Presentation on theme: "Lecture Goals To discuss why nitrogen and phosphorus are important nutrients in freshwater systems. To trace how nitrogen and phosphorus move through freshwater."— Presentation transcript:
Lecture Goals To discuss why nitrogen and phosphorus are important nutrients in freshwater systems. To trace how nitrogen and phosphorus move through freshwater systems, how they are transformed in the process. To identify important ecological factors that influence movement and transformation of nitrogen and phosphorus.
Why are N and P important? N and P commonly the nutrients in greatest demand by plants and heterotrophic microbes relative to supply (i.e., limiting resources). N commonly limiting in terrestrial systems, estuaries, and oceans. P commonly limiting in freshwater systems.
The problem with N Nitrogen is an essential part of amino and nucleic acids N is abundant on Earth (78% of atmosphere) Only 2% available to organisms as reactive N (bonded to C, O, or H) The rest is unreactive N (triple-bonded N 2 )
Requires high O 2 Also very sensitive to pH → rates severely reduced at pH < 5.0 When O 2 or pH too low, then stops at intermediate forms: NO 2 - (nitrite) and N 2 O (nitrous oxide) In freshwater systems, interested in nitrification because N needs to be in oxidized forms (NO 3 - and NO 2 - ) to partake in denitrification
Who is doing the work and what are they working with? N fixation: Cyanobacteria and terrestrial N-fixers Light + N 2 NH 4 + immobilization and uptake: Microbes and plants NH 4 +, Light or No light, O 2 or CO 2 Nitrification: Chemoautotrophic microbes NH 4 +, O 2, moderate pH Denitrification: Anaerobic bacteria and fungi NO 3 - (NO 2 - or N 2 O), Carbon, low O 2
Nitrogen in Rivers: Effects of surrounding forests Retentive Leaky
Whole-Watershed Manipulations: Control vs. Cut and Leave
Whole- Watershed Results Similar results from fire, but if build-up of charcoal in soil, then sorption of NO 3 -. Can also have formation of NH 4 + in atmosphere due to heat (energy from fire), then direct deposition.
The problem with P P is a major cellular component, but occurs at VERY low levels in freshwater systems P often limits primary production in freshwater systems
Phosphorus in freshwater systems PO 4 3- Phosphate
PO 4 3- Organic P Bound in living or decomposing material Phosphorus in freshwater systems
PO 4 3- Organic P Particulate P Stuck to particles, especially metal- oxides (e.g., FeOOH + ) Also in sedimenting organic particles Carried to sediments Phosphorus in freshwater systems
PO 4 3- Organic P Particulate P Dissolved P aka, SRP Released via decomposition by anaerobic bacteria in sediment Also some decomp. in water column Phosphorus in freshwater systems
Sources of P in freshwater systems Runoff from land Direct deposition from atmosphere Pollution: wastewater, detergents, fertilizers, animal excretion
Cycling of P in freshwater systems PO 4 3- Biological Immobilization PO 4 3-
Cycling of P in freshwater systems PO 4 3- Biological Immobilization Sedimentation Metal-oxides (e.g., FeOOH+) Organic particles
Cycling of P in freshwater systems PO 4 3- Biological Immobilization Sedimentation Metal-oxides (e.g., FeOOH+) Organic particles HOT SPOT
Controls on P-exchange between sediment and water Decomposition by anaerobic bacteria and turbulence at mud-water interface.
Controls on P-exchange between sediment and water Decomposition and turbulence at mud- water interface Redox conditions within the sediment > Oxidized zones = retention by sorption > Anoxic zones = release by reduction
Controls on P-exchange between sediment and water Decomposition and turbulence at mud- water interface Redox conditions within the sediment Water acidity > As pH increases, PO 4 3- released