Russia China Iranian Plateau and the Middle East

Large areas of southern Russia and Central Asia are endorheically drained. Saline lake regions here include one associated with the Black Sea and another within the Aral-Caspian depression. The Aral-Caspian depression contains two of the largest saline lakes in the world, the Caspian Sea and the now severely depleted Aral Sea. Northeast is Lake Tengiz, a major habitat for the greater flamingo and located in the Baraba-Kulunda steppe region. Southeast of Lake Tengiz is the Balkhash region whose...

Modern Analyses of Limnicity and Lake Size Distribution

Www Spatialresolution Gool Com

Nearly concurrently, Lehner and Doll and an international team of scientists working with Downing at the US National Center for Ecological Analysis and Synthesis applied modern GIS methods and updated geographic imagery to updating inventories of world lakes. These two efforts used divergent approaches but both had the objective of using new technologies to provide a more accurate estimate of the global extent and distribution of lakes and other water bodies. The approach used by Lehner and...

Formation

With the exception of glacial lakes, all other types of lake formation systems are represented in sub-Saharan Africa ranging from floodplain, depression and volcanic to rift valley. Among them, the most notable ones are the African Great Lakes found in the Eastern and Western Rift Valley regions of Africa (Figure 1). In contrast to the Laurentian Great Lakes, African Great Lakes are known to be very old. Using sediment-aging techniques, Lakes Tanganyika and Malawi Nyasa Niassa date their origin...

Introduction To Lake Ecosystem Ecology A Global Perspective

The scientific discipline of limnology is focused on the study of inland waters, fresh and saline, large and small, and young and old. For example, the 5 Laurentian Great Lakes in North America contain some 20 of the Earth's surface fresh water, and Lake Baikal in Siberia contains another 18 (Likens, 2009). The recently constructed Three Gorges Dam Reservoir in China, to be completely filled by the end of 2009, will contain about 40 km3, or about 8 of what Laurentian Lake Erie (484 km3)...

Salinity

Salinity is usually defined as the sum of ionic compounds dissolved in water and can be measured in several ways. Specific conductivity quantifies the relative ease with which an electrical current passes through a water sample and is usually expressed as milli or micro Siemens per centimeter (mS or p.S cm-1). Because the conductivity of NaCl increases 2 for every degree increase in temperature, specific conductivity is always measured at 25 C. Salinity can also be expressed as milligrams per...

Threats to Saline Lakes

Perhaps the greatest threat to saline lakes is anthropogenic or secondary salinization - in other words increased lake salinity as a result of human activity (industry, agriculture, construction) in the lake basin (Figure 6). In fact, W.D. Williams has stated that 'in some countries, anthropogenic salinization represents the most important threat to water resources.' For example, the disruption of the hydrological cycle by agriculture or diversion or damming of lake inflows can lead to...

Basin Scale Standing Wave Motions Seiches

Interfacial Waves in a Layered Stratification Horizontal modes When steady winds cease and the surface stress condition is relaxed, the gravitational restoring force associated with the tilted interface (water surface or thermocline) becomes unbalanced. The available potential energy embodied in the tilt is released under the action of gravity and converted to kinetic energy as the interface oscillates in the form of a sinusoidal standing waves or seiche. Antinodes are found at the basin end...

Morphometric Parameters

In the past, mapping lakes was a laborious task. Lake shorelines had to be established by such methods as transverse, stadia or plane table surveys, all time consuming, and spot depths by lead lines at fixed positions. Today, outlines of shores are easily obtained from aerial or satellite images and depth profiling done by echosounders. Exceptions include shallow ephemeral lakes, like many in Australia, which are best mapped when dry using modern terrestrial surveying equipment. Once, the basic...

South America

In South America there are two major saline lake areas. The first is the Bolivian Altiplano region and its northern extension into Peru, which contains many shallow permanent saline lakes as well as ephemeral salt pans. Some of the highest saline lakes in the world are located here (4000-4500 masl). The second region is found in the Pampas of central Argentina and stretches into northern Patagonia. Its Table 2 Divergent chemical composition of selected Saskatchewan and African saline lakes...

[7

Where g is the acceleration due to gravity, and z is the vertical coordinate. The magnitude N is also called stability frequency or Brunt-Vaisala frequency (s-1), which indicates the maximum frequency (o) for internal waves that can propagate in the respective stratification. N2 indicates how much energy is required to exchange water parcels in the vertical. As a consequence, chemical gradients can only persist for longer time periods where density gradients limit the vertical transport of...

Gravity Waves

Of the two classes of periodic motions outlined earlier, gravity waves are the most well-studied and best understood in inland waters. We will consider only linear waves, that is, motions where the amplitude of the oscillations of the thermocline is small compared with the depth of the surface and bottom layer. This is not a major restriction on the analysis, as the inclusion of nonlinear effects has been shown in most cases to require only a minor correction to the linear approximation. In...

Historical Estimates of Limnicity

The 'limnicity' of land surfaces has been speculated upon since the early 1900s. In 1925, August Thiene-mann1 concluded from map data summarized in 1914 by Wilhelm Halbfass, that around 2.5million km2, that is about 1.8 of dry lands, are covered with freshwaters in Germany, the area of all lakes covers about 5200 km2, or about 1 of the land surface. The largest lake on Earth is the Caspian Sea which has a surface area of 438 000 km2.'' Several modern assessments of the global area covered by...

Surface Momentum Transfer and Wind SetUp

The action of the wind across the lake surface results in frictional momentum transfer from the wind to the water. This transfer occurs in the form of a stress (N m 2) applied at the free surface. The stress may be parameterized as where CD is the drag coefficient, pa 1.2 kg m 3 is the air density, and Ui0 the wind speed measured at 10 m above the water surface. Typically CD 1.3 x 10 3, but this value may vary by 40 depending upon the wind speed, water depth, and relative temperature Figure 1...

Vorticity Waves

From the above equations, allowing either f to vary as a function of y (the b-plane) or allowing H to vary as a function of x and y allows a similar class of waves to exist. In the ocean, where f does vary, a class of waves called Rossby waves (or planetary Rossby waves) exist because of the conservation of angular momentum. In inland waters such as lakes, these effects can be ignored as they are generally smaller than 500 km and f can be assumed to be constant. However, variations in water...

Natural Basins Andean Lakes

Most Andean lakes were formed by tectonic activity, vulcanism or glaciers. Tectonic and volcanic events played important roles in lake formation throughout the Andean ranges. However, given that these processes have been more active in arid regions, there are fewer tectonic lakes than glacial lakes. Lake Titicaca is perhaps the best known example of an Andean tectonic lake. Tectonic forces are also responsible for the creation of salt lakes in endorreic areas within the Altiplano (shared by...

Io2

Figure 1 Reported density of zoobenthos as a function of sieve mesh size in a series of lakes from the northern temperate zone (r2 0.72, p < 0.000001). The vertical gray line marks the 500-mm mesh commonly used for macrobenthos. 1 10 100 1000 10000 Net phytoplankton production (g DM m -2 yr-1) Figure 3 Relationship between production of macrobenthos and production of phytoplankton in a series of lakes (r2 0.34, p 0.02). Adapted from data of Kajak et al. (1980). 1 10 100 1000 10000 Net...

Natural Lakes of the Interior Plains and Southeastern US

Glaciated interior plains In the northern, glaciated, interior plains, the Pleistocene glaciers originating in the Canadian Shield flowed westward to the base of the Rocky Mountains. There they met ice flowing eastward out of the Rockies. Thus, the entire width of the plains was glaciated for most of the extent of the Cordillera in Canada. Lakes are much less abundant on the glaciated interior plains than in the Shield. Lake Claire (1415 km2) and Lesser Slave Lake (1167 km2), both in northern...

Mixing Dynamics in Lakes Across Climatic Zones

S MacIntyre and J M Melack, University of California, Santa Barbara, CA, USA 2009 Elsevier Inc. All rights reserved. Interactions between climatic and geographic conditions lead to variations and gradients in hydrological, physical, chemical, and biological conditions in lakes. The annual cycle of solar irradiance with seasonal amplitude increasing at higher latitudes causes well-known gradients in photoperiod and temperature. Continental interiors differ from coastal regions that tend to be...

Origins of Meromixis

The modes of origin of meromixis may also be classified, with the same kinds of caveats. (Note To avoid creating new 'Type' designations in this chapter, and possibly adding confusion, we will use the same Roman numeral designations in the text and in Table 2 as in the 1975 usage of Walker and Likens. However, we are not including the Type II category of Walker and Likens. See Further Reading.) This type results when more dense, usually saline, water from an external source enters the waters of...

Characteristics of Density Currents

Density currents are driven by differences in water density, which can result from gradients in water temperature, salinity, dissolved uncharged substances, or suspended particles and are also affected by pressure. If a water mass with higher density is situated above a water mass with lower density, the stratification is unstable and buoyancy causes the upper water mass to sink. In the sinking process ambient water is mixed into the sinking water mass and thus alters its density (Figure 1),...

The McMurdo Region Inland Lakes

Location The McMurdo Dry Valleys (MCM) (77 30' S) of southern Victoria Land have a surface area of 4000 km2, representing the largest and most southerly ice-free area on the Antarctic continent (Figure 3). The MCM comprise three large valleys (Victoria, Wright, Taylor) along with many adjoining areas and consist of a mosaic of landscape features including glaciers, ephemeral streams, perennially ice-covered lakes, and exposed bedrock and soils. The region is ice-free because the Transantarctic...

Small Scale Turbulence and Mixing Energy Fluxes in Stratified Lakes

A Wuest, Eawag, Surface Waters - Research and Management, Kastanienbaum, Switzerland A Lorke, University of Koblenz-Landau, Landau Pfaly, Germany 2009 Elsevier Inc. All rights reserved. Density Stratification and Mixing - the Basin Scale Nearly all lakes, reservoirs, and ponds that are deeper than a few meters, experience cycles of density stratification and destratification. Most important for this variation is the temperature-dependence of water density. During spring summer - or the wet...

Turbulence and Mixing in Stratified Lakes and Reservoirs

Turbulence Production in the Surface and Bottom Boundaries There are fundamentally two mechanisms generating turbulence in the SL (i) the action of wind causing Table 1 Typical values of dissipation, stability and vertical diffusivity in stratified waters Dissipationa e (Wkg1) Stability N2 (s 2) Diffusivity* Kz (m2s Table 1 Typical values of dissipation, stability and vertical diffusivity in stratified waters Dissipationa e (Wkg1) Stability N2 (s 2) Diffusivity* Kz (m2s aDuring storm events...

Human Culture Freshwater Vectors and Disease

Cultural practices may make humans more susceptible to certain diseases with freshwater vectors. For example, fish and other organisms can be hosts to parasites, some of which can be transmitted to humans through eating raw or partially cooked fish such as salmonids, pike, perch, and burbot, carp and other cyprinids. Jewish women have had higher rates of infection by the broad fish tapeworm (Diphyllobo-thrium latum) than women of other cultures. This is because they often ingested infective...

Coastal Ponds

Location Coastal lakes and ponds are distributed around the margins of the Antarctic continent, and are particularly abundant around the ice free areas of McMurdo Sound. These shallow coastal aquatic systems typically freeze solid over the winter months and cryoconcentrate the organisms in the ice, forcing the majority of the organisms, gases, and dissolved organic matter to the bottom (Figure 6). Most of the lakes studied are on Ross Island, east of McMurdo Sound near capes Evans, Royds and...

Signy Island South Orkney Islands

Location Signy Island (60 43' S, 45 36' W) is a 20 km2 island in the South Orkney archipelago. It lies at the confluence of the ice-bound Weddell Sea and the warmer Scotia Sea, and its climate is influenced by the cold and warm air masses from these two areas. The lakes on Signy Island share characteristics of Antarctic and subAntarctic environments, a fact reflected in the diverse flora and fauna. This region of the continent has been ice free for the past 6000 years and is referred to as the...

Density Plumes Generated by Internal Processes

A key parameter affecting water density is temperature. However, for density currents to be induced on the basis of the temperature of water, horizontal gradients in temperature are required. Horizontal temperature gradients are generated by external surface and subsurface inflows (see earlier text) but also by internal processes. In most lakes the heat flux at the lake surface (expressed per unit area) can be considered as horizontally homogeneous because meteorological parameters and...

Density Plumes Generated by External Inputs

The density differences required to drive density plumes originate from processes that generate horizontal or vertical gradients in water properties. An obvious example is river inflow (Figure 3). River water usually contains an increased load of suspended particles and has a different temperature and salinity than the lake water. Hence, river inflow is commonly associated with density plumes propagating from the river mouth to larger depths. The kinetic energy associated with the inflow of the...

Reinforcing Recovery

To reinforce recovery, numerous physicochemical and biological restoration methods have been developed. Here we present the most frequently applied methods and an overview of some of the syntheses and notable case studies on each method (Table 1). Informative books or overview papers on the response of lakes to nutrient loading reduction and restoration are listed in 'Further reading' section. Various physicochemical methods have been used to reduce internal P loading. These include sediment...

Features and Origins of Natural Lakes

Australia is an ancient, weathered continent and the landscape has undergone considerable environmental changes since stretching and rifting from the supercontinent Gondwana in the Jurassic (150m.y.a.) and traveling northward with separation off of NZ 80-60 m.y.a, and finally separation of Antarctica 45 m.y.a. Large parts of the north-east and south-west of NZ are remnants of the former eastern margin of Gondwanaland, but the NZ landscape has also been strongly influenced by recent tectonic and...

Lakes of the Cordillera

The cordilleran system of North America, extending from the Brooks Ranges and Aleutian peninsula in Alaska to the isthmus of Panama, is home to a great many natural lakes. Two processes are responsible for the formation of most of these glaciation and tectonics. The glacial lakes are mainly in the northern half of the cordillera, where Pleistocene ice was most extensive. Lakes of tectonic origin are found throughout the region, although in the north most of these are also modified by glacial...

History

As with human exploration of the Earth's poles in general, scientific expeditions to the Arctic have been relatively recent. In the 1800s there were casual observations of freezing and thawing limited in extent to lakes found along seafaring routes, such as the discovery of and records made for Lake Hazen by the Greely expedition to Ellesmere Island in 1882. Ancillary information on lakes from such expeditions continued through the early 1900s, but following World War II several permanent bases...

Climate

Climate influences physical, chemical, and biological processes in and around lakes. Although much of Europe lies in the northern latitudes, the relatively warm seas that border the continent give most of Central and Western Europe a moderate climate, with cool winters and mild summers. From approximately central Poland eastward, the maritime effects are reduced, and cooler, drier, and more continental conditions prevail (Figure 2). Temperature differences between summer and winter are low,...

Lakes And Reservoirs Of The World

Origins of Types of Lake Basins D KBranstrator 191 Geomorphology of Lake Basins B Timms 203 Abundance and Size Distribution of Lakes, Ponds and Impoundments JA Downing and Saline Inland Waters M J Waiser and R D Robarts 230 Antarctica J C Priscu and C M Foreman 241 Africa North of Sahara M Ramdani, N Elkhiati, and R J Flower 265 Africa South of Sahara O V Msiska 276 Australia and New Zealand J D Brookes and D P Hamilton 302 Europe G A Weyhenmeyer, R Psenner, and L J Tranvik 313 South America M...

Definition of Shallow Lakes and Ponds and World Distribution

Shallow lakes and ponds are the most abundant lake types in the global landscape. They provide a myriad of ecosystemic and social services as well as goods and materials, while having great conservation value (for example for migratory birds). Such shallow systems usually occur in lowland areas, many in association to seasonal changes in the flood regimes of rivers. The origin of many of these systems can also be related to geological disturbances, such as glacial movements or other processes...

Subglacial Lakes

Location The earliest evidence of subglacial lakes was from Russian aircraft pilots flying missions over the Antarctic continent, claims subsequently verified by airborne radio-echo sounding during the 1960s and 1970s. We now know that more than 150 lakes exist beneath the Antarctic ice sheet (Figure 1), many of which may be connected by large subglacial rivers. Approximately 81 of the detected lakes lie at elevations less than 200 m above mean sea level, while the majority of the remaining...

Major Reservoir Development Programs

Hydroelectric power in Canada Hydroelectric power generation in Canada began in the last decades of the 19th century, with construction of facilities near waterfalls in Ontario, and grew steadily in the 20th century. Dam construction slowed in Canada during the Depression of the 1930s, but increased rapidly in the years following World War II. Several large reservoirs were constructed in the Ottawa River system bordering Ontario and Quebec. In the 1960s, a few very large hydroelectric dams were...

Meromixis as a Pattern

In limnology (the physics, chemistry, and biology of inland waters), the circulation patterns of lakes are classified by the extent to which the water mixes vertically, from top to bottom, during the course of a year (Table 1). The scheme is merely a guide because lake circulation patterns, like most natural phenomena, do not fall easily into discrete categories. A more accurate, but certainly more arduous, approach would be to characterize lakes only after long term data are available. Another...

Lakes and Reservoirs

Taken as a whole, South America is predominantly a rivers continent. In fact, many floodplain lakes, lagoons and reservoirs originate from rivers particularly, from the Amazon, Orinoco and Parana-Plata rivers, which rank among the largest river systems of the world. On the other hand, the proportion of 'archetypical' lakes is relatively small, and they could hardly compete for the size record with lakes in other continents. Nevertheless, South America does have a great number and diversity of...

Alternative States Hypothesis

Despite their prevalence in the world landscape, shallow lakes and ponds had historically received little scientific attention than deep lakes until the early 1990s, when several seminal works proposed ideas to explain the functioning of these unique and complex ecosystems. Shallow lakes do not always change smoothly from one condition to another in response to external pressures. Instead, changes are often sudden and may trigger important modifications in the complex network of stabilizing...

Major Threats

Threats to freshwater systems and species are numerous, overlapping, and operate over a range of scales. The embeddedness of freshwaters within the larger landscape, coupled with the fact that human communities require freshwater resources to survive, means that few freshwaters around the world remain pristine. Most freshwaters are subject to multiple anthropogenic stresses, and this multiplicity can complicate the identification of threat pathways and appropriate conservation levers. Threats...

Impoundments

Parallel with the analysis of natural lakes above, one can fit the Pareto distribution to the sizes of large impoundments. Downing and coworkers did this using data from the International Commission on Large Dams who publish data on dams around the world that are of safety, engineering or resource concern (e.g., Figure 7). These data are purposefully biased toward large dams so the data provide the most accurate estimate of impoundments with the largest impounded areas, and progressively less...

Benthic Pelagic Coupling

The periphyton developed on sediments (or epipelon) may contribute substantially to the whole-lake primary production in shallow water bodies. Turbid lakes seem more productive than clear lakes if phy-toplankton is the only contributor to total annual production. However, the proportional habitat distribution of the primary producers changes under contrasting turbidity and nutrient states, benthic production being highest in clear lakes. Under nutrient-rich conditions, high phytoplankton...

Circulation Patterns in Natural Systems Lakes and Reservoirs

Large-scale circulation patterns for a suite of lakes of different sizes and geometries are illustrated in Tables 1 (for HB) and 2 (for SML). The patterns were obtained from observations using drogues, velo-cimetry or other measurements, numerical model simulations, or both. (1) Double-gyre wind-driven circulation In Lake Erie. Figure shows the main winter circulation from observed patterns. - Source Beletsky D, Saylor JH, and Schwab DJ (1999) Mean circulation in the Great Lakes. Journal of...

Lateral Circulation

Generation of Circulation in Homogenous Layers To characterize the spatial patterns of the horizontal currents use is customarily made of a variable called vorticity Z defined as the curl (a mathematical operation, denoted by the symbol Vx, involving spatial derivatives) of the horizontal velocity vector u, i.e., A flow field where a fluid particle describes counterclockwise (or cyclonic) loops will have a positive vor-ticity a flow field with negative vorticity, in turn, will make a fluid...

Lakes in the Boreal Region

The boreal region covers a large part of Europe, and the lake density is high. Consequently, the lake types representative of the boreal region may also be the most common ones of Europe as a whole. The lakes of the region are usually small and shallow, and of glacial origin. They range from low to high contents of humic substances, depending on catchment characteristics and hydraulic retention time. The most common lake type in the boreal region in the northeast of Europe, especially in the...

Vector Control Strategies

Control Blindness

In addition to advances in chemotherapy and vaccination strategies to control the disease agents, a great deal of attention has been applied to control strategies that can reduce populations of freshwater vectors of human diseases. The most commonly used approach is the application of toxicants to control the vectors. These can be done over large spatial scales (e.g., aerial applications of insecticides in 11 West African counties to control black fly vectors of onchocercia-sis) or locally...

Vertical Circulation

The wind stress applied to the lake surface is directly transmitted through internal friction to a surface shear layer which, in general, is much thinner than the water column. In stratified water bodies, the thickness of that shear layer is determined by stratification the vertical flux of momentum beyond the bottom of the SML, by viscous or turbulent processes, is considerably reduced by the existence of large density gradients. In homogeneous water bodies, those shear layers are referred to...

Modeling of Lake Ecosystems

L Hakanson, Uppsala University, Uppsala, Sweden 2009 Elsevier Inc. All rights reserved. Introduction Basic Concepts and Problems in Modeling of Lake Ecosystems Every aquatic ecosystem is unique, but only a few are studied ecologically in great detail. For reasons related to the practical value of lakes, including fisheries, recreation, and water supply, there are demands for analytical information or predictions concerning lakes for which no detailed studies are available. Ecosystem modeling is...

Functioning of Shallow Lakes and Ponds Nutrient Dynamics and Retention

Most shallow lakes and ponds tend to be located in the more fertile lowland regions and are therefore more sensitive to human activities in the catchments. Nutrient loading is proportionally higher in shallow than in deep systems. In deep stratified lakes, nutrients are typically lost through sedimentation from the surface layer (epilimnion) to the bottom layers (hypo-limnion) during the summer stratification. These nutrients only return to the epilimnion when the water column becomes mixed...

Lakes as Ecosystems

Energy Flow Aquatic Ecosystem

W M Lewis, University of Colorado, Boulder, CO, USA 2009 Elsevier Inc. All rights reserved. Introduction of the Ecosystem Concept Scientific studies of lakes began as early as the seventeenth century, but at first were descriptive rather than analytical. Toward the end of the nineteenth century, measurements and observations on lakes became more directed. For example, the thermal layering of lakes was attributed to specific physical causes, and such phenomena as the movement of plankton in the...

Further Reading

Alcocer J, Lugo A, Sanchez MR, and Escobar E (1998) Isabela Crater-lake a Mexican insular saline lake. Hydrobiologia 381 1-7. Anati DA (1998) Dead Sea water trajectories in the T-S space. Hydrobiologia 381 41-49. (Note The Dead Sea seems to alternate between uneven periods of meromixis and holomixis). Anderson RY, Dean WE, Bradbury JP, and Love D (1985) Mero-mictic lakes and varved lake sediments in North America. U.S. Geological Survey Bulletin 1607 19. Aplikowski S (Ecologist) Minneapolis...

Density Stratification and Stability

B Boehrer and M Schultze, UFZ - Helmholtz Centre for Environmental Research, Magdeburg, Germany 2009 Elsevier Inc. All rights reserved. In most lakes, water properties change from the surface to greater depth, i.e., these lakes show a vertical stratification of their water masses at least for some extended time periods. Heat exchange with the atmosphere and the forming of gradients of dissolved substances controls internal waves and the vertical exchange of water within the lakes. This has...

Ecological Zonation in Lakes

W M Lewis, University of Colorado, Boulder, CO, USA 2009 Elsevier Inc. All rights reserved. Lakes show many kinds of spatial variation in both vertical and horizontal dimensions. Variation can be chemical, physical, or biotic, and is important to the understanding of ecosystem functions. Although some types of variation are unique to specific classes of lakes, others are common to most lakes, and correspond to an obvious spatial organization of the biota in lakes. The existence of certain...

Human Made Lakes Reservoirs

Human-made lakes are an important and prominent feature of the Asian landscape. Their construction dates back to antiquity in response to the vagaries of the monsoon, which causes frequent floods and droughts often in the same area, and the need of water for domestic supplies as well as agriculture. In recent times, huge multipurpose reservoirs have been constructed for irrigation and hydropower generation as well as flood control. Some of the world's largest and highest dams have been built in...

Paleolimnology

J P Smol, Queen's University, Kingston, ON, Canada 2009 Elsevier Inc. All rights reserved. The ecological and environmental conditions in lakes and rivers change on a variety of time scales. However, one of the greatest challenges faced by limnolo-gists (as well as other environmental and ecological scientists) is the general lack of long-term data. Without such data, it is difficult to determine if changes are occurring in an aquatic system, and if so, to identify the likely drivers of these...

Trophic Dynamics in Aquatic Ecosystems

U Gaedke, University of Potsdam, Potsdam, Germany 2009 Elsevier Inc. All rights reserved. An understanding of the role of species populations within an ecosystem is possible only when information on multiple species is systematically joined in a way that reflects mutual interactions. A synthesis of this type produces a view of ecosystem processes that are the by-product of many simultaneous interactions among populations. Feeding relationships have proven to be an effective means of bridging...

Global Distribution of Reservoirs

There are nearly 50 000 dams in the world with heights above 15 m- defined as large dams - and an almost innumerable number of small dams built for farm ponds and other tiny impoundments. These dams can retain > 6500 km3 of water, which represents > 15 of the annual global runoff (Figure 1). The area of former terrestrial habitat inundated by all large (> 108 m3) reservoirs in the world is comparable to the area of California or France. The environmental values that were lost as a result...

Conclusions

Although data have been available on the world's largest and most spectacular lakes since the early 1900s, global estimates of the abundance and size distribution have underestimated the abundance and area of small natural lakes. When appropriate GIS Figure 8 Relationship between the surface area of farm ponds and the annual average precipitation in several political units (after Downing and coworkers). The line is a least squares regression (r2 0.80, n 13) where the area of farm ponds...

Trophic Interactions in the Pelagial

The biomass and production of fish per unit of area at a given nutrient level do not depend on lake depth. Therefore, shallow lakes have a substantially higher fish biomass per unit of volume than deep lakes. This relationship may reflect the higher nutrient recycling and availability from settled material and probably as well the availability of feeding and spawning sites for fish offered by the aquatic plants. The biomass and production of benthic invertebrates are also generally higher in...

Environmental Change in North African Lakes

Exploitation of water resources and intensity of land usage have increased rapidly throughout the SMR during the twentieth century. This has occurred especially in Morocco, Tunisia, Egypt, Lebanon, and Israel, and on the Mediterranean islands and has paralleled regional population growth. Lakes are especially vulnerable habitats and many of North Africa's natural standing waters are now degraded by human activities. Although past human impacts on North African landscapes began in a major way...

Littoral Zone

J A Peters and D M Lodge, University of Notre Dame, Notre Dame, IN, USA 2009 Elsevier Inc. All rights reserved. The littoral zone of a lake is the nearshore interface between the terrestrial ecosystem and the deeper pelagic zone of the lake. It is the area where at least one percent of the photosynthetically active light 400-700 nm entering the water reaches the sediment, allowing primary producers macrophytes and algae to flourish. The littoral zone is structurally and functionally an...

Eutrophication of Lakes and Reservoirs

V Istvanovics, Budapest University of Technology and Economics, Budapest, Hungary 2009 Elsevier Inc. All rights reserved. Eutrophication is the process of enrichment of waters with excess plant nutrients, primarily phosphorus and nitrogen, which leads to enhanced growth of algae, periphyton, or macrophytes. Abundant plant growth produces an undesirable disturbance to the balance of organisms structural and functional changes, decrease in biodiversity, higher chance for invasions, fish kills,...