Gilroy D.J.,University of Wisconsin - Madison |
Jensen O.P.,University of Wisconsin - Madison |
Jensen O.P.,Rutgers University |
Allen B.C.,Tahoe Environmental Research Center |
And 5 more authors.
Ecology of Freshwater Fish
Taimen, Hucho taimen, is the world's largest salmonid and a prized sport fish. We used radio and acoustic telemetry to characterise movements of adult taimen in an extensive river system, the Eg-Uur, in north-central Mongolia. Forty-six taimen were tagged with transmitters (27 radio, 17 acoustic and 2 radio-acoustic combined) and tracked from 2004 to 2008 using mobile surveys and fixed receivers. The mean home range of individual taimen tracked for an average of 2.4 years was 23 km (N = 41, range = 0.5-93.2 km). Of the fish with over 10 relocations (N = 16), 90% remained within a range of 38 km. Four distinct movement patterns were observed: (i) restricted core home range, (ii) core range with seasonal departures, (iii) core range with separate seasonal range and (iv) home range transfer. Movement was greatest in May and June (spawning and postspawning period) with another peak period of movement in September and October (water temperature cooling). © 2010 John Wiley & Sons A/S. Source
Crawled News Article
Lake Tahoe has had a record-breaking year — and not in a good way. A team of scientists from the University of California, Davis (UC Davis) has revealed in a new study that Lake Tahoe is getting warmer at a rate that is 15 times faster than its historic average. In a new State of the Lake report, researchers say Lake Tahoe's rising water temperatures are threatening the lake's iconic clarity by affecting many features of its ecology. Professor Geoffrey Schladow says the incidence of rising air temperatures at the lake has been known for many years now, as well as the warming waters. But what's different this time is that scientists are seeing more aspects of Lake Tahoe's internal physics changing. "[T]hat is bound to alter the ecology," says Schladow, who is the director of the Tahoe Environmental Research Center (TERC). When researchers began keeping records of the lake's water temperature in the 1970s, the lake had an average of 50.3 degrees Fahrenheit (10.17 degrees Celsius) year round. In 2015, Lake Tahoe averaged 53.3 degrees Fahrenheit (11.83 degrees Celsius), the report says. Although the increase may appear statistically insignificant, scientists say much of the warming happened in the past decade and a half. This sign has left experts concerned. The increasing water temperatures may likely be linked to shifting air temperatures. Scientists have detected a daily air temperature increase of 4.3 degrees Fahrenheit on the northwest shore of Lake Tahoe since 1916. Waters with different temperatures mix deep in the lake during the winter. This mixing often leads to a clearer view. However, Lake Tahoe did not mix at its maximum depth this year, which scientists blame on the warmer influx of water. Water clarity dropped to 73.1 feet in 2015 — almost a 5-foot decrease in recent years. Furthermore, swimmers have observed algal blooms spread on the lake in previous years. Experts say longer algal blooms have been associated with climate change because algae likes warmer water. What is happening at Lake Tahoe is not only alarming for tourists who use the lake for recreation, but also for those concerned about the impacts of climate change to the beauty of natural resources, researchers say. Lake Tahoe is unique, but scientists explained that the forces and processes that affect it are the same as those that act in most natural ecosystems. Because of that, Lake Tahoe is a microcosm of other natural systems in the Western United States and around the world. How can residents and tourists keep the iconic lake as healthy as possible? Experts say attention to the lake's natural filtration systems as well as stormwater collection may help prevent harmful substances that accelerate the growth of algae such as phosphates out of Lake Tahoe. Darcie Goodman Collins, director of the League to Save Lake Tahoe, believes not much can be done to manipulate global warming. "But we can influence the lake's health," Goodman Collins added. Meanwhile, the UC Davis "Tahoe: State of the Lake" report can be read and downloaded (PDF) from the university's website. © 2016 Tech Times, All rights reserved. Do not reproduce without permission.
Sahoo G.B.,Tahoe Environmental Research Center |
Forrest A.L.,University of Tasmania |
Schladow S.G.,Tahoe Environmental Research Center |
Reuter J.E.,Tahoe Environmental Research Center |
And 2 more authors.
Limnology and Oceanography
Using water column temperature records collected since 1968, we analyzed the impacts of climate change on thermal properties, stability intensity, length of stratification, and deep mixing dynamics of Lake Tahoe using a modified stability index (SI). This new SI is easier to produce and is a more informative measure of deep lake stability than commonly used stability indices. The annual average SI increased at 16.62 kg/m2/decade although the summer (May-October) average SI increased at a higher rate (25.42 kg/m2/decade) during the period 1968-2014. This resulted in the lengthening of the stratification season by approximately 24 d. We simulated the lake thermal structure over a future 100 yr period using a lake hydrodynamic model driven by statistically downscaled outputs of the Geophysical Fluid Dynamics Laboratory Model (GFDL) for two different green house gas emission scenarios (the A2 in which greenhouse-gas emissions increase rapidly throughout the 21st Century, and the B1 in which emissions slow and then level off by the late 21st Century). The results suggest a continuation and intensification of the already observed trends. The length of stratification duration and the annual average lake stability are projected to increase by 38 d and 12 d and 30.25 kg/m2/decade and 8.66 kg/m2/decade, respectively for GFDLA2 and GFDLB1, respectively during 2014-2098. The consequences of this change bear the hallmarks of climate change induced lake warming and possible exacerbation of existing water quality, quantity and ecosystem changes. The developed methodology could be extended and applied to other lakes as a tool to predict changes in stratification and mixing dynamics. © 2015 Association for the Sciences of Limnology and Oceanography. Source
Acosta M.,University of Granada |
Anguita M.,University of Granada |
Fernandez-Baldomero F.J.,University of Granada |
Ramon C.L.,University of Granada |
And 3 more authors.
Environmental Modelling and Software
This work evaluates the implementation of a nested Cartesian grid in a 3D semi-implicit hydrodynamic model with synthetic and real examples. The outer model provides all the values needed by the governing equations of the nesting (inner) subdomain at the boundary (including tangential velocities). A 3D flux relaxation scheme is applied to prevent mass and energy drift. The influence of tangential velocities in the solution is evaluated, showing a substantial reduction on the results' quality when they are considered negligible and lateral circulation exists. The inner/outer coupling implemented achieves a simulation time equal to the inner execution time and allows a transfer step equal to the inner time-step, removing time interpolation errors. This coupling makes feasible the 3D relaxation implemented. A dramatic improvement in memory requirements and simulation time is achieved, that allows the use of low-cost low-power consumption platforms in the simulations. © 2014 Elsevier Ltd. Source