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  • Articles  (23,912)
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  • 1
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    The abiotic and biotic factors limiting establishment of predatory fishes at their expanding northern range boundaries in Ontario, Canada (2014)
    Wiley
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    Publication Date: 2014-12-31
    Description: There is a poor understanding of the importance of biotic interactions in determining species distributions with climate change. Theory from invasion biology suggests that the success of species introductions outside of their historical ranges may be either positively (biotic acceptance) or negatively (biotic resistance) related to native biodiversity. Using data on fish community composition from two survey periods separated by approximately 28 years during which climate was warming, we examined the factors influencing the establishment of three predatory centrarchids: Smallmouth Bass ( Micropterus dolomieu ), Largemouth Bass ( M. salmoides ) and Rock Bass ( Ambloplites rupestris ) in lakes at their expanding northern range boundaries in Ontario. Variance partitioning demonstrated that, at a regional scale, abiotic factors play a stronger role in determining the establishment of these species than biotic factors. Pairing lakes within watersheds where each species had established with lakes sharing similar abiotic conditions where the species had not established revealed both positive and negative relationships between the establishment of centrarchids and the historical presence of other predatory species. The establishment of these species near their northern range boundaries is primarily determined by abiotic factors at a regional scale, however, biotic factors become important at the lake-to-lake scale. Studies of exotic species invasions have previously highlighted how spatial scale mediates the importance of abiotic versus biotic factors on species establishment. Our study demonstrates how concepts from invasion biology can inform our understanding of the factors controlling species distributions with changing climate. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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  • 2
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    Greater deciduous shrub abundance extends tundra peak season and increases modeled net CO2 uptake (2014)
    Wiley
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    Publication Date: 2014-12-31
    Description: Satellite studies of the terrestrial Arctic report increased summer greening and longer overall growing and peak seasons since the 1980s, which increases productivity and the period of carbon uptake. These trends are attributed to increasing air temperatures and reduced snow cover duration in spring and fall. Concurrently, deciduous shrubs are becoming increasingly abundant in tundra landscapes, which may also impact canopy phenology and productivity. Our aim was to determine the influence of greater deciduous shrub abundance on tundra canopy phenology and subsequent impacts on net ecosystem carbon exchange (NEE) during the growing and peak seasons in the arctic foothills region of Alaska. We compared deciduous shrub-dominated and evergreen/graminoid-dominated community-level canopy phenology throughout the growing season using the normalized difference vegetation index (NDVI). We used a tundra plant-community specific leaf area index (LAI) model to estimate LAI throughout the green season, and a tundra specific NEE model to estimate the impact of greater deciduous shrub abundance and associated shifts in both leaf area and canopy phenology on tundra carbon flux. We found that deciduous shrub canopies reached the onset of peak greenness 13 days earlier and the onset of senescence 3 days earlier compared to evergreen/graminoid canopies, resulting in a 10-day extension of the peak season. The combined effect of the longer peak season and greater leaf area of deciduous shrub canopies almost tripled the modeled net carbon uptake of deciduous shrub communities compared to evergreen/graminoid communities, while the longer peak season alone resulted in 84% greater carbon uptake in deciduous shrub communities. These results suggest that greater deciduous shrub abundance increases carbon uptake not only due to greater leaf area, but also due to an extension of the period of peak greenness, which extends the period of maximum carbon uptake. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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  • 3
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    Analysis of Thermal Behaviour in the Active Layer of Degrading Mountain Permafrost (2014)
    Wiley
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    Publication Date: 2014-12-30
    Description: ABSTRACT Mountain permafrost is highly susceptible to the effects of climate warming, because its thermal regime is close to 0 °C. This can be evidenced by the acceleration of average annual creep rates of several rock glaciers in the Swiss Alps, whereby some exhibit even more extreme signs of degradation. Measurements obtained from a borehole drilled from a relatively flat area on a rock glacier, below the Furggwanghorn peak, Turtmanntal (Switzerland), showed positive mean annual values of ground temperatures in the active layer over two hydrological years, from 1 October 2010 to 30 September 2012. The thermal conditions in this borehole were much warmer than those measured at the same time in other boreholes in the same rock glacier. A test pit excavated in the active layer close to this borehole, and instrumented with thermistors, indicated similar thermal conditions. It was hypothesised that the thick snow cover that accumulated on the flat area during winter and an existing supra-permafrost talik were responsible for the warm thermal regime, given the relevant meteorological inputs over this period. The degradation of the rock glacier in this flat area was probably driven by a high summer heat flux into the rock glacier, which could not be reversed in winter due to a thick insulating snow layer that accumulated from October onwards. A coupled one-dimensional numerical model, based on SNOWPACK and HYDRUS, was developed to interpret the thermal behaviour in the active layer. The resulting numerical analysis was validated, showing that the simulated ground temperatures agreed well with measured values at various depths. The heat loss from the ground was found to be very small during the winter, due to insulation by autumnal snowfalls, whereas the heat flux to the ground had been relatively high in recent summers. The mean positive heat flux to the supra-permafrost talik was calculated to be 1.75 Wm -2 over the 2 year period, which is sufficient to cause considerable ice melt. Furthermore, water flow in the supra-permafrost talik appeared to limit temperature variations in the active layer to 0.12 °C in summer. Copyright © 2014 John Wiley & Sons, Ltd.
    Print ISSN: 1045-6740
    Electronic ISSN: 1099-1530
    Topics: Geography , Geosciences
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  • 4
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    A bivariate extension of the Hosking and Wallis goodness-of-fit measure for regional distributions (2014)
    Wiley
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    Publication Date: 2014-12-30
    Description: This study presents a bivariate extension of the goodness-of-fit measure for regional frequency distributions developed by Hosking and Wallis [1993] for use with the method of L-moments. Utilising the approximate joint normal distribution of the regional L-skewness and L-kurtosis, a graphical representation of the confidence region on the L-moment diagram can be constructed as an ellipsoid. Candidate distributions can then be accepted where the corresponding theoretical relationship between the L-skewness and L-kurtosis intersects the confidence region, and the chosen distribution would be the one that minimises the Mahalanobis distance measure. Based on a set of Monte Carlo simulations it is demonstrated that the new bivariate measure generally selects the true population distribution more frequently than the original method. Results are presented to show that the new measure remains robust when applied to regions where the level of inter-site correlation is at a level found in real world regions. Finally the method is applied to two different case studies involving annual maximum peak flow data from Italian and British catchments to identify suitable regional frequency distributions. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Net ecosystem production and organic carbon balance of U.S. east coast estuaries: A synthesis approach (2014)
    Wiley
    Details
    Publication Date: 2014-12-30
    Description: Net ecosystem production (NEP) and the overall organic carbon budget for the estuaries along the east coast of the United States are estimated. We focus on the open estuarine waters, excluding the fringing wetlands. We developed empirical models relating NEP to loading ratios of dissolved inorganic nitrogen to total organic carbon, and carbon burial in the sediment to estuarine water residence time and total nitrogen input across the landward boundary. Output from a data-constrained water quality model was used to estimate inputs of total nitrogen and organic carbon to the estuaries across the landward boundary, including fluvial and tidal-wetland sources. Organic carbon export from the estuaries to the continental shelf was computed by difference, assuming steady state. Uncertainties in the budget were estimated by allowing uncertainties in the supporting model relations. Collectively, U.S. east coast estuaries are net heterotrophic, with the area-integrated NEP of −1.5 (−2.8, −1.0) Tg C yr −1 (best estimate and 95% confidence interval) and area-normalized NEP of −3.2 (−6.1, −2.3) mol C m −2  yr −1 . East coast estuaries serve as a source of organic carbon to the shelf, exporting 3.4 (2.0, 4.3) Tg C yr −1 or 7.6 (4.4, 9.5) mol C m −2  yr −1 . Organic carbon inputs from fluvial and tidal-wetland sources for the region are estimated at 5.4 (4.6, 6.5) Tg C yr −1 or 12 (10, 14) mol C m −2  yr −1 and carbon burial in the open estuarine waters at 0.50 (0.33, 0.78) Tg C yr −1 or 1.1 (0.73, 1.7) mol C m −2  yr −1 . Our results highlight the importance of estuarine systems in the overall coastal budget of organic carbon, suggesting that in the aggregate, U.S. east coast estuaries assimilate (via respiration and burial) ~40% of organic carbon inputs from fluvial and tidal-wetland sources and allow ~60% to be exported to the shelf.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 6
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    Is geomorphology sleepwalking into oblivion? (2014)
    Wiley
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    Publication Date: 2014-12-30
    Description: ABSTRACT This commentary uses Google Books N-grams to briefly explore the changing use of the word geomorphology in books published in British English and American English. Both show a decline in the use of the term geomorphology in recent years. A singular feature of the British data is a very sharp rise and fall in the use of term geomorphology in books published since 1980. The steep falling limb (post 1993) of this curve is of particular concern and several possible explanations are put forward including, since 1986, the influence exerted by Research Assessment Exercises on publication practice in UK universities. The N-gram trends pose important questions for all geomorphologists and we should monitor them to gain a better understanding of where we need to be most visible to ensure the long-term health of our discipline. Copyright © 2014 John Wiley & Sons, Ltd.
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
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  • 7
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    Net Community Production in the North Atlantic Ocean derived from Volunteer Observing Ship data (2014)
    Wiley
    Details
    Publication Date: 2014-12-30
    Description: The magnitude of marine plankton net community production (NCP) is indicative of both the biologically driven exchange of carbon dioxide between the atmosphere and the surface ocean, and the export of organic carbon from the surface ocean to the oceaninterior. In this study the seasonal variability in the NCP of five biogeochemical regions in the North Atlantic was determined from measurements of surface water dissolved oxygen and dissolved inorganic carbon (DIC) sampled from a Volunteer Observing Ship (VOS). The magnitude of NCP derived from dissolved oxygen measurements (NCP O 2 ) was consistent with previous geochemical estimates of NCP in the North Atlantic, with an average annual NCP O 2 of 9.5 ± 6.5 mmol O 2 m −2 d −2 . Annual NCP O 2 did not vary significantly over 35 degrees of latitude, and was not significantly different from NCP derived from DIC measurements (NCP DIC ). The relatively simple method described here is applicable to any VOS route on which surface water dissolved oxygen concentrations can be accurately measured, thus providing estimates of NCP at higher spatial and temporal resolution than currently achieved.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 8
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    The stoichiometry of carbon and nutrients in peat formation (2014)
    Wiley
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    Publication Date: 2014-12-30
    Description: Northern peatlands have stored large amounts (~500 Pg) of carbon (C) since the last glaciation. Combined with peat C are nutrients such as nitrogen (N), phosphorus (P), calcium (Ca), magnesium (Mg) and potassium (K), each of which plays an important role in plant production, litter decomposition and the biogeochemical functioning of peatlands. Yet little attention has been given to the amounts of these nutrients stored in northern peatlands and their stoichiometry with C. Here, we use data on nutrient concentrations in over 400 peat profiles in Ontario, Canada, representing bogs, fens and swamps and their vegetation. We show that the C:N ratio is high (〉 40:1) in vegetation and litter, but declines through the peat profiles to reach ratios between 22:1 and 29:1 in peat below 50 cm. In contrast, the C:P ratio rises from vegetation and litter (500:1 to 1300:1) to 1500:1 to 2000:1 in the lower part of the peat profile. Ratios of C to Ca, Mg and K vary with peatland type. Most of these stoichiometric changes occur in the early stages of organic matter decomposition, where the litter structure remains intact. We estimate that ~18 Pg of N has been stored in northern peatlands since deglaciation, reflecting high N accumulation rates (~0.8 g m −2 y −1 ), whereas P accumulation is small (~0.3 Pg, ~0.016 g m −2 y −1 ), indicating that P is recycled quickly in the surface layers.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 9
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    Idealized simulations of the effect of local and remote topographies on tropical cyclone tracks (2014)
    Wiley
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    Publication Date: 2014-12-30
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
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  • 10
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    Co-evolution of riparian vegetation and channel dynamics in an aggrading braided river system, Mount Pinatubo, Philippines (2014)
    Wiley
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    Publication Date: 2014-12-29
    Description: ABSTRACT Increased bank stability by riparian vegetation can have profound impacts on channel morphology and dynamics in low-energy systems, but the effects are less clear in high-energy environments. Here, we investigate the role of vegetation in active, aggrading braided systems at Mount Pinatubo, Philippines, and compare results with numerical modelling results. Gradual reductions in post-eruption sediment loads have reduced bed reworking rates, allowing vegetation to finally persist year-round on the Pasig-Potrero and Sacobia Rivers. From 2009-2011, we collected data detailing vegetation extent, type, density, and root strength. Incorporating these data into RipRoot and BSTEM models shows cohesion due to roots increases from zero in unvegetated conditions to 〉10.2 kPa in densely-growing grasses. Field-based parameters were incorporated into a cellular model comparing vegetation strength and sediment mobility effects on braided channel dynamics. The model shows both low sediment mobility and high vegetation strength lead to less active systems, reflecting trends observed in the field. The competing influence of vegetation strength vs. channel dynamics is a concept encapsulated in a dimensionless ratio between timescales for vegetation growth and channel reworking known as T* . An estimated T* between 1.5 – 2.3 for the Pasig-Potrero River suggests channels are still very mobile and likely to remain braided until aggradation rates decline further. Vegetation does have an important effect on channel dynamics, however, by focusing flow and thus aggradation into the unvegetated fraction of braidplain, leading to an aggradational imbalance and transition to a more avulsive state. The future trajectory of channel-vegetation interactions as sedimentation rates decline is complicated by strong seasonal variability in precipitation and sediment loads, driving incision and armoring in the dry season. By 2011, incision during the dry season was substantial enough to lower the water-table, weaken existing vegetation, and allow for vegetation removal in future avulsions. This article is protected by copyright. All rights reserved.
    Print ISSN: 0197-9337
    Electronic ISSN: 1096-9837
    Topics: Geography , Geosciences
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