Biology 2F03: Fundamental and Applied Ecology Chapter 3: Life in ...
Biology 2F03: Fundamental and Applied Ecology Chapter 3: Life in Water 3.1 The Hydrologic Cycle - 71% of the earth’s surface is covered by water - Oceans contain over 97% of water in the biosphere, polar ice caps and glaciers contain 2% and less than 1% is freshwater in rivers, lakes, and actively exchanged groundwater - 20% of the planet’s freshwater is found in Canada - Across earth, over 65% of freshwater us found in glaciers and ice fields and 30% is groundwater - Ex.: Alberta - Because of changes to freshwater supplies and demands, the distribution of water across the biosphere is dynamic - Hydrologic cycle: exchanges of water among reservoirs - During the hydrologic cycle, water enters each reservoir either as precipitation or surface/subsurface flow and exits as evaporation or flow - Hydrologic cycle is powered by solar energy, which drives the winds and evaporates water - Water vapour cools as it rises and condenses, forming clouds - Clouds are then blown by solar-driven winds across the planet, eventually yielding to rain or snow, the majority of which falls back on the oceans and some of which falls on land - Reservoirs will be replenished at different rates, and ecologists of measure turnover times, the time required for the entire volume of a particular reservoir to be renewed - Reservoir size and rates are two of the main determinants of turnover time - Water in the atmosphere turns over every 9 days, river water 12 to 20, lake renewal are longer, oceans 3,100 years 3.2 Life in Water and the Natural History of Aquatic Environments - The biology of aquatic environments corresponds broadly to variations in physical factors such as light, temperature and water movements and to chemical factors such as salinity and oxygen - The Ocean: Geography: Covers over 360 million km2 of earth’s surface (70%), and consists of one continuous, interconnected mass of water Arctic, Atlantic, Indian, Pacific, and Southern oceans Largest and deepest: Pacific (180 million km2, depth 4km) Structure: Intertidal zone: shallow shoreline under the influence of the rise and fall of the tides Neritic zone: extends from the coast to the margin of the continental shelf, where the ocean is about 200m deep
Oceanic zone: beyond the continental shelf Epipelagic zone: surface layer of the oceans that extends to a depth of 200m Mesopelagic zone: extends from 200 to 1,000m Bathypelagic zone: extends from 1,000 to 4,000m Abyssal zone: from 4,000 to 6,000m Hadal zone: deepest parts of the ocean Benthic: habitats on the bottom of the ocean and other aquatic environments Pelagic: habitats off the bottom regardless of depth Physical conditions: Light: o Approximately 80% of the solar energy striking the ocean is absorbed in the first 10m o Most ultraviolet and infrared light is absorbed in the first few meters blue light is absorbed less rapidly o In the open ocean algae are at low concentrations and very little of the blue light available is used in photosynthesis, which is why the ocean appears blue Temperature: o Sunlight absorbed by water increases the kinetic state, of water molecules o Because more rapid molecular motion decreases water density, warm water floats on cold water o Warm and cold layers are separated by thermocline, a layer of water in which temperature changes with depth o Thermal stratification: layering of water column by temperature o Temperate oceans are stratified only in summer, and the thermocline breaks down as surface waters cool during fall and winter o Lowest oceanic temperature, -1.5oC, highest 27oC o Annual variation in surface temperature: 7oC-9oC o At 100m depth, annual variation in temperature is less than 1oC Water movements: o Prevailing winds drive currents that transport nutrients, oxygen and heat, as well as organisms across the globe o Currents moderate climates, fertilize surface waters off the continents, stimulate photosynthesis, and promote gene flow among populations of marine organisms o Wind-driven surface currents sweep across vast expanses of open ocean to create great circulation systems called gyres
o Oceanic gyres transport warm water from equatorial regions towards the poles o Deepwater currents produced as cooled, high-density water sinks and then moves along the ocean floor o Upwelling: winds blow surface water offshore, allowing colder water to rise to surface Chemical conditions: Salinity: o When an organism’s internal salinity differs from the salinity of the surrounding water, that organism will be under osmotic stress o Salinity varies with latitude, and among the seas that fringe the oceans o In the open ocean, it varies from 34g/kg-36.5g/kg o Lowest salinities occur near the equator and above 40oN and S latitudes o Highest salinities occur in the subtropics o Salinity varies a great deal more in the small, enclosed basins along the margins of the major oceans o Relative proportions of the major ions [Na+], [Mg2+], and [Cl-] remain constant from one part of the ocean to another Oxygen: o Present in far lower concentrations and varies much more in the oceans o Litre of water contains a maximum of 9mL of oxygen o Concentrations are highest near the ocean surface, and decrease with depth o Below 1,000m oxygen concentrations increase as one travels deeper in the ocean Biology: Correspondence between physical and chemical conditions and the diversity, composition, and abundance of oceanic organisms Photosynthetic inhabitants in the photic zone: phytoplankton and zooplankton Most deep-sea organisms are nourished by organic matter fixed by photosynthesis near the surface Biological communities on the seafloor that are nourished by chemosynthesis on the ocean floor The open ocean is an area nearly devoid of life Contribute to one-fourth of total photosynthesis in the biosphere Most fish are found along the coasts
Open ocean is home for thousands of organisms with no counterparts on land Marine environment supports 28 phyla, 13 of which are endemic to the marine environment Human influences: Overfishing Dumping of wastes Deep ocean petroleum extraction Shallow marine waters – kelp forests and coral gardens: Geography: In temperate to subpolar regions there are growths of kelp As you get closer to the equator, kelp forests are replaced by coral reefs, occurring in relatively shallow water Some corals may live more than 4,000 years Structure: Fringing reefs: hug the shore of a continent or island Barrier reefs: stand some distance offshore, between the open sea and lagoons Coral atolls: coral islets that have built up from a submerged oceanic island and ring a lagoon Reef crest: corals grow in the surge zone created by waves coming from the open sea Below the reef crest in a buttress zone, where coral formations alternate with sand-bottomed canyons Behind the reef crest lies the lagoon, which contains numerous small coral reefs called patch reefs and sea grass beds Beds of kelp have structural features similar to terrestrial forests At the water’s surface is the canopy, the stems of kelp extend from the canopy to the bottom and are anchored with structures called holdfasts Physical conditions: Light: o Seaweeds and reef-building corals grow only in surface waters, where there is sufficient light to support photosynthesis Temperature: o Most kelp are limited to temperate shores, 10oC in winter, 20oC in summer o Reef-building corals are restricted to warm waters (20oC-29oC) Water movements: o Continuously washed by oceanic currents delivering oxygen and nutrients and removing waste
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o Biological productivity may depend upon the flushing action of these currents Chemical conditions: Salinity: o Coral reefs grow in waters with stable salinity o Kelp beds appear to be more tolerant of freshwater runoff and grow well along temperate showers Oxygen: o Occur where waters are well oxygenated Biology: Coral reefs face intense biological disturbance Coral reefs and kelp beds are among the most productive and diverse of all ecological systems in the biosphere Human influences: Kelp are harvested for use as a food additive or for fertilizer, and are replaced by rapid kelp growth Corals are harvested and bleached for decorations, do not grow quickly Fish and shellfish of kelp forests and coral reefs have also been exploited Coral reefs buffer the effects of waves Increased temperatures, light, and pollution, can lead to coral bleaching Where waves meet rocks – intertidal zones: Geography: Thousands of kilometers of coastline around the world have intertidal zones Exposed and sheltered shores Rocky and sandy shores Structure: Supreatidal fringe: highest zones, covered by high tides but is often wetted by waves Below fringe is the intertidal zone proper Upper intertidal zone is covered only during the highest tides, and the lower intertidal zone is uncovered only during the lowest tides Middle intertidal zone is covered and uncovered during average tides Subtidal zone: remains covered by water even during the lowest tides Physical conditions: Light: o Intertidal organisms are exposed to wide variations in light intensity o At high tide, water turbulence reduces light intensity
o At low tide, intertidal organisms are exposed to the full intensity of the sun Temperature: o Intertidal temperatures are always changing o At high latitudes, tide pools, small basins that retain water at low tide, can cool to freezing temperatures during low tides, while tide pools alon tropical and subtropical shores can heat to temperatures in excess of 40oC Water movements: o Two most important water movements affecting the distribution and abundance of intertidal organisms are the waves that break upon the shore and the tides o Tides vary in magnitude and frequency o Most tides are semidiurnal: two low tides and two high tides each day o Main tide-producing forces are the gravitational pulls of the sun and moon on water o Pull of the moon is greater because the moon is closer o Tidal fluctuations are greatest when the sun and moon are working together which happens at full and new moons o Maximum tidal fluctuations are called spring tides o Tidal fluctuations is least when the sun and moon are working in opposition: neap tides o Size and geographic position of a bay, sea, or section of coastline determine whether the influences of sun and moon are amplified or damped and are responsible for the variations in tides from place to place o Amount of wave energy varies considerably from one section of cost to another Chemical conditions: Salinity: o Salinity in the intertidal zone varies more than in open sea o Rapid evaporation during low tide increases salinity within tide pools along desert shores o Along rainy shores at high latitudes and in the tropics during the wet season, tide pool organisms can experience reduced salinity Oxygen: o Intertidal species exposed to oxygen-rich air at low tide o Water of wave-swept shores is thoroughly mixed and well oxygenated Biology:
Inhabitants of intertidal zone are adapted to amphibious existence Zonation of species: some species inhabit the highest levels of the intertidal zone, others are only exposed during low tides Substratum also affects the distribution of intertidal organisms Human influences: People have sought out intertidal areas for food, recreation, education, and research Ocean-land transitions – salt marshes and mangrove forests: Geography: Salt marshes: concentrated along sandy shores from temperate to high latitudes Mangrove forests: in tropical and subtropical latitudes Structure: Salt marshes include channels (tidal creeks) that fill and empty with the tides Tidal creeks bordered by natural levees, beyond the levees are marsh flats, which may include small basins (salt pans) that collect water that evaporates, leaving a layer of salt Mangrove trees distributed according to height Physical conditions: Light: o Fluctuations in tidal level: variable light conditions o Waters are usually turbid Temperature: o Water temperature varies with air temperature o Difference in seawater and fresh water temperature Water movement: o Tidal currents Chemical conditions: Salinity: o Fluctuates where river and tidal flow are substantial o Interaction between plants, animals, and water o Evaporation Oxygen: o Variable and reaches extreme levels o Decomposition o Isolation of saline bottom water o Photosynthesis Biology: Salt marshes dominated by grasses, glasswort, and rushes Mangrove forest dominated by trees Estuaries and salt marshes: high primary production Human influences: Human settlement
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Discharge of organic waste and nutrients Running waters – rivers and streams: Geography: Rivers drain most of the landscapes of the world River basin: area that is drained by a river drainage network Flow out to sea or inferior basin, or dry out River basins are separated by watersheds Structure: Rivers and streams can be divided by: length, width, vertically Wetted channel: contains water even during low flow Active channel: extends from both sides of wetted channel Riparian zone: transition between aquatic and terrestrial environment Water surface, water column and benthic zone Benthic zone: surface of the bottom substrate and inferior of the substrate through depths at which substantial surface water still flows Hyporheic zone: transition between areas of surface water flow and groundwater Phreatic zone: area containing groundwater Streams and rivers within a drainage network classified by stream order Headwater streams are first order, stream formed by joining of 2 first order streams are second order stream and so on Physical conditions: Light: o Depends on how far light penetrates into water column and how much light shines on surface o Materials continuously fall into rivers o River turbulence erodes bottom sediments o Shading increases downstream Temperature: o Track air temperature Water movements: o Continuous movement of water o Lotic: free-flowing water o Lentic: standing water o Amount of water carried by rivers (river discharge), differs from one climatic regime to another o Flood pulse concept: historical patterns of flooding have influences on river ecosystem processes, i.e. nutrients Chemical conditions: Salinity: o Amount of salt dissolved in river water reflects history of leaching in its basin
Oxygen: o Inversely correlated with temperature Biology: Large number of species inhabit tropical rivers Change from headwaters to mouth River continuum concept: in temperate regions, leaves are major source of energy available to stream ecosystem Most invertebrates live on or in the sediments Human influences: Commerce, transportation, energy, irrigation, and waste disposal Rivers have been channelized, poisoned, filled with sewage, dammed, filled with non-native fish species, and dried Still waters – lakes and ponds: Geography: Basins in the landscape that collect water Found in regions worked by geological forces producing basins Most of the world’s freshwater resides in lakes Structure: Littoral zone: shallowest waters where aquatic plants grow Limnetic zone: open lake Epilimnion: warm surface layer of lakes Metalimnion: thermocline, temperature and other physical and chemical factors change with depth Hypolimnion: water is cold and dark and lack dissolved oxygen Physical conditions: Light: o Light absorption influenced by chemistry, biological activity and depth Temperature: o Become thermally stratified as they warm o 4oC temperature at which the density is highest Water movements: o Wind-driven mixing, thermally stratified Chemical conditions: Salinity: o Variable Oxygen: o Lakes of low productivity are oligotrophic and well oxygenated o Lakes of high production are eutrophic and depleted of oxygen Biology: Oligotrophic and eutrophic lakes support distinctive biological communities
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Oligotrophic lakes supper highest diversity of phytoplankton Human influences: Domestic and industrial uses Introduction of new species Peatlands – bogs and fens: Peat consists of partially decomposed plant material that builds up in certain poorly drained habitats Geography: Occupy 5% of the world’s land base 80% located in high latitudes of the boreal and subarctic Structure: Well-developed layer of mosses and sedges Low rates of decomposition Bogs found in depressions in the landscape Fens fed by precipitation and connections to ground or surface water Fens are typically flat Bogs exhibit patterning of raised hummocks and lower hollows Physical conditions: Light: o How much light hits the moss layer is influenced by the presence of taller plants Temperature: o Peatlands occur when decomposition is lower than production, and when water input is greater than output o Temperature can have an affect on these processes Water movement: o Still waters are a prerequisite for formation, and peat accumulation is possible when water levels are stable over extended periods of time Chemical conditions: Salinity: o Not a major factor influencing the organisms o Influenced by pH Oxygen: o Water-logged anaerobic environment Biology: More productive areas dominated by trees and shrubs, and acidic areas having few vascular plants. Moss layer, carnivorous plants Low calcium levels reduce abundance of vertebrates Human impact: Peat is mined Climate change and carbon release
Oceanic zone: beyond the continental shelf Epipelagic zone: surface layer of the oceans that extends to a depth of 200m Mesopelagic zone: extends from 200 to 1,000m Bathypelagic zone: extends from 1,000 to 4,000m Abyssal zone: from 4,000 to 6,000m Hadal zone: deepest parts of the ocean Benthic: habitats on the bottom of the ocean and other aquatic environments Pelagic: habitats off the bottom regardless of depth Physical conditions: Light: o Approximately 80% of the solar energy striking the ocean is absorbed in the first 10m o Most ultraviolet and infrared light is absorbed in the first few meters blue light is absorbed less rapidly o In the open ocean algae are at low concentrations and very little of the blue light available is used in photosynthesis, which is why the ocean appears blue Temperature: o Sunlight absorbed by water increases the kinetic state, of water molecules o Because more rapid molecular motion decreases water density, warm water floats on cold water o Warm and cold layers are separated by thermocline, a layer of water in which temperature changes with depth o Thermal stratification: layering of water column by temperature o Temperate oceans are stratified only in summer, and the thermocline breaks down as surface waters cool during fall and winter o Lowest oceanic temperature, -1.5oC, highest 27oC o Annual variation in surface temperature: 7oC-9oC o At 100m depth, annual variation in temperature is less than 1oC Water movements: o Prevailing winds drive currents that transport nutrients, oxygen and heat, as well as organisms across the globe o Currents moderate climates, fertilize surface waters off the continents, stimulate photosynthesis, and promote gene flow among populations of marine organisms o Wind-driven surface currents sweep across vast expanses of open ocean to create great circulation systems called gyres
o Oceanic gyres transport warm water from equatorial regions towards the poles o Deepwater currents produced as cooled, high-density water sinks and then moves along the ocean floor o Upwelling: winds blow surface water offshore, allowing colder water to rise to surface Chemical conditions: Salinity: o When an organism’s internal salinity differs from the salinity of the surrounding water, that organism will be under osmotic stress o Salinity varies with latitude, and among the seas that fringe the oceans o In the open ocean, it varies from 34g/kg-36.5g/kg o Lowest salinities occur near the equator and above 40oN and S latitudes o Highest salinities occur in the subtropics o Salinity varies a great deal more in the small, enclosed basins along the margins of the major oceans o Relative proportions of the major ions [Na+], [Mg2+], and [Cl-] remain constant from one part of the ocean to another Oxygen: o Present in far lower concentrations and varies much more in the oceans o Litre of water contains a maximum of 9mL of oxygen o Concentrations are highest near the ocean surface, and decrease with depth o Below 1,000m oxygen concentrations increase as one travels deeper in the ocean Biology: Correspondence between physical and chemical conditions and the diversity, composition, and abundance of oceanic organisms Photosynthetic inhabitants in the photic zone: phytoplankton and zooplankton Most deep-sea organisms are nourished by organic matter fixed by photosynthesis near the surface Biological communities on the seafloor that are nourished by chemosynthesis on the ocean floor The open ocean is an area nearly devoid of life Contribute to one-fourth of total photosynthesis in the biosphere Most fish are found along the coasts
Open ocean is home for thousands of organisms with no counterparts on land Marine environment supports 28 phyla, 13 of which are endemic to the marine environment Human influences: Overfishing Dumping of wastes Deep ocean petroleum extraction Shallow marine waters – kelp forests and coral gardens: Geography: In temperate to subpolar regions there are growths of kelp As you get closer to the equator, kelp forests are replaced by coral reefs, occurring in relatively shallow water Some corals may live more than 4,000 years Structure: Fringing reefs: hug the shore of a continent or island Barrier reefs: stand some distance offshore, between the open sea and lagoons Coral atolls: coral islets that have built up from a submerged oceanic island and ring a lagoon Reef crest: corals grow in the surge zone created by waves coming from the open sea Below the reef crest in a buttress zone, where coral formations alternate with sand-bottomed canyons Behind the reef crest lies the lagoon, which contains numerous small coral reefs called patch reefs and sea grass beds Beds of kelp have structural features similar to terrestrial forests At the water’s surface is the canopy, the stems of kelp extend from the canopy to the bottom and are anchored with structures called holdfasts Physical conditions: Light: o Seaweeds and reef-building corals grow only in surface waters, where there is sufficient light to support photosynthesis Temperature: o Most kelp are limited to temperate shores, 10oC in winter, 20oC in summer o Reef-building corals are restricted to warm waters (20oC-29oC) Water movements: o Continuously washed by oceanic currents delivering oxygen and nutrients and removing waste
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o Biological productivity may depend upon the flushing action of these currents Chemical conditions: Salinity: o Coral reefs grow in waters with stable salinity o Kelp beds appear to be more tolerant of freshwater runoff and grow well along temperate showers Oxygen: o Occur where waters are well oxygenated Biology: Coral reefs face intense biological disturbance Coral reefs and kelp beds are among the most productive and diverse of all ecological systems in the biosphere Human influences: Kelp are harvested for use as a food additive or for fertilizer, and are replaced by rapid kelp growth Corals are harvested and bleached for decorations, do not grow quickly Fish and shellfish of kelp forests and coral reefs have also been exploited Coral reefs buffer the effects of waves Increased temperatures, light, and pollution, can lead to coral bleaching Where waves meet rocks – intertidal zones: Geography: Thousands of kilometers of coastline around the world have intertidal zones Exposed and sheltered shores Rocky and sandy shores Structure: Supreatidal fringe: highest zones, covered by high tides but is often wetted by waves Below fringe is the intertidal zone proper Upper intertidal zone is covered only during the highest tides, and the lower intertidal zone is uncovered only during the lowest tides Middle intertidal zone is covered and uncovered during average tides Subtidal zone: remains covered by water even during the lowest tides Physical conditions: Light: o Intertidal organisms are exposed to wide variations in light intensity o At high tide, water turbulence reduces light intensity
o At low tide, intertidal organisms are exposed to the full intensity of the sun Temperature: o Intertidal temperatures are always changing o At high latitudes, tide pools, small basins that retain water at low tide, can cool to freezing temperatures during low tides, while tide pools alon tropical and subtropical shores can heat to temperatures in excess of 40oC Water movements: o Two most important water movements affecting the distribution and abundance of intertidal organisms are the waves that break upon the shore and the tides o Tides vary in magnitude and frequency o Most tides are semidiurnal: two low tides and two high tides each day o Main tide-producing forces are the gravitational pulls of the sun and moon on water o Pull of the moon is greater because the moon is closer o Tidal fluctuations are greatest when the sun and moon are working together which happens at full and new moons o Maximum tidal fluctuations are called spring tides o Tidal fluctuations is least when the sun and moon are working in opposition: neap tides o Size and geographic position of a bay, sea, or section of coastline determine whether the influences of sun and moon are amplified or damped and are responsible for the variations in tides from place to place o Amount of wave energy varies considerably from one section of cost to another Chemical conditions: Salinity: o Salinity in the intertidal zone varies more than in open sea o Rapid evaporation during low tide increases salinity within tide pools along desert shores o Along rainy shores at high latitudes and in the tropics during the wet season, tide pool organisms can experience reduced salinity Oxygen: o Intertidal species exposed to oxygen-rich air at low tide o Water of wave-swept shores is thoroughly mixed and well oxygenated Biology:
Inhabitants of intertidal zone are adapted to amphibious existence Zonation of species: some species inhabit the highest levels of the intertidal zone, others are only exposed during low tides Substratum also affects the distribution of intertidal organisms Human influences: People have sought out intertidal areas for food, recreation, education, and research Ocean-land transitions – salt marshes and mangrove forests: Geography: Salt marshes: concentrated along sandy shores from temperate to high latitudes Mangrove forests: in tropical and subtropical latitudes Structure: Salt marshes include channels (tidal creeks) that fill and empty with the tides Tidal creeks bordered by natural levees, beyond the levees are marsh flats, which may include small basins (salt pans) that collect water that evaporates, leaving a layer of salt Mangrove trees distributed according to height Physical conditions: Light: o Fluctuations in tidal level: variable light conditions o Waters are usually turbid Temperature: o Water temperature varies with air temperature o Difference in seawater and fresh water temperature Water movement: o Tidal currents Chemical conditions: Salinity: o Fluctuates where river and tidal flow are substantial o Interaction between plants, animals, and water o Evaporation Oxygen: o Variable and reaches extreme levels o Decomposition o Isolation of saline bottom water o Photosynthesis Biology: Salt marshes dominated by grasses, glasswort, and rushes Mangrove forest dominated by trees Estuaries and salt marshes: high primary production Human influences: Human settlement
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Discharge of organic waste and nutrients Running waters – rivers and streams: Geography: Rivers drain most of the landscapes of the world River basin: area that is drained by a river drainage network Flow out to sea or inferior basin, or dry out River basins are separated by watersheds Structure: Rivers and streams can be divided by: length, width, vertically Wetted channel: contains water even during low flow Active channel: extends from both sides of wetted channel Riparian zone: transition between aquatic and terrestrial environment Water surface, water column and benthic zone Benthic zone: surface of the bottom substrate and inferior of the substrate through depths at which substantial surface water still flows Hyporheic zone: transition between areas of surface water flow and groundwater Phreatic zone: area containing groundwater Streams and rivers within a drainage network classified by stream order Headwater streams are first order, stream formed by joining of 2 first order streams are second order stream and so on Physical conditions: Light: o Depends on how far light penetrates into water column and how much light shines on surface o Materials continuously fall into rivers o River turbulence erodes bottom sediments o Shading increases downstream Temperature: o Track air temperature Water movements: o Continuous movement of water o Lotic: free-flowing water o Lentic: standing water o Amount of water carried by rivers (river discharge), differs from one climatic regime to another o Flood pulse concept: historical patterns of flooding have influences on river ecosystem processes, i.e. nutrients Chemical conditions: Salinity: o Amount of salt dissolved in river water reflects history of leaching in its basin
Oxygen: o Inversely correlated with temperature Biology: Large number of species inhabit tropical rivers Change from headwaters to mouth River continuum concept: in temperate regions, leaves are major source of energy available to stream ecosystem Most invertebrates live on or in the sediments Human influences: Commerce, transportation, energy, irrigation, and waste disposal Rivers have been channelized, poisoned, filled with sewage, dammed, filled with non-native fish species, and dried Still waters – lakes and ponds: Geography: Basins in the landscape that collect water Found in regions worked by geological forces producing basins Most of the world’s freshwater resides in lakes Structure: Littoral zone: shallowest waters where aquatic plants grow Limnetic zone: open lake Epilimnion: warm surface layer of lakes Metalimnion: thermocline, temperature and other physical and chemical factors change with depth Hypolimnion: water is cold and dark and lack dissolved oxygen Physical conditions: Light: o Light absorption influenced by chemistry, biological activity and depth Temperature: o Become thermally stratified as they warm o 4oC temperature at which the density is highest Water movements: o Wind-driven mixing, thermally stratified Chemical conditions: Salinity: o Variable Oxygen: o Lakes of low productivity are oligotrophic and well oxygenated o Lakes of high production are eutrophic and depleted of oxygen Biology: Oligotrophic and eutrophic lakes support distinctive biological communities
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Oligotrophic lakes supper highest diversity of phytoplankton Human influences: Domestic and industrial uses Introduction of new species Peatlands – bogs and fens: Peat consists of partially decomposed plant material that builds up in certain poorly drained habitats Geography: Occupy 5% of the world’s land base 80% located in high latitudes of the boreal and subarctic Structure: Well-developed layer of mosses and sedges Low rates of decomposition Bogs found in depressions in the landscape Fens fed by precipitation and connections to ground or surface water Fens are typically flat Bogs exhibit patterning of raised hummocks and lower hollows Physical conditions: Light: o How much light hits the moss layer is influenced by the presence of taller plants Temperature: o Peatlands occur when decomposition is lower than production, and when water input is greater than output o Temperature can have an affect on these processes Water movement: o Still waters are a prerequisite for formation, and peat accumulation is possible when water levels are stable over extended periods of time Chemical conditions: Salinity: o Not a major factor influencing the organisms o Influenced by pH Oxygen: o Water-logged anaerobic environment Biology: More productive areas dominated by trees and shrubs, and acidic areas having few vascular plants. Moss layer, carnivorous plants Low calcium levels reduce abundance of vertebrates Human impact: Peat is mined Climate change and carbon release
