Freshwater Ecosystem Recovery Flashcards
Streams+ Rivers, Ponds+ Lakes and Wetlands
1) black water rivers high acidity so kills bacteria.
2) temperature fairly evenly distributed between the body of water. Water layers may occur varies in temperature in different levels.
3) vast areas which flood could have different purposes throughout the year, e.g. grassland. Got to have water at some point throughout the year. Over half the worlds wetlands have disappeared since 1900.
Changing anyone of these processes or factors may affect the overall balance of the water quality –> determining factors. Leads to a functional aquatic ecosystem.
Past the industrialisation and development stage will then mean that countries will focus and look at their ecosystem services.
Benthic Assemblages
Algae, bacteria, fungi, invertebrates. Transforms matter and energy into life. Bottom of food chain.
Unique adaptations provide valuable services. Break down organic material.
Break down organic matter within the water in order to purify it and make it fresher.
Colorado River
flowed to Mexico and to the Gulf of California. Rich wetlands, one of the most regulated rivers in the world, flow down that river is in now way natural. Lots of sediment within the rivers. Changing the seasonality, relatively warm in the river because it is protected from the frost. Due to over abstraction the water barely ever reaches the estuary in Baja California, only 10% may reach it. Sediment may be supplied by algae. Not a lot of water actually reaching Mexico. Took 1.5 million m3.
US and Mexico water agreement carried on after 2017, instead of pulses they had sustained flow.
Water shortage in the US is continuing therefore impacting upon Mexico.
Habitat Alteration
Inappropriate land-use or poor management (afforestation, overgrazing, land drainage).
SFO built on an estuary, by 1961 –> 90% of wetlands have disappeared .
Urban industrial and agricultural development. London many rivers built over to be used as sewers e.g. River Westbourne or River Fleet. 14 or so restoration projects.
Inappropriate development of recreation and navigation.
Over Abstraction of groundwater and surface water
-Donor Basin: Serious environmental Impacts Reduced flows Threats to endangered species -Recipient Basin: Strong dependence on IBT No demand management On-going water shortages Needs supplementation Groundwater -Over-exploitation: Desalination recycling Economic benefits in Recipient Basin at cost to Donor Basin Catalyst for social conflict Mitigation costs high
Dams and reservoirs, in japan as of 2005, only 3 rivers were not dammed, stop fish migration.
Of 30,000 rivers in Japan, only 3 were not dammed or modified in 2005.
Since 1980s, many restoration programs
Fish migration/pathways constructed
Restoration of wet paddy fields
River restoration
Fish Passes
Need to consider cumulative impact of dams
50% fish pass is considered good – but each additional dam would reduce migrant populations
Only 12.5% of stock would remain after 3rddam
Also need appropriate conditions above passage (access to spawning grounds and nursery areas)
invasive plant and animal species
The rich endemic ichthyofauna of Lake Victoria in Africa have been reduced by
predatory Nile perch (to convert trash fish to consumable fish), massive fish which grows up to 2m too big for previous fishing methods
overfishing (30 mill inhabitants around Lake)
eutrophication (correlated with increase in population)
Restoration and Rehabilitation
Restoration: a complete structural and functional return to the natural ‘pre-disturbance’ state.
Rehabilitation: a partial structural and functional return to the natural, ‘pre-disturbance’ state.
3 main aspect of rivers which require restoration work
The channel
The channel margins
The floodplain
Los Angeles River
turned into a concrete drain in 1940’s to prevent flooding.
Increase speed of flow/capacity of channel by:
widening, deepening the channel to increase cross sectional area
increasing the channel slope by removing meanders
Removal of in-channel obstructions to decrease hydraulic roughness and hence increase flow velocities
Disconnection of the river from it’s floodplain
(Flood barriers, levees, walls etc also do this)
Increases available energy
River out of equilibrium
Bed erosion; cutting new meanders
Increase in peak discharge
Ecological and environmental degradation
IWRM: Flood risk
Hard Engineering approach can cause environmental problems. Integrated Hard/Soft Engineering methods, which takes account of ESS more favoured now
Reconnect river to floodplain
Restore to create additional targeted floodplain storage
Slow and lower flood wave (decrease flood peak, release water later)
Natural Flood Risk Mitigation Methods + Restoration methods include
- trees or channels or flows of trees.
- Restoring meanders to straight rivers
- Enhancing redundant river channels (backwaters)
- Enhancing straight river channels
- Reverting and supporting river banks
- Modifying river bed levels, water levels and flows
Urban Pressures on Rivers
- Much larger population than rural areas
- Many competing uses
- However, more people also mean more money to restore or rehabilitate.
- Restoration of the Pasig River.
Invasive Species
Zebra mussels are paving the shallows of the Great Lakes, displacing native mussels and changing ecosystems.
Quagga mussels are outcompeting xebra mussels lower lakes. Introduced 2005 from Ukraine
Transported by hitch-hiking on boats (ballast water), barges, sea-planes, engines, hulls, anchors, bait buckets, SCUBA gear etc
Low in fat and shell has no nutritional value therefore fish use lots of energy to crush and digest it. Mussels displace other more energy-rich food sources. Leads to fish decline
Filter feeders accumulate pollutants and pass them up the food chain. They eat food that native fish need to survive and clog-up water intakes for urban water supplies and power plants.
How do we restore?
Control and eradicate harmful non-native species
Electric fields for silver carp (stuns, they float), or trawler net
Mussels: chlorine, metal-based solutions, filtering systems, hot water , pesticide development (bacteria)
Pollution control
Greater regulation of point-source pollution
Clean up Persistent Pollutants
Re-introduce native fish species
Lake trout, wild lake sturgeon (most < 25 yrs old)
Fishing closures (sturgeon)
Fish barrier removal
Work to identify, restore, protect habitat
Spawning reefs
Foster CC resiliency
Education
Science-based adaptive management approach
