1. Presented by Jane Covey

2. Methods  Mass balance analysis of nitrogen budgets in streams and lakes.  Bacterial processes and sedimentation rates indirectly obtained.  Budgets allow characterization of inputs, outputs, losses and retention of nitrogen.  Used studies of up to 40 ecosystems to quantify data.

3. Inputs  ~10,000 tons per year of atmospherically derived nitrogen (N2).  ~1300 tons entered through rain/snow.  Nitrogen fixation in groundwater/surface water and sediments by bacteria.  Most common forms: N2, NH4+, NO2-, NO3-, and organic compounds [i.e. proteins].

4. Outputs/Losses  Nitrogen removed by processes of sedimentation, denitrification and outflow [DIN/DON].

5. Nitrogen Cycle 1  Nitrogen moves downstream  bound by processes  released  moves farther down.  “Nutrient spiraling” refers to the process above.  Processing involves: ‘chemical ionic transformations, sorption and desorption, and metabolically mediated uptake and assimilation by biota’.

7. Nitrogen Cycle 2  Velocity of nitrogen can equal stream velocity, but usually much slower.  “Spiralling length” {S}=average distance an atom travels in 1 cycle.  Spiralling length indicates which nutrient is limiting. The shorter the length, the more it is in demand.  The cycle is controlled by biologic materials for growth and oxidation-reduction reactions.

9. Nitrogen Cycle 3  DIN: NO3-, NO2-, NH4+. Ammonia (NH4+) concentrations stay relatively low in natural systems [<1.5%].  Polluted systems contain anywhere from 15 to >80 % DIN.  Concentrations of nitrogen are higher when vegetation is dying or dormant.  Stream margins and the riparian zone control DIN interactions between stream and groundwater.

10. http://www.macroevolution.net/nitrogen-cycle- diagram.html

11. Nitrogen Cycle 4  DON: majority of dissolved nitrogen in systems, averaging between 40-90% globally.  PON: adsorbed ammonia/nitrogen adsorbed to particles.  Riparian, parafluvial and hyporheic zones as major sources of ammonium and DON to streams.  Microbes (bacteria, fungi, algae) within streams uptake DON and vary the concentrations.

13. Nitrogen Cycle 5  Nitrogen (various) alteration by: fixation, assimilation and reduction of nitrate to N2 [denitrification].  Oxidation + reduction+ photosynthesis= use by algal blooms, bacteria and plants.  Nitrification: NH4+  NO2-  NO3-[IN]  N2O  N2  Nitrification/denitrification occur simultaneously/reciprocally in hyporheic zone.

17. Variables  Flooding can cause changes in nitrogen concentrations.  Loss of biota reduces nitrogen retention, recovery increases retention.  Agriculture [fertilizers], sewage, industrial waste, atmosphere pollution can throw off concentration of DON/DIN.  Overloading systems with phosphorous can make nitrogen a limiting nutrient.

18. Results  Storage in woody debris/vegetation (59-90%) of forested systems.  Storage in algae/autochthonous detritus (93%) of desert systems.  Steady state assumes inputs = outputs.  Retention is high among low order systems, intensively recycled by organisms and were <50-60 micrograms/L.

20. Discussion questions/ Answers * Considering nitrogen in an ecosystem, is it considered a' non-conservative' substance? How might nitrogen be considered a limiting factor in an ecosystem and what role do humans play in the cycle?