1. 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.

2. 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.

3. 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 )

4. N2N2 fixation The Nitrogen Cycle

5. N2N2 fixation Nitrogen Fixation

6. Cyanobacteria with Heterocysts

7. N2N2 fixation Nitrogen Mineralization, Immobilization, and Uptake

8. N2N2 fixation Nitrification

9. 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

10. Nitrification at high pH

11. N2N2 fixation Denitrification

12. Sites of Denitrification Debris Dams Sediments Emergent Plants Lower metalimnion Sewage treatment plants

13. 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

14. Nitrogen Distribution in Lakes

15. Nitrogen in Rivers: Effects of surrounding forests Retentive Leaky

16. Whole-Watershed Manipulations: Control vs. Cut and Leave

17. 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.

18. The 1998 Ice Storm

19. Post-Storm N Spike Ice storm ~ Deforestation Ice storm ~ Deposition

20. In-Stream Retention of N

21. Nitrogen and Humans

22. Natural N-fixation: N 2 → SOLAR ENERGY→ NH 4 + Industrial N-fixation via Haber-Bosh process N 2 (g) + 3H 2 (g) → HEAT → 2NH 3 (g) Combustion of fossil fuels → NO x

23. Nitrogen and Acid Rain HNO 3 H 2 SO 4

24. Delivery of N to Coastal Ecosystems

25. Eutrophication of Coastal Ecosystems

26. The Dead Zone

27. 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

28. Phosphorus in freshwater systems PO 4 3- Phosphate

29. PO 4 3- Organic P Bound in living or decomposing material Phosphorus in freshwater systems

30. 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

31. 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

32. Sources of P in freshwater systems Runoff from land Direct deposition from atmosphere Pollution: wastewater, detergents, fertilizers, animal excretion

33. Cycling of P in freshwater systems PO 4 3- Biological Immobilization PO 4 3-

34. Cycling of P in freshwater systems PO 4 3- Biological Immobilization Sedimentation Metal-oxides (e.g., FeOOH+) Organic particles

35. Cycling of P in freshwater systems PO 4 3- Biological Immobilization Sedimentation Metal-oxides (e.g., FeOOH+) Organic particles HOT SPOT

36. Controls on P-exchange between sediment and water Decomposition by anaerobic bacteria and turbulence at mud-water interface.

37. 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

38. 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

39. Phosphorus Distribution in Lakes

40. 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

41. Eutrophication of Lakes

42. 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

43. The Nutrient Spiraling Model “How far downstream does the average atom of [YOUR FAVORITE NUTRIENT] travel before being taken up by the biota?”

44. The Nutrient Spiraling Model P

45. Estimating S S Low = Retentive S High = Leaky Labeled Nutrient (e.g., PO 4 3- or NO 3 - ) + Inert Tracer (e.g., Br or Cl) Concentration Downstream Nutrient Tracer