Tree Carbon Sequestration Tree Height: 20 m Tree Circumference: 40 cm Tree age: 32 yrs. Tree Core Length: 17 mm Tree Core Diameter: 1.5 mm Tree Core Dry Mass: 2 g Tree Core Carbon Mass: 0.8 g

Biogeochemical Cycles Nitrogen and Phosphorus

Nitrogen Cycle What form does most nitrogen exist in? Nitrogen gas in the atmosphere (N2) Why is this a bad thing? This form is not readily usable by most organisms and is often considered inert. “Inert” because of a triple covalent bond, which is a very strong chemical bond. Why is Nitrogen essential to living things?

Biological Nitrogen

Nitrogen Cycle How do we get to a usable form? Bacterial nitrogen fixation Atmospheric nitrogen fixation Decomposition and excretion Haber-Bosch process = synthetic fertilizer What are these usable forms? Ammonia (NH3), Nitrate (NO3-) and nitrite (NO2-).

Fixing Nitrogen What can “fix” nitrogen to a usable form? Bacteria On root nodules of legumes such as beans; convert nitrogen gas to ammonia. In soils, convert ammonia to nitrates and nitrites Enzyme necessary for this requires that no oxygen be present.

Removing Nitrogen What process removes usable nitrogen? Denitrification Bacteria convert nitrates back into nitrogen gas

Human Impacts 1. Addition of nitric oxide (NO) From burning fossil fuels Can be converted to nitric acid (HNO3), then fall back to land as acid deposition (acid rain) 2. Addition of nitrous oxide (N2O) Through anaerobic bacteria on livestock wastes and fertilizers Warm the troposphere and deplete ozone 3. Release large quantities of stored nitrogen Destruction of forests, grasslands, and wetlands 4. Adding excess nitrates to aquatic ecosystems Adding fertilizers to crops Rain water run-off leach nitrogen from soils and drains into water Sewage run-off 5. Remove topsoil nitrogen Harvest nitrogen-rich crops, irrigate crops, and burn or clear grasslands and forests

Phosphorus Cycle Where is a majority of phosphorus located? On land in rock and soil minerals. In the ocean as sediment. Small amount in living organisms, bound within organic molecules such as DNA and RNA as well as in skeletons of animals. Unlike other nutrients, it DOES NOT enter the atmosphere.

Phosphorus Cycle What is the major form that phosphorus is found in? Phosphate compounds (PO43-) Because soils contain little phosphate, it is often the limiting factor for plant growth on land.

Human Effects 1. Mining large quantities of phosphorus to make commercial inorganic fertilizers. 2. Reduce available phosphate in tropical soils when trees are cut down in those areas. 3. Disrupt aquatic ecosystems with phosphate run-off Animal wastes Fertilizers Sewer discharges

How Nutrients Effect an Ecosystem Nutrient limitation Similar to when a person has a deficiency in a vitamin or necessary nutritional component (like iron or calcium), ecosystems can have a deficiency in a given nutrient. This nutrient is called the limiting nutrient, because it limits the primary productivity of an ecosystem.

How Nutrients Effect an Ecosystem What is primary productivity? The rate at which organic material is created by producers, such as plants on land or phytoplankton in the ocean. What happens when a limiting nutrient no longer becomes limiting? In the water, this creates an algal bloom.

Algal Blooms Increase in algae as a result of increased nutrient. Step 1: Algae grow and reproduce rapidly. Step 2: Algae die. Step 3: Decomposers (bacteria) in the water take up all the oxygen via respiration as they break down the dead algae. Step 4: Limited to no oxygen left for other animals in the water column. Step 5: Other animals such as fish, die due to lack of oxygen.

Harmful Algal Blooms Chemicals released from bloom can be dangerous Paralytic shellfish poisoning (picture on right - Alexandrium tamarense) Ciguatera (picture on left - Gambierdiscus toxicus) Neurotoxic shellfish poisoning (Gymnodinium breve)