OALib Journal期刊

ISSN: 2333-9721

費用:99美元

投稿

時間不限

2020 ( 273 )

2019 ( 657 )

2018 ( 710 )

2017 ( 699 )

自定義范圍…

匹配條件: “Karl M. Wantzen” ,找到相關結果約405064條。
列表顯示的所有文章,均可免費獲取
第1頁/共405064條
每頁顯示
Soil Erosion from Agriculture and Mining: A Threat to Tropical Stream Ecosystems
Karl M. Wantzen,Jan H. Mol
Agriculture , 2013, DOI: 10.3390/agriculture3040660
Abstract: In tropical countries soil erosion is often increased due to high erodibility of geologically old and weathered soils; intensive rainfall; inappropriate soil management; removal of forest vegetation cover; and mining activities. Stream ecosystems draining agricultural or mining areas are often severely impacted by the high loads of eroded material entering the stream channel; increasing turbidity; covering instream habitat and affecting the riparian zone; and thereby modifying habitat and food web structures. The biodiversity is severely threatened by these negative effects as the aquatic and riparian fauna and flora are not adapted to cope with excessive rates of erosion and sedimentation. Eroded material may also be polluted by pesticides or heavy metals that have an aggravating effect on functions and ecosystem services. Loss of superficial material and deepening of erosion gullies impoverish the nutrient and carbon contents of the soils; and lower the water tables; causing a “lose-lose” situation for agricultural productivity and environmental integrity. Several examples show how to interrupt this vicious cycle by integrated catchment management and by combining “green” and “hard” engineering for habitat restoration. In this review; we summarize current findings on this issue from tropical countries with a focus on case studies from Suriname and Brazil.
The Lower Paraguay river-floodplain habitats in the context of the Fluvial Hydrosystem Approach
Edmundo C. Drago , Karl M. Wantzen , Aldo R. Paira
Ecohydrology & Hydrobiology , 2008, DOI: 10.2478/v10104-009-0004-1
Abstract: We report herein the first description of the physical structure of the aquatic habitats of the Lower Paraguay River along 390 km from Asunción city (Paraguay) to the confluence with the Paraná River. The hierarchical ordination of the Fluvial Hydrosystem Approach (FHA) allowed us to classify the Lower Paraguay as a meandering functional sector where five functional sets were identified: (a) main channel, (b) floodplain channel, (c) floodplain lentic water body, (d) tributary, and (f) aquatic-terrestrial transition zone. These functional sets encompassed twenty one functional units and fifty eight major mesohabitats. We attribute the riverine habitat diversity to the changes in the channel-floodplain morphology and in the strength, duration and frequency of their hydrological connectivity. The variable river-floodplain-tributary complex developed several types of fluvial-lacustrine boundaries and riverine ecotones.
Channel-floodplain geomorphology and connectivity of the Lower Paraguay hydrosystem
Edmundo C. Drago , Aldo R. Paira , Karl M. Wantzen
Ecohydrology & Hydrobiology , 2008, DOI: 10.2478/v10104-009-0003-2
Abstract: The Paraguay River is the main tributary of the Paraná River hydrosystem. Despite several studies resulting from the proposed navigation project known as the Hidrovía Paraguay-Paraná, little is known about the physical structure of their aquatic environments and its biota. The main purpose of this work is the knowledge of the primary factors which form the structure of the physical habitats in this fluvial segment. In this way, the hydrological and hydraulic regime, channel shape, substrate, hydrological connectivity and the floodplain ontogeny and its evolution were analyzed. Synthesizing we stressed herein that the dynamics of the river-floodplain morphology dependent on the large-scale longitudinal and lateral hydrological connections, and the type and degree of these connections between lotic and lentic environments drive the changes of this seasonally inundated floodplain and its water bodies. In a second paper in this volume, is presented a classification of the Lower Paraguay physical habitats and their relationships with the main physical factors.
Structures of Human Societies  [PDF]
Karl M. van Meter
Sociology Mind (SM) , 2014, DOI: 10.4236/sm.2014.41005
Abstract:

We have previously shown (“How People See Society: The Network Structure of Public Opinion Concerning Social Conflicts”, Connections, 2004, 26(1): 71-89) that opinions on social conflict are structured in very stable networks at the level of individuals, of arbitrary collections of individuals, of structured social groups and of representative samples of the French population, for more than thirty years. Similar surveys in Great Britain and Russia, for over ten years in Costa Rica, show the stability and extent of application of these results. Our first working hypothesis is that this network structure with two axes openness/closure and emotional/non-emotional—applies to all human societies. For this, we look at recent developments in archaeology, which describe two and only two types of structure for Neolithic human groups: hierarchical structures and cooperative structures. We show that these two types of structure are the poles delimiting the openness/closure axis, that there are no other stable structures, and that human societies can thus be characterized by the set of “tools” elaborated in common, this is, socially, for managing social conflicts inherent in any viable and stable group of human beings. And finally, these “tools” form the system of “values” characteristic of each society.

The future of control
Karl J. ?str?m
Modeling, Identification and Control , 1994, DOI: 10.4173/mic.1994.3.1
Abstract: This paper gives a personal view of the emergence, development and future of automatic control. The assessment is that automatic control has been very successful, but that we are now at a crossroads where we have to decide if we want to take an holistic view with full systems responsibility or if we want the field to fracture into a collection of subspecialities.
Oceanic Ecosystem Time-Series Programs: Ten Lessons Learned
David M. Karl
Oceanography , 2010,
Abstract: Since its creation within UNESCO a half-century ago, the Intergovernmental Oceanographic Commission (IOC) has been at the vanguard of ocean observation, serving to promote international cooperation, coordinate ocean research, and facilitate capacity development. Beginning with the International Indian Ocean Expedition in the early 1960s, and through meaningful partnerships with the Scientific Committee of Ocean Research (SCOR), the International Geosphere-Biosphere Program (IGBP), the Partnership for Observation of the Global Ocean (POGO), and related organizations, IOC has provided invaluable leadership needed to help justify and promote large-scale ocean observation programs. A recent international meeting, co-sponsored by IOC, OceanObs’09: Ocean Information for Society – Sustaining the Benefits, Realizing the Potentials was held in Venice, Italy, in September 2009. The conference was attended by more than 600 participants from 36 nations to present and discuss ongoing and planned global ocean observation activities. These field efforts represented a diverse spectrum of time-series programs, including the use of satellite remote sensing, moored buoys, autonomous gliders, repeat hydrographic surveys, volunteer ships of opportunity, profiling floats, cabled seafloor observatories, and ship-supported time-series programs, to name a few examples. Each observation program is designed to address a specific set of scientific goals, and each has its own set of challenges to sustain and optimize data return. This article focuses on ecosystem-based, time-series programs that presently rely on ships to make observations, collect samples, and conduct experiments. These ecosystem investigations are an important subset of the much larger portfolio of research-based, ocean time-series programs that derive, in large part, from sustained IOC leadership (Valdés et al., 2010).
Responses to the Foraging/Predation Risk Trade-Off and Individual Variability in Population-Level Fitness Correlates
Karl M. Polivka
ISRN Ecology , 2011, DOI: 10.5402/2011/376083
Abstract: Foraging under the influence of interspecific interactions such as competition and predation risk can have effects on the energetic reserves of the forager. Measurements of condition in species such as fish are usually correlated with individual fecundity and, hence, fitness. From work in two study systems in which predation risk regulates habitat selection and foraging behavior of benthic fishes I examined whether risk dependence led to reduced variability in fish condition. In field populations of cottid fishes, observed in an estuarine system and in the near-shore habitat of an oligotrophic lake, I found that individuals that experienced higher predation risk showed reduced variability in CI. Estuarine cottids with high food availability and substantial predation risk varied less in CI among individuals than in the associated tidal creek. In the lake, where there is considerable heterogeneity in benthic food resources, a related cottid species showed reduced variation in CI with increasing predation risk from adults. Finally, I examine my previous experiments showing that the estuarine species is limited in its use of high resource availability in estuaries by competition and predation risk. Here I found that variability in individual condition index (CI) was higher when intraspecific and interspecific competition increased and did not increase in the face of predation risk. 1. Introduction Research into how animals select habitats in heterogeneous environments has been informed by how the complementary use of safe, relatively unproductive habitats or patches and more productive yet very risky patches influences overall fitness [1, 2]. By using food and safety from predation risk in a complementary manner, foraging animals benefit from time spent in safety (i.e., in less risky habitats/patches or through vigilance behaviors; e.g., [1, 3]) when the marginal value of food obtained no longer exceeds the cost of predation. Field measurement of the forager’s giving up density (GUD) facilitates study of the behavioral optimization of this trade-off (e.g., [1, 2, 4–6]). GUDs are applicable to a suite of predation-avoidance behaviors such as vigilance [2, 7] and apprehension [2, 8] and represent the marginal value of food in terms of the risk involved in obtaining it (e.g., [1, 3, 9, 10] and reviewed in [11]). A forager’s present condition (e.g., [4, 12–14]) and the density-dependent distribution of predators [15] affect the amount of risk taken to obtain food, leading to variation in that condition through time (e.g., [12, 16]), in turn affecting subsequent
Assessing ocean changes without data centers?
Karl M. Banse
Frontiers in Marine Science , 2014, DOI: 10.3389/fmars.2014.00029
Abstract:
Kaon Condensation in the Bound-State Approach to the Skyrme Model
Karl M. Westerberg
Physics , 1994, DOI: 10.1103/PhysRevD.51.5030
Abstract: We explore kaon condensation using the bound-state approach to the Skyrme model on a 3-sphere. The condensation occurs when the energy required to produce a $K^-$ falls below the electron fermi level. This happens at the baryon number density on the order of 3--4 times nuclear density.
IAU (Maser) Symposium 287 Summary
Karl M. Menten
Physics , 2012, DOI: 10.1017/S1743921312007624
Abstract: I'm trying to summarize the science communicated via oral presentations and by posters at the IAU Symposium 287 "Cosmic Masers - from OH to H_0", which took place from January 29 to February 3, 2012 in Stellenbosch, South Africa.
第1頁/共405064條
每頁顯示


Home
Copyright ? 2008-2017 Open Access Library. All rights reserved.

久草在现在线中文字幕