Lecture 14 - (Freshwater Ecology) - Acidification

what is the natural pH of freshwaters?

5.6 - due to reaction of CO2 and rainfall

what pH is acid rain?

where pH = <5.6

how does industrial atmospheric pollution?

from oil / coal burning = forming sulphuric acid

How does car exhausts and industrial combustion cause acidification?

forms nitric acid with rainfall to produce acid rain

What is wet deposition?

a process where pollutants in the atmosphere are mixed and brought down to the earth’s surface through percipitation

how does wet deposition affect granite bedrock

• acid accumulates, meaning the pH decreases, and increases acidity

How is limestone affected by wet deposition

sufficient buffering capacity to absorb the hydrogen ions = so the pH doesn’t fall

How does soil sensitivity differ with acid rain

• soils differ in their capacity to neutralise acidity

  • e.g areas of northern europe are most sensitive to low pH

How is the river Wye in Wales an example of surface water acidification?

• acidification made worse by land use, afforestation of conifers = trees uptake base cations = reducing buffering capacity

• ionic exchanges in the soil - can cause aluminium (AL) to be release = where soils are poor in the base cations Ca2+ Mg2+

  • Oligotrophication can occur - the process of reduced nutrient cycling = reducing plant and animal production

what are the effects of acidifcation of aquatic communities

• example: atlantic salmon - can have a knock on effect on communities

• once pH goes below 5.5 - fish and eggs can be wiped out

• the availability of wildlife to osmoregulate is impaired - in acidified waters H+ ions are absorbed over Na+ ions

  • excessive loss Na ions can cause mortality

What are the effects of acidifcation on macroinvertebrates?

• in acid waters H+ and Al3+ dominate = may be absorbed instead of essential nutrients like Na, K = could cause death

• e.g gammarus - very sensitive to pH <7 = reduced number of shredders like gammarus = results in less herbivory

  • e.g stoneflies = less sensitive = dominate where pH are lower

What are the impacts of acidification on microbial communities?

• reduction in microbial communities = leads to reduction in nutrient processing - because reduction in deomposition

  • may impact CPOM available

What is the impact of acidification on microbial communities?

• causes shifts in algal assemblages = may influence primary production / food availability for invertebrate grazers

how does acidification affect the food web?

• loss of fish = loss of predators

• increase in invertebrate predators

• these communities become more detritus based = decrease in grazers breaking down CPOM

• shredders persist - because of abundance of stoneflies = acidic communities shift to detrivory

What are the solutions to freshwater acidification?

• decline in air pollution in the UK - e.g concentrations of sulphur dioxde have decreased

• = improvement in lakes and rivers = e.g lake doon in 1978 = 4.3 pH to 1998 pH of 5.0

  • liming = adding base materials to provide buffering capacity

What is the downside to liming?

very fish focused - does not consider the surrounding landscape

give the example of Llyn Brianne, Wales (experiment) to show impacts of acidification on freshwater communities

• looked at different streams on Llyn Brianne = used liming to assess the impacts of it on acidity

• also had streams that were not limed

• results = from one single liming = streams showed sustained increase in pH and reduction in aluminium, and increase in calcium

  • results for invertebrates = no marked increase in biodiversity

Why does liming in streams not mean biodiversity will increase?

chemical recovery does no equate to biological recovery

• option A: colonists arrives but do not persist = may take time to establish themselves

• option B - colonists not arriving at sufficient rate

• geographical isolation of recovering sites = dispersal could be a limiting factor