Test 2.3 Acidification of Freshwaters Flashcards
Natural pH of rainfall
5.6 due to CO2 reaction and rainfall
What is the cause of anthropogenic acidification?
Burning of fossil fuels and wet & dry deposition of acids
Equation for acidification of rain
CO2 + H2O H2CO3 (Carbonic acid)
At what pH determines whether rain is acidic or not
<5.6
Causes of acid rain
- Industrial pollution 9SO2 & H2S) from oil & coal burning power stations and industrial plants. - Forms sulphuric acid
- NOX from car exhausts, power stations and industrial combustion. Forms nitric acid with rainfall
- Land use change, such as afforestation, has enhanced acidification processes
What is wet acid deposition?
Acids in forms of precipitation
What is dry deposition?
Oxides of sulphur and nitrogen adsorbed onto surface of particles in the atmosphere e.g. fine dust & sand
Can be intercepted by ground e.g. trees
Global biggest 3 sources of sulphur and oxides of nitrogen production?
Europe, China & North America
Westerly flow of air wafts pollution across Scandinavia: killing off artic char & brown trout
Globally where are soils most sensitive with the lowest buffering capacity?
North America
Northern & western Britain, parts of Ireland
How can afforestation of conifers cause more acid pollution?
Afforestation of conifers
-Increased deposition of gases and particles intercepted by canopy
Ion exchange of nutrients in roots as they pump hydrogen ions into soil.
Al3+ released where soils lack Ca2+ & Mg2+: Increased conc.s enter streams
-Al complexes with P making it biologically unavailable and lakes become oligotrophic
Increased acidity from litter fall
Increased base cation uptake (Ca, Mg) lowers buffering capacity
More rapid runoff due to drainage; reduced buffering capacity
What are the impacts of acid pollution on fish?
Eggs, juveniles and adults cannot survive pH lower than 5
Particularly in NW Britain, Scandinavia; salmonids and trout
Impacts on fish in water with pH <5.0
Ionic damage occurs: blood has high levels of Na and Cl ions
Reduces osmotic potential of gills
Aluminium causes secretion of mucous on gill surface: cannot take up oxygen
How does species abundance in terms of vertebrates and invertebrates change in acidic waters?
System dominated by vertebrate predators –> Dominated by invertebrate predators e.g. caddisflies
What are the tolerance pH levels of macro invertebrates?
Gammarus very sensitive pH <7
Mayflies pH <6.5 lose Baetidae and Heptageniidae
Most tolerant are stoneflies where pH 4-5
How do acidic waters affect snails?
Calcium difficult to obtain in low pH
Shells become thin and break
How do acidic waters affect microbes?
Loss of aquatic fungi
reduce nutrient procession- reduction in decomposition
Extends amount of CPOM available for shredders as it not broken down by fungi
How do acidic waters affect algae?
Change from diverse and complex diatom algal community in non acid streams to more specialised group.
Eutonia very acid tolerant
How are grazers, collectors and shredders affected by acid waters?
Grazers and collectors are eliminated
Shredders dominant
What are the solutions to acid pollution?
Liming: added powdered limestone to catchment rivers and lakes: rehabilitation by natural processes
What are acid reference sites?
Streams that are acid polluted but unlined
What are the reasons for improvement in water quality but not biodiversity after liming?
Adults would need to fly in and lay eggs to repopulate. Have not arrived or cannot physically get there yet: geographical isolation
What is community closure?
Chemical problems still, resources altered. System has been changed due to pollution.
Animals can and do get there but conditions don’t allow them to colonise
Malaise trap
Black mesh; heats in sun> attracts insect> hide underneath in shade> crawl up and fall in pots
How do malaise traps work and what do they show?
Show adult fly populations surrounding the streams
Black mesh; heats in sun> attracts insect> hide underneath in shade> crawl up and fall in pots
What are the differences in malaise trap findings between polluted & unpolluted sites
Unpolluted: lots of adult and larvae on bank
Polluted: missing larvae from stream and adults from the bank
Post limed sites: Adults present at banks but larvae not in water; shows they can reach the stream but conditions aren’t quite right yet
