Groundwater flux as a determinant of coastal-zone upland loss: a case study from the Pennsylvania coast of Lake Erie,USA

Climate change in the Great Lakes Basin of North America over the next several decades is projected to lead to significant changes to coastal environments. Groundwater-driven coastal bluff recession should increase in areas where groundwater forcing is important and lead to increased loss of coastal uplands. The latter is an issue in NW Pennsylvania because of coastal development pressures, and because the state ranks within the top five US states in grape production, most of which occurs within 5 km of the Lake Erie coastline. In 2007, viticulture contributed almost $2.4 billion to the state economy. An analysis of a 20-km stretch of coast shows that bluff retreat is pervasive and variable under current climatic conditions. Over a 9-year time frame, bluff change rates ranged from ?4.2 to +0.98 m/year. In general, higher retreat rates (?0.2 to ?0.65 m/year) occurred along the sandy central beach–ridge sector which lacks significant surface drainage. Lower retreat rates (?0.10 to ?0.25 m/year) occurred along coastal sectors where surface drainage networks are well developed. Conservative estimates of groundwater discharge at the bluff correlate strongly (r = 0.74, p < 0.001) with bluff retreat rate. Groundwater is inferred to be the principal driving mechanism for both bluff retreat and spatial variability in retreat rates on this coast. Other common factors that may spatially influence bluff retreat elsewhere (bluff height, land use, beach width) do not correlate strongly with retreat rate.     

Anthropogenic gadolinium as a micropollutant in river waters in Pennsylvania and in Lake Erie, northeastern United States

“Anthropogenic” gadolinium, Gd, used in contrast agents in magnetic resonance imaging, is a micropollutant that enters river and lake waters with the discharge from wastewater treatment plants, WWTPs. Such discharge is also the source of other micropollutants, for example pharmaceuticals, such as steroids, antihistamins, and antibiotics. Together with the “natural” Gd, the anthropogenic Gd produces positive Gd anomalies in rare-earth element distribution patterns and is, therefore, easily detectable. This pilot study reports on the occurrence of anthropogenic Gd in rivers in Pennsylvania (Ohio, Beaver, Allegheny, Monongahela, Juniata, and Susquehanna) and in near-shore surface water from Lake Erie close to the city of Buffalo. Additional data are reported for the Delaware River and the headwaters of Spring Creek in Central Pennsylvania, and for Lake Ontario and Niagara River, all of which do not show significant anthropogenic Gd. Most pronounced impact of anthropogenic Gd discharged from WWTPs is observed in the Pittsburgh Metropolitan area. Such contamination is similar to that observed in densely populated areas with highly developed medical and healthcare systems in Europe and Japan. Its worldwide applicability adds to the promising potential of anthropogenic Gd as a cost-effective tracer for the presence of WWTP effluent in river, lake, ground, and drinking waters.     

Paleoenvironmental records of water level and climatic changes from the middle to late Holocene at a Lake Erie coastal wetland, Ontario, Canada

Pollen and diatom assemblages, and peat stratigraphies, from a coastal wetland on the northern shore of Lake Erie were used to analyze water level and climatic changes since the middle Holocene and their effects on wetland plant communities. Peat deposition began 4700 cal yr B.P. during the Nipissing II transgression, which was driven by isostatic rebound. At that time, a diatom-rich wild rice marsh existed at the site. Water level dropped at the end of the Nipissing rise at least 2 m within 200 yr, leading to the development of shallower-water plant communities and an environment too dry for most diatoms to persist. The sharp decline in water level was probably driven primarily by outlet incision, but climate likely played some role. The paleoecological records provide evidence for post-Nipissing century-scale transgressions occurring around 2300, 1160, 700 and 450 cal yr B.P. The chronology for these transgressions correlates with other studies from the region and implies climatic forcing. Peat inception in shallow sloughs across part of the study area around 700 cal yr B.P. coincides with the Little Ice Age. These records, considered alongside others from the region, suggest that the Little Ice Age may have resulted in a wetter climate across the eastern Great Lakes region.     

Geochemical evaluation of flowback brine from Marcellus gas wells in Pennsylvania,USA

Large quantities of highly saline brine flow from gas wells in the Marcellus Formation after hydraulic stimulation (“fracking”). This study assesses the composition of these flowback waters from the Marcellus shale in Pennsylvania, USA. Concentrations of most inorganic components of flowback water (Cl, Br, Na, K, Ca, Mg, Sr, Ba, Ra, Fe, Mn, total dissolved solids, and others) increase with time from a well after hydraulic stimulation. Based on results in several datasets reported here, the greatest concentration of Cl⁻ in flowback water is 151,000 mg/L. For total Ra (combined ²²⁶Ra and ²²⁸Ra) in flowback, the highest level reported is 6540 pCi/L. Flowback waters from hydraulic fracturing of Marcellus wells resemble brines produced from conventional gas wells that tap into other Paleozoic formations in the region. The Br/Cl ratio and other parameters indicate that both types of brine formed by the evaporation of seawater followed by dolomitization, sulfate reduction and subsurface mixing with seawater and/or freshwater. Trends and relationships in brine composition indicate that (1) increased salt concentration in flowback is not mainly caused by dissolution of salt or other minerals in rock units, (2) the flowback waters represent a mixture of injection waters with highly concentrated in situ brines similar to those in the other formations, and (3) these waters contain concentrations of Ra and Ba that are commonly hundreds of times the US drinking water standards.     

Transport, sorting, and reworking of late Wisconsinan plant macrofossils from Lake Erie, Canada

Stratigraphic, sedimentological, and plant macrofossil studies on proglacial lacustrine and deltaic sequences dating from the Mackinaw Interstadial on the north shore of Lake Erie, Canada, indicate long-distance transport, selective sorting and reworking of the plant fossils. Transport, sorting, and reworking may make detailed paleoclimatic indices irrelevant and may account for incongruent phytogeographic indicators in the fossil assemblage. Details of the stratigraphic and sedimentological setting of the study site and the state of preservation of the fossils should be considered more carefully as aids to the interpretation of macrofossil assemblages.     

A 2200-yr record of hydrologic variability from Foy Lake, Montana, USA, inferred from diatom and geochemical data

A 2200-yr long, high-resolution (∼5 yr) record of drought variability in northwest Montana is inferred from diatoms and δ¹⁸O values of bio-induced carbonate preserved in a varved lacustrine core from Foy Lake. A previously developed model of the diatom response to lake-level fluctuations is used to constrain estimates of paleolake levels derived from the diatom data. High-frequency (decadal) fluctuations in the de-trended δ¹⁸O record mirror variations in wet/dry cycles inferred from Banff tree-rings, demonstrating the sensitivity of the oxygen-isotope values to changes in regional moisture balance. Low frequency (multi-centennial) isotopic changes may be associated with shifts in the seasonal distribution of precipitation. From 200 B.C. to A.D. 800, both diatom and isotope records indicate that climate was dry and lake level low, with poor diatom preservation and high organic carbon: nitrogen ratios. Subsequently, lake level rose slightly, although the climate was drier and more stable than modern conditions. At A.D. 1200, lake level increased to approximately 6 m below present elevation, after which the lake fluctuated between this elevation and full stage, with particularly cool and/or wetter conditions after 1700. The hydrologic balance of the lake shifted abruptly at 1894 because of the establishment of a lumber mill at the lake's outlet. Spectral analysis of the δ¹⁸O data indicates that severe droughts occurred with multi-decadal (50 to 70 yr) frequency.     

Depositional processes and the inferred history of ice-margin retreat associated with the deglaciation of the Cordilleran Ice Sheet: The sedimentary record from Flathead Lake,northwest Montana,USA

A series of piston cores from Flathead Lake, Montana, USA and a new radiocarbon date from the sedimentary record provide the basis for describing sedimentary processes related to deglaciation of the Flathead Lobe of the Cordilleran Ice Sheet and for interpreting the retreat history of the lobe. The oldest part of Flathead Lake sediment core records is Late Pleistocene in age and consists of cm-scale rhythmites of silt and clay, interpreted here as annual varves. Each varve contains a light-colored coarser-grained portion, inferred to represent deposition during peak annual runoff, and a darker-colored finer-grained portion interpreted to represent sediment accumulation during seasonal low-flow conditions. The coarser-grained portions, especially in the stratigraphically older sections of each core, contain sedimentary structures that reflect traction transport. Based on these sedimentary structures, their facies characteristics, and their spatial distribution within the lake, we interpret the thicker, light-colored portion of each varve to be deposited by hyperpycnal flows caused by seasonal melt events rather than more classic turbidity currents.Immediately overlying Late Pleistocene rhythmites in all Flathead Lake cores is a unique, significantly coarser-grained dm-scale silt bed with a median grain size up to 50 µm. This silt bed has a sharp, locally erosional base and fines upward but does not contain any other sedimentary structures. In contrast to the rhythmites, we interpret this silt bed to represent a single, short-lived catastrophic sedimentation event generated by a large glacial outburst flood. Overlying this distinct bed are several other cm-scale beds of mainly silt that exhibit a basal upward-coarsening followed by an upward-fining median grain size profile. We interpret these beds and their grain size trends as reflecting the rising and falling hydrograph limbs of outburst floods derived from more distal sources located in the upstream parts of the upper Flathead watershed.The sediment record from Flathead Lake, together with results from geologic and geomorphologic 1:24,000 scale mapping around the lake margins, provide a series of constraints regarding the paleogeographic evolution of the area during deglaciation. Overall upward-thinning and upward-fining of the varved portion of the sediment core records reflects northward retreat of the southern Flathead Lobe ice margin starting at latest 14,475 ± 150 cal yr BP, the depositional age of the oldest varve in any of our cores. The depositional age of silt beds overlying the varved records is constrained as between 14,150 ± 150 cal yr BP and 13,180 ± 120 cal yr BP. Within the available chronostratigraphic constraints, the outburst floods interpreted to have delivered this silt to the Flathead Lake basin also downcut a bedrock nick point below the Flathead Lake outlet, oriented a series of large boulders downstream, and deposited a series of large flood bars on the lower Flathead River floodplain.     

A late Pleistocene long pollen record from Lake Urmia, NW Iran

A palynological study based on two 100-m long cores from Lake Urmia in northwestern Iran provides a vegetation record spanning 200 ka, the longest pollen record for the continental interior of the Near East. During both penultimate and last glaciations, a steppe of Artemisia and Poaceae dominated the upland vegetation with a high proportion of Chenopodiaceae in both upland and lowland saline ecosystems. While Juniperus and deciduous Quercus trees were extremely rare and restricted to some refugia, Hippophaë rhamnoides constituted an important phanerophyte, particularly during the late last glacial period. A pronounced expansion in Ephedra shrub-steppe occurred at the end of the penultimate late-glacial period but was followed by extreme aridity that favoured an Artemisia steppe. Very high lake levels, registered by both pollen and sedimentary markers, occurred during the middle of the last glaciation and late part of the penultimate glaciation. The late-glacial to early Holocene transition is represented by a succession of Hippophaë, Ephedra, Betula, Pistacia and finally Juniperus and Quercus. The last interglacial period (Eemian), slightly warmer and moister than the Holocene, was followed by two interstadial phases similar in pattern to those recorded in the marine isotope record and southern European pollen sequences.     

Changes in beach gravel lithology caused by anthropogenic activities along the southern coast of Lake Michigan, USA

The southern coast of Lake Michigan is the most urbanized and most densely populated area in the Great Lakes region. Development of steel mills, harbors, and municipalities in NW Indiana and in NE Illinois in the last century and a half altered the nearshore environment so much that native beach gravel (>8 mm) now exist only in the exhumed paleo-beach remnants from the Nipissing Phase (~4,500 years ago) of Lake Michigan. Native gravel, collected from paleo-beach remnants at Mount Baldy Dune and Beach House Blowout, contain predominantly beach shingle, very platy siltstones (71–78 %), with secondary crystalline pebbles (18 %) in the east, and carbonate pebbles (12 %) in the west. A large amount of anthropogenic fill (steel industry waste, waste from power generating plants, construction debris, railroad, and road fill) has been added since the late 1800s to fill Lake Michigan and expand industrial land. Four areas of major coastal structures—Michigan City Pier and Breakwater, Burns Harbor Pier and Breakwater, Gary Works Pier, and Indiana Harbor Peninsula—altered the natural littoral drift and created four independent sectors on Indiana’s coast—Northeastern, Eastern, Central, and Western—between which no natural transfers of coarse sediments occur. Downdrift from the coastal structures, severe beach erosion has prompted extensive beach nourishment with non-native sandy gravel. Four distinct populations of modern beach gravel now exist along Indiana’s coast of Lake Michigan: (1) native gravel with diluted beach nourishment influence, (2) native gravel with a minor industrial influence, (3) compact gravel of nourished origin, and (4) anthropogenic gravel of industrial origin. Native gravel with diluted nourishment influence is found in the western, downdrift areas of the Northeastern (from Long Beach to Washington Park Beach) and Eastern Sectors (from eastern Indiana Dunes State Park to western Dune Acres) and contains up to 40 % compact carbonate and crystalline pebbles in addition to native beach shingle. Native gravel with minor industrial influence is found in the Central Sector of Indiana’s coast (from central Ogden Dunes to Marquette Beach) and contains predominantly beach shingle, platy clastic lithology, but also up to 30 % of chert and other pebbles released by industry. Compact gravel of nourished origin contains 60–90 % of carbonate and crystalline pebbles, and is found in the eastern, updrift areas of the Northeastern (Michiana Beach and Duneland Beach) and Eastern Sectors (from Crescent Beach to the western Beverly Shores). Anthropogenic gravel of industrial origin contains 70–90 % compact chert and slag and is found in every beach of the Western Sector and in the westernmost beach of the Central Sector. Streams draining into southern Lake Michigan generally contain little coarse sediment except in their channels near the roads and railroads, where angular to subangular anthropogenic pebbles predominate (70–90 %). However, streams have very little influence on gravel lithology along the coast because they seldom discharge anthropogenic gravel into Lake Michigan. Recent changes in gravel lithology along the southern Lake Michigan coast may affect changes in nearshore benthic flora and fauna as well as algal and bacterial blooms during warm summer months.     

Combined interpretation of radar, hydraulic, and tracer data from a fractured-rock aquifer near Mirror Lake, New Hampshire, USA

An integrated interpretation of field experimental cross-hole radar, tracer, and hydraulic data demonstrates the value of combining time-lapse geophysical monitoring with conventional hydrologic measurements for improved characterization of a fractured-rock aquifer. Time-lapse difference-attenuation radar tomography was conducted during saline tracer experiments at the US Geological Survey Fractured Rock Hydrology Research Site near Mirror Lake, Grafton County, New Hampshire, USA. The presence of electrically conductive saline tracer effectively illuminates permeable fractures or pathways for geophysical imaging. The geophysical results guide the construction of three-dimensional numerical models of ground-water flow and solute transport. In an effort to explore alternative explanations for the tracer and tomographic data, a suite of conceptual models involving heterogeneous hydraulic conductivity fields and rate-limited mass transfer are considered. Calibration data include tracer concentrations, the arrival time of peak concentration at the outlet, and steady-state hydraulic head. Results from the coupled inversion procedure suggest that much of the tracer mass migrated outside the three tomographic image planes, and that solute is likely transported by two pathways through the system. This work provides basic and site-specific insights into the control of permeability heterogeneity on ground-water flow and solute transport in fractured rock.

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Resumen Una interpretación integrada de radar experimental de campo transversal a pozos, trazadores, y datos hidráulicos demuestra el valor de combinar el monitoreo geofísico realizado en periodos de tiempo con mediciones hidrológicas convencionales en la caracterización mejorada de un acuífero rocoso fracturado. Se llevó a cabo tomografía de radar por periodos de tiempo y diferencia de atenuación durante un experimento con trazadores salinos en el sitio de investigación hidrológica de roca fracturada del Servicio Geológico de Estados Unidos cerca del Lago Espejo, Condado Grafton, New Hampshire, USA. La presencia del trazador salino eléctricamente conductivo refleja efectivamente fracturas permeables o trayectorias para imágenes geofísicas. Los resultados geofísicos orientan la construcción de modelos numéricos tri-dimensionales de flujo de agua subterránea y transporte de solutos. En un esfuerzo por explorar explicaciones alternativas para los datos tomográficos y trazadores se considera un conjunto de modelos conceptuales que involucran campos de conductividad hidráulica heterogéneos y transferencias de masa de ritmo limitado. La calibración de datos incluye concentraciones de trazadores, el tiempo de llegada de la concentración pico en la salida, y presión hidráulica en régimen permanente. Los resultados del procedimiento de acoplamiento invertido sugieren que mucho de la masa del trazador migró fuera de los tres planos de imagen tomográfica, y que el soluto es probablemente transportado por dos trayectorias a través del sistema. Este trabajo aporta ideas básicas y específicas del sitio en relación con el control de la heterogeneidad de permeabilidades en el flujo de agua subterránea y transporte de solutos en rocas fracturadas.

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Résumé Une interprétation intégrée détudes de terrain (radar entre puits, traçages, données hydrauliques) démontre la valeur de la combinaison entre la géophysique des temps finis et les mesures hydrologiques conventionnelles pour une interprétation améliorée dun aquifère de roche fracturée. La tomographie au radar a été mise en uvre durant un traçage artificiel au sel au site de recherche sur lhydrologie des roches fracturées du Service Géologique des US, à proximité du Lac Mirror, Conté de Grafton, Nouvel Hampshire, USA. La présence du traceur électriquement conducteur met en relief, grâce à la géophysique, la présence de fractures ou découlements préférentiels. Les résultats de la géophysique ont permis la construction de modèle hydrogéologique tri-dimensionnel des écoulements et du transport de soluté. Dans loptique dexplorer des interprétations alternatives des données de traçage et de tomographie, différents modèles conceptuels sont utilisés concernant lhétérogénéité des conductivités hydrauliques et des taux limités de transferts de solutés. Les données du calibrage incluent les données de concentration du traceur, le temps darrivée du pic de restitution et les données piézométriques en régime permanent. Les résultats de la procédure dinversion couplée suggèrent quune quantité très importante du traceur migre au delà de la fenêtre de visualisation des tomographies, et que le soluté est transporté via deux voies découlement préférentiel. Ce travail apporte des connaissances de base et spécifiques au site concernant la distribution de la perméabilité dans laquifère et le transport de soluté dans les roches fracturées.

     

Chemical characteristics of coastal rainwater from Puducherry to Neithavasal,Southeastern coast of India

The chemistry of the rainwater indirectly reflects the composition of the ions in the atmosphere. The study of the rainwater gains its own importance as it forms the basis for the agricultural, domestic and drinking water. Twelve rainwater samples were collected along the southeastern coast of India during southwest monsoon. The samples were analyzed for the major anions (Cl^?, SO₄ ^2?, PO₄ ^3? and HCO₃ ^?) and cations (Na⁺, K⁺, Ca²⁺ and Mg²⁺). The majority of the samples reflect acidic pH. The general dominance of the cations is in the order of Na⁺ > Ca²⁺ > K⁺ > Mg²⁺ and that of anions is HCO₃ ^? > Cl^? > SO₄ ^2? > PO₄ ^3?. The water is classified as calcium bicarbonate to sodium bicarbonate type. The decrease of pH value also increases the pCO₂. In order to study the impact of acidic and alkaline species on rainwater, correlation coefficients were determined for establishing the relationship between different ions. Good correlation was established between cations, and sulfate has no correlation with other ions and pH. Factor analysis reveals that land use pattern, marine source and methanogenesis from the tidal influenced mangroves play a major role in determining the rainwater chemistry of the region.     

Migration and sedimentology of longshore sandwaves, Long Point, Lake Erie, Canada

This paper describes the formation, migration and sedimentology of sandwaves along the distal end of Long Point, a 40 km long spit in Lake Erie. Some seven to nine sandwaves occur in a zone over the last 14 km of the spit. They are characteristically 50–100 m wide at the downdrift end, range in length from 350 m to > 1500 m and migrate alongshore at rates that are typically 100–300 m year⁻¹. Measurements over a 7-year period show two forms of alongshore sandwave migration: (1) a migratory jump; and (2) downdrift accretion. The migratory jump is commonly 200–500 m year⁻¹ and results from the onshore migration and welding of an inner nearshore bar to the downdrift end of the sandwave. This in turn leads to emergence of the bar over a distance of several hundred metres downdrift of the sandwave and isolation of the trough landward of the bar. Infilling of the trough abstracts large volumes of sediment from the local sediment transport system and may affect movement of the sandwave in the following year or movement of the next sandwave downdrift. Downdrift accretion commonly results in migration of 50–150 m year⁻¹ and results from the refraction of waves around the distal end of the sandwave and episodic accretion of small swash bars. This mechanism occurs less frequently and appears to reflect a local condition of lower sediment abundance, often triggered by a large migratory jump in the previous year. The process of bar emergence and infilling produces a distinct suite of sedimentary structures associated with the infilling of the landward trough and building of the sandwave berm. The initial shoreline perturbation that generates the sandwave results from onshore migration and welding of inner nearshore bars, and the development and growth of the sandwaves is promoted by refraction of highly oblique waves.     

Classification of paraglacial barrier systems: coastal New England, USA

The New England coast harbours a wide variety of barrier forms, which we organize into six barrier-coastline types. The barriers develop in response to the relative importance of several spatially and temporally variable parameters, particularly antecedent topography and geology, sediment abundance and size, exposure to wave and tidal energy and sea-level history. The six coastline types can also be identified in other paraglacial regions. Existing barrier-coastline classification schemes do not allow consistent subdivision of paraglacial barrier coasts. This paper presents a new scheme that is applicable to paraglacial and non-paraglacial barrier coasts alike. Aside from hydrodynamic regime, which forms the basis of the barrier classification most commonly used to date, it includes a compartmentalization factor. Sediment-starved ‘isolated’ (‘type 1’) barrier coastlines are characterized by short, widely spaced barriers. Small, localized updrift and offshore sources have provided sediment for short barriers along ‘clustered headland-separated’ (‘type 2’) barrier coastlines. Various amounts of sediment from larger updrift and offshore glaciofluvial deposits or directly from rivers have formed the longer barriers along ‘wave-dominated mainland-segmented’ (‘type 3a’), ‘mixed-energy mainland-segmented’ (‘type 3b’), ‘wave-dominated inlet-segmented’ (‘type 4a’) and ‘mixed-energy inlet-segmented’ (‘type 4b’) barrier coastlines. Geomorphic form, grain size and stratigraphy can be used to characterize individual barriers along barrier coastlines. Most paraglacial barriers form as spits, but many are transformed subsequently. Welded barriers are common along ‘type 1’ and ‘type 2’ coasts. Baymouth barriers are characteristic of ‘type 3’ coasts, and barrier islands occur exclusively along ‘type 4’ coasts. The coarsest grained barriers are located along ‘type 1’ and ‘type 2’ coasts. Progradational barrier sections are concentrated along ‘type 3’ and ‘type 4’ coasts with abundant sediment supply, but are also present along ‘type 2’ coasts. Temporary increases in sediment supply, common in paraglacial regions, result in transitions between retrogradational and progradational barrier behaviour, which may be recognized on shore-perpendicular stratigraphic cross-sections.     

Anthropogenic affects on lake sedimentation process: a case study from Lake Sapanca, NW Turkey

Lake Sapanca in NW Turkey is a fault originated freshwater basin fed by seasonally variable flows of 15 streams. Considerations of lake–river interaction, supported by statistical measures of 47 bottom samples, suggest that sediment transport and deposition within the lake is controlled by two types of human constructed structures in addition to natural factors: (1) the dykes constructed in the front of streams, which feed the lake by strong flows, to prevent the filling of lakebed by coarse-grained sediments; (2) the constructed regulator on the outflowing Çarksuyu stream results in a higher sedimentation rate of clay-sized material on the NE corner of the lake, which is extraordinary in the shelf environment.     

Sedimentary record from Lake Hovsgol, NW Mongolia: Results from the HDP-04 and HDP-06 drill cores

The Hovsgol Drilling Project retrieved Pleistocene sediment section with the basal age of ca. 1 Ma from the Hovsgol rift basin, NW Mongolia. Detailed lithologic data on drill cores is presented and compared with analogous sediment facies in the radiocarbon-dated records of the last glacial–interglacial transition. Drill cores from two sites, presently in 239 m and 235 m water depth, represent somewhat different depositional settings. The shorter HDP-06 drill core (26 m) at the base of the gentler SE slope of the rift basin contains lithologic evidence for several recent lake lowstands on the order of −200 m. The longer HDP-04 drill core (81 m) some 8 km away at the base of the steep NW underwater slope is composed of finer sediments and contains at least 10 characteristic transitions from calcareous to carbonate-free (diatomaceous) layers. These lithologic transitions are interpreted here as signals of repeated Pleistocene lake transgressions in the Hovsgol basin. Transgressions appear to have been associated with lower sedimentation rates and with the deposition of thin turbidite beds at the drill site. Comparison of drill core lithology with the available seismic data shows reasonable agreement in terms of the number of lowstand events and the general trends of changing lake level. HDP-04 drill core retrieved shallow-water facies containing sand and carbonate oolites deposited at the time of the most dramatic mid-Pleistocene regression of the lake. At ca. 24 m core depth, this interval corresponds to a major basinwide angular unconformity apparent in the seismic pattern. Lake Hovsgol, a smaller sister rift lake of the grand Lake Baikal, has a confined local catchment, which makes it very sensitive to regional variations in the effective moisture. Consisting primarily of calcareous mud, the sedimentary record of Lake Hovsgol provides a unique regional sedimentary archive. Future multi-proxy studies of the Hovsgol sedimentary records will allow constraint of the mid-late Pleistocene history of the hydrologic budget in the Baikal region of continental interior Asia.     

Radar facies of paraglacial barrier systems: coastal New England, USA

Analysis of a large data base of ground-penetrating-radar (GPR) profiles from both natural and developed paraglacial barriers along the coast of New England has allowed identification of eight reflection configurations that characterize this type of mid- to high-latitude coastal environment. Bedrock anchor points yield primarily hyperbolic configurations, whereas glacial anchor points and sediment-source areas are characterized by chaotic, parallel, and tangential-oblique configurations. Beaches and dunes produce predominantly sigmoidal oblique, hummocky, reflection-free, and bounding-surface configurations. Back-barrier sediments may yield basin-fill configurations, but generally include abundant signal-attenuating units.
The GPR data, calibrated with information from cores, were collected across swash-aligned and drift-aligned barriers in a variety of wave- and tidal-energy settings. Application of a 120-MHz antenna, as used in this study, enables portrayal of a range of sedimentary units, from individual bedforms (on single records) to entire barrier elements (using large numbers of intersecting GPR sections), at maximum vertical resolutions that vary between 0·2 m and 0·7 m.
The most important drawback of GPR in the coastal environment is attenuation of the electromagnetic (EM) signal by layers of salt-marsh peat or by brackish or salty groundwater, primarily along barrier edges. This disadvantage is offset by many benefits. Data can be collected at rates of several km per day, making GPR an excellent reconnaissance tool. A core that is used in the calibration of GPR data can be matched with great accuracy to its position on the complementary GPR record, allowing detailed correlation between lithostratigraphy and reflection configuration.     

Offshore petroleum and commercial fishery interactions: The case of Long Point,Port Dover,Lake Erie

GeoJournal - From a human ecological perspective, research was undertaken on interactions between Lake Erie fisheries and offshore petroleum (gas) development from 1913 to summer, 1981. In an...     

A Holocene pollen record of persistent droughts from Pyramid Lake, Nevada, USA

Pollen and algae microfossils preserved in sediments from Pyramid Lake, Nevada, provide evidence for periods of persistent drought during the Holocene age. We analyzed one hundred nineteen 1-cm-thick samples for pollen and algae from a set of cores that span the past 7630 years. The early middle Holocene, 7600 to 6300 cal yr B.P., was found to be the driest period, although it included one short but intense wet phase. We suggest that Lake Tahoe was below its rim for most of this period, greatly reducing the volume and depth of Pyramid Lake. Middle Holocene aridity eased between 5000 and 3500 cal yr B.P. and climate became variable with distinct wet and dry phases. Lake Tahoe probably spilled intermittently during this time. No core was recovered that represented the period between 3500 and 2600 cal yr B.P. The past 2500 years appear to have had recurrent persistent droughts. The timing and magnitude of droughts identified in the pollen record compares favorably with previously published δ¹⁸O data from Pyramid Lake. The timing of these droughts also agrees with the ages of submerged rooted stumps in the Eastern Sierra Nevada and woodrat midden data from central Nevada. Prolonged drought episodes appear to correspond with the timing of ice drift minima (solar maxima) identified from North Atlantic marine sediments, suggesting that changes in solar irradiance may be a possible mechanism influencing century-scale drought in the western Great Basin.     

Multiple-methods investigation of recharge at a humid-region fractured rock site,Pennsylvania, USA

Lysimeter-percolate and well-hydrograph analyses were combined to evaluate recharge for the Masser Recharge Site (central Pennsylvania, USA). In humid regions, aquifer recharge through an unconfined low-porosity fractured-rock aquifer can cause large magnitude water-table fluctuations over short time scales. The unsaturated hydraulic characteristics of the subsurface porous media control the magnitude and timing of these fluctuations. Data from multiple sets of lysimeters at the site show a highly seasonal pattern of percolate and exhibit variability due to both installation factors and hydraulic property heterogeneity. Individual event analysis of well hydrograph data reveals the primary influences on water-table response, namely rainfall depth, rainfall intensity, and initial water-table depth. Spatial and seasonal variability in well response is also evident. A new approach for calculating recharge from continuous water-table elevation records using a master recession curve (MRC) is demonstrated. The recharge estimated by the MRC approach when assuming a constant specific yield is seasonal to a lesser degree than the recharge estimate resulting from the lysimeter analysis. Partial reconciliation of the two recharge estimates is achieved by considering a conceptual model of flow processes in the highly-heterogeneous underlying fractured porous medium.