Transcript Lecture 20
BIOL 4120: Principles of Ecology Lecture 20: Ecosystem Ecology Dafeng Hui Room: Harned Hall 320 Phone: 963-5777 Email: [email protected] Outline (Chapter 22) Biogeochemical cycles Biogeochemical cycles: Bio-living things; geo-rocks and soil; chemicalprocesses involved. All nutrients (or elements) flow through from the nonliving to the living and back to the nonliving components of the ecosystem in a cyclic path 22.1 Two major types of biogeochemical cycles All nutrients follow biogeochemical cycles Two types of cycle • Gaseous Major reservoirs are atmosphere and oceans Global in nature, important gases • Oxygen 21% • Nitrogen 78% • Carbon of carbon dioxide 0.03% • Sedimentary Major reservoirs are soil, rocks and minerals Rock phase and salt solution phase Salt solution is the available form • Phosphorus • Metals, eg Calcium, Magnesium, etc Some cycles are hybrid • Sulfur (S) • Major pools in Earth’s crust and atmosphere Two major types of biogeochemical cycles Common features: • Involve biological and non-biological processes • Driven by the flow of energy through ecosystem • Tied to water cycle (water is the important medium; Without water cycle, biogeochemical cycle would cease). Share three basic components: • inputs, • internal cycling • outputs. 22.2 Inputs and outputs Nutrients enter the ecosystem via inputs • Gaseous cycle from atmosphere (C,N) • Sedimentary from rocks and minerals (P, Ca) Wetfall and dryfall • Precipitation -- wetfall • Airborne particular and arsenal (rainfall on the forest floor is nutrient rich than on the bare soil) -- dayfall Nutrient in aquatic ecosystem • From surround lands in the form of drainage water, detritus, sediment and precipitation. Inputs and outputs There are also outputs to the biogeochemical cycles • Carbon to carbon dioxide, release back to atmosphere • Nutrient to gaseous form (denitrification) • Loss of organic matter from ecosystem by washout (from terrestrial to aquatic) • Herbivores between aquatic and terrestrial Moose (feed on aquatic plants, deposit nutrient in terrestrial ecosystem in the form of feces) Hippopotamus (move organic matter from terrestrial to aquatic) • Harvesting may be replaced by fertilization • Loss of nutrient (e.g.Leaching) may be balanced by inputs (weathering of rocks and minerals) Internal cycling Nutrients are recycled within the ecosystem • Internal recycling important within ecosystem • Some systems have large amount of short term recycling Lakes • Other have most stored as biomass Forests • Long term storage in water systems is in the sediment System dependent on primary production and decomposition • Without latter, everything will become locked up A generalized biogeochemical cycle Note input, internal cycling, and output Pools and fluxes Three calcium pools: Plants, dead OM and soil Pool size: 290, 140, 440 kg ha-1 Fluxes (kg ha-1 yr-1) F1: uptake F2: litterfall F3:leaching from plants? F4:net mineralization Turnover time: t=P/f steady-state t_p=4.8, t_OM=2.3, t_s=7.3 22.3 Carbon cycle Tightly linked to energy flow Difference between production and loss NPP=GPP-Ra Net ecosystem productivity • NEP=GPPRa-Rh • NEP=NPP-Rh Note storage • Carbonates • • • • Coral reefs Limestone Coal Oil Gas Peat Carbon cycle varies daily and seasonally High CO2 concentration on the forest floor is caused by microbial respiration. CO2 high in winter and decline with onset of photosynthesis (May to June, in Alaska) Global carbon cycle Carbon budget of Earth is closely linked to atmosphere, land and ocean and mass movement around planet. Unit in gigatons (Gt= 10^9 metric ton=10^15 g) Earth contains 10^23 g of C Missing carbon Atmospheric increase= • • • • Emissions from fossil fuels +Net emissions from changes in land use -Oceanic uptake -Missing carbon sink 3.2 (±0.2)=6.3 (±0.4)+2.2 (±0.8)2.4 (±0.7)-2.9 (±1.1) http://www.whrc.org/carbon/index.htm 22.4 Nitrogen cycle Nitrogen is essential to life Starts with nitrogen fixation from atmosphere Plants can only utilize nitrate or ammonia • Atmospheric deposit Dryfall+wetfall • Nitrogen fixation High energy (lightning, 0.5 kg N ha-1) Biological • Bacteria, 10 kg N ha-1. N fixation: N2 is converted into NH3 (NH4+ when ) by bacteria. Ammonization: a process that organic N is converted to NH4+ Nitrification: a process that NH4 is oxidized to NO2- and to NO3Denitrification: under anaerobic condition, NO3- is reduced to N2O and N2 and returned to atmosphere. Global nitrogen cycle Unit: 10^12 g N yr1 22.5 Phosphorus cycle has no atmospheric pool No atmospheric reservoir (rock and natural phosphate deposits) Permanent loss of phosphorus to oceans Input limited to weathering of rocks Terrestrial systems can be limited by phosphorus availability Phosphorus is more abundant in marine and freshwater systems • Particular • Dissolved organic phosphorus Rapidly utilized by zooplankton Secrete inorganic • Dissolved inorganic phosphorus Rapidly utilized by phytoplankton Phosphorus can sink as particulate phosphorus and become locked in bottom sediment • Depletion of surface layers Global phosphorus cycle Unit 10^12 g P yr-1 22.6 Sulfur cycle is both sedimentary and gaseous (hybrid) Global sulfur cycle (poorly understood) 22.7 Oxygen cycle in largely under biological control Sources of O2 1. Breakup of water 2. Photosynthesis Now in balance Three pools 22.8 Various biogeochemical cycles are linked All elements are components of living organisms and constituents of organic matter Thus all cycles are linked: Chemically Energetically Biologically Stoichimetry: quantitative relationship of elements in combination. Example: C:N ratio, 8 to 15 for microbes, 30 for leaf, etc C:N:P ratio End