Lecture 3 CM

Question 1

Secondary succession: peatlands

Answer 1

• vegetation in Ireland has developed since the end of the Pleistocene glaciation c.15000 ya
• bogs began forming around 9000 ya, once initial forest/scrub has become established
• vegetation developed along different pathways in different areas

Question 2

What happened approx 15000 ya in Ireland?

Answer 2

• Ireland had a mosaic of deep glacial sediment and shallow lakes. slow formation of soil by bacteria, lichen, mosses and artic herbs.
• it looked like present-day Iceland

Question 3

What happened approx 10000 ya in Ireland?

Answer 3

• Ireland had a mosaic of shallow lakes and sparse forests on poor soils. Peatlands became extensive after this point
• it looked like present-day Finland

Question 4

What methods are used to date sites?

Answer 4

• Deglaciation events
• Volcanic eruptions

Question 5

Deglaciation events

Answer 5

time point where ice recedes from landscapes

Question 6

volcanic eruptions

Answer 6

• time point where ash is deposited
• they disperse airborne particles across the globe
• each eruption creates a unique array of rock particles and crystals
• these deposits uniformly across the surface of the Earth and are used to calibrate dates between sites

Question 7

What are the 3 Irish peatland types?

Answer 7

1. raised bogs
2. atlantic/lowland blanket bogs
3. mountain blanket bogs

Question 8

What are peatlands characterised by?

Answer 8

• very acid soils
• mor type soils
• permanently waterlogged
• anoxic
• acidic
• very low biological activity

Question 9

Poor degradation of organic material leads to peat accumulation…

Answer 9

• 5 m deep (blanket bogs)
• 10 m deep (raised bogs)

Question 10

What plants dominate peatlands?

Answer 10

• Sphagnum mosses (acidifiers)
• Ericaceae (heathers)
• Cyperaceae (sedges)
• some Poaceae (grasses)

Question 11

Blanket bogs

Answer 11

• approx 10000 ya before present, forest became established on the shallow soils that had formed over glacial mineral gravel
• approx 4500 ya, climate became wetter and cooler, rainfall began to leech nutrients from topsoil
• gradually all highly soluble nutrients were washed away completely
• soluble elements, especially iron came out of the solution in the subsoil and bound with anoxic clays to form iron pan

Question 12

What is iron pan impermeable to?

Answer 12

water and plant roots

Question 13

What did waterlogging in blanket bogs lead to?

Answer 13

• waterlogging ensued and combined with acidic surface soil conditions providing an ideal habitat for colonisation by acid loving plants
• this lead to a successional sequence where Sphagnum moss began to colonise the soils in place of tree seedlings, especially in poorly draining areas
• heathers, sedges, grasses and Sphagnum moss take over the habitat and peat begins to form

Question 14

Sphagnum moss

Answer 14

• K selected dominant species that controls growth of bogs
• high water retention : wet weight = 95%
• cell differentiation is evident but no vascular system
• secretion of the antibiotic Sphagnol impedes microbial degradation of dead plant tissue

Question 15

What are Sphagnum moss specialised structures?

Answer 15

• hyaline cells, non-photosynthetic with large open pores
• hanging branches that draw water upwards
• hydrogen ion pumps are present in the cell wall
  –> exchange free hydrogen ions (H+) for CA++, Mg++, K+ etc
  –> facilitates efficient nutrient foraging in mor soil conditions
  –> acidification of soil and water

Question 16

What is the general morphology of Sphagnum moss?

Answer 16

• head/rosette
• stem
• spreading branches
• hanging branches

Question 17

Raised bogs

Answer 17

• associated with inland freshwater ecosystems
• form from fens (alkaline peats)
• fens develop through colonisation of nutrient-rich lake margins by reeds causing accumulation of nutrient-rich fen peat
• the fen peat eventually accumulates above the water table, reducing level of available nutrients
• gradual acidification of upper layers, colonisation by acid-loving flora, including Sphagnum
• rapid accumulation of acid, poorly degraded peat leads to development of a dome-like structure

Question 18

types of fen peat

Answer 18

• Phragmites australis (common reed)
• Typha latifolia (bulrush)
• Phalaris arundinacea (reed canary grass)

Question 19

What are the pH levels of peat accumulation above/below the water table?

Answer 19

• above the water table is acidic (influenced by rainfall and acidifying action of Sphagnum moss)
• below the water table is alkaline (influenced by groundwater chemistry e.g. limestone)