Lesson 3: Biogeochemical Cycles Chapter 3 is about biogeochemical cycles, one of my specialties (though the scale at which I usually study cycling of elements is at the ecosystem level, not the global). However, it is surprising how quickly local can be come global. When I worked at Oak Ridge National Laboratory, the 1986 accident at Chernobyl occurred (see pages 199-200 in text). One of the scientists (I was a peon post-doc) called us in and asked us all of us go out and mow our lawns for the next couple of weeks. He expected that it would take about two weeks for radiation from Chernobyl to circle around the world to us and deposit enough on our lawns to be detectable. If I recall right, it took three days. Never underestimate the power of nature to act on a global scale. Big Question: Why Are Biogeochemical Cycles Essential to Long-Term Life on Earth?

What is a Biogeochemical Cycle? A biogeochemical cycle is the complete path a chemical takes through the Earth’s four major reservoirs: atmosphere hydrosphere (oceans, rivers, lakes, groundwaters, and glaciers) lithosphere (rocks and soils) biosphere (plants and animals). A biogeochemical cycle is the complete path a chemical takes through the four major components, or reservoirs, of Earth’s system: (1) atmosphere, (2) hydrosphere (oceans, rivers, lakes, groundwaters, and glaciers), (3) lithosphere (rocks and soils), and (4) biosphere (plants and animals). We term this a biogeochemical cycle because bio pertains to life, geo pertains to Earth (atmosphere, water, rocks, and soils), and it is chemicals that are cycled.

Chemical Sinks Chemicals enter storage compartments - sinks Amount that moves between compartments is the flux net sink - when input exceeds output net source - if output exceeds input. As an example of a chemical in a biogeochemical cycle, consider the very timely carbon (C) atom. A C atom might be emitted from burning coal (which is made up of fossilized plants hundreds of millions of years old). The carbon atom is released into the atmosphere and then taken up by a plant and incorporated into a seed. The seed is eaten by a mouse. The mouse is eaten by a coyote, and the carbon atom is expelled as scat following digestion. Decomposition of the scat allows our carbon atom to enter the atmosphere again. It may also enter another organism, such as an insect, which uses the scat as a resource.

New Carbon versus Fossil Carbon Here is a diagram of a cycle a student drew to illustrate how burning wood doesn’t contribute to global CO2 the way burning coal (a fossil fuel) does. The CO2 2 emitted into the atmosphere is removed by new forest growth. When those trees are cut and burned anew, this completes the cycle and has no net CO2 added to the global C cycle, as long as the forest growth can be continued sustainably.

Essential Elements 24 elements are required for life Macronutrients are required in large quantities carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. Micronutrients are required in small/medium quantities, or not at all in some organisms copper, sodium, iodine See dhmo.org for a discussion of the deadly chemical dihydrogen monoxide. Living things need just 24 elements (depending on how biologists are counting them these days, as it can be hard to establish some elements as essential). All living things are made up of chemical elements, but of the known elements, only 24 are required for life processes. These 24 are divided into two categories: macronutrients, elements required in large amounts by all life; and micronutrients, elements required either in small amounts by all life or in moderate amounts by some forms of life and not at all by others. Macronutrients include the “big six”—elements that form the fundamental building blocks of life: C, H, O, N, P and S. Each of these elements plays a special role in organisms. Carbon is the basic building block of organic compounds. Along with oxygen and hydrogen, carbon forms carbohydrates. Nitrogen, along with these other three, makes proteins. Phosphorus is the “energy element”; it occurs in compounds that are important in the transfer and use of energy within cells in chemicals such as ATP. It is relatively easy to think of life as just a series of chemical reactions, though this is not a very comforting thought for many people. In fact, as an environmental chemist, I’ve learned to "bite my tongue" when people tell me "I don't want chemicals in my food." I kind of know what they mean, but it is an absolutely ridiculous statement. Actually, it is quite possible to make nearly any chemical seem undesirable. For example, please visit the site "www.dhmo.org" and read about the perils of dihydrogen monoxide, a very deadly and potentially toxic substance. What we want to learn in this class is how to have perspective and environmental wisdom.

Essential Elements Here is an interesting look at essential elements. If you’ve studied a little chemistry, you'll note that there are some clear patterns in the distribution of essential elements on the periodic table of the elements. First, as we move across the periodic table from left to right, different number of electrons are transferred (taken or given) during general chemical reactions. The chemistry represented by moving from left to right means that most potential chemical reactions can take place since the range of possibilities for transferring electrons are then well-covered. Second, most essential elements are at the top, which usually means that they are relatively abundant. This is quite helpful, because if a nutrient didn't exist in nature and was required, life couldn't exist. Third, note that the far right column, sometimes call "inert gases" or "noble elements" isn't essential. These atoms have complete electron shells, and don't normally participate in chemical reactions. Inert also means "dead" so these elements aren't likely to do anything for necessary chemical reactions for life.

Geological Cycle The formation and change of Earth materials through physical, chemical, and biological processes. Here is a great move about the Geological Cycle: http://www.britannica.com/EBchecked/topic/229677/geologic-cycle The Earth is about 4.6 billion years old, and during that time, rocks and soils have been continuously created, maintained, changed, and destroyed by physical, chemical, and biological processes. Collectively, the processes responsible for formation and change of Earth materials are referred to as the geologic cycle. The geologic cycle is actually a group of cycles: tectonic, hydrologic, rock, and biogeochemical.

Tectonic Cycle The lithosphere is comprised of several plates floating on denser material. Plates move slowly relative to each other – plate tectonics, Divergent plate boundaries occur at spreading ocean ridges. Convergent plate boundaries occur when plates collide. Plate movements change the location of continents and alter atmospheric and ocean circulation patterns. Plate boundaries are geologically active, producing volcanoes and earthquakes. Though it is comforting to think of the earth as a solid mass, this is not an accurate picture at all. It is well accepted now that the crust of the earth is composed of unique pieces, called tectonic plates, that float on the Earth's mantle (this is the current paradigm). From the original land mass, these plates have slid slowly on the mantle, sometimes away from each other and sometimes bumping into each other. The plates do not move very fast (about 1-12 inches a year), and this distance is too small for us to perceive. Sometimes, however, that overall average movement is seen in rapid shifts that result in earthquakes. There is debate as to what has actually caused plates to move, but many scientists believe that convection currents in the earth's mantle lead to this movement. This convection is exactly the same as warm air rising in a room, and it acts to mix all materials together.

Major Tectonic Plates This slide shows the major tectonic plates. Note the little plate off the northwest coast of the U.S.). This is the Juan de Fuca plate. The forces generated by tectonic plates are responsible for the building of mountains like the Olympics and Cascades in Washington State, and are also responsible for the birth and activity of volcanoes like Washington State's Mt. Rainier. In the case of Seattle, the Pacific plate and the much smaller Juan de Fuca plate all are being forced underneath the North American plate. The process of one plate being pulled underneath another is called tectonic subduction. The forces released under these subductive conditions are some of the most powerful forces in nature. In the history of this region, the occurrence of earthquakes with forces up to 9.0 on the Richter scale are likely. Such an earthquake would release energy nearly a thousand times greater than the energy released by the Seattle earthquake of 2001. That quake caused over a billion dollars in damage. You might imagine what an impact a 9.0 quake would have.

Hydrologic Cycle Evaporation Precipitation Runoff Groundwater The hydrologic cycle includes the transfer of water from the oceans to the atmosphere to the continents and back to the oceans again. As with elements in an ecosystem, there are areas where water is stored for different periods of time, and it cycles from pool to pool over time.

Where Is the Earth's Water? 97% of water is stored in oceans, 2% in glaciers and ice caps, 1% as freshwater on land or atmosphere. Drainage basins or watersheds are the area contributing runoff to a stream or river. Vary in size from a hectare to millions of square miles (e.g. Mississippi River drainage basin). Human impacts include dam construction, irrigation, stormwater runoff. Most of the water on the earth is located in the oceans and saline lakes, with just 2.4% of the Earth's water in the form of fresh water. Eighty-seven percent of earth's fresh water is located in ice and snow, primarily in the world's glaciers. Most of this ice occurs in Greenland and Antarctica. Of the 13% of earth's freshwater that is in the form of liquid water, most is in the earth's groundwater; and most of this groundwater is relatively inaccessible to society. About 3% of the total liquid fresh water on the earth is located in lakes, rivers, and streams, and roughly 2% is stored as soil moisture. Most of the water that society uses comes from lakes, rivers and streams, though only a small proportion of those are near enough to the areas where water is used to be practical. In certain areas (for instance, in the area east of Tacoma, Washington, called the Clover-Chambers Creek region) groundwater is the primary source of fresh water for societal consumption. In some areas, (such as parts of Saudi Arabia where fresh water is very scarce) salt water resources are utilized to produce fresh water for human consumption and even for irrigation of crops. Desalination requires tremendous amounts of energy, and most of that energy is acquired from the abundant oil resources in Saudi Arabia. There also have been proposals to tow icebergs to regions that need fresh water. Though this has never been carried out, glaciers in the oceans are composed of freshwater and also could be a potential source of water for society.

Rock Cycle We have examples of the rock cycle all around us, and studying rocks as a profession or hobby is very popular. I highly recommend ESS101 "Geology" if you like ESRM100.

Rock Cycle Igneous rocks form from molten material such as lava, and are broken down by physical and chemical weathering. Sedimentary rocks form from accumulation of weathered material in depositional basins. Metamorphic rocks are formed from sedimentary rocks exposed to heat, pressure or chemically active fluids.

Biogeochemical Cycle of Ca in a Forest Soluble in water and easily lost through runoff Biogeochemical cycles in ecosystems begin with inputs from reservoirs such as the atmosphere, volcanic ash, stream runoff, ocean currents, or submarine vents. Chemicals cycle through physical transport and/or change their chemical form through chemical reactions such as decomposition. All ecosystems “leak” chemicals to other ecosystems. A good example is calcium cycling through a forest terrestrial ecosystem. This diagram is from work done in Hubbard Brook, New Hampshire. I lived in the "Life Free or Die" state (imagine that!) for three years, and studied forest nutrient cycling in New Hampshire's White Mountains as part of my M.S. degree. The White Mountains have perhaps the most striking fall colors of any forest ecosystem in North America, and that is also part of the forest nutrient cycle there.

Sulfur Cycle In a Forest Ecosystem Includes gaseous forms (sulfur dioxide and hydrogen sulfide) and cycles much faster than calcium Here is a picture of the cycling of sulfur. Note that the total numbers and the relative fluxes have changed.

Nitrogen Cycle In a Forest Ecosystem Here are several parts of the nitrogen cycle of a Douglas-fir forest in the Cedar River watershed near Seattle, and a eucalyptus forest in Sao Paulo state in Brazil. Note the relative differences in the pools and the fluxes.

Carbon Cycle Carbon is vital for life but is not abundant Enters biological cycles through photosynthesis to produce organic forms of carbon Carbon is rapidly becoming the most studied element because of its implications on global warming. Its sometimes said that life is "based on carbon" because of the central role of organic chemistry in building the structure of living cells. Most of the useful energy for life also comes from carbon being fixed into organic molecules by photosynthesis, as is show in this diagram.

Carbon Cycle in a Lake Rob's daughter Joanna (on right) removes C in trout. Here is an example of a carbon cycle in a freshwater pond. Note the largemouth bass eating the small fish. That’s the one that Rob will try and catch. Mostly we prefer trout, but bass are also fun to fish for. In this diagram there are the following fluxes into different pools, 1) organic carbon is released to the atmosphere as CO2 by respiration; 2) there is a net decrease in atmospheric CO2 as a result of photosynthesis; 3) C cycles within organisms (C can be exported as dissolved C in water); and, of course, 4) the removal of C in large trout by fisherman. ; >)

Fossil Fuels Fossil Fuels are created by the accumulation of carbon from dead organisms in rock strata. Their decomposition is prevented by lack of oxygen or low temperatures after their burial in sediments. After thousands or millions of years of burial the stored organic carbon is transferred into coal, oil or natural gas. Fossil Fuels are created by the accumulation of carbon from dead organisms in rock strata. Their decomposition is prevented by lack of oxygen or low temperatures after their burial in sediments. After thousands or millions of years of burial the stored organic carbon is transferred into coal, oil or natural gas.

Global Carbon Cycle When an organism dies, most of its organic material decomposes to inorganic compounds, including carbon dioxide. But where there is not enough oxygen to make this conversion possible, or where temperatures are too low for decomposition, some carbon may be buried and stored in organic forms. Over years, decades, and centuries, storage of carbon occurs in wetlands, including parts of floodplains, lake basins, bogs, swamps, forests, deep-sea sediments, and near-polar regions. Some carbon may be buried with sediments that, over thousands or even several million years, become sedimentary rocks. This carbon is transformed into fossil fuels, such as natural gas, oil, and coal. Nearly all of the carbon stored in the lithosphere exists as sedimentary rocks. Most of this is in the form of carbonates, such as limestone, much of which has a direct biological origin.

Missing Carbon Sink Several hundred million tons of carbon released from the burning of fossil fuels cannot be accounted for. Possible sinks include terrestrial forests, soils, and ocean ecosystems. Because carbon forms two of the most important greenhouse gases—carbon dioxide and methane—much research has been devoted to understanding the carbon cycle. However, at a global level, some key questions remain unanswered. For example, monitoring of atmospheric carbon dioxide levels over the past several decades suggests that of the approximately 8.5 billion tons released into the atmosphere each year by human activities, approximately 3.2 billion tons remain there. It is estimated that at least 2.4 billion tons diffuse into the ocean. This leaves about 2.9 units unaccounted for. Several hundred million tons of carbon are burned each year from fossil fuel and end up somewhere not entirely known to science. Inorganic processes do not account for this "missing carbon sink." Marine or land photosynthesis, or both, must provide the additional flux. At this time, however, scientists do not agree on which processes dominate or in what regions of the Earth this missing flux occurs; however, we do know that forests in Washington State are currently accumulating net carbon, and many are growing at rates not seen even decades ago. Additional CO2 in the atmosphere may be acting as a "fertilizer" for growing trees.

Nitrogen Cycle Essential for manufacturing proteins and DNA Although 80% of atmosphere is molecular nitrogen, it is unreactive and cannot be used directly Nitrogen fixation converts nitrogen to ammonia or nitrate Nitrogen is essential to life: it is needed to manufacture proteins and DNA. Free nitrogen (N2 uncombined with any other element) makes up about 80% of Earth’s atmosphere. However, many organisms cannot use this nitrogen directly, an interesting "paradox": the raw nutrient is abundant, but little is available in forms that organisms can use. Some organisms, such as animals, require nitrogen in an organic compound, but others, including plants, algae, and bacteria can take up nitrogen either as the nitrate ion (NO3) or the ammonium ion (NH4). Because nitrogen is a relatively unreactive element, few processes convert molecular nitrogen to one of these compounds. Lightning oxidizes nitrogen, producing nitric oxide. However, bacteria perform nearly all conversions of molecular nitrogen to biologically useful forms. Some organisms have a symbiotic relationship with nitrogen-fixing bacteria, found in root nodules in some plants or in the stomach of some herbivores. Nitrogen fixation also occurs through lightning and industrial processes. The production of nitrogen is also a major industrial process. When organisms die, denitrifying bacteria convert organic nitrogen to ammonia, nitrate, or molecular nitrogen through a process called denitrification. This completes the cycle of nitrogen, which is also shown in the next slide.

Global Nitrogen Cycle This slide shows the approximate global pools and fluxes of nitrogen. Units are in million metric tons or 1012 g. Note that there are 4 billion million metric tons of N2 in the Earth's atmosphere, an enormous pool. About 80% of the total atmosphere is nitrogen gas; however, this pool is not directly available as a nutrient. Human activities have a fairly large impact on the N cycle, at least of the N that is cycled as a nutrient. Industrial manufacture of nitrogen fertilizer is a significant source of water pollution, and the combustion of fossil fuels produces nitrogen oxides, which contribute to urban smog.

Phosphorus Cycle No gaseous phase Slow rate of transfer Released by erosion of exposed rock Absorbed by plants, algae, and some bacteria Exported from terrestrial ecosystems by runoff to oceans May be returned through seabird guano Phosphorus, one of the "big six" elements required in large quantities by all forms of life, is often a limiting nutrient for plant and algal growth, particularly in areas where nitrogen is not already limiting. For instance, if it is not present in sufficient amounts, plants and algae will not thrive. However, if phosphorus is too abundant, it can cause environmental problems. Lake Sammamish (east of Seattle), for instance, is currently having serious problems with summer algal blooms because of excess inputs of P into the lake. Seattle's Lake Washington experienced similar problems before the current wastewater collection and treatment system was installed in the 1960s and 70s. Unlike carbon and nitrogen, phosphorus does not have a gaseous phase, so transfers are relatively slow. Thus, the phosphorus cycle is significantly different from the carbon and nitrogen cycles. The rate of transfer of phosphorus in Earth’s system is slow compared with that of carbon or nitrogen. Phosphorus exists in the atmosphere only in small particles of dust. In addition, phosphorus tends to form compounds that do not easily dissolve in water. Consequently, phosphorus is not readily weathered chemically. It does occur commonly in an oxidized state as phosphate, which combines with calcium, potassium, magnesium, or iron to form minerals.

Global Phosphorus Cycle Here is an example of the pools and fluxes of P, also in units of millions of metric tons or 1012 g. The fish harvest in this case is a cutthroat trout.

Chapter 3: Biogeochemical Cycles This is yet another request to email us if you have question eschelp@u.washington.edu Questions? E-mail your TA. 26