Wetland Nitrogen and Carbon Cycling (Exam 1 Pt 3 PDF)

1. Explain the major pathways of wetland nitrogen cycling Intra-system cycling - transformation processes within the wetland Exchange cycling - cycling between wetland and surrounding systems (waters, land, atmosphere) Often the most limiting nutrient in flooded soils, major limit...

1. Explain the major pathways of wetland nitrogen cycling Intra-system cycling - transformation processes within the wetland Exchange cycling - cycling between wetland and surrounding systems (waters, land, atmosphere) Often the most limiting nutrient in flooded soils, major limiting factor in coastal waters, wetlands are significant sources of N2 released to atmosphere, source of greenhouse gas N2O (important for treatment wetlands) Major pathways a) Mineralization - aka ammonification - makes usable chemicals i) Biological decomposition and degradation (aerobic and anaerobic, soluble organic nitrogen (waste), proteins, urea), microbiota (primarily bacteria and fungi) b) Ammonia transformations and nitrification - biological uptake i) Plant roots and anaerobic microorganisms convert to organic matter, high pH >8 lead to volatilization and ammonia (NH3) release to atmosphere ii) Immobilization onto negatively charges soil particles, oxidation to nitrate/nitrite in thin oxidized soil layer (bacteria) and oxidized rhizosphere (plants) c) Nitrate transformations and denitrification - change N to be soluable i) Highly soluble; lost to groundwater, plant roots and microorganisms convert to organic matter, anaerobic microorganisms convert to ammonium (NH4+) ii) Denitrification - facultative bacteria under anaerobic conditions, inhibited in acid soils and peat, significant loss of nitrogen in wetlands (N2 = no problem, N2O = green house gas) d) Fixation i) Aerobic and anaerobic bacteria; blue-green algae, certain fungi (depends on wetland type and current conditions), use the enzyme nitrogenase, significant source of nitrogen input in wetlands e) Nitrate reduction to ammonia - conversion from nitrate to ammonia i) Dissimilatory- not used in biological cell but performed by bacteria for energy, anaerobic soils but secondary to nitrification, specific conditions can make this process primary (high organic carbon and or low nitrate) f) Anammox - bacteria converts nitrate and ammonia to N gas i) Bacterially mediated, potentially important in wetlands with limited organic carbon (treatment wetlands), new area of research  2. Explain the major pathways of wetland carbon cycling Formation and breakdown of matter, aerobic and anaerobic processes, aerobic processes are energy efficient (facultative organisms deplete oxygen before switching, variability of anoxic conditions means these can occur quite close together) Major pathways a) Photosynthesis b) Aerobic respiration c) Fermentation - aka glycolysis (glucose breakdown) i) Facultative or obligate anaerobes (microorganisms), can occur in presence of oxygen but does not use oxygen, products are dissolved organic carbon (DOC) (primarily ethanol and lactic acid), products are substrates for methanogenesis d) Methanogenesis i) Performed by methanogens - domain archaea, produces methane gas (greenhouse gas 30x more potent than CO2, occurs under extremely reduced conditions, only after others have been reduced (oxygen, nitrate, sulfate) e) Methane oxidation i) Methanotrophs may “intercept” methane formed in anoxic zone, methanotrophic bacteria and nitrifiers (primarily occur in non-flooded soils (methane sinks) BUT wetland soils have anoxic horizons), methanotrophs can tolerate extended anoxia, but methanogens cannot tolerate oxygen 3. Explain how wetland nitrogen and carbon cycles relate to pollution Nitrogen Nitrate pollution - N from enzymes, proteins, excess N from fertilizer/manure/wastewater treatment/atmospheric deposition, nitrate soluble so easily carried off land moves into streams/lakes/areas of drinking water; consuming too much nitrate = hard for blood to transport oxygen (blue baby syndrome), increased risk of colon cancer, thyroid disease, and neural tube birth defects; waterways with too much nitrate = too much N taken by plants = algae bloom > block sunlight, increase water temp, deplete dissolved oxygen = creating dead zones; toxic cyanobacteria to humans = dangerous and deadly; costly - removal and treatment and reduced rec fishing, $210,000,000 cost to economy Dead zone in gulf of mexico - area of low oxygen harmful to fish and aquatic vegetation, fertilizer allows N to runoff into mississippi river as well as sewer discharge, cause algae blooms  Working wetlands - natures kidneys to filter water runoff, target wetland locations, designed for water quality improvement on agriculture lands, used to filter n and nitrate, 4. Discuss the role of wetland nitrogen and carbon cycles in climate change Carbon Wetlands and carbon capture - store carbon in soils, layer of humus and then organic soil, wetland forest stores 10x as much carbon as upland forests Methane emissions from wetlands - wetlands largest source of methane, methane 25x worse than carbon dioxide, trees channel methane from soils into atmosphere, trees in wetlands have no access to oxygen so they made a mechanism to get oxygen from air into roots resulting in methane released from trees, how to fix - focus on human emissions Wetlands and methane - methane produced by decomposition of organic matter in areas with no oxygen, natural methane emissions - always a part of ecosystem so it does not affect climate change, human methane emissions are harmful to climate, need to reduce emissions, wetlands great carbon sinks, anthropogenic losses of wetlands detrimental to climate, methane will disappear from atmosphere in decade, restoring wetlands decreases carbon dioxide emissions 5. Explain wetland sulfur cycling Sulfur is rarely limiting in wetlands, high concentration in saltwater wetlands, pathways mediated by microbes, cause of “rotten egg” smelling “swamp gas” (Hydrogen sulfide H2S) Sulfate sources - natural (mineral weathering, volcanic activity, decomposition, combustion, sea spray), and anthropogenic (acid mine drainage, fertilizer runoff, wastewater, sea level rise) Major sulfur pathways a) sulfate reduction i) Highest rates at neutral pH, saltwater wetlands much greater H2S emissions then freshwater, greatest loss of sulfur from wetlands via H2S b) sulfate oxidation (anoxygenic photosynthesis) i) Aerobic conditions - chemoautotrophic and photosynthetic microorganisms ii) anaerobic conditions - photosynthetic sulfur-oxidizing bacteria, anoxygenic photosynthesis 6. Discuss how hydrogen sulfide impacts wetland biota - H2S Toxicity in plants - direct toxicity (root damage, poor growth, leaf death), reduces sulfur availability, immobilization of zinc and copper (leads to deficiency), high iron can reduce toxicity Toxicity in animals - direct irritant to moist membranes (eyes, mouth, gills, skin), inhibition of cytochrome c oxidase, the terminal enzyme in aerobic respiration (lung edema, organ failure) 7. Explain the link between sulfur and carbon cycles Sulfur is abundant in saline wetlands; competition, inhibition, and or dependence amongst sulfite and methane bacteria that results in less methane released. Carbon oxidation : methane production 8. Explain wetland phosphorus cycling Phosphorus sources: natural (mineral weathering, atmospheric deposition, waterfowl/animal waste, sediment runoff) and anthropogenic (fertilizer runoff, wastewater inc septic, urban runoff, stormwater runoff) Critical limiting nutrient, retention important in “working” wetlands, sedimentary cycle (organic litter/peat, inorganic sediments), usable forms: soluble inorganic phosphorus Working wetlands - created to breakdown and store nutrients from wastewater Major pathways - Plant/microbial uptake, mineralization, adsorption/precipitation, sedimentation, Anaerobic release Phosphorous unavailable to organisms when it precipitates (precipitation occurs under aerobic conditions, precipitates with ferric iron and aluminum in acidic soils, precipitates with calcium magnesium in alkaline soils, high algal productivity -> high pH -> co-precipitation with calcium carbonate Phosphorus unavailable to organisms when it adsorbs to clay, peat, and ferric/aluminum oxides (soliton to clay is very important in wetlands, Phosphorus inputs via flooding are usually adsorbed into sediment) Phosphorus unavailable to organisms when incorporated into other living matter (plants then form indirect pathway to bioavailability and or export, Flooding and anoxia can release phosphorus to soluble forms) 9. Discuss how hydrological inputs influence wetland water chemistry Elemental inputs to wetlands dominated by hydrological processes - tides, steam/river inputs, flooding, groundwater a) Tides/estuaries - seawater chemically similar worldwide, salinity 33-37 parts per thousand, where sea and river meet: dilution and many chemical reactions, rivers (nitrogen, phosphorus, silicon, iron), ocean (sodium, potassium, magnesium, sulfates, bicarbonates/carbonates) b) Streams/rivers/floods/groundwater - water cycle, water is universal solvent (more than other liquids but not everything), water picks up and drops off nutrients and material throughout the cycle, no typical chemical concentration, ranges are highly variable Nutrients also input via - geologic weathering of rock, biological inputs 10. Recognize the components of a wetland nutrient budget Describe how ecosystem functions and how important it is for specific nutrient cycle - place it into global nutrient cycle; where nutrients are coming from and going is important Inter-related physical, chemical, and biological processes, huge determinant of wetland productivity Intra-system cycling - transformation processes within the wetland Exchange cycling - exchange between wetland and surrounding systems (waters, land, atmosphere) 11. Discuss the variability and generality of nutrient budgets among wetland types Generality- nutrient update and release often has seasonal pattern (temperate climates - high retention during growing season, climates with distinct water have very distinct nitrate pattern), wetlands are coupled to adjacent terrestrial systems (upstream areas are sources while downstream benefits from retention and or export), nutrient cycling in wetlands is unique (more nutrients in sediments/peat than terrestrial systems, less dependent on nutrients in water column than deep water systems), anthropogenic activity impacts wetland nutrient cycling (resilient and essential, kidneys of earth, do not have limitless capacity)