Test 2.3 Deforestation, Afforestation, Mining and Agriculture Flashcards
Why is wood important In rivers?
Wooded debris: source of food
Structure for habitat
Meaning of CWD & LWD
Coarse wooded debris
Large wooded debris
Importance of CWD & LWD
LWD contributes to heterogeneity (diversity) of habitat: riffles, runs, pools
- Traps gravel- especially important for fish spawning
- Protects banks from debris
- Provides habitat for macroinvertebrates
- Stabilizes flows- evapotranspiration
- Stabilises temperature regimes
Importance of riparian vegetation in terms of LWD
Provides cover and produces leaf litter CPOM - food for fish
What is ideal about salmonid spawning gravels?
• Ideal habitat: coarse gravel with little ‘matrix’ of fine sediments
- Allows flow of clean, well-aerated water for egg development
• Problem if excessive amounts of ‘fines’
- Especially <0.84mm
- Clogs gravels & reduces flow and DO
What is the effect on light due to timber harvesting on streams?
• Light levels & nutrients
- Opening up canopy increases light
- Nutrients leached from soils
- Greater development of phytobenthos (algae)
- Greater densities of invertebrates – food for juvenile salmon:
What is the effect on stream flows due to timber harvesting on streams?
- Less evapotranspiration
- Increased flood events
- Lower base flows
What is the effect on temperature due to timber harvesting on streams?
- Greater variability in temperature
What is the effect on fine sediment harvesting on streams?
- Clogging of interstital spaces / under stones bad for some mayflies; caddisflies; stoneflies
- May favour burrowing forms: some worms, fly larvae
- Algae on stone surfaces reduced (smothered
Best management practices of streams:
• Leave a buffer strip of 30m either side of rivers
• Manage drainage patterns
- Prevent runoff of fine sediments
- Slash debris
Best management practices in mining operations
- Use settling ponds- trap & remove sediments
- Re-contour streams
- Remove tailings
- Replant with natural vegetation
Name forms of organic wastes
- Manures: direct or sprayed onto fields
- Slurry & washings from buildings
- Milk and dairy washings
- Silage liquors
What % of the world do forests cover?
30%
What % of the UK do forests cover?
13%
-2.3% ‘ancient’ but not post ice-age ‘old growth’ forest
Meaning of Obligate wood species
Meaning of Facultative wood species
Obligate: Only found on wood in streams- e.g. Chironomidae
Facultative: May be found on other substrates
How are old growth forest river streams important for fish (salmon) species?
LWD streams provide habitat for all stages of life cycle:
Deep pools
Refuges under logs for adults
Clean gravels trapped by woody debris for spawning
Rich food resource and cover for young fry fish
Why are salmonid spawning gravels an ideal habitat
Allows flow of clean, well-aerated water for egg development
Problems if excessive amounts of ‘fines’ (<0.84mm)
-Clogs gravels & reduces flow & DO
What is yarding and what are its ecological effects?
The dragging of logs to central area for transport generating disturbance to soils and creates sediment
Disturbance generates disturbance; fine trashy material when wood is sawn
Effects of timber harvest on stream channels path?
More simplified river channels: traded & complex to simple single channel system
e.g. Willamette River Oregon
Effects of timber harvest on stream light & nutrients?
- Opening up canopy increases light
- Nutrients leached from soils
- Greater development of algae
- Greater densities of invertebrates
- Food for juvenile salmon
Old growth forest: lower algal growth
Clear cut forest: highest algal grow
Density of salmon fry strongly correlate with algal biomass
Effect of timber harvest on stream flows
- Less evaporations-transpiration
- More rapid runoff
- Increased flood events
- Lower base flows
Effects of timber harvest on temperature
-Greater variability in temperature due to reduced shading
- Increased summer temperatures (heat/DO stress)
- Greater algal production
-Extreme winter cold temperaturesger
How does amount of fine sediment affect permeability & oxygen?
As the amount of fine sediment (<0.88mm) amongst the gravel particles increases - the permeability (allowing oxygen flow) declines rapidly
How does fine sediment affect invertebrates?
Clogging of interstitial spaces / under stones: bad for some mayflies, caddisflies, stoneflies
May favour burrowing forms. Some worms, fly larvae
Algae on stone surfaces reduced (smothered)- fewer grazers
How does turbidity affect invertebrates?
Reduced light penetration
Algae on stone surfaces reduced»_space; fewer grazers
Meaning of ‘Slash’
Woody debris especially in small streams
-Decays & uses up oxygen
May change hydrology & ecology
What is the most valuable part of the forest with respect to the stream?
The riparian zone 30m from the bank
40% of woody debris comes from first meters away from stream
How can timber harvest be managed better? (Ecologically with fish communities in mind)
Leave 30m riparian zone untouched
Manage drainage patterns
- prevent runoff of fine sediments
-
What is the relationship between Coho salmon and volume of large woody debris?
Positive relationship
More woody debris = better for salmon
Describe fish productivity in old growth streams
Lots of CWD LWD provides refuge from fast flows. Good proportion of fish survive the fast flows through to the spring
Describe fish productivity in Clear-cut streams
More light due to cut back trees, algal growth, greater density of invertebrates, increase in number of young fish.
No protection from winter flood flows, a lot wash out and die. Productivity less than old growth forest
Describe fish productivity in buffered streams
Happy medium
Logs providing refuge: production in spring is higher
Light allowed to reach stream; increase in young fish
Strip of trees still provides woody debris providing refuge from high flows in winter so fry production in spring is higher
Name afforestation common commercial species and their beneficial features
Sitka spruce (UK) Monterey Pine (NZ) -Fast growing on nutrient-poor soils (28 years from planting to harvesting)
Current UK woodland cover
12.9% most of which commercial forest
Minimum 5% between WW1 & 2
Big increase in planting post war- Forestry Act
Incentive to replace commercial woodland with native species
Current NZ % of forest that is commercial
96% - major exporter
Three stages of commercial forestry
Ground preparation
Closure of canopy
Felling
What occurs in the Ground Preparation phase of commercial forestry and what are the impacts?
-ploughing, draining, road construction, planting
Impacts:
- Increased sediment and turbidity- infilling of channels
- Increased flows during periods of high rainfall
- Leaching of nutrients (& herbicides) from soils
What occurs in the Closure of Canopy phase of commercial forestry and what are the impacts?
Rapid, dense growth
Impacts:
- Interception of wet and dry deposition; acidification
- Exclusion of light
- Reduced summer temps; raised winter temps
- Reduced primary productivity
- Reduced macro invertebrate abuncance
- Study in Scotland showed 15% reduction in trout growth in afforested streams
What occurs in the Felling/Logging phase of commercial forestry and what are the impacts?
Similar effects to removal of old-growth forests but not as marked
Impacts:
- Altered flow regimes
- Increased sedimentation
- Acidification
- Reduction in light penetration and productivity
Best management practices for afforestation
30m riparian vegetation buffer strips
Good ditching and interception of runoff
Removal of ‘slash’ from small streams
Minimise use of pesticides & nutrient additions
Effect of gold mining in Alaska on rivers
Before:
Natural braided river
Natural riparian zones
After:
Channel moved
Sediments excavated and gravels sorted - washed
Huge amounts of sediment generated
Impacts of left tailings (abandoned gravel heaps) on rivers
Leach heavy metals: As, Al, Zn, Pb, Cu, Hg
- Toxic effects
- Example of ‘press’ disturbance
Mining impacts
Heavy metals Chlorides Ferric hydroxide - smothers substrate Impacts on algae, invertebrates, spawning
Best management practices in maintaining rivers affected by mining operations
Using settling ponds- trap & remove sediment
Re-contour streams
Remove tailings
Replant with natural vegetation
What are some common practices and characteristics of agricultural activities?
- Removal of natural vegetation
- Altered hydrology
- Reduced inputs of natural organic material
- Increased erosion ‘poaching’ - sediments e.g. potato turning
- Livestock manures
- Artificial fertilisers
Name dominant forms of pollution in agricultural activities
Farm wastes
Nitrates
Pesticides
Sediments
How do pollutants from farmlands reach rivers?
Wash in directly
Leach through soils
Manure spread on ground- wash into rivers
Animals may have direct access to rivers
Name forms of organic wastes
- Manures
- Slurry & building washings
- Milk & dairy
- Silage liquors
What pollutants have the lowest Biological Oxygen Demand (BOD) in order in mg l-1?
Clean river water <5mg l-1
Treated sewage ~20mg l-1
Untreated sewage ~300mgl-1
Dilute dairy parlour & year washings 1000-5000 mg l-1
Liquid effluents draining slurry stores 1000-12,000 mg l-1
Cattle slurry 10,000-20,000 mg l-1
Pig slurry 20,000-30,000 mg l-1
Silage effluents 30,000-80,000 mg l-1
Milk 80,000-120,000 mg l-1
What are the % sources of N in rivers?
Agricultural land 60%
Sewage treatment works 35%
Other land 5%
What are the % losses of N in crops?
Potatoes 100%
OSR 70%
Peas 70%
Beans 60%
Impacts of nutrients (increased N & K)
Eutrophication
- Rapid plant growth
- Death & decay
- Microbes use up O2
^Increases turbidity: even more reduced light
How does increasing nutrients effect the vegetation in a stream?
With increasing levels of nutrients there tends to be a move from rivers dominated by macrophytes (rooted) to algae
Impacts of herbicides and insecticides
Herbicides
- weed control in crops
Insecticides
- Crop pests
- Livestock treatment for worms
- Sheep dipping for ectoparasites
Impacts:
- Death of natural plants; invertebrates; fish
- Potential increase in more tolerant organisms
Best management practices to protect water courses from agricultural activities
Decrease ploughing in autumn Delay ploughing in crop residue (winter stubble) Sow autumn crops early Sow cover crops in winter Carefule storage of farm wastes Decrease amounts of fertiliser, manure & sewage applied Leave minimum 10m buffer zone Fence off livestock
