Published on February 5, 2008
Nutrient Cycling: Nutrient Cycling Chapter 25, Smith and Smith 6th Edition Page 503-523 Types of Nutrient Cycles: Types of Nutrient Cycles Biogeochemical: Bio: Processes thru living organisms Geo: Geological processes Chemical: Chemical processes (interactions of chemicals in the environment) Gaseous Cycle: Gaseous Cycle Main source of nutrients are the atmosphere and ocean (freshwater to a much lesser extent) Have global circulation patterns (follow ocean currents and prevailing weather currents) Sedimentary Cycles: Sedimentary Cycles Main source of nutrients are the soil and rocks of the Earth’s crust Rely upon weathering to release nutrients Salt Phase: After weathering, nutrients enter water as soluble salts Rock Phase: Accumulation of salts, silts, etc. become rock General Model of Nutrient Cycling: General Model of Nutrient Cycling Inputs Internal Cycling Outputs Inputs to the Cycle: Inputs to the Cycle Thru either gaseous or sedimentary cycles Wetfall- Precipitation takes nutrients from the atmosphere or as water runs off surfaces Dryfall- from airborne particles and aerosols (can be very substantial!!) Internal Cycling: Internal Cycling Recycling of nutrients WITHIN an ecosystem Requires microbial decomposers to transform organic nutrients into mineral forms (Mineralization) This makes these nutrients available for plant uptake (Primary production which drives the ecosystem) Witherspoon’s radioisotope study: Witherspoon’s radioisotope study Internal Cycling: Ecosystem Effects: Internal Cycling: Ecosystem Effects Largely determined by Primary production and decomposition Internal Cycling: Climate: Internal Cycling: Climate Weathering of rocks and minerals & soil formation Influence rates of primary production and decomposition which increase with temperature and moisture Internal Cycling: Climate: Internal Cycling: Climate Internal Cycling: Species effects: Internal Cycling: Species effects Short-lived organisms: quickly uptake nutrients and quickly return them (e.g. Zooplankton) Long-lived organisms: Larger,slower growing, and release more nutrients over a long period of time when they decompose. Nutrients they uptake are taken out of the short-term cycle (e.g. Trees) Outputs: Outputs Loss of nutrients from the ecosystem, inputs must be equal for the system to not experience a net loss of nutrients. CO2 cycling in the atmosphere Downstream transport in lotic aquatic systems (River Continuum Concept based on nutrient flow) Ecosystems are interrelated and depend upon processing occurring at larger scales Outputs: Disruptions: Outputs: Disruptions Harvesting, particularly forestry and agriculture, removes biomass from the ecosystem and consequently nutrients May also alter internal cycling (esp. logging) Other disruptions: Fire, flooding, any others?? Nitrogen cycling after forest harvest: Nitrogen cycling after forest harvest Forest harvest and Outputs: Forest harvest and Outputs Terrestrial vs. Aquatic Ecosystems: Terrestrial vs. Aquatic Ecosystems The magnitude of the link between terrestrial and aquatic systems depends upon the ecosystem In shallow water shorelines, there is a very direct link between aquatic and terrestrial Other links include: Flood pulses, downstream transportation, etc. Vertical Zones of Production: Vertical Zones of Production Lentic/Oceanic Aquatic Systems: Lentic/ Oceanic Aquatic Systems Seasonality of Aquatic Systems: Seasonality of Aquatic Systems Major Biogeochemical Cycles: Major Biogeochemical Cycles Carbon Cycle Nitrogen Cycle Sulfur Cycle Phosphorus Cycle Carbon Cycle: Carbon Cycle Basis of all life Carbon is extremely closely tied to energy flow Source of all fixed carbon (living organisms and fossil deposits) is CO2 (atmospheric and dissolved aquatic) Carbon Cycle: Model: Carbon Cycle: Model Nitrogen Cycle: Nitrogen Cycle Essential to building proteins 4 Major processes: Fixation – convert N2 to NH3 & NO3- Mineralization (ammonification) – Conversion of dead organic material to energy and NH3 Nitrification – Process where NH3 yields NO3- & NO2 and Energy Denitrification – Nitrates (NO3) reduced to gaseous Nitrogen (N2) Bacterial Processing of Nitrogen: Bacterial Processing of Nitrogen The Nitrogen Cycle: The Nitrogen Cycle The Sulfur Cycle: The Sulfur Cycle Released by weathering after a long sedimentary phase H2S released by combustion of fossil fuels, volcanic eruptions. H2S quickly changes to SO2 and rainwater delivers it in the form of sulfuric acid (H2SO4) Acid precipitation linked to burning of fossil fuels The Sulfur Cycle: Model: The Sulfur Cycle: Model The Phosphorus Cycle: The Phosphorus Cycle Very little P occurs in the atmosphere, most is released by weathering, occurs in small quantities. Often the limiting factor in aquatic ecosystems P binds with soil particles which are transported to aquatic systems, can cause noxious algal blooms. The Phosphorus Cycle: Model: The Phosphorus Cycle: Model Linkages in Biogeochemical Cycles: Linkages in Biogeochemical Cycles These elements obviously occur in molecules and organisms together linking these nutrient cycles. Elements must be present in sufficient quantities for chemical reactions to occur Other essential nutrients are important and may be limiting factors as well.