Transcript Slide 1
Biogeochemical Cycles and Energy Flow - biogeochemical - bio (living organisms); geo (environment: soil, water, air) - nutrient cycles - cycles of elements essential to the growth of living organisms - essential to plants - C, H, O, P, K, I, N, S, Ca, Fe, Mg, Cl, Cu, B, Mn, Zn, Mo - essential to animals - same except B; also Se, Co, F, Cr, Si - why study cycles? important to understanding ecosystem function - 4 important cycles - N, CO2, S, and H20 N, p 31 - N is the primary element for amino acid production (protein) - N2 is an inert gas in the atmosphere and unusable to plants in this form; air is about 80% N - N fixation - conversion of inert N2 to NH3 (ammonia), nitrites (NO2), or nitrates (NO3) -some plants (legumes: Family Fabaceae includes beans, peas, peanuts) and symbiotic (interacting species that are closely or completely dependent on each other) bacteria in root nodules (bacteria clusters) fix N to NH3 making it free to plants and animals -other free-living aerobic bacteria in soil and blue-green algae in aquatic systems serve the same purpose -bacteria make NH3 by splitting N2 and combing it with H (very high biological energetic costs) -non-biological fixation - lightning (chemical reaction) and volcanoes (by emission) produce NO3 -other changes to N - bacteria convert NH3 to NO2 and NO2 to NO3; denitrifying bacteria in anaerobic conditions convert above molecules to N2 that goes back to the atmosphere -amount of daily fixation and release of N is roughly equal C, p 32 -all life on earth is carbon based; all living tissue contains C - C cycle is important for possible role in global warming - CO2 required by plants for photosynthesis; very small amount in atmosphere (0.03%) but very important - CO2 is produced by plants and animals thru cellular respiration (cell activities) - dynamic equilibrium among C forms in water (bicarbonates, carbonates), sediments and fossil fuels (oil, natural gas, coal), atmosphere, plants, and soils The World's Carbon Reservoirs Reservoir Size (Gigatons of C) Atmosphere 750 1.6% Forests 610 1.3% Soils 1580 3.4% Surface ocean 1020 2.2% Deep ocean 38,100 81.0% Coal 4,000 8.5% Oil 500 1.1% Natural gas 500 1.1% Fossil fuels Total fossil fuel 5,000 S, p 34 - important for forming some amino acids and enzymes; in organic (dead plants and animals) and inorganic (sulfur containing rocks) deposits - released into the environment by decomposition of organic matter, erosion, volcanoes, salt spray from oceans -occurs as H2S then SO2 in air and water, and SO4 in water and soil; forms H2SO4 in water and falls with rain to earth and becomes available (too much causes acid rain) -decomposers (bacteria and fungi) release sulfur from organic material -plants mainly get S from SO4 in soil and water; animals by eating plants and other animals -mining (especially coal) and industry release S and acidifies the environment from runoff from strip mines and burning poor grades of coal H20 p 35 -hydrologic cycle - water comes from oceans to continents via rainfall; it then evaporates, gets stored (surface or ground), or goes back via rivers -not much in atmosphere and the turnover rate is high -human activities can affect cycle: reduce aquifers or change evaporation rates and runoff by construction of cities Energy Flow - from sun to plants (photosynthesis) to system (consumers in the food web) then lost as heat - laws of thermodynamics 1) energy cannot be created or destroyed 2) when energy is transferred, it is transformed, and much is lost to unusable forms (heat) -plants capture energy in chemical bonds which animals in the food web eat and pass on; energy does not cycle but flows out of the system as heat - photosynthesis — uses CO2 and H2O in a reaction by light energy; green chlorophyll captures light energy — sugars and O2 are produced; also other organic products (fats, vitamins, and proteins) — 6 CO2 + 6 H2O w/sunlight yields C6H12O6 + 6 O2 - decomposition - break down of organic compounds, releases CO2 and H2O, returns nutrients to inorganic state (vitamins and minerals are freed from C based molecules) — done by microflora (fungi for plant litter, bacteria for animal matter; actually do the decomposition) and detritivores (invertebrates that feed on detritus, dead organic matter, and really just break it down into smaller bits) — other important factors: activities and ingestion by larger organisms and leaching by precipitation — detritivores (mites, protozoans, nematodes, earthworms, millipedes) fragment organic material and inoculate it with bacteria and fungi — microbivores (larval beetles, flies, mites, amoebas) feed on nutrients and energy of microflora — decomposers temporarily remove nutrients from circulation (nutrient immobilization) Food Webs and Energy Pyramids - autotrophs - producers; produce own food; living base of food web - heterotrophs - consumers; use producers or other consumers as food - trophic levels - feeding levels through which energy is passed; begins with producers - food chain - path of energy flow from producer to consumer better seen as food web - order: 1) primary producers (phytoplankton and large plants) 2) primary consumers - herbivores or prey; land and water grazers (carp, ducks, deer, mice) and zooplankton 3) secondary consumer (carnivores or predators); can go to more levels – omnivores - eat both autotrophs (plants) and heterotrophs – other contributors: decomposers, detritivores, microbivores, scavengers, saprophytes (fungi that feed on dead plant material; decomposers), and parasites – intricate “web” of energy exchange; many organisms shift roles and can be predators and prey - about 90% loss of energy at each step of the web (energy is lost as heat when chemical bonds are broken and used to warm bodies); 2nd law of thermodynamics Relative Number Of Organisms As You Follow A Food Web Relative Biomass Of Organisms As You Follow A Food Web – limits how much energy, how many individuals, and how much biomass can accumulate up chains; called ecological pyramids – fisheries managers deal with 2nd and 3rd level consumers; wildlife managers mostly deal with 1st level consumers (predators at higher levels cannot reach numbers of 1st level consumers)