University of Khartoum Institute of Environmental Sciences Dip/ M University of Khartoum Institute of Environmental Sciences Dip/ M.Sc in Enviromental Sciences Fundamentals of Environmental Science By: Dr. Zeinab Osman Saeed

Ecosystem Interactions Lecture nu 5

Ecosystem An 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.

1. 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.

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

Biogeochemical Cycles nutrient flow through ecosystems Primary 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 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

Oxygen 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.

Nitrogen Cycle

Nitrogen Cycle Nitrogen (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.

Phosphorus 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

Sulfur 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.