Lecture #5 Biogeochemical Cycles Unit 1: Ecology

Biogeochemical Cycles A biogeochemical cycle is the cyclic movement of a substance (for example, water, carbon, nitrogen, or phosphate) through the biotic (living) and abiotic (non-living) environments. Biogeochemical cycles are a key component of ecosystems ecology.

Nature reuses everything. All of the matter that cycles through living organisms are important in maintaining the health of the ecosystem.

– Biogeochemical cycles of matter involve biological processes, geological processes, and chemical processes. – As matter moves through these cycles, it is never created or destroyed—just changed.

* In almost all biochemical cycles, there is much less of the substance in the living reservoir than the nonliving reservoir.

We’re in the Driver’s Seat - Human Activities greatly impact Many Biogeochemical Cycles

1. The Water (hydrologic) Cycle  Plants absorb water from the soil  Water may percolate down through the soil and eventually collect in pools (groundwater)  Transpiration (release of water through leaves due to the sun) and respiration return water to the atmosphere  Precipitation (rain, snow, etc) returns water to the soil  Plants absorb water from the soil  Water may percolate down through the soil and eventually collect in pools (groundwater)  Transpiration (release of water through leaves due to the sun) and respiration return water to the atmosphere  Precipitation (rain, snow, etc) returns water to the soil

The Water Cycle Only about 40% of precipitation on land comes from water evaporated over oceans; roughly 60% comes from transpiration of water through plants.

Freshwater Is a Precious and Often Scarce Resource

The Percentage of Available Global Freshwater is Very Small

Human Impact on the Water Cycle Withdraw large quantities of fresh water – water diversion, groundwater depletion, wetland drainage Clearing vegetation from land – Increases runoff, reduces infiltration, increases flooding, increases soil erosion Modify water quality-adding nutrients (phosphates, nitrates)

2. The Carbon Cycle Carbon is fixed by plants Carbon is fixed by plants CC – 6 CO H 2 O  C 6 H 12 O O 2 Carbon is given off by consumers Carbon is given off by consumers CC – C 6 H 12 O O 2  6 CO H 2 O Organisms containing carbon form fossil fuels Organisms containing carbon form fossil fuels Burning fossil fuels releases carbon Burning fossil fuels releases carbon CC – 2 C 8 H O 2  16 CO H 2 O Carbon is fixed by plants Carbon is fixed by plants CC – 6 CO H 2 O  C 6 H 12 O O 2 Carbon is given off by consumers Carbon is given off by consumers CC – C 6 H 12 O O 2  6 CO H 2 O Organisms containing carbon form fossil fuels Organisms containing carbon form fossil fuels Burning fossil fuels releases carbon Burning fossil fuels releases carbon CC – 2 C 8 H O 2  16 CO H 2 O Photosynthesis and Cell Respiration cycle carbon and oxygen through the environment

The Carbon Cycle

Carbon Cycle

Human Impact on the Carbon Cycle Burning of fossil fuels & biomass (wood) generates huge amounts of carbon dioxide that cannot be taken up fast enough by the carbon sinks (oceans, forests). This excess carbon dioxide contributes to global warming, which may lead to loss of biodiversity globally, rising sea levels, more violent storms, and changes in precipitation patterns.

Human Impact on Carbon Cycle Removal of vegetation – decreases primary production (decreases carbon fixation) and subsequently, biodiversity

3. The Nitrogen cycle Atmospheric nitrogen (N 2 ) makes up nearly 78%-80% of air. Organisms cannot use it in that form. Lightning and some species of bacteria convert nitrogen into usable forms.

Nitrogen-fixing bacteria- Bacteria that live in a symbiotic relationship with plants of the legume family (e.g., soybeans, clover, peanuts).

Nitrogen fixation-convert atmospheric nitrogen (N 2 ) into ammonium (NH 4 + ) which can be used to make organic compounds like amino acids. N 2 NH 4 + Only in certain types of bacteria and industrial technologies can fix nitrogen.

Ammonia is further changed by other types of soil bacteria (nitrification) into nitrate, which is taken up by plants and passed on to animals as they consume the plants. Eventually this is returned to the nonliving reservoir when the organism dies and decays.

The Nitrogen Cycle

Humans Play a Major Role in the Nitrogen Cycle Aerial fertilization (with nitrogen) of sugar beets.

Human Impact on the Nitrogen Cycle Use of synthetic nitrogen fertilizers may stimulate algal blooms (due to agricultural runoff), which depletes oxygen and decreases biodiversity.

A ‘dead zone’ forms seasonally near the area where the Mississippi river dumps into the Gulf of Mexico. Virtually all marine life is killed due to the lack of oxygen available.

VIDEO CLIP ON THE DEAD ZONE

Human impact on the Nitrogen Cycle Continued…. Land management: Nitrogen-fixing crops (legumes) add more useable nitrogen to the soil. (Example of crop rotation: corn, soybeans, corn, soybeans) – On the other hand, overplanting of crops depletes nitrogen from soil.

Human Impact on the Nitrogen Cycle Cont. Burning fossil fuels- forms nitrogen dioxide (NO 2 ) in atmosphere, which can react with water to form nitric acid (HNO 3 ) & causes acid rain

The Phosphorous Cycle Phosphorus - usually found in soil and rocks in the form of calcium phosphate. Calcium phosphate dissolves in water and forms phosphate ions. We can’t use this inorganic form of phosphorous. ** Phosphorous is an important component of DNA, bones and teeth

Plants take up inorganic phosphate via their roots. It is then used to build organic phosphate. Consumers get organic phosphate from plants. Decomposers return phosphate to soil Phosphate leaches into water supply – May form new phosphate containing rock

How is this cycle unique from the others? Answer: There is NO atmospheric phase in the phosphorous cycle!

Phosphorous Cycle

Human Impact on the Phosphorous Cycle Mining of large quantities of phosphate rock-used for organic fertilizers and detergents Runoff of wastes and fertilizers causes accumulation in lakes and ponds killing aquatic organisms – leads to excessive algal growth, depletion of oxygen, & decrease in biodiversity; eutrophication ("over nourishment")

Take 2 minutes to summarize how matter cycles through the biosphere, how human activity impacts these cycles and the effect these impacts have on global biodiversity.