Puget Sound Oceanography 2011

Nutrients

Deviation from Redfield Ratios:

The Nitrogen

Cycle

“Nitrogen Fixation”

We can make ammonia in factories, using atmospheric nitrogen and hydrogen (usually from natural gas or petroleum).

Lightening makes about 5-8% of the total nitrogen fixed.

Nitrogen-fixing bacteria (marine cyanobacteria, or living symbiotically with legumes).

Denitrifying bacteria, particularly ones living in anaerobic conditions, use nitrate as a substitute for oxygen in their metabolism. Produce N2 gas as a by-product.

Units you’ll see in the literature:

Unit Abbreviation

Meaning

microgram-atoms per liter

µg-at l-1 10-6 g-atoms per liter

milligram-atoms per cubic meter

mg-at m-3 10-3 g-atoms per m3

[=µg-atom per liter]

Micromolar µM[not µM l-1]

10-6 moles per liter

micromoles per liter

µmol l-1

[not µM l-1]10-6 moles per liter[=µM]

millimoles per cubic meter

mmol m-3

[not mM l-1]10-3 moles per m3

micrograms per liter

µg l-1 10-6 grams per liter[=parts per billion]

milligrams per liter mg l-1 10-3 grams per liter[=parts per million]

metric tonne tonne 1000 kgUse the element’s molecular weight to convert:e.g., 1 µg-at l-1 of nitrogen = 14 µg N l-1

Salish Sea nitrogen inputs

• Ocean: 30 µM; 2600-2900 tonnes /day• Sewage inputs:

• Vancouver: 20-22 tonnes / day• Seattle: 15-16 tonnes / day• Total sewage: <100 tonnes / day

• Rivers and Runoff: • Fraser River: 2-4µM; 50 tonnes / day• Skagit River: 2-4µM; 7 tonnes / day • Total Rivers+Runoff: <75 tonnes / day

• Atmospheric inputs: <10 tonnes / day

From Mackas & Harrison 19971 tonne = 1000 kg

Fraser River: timing of flow

Feb. peaknitrate concentration

summer minimumnitrate concentrationflow

Mackas and Harrison 1997Newton et al, 2002 Washington State Marine Water Column Quality Report

But, nutrient limitation is found in Puget Sound!

Nitrate+Nitritefrom 1998-2000 PRISM samples

Short-term variability in surface concentrations:

1972 USGS survey

Riverine sources of nutrients

Where does the N go?(Total inputs = 2600-3100 tonnes

/day)losses

We have become the dominant source of nitrogen fixation on the Earth – partly by making

fertilizerand partly by growing legumes