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121.
122.
Climate change will affect future flow and thermal regimes of rivers. This will directly affect freshwater habitats and ecosystem health. In particular fish species, which are strongly adapted to a certain level of flow variability will be sensitive to future changes in flow regime. In addition, all freshwater fish species are exotherms, and increasing water temperatures will therefore directly affect fishes’ biochemical reaction rates and physiology. To assess climate change impacts on large-scale freshwater fish habitats we used a physically-based hydrological and water temperature modelling framework forced with an ensemble of climate model output. Future projections on global river flow and water temperature were used in combination with current spatial distributions of several fish species and their maximum thermal tolerances to explore impacts on fish habitats in different regions around the world. Results indicate that climate change will affect seasonal flow amplitudes, magnitude and timing of high and low flow events for large fractions of the global land surface area. Also, significant increases in both the frequency and magnitude of exceeding maximum temperature tolerances for selected fish species are found. Although the adaptive capacity of fish species to changing hydrologic regimes and rising water temperatures could be variable, our global results show that fish habitats are likely to change in the near future, and this is expected to affect species distributions. 相似文献
123.
Talitha L. F. Costa Michelle P. Araújo Bastiaan A. Knoppers Renato S. Carreira 《Aquatic Geochemistry》2011,17(1):1-19
In the present work, we evaluated the origin of organic matter in the tropical estuarine-lagoon system of Mundaú–Manguaba,
NE Brazil, by considering the bulk (organic carbon and chlorophyll-a) and lipidic (n-alcohols and sterols) composition of suspended particles. Water samples were collected in August 2006 from
24 stations covering the salinity gradient from the rivers down to the sea outlet. Chlorophyll-a (Chl-a) varied from 22.7 to 134.1 μg L−1 in the lagoons, indicating eutrophic to hypertrophic conditions at the time of sampling. The high correlation between Chl-a and phytol together with the molar C:N ratio indicated the presence of fresh and recently produced autochthonous particulate
organic matter throughout the system, except for the river samples. The elevated concentrations of short-chain n-alcohols
and phytosterols, mainly 24-methylcholesta-5,24(28)-dien-3β-ol, also corroborated the predominance of autochthonous organic
matter in the lagoons but were generated by distinct sources: cianobacteria in the freshwater Manguaba lagoon and diatoms
in the brackish Mundaú lagoon compartments. Input of terrestrial organic matter was only detected in the rivers themselves
or at the upper river–lagoon interfaces. Coprostanol indicated contamination by sewage in Mundaú lagoon and in some rivers,
but at lower levels when compared to other Brazilian coastal lagoons and estuaries. 相似文献
124.
125.
Markus Stoffel Michelle Bollschweiler Lorenzo Vázquez‐Selem Osvaldo Franco‐Ramos David Palacios 《地球表面变化过程与地形》2011,36(9):1209-1217
Dynamics and rates of rockfalls have been repeatedly studied in mountain environments with archival records as well as lichenometric, radiocarbon or dendrogeomorphic approaches. In this study, we test the potential of conifers growing at a low‐latitude, high‐elevation site as a dendrogeomorphic tool to reconstruct to calendar dates associated rockfall activity. Analysis is based on tree‐ring records of Mexican mountain pine (Pinus hartwegii Lindl.) growing at timberline [~4000 m above sea level (a.s.l.)] and at the runout fringe of a north–northeast (NNE)‐facing slope of the dormant Iztaccíhuatl volcano (Mexico), which is subject to frequent rockfalls. The potential and limitations of tree‐ring data are demonstrated based on 67 rockfall impacts dated in the increment‐ring series of 24 trees since ad 1836. While findings of this paper are site‐specific, the study clearly shows the potential of dendrogeomorphic approaches in extra‐Alpine, low‐latitude environments and for the understanding of rockfall processes in space and time. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
126.
Jayantha Obeysekera Michelle Irizarry Joseph Park Jenifer Barnes Tibebe Dessalegne 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(4):495-516
Recent climate change projections suggest that negative impacts on flood control and water supply functions and on existing
and future ecosystem restoration projects in south Florida are possible. An analysis of historical rainfall and temperature
data of the Florida peninsula indicates that there were no discernible trends in both the long-term record and during the
more recent period (1950–2007). A comparison of General Circulation Model (GCM) results for the 20th century with the historical
data shows that many of the GCMs do not capture the statistical characteristics of regional rainfall and temperature regimes
in south Florida. Investigation of historical sea level data at Key West finds evidence for an increase in the occurrence
and variance of maximum sea level events for the period 1961–2008 in relation to 1913–1960, along with a shift of energy from
shorter to longer timescales. In order to understand the vulnerability of the water management system in south Florida in
response to changing precipitation and evapotranspiration forcing, a sensitivity analysis using a regional-scale hydrologic
and water management model is conducted. Model results suggest that projected climate change has potential to reduce the effectiveness
of water supply and flood control operations for all water sectors. These findings emphasize that questions on the potential
impacts of climate change need to be investigated with particular attention paid to the uncertainties of such projections. 相似文献
127.
Based on observational meteorological data since A.D. 1864 and tree-ring records of debris-flow activity, this paper assesses changes in rainfall characteristics and their impact on the triggering of geomorphic events in a high-elevation watershed of the Swiss Alps since the end of the Little Ice Age. No trends are visible in the frequency of heavy rainfall events, but we observe a reduced number of heavy, short-lived rainfalls in summer and a concentration of advective storms is recorded in late summer and early fall since the late 1980s. These changes in triggering meteorological conditions resulted in a cluster of debris flows in the early decades of the twentieth century and a lowering of debris-flow activity since the mid 1990s, and may be mirroring the observed changes in persistent high-pressure systems over the Alps. We also observe intra-seasonal differences in debris-flow system response reflecting the state of the permafrost body in the source area of debris flows, allowing for very small debris flows to be released by limited rainfall inputs (<20 mm) in June and July. The same quantities of rain will not trigger debris flows in August or September, when a thick active layer of the permafrost body is capable of absorbing water. With the projected amplitude of climatic change, seasonality, return intervals and volumes of debris flows are likely to be altered. RCM projections based on the IPCC A2 scenario suggest a decrease in heavy summer rainfalls which will most likely result in a (further) reduction of the overall frequency of debris flows, leaving more time for sediment to accumulate in the channel. Such an increase of channel accumulation rates along with the projected destabilization of the steep rock-glacier body is likely, in turn, to exert control ultimately on sediment volumes released from the source areas during future events. Observations from adjacent catchments suggest that extremely large debris flows, beyond historical experience, could occur at the study site and in similar debris-flow systems of the Valais Alps originating from periglacial environments. 相似文献
128.
Joseph Park Jayantha Obeysekera Michelle Irizarry Jenifer Barnes Paul Trimble Winifred Park-Said 《Climatic change》2011,107(1-2):109-128
Water resource management in South Florida faces nearly intractable problems, in part due to weather and climate variability. Rising sea level and coastal storm surge are two phenomena with significant impacts on natural systems, fresh water supplies and flood drainage capability. However, decision support information regarding management of water resources in response to storm surge is not well developed. In an effort to address this need we analyze long term tidal records from Key West, Pensacola and Mayport Florida to extract surge distributions, to which we apply a nonlinear eustatic sea level rise model to project storm surge return levels and periods. Examination of climate connections reveals a statistically significant dependence between surge distributions and the Atlantic Multidecadal Oscillation (AMO). Based on a recent probabilistic model for AMO phase changes, we develop AMO-dependent surge distributions. These AMO-dependent surge projections are used to examine the flood control response of a coastal water management structure as an example of how climate dependent water resource forcings can be used in the formulation of decision support tools. 相似文献
129.
Markus Stoffel Thomas Mendlik Michelle Schneuwly-Bollschweiler Andreas Gobiet 《Climatic change》2014,122(1-2):141-155
This study uses a long dataset of past debris flows from eight high-elevation catchments in the Swiss Alps for which triggering conditions since AD 1864 have been reconstructed. The torrents under investigation have unlimited sediment supply and the triggering of debris flows is thus mainly controlled by climatic factors. Based on point-based downscaled climate scenarios for meteorological stations located next to the catchments and for the periods 2001–2050 and 2051–2100, we study the evolution of temperature and rainfall above specific thresholds (10, 20, 30, 40 and 50 mm) and durations (1, 2 or 3 days). We conclude that the drier conditions in future summers and the wetting of springs, falls and early winters are likely to have significant impacts on the behavior of debris flows. Based on the current understanding of debris-flow systems and their reaction to rainfall inputs, one might expect only slight changes in the overall frequency of events by the mid-21st century, but possibly an increase in the overall magnitude of debris flows due to larger volumes of sediment delivered to the channels and an increase in extreme precipitation events. In the second half of the 21st century, the number of days with conditions favorable for the release of debris flows will likely decrease, especially in summer. The anticipated increase of rainfall during the shoulder seasons (March, April, November, December) is not expected to compensate for the decrease in future heavy summer rainfall over 2 or 3 days. 相似文献
130.
Estuarine sediment deposition during wetland restoration: A GIS and remote sensing modeling approach
Michelle Elizabeth Newcomer Amber Jean Michael Kuss Tyler Ketron Alex Remar Vivek Choksi J. W. Skiles 《国际地球制图》2013,28(4):451-467
Restoration is currently underway in the industrial salt flats of San Francisco Bay, California. Remote sensing of suspended sediment concentration and other GIS predictor variables were used to model sediment deposition within recently restored ponds. Suspended sediment concentrations were calibrated to reflectance values from Landsat TM 5 and ASTER satellite image data using three statistical techniques—linear regression, multivariate regression, and Artificial Neural Network (ANN) regression. Multivariate and ANN regressions using ASTER proved to be the most accurate methods, yielding r2 values of 0.88 and 0.87, respectively. Predictor variables such as sediment grain size and tidal frequency were used in the Marsh Sedimentation (MARSED) model for predicting deposition rates. MARSED results show a root mean square deviation (RMSD) of 66.8 mm (<1σ) between modeled and field observations. This model was applied to a pond breached in November 2010 and indicated that the pond will reach sediment equilibrium levels after 60 months of tidal inundation. 相似文献