated mudstone with minor sandstone and is interpreted to represent deposition in a lacustrine-basin setting by suspension settling linked to density flows. FA1 transitions upward into FA2, defining a rapid transgression substantial enough to facilitate the deposition of distal lake facies above delta plain facies. The abrupt transition from FA2 back to FA1 deltaic deposits is suggestive of forced regression. Facies in FA1 and FA2 are consistent with the prevalence of aqueous environments recorded in other Murray formation members and extend our understanding of the dynamic sedimentary processes that characterized ancient lacustrine systems at Gale crater.

Journal of Geophysical Research - Planets↗

USGS2012

Heat-flow data and their relation to observed geothermal phenomena near Klamath Falls, Oregon

Two holes were drilled to depths of about 180 m in the Lower Klamath Lake basin south of Klamath Falls, Oregon, to obtain heat flow data and to provide estimates of the thermal conductivity of the valley fill. Twenty-nine thermal conductivity determinations on eight cores give a mean conductivity of 1.82 mcal/cm s °C (0.75 W/m °K). Curvature in the upper 50 m of both terriperature profiles indicates a decrease in surface temperature of about 1.8°C, presumably resulting frorn reclamation of what was marshland in the early part of this century. A surprisingly low heat flow of 0.3 HFU (1 HFU = 10 −6 cal/cm 2 s = 41.8 mW/m 2 ) was measured at site LS near the center of the basin. At site OC-1, 7 km east of LS and 2 km from the Klamath Hills geothermal zone, the heat flow was 1.44 HFU, also a low value in this setting. Temperature profiles in 15 unused water wells in the area had linear gradients ranging from 47° to 170°C/km. The corresponding lower limits of heat flow (conductivities measured at the two heat flow sites being used) range from 0.8 to 3.1 HFU. These variations in heat flow evidently are caused by temperature variations in a convecting system within the near-surface volcanic rocks and do not provide firm constraints on the nature of heat sources at depth.

Journal of Geophysical Research↗

USGS2021

Effects of climate and irrigation on GRACE-based estimates of water storage changes in major US aquifers

Understanding climate and human impacts on water storage is critical for sustainable water-resources management. Here we assessed climate and human drivers of total water storage (TWS) variability from Gravity Recovery and Climate Experiment (GRACE) satellites compared with drought severity and irrigation water use in 14 major aquifers in the United States. Results show that long-term variability in TWS tracked by GRACE satellites is dominated by interannual variability in most of the 14 major US aquifers. Low TWS trends in the humid eastern U.S. are linked to low drought intensity. Although irrigation pumpage in the humid Mississippi Embayment aquifer exceeded that in the semi-arid California Central Valley, a surprising lack of TWS depletion in the Mississippi Embayment aquifer is attributed to extensive streamflow capture. Marked storage depletion in the semi-arid southwestern Central Valley and south-central High Plains totaled ∼90 km 3 , about three times greater than the capacity of Lake Mead, the largest U.S. reservoir. Depletion in the Central Valley was driven by long-term droughts (⩽5 yr) amplified by switching from mostly surface water to groundwater irrigation. Low or slightly rising TWS trends in the northwestern (Columbia and Snake Basins) US are attributed to dampening drought impacts by mostly surface water irrigation. GRACE satellite data highlight synergies between climate and irrigation, resulting in little impact on TWS in the humid east, amplified TWS depletion in the semi-arid southwest and southcentral US, and dampened TWS deletion in the northwest and north central US Sustainable groundwater management benefits from conjunctive use of surface water and groundwater, inefficient surface water irrigation promoting groundwater recharge, efficient groundwater irrigation minimizing depletion, and increasing managed aquifer recharge. This study has important implications for sustainable water development in many regions globally.

Environmental Research Letters↗

USGS2015

The Mw6.0 24 August 2014 South Napa earthquake

The M w 6.0 South Napa earthquake, which occurred at 10:20 UTC 24 August 2014 was the largest earthquake to strike the greater San Francisco Bay area since the M w 6.9 1989 Loma Prieta earthquake. The rupture from this right‐lateral earthquake propagated mostly unilaterally to the north and up‐dip, directing the strongest shaking toward the city of Napa, where peak ground accelerations (PGAs) between 45% g and 61% g were recorded and modified Mercalli intensities (MMIs) of VII–VIII were reported. Tectonic surface rupture with dextral slip of up to 46 cm was observed on a 12.5 km long segment, some of which was along a previously mapped strand of the West Napa fault system, although the rupture extended to the north of the mapped Quaternary strand. Modeling of seismic and geodetic data suggests an average coseismic slip of 50 cm, with a maximum slip of about 1 m at depths of 10–11 km. We observed up to 35 cm of afterslip along the surface trace in the week following the mainshock, primarily along the southern half of the surface rupture that experienced relatively little coseismic offset. Relocation of the sparse aftershock sequence suggests en echelon southwest‐ and northeast‐dipping fault planes, reflective of the complex fault geometry in this region. The Napa basin and historic and late Holocene alluvial flood deposits in downtown Napa amplified the ground motions there. Few ground failures were mapped, reflecting the dry season (as well as a persistent drought that had lowered the groundwater table) and the short duration of strong shaking in the epicentral area.

California↗

USGS1975

Ordovician and middle Silurian rocks of the Wildhorse window, northeastern Pioneer Mountains, central Idaho

Along Wildhorse Creek in the northeastern Pioneer Mountains, autochthonous Ordovician and Silurian rocks of an eastern carbonate assemblage are exposed in a structural window through allochthonous flysch deposits of the Mississippian Copper Basin Group. Graptolite-bearing Middle and Upper Ordovician dolomite and cherty dolomite 210 ft (64 m) thick are lithologically and faunally similar to the Hanson Creek Formation of central Nevada and the Saturday Mountain Formation of central Idaho. Monograptus -bearing Middle Silurian platy limestone at least 130 ft (40 m) thick resembles the Roberts Mountains Formation of central Nevada and rocks improperly designated Trail Creek Formation in the Bayhorse region of central Idaho. Allochthonous age-equivalent units of a more western transitional assemblage (the type Phi Kappa and Trail Creek Formations) occur 5 mi (8 km) west of the Wildhorse window, along the crest of the Pioneer Mountains.

Idaho↗

USGS2025

Long-term patterns in growth of White Sturgeon in the Sacramento-San Joaquin River basin, California.

Introduction: The Sacramento-San Joaquin River system (SSJ) of California includes both riverine, delta, and estuarine habitats and is among the most modified aquatic ecosystems in the United States. Water development projects in the system are associated with declines of many native species, including White Sturgeon Acipenser transmontanus . Methods: We used White Sturgeon pectoral fin rays collected from 1983 to 2016 throughout the SSJ to assess long-term changes in growth and associations with thermal and hydrological conditions (i.e., temperature, discharge, salinity). Age and growth were estimated from 1,897 White Sturgeon varying in fork length from 25 to 210 cm and from age 0 to 33. Results: Age structure varied through time with the oldest fish generally sampled during the mid-1980s. Growth of White Sturgeon in 1951–1970 was slower than growth of fish in 1971–1990 and 1991–2012. Growth of White Sturgeon during 1991–2012 was ~10% higher than during other time periods. Discussion: Little variation in growth was explained by environmental covariates, suggesting that annual growth was likely influenced by factors not measured in our study. Alternatively, population structure and movement behavior of White Sturgeon in the SSJ may be such that the scale (i.e., spatial or temporal) of available habitat covariates was mismatched to the scale at which growth of White Sturgeon responds. Increased growth in recent times may be partly due to density-dependent processes in association with substantial declines in White Sturgeon population abundance over the last several decades. This research provides important information on long-term patterns in growth that contributes to the conservation and management of White Sturgeon in the SSJ and beyond.

California↗

USGS2016

Regional land subsidence caused by the compaction of susceptible aquifer systems accompanying groundwater extraction

Land subsidence includes both gentle downwarping and sudden sinking of segments of the land surface. Major anthropogenic causes of land subsidence are extraction of fluids including water, oil, and gas. Measurement and detec- tion of land subsidence include both ground-based and remotely sensed air- borne and space-based methods. Methods for measurement of subsidence at points include differential leveling, global positioning system surveys, and extensometers. Satellite-borne differential interferometric synthetic aperture radar and airborne LiDAR techniques can detect land-surface movement over wide areas of interest. Aquifer-system compaction and subsidence owing to groundwater extraction typically occurs in areas of unconsolidated alluvial or basin-fill aquifer systems comprising aquifers and aquitards. Approaches to analyzing and modeling deformation of aquifer systems follow from the basic relations between head, stress, compressibility, and groundwater flow. Analysis and simulation of aquifer-system compaction have been addressed primarily using either an approach based on conventional groundwater flow theory or an approach based on linear poroelasticity theory. Both approaches rely on the principle of effective stress outlined by Karl Terzaghi in 1925. In the approach based on conventional groundwater flow theory, an aquitard drainage model explains the compaction of fine grained material using the principle of effective stress and theory of hydrodynamic lag. Packages for the widely-used MODFLOW groundwater model are available to simulate aqui- fer-system compaction and land subsidence using the aquitard-drainage approach. Poroelasticity theory describes the more fully coupled processes of groundwater flow and three-dimensional deformation of aquifer systems. The general theory accounts for compressible fluid, porous matrix and solid grains. Simulation codes using the poroelastic theory include some commer- cial software products and a few research codes.

Book chapter↗

USGS2009

Recent increases in the large glacial-relict calanoid Limnocalanus macrurus in Lake Michigan

Since 2004, population density of the large hypolimnetic calanoid Limnocalanus macrurus Sars. has increased dramatically in Lake Michigan. The average summer biomass of this species between 2004 and 2006 was roughly three times that of the period 1984–2003, and at levels unprecedented in our 22-year dataset, making L. macrurus the dominant zooplankter in the lake in terms of biomass. These increases have been accentuated by coincident population declines of the main daphnid, Daphnia mendotae, in the lake with the result that in 2006, L. macrurus accounted for 75% and 50% of the large (> 0.9 mm) crustacean biomass in the northern and southern basins of Lake Michigan, respectively. The increases in L. macrurus populations have closely coincided with equally dramatic increases in summer water clarity. Recent extinction coefficients are among the lowest recorded for the lake, and deepening light penetration has permitted increases in the size of the deep chlorophyll layer. In addition, planktivorous fish populations have declined coincidently with the increases in L. macrurus. It seems likely that an increase in sub-epilimnetic production has resulted in increased food resources for the deep-living L. macrurus, while low planktivore abundances have reduced predation loss, permitting L. macrurus to respond to these increases in sub-epilimnetic production.

Lake Michigan↗