Lecture 12 - (Ecological Systems) - Human Impacts: Deforestation, afforestation, mining and agriculture

What is deforestation?

the removal of natural forest, sometimes which hasnt been touched by humans

What is the importance of old growth forests

they have successional dynamics over time, supporting rich ecological communities

Why are trees important for streams?

• stabilising temperature - through shading

• stabilising soils

  • provides detritus (e.g leaf litter) - organic matter and nutrients

What are species in river ecosystems largely fed by

terrestrial carbon sources - not aquatic.

• Shown by stable isotopes which trace energy flow through the food web

How does large woody debris affect rivers

• creates a step profile = creating energy dissipation of the water

• provides bank protection

• creates debris dam = retention of organic matter

  • log jams can stop the water from flooding, and force new channels

How does large woody debris impact wildlife in river ecosystems

• acts as a food resource e.g for scrapers, tunnelers etc.

  • Acts as a habitat - some insects bury in the wood 

How does large woody debris affect sockeye salmon

• they live in old undisturbed freshwaters their whole lives

• habitat is a key limiting factor to salmonoid production

  • large wood debris provides cover for spawning fish

What is the ideal environment for salmonoid spawning

course gravel with little matrix of fine sediments

• allows clean, well oxygenated water for egg development

Why is silt problematic to salmonoid production

reduces flow and dissolved oxygen = affects egg development

What is yarding?

dragging the logs to a central area for transport = disturbing the soil and generating sediments

Give an example showing how timber harvest affects salmon

Williamette river - Oregon

• logging there has created a more simple flow

• more light and nutrients from the soil = more algae

• more sediment being washed into the river = reduces permeability of gravels = reduces egg fry survival

• 20% fine sediment = no survival of fish

What is phase 1 of the effects of timber harvest on streams

• high algal growth = more autotrophic

  • optimal light and nutrients

  • less CPOM

What is phase 2 of the effects of timber harvest on streams

• low to moderate algal growth

• low nutrients

  • nutrient limitation contains patchiness

What is phase 3 of the effects of timber harvest on streams

• low algal growthlow nutrients 

  • light nutrient interactions create small scale interactions in patchiness in algae growth

Why would creating a buffer zone help act as a best management practice

• most valuable forest in the zone 30m from the bank = would be main source of CWD and leaf litter

• the less wood that is in streams = the less fish present

  • However - the best timber is found in this 30m strip

Why would managing drainage patterns act as a best management practice

• to prevent runoff of pollution from roads from deforestation

why would preventing conifers from being planted in catchments sensitive to acidification be a best management practice

prevents the trees from dying

• however limestone in areas can make trees less vulnerable through its natural buffering capacity

What are the three main stages of tree production

• ground preparation

• closure of canopy

  • felling

Explain ground preparation as a stage of tree production

• ploughing, draining and road construction before planting

  • impacts: high sediment into channels, increased storm flows, leaching from soils

explain closure of canopy as a stage of tree production

• increased interception of deposition

• reduces temperature extremes

• reduces light availability

  • reduces macroinvertebrate abundance and trout

Explain felling / logging as a stage of tree production

increased sedimentation, altered flow regimes etc.

How does grazing affect freshwater systems

• removal of natural vegetation

• altered hydrology

• reduced inputs of natural organic material

• increased sediment erosion

  • livestock manures

How does arable farming affect freshwater systems

• removal of natural vegetation

• reduced inputs of natural organic material

• increased sediment erosion ploughing

= creates diffuse pollution = more difficult to manage than point sources

does organic pollutants have high BOD (biochemical oxygen demand) ?

• organic pollutants (e.g manures) have very high BOD

• clean river water = <5mg L^-1

• cattle slurry = 10,000-20,000 mg L^-1

What are the impacts of nutrients?

• increased turbidity = limits light = less rooted plants

  • less biodiversity - some plants can outgrow the others

What are the sources of nutrients and sediments?

• sewage works

• domestic septic tanks

  • sediment erosion is increased by seed drilling, livestock trampling

What are the impacts of sediments on streams

• reduced space in gravels

• reduced flow and dissolved oxygen

  • reduced light penetration

What are the impacts of pesticides?

• death of natural plants, invertebrates etc.

• potential increase in more tolerant organisms

  • Example: chironomids - stress tolerant - can survive in low oxygen environments.

What are neonicotinoids?

= an insecticide which is normally soaked into seeds = has multiple ways of leaching into the river - most of it stays in the soil

• largely banned in the UK - but farmers can apply it to increase sugar beet yields

What are the best management practices for fertilisers?

• sow autumn crops early

• sow cover crops in winter

• careful management of farm wastes

  • fence off livestock

How does mining affect rivers?

• huge amounts of sediment generated

• abandoned gravel heaps (tailings) = leaches heavy metals into the river

  • causes formation of ferric hydroxide = impacts on algae, invertebrates etc.

what are the best management practices for mining for protecting rivers?

• use settling ponds - traps and removes sediments

• recontour streams - to return to its natural course

• remove tailings - so it doesn’t leach

• replant with natural vegetarian