Lecture Goals To discuss why nitrogen and phosphorus

Lecture Goals  To discuss why nitrogen and phosphorus

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 N2) N2 io at fix n

The Nitrogen Cycle N2 io at fix

n Nitrogen Fixation Cyanobacteria with Heterocysts N2

io at fix n Nitrogen Mineralization, Immobilization,

and Uptake io at fix Nitrification

N2 n Nitrification Requires high O2 Also very sensitive to pH rates severely reduced at pH < 5.0 When O2 or pH too low, then stops at intermediate

forms: NO2- (nitrite) and N2O (nitrous oxide) In freshwater systems, interested in nitrification because N needs to be in oxidized forms (NO3and NO2-) to partake in denitrification Nitrification at high pH io at

fix Denitrification N2 n Sites of

Denitrification Debris Dams Emergent Plants Sediments

Lower metalimnion Sewage treatment plants Who is doing the work and what are they working with? N fixation: Cyanobacteria and terrestrial N-fixers

Light + N2 NH4+ immobilization and uptake: Microbes and plants NH4+, Light or No light, O2 or CO2 Nitrification: Chemoautotrophic microbes NH4+, O2, moderate pH Denitrification:

Anaerobic bacteria and fungi NO3- (NO2- or N2O), Carbon, low O2 Nitrogen Distribution in Lakes Nitrogen in Rivers:

Effects of surrounding forests Leaky Retentive Whole-Watershed Manipulations: Control vs. Cut and Leave

WholeWatershed Results Similar results from fire, but if build-up of charcoal in soil, then sorption of NO3-. Can also have formation of NH4+ in

atmosphere due to heat (energy from fire), then direct deposition. The 1998 Ice Storm Post-Storm N Spike Ice storm

~ Deforestation Ice storm ~ Deposition In-Stream Retention of N

Nitrogen and Humans Nitrogen and Humans Natural N-fixation: N2 SOLAR ENERGY NH4+ Industrial N-fixation via Haber-Bosh process N2(g) + 3H2(g) HEAT 2NH3(g)

Combustion of fossil fuels NOx Nitrogen and Acid Rain H2SO4 HNO3

Delivery of N to Coastal Ecosystems Eutrophication of Coastal Ecosystems The Dead Zone

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

Phosphate PO43- Phosphorus in freshwater systems PO43- Organic P Bound in living

or decomposing material Phosphorus in freshwater systems PO43- Organic P Particulate P

Stuck to particles, especially metaloxides (e.g., FeOOH+) Also in sedimenting organic particles Carried to sediments Phosphorus in freshwater systems PO43- Organic P

Dissolved P Particulate P aka, SRP Released via decomposition by anaerobic bacteria in sediment Also some decomp.

in water column 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 PO43- Biological Immobilization PO43-

Cycling of P in freshwater systems PO43o talMe e xid .g., s (e FeO

Biological Immobilization +) OH Organic particles

Sedimentation Cycling of P in freshwater systems PO43o talMe e xid

.g., s (e FeO Biological Immobilization +)

OH Organic particles Sedimentation 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 mudwater 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 mudwater interface

Redox conditions within the sediment Water acidity > As pH increases, PO43- released Phosphorus Distribution in Lakes Internal Loading of P Change in internal conditions of lake

cause massive release of P in sediments Mixing of sediment Increased pH Whole-lake anoxia Eutrophication of Lakes P in rivers

Pulse with high runoff or early stages of snowmelt Generally see higher P levels in rivers and streams than in lakes because access to biota limited by flow dynamics The Nutrient Spiraling Model How far downstream does the average

atom of [YOUR FAVORITE NUTRIENT] travel before being taken up by the biota? The Nutrient Spiraling Model P Labeled Nutrient

3(e.g., PO4 or NO3 ) + Estimating S Concentration Inert Tracer

(e.g., Br or Cl) S Low = Retentive S High = Leaky Tracer Nutrient Downstream

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