University of KhartoumInstitute of Environmental Sciences

Dip/ M.Sc in Enviromental Sciences

Fundamentals of Environmental Science

By: Dr. Zeinab Osman Saeed

Basic ecological principles

lecture nu 2

Dr. Zeinab Osman

The world's biomes Biomes are defined as "the world's major communities, classified according to the predominant vegetation and characterized by adaptations of organisms to that particular environment.The importance of biomes cannot be overestimated.

The world's biomes Biomes have changed and moved many times during the history of life on Earth. More recently, human activities have drastically altered these communities. Thus, conservation and preservation of biomes should be a major concern to all.

The freshwater biome Freshwater is defined as having a low salt

concentration — usually less than 1%. Plants and animals in freshwater regions are adjusted to the low salt content and would not be able to survive in areas of high salt concentration (i.e., ocean). There are different types of freshwater regions:

Ponds and lakes Streams and rivers Wetlands

A lake at Maine.

The marine biome Marine regions cover about three-fourths of

the Earth's surface and include oceans, coral reefs, and estuaries. Marine algae supply much of the world's oxygen supply and take in a huge amount of atmospheric carbon dioxide. The evaporation of the seawater provides rainwater for the land.

Oceans Coral reefs Estuaries

Reef fish and coral in the central Pacific.

The desert biomeDeserts cover about one fifth of the Earth's

surface and occur where rainfall is less than 50 cm/year. Most deserts have a considerable amount of specialized vegetation, as well as specialized vertebrate and invertebrate animals. Soils often have abundant nutrients because they need only water to become very productive and have little or no organic matter. Disturbances are common in the form of occasional fires or cold weather, and sudden, infrequent, but intense rains that cause flooding.

Sand dunes in Death Valley, California.

The desert biomeThere are relatively few large mammals

in deserts because most are not capable of storing sufficient water and withstanding the heat. Deserts often provide little shelter from the sun for large animals. The dominant animals of warm deserts are non mammalian vertebrates, such as reptiles. Mammals are usually small, like the kangaroo mice of North American deserts.

The desert biomeDesert biomes can be classified according to several characteristics.There are four major types of deserts:

Hot and dry Semiarid Coastal Cold

The Forest BiomeForests occupy approximately one-

third of Earth's land area, account for over two-thirds of the leaf area of land plants, and contain about 70% of carbon present in living things. However, forests are becoming major casualties of civilization as human populations have increased over the past several thousand years, bringing deforestation, pollution, and industrial usage problems to this important biome.

The Forest BiomePresent-day forest biomes, biological communities that are dominated by trees and other woody vegetation can be classified according to numerous characteristics, with seasonality being the most widely used. Distinct forest types also occur within each of these broad groups.

The Forest BiomeThere are three major types of forests, classed according to latitude:

Tropical Temperate Boreal forests (taiga)

A Wisconsin forest.

The grassland biome  Grasslands are characterized as lands dominated by grasses rather than large shrubs or trees There are two main divisions of grasslands:

Tropical grasslands or savannas Temperate grasslands

A grassland in California.

The tundra biome Tundra is the coldest of all the

biomes. It is noted for its frost-molded landscapes, extremely low temperatures, little precipitation, poor nutrients, and short growing seasons. Dead organic material functions as a nutrient pool. The two major nutrients are nitrogen and phosphorus. Nitrogen is created by biological fixation, and phosphorus is created by precipitation.

The tundra biomeCharacteristics of tundra include:Extremely cold climate Low biotic diversity Simple vegetation structure Limitation of drainage Short season of growth and reproduction Energy and nutrients in the form of dead

organic material Large population oscillations

The tundra biomeTundra is separated into two types:

Arctic tundra Alpine tundra

Tundra along the Colville River, Alaska.

ECOSYSTEM INTERACTIONSEcosystems (short for ecological systems) are functional units that result from the interactions of abiotic, biotic, and cultural (anthropogenic) components. Like all systems they are a combination of interacting, interrelated parts that form a unitary whole.

ECOSYSTEM INTERACTIONSAll ecosystems are "open" systems in the sense that energy and matter are transferred in and out. The Earth as a single ecosystem constantly converts solar energy into organic products, and has increased in biological complexity over time.

ECOSYSTEM INTERACTIONSNatural ecosystems, made up of

abiotic factors (air, water, rocks, energy) and biotic factors (plants, animals, and microorganisms). The Earth’s biosphere, including the atmosphere (air), hydrosphere (water), and litosphere (land), constitutes a co-evolutionary process between living things and their physical and chemical environments.

ECOSYSTEM INTERACTIONSEcosystem is made up of many

smaller ecosystems interlocked through cycles of energy and chemical elements. The flow of energy and matter through ecosystems, therefore, is regulated by the complex interactions of the energy, water, carbon, oxygen, nitrogen, phosphorus, sulfur, and other cycles that are essential to the functioning of the biosphere.

EcosystemAn array of organisms and their physical environment, all of which interact through a one-way flow of energy and a cycling of materials. Most of the energy originally fixed by the autotrophs is lost to the environment as metabolic heat.

Structure of ecosystemsTrophic levels: All the organisms in an ecosystem that are the same number of transfer steps away from the energy input into the system

Structure of ecosystems1. Producers: autotrophic ("self-

feed") organisms; produce the carbon and energy they need. Examples: photoautotrophs (plants, plankton) and chemoautotrophs (sulfur bacteria)

2. Consumers: heterotrophic organisms; obtain energy and carbon by feeding on the tissues of other organisms. Herbivores, carnivores, and parasites are examples.

Biogeochemical Cycles

Biogeochemical Cycles nutrient flow through ecosystemsPrimary producers require carbon, oxygen, and hydrogen, which they obtain from water and air. They also require nitrogen, phosphorus, and other minerals. Chemical elements and nutrients move in biogeochemical cycles. In such cycles, ions or molecules of a nutrient are transferred from the environment to organisms, then back to the environment--part of which serves as a reservoir for them.

Biogeochemical Cycle The cycling of chemical elements required by life between the living and nonliving parts of the environment. Some examples of these chemical elements are H2O, P, S, N2, O2 and C.

These elements cycle in either a gas cycle or a sedimentary cycle; some cycle as both a gas and sediment.

In a gas cycle elements move through the atmosphere. Main reservoirs are the atmosphere and the ocean.

In a sedimentary cycle elements move from land to water to sediment. Main reservoirs are the soil and sedimentary rocks.

Gas                                         Sedimentary Carbon                                               

Phosphorus Nitrogen                                              Sulfur Oxygen

Carbon Cycle Carbon (C) enters the biosphere

during photosynthesis:     CO2 + H2O ---> C6H12O6 + O2 + H2O

Carbon is returned to the biosphere in cellular respiration:   O2 +H2O + C6H12O6 ---> CO2 +H2O + energy

Carbon Cycle

Oxygen Cycle 1)As a constituent of CO2 it circulates freely

throughout the biosphere.2) Some CO2 combines with Ca to form carbonates.3) O2 combines with nitrogen compounds to form

nitrates.4) O2 combines with iron compounds to form ferric

oxides. 5) Photosynthesis and respiration 6) O2 in the troposphere is reduced to O3 (ozone).

   Ground level O3 is a pollutant which damages lungs.  

Oxygen Cycle

Nitrogen CycleNitrogen (N) is an essential constituent of protein, DNA,RNA, and chlorophyll.

N is the most abundant gas in the atmosphere, but it must be fixed or converted into a usable form.

Nitrogen Fixation Methods  1) High energy fixation- a small amount of

atmospheric nitrogen is fixed by lightening. The high energy combines N and H2O resulting in ammonia (NH3) and nitrates (NO3). These forms are carried to Earth in precipitation.

2) Biological fixation: achieves 90% of the nitrogen fixation. Atmospheric nitrogen (N2) is split and combined with hydrogen (H) atoms to form ammonia (NH3).

Who performs nitrogen fixation?- symbiotic bacteria (eg. Rhizobium spp.) living in

associatin with leguminous ( plants in the pea family), and root-noduled non- leguminous plants (eg. Alnus spp.). - free-living anaerobic bacteria - blue-green algae (cyanobacteria)

Once NH3 is in the soil it combines with H+ ions to form ammonium ion (NH4), or without it to form NO3. NH4+ and NO3 are readily absorbed by plants.

Nitrogen Cycle

Phosphorus Cycle - Component of DNA, RNA, ATP, proteins and

enzymes  - Cycles in a sedimentary cylce. A good example

of how a mineral element becomes part of an organism.

- The source of Phosphorus (P) is rock. - It is released into the cylce through erosion or

mining. - It is soluble in H2O as phosphate (PO4) - It is taken up by plant roots, then travels

through food chains. - It is returned to sediment

Phosphorus Cycle

Sulfur Cycle - Component of protein

- Cycles in both a gas and sedimentary cycle. - The source of Sulfur is the lithosphere(earth's crust). - Sulfur (S) enters the atmosphere as  hydrogen sulfide (H2S) during fossil fuel combustion, volcanic eruprtions, gas exchange at ocean surfaces, and decomposition.               

Sulfur Cycle - H2S is immediately oxidized to sulfur

dioxide (SO2)- SO2 and water vapor makes H2SO4 ( a

weak sulfuric acid), which is then carried to Earth in rainfall.

- Sulfur in soluble form is taken up by plant roots and incorporated into amino acids such as cysteine. It then travels through the food chain and is eventually released through decomposition.  

Sulfur Cycle