Biogeochemical Cycles Review

The Water Cycle (Hydrologic Cycle)

3 important needs for water Photosynthesis Respiration Digestion Major Reservoir Oceans (97%), Ice Caps

The Water Cycle Water is released from the surface through evaporation. Evapotranspiration is the loss of H2O from the leaves of plants as they exchange gases. Once in the atmosphere, water molecules undergo condensation. This gives us precipitation which sends the H2O back to the Earth. Precipitation: Rain, snow, sleet, hail

The Water Cycle Precipitation infiltrates the soil and percolates down into the deeper layers of the soil or it will become runoff. Percolated H2O may become part of the groundwater, which flows underground to the ocean. Aquifer: water saturated rock/soil Percolated water may also be used by plants for photosynthesis.

Human Intervention in the Hydrologic Cycle Ground & surface water depletion. Ground & surface water pollution. Deforestation, particularly in temperate and tropical forests, which interferes with the cycle by decreasing transpiration and increasing runoff/flooding

The Carbon Cycle

The Carbon Cycle CO2 makes up ~0.035% of the atmosphere Used by plants during photosynthesis to make carbohydrates (sugar) Carbs are then used during cellular respiration, which is a process that gives off CO2 into the atmosphere

The Carbon Cycle Decomposers degrade the remains of plants & animals and return the CO2 to the atmosphere as well.

The Carbon Cycle Sinks: Most of the C on earth is in the form of limestone, a type of sedimentary rock. In the ocean, C is found dissolved as carbonate and bicarbonate ions. Old growth forests because they store large amounts of carbon in the biomass. Limestone contains ~80% CaCO3

The Carbon Cycle Exists in abiotic environment as: CO2 Carbonate rocks Fossil fuel Dead organic matter Enters biotic environment through: Photosynthesis Returns to atmosphere by: Respiration Decomposition Burning/Combustion

The Carbon Cycle How does C get into the Ocean? Carbon dioxide dissolves/diffuse into water. Combines with calcium in water to form CaCO3 (calcium carbonate) Large amounts of CaCO3 deposits are found on the ocean floor Come from the remains or organisms such as mollusks and coral Shells decay and turn into limestone, limestone dissolves in water and releases carbon back into atmosphere

Human Intervention in the Carbon Cycle Since the Industrial Revolution we have dramatically increased CO2 in our atmosphere due to: Deforestation: decreases the plants available for photosynthesis, thus decreasing the uptake of CO2 Forests burning and releasing the carbon in the “carbon sink” Increased combustion of fossil fuels Increased CO2 in the atmosphere has exacerbated global climate change by holding in infrared heat around earth that would normally escape into space.

The Nitrogen Cycle

The Nitrogen Cycle Atmosphere is 78% N Essential to life because it is used to form amino acids (proteins), nucleic acids (DNA/RNA), and ATP (cell energy) Plants and animals are unable to use N2 it must be “fixed” to a usable form Ammonia or Nitrates By Bacteria or Lightning

The Nitrogen Cycle The N cycle has 5 main steps: N fixation is the conversion of atmospheric N2 into ammonia (NH3) The bacteria, Rhizobium, are able to fix N Rhizobium is found in the root nodules of legumes Peas, beans, clover, alfalfa Some plants use ammonia, but more can use nitrates Nitrification Other bacteria convert ammonia into Nitrites NO2- which is not usable by plants. Therefore, different bacteria must convert NO2- into nitrates (NO3-) that plants can use.

The Nitrogen Cycle Assimilation is when plant roots absorb ammonia, ammonium ions, or nitrates and make the substance they require for life. Ammonification takes place when dead N rich organisms, their parts, or their metabolic wastes are converted to ammonia and ammonium ions by decomposing bacteria. Soil is major reservior Denitrification is the process of nitrate ions being converted back to gas & released into the atmosphere.

Human Intervention in the N Cycle NO is released when fossil fuels are combusted. NO in the atmosphere forms nitric acid, which results in acid deposition and smog formation. N2O gas is a greenhouse gas and is derived from livestock waste and used as a fertilizer. N is removed from an ecosystem if plants are removed. N, when added to aquatic ecosystems from agricultural runoff and municipal waste treatment, induces eutrophication, an enrichment of the ecosystem resulting in algal blooms.

Eutrophication/Cultural Eutrophication Caused by excess Nitrogen Phosphorus

Phosphorus Cycle

Phosphorus Cycle Important b/c it makes up cell membranes, part of nucleic acids, and ATP Very slow cycle because there is no atmospheric/gas stage. Major reservoir: Rocks Phosphorous is in rocks and P ions do not dissolve very well in water. Most is insoluble and found on the ocean floor as a phosphorus sink.

Phosphorus Cycle Rock containing P must be weathered to release the minerals or removed via mining. P is taken up by producers and transferred to consumers. Waste and Decay of organisms releases P

Phosphorus Cycle Leaching: water dissolves phosphates in rocks and carries to lake, stream, etc Dissolved phosphate: used by plants and passed through food chain Animals return phosphorus to environment by Excretion of Waste Death/Decay

Human Intervention in the Phosphorus Cycle Phosphate mines that form large pits & result in runoff pollution Removing vegetation lowers phosphorus availability in an ecosystem Similar to increases in N, increases in P leads to eutrophication in aquatic ecosystems. P is found in sewage

Sulfur Cycle

Sulfur Cycle Most S is found in rocks as iron disulfide (pyrite) or mineral salts like calcium sulfate (gypsum). Sulfur is released by weathering, volcanic activity & hydrothermal vents. S is take up by producers and passed to consumers and released again after decomposition.

Human Intervention in the Sulfur Cycle Fossil fuel combustion releases sulfur dioxide, which forms sulfuric acid in the atmosphere and results in acid deposition Refining of petroleum and smelting releases sulfur compounds Coal mining results in sulfur release, causing damage to aquatic ecosystems Large amounts of sulfur dioxide and sulfate aerosols cool the atmosphere because they prevent the penetration of UV radiation