Flashcards in Nitrates Deck (28)
What is the most abundant element in our atmosphere?
Nitrogen ~ 80%
What type of organism are the only ones able to make atmospheric nitrogen usable?
How is usable nitrogen added to the earth each year?
Biological fixation ~ 50%
Adding fertilisers to crops ~ 45%
High energy fixation (nitrates as nitric acid in rainwater) ~ 5%
What enzymes catalyse the splitting of N2?
Feredoxin, nitrogen reductase and nitogenase
Chemical formula for production of ammonia?
N2 + 3H2 ---> 2NH3
Types of nitrogen fixers?
Most important free living fixers in the genus Clostridium
Most important aquatic fixers include Cyanobacteria like Anabaena
Some bacteria also associate with plants in root nodules (esp. Legumes), genus Rhizobium
Some non-legumes plants also have nodules (eg. Alder, tea, olive)
Which genus' can further oxidise ammonia/ammonium into nitrate and nitrite?
Nitrosomonas and Nitrobacter
What is the process called where N2 is returned to the environment and name a genus of bacteria that do this?
Denitrification - Pseudomonas
How has agriculture increased nitrogen in aquatic environments?
Land conversion exposes soil to elements, nitrates leach easily
Soil cultivation speeds up decomposition (soil microbial activity) and associated leaching
Harvesting removes nitrogen (fertilisers used)
Farm specialisation (point source pollution: livestock, fish farms)
What 4 impacts can increased nitrate levels have?
Acidification of water
Toxicity to aquatic life
Toxicity to humans
What does acidification of aquatic environments increase?
Trace metals (aluminium, lead, cadmium etc)
Effects of acidification of water?
Decline in invertebrate species (esp. Crustaceans)
Decline in fish (esp. Salmonids)
Microbial activity in freshwater is impaired below pH 5, stopping or slowing decomposition
What do algal blooms lead to?
Decreased light penetration (productivity of deep water plants diminishes)
Algae die and decomposition proceeds leading to an increase in biological oxygen demand (BOD) so decreasing dissolved oxygen content (hypoxia)
Examples - Baltic Sea, Black Sea, Gulf of Mexico
Less oxygen leads to?
Death of invertebrate species
Death of fish
Build up of hydrogen sulphide (toxic to many aquatic species)
What kind of algae can produce toxins?
Cyanobacteria, dinoflagellates and diatoms
Why are non heterocystous species of blue green algae dangerous to aquatic life?
Cannot fix N2
Most common bloom forming genus is Microcystis which produces the toxin microcystin (this can kill fish and various invertebrates)
What are the characteristics of Dinoflagellates?
Red-brown algae (eukaryotes)
Produce so-called red tides
Most well known genus are Karenia
Produce numerous toxins that can kill both vertebrates and invertebrates
Clear link with elevated levels of nitrate in water courses
Characteristics of diatoms?
Eukaryotic siliceous algae produce the neurotoxin Domoic acid
Kills vertebrates and invertebrates
Linked to elevated nitrate levels
Elevated nitrate levels in water can have what effects on humans?
Illness related to toxins from algal blooms
What is methaemoglobinaemia?
Blue baby syndrome
Nitrates convert to nitrites in digestive tract
Nitrites react with haemoglobin to form methaemoglobin which has reduced oxygen transport capacity
Occurs when normal methaemoglobin levels rise from 1-3% to over 10%
Causes tachycardia, cyanosis, convulsions, coma and ultimately death
Why are infants more at risk of methaemoglobinaemia?
Larger fluid intake relative to body size
Fetal haemoglobin has a high affinity for nitrite
Higher stomach pH favours nitrite/haemoglobin reaction
Lower levels of methaemoglobin reductase activity
Why is elevated nitrates a cancer risk?
Formation of dimethylnitrosamines in digestive tract
Caused by nitrite and amines (from meat) reacting
Cancers include stomach, oesophageal and colorectal
Other effects of elevated nitrates to humans and other vertebrates?
Algal toxins - blooms can lead to rashes, vomiting, fever, pneumonia etc
Paralytic shellfish poisoning - approx 2,000 cases per year with some fatalities. Caused by exposure to toxins concentrated in shellfish
Amphibians in worldwide decline possibly because of exposure to nitrite and nitrate
What is the aim of EU act (91/676/EC)?
To reduce nitrate levels in ground and surface waters caused by agricultural sources - manure/chemical fertilisers
Directive requires member states to establish action plans (by 1996) on areas designated as nitrate vulnerable zones (NVZs)
What water courses are regarded as NVZs?
Nitrate levels are above 50mg/L
Where eutrophication exists (algal blooms etc)
Where water body may become eutrophic
How much of Scotland and England are NVZs?
Which countries are designated 100% NVZs?
Scotland - 20% of land on East Coast
England - 68 identified mostly in Midlands expanded in 2012
Germany Sweden and Denmark designated 100%
What are the action plans, assistance and policing of the act 91/676/EC?
Plan - farms must have sufficient manure storage capacity
Fertiliser applications based in crop requirements
Livestock manure limited to 170kg N/ha/year
Records on fertiliser application kept
No application to steep slopes if rain is forecast
Assistance - Grants up to 40% available to help with manure storage
Policing - SEPA in Scotland and Environment Agency in England