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EUTROPHICATION, etc. READINGS: FREEMAN, 2005 Chapter 54 Pages 1261-1262.

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Presentation on theme: "EUTROPHICATION, etc. READINGS: FREEMAN, 2005 Chapter 54 Pages 1261-1262."— Presentation transcript:

1 EUTROPHICATION, etc. READINGS: FREEMAN, 2005 Chapter 54 Pages 1261-1262

2 EUTROPHICATION Eutrophication is the accumulation of nutrients in aquatic ecosystems. It alters the dynamics of a number of plant, animal and bacterial populations; thus, bringing about changes in community structure. It is a form of water pollution and like all other forms of pollution is the result of human activities influencing ecological cycles.

3 POLLUTION Pollution is the contamination of the environment by humans adding any substance or energy. Heavy metals, gases, oil, sewage, noise, heat, radiation and pesticides are common pollutants that can affect the environment adversely. A pollutant is any matter or energy introduced by human activities that produces harmful effects on resident populations thus altering community structure.

4 Pollutants, Population Dynamics and Community Structure Pollutants may be toxic (effect survival and/or reproduction of individuals) thus directly affect population dynamics. 1. Radioactive Atoms (Radioisotopes) ….. I 131, St 90, etc. 2. Heavy Metals ….. Cu, Hg, Pb, etc. 3. Man-made Organic Molecules ….. DDT, PCB’s, Dioxin, 2-4-5 T, etc.

5 Pollutants, Population Dynamics and Community Structure Pollutants may alter the abiotic environment thus indirectly affect population dynamics 1. Increases in Atmospheric Gases …ozone (smog, uv radiation) …sulfur dioxide (acid rain) …CO 2 (greenhouse effect) …ammonia/nitrates (nitrogen deposition) 2. Waste Heat (thermal pollution) 3. Nutrient Enrichment (eutrophication)

6 Trophic Transfer, Biological Magnification and Toxic Substances I The movement on compounds (molecules) through trophic levels is called trophic transfer. Toxic substances, like nutrients, can be transferred through trophic levels. Substances that can not be metabolized are particularly suitable for trophic transfer, as are radioactive atoms.

7 Trophic Transfer, Biological Magnification and Toxic Substances II Biological magnification is the increase in concentration of a substance in successive members of a food chain. Toxic substances may accumulate in members of higher trophic levels as a result of biomagnification. Two classic examples of substance that are biomagnified are 1) Strontium 90 and 2) DDT.

8 Trophic Transfer and Biological Magnification of Strontium 90 I St 90 is a radioactive material with a 1/2 life of 28.1 years. Half life is a measure of how long it will take for the mass of the substance to decrease over time. For example, a kilogram of a radioactive compound with a 1/2 life of 10 years will weigh one half of a kilogram is left to sit from 1996 to 2006. By 2016, it will weigh one quarter of a kilogram.

9 Trophic Transfer and Biological Magnification of Strontium 90 I St 90 is a radioactive material with a 1/2 life of 28.1 years. Half life is a measure of how long it will take for the mass of the substance to decrease by half.

10 Trophic Transfer of Strontium 90 in a Canadian Lake II The concentration of St 90 tends to increase at successive trophic levels. The lake was thousands of miles from the South Pacific location of the nuclear test. The radioactive materials had been carried by atmospheric circulation.

11 Trophic Transfer and Biological Magnification of Strontium 90 III The Canadian lake example shows how a radioactive material is concentrated as it enters a food web. This is known as biomagnification. Biomagnification of St 90 is due to: 1) physiological similarity with calcium; a mineral nutrient retained by plants and animals; 2) biomass transfer through food chains.

12 Trophic Transfer and Biological Magnification of DDT (I) DDT is one of a class of compounds known as chlorinated hydrocarbons. Widely used to kill mosquitoes after WWII. Widespread use banned in US in 1972.

13 Trophic Transfer and Biological Magnification of DDT (II) DDT, like radioactive elements, once released into the environment may enter meteorological and ecological cycles that distribute it and concentrate it to dangerous levels. Studies show that it can persist in the environment for 15 to 25 years.

14 Trophic Transfer and Biological Magnification of DDT (III) The concentration of DDT tends to increase in food chain from one trophic level to the next. Those at the top of the food chain receive the largest doses. Biomagnification of DDT is due to: 1) high solubility in tissue fats; low in water; 2) very low rate of metabolism; low loss from body; 3) biomass transfer from one trophic level to next.

15 Trophic Transfer, Biological Magnification and Toxic Substances Pesticides, PCB’s, dioxins, radioisotopes, heavy metals and similar substances are biomagnified. As a rule of thumb, their concentration increases 10 fold as biomass is transferred from one trophic level to the next. See illustration.

16 Pollutants that Act Through the Abiotic Environment There are groups of pollutants that are not directly toxic as they are emitted into the abiotic environment but accumulate to such an extent that they effect community structure. Examples are: 1. Increases in Atmospheric Gases …nitrogen oxides (smog, uv radiation) …sulfur dioxide (acid rain) …CO 2 (greenhouse effect) …ammonia/nitrates (nitrogen deposition) 2. Waste Heat (thermal pollution) 3. Nutrient Enrichment (eutrophication)

17 Nitrogen Oxides and Ozone (I) Nitrogen oxides (N 2 O, NO and NO 2 ) form a major component of photochemical smog. When they combine with hydrocarbons in the presence of sunlight, the result is ozone (O 3 ), the major component of smog.

18 Pollution Sources of Nitrogen Oxides Photochemical smog in urban areas is common due to the fact that vehicles emit both nitrogen oxides and hydrocarbons. It is responsible for respiratory problems. It is also known to result in damage to crops.

19 Global Effects of Nitrous Oxide (N 2 O) The concentration of nitrous oxide has been increasing in the atmosphere for the last 30- 40 years at a rate of 0.2-0.3% per year. It absorbs infrared radiation (heat); thus, contributes to global warming. In the stratosphere, it reacts with ozone in the stratosphere and thus contributes to ozone depletion. Thus, allowing increased ultraviolet radiation to reach the earth.

20 Sulfur Dioxide and Acid Rain Sulfur dioxide (SO 2 ) is a colorless gas produced by combustion of fossil fuels at power plants and certain industrial sources. It along with nitrogen oxides results in acid rain. The impact of acid rain in Europe has been sever and is most noticed in forests of the northeastern US.

21 Other Pollutants that Act Through the Atmosphere The increased use of fossil fuels has resulted in an increase in CO 2, a greenhouse gas. Its effects will be discussed in the lecture on climate change. Increases in atmospheric ammonia and nitrate find their way into the rain that hits the earth. The potential effects of nitrogen deposition on natural ecosystems will be discussed in lecture in two weeks.

22 Acid Rain Sulfuric and nitric acids formed in cloud droplets can give extremely low pH. Water collected at the base of clouds in eastern US have been as low as 2.6 In L.A, values as low as 2 have been recorded- the acidity of lemon juice.

23 Thermal Pollution Many industries take water from a lake, stream or inlet and use it to cool equipment or products. Often this increases the temperature of the water so that it kills fish or stimulates algal growth. The result is eutrophication. Sometimes this increase in productivity is beneficial.

24 EUTROPHICATION The nutrient enrichment of an aquatic ecosystem. Natural Eutrophication -- a process that occurs as a lake or river ages over a period of hundreds or thousands of years. Cultural Eutrophication -- a process that occurs when humans release excessive amounts of nutrients; it shortens the rate of aging to decades.

25 Natural Eutrophication Lake classification based on nutrient content and production of organic matter. Oligo- nutrient poor; meso- middle nutrient; eu- nutrient rich.

26 Cultural Eutrophication The addition of excess nutrients from a variety of sources results in the rapid aging of aquatic ecosystems. During this process the species composition of the aquatic community changes.

27 Water Chemistry and Eutrophication (I) Eutrophication brings about changes in water chemistry. These include: pH Dissolved O 2 CO 2 Ammonia Nitrates/Nitrites Phosphates

28 Water Chemistry and Eutrophication (II) pH -- The pH of water reflects the CO 2 contents as well as the presence of organic and inorganic acids. Values below 5 and above 9 are definitely harmful to fish and limit growth of algal and invertebrate populations. Dissolved O 2 -- The amount of dissolved oxygen in water varies with temperature and pressure; high temperature or pressure, low oxygen. Most invertebrates die if oxygen levels fall below 4-5 mg/l for extended periods of time. Game fish (bass, perch, trout, etc) require oxygen to be in the range of 8-15 mg/l.

29 Water Chemistry and Eutrophication (III) CO 2 -- Carbon dioxide is largely a product of aerobic and anaerobic decomposition of organic matter. It reacts with water to form carbonic acid. Normal concentrations are usually less than 1 mg/l. Fish are affected at higher levels and continued exposure to 10mg/l or more is fatal to many species. Phosphates -- Present in low quantities in natural waters; less than 0.01 mg/l. Released during decomposition. High levels stimulate algal blooms.

30 Water Chemistry and Eutrophication (IV) Ammonia (NH 3 or NH 4 + ) -- Ammonia is a product of decomposition of animal and plant protein. It is an important plant nutrient. Natural bodies of water contain > 1 mg/l. Levels higher than this stimulate algal growth and are toxic to fish. Nitrates/Nitrites -- These N containing compounds are formed during decomposition and are inter-converted by certain species of bacteria. Natural concentrations rarely exceed 10 mg/l and are often > 1mg/l.

31 Major Sources of Excess Nutrients Major sources of excess nutrients are agricultural fertilizers, domestic sewage and livestock wastes. Agricultural fertilizers provide inorganic nutrients. Sewage and wastes provide both inorganic and organic nutrients.

32 Overview of Cultural Eutrophication Start with clear water stream or blue water lake. Introduction of organic and/or inorganic nutrients. The pathways of these two nutrient sources differ. Follow organic pathway first; inorganic nutrient pathway second.

33 Oligotrophic Aquatic Ecosystems A clear water stream or deep blue lake contains enough bacteria to decompose organic material from organisms that die. Water is neither acidic or basic. Inorganic nutrients are present in low concentrations. Ammonia produced by animals and bacteria is taken up and used for plant growth.

34 Excess Organic Matter Untreated sewage, manure, paper pulp, packing plant wastes are sources of excess organic matter added to aquatic ecosystems. Results in exponential growth of bacterial populations. Bacteria deplete dissolved oxygen in the water.

35 Low Oxygen Levels Cause Die-off Rapidly growing bacterial populations need exponentially increasing amounts of oxygen. Once dissolved oxygen levels become too low, fish and many freshwater invertebrates die, thus adding more organic matter.

36 Oxygen Depleted Waters As oxygen disappears, anaerobic bacteria produce methane, hydrogen sulfide and ammonia. Bacterial respiration increases carbonic acid. In all but the most oxygen depleted waters, tubificid worms, midge larvae and mosquito larvae replace oxygen-loving invertebrates.

37 Oxygen Replenishment If organic material is not continually added or the water moves downstream, bacteria eventually use up their food and populations decline. The concentration of dissolved oxygen increases, either through atmospheric replenishment or increased photosynthesis.

38 Recovering Aquatic Ecosystem If stocks are available then fish can recolonize and the stream or lake will recover. Carp, which tolerate low oxygen levels, do well. Oxygen-loving species such as trout, bass and other game fish may return.

39 Recovering Aquatic Ecosystem If available freshwater invertebrates recolonize, then the stream or lake can recover. Oxygen-loving species such dragonfly, mayfly, caddis fly, stone fly larvae may return.

40 Oligotrophic Aquatic Ecosystems A clear water stream or deep blue lake contains enough bacteria to decompose organic material from organisms that die. Water is neither acidic or basic. Inorganic nutrients are present in low concentrations. Ammonia produced by animals and bacteria is taken up and used for plant growth.

41 Excess Inorganic Nutrients Agricultural runoff from fertilizers and effluent from secondary sewage treatment plants are the primary sources of inorganic nutrient addition to aquatic ecosystems. These sources are rich in nitrogen and phosphorus.

42 Nutrients Stimulate Algal Blooms Nitrogen and phosphorus from runoff and effluents or decay of organic matter stimulates aquatic plant growth. In particular, algal “blooms” give the water a green or blue-green color.

43 Plants Die, Bacteria Grow, Deplete Oxygen, Fish Die 1.Plants exhaust nutrients and die. 2.Bacteria thrive on organic decay of plants and lower dissolved oxygen. 3.Fish and invertebrates die when oxygen gets too low.

44 Oxygen Replenishment and Ecosystem Recovery In temperature regions, the growing season ends. Bacteria eventually use up their food and populations decline. The concentration of dissolved oxygen increases, either primarily through atmospheric replenishment. If stocks are available then fish and invertebrates can recolonize and the stream or lake will recover.

45 The Good News Since the 1970’s, many of the worst conditions that lead to air and water pollution have been abated. The last above ground nuclear tests occurred in China. The catalytic converters lowered hydrocarbon emissions, but increased nitrogen oxide emissions; thus requiring new technology. Some of the worst cases of water pollution have been addresses and in some cases reversed.

46 EUTROPHICATION, etc. READINGS: FREEMAN, 2005 Chapter 54 Pages 1261-1262


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