Presented by Jane Covey

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.

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].

Outputs/Losses

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

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’.

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.

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.

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

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.

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] N2ON2

Nitrification/denitrification occur simultaneously/reciprocally in hyporheic zone.

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.

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.

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?