BIOGEOCHEMICAL CYCLES

Transcription

1 BIOGEOCHEMICAL CYCLES

2 BASICS Biogeochemical Cycle: The complete path a chemical takes through the four major components, or reservoirs, of Earth s system (atmosphere, lithosphere, hydrosphere and biosphere) Atmosphere: Layer of gasses surrounding the Earth. Divided into 4 layers (troposphere, stratosphere, mesosphere, thermosphere) Lithosphere: The outer layer of the Earth, approx. 100km thick, of which the plates that contain the ocean basin and continents are composed Hydrosphere: The water portion of our planet consisting of surface freshwater, oceans, glaciers, groundwater and atmospheric water (clouds) Biosphere: 1. That part of a planet where life exists 2. The planetary system that includes and sustains life

3 BASICS BIOGEOCHEMICAL It is bio because it involves life It is geo because the cycle may include the atmosphere, hydrosphere, rocks and soil It is chemical because it is chemicals that are cycled

4 GENERAL CONCEPTS 1. Some chemical elements (e.g. O, N) cycle quickly and are readily regenerated for biologic activity. Typically these elements have a gas phase and are present in the atmosphere and/or easily dissolved in water and carried by the hydrologic cycle 2. Other chemicals are easily tied up in relatively immobile forms and are returned slowly, by geologic processes, to where they can be reused by life. They typically lack a gas phase and are not found in significant concentrations in the atmosphere. They are also relatively insoluble in water (e.g. P)

5 GENERAL CONCEPTS 3. Most required nutrient elements have a light atomic weight. The heaviest required micronutrient is iodine 4. Since life evolved it has greatly altered biogeochemical cycles and this alteration has changed our planet in many ways 5. The continuation of processes that control biogeochemical cycles is essential to the long term maintenance of life on Earth

6 GENERAL CONCEPTS All living things are made up of chemicals (24 out of the more than 103 known chemicals are required for life) Macronutrients: Elements required in large amounts by living things. Include the big 6 (C, H, O, N, P, S) Micronutrients: Chemical elements required in very small amounts by at least some forms of life. (e.g. B, Cu, Mo) Limiting Factor: The single requirement for growth available in the least supply in comparison to the need of the organism Some elements can be toxic even at low concentrations (e.g. Hg) while other elements that are essential in small concentrations can be toxic at higher concentrations (e.g. Cu)

7 PERIODIC TABLE OF THE ELEMENTS

8 SIMPLIFIED BIOGEOCHEMICAL CYCLE Source: Refers to a compartment that donates to another compartment Sink: Refers to a compartment the receives materials (e.g. a chemical element)

9 GEOLOGICAL CYCLE Geologic Cycle: The processes responsible for the formation and change of Earth materials Encompassing term for: Tectonic cycle Rock Cycle Hydrologic Cycle Biogeochemical cycle

10 TECTONIC CYCLE It involves the creation/destruction of the Earth s outer layer (lithosphere) The lithosphere is broken into large plates that move relative to each other (plate tectonics) at a rate of 2-15cm per year Process driven by heat from the interior (which rises) while at the same time cooler denser slabs sink bank into the Earth s crust setting the plates in motion Impacts: Changes the position, size and shape of continents Can change ocean and atmospheric circulation patterns leading to environmental change Can also create ecological islands, leading to the development of new species Boundaries are geologically active areas (earthquakes and volcanoes) Types of plate boundary: Convergent, divergent, transform

11 TYPES OF PLATE BOUNDARIES Convergent boundaries Plates move into each other Leads to the destruction of lithosphere Types: Continental crust and oceanic crust Continental crust less dense than oceanic crust Therefore oceanic crust gets subducted while the continental crust floats on top Can lead to extensive volcanism e.g. The Andes mountains of South America Continental crust and Continental Crust Both crusts of equal density Leads to buckling, fracturing and deformation of the crust e.g. The Himalaya s Oceanic Crust and Oceanic Crust One is thrust underneath another Leads to extensive volcanism Can lead to the formation of volcanic island arcs e.g. Mariana islands

12 TYPES OF PLATE BOUNDARIES Divergent boundaries Plates are moving apart, leads to the production of new lithosphere Typically occurs at mid-ocean ridges (seafloor spreading) e.g. The Atlantic Ocean Transform boundaries Occurs where plates grind past each other Lithosphere is not being created or destroyed e.g. San Andreas Fault

13 MAJOR GLOBAL TECTONIC PLATES

14 THE HYDROLOGIC CYCLE The transfer of water from the oceans, to the atmosphere, to the land and then eventually back to the oceans Has the following components Evaporation from the ocean Precipitation on land Evaporation from land Transpiration by vegetation Surface runoff (streams, rivers) Subsurface flow Storage on land (lakes, dams, glaciers) Evaporation from lakes and dams

15 THE HYDROLOGIC CYCLE Process driven by solar energy Distribution of water: Oceans: 97% Glaciers and ice caps: 2% Shallow ground water: 0.8% Lakes and rivers: 0.01% Atmosphere: 0.001% The rate of transfer of water from the land to the ocean is relatively low The land and ocean somewhat isolated from the hydrologic cycle Most of the rainfall in the ocean came from water evaporated from the ocean and likewise for land

16 THE HYDROLOGIC CYCLE Units: thousands of km 3 /yr Approx. 60% of the water that precipitates on land evaporates back to the atmosphere, while 40% flows back to the ocean Water is not evenly distributed on land as this has environmental implications

17 THE ROCK CYCLE A group of processes that produce igneous, sedimentary and metamorphic rocks The rock cycle can serve as a sink for carbon (formation of coal or anthracite) Additional elements can also be incorporated into rock such as limestone (a sink for Ca) Additionally certain gasses can be released into the atmosphere during the formation of igneous rocks (the extrusive variety) Rocks, through the process of weathering, can be a source of a variety of chemical elements into the environment

18 THE CARBON CYCLE Atmosphere: Exists in a gaseous state (CO 2, CH 4 ) Removed from atmosphere by: Photosynthesis Diffusion with ocean Introduced into atmosphere by: Respiration Wildfires Burning of fossil fuels Decomposition of organic materials Diffusion with ocean Volcanic eruptions

19 THE CARBON CYCLE Hydrosphere Exists as dissolved CO2, or as CO -2 3, HCO - 3 Removed from ocean by: Photosynthesis of algae and photosynthetic organisms Diffusion with atmosphere Formation of CaCO 3 in sea shells Introduced into ocean by: Respiration of marine organisms Diffusion with atmosphere Rivers (dissolved CO 2, organic particles) Wind

20 THE CARBON CYCLE Biosphere Plants take up C during the process of photosynthesis Higher trophic levels obtain their C by feeding on the lower trophic levels Decomposition of material is decomposed into organic compounds as well as CO 2 In areas where there is not enough oxygen or the temperature is too low, the rate of decomposition slows down and organic material accumulates

21 THE CARBON CYCLE Lithosphere Very small constituent of crust (0.035% by weight) The accumulated organic material in land systems can over time become compressed by geologic forces This compression squeezes out O and H (contained within the organic material) increasing the carbon content leading to the formation of coal In marine systems the compression of organic material (mostly phytoplankton) leads to the formation of oil and natural gas The formation of limestone (CaCO 3 ) in marine environments is also a sink for carbon

22 THE CARBON CYCLE Units: billions of metric tonnes

23 THE PHOSPHOROUS CYCLE Atmosphere: P does not have a gaseous phase on Earth Found in the atmosphere only in small particles of dust Hydrosphere: P tends to form compounds that are relatively insoluble in water Transported by rivers to the oceans in soluble form or as suspended particles Runoff of industrial and agricultural wastes can introduce phosphates into water systems. (can lead to environmental degradation -Eutrophication)

24 THE PHOSPHOROUS CYCLE Biosphere Enters biota through uptake of phosphate by plants, algae and photosynthetic bacteria Can be returned to land by pelagic birds that feed on fish which in turn feed on plankton which take up P These birds nest on off shore islands and their P rich excrement accumulates (guano). These accumulations can be up to 40m thick Lithosphere Occurs in an oxidised state (phosphate) Combines with Ca, Mg, K, Fe to form minerals Rate of transfer slow compared to that of C or N Recycled in marine sediments to become part of the rock cycle

25 THE PHOSPHOROUS CYCLE