Nitrogen Flashcards
(17 cards)
Eutrophication process
80% rivers and 75% gw degraded by diffuse poll from agri
Nutrient enrichment problem
Anthropogenic processes alter cycle so nitrogen no longer tightly cycled, leads to excess
The nitrogen problem -what is the source of anthro N?
Industry - nitrous oxide, GHGs, ozone loss, particulate matter
Fertiliser - ammonia, soil acidification, terrestrial fw and marine eutrophication
Eutrophication: what is the EC nitrates directive and drinking water directive standard for N is sw and gw?
11.3mgNO-3 Nl-1
What is the WFD ecological threshold for N?
There is none.
70 streams in Canada studied. Showed 0.2-1.2 mg Nl-1 results in decrease of benthic algae and increase in macro invertebrates.
Therefore limit of 11.3 too high for natural waters, need lower threshold
(Chambers et al, 2012)
Gw contamination: is it increasing?
Yes. Average Nitrate increase of 0.34mg NO3 L-1 yr-1
Highest in Lincolnshire limestone
In 2000 34% of sites exceeded 50mg L-1 standard
By 2015 could be 41%
What is the nitrate time bomb?
In unsaturated zone above aquifer , peaks in nitrate since 1970s (peak input)
Yet to reach saturated zone, thus nitrate conc in abstractions. May continue to increase despite a change in practice/ land use
Areas with pronounced relief thus thick unsaturated zone yet to be fully impacted
What are water companies doing to try and overcome nitrate problems in water?
Blend water with low nitrate conc water
Also costly ion exchange installations - end-users are paying for it!
Treatment not option under WFD
Nitrous oxide problem
Molecule for molecule has global warming potential x310 higher than CO2
Increase of 0.2% per year in troposphere
Agri biggest source - 78%
What are nitrous oxide sources?
Manure
Inorganic fertiliser
Livestock waste
Erosion of N rich soils
Point source
Atmospheric
Mobilisation and pathways : name the 6 pathways for N to enter water bodies and their corresponding zone
- Percolation - root zone and Vadose zone
- Overland flow (particulate N)
- Shallow gw flow - gw
- Deep gw flow - gw
- Inter flow - Vadose zone
- Return flow - hyporheic zone
Look in photos
What are the catchment characteristics which affect mob and pathways?
Soil type Geology Vadose zone Precip and irrigation Crop uptake of N
Wensum DTC N characteristics
VZ = v thin as water table is shallow. This allows rapid transport of nitrates from fertiliser to gw when catchment ‘west up’ - when field drains connect to surface water
What processes can occur? Indirect and direct
Nutrient spiralling between sediment, water column and atmos
Hydraulic flushing can prevent algal blooms, hydraulic drag prevents vertical growth of macrophytes
Direct:
Biogenic soil formation N2O From fertiliser
Indirect:
Conversion of leached N in N2O in water body. This can be quite high due to intensive agri, connectivity of field drains, and slow flowing dense networks of drainage channels = perfect conditions for DENITRIFICATION
Mitigation methods - example of how to tackle source
- Tackle source : - decrease livestock density and length of grazing
- precision application using GPS variable rate and time carefully with weather
- use nitrification inhibiting fertilisers (expensive)
- use plants with high N efficiency
- don’t apply in high risk areas e.g. Next to water bodies
- retrofit septic tanks
Mit methods - limit mobilisation
- Slow the pathway - store solid manure on impermeable surface and collect leachate
- cover manure store with sheeting
- cover crops in autumn
Difficult though as nitrate soluble
MIT methods - protect receptor
Fertiliser and. Crops: - establish artificial wetlands, this can lead to denitrification to N2 and N2O - not good for atmos = ‘ pollution swapping’
