Environmental Science The study of the impact of humans on the environment Draws from all science disciplines and other fields. Gives an understanding of the relationship between Humans and the world we live in. Achieves many of its goals using pure sciences such as chemistry and biology. Environmental science focuses on three main areas: 1. Conservation and Protection of natural resources 2. Communicating and Educating about environmental issues. 3. Research Environmental science began when scientists realised that parts of the subjects used, such as ecology, biology, chemistry, geography and geology, all played a part in the environment. So what is the environment? The environment is everything that surrounds us; both natural and produced by Humans Systems Humans and Their Models One common conclusion of scientific inquiry is that the world of nature is often very complex. To understand this complexity, scientists usually try to envisage the phenomena of nature as simplified versions of reality known as a system. A system can be defined as a collection of interrelated parts that work together by way of some driving process. In the world of science, the word model is quite similar in meaning to the term system. Models in science tend to be simplified representations of reality that can be explained mathematically and through the use of graphics. The following graphical model is used to help explain the processes involved in scientific understanding. The arrows in this graphically model suggest a continuous interaction between perceptible phenomena and theory through the processes of explanation and validation. This simple graphical model, while an extreme abstraction of the real world, is quite useful in explaining how scientific understanding works. The general relationship between perceptible phenomena and theory using scientific method for understanding. The interaction between perceptible phenomena and theory is arrived at through the processes of explanation and validation. In Physical Geography, and many other fields of knowledge, systems and models are used extensively as aids in explaining natural phenomena around us. Definitions of Systems and Models As suggested in the previous section, a system is an assemblage of interrelated parts that work together by way of some driving process (see diagram below). Systems are often visualized or modeled as component blocks that have connections drawn between them. For example, the illustration below describes the interception of solar radiation by the Earth. In this system, the Earth and Sun, the parts or component blocks, are represented by two colored circles of different size. The process of solar emission and the interception of the Sun's emitted radiation by the Earth (the connection) is illustrated by the drawn lines. Simple visual model of solar radiation being emitted from the Sun and intercepted by the Earth. Most systems share the same common characteristics. These common characteristics include the following: 1. Systems have a structure that is defined by its parts and processes. 2. Systems are generalizations of reality. 3. Systems tend to function in the same way. This involves the inputs and outputs of material (energy and/or matter) that is then processed causing it to change in some way. The various parts of a system have functional as well as structural relationships between each other. 4. The fact that functional relationships exist between the parts suggests the flow and transfer of some type of energy and/or matter. 5. Systems often exchange energy and/or matter beyond their defined boundary with the outside environment, and other systems, through various input and output processes. 6. Functional relationships can only occur because of the presence of a driving force. 7. The parts that make up a system show some degree of integration - in other words the parts work well together. Within the boundary of a system we can find three kinds of properties: Elements - are the kinds of parts (things or substances) that make up a system. These parts may be atoms or molecules, or larger bodies of matter like sand grains, rain drops, plants, animals, etc. Attributes - are characteristics of the elements that may be perceived and measured. For example: quantity, size, colour, volume, temperature, and mass. Relationships - are the associations that occur between elements and attributes. These associations are based on cause and effect. We can define the state of the system by determining the value of its properties (the elements, attributes, and/or relationships). Scientists have examined and classified many types of systems. Some of the classified types include: Isolated System - a system that has no interactions beyond its boundary layer. Many controlled laboratory experiments are this type of system. Closed System - is a system that transfers energy, but not matter, across its boundary to the surrounding environment. Our planet is often viewed as a closed system. Open System - is a system that transfers both matter and energy can cross its boundary to the surrounding environment. Most ecosystems are example of open systems. Control System - a system that can be intelligently manipulated by the action of humans. Ecosystem - is a system that models relationships and interactions between the various biotic and abiotic components making up a community or organisms and their surrounding physical environment. Structure of Systems Systems exist at every scale of size and are often arranged in some kind of hierarchical fashion. Large systems are often composed of one or more smaller systems working within its various elements. Processes within these smaller systems can often be connected directly or indirectly to processes found in the larger system. A good example of a system within systems is the hierarchy of systems found in our Universe. o At the top level we have what we call the Cosmos or Universe. o Elements of that system are galaxies, stars, planets, black holes etc. o The structure of this system is thought to have been brought about by a massive explosion called the BIG BANG and it is controlled by gravity and the other 3 forces: the electromagnetic force, the strong force and the weak force. o Within this system (our Universe) there are Solar Systems. o Within this system there are planetary systems for example, Earth. o On Earth there is interaction between its lithosphere (crust), atmosphere and hydrosphere and this is known as a biosphere. Biospheres are regions of the Earth, or other planet, where living organisms exist. If a planetary system has a biosphere, dynamic interactions between the lithosphere, atmosphere and hydrosphere will develop. These interactions can be called an environmental system. The scale of this can range from massive to a single plant. The Earth’s biosphere is made up of ECOSYSTEMS. A population of species grouped together into communities that interact with each other and the ABIOTIC environment. An organism is alive because it is a biological system. Environmental Systems as Energy Systems We define an environmental system as a system where life interacts with the various abiotic components found in the atmosphere, hydrosphere, and lithosphere. Environmental systems also involve the capture, movement, storage, and use of energy. Thus, environmental systems are also energy systems. In environmental systems, energy moves from the abiotic environment to life through processes like plant photosynthesis. Photosynthesis packages this energy into simple organic compounds like glucose and starch. Both of these organic molecules can be stored for future use. The following chemical formula describes how plants capture the Sun's light energy and convert it into chemical energy: 6CO2 + 6H2O + light energy → C6H12O6 + 6O2 The energy of light is used by plants in this reaction to chemically change carbon dioxide (CO2) and water (H2O) into oxygen (O2) and the energy rich organic molecule glucose (C6H12O6). The chemical energy of photosynthesis can be passed on to other living or biotic components of an environmental system through biomass consumption or decomposition by consumer organisms. When needed for metabolic processes, the fixed organic energy stored in an organism can be released to do work via respiration or fermentation. Food Chain as an Example of a System A food chain models the movement of energy in an ecosystem (a form of environmental system). The diagram below illustrates the movement of energy in a typical food chain. In this diagram, we begin the food chain with 100,000 units of light energy from the Sun. Note the amount of energy available at each successive level (called trophic levels) of this system becomes progressively less. Only 10 units of energy are available at the last level (carnivores) of the food chain. A number of factors limit the assimilation of energy from one level to the next. The Sun is the original source of energy, in the form of light, for the food chain. (100,000 Units of Energy) Plants capture approximately 1% of the available light energy from the Sun for biomass production by way of photosynthesis. Photosynthesis can be described chemically as: Light Energy + 6CO2 + 6H2O ==> C6H12O6+ 6O2 (1,000 Units of Energy) Herbivores consume approximately 10% of the plant biomass produced in a typical food chain.(100 Units of Energy) Carnivores capture and consume about 10% of the energy stored by the herbivores. (10 Units of Energy) Why is the above illustration an example of a system? The concept of what makes something a system was fully explained in part b above. In this topic, it was suggested that all systems share the following seven common characteristics: 1. Systems have a structure that is defined by its parts and processes. In the above example, the structure consists of the system's three types of properties. This system has the following elements: the Sun, plants, herbivores and carnivores. Within this system the main characteristic, or attribute, of the elements being perceived is units of energy. The last component that makes up the structure of this system is the cause and effect relationships between the elements and attributes. For example, the Sun creates energy via nuclear fusion. This energy is radiated from the Sun's surface and received by the surface of the Earth. On the surface of the Earth plants capture some of this solar radiation in the chloroplasts that exist in their tissues. Through photosynthesis the plants convert the radiant energy into energy rich organic matter. Some of the energy fixed by the plants is passed on to herbivores through consumption. Finally, a portion of the energy assimilated by the herbivores is then passed on to carnivores through consumption. 2. Systems are generalizations of reality. The food chain process described above is a simple abstraction of what actually happens in a variety of different types of terrestrial ecosystems of much greater complexity. Systems tend to function in the same way. All systems consist of groups of parts that interact with each other according to various cause and effect processes. In the food chain model, the parts are the Sun, plants, herbivores and carnivores. There are two main processes taking place in this system. The first involves the movement of energy, in the form of radiation, from the Sun to the plants. The second process involves the movement of energy, in the form of organic molecules, from plants to herbivores, and then finally to carnivores through biomass consumption. 3. The various parts of a system have functional as well as structural relationships between each other. The structure within the food chain is defined by the functional relationships between the elements and attributes of the system. 4. The fact that functional relationships exist between the parts suggests the flow and transfer of some type of energy or matter. Systems exchange energy and matter internally and with their surrounding environment through various processes of input and output. The main material being transferred into this system (input) is energy in the form of solar radiation. The solar radiation is then fixed into organic matter (output) by way of photosynthesis in the plants. Herbivores consume the constructed plant organic molecules for nutrition to run their metabolism. The herbivores then provide food for the carnivores. 5 Systems often exchange energy and/or matter beyond their defined boundary with the outside environment, and other systems, through various input and output processes. The organisms found in a food chains transfer organic matter into the detritus food chain when they shed tissues or die. This transfer represents a net output of matter out of the food chain. With decomposition, the organic matter is converted into inorganic nutrients which can be taken up by plants in the food chain to produce new organic matter. This transfer represents a net input of matter into the food chain system. 6 Functional relationships can only occur because of the presence of a driving force. The driving force in the food chain is the Sun. The parts that make up a system show some degree of integration - in other words the parts work well together. Integration in the food chain comes primarily from the process of evolution. It was through evolution that plants, herbivores, and carnivores came about and developed ecological associations between each other. Biomes A biome is described by its vegetation, precipitation and temperature. An ecosystem is a POPULATION of SPECIES grouped together into COMMUNITIES that interact with each other and the ABIOTIC environment. A biome is a group of ecosystems in a larger region. Therefore the ecosystems of the world are grouped into regions called biomes. A biome is therefore a large region characterised by a certain type of climate and certain types of animal and plant communities. The hierarchy is: The biosphere is divided into Biomes which are divided into Ecosystems. Biomes are described by the vegetation because the plants that grow in a particular region are the most noticeable thing about that region. The plant life also determines the other organisms that live there. E.G. Mahogany trees grow in tropical rainforests because they cannot survive dry, cold weather and it follows that organisms that depend on those trees, live where they grow. Plants in biomes have adaptations that enable them to survive there. These adaptations may size, shape or colour for example. E.G. Desert plants such as cacti have no leaves but have specialised structures instead that allow them to conserve and retain water. Plants that grow in the tundra are usually short because of a lack of water and a short summer growing season. Biomes and Climate The plants that grow in the biomes are determined by the climate of those regions. The climate of a region refers to the weather conditions such as: Precipitation, Temperature, Wind and Humidity; over a long period of time. The 2 main factors that determine a regions climate are TEMPERATURE and PRECIPITATION. Most organisms are adapted to survive within a specific range of temperatures and cannot survive if the temperature goes too far outside that range. Plants are also affected by the length of the growing season. Precipitation is another factor that limits the organisms found in a biome as all organisms need water. Look at the Temperature-Precipitation Pyramid. Notice how much more vegetation exists in hot, wet tropical ran forest than in a dry, desert area. Different species live in different parts of the world. However, species that live in the same biome look and act similar although they may live far away from each other. This happens because similar niches become available in each biome. In order to fill these niches animals adapt and begin to behave and look similar to other animals in other parts of the world. Latitude and Altitude These are factors that cause biomes and vegetation to vary. Latitude is the distance north or south of the equator and is measured in degrees. Altitude is the height of an object above sea-level. Climate varies with latitude and altitude. E.G. Climate gets colder as latitude and altitude increase. Therefore, as they change so do biomes and vegetation. Trees of the tropical rain forests usually grow near the equator while the mosses and lichens of the tundra usually grow nearer to the poles. Layers of the Rain Forest Different types of plants grow at different levels, or layers, of the rain forest. The 4 main layers are: o The Emergent Layer o The Upper Canopy o The Lower Copy o The Understory The top layer, or emergent layer, contains the tallest trees which grow to around 60m or 70m and grow and emerge into direct sunlight. The layer below is known as the canopy and trees grow to a height of over 30m. These trees form a dense layer and can absorb up to 93% of the sunlight (Environmental Science, page 158). The canopy can be split into the upper and lower canopies. As one might imagine, the lower canopy receives less sunlight than the upper. Plants known as Epiphytes, such as orchids, use the whole surface of a tree as a place to live using them for support. Some grow high up where their leaves can reach the sunlight needed for photosynthesis to occur. Growing on these trees allows the epiphytes to absorb water and nutrients that run down the trees after it rains. Most animals that live in the rain forest live in the canopy because they rely on the abundant supply of flowers and fruits that grow there. Very little light reaches below the canopy and this layer is known as the understory. The trees and shrubs that grow here have adapted to living in shaded areas. The majority of the plants that grow here do not grow taller than about 3.5m. Plants with large, flat leaves grow on the forest floor and capture the small amount of sunlight that gets through. Many medicines come from tropical rain forest plants. Chemists extract chemicals from them to ascertain if they have any use in fighting or curing disease. E.G. The Rosy Periwinkle of Madagascar contain 2 chemicals of medical use: VINBLASTINE and VINCRISTINE o Vinblastine is used to treat Hodgkin’s Disease – a form of cancer. o Vincristine is used to treat childhood leukaemia. Diversity of Species The tropical rain forest is the biome with the greatest variety of species. The diversity of the vegetation has led to the evolution of a community with a wide variety of animals. Some of these animals have fantastic adaptations for capturing prey while others have adaptations that they use to avoid and escape predators. The Collared Anteater The Costa Rican Mantis The Wreathed Hornbill Threats to the Rain Forests 20% of the Earth was once covered in tropical rain forests but today they cover only about 7%!!!! (Environmental Science, page 160). This is due to them being cleared for agriculture, logging or the search for more oil. Approximately 100 acres of tropical rain forest are cleared every minute of the day (Environmental Science, page 160). This process is destroying habitats and it is this habitat destruction that is the main reason for species becoming extinct. The plants and animals are threatened by trading. Many species of plant, that are only found here, are valuable to industries. Animals are threatened because of the ‘exotic pet’ market. They are illegally trapped and sold at high prices. It is estimated that 50 million people live in the tropical rain forests and they too are threatened by habitat destruction. Their building materials, food, traditions and culture come from the rain forests and are uniquely connected to them. LOSING THEIR HABITAT MEANS LOSING THEIR WAY OF LIFE. Deforestation Plants absorb water through their roots and transport it to their stems and leaves. Water then evaporates through the pores (stomata) in the leaves through the process of TRANSPIRATION. When The water transpires into the air, it will travel downwind and fall as rain elsewhere. Deforestation can therefore change the climate. Cutting a forest down or replacing it with smaller plants means that a lot of the rainfall is not absorbed. Instead it runs of the soil causing flooding and soil erosion and the climate downwind will become dryer. Temperate Rain Forests These are found in Australia, New Zealand and North America. They have high humidity, large amounts of precipitation and moderate temperatures. The picture shows the only temperate rain forest in North America. It is located in the Pacific Northwest in the Olympic National Park, Washington State. The forest is dominated by trees that grow to 90m tall such as the Silka spruce and the Douglas fir. Other trees that can be found here are the Pacific silver fir and the Redwood. The temperate rain forest rarely freezes because of its year round moderate temperatures. This is due to the Pacific Ocean blowing cool ocean winds over the forest. As the winds meet the coastal mountains, a large amount of rainfall is produced and this keeps the temperate rainforest cool and moist. Temperate Deciduous Forests In these forests trees drop their flat, broad leaves every autumn and if you were to walk through such a forest in North America at this time you will see a vivid array of yellows, oranges and reds on the trees and forest floor. It is much quieter than it would be in the summer months as the majority of the bird population have flown south for the winter. However, there would be a great deal of activity amongst the squirrel and chipmunk communities as they gather up and store the food they will need during the long cold winter. This type of forest once dominated massive areas of the Earth but these days they are mainly found between the latitudes of 30o and 50o north. The growing season lasts for between 4 to 6 months, the range of temperatures can go from 35oC to below freezing (0oC) and because of this extreme range of temperatures there is very little water available for the plants. Earlier I mentioned the variety of colour during autumn as the deciduous trees shed their leaves and there is also a change in temperature. There is enough moisture for decomposition of the leaves and other vegetation to occur but the temperature is low. This causes the decomposition of any organic matter to occur at a slow rate which means that the soil will contain a lot more nutrients and organic matter than a tropical rain forest. Plants of the deciduous forest grow in layers – similar to a tropical rain forest. The canopy is dominated by trees such as the mighty oak, birch trees and maple trees. The understory is covered with shrubs and small trees but because more light can penetrate the floor of the deciduous forest, in comparison to the tropical rain forest, more plants such as herbs, mosses and ferns grow there. These temperate forest plants have adapted so as to be able to survive seasonal changes. The bulbs and seeds of plants such as herbs lay dormant. In the winter time the moisture in the soil freezes causing any remaining leaves on the trees to fall. When spring breaks the sunlight increases and the temperature rises. The seeds germinate, rhizomes (underground stems) grow new shoots and stems and the trees grow new leaves. The cycle begins once more. The plants are also used by the forest animals for food and shelter. Deer and other herbivores feed on grass and leaves from trees and shrubs. Many birds nest in the safety of the canopy. Because many of these birds cannot survive the winter here they fly south in the autumn in search of warmer weather and a good supply of food. These birds are known as MIGRATORY. Every spring they will return north to nest and feed. Animals that don’t migrate have different ways of surviving the winter. For example, certain mammals reduce their activity levels in order to eat less food for energy. Grasshoppers will eat most types of vegetation that is found in the forest. Taiga This is the coniferous forest of the north which stretches across the northern hemisphere just below the Artic Circle. Winters can last anywhere from 6 to 10 months and average temperatures are below freezing; sometimes reaching -20oC. Plant growth occurs during the very short summer due to almost constant daylight and large amounts of precipitation. Students to research how animals avoid predation in the Taiga and how this affects the animals that depend on them to survive. Grassland, Desert and Tundra Biomes are dominated by smaller plants in areas of not enough precipitation for the larger trees to grow. Deserts are found where there is little or no rainfall causing very few plants to grow. Therefore, warm areas with very little precipitation are savannas’ and deserts. Temperate regions have grassland, chapparal and deserts. Cold areas have tundra and deserts. Savanna Some parts of South America, western India, northern Australia and Africa are covered in grassland known as savanna. This is a tropical biome dominated by, as you might imagine, grasses, small trees and shrubs. The aptly named ‘wet season’ is when the majority of the rain falls which only lasts for a few months of the year and this is the only time that the plants get a chance to grow. This vegetation supports many different herbivores including elephants, antelope and giraffes and, of course, the carnivore predators that hunt, kill and eat them such as lions and cheetahs. Plants of the savanna need to be able to survive long periods of time without water and so during the dry season plants either lose their leaves or die down to the ground and lay dormant. When the wet season arrives they start to grow again. The root systems of many of the plants are horizontal allowing them to draw water from as large an area as possible. The coarse grasses have vertical leaves in order to expose less of the surface area of the leaves to the sun and conserve water. Some trees lose their leaves during the dry season too in order to conserve water. As a defence against hungry herbivores, some shrubs and trees have sharp leaves or thorns to protect them. Elephants and other grazing herbivores, have a migratory way of life. They follow the rains in order to find watering holes and newly sprouted grass and of course some of these animals are stalked by predators for food. Different species of herbivores eat vegetation at different heights. For example, gazelles eat grasses whereas giraffes eat leaves from the higher branches of trees The majority of the animals of the savanna give birth during the wet season because there is plenty of food and therefore the new born are more likely to survive. Temperate Grasslands These grasslands cover large areas of the interior of continents where the rainfall is moderate but not enough for trees to grow. The pampas of South America, the prairies of North America, the steppes of Asia and the veldt in South Africa are all temperate grasslands. The South American Pampas A major role is sometimes played by mountains in the maintenance of grasslands. E.g. rain clouds moving east, from the west, in North America release the majority of their moisture as they move over the Rocky mountains. Because of this the shortgrass prairie (east of the Rockies) gets very little rain which makes it look almost like a desert. The growth of taller grass and shrubs occurs further east as the amount of rainfall increases. Plants of the grassland dry out in summer causing fires to start through lightning strikes! The vegetation consists of only a single layer but contains many species of grasses and wild flowers The height of the different grasses and the depth of their roots vary depending on the amount of rainfall that grassland receives. The root systems of the various plants form dense layers that can survive fire and drought! Trees and shrubs will grow only in areas where the soil contains extra water and so they will usually be found on the banks of rivers and streams. The soils of the grasslands are very fertile. As can be seen from the climatogram, the winters on these grasslands are cold and the summers warm and the plants die back to their roots in winter. Because of the low temperatures during the winter months, decomposition of organic matter is very slow and the rate at which the dead plants die is slower than the rate at which new plants are added each year. This means that the amount of organic matter in the soil increases year by year. This therefore means that the grasslands have the most fertile soil in the world and because of this the majority of grasslands have been converted to farmland to grow crops like wheat and corn. Farming and overgrazing have altered the grasslands because the grain crops mentioned earlier cannot hold the soil in place as well as the grasses they have replaced. This is because the crop roots are a lot shallower and the ground is ploughed regularly causing soil erosion to happen eventually. Erosion also happens due to overgrazing because when the grasses are constantly eaten and trodden on they cannot regrow or hold the soil. This constant use can turn once extremely fertile grasslands into desert like biomes. Chaparrals Temperate woodland biomes have fairly dry climates but get enough rainfall to support more plants than a desert can. Chaparrals are temperate shrublands that have communities of scattered coniferous trees such as junipers and piñon pines. Temperate woodlands are too dry to support forests but receives enough precipitation so that vegetation grows in ‘bunches’. The chaparral is found in all 5 areas of the world that have Mediterranean climates. These parts of the world have fairly dry, coastal climates with little or no rain during the summer. They are found in the mid- latitudes at about 30o north and south of the equator. Most plants in chaparrals are small trees and low lying evergreen shrubs that grow in dense patches. These include manzanita and herbs such as bay and sage. These plants have small leathery leaves that hold water. Their leaves also contain oils that promote burning which is an advantage due to the fact that naturally occurring fires destroy the trees that could compete for light and space. They can also resprout from only the smallest surviving piece of plant material. A very common adaptation of chaparral animals is camouflage. Camouflage is the ability to blend into the environment because of shape and/or colouring which then allows the animal to move through the brush without being noticed. The greatest threat to chaparral biomes is Man! Because they get a lot of sun, have mild climates and are near the oceans, we have seen them as areas that can be developed for residential and commercial use. Golf courses on the south coast of Spain are a good example of this. Deserts These are areas that receive very little rainfall and have widely scattered vegetation. In extreme cases it never rains and so there is no vegetation present in that area. They are the driest places on Earth! Even in hot deserts near the equator there is very little moisture in the air giving rise to rapid temperature changes over any 24 hour period; ranging anywhere from around 40oC during the day to 0oC at night. One can often find deserts near mountain ranges which will stop the movement of rain clouds over the area. As one would expect, for plants to live in the desert, they have all have adapted in order to be able to obtain and conserve water. Plants known as succulents, such as cacti, have fleshy, thick stems and leaves that can store water and a waxy coating that stops water loss. Sharp spines on the cacti help protect it from being eaten by thirsty animals. Because deserts are so dry, rainfall hardly ever gets deep into the soil and so the roots of many of the plants spread out near to the surface of the soil so as to obtain as much water as possible. If the water level of a plant falls below between 50% and 75% of its mass it is usually fatal for the plant. However, some desert plants have adapted to be able to survive even their water level drops to as low as 30% of their mass! (Environmental Science pg 170). Other plants have adapted so that when it gets too dry they die off and drop seeds that lay dormant in the soil until it rains again. Once it rains again, the seeds quickly germinate and grow then bloom before the soil dries out again. A lot of the shrubs shed their leaves when it’s dry and grow new ones when the rains come again. Desert animals, such as the amphibious Spadefoot Toad, survive the desert heat by aestivating. They bury themselves in the ground and sleep. Reptiles have scaly skin that is thick and stops water loss. The Elf Owl nests in cacti to avoid predators. Insects have bodies covered in armour in order to retain water. However, the majority of desert creatures are nocturnal – they are active at night time when it is cooler. Tundra This is situated in the northern arctic regions and no trees grow here as the winters are too cold and dry. In some areas of the tundra the permafrost (the deeper layers of soil) is frozen permanently and because of this the top layer of soil, or topsoil, is very thin. When the thin layer of topsoil thaws in the summer, the terrain becomes very spongy and moist and has bogs dotted all over it. These wet areas are ideal breeding grounds for massive numbers of swarming insects such as mosquitoes and black flies. This also makes it an ideal breeding ground for the many birds that feed on the insects. Aquatic Ecosystems Freshwater ecosystems are made up of rivers, lakes and wetlands. Marine ecosystems include coral reefs, estuaries and the oceans. These aquatic ecosystems perform many environmental functions and support many animal and plant species. However, pollution, development and overuse are threatening to harm and disrupt many of these ecosystems. For example the Manatee lives in both fresh and salt water. In North America most manatees are found in the estuaries, bays and coastal ecosystems of states such as Florida. They are often called sea cows because of the way they lazily graze on the aquatic vegetation. They grow to 3m to 4m in length and weigh between 360kg to 545kg. However, manatees are, unfortunately, sometimes hit by boats because they live in shallow water and cannot swim fast enough to get out of the way of the boats. Freshwater Ecosystems The types of organisms that live in an aquatic ecosystem depends on the salinity of the water (the amount of dissolved salts that are contained in the water). Factors such as sunlight, oxygen, temperature and nutrients determine which organisms live in which areas of the water. For example the Sun can only reach a certain distance below the surface of the water and so the majority of photosynthetic organisms live on or near to the surface. The organisms are grouped by their location and by their adaptations. Three groups of these aquatic organisms include plankton, nekton and benthos. Plankton are organisms that cannot swim against the current – they drift and phytoplankton are microscopic drifting plants that are the food base for most aquatic systems. Drifting animals, that maybe microscopic or as big as jellyfish, are called zooplankton. Nekton are free swimming organisms such as fish, whales or turtles for example. Benthos are bottom dwelling organisms such as worms, clams, mussels or barnacles and many of these organisms live their lives attached to hard surfaces. Organisms called decomposers, which break down dead organic matter, are also present in aquatic ecosystems. Lakes, ponds, rivers, streams and wetlands are the various types of freshwater ecosystems. Lakes, ponds and wetlands can form naturally where the groundwater reaches the surface of the Earth. Beavers can create ponds by damming up streams. Humans create artificial lakes intentionally in order to use them for irrigation, energy, water storage and recreation. Lakes and ponds can be structured into horizontal and vertical zones and in the nutrient rich littoral zone - near the shore - the aquatic life is diverse and abundant. Reeds etc. are rooted in the mud under the water and their stems or leaves are above the water. Pond lilies and other plants that have floating leaves are also rooted there too. Further from the shoreline in the open water, there are no rooted plants. This is where the phytoplankton make their own food through the process of photosynthesis. As can be seen in the diagram the amount of sunlight and nutrients influence the types of organisms in ponds and lakes and where they will be located in the lakes and ponds. In some bodies of freshwater some areas are so deep that photosynthesis does not occur because there is too little light. In these areas decomposers such as bacteria feed on dead animals and plants that drift down. Fish that are adapted to cooler water also live here. The dead and decaying plants and animals eventually fall to the bottom of the pond or lake (the benthic zone) where decomposers, clams and insect larvae live. Some of the animals that live in the ponds and lakes have interesting adaptations that help them to gain what they need to survive there. For example, cat fish have whiskers that help them sense food as they swim along the dark bottom of the lake. Water beetles use hairs under their bodies to trap air in order to breathe while they dive for food. Amphibians burrow into the mud in the littoral zone to avoid very cold temperatures in regions where the ponds and lakes freeze over. An increase in the amount of nutrients in an aquatic ecosystem is known as eutrophication. A pond or lake that has large amounts of algae and plant growth, as can be seen here, is known as a eutrophic lake or pond. As the amount of algae and plants grows, the number of bacteria feeding on the decaying organisms also grows and these bacteria use the oxygen that is dissolved in the water. This reduces the amount of dissolved oxygen in the water eventually killing the organisms that need oxygen to survive. Lakes and ponds can become eutrophic over a long period of time but this can be speeded up through ‘runoff’. Runoff is precipitation, such as rain, that can wash fertilisers, sewage and animal waste into the body of water. Freshwater Wetlands These are areas of land that are covered in water for at least part of the year. There are two man types: swamps and marshes. Swamps are dominated by woody plants such as trees and shrubs while marshes contain non-woody plants such as reeds. Wetlands perform many environmental functions: Trapping and filtering pollutants, nutrients and sediments and thereby stopping them from entering the reservoirs, lakes and oceans. Reducing the threat of floods, protecting agriculture, buildings, roads and human health and safety. Buffering shorelines against erosion. Providing habitat for rare, threatened, endangered and migratory species. Providing spawning grounds and habitat for commercially important fish and shellfish. Providing recreational areas for activities such as fishing, bird watching, photography and painting, canoeing and hiking. Wetlands act as filters and sponges because they absorb and remove pollutants from the water that flows through them and in doing so improve the water quality of rivers, lakes and reservoirs downstream. Wetland vegetation also traps carbon which could otherwise be released as carbon dioxide (CO2) that may be linked to rising atmospheric temperature. Marshes Freshwater marshes tend to occur on low, flat lands that have little water movement. Plants such as reeds and rushes root themselves in the rich bottom sediments of the shallows and the leaves of these plants stick out above the surface of the water all year round. The nutrient rich benthic zones of the marshes contain plants, many types of decomposers and scavengers. Water fowl such as ducks have flat beaks that have adapted in order for the bird to sift through the water for fish and insects. Herons have spear like beaks that enable them to grab fish and probe the mud for frogs. Marshes also attract many migratory birds from tropical and temperate habitats. The salinity of marshes varies. Some have water that is as salty as the oceans whereas others have only slightly salty (brackish) water and this dictates the organisms that live in and around the marshes as they will be adapted to a specific range of water salinity. Swamps Swamps are found on flat, badly drained land that is usually near a stream. The plant life (trees and shrubs etc.) in a swamp depends on the salinity of the water and the climate of the area; e.g. mangroves are trees that grow in saltwater swamps in tropical climates. Freshwater swamps are great habitats for amphibians such as frogs, newts and salamanders because of the consistent moist environment. Swamps also attract birds such as wood ducks that nest in hollow trees that are near or over the water. Reptiles such as alligators are the predators of the swamps and will eat any organism that crosses their path!! The Impact of Humans on Wetlands At one time wetlands were considered to be wastelands that provided breeding grounds for disease carrying insects and because of this many wetlands have been drained, filled and cleared for farms and residential and commercial developments. For example the Florida Everglades once covered 8 million acres of southern Florida but now covers less than 2 million acres (Environmental Science, Arms, page 189). The importance of the wetlands as water purifiers and flood preventors has now been recognised. Wetlands are vital habitats for wildlife and laws are now in place to protect them. Rivers Many rivers originate from snow melt in mountains and at its headwaters it is usually cold, full of oxygen and moves quickly through a shallow riverbed. As a river flows down a mountain it becomes slower, wider, warmer and contains more vegetation and less oxygen. A river changes with the land and the climate it flows through. For example, as we mentioned earlier, runoff may wash sediment and nutrients from the land into the water and these substances will affect the health and growth of the organisms in the water. Near the headwaters, mosses anchor themselves to rocks using root like structures called rhizoids. Fish such as trout and minnows are adapted to the oxygen rich cold waters. The trout is a powerful swimmer and has a streamlined body that gives very little resistance to the strong currents of the headwaters. Further downstream plants set roots in the rich sediment and some plants leaves vary in shape depending on the strength of the current. Fish such as carp and catfish also live in these calmer waters. The human population and industry have affected the health of the rivers. We use the water from the rivers to use in the home and industry take water to use as a coolant, for example. Sewage (treated to various levels or, in some cases, not at all) is disposed of in rivers as well as garbage and this has polluted the water with toxins. These toxins, in some areas, have made river fish unsuitable to eat and have killed many other river organisms. Runoff from the land puts pesticides and other poisons into the watercourse and covers the riverbed with toxic sediments. The massive dams that have been built also alter the ecosystems in and around the rivers. Marine Ecosystems These are ecosystems that contain salt water and are found in and around the world’s oceans. In open water the amount of sunlight and nutrients vary for one part of the ocean to another. In coastal areas we usually find that the salinity and water level change during the day. Coastal Wetlands These areas are covered with salt water for all or at least part of the day. They provide nesting and habitat for a wide variety of fish and other wildlife. The coastal wetlands also protect areas from flooding by absorbing the excess rain. They filter out sediments and pollutants and support recreational areas for hunting fishing and boating. Many of these wetlands form in estuaries. An estuary is an area where fresh river water and salty sea water mix. Populations This section will introduce basic concepts that ecologists use to study ecosystems. It will explore Properties of populations, how populations change in size in response to their environment and how populations of different species interact. Orcas – AKA Killer Whales – hunt and eat sea lions. Would a change in the number of sea lions have an effect on the orcas? Would it make a difference if the sea lions were the only food source for the orcas? A population is the members of a species living in the same area at the same time. It is a reproductive group because organisms usual breed with members of their own population. For example, a field full of poppies will breed with each other and not with poppies in a field in another county. Population refers to the group in general and the number of individuals in it. The famous biologist Charles Darwin calculated that a pair of elephants could theoretically produce 19 million descendants inside 750 years pointing out that the actual number of elephants was limited by their environment. Activity: You have been offered a job for one month (31 days) and you have been given 2 salary options. You can either receive £10 per week with a £5 per week raise every week or you can receive 1 penny for your first day and then double the previous day’s pay for each of the remaining 30 days. Choose one of the two options and calculate your salary for the month. Once you have done that calculate what the other option would pay. Populations may grow in size by either of these 2 ways as we will see as we investigate. Populations can be described in terms of density, dispersion or size. A population’s density is the number of individuals per unit area or volume such as the number of a particular species of fish in a lake. A population’s dispersion is the relative arrangement or distribution of the individuals within a known amount of space. This dispersion could be random, clustered or evenly spread and these properties can be used to predict changes within populations. Populations Growth Each new offspring or birth increases the number of individuals in a population and each death decreases that number of individuals. The change n the size of a population over time can be shown by the following equation: CHANGE IN POPULATION SIZE = BIRTHS - DEATHS A change in the size of a population over a specific period of time is known as its GROWTH RATE. GROWTH RATE = BIRTH RATE - DEATH RATE The growth rate and death rate of a population changes over time because birth rates and death rates increase and/or decrease. Growth rates can be positive, negative or zero and for the growth rate to be zero, the average number of births must equal the average number of deaths. For example, if each pair of adults in the population managed to produce 2 offspring, and each of the offspring survived to reproduce, the population would stay the same size. If the adults are not replaced in the population by new births then the population will decrease; that is the growth rate will be negative. (complete lab worksheet) How Fast? A female sea turtle could lay as many as 2000 eggs n her lifetime and if all of them were to survive, the turtle population would grow extremely fast!! Unfortunately not all of the hatchlings survive and populations usually remain about the same size year after year. This is because various factors kill many individuals before they have a chance to reproduce and it is these factors that control the size of populations. The fastest rate that a species’ population can grow s called its biotic potential and it is limited by the maximum number of offspring each member of the population can produce. This is called its reproductive potential. As one might imagine, some species have a much higher reproductive potential than others. For example, as mentioned earlier, Darwin calculated that a pair of elephants could produce 19 million descendants in under 750 years; whereas a single bacterium can produce 19 million descendants in of days or weeks!!! Environmental Science 2010-2011 Population Growth Lab Worksheet Count out 5 beans to represent the starting population of a species. Assume that 20% of the species each have 2 offspring and also assume that 20% of the species die each year. Use the equation: CHANGE IN POPULATION SIZE = BIRTHS - DEATHS Calculate the number of beans to add or subtract for 1 year. If necessary, round to whole numbers and add to or remove beans from your population as required. Record the change, if any, in population size. Repeat modelling your species population over a period of 10 years. Draw a graph of your results. Independent variable on the x-axis, dependent variable on the y-axis.