Centre for Environmental Sciences

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Centre for Environmental Sciences
Hampshires Chalk Stream Headwaters Forum
Scientific Research
Dr Peter J Shaw, Centre for Environmental
Sciences, School of Civil Engineering and the
Environment, University of Southampton, SO17 1BJ
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Centre for Environmental Sciences
Characteristics and status of chalk streams
Around 90 of the annual discharge may derive
from groundwaters (1) Relatively persistent
hydrology and flow Maximum minimum daily
flows typically 31 generally less than 101
(2) Large floods are rare (3) (1) Mainstone,
1999 (2) Ladle Westlake, 1995 (3) Casey
Smith, 1994
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Characteristics and status of chalk streams

• Relatively constant temperature due to the
  influence of aquifers (4)
• Spring waters generally circa 11C
• Generally range 5 to 17C
• (4) Berrie, 1992

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Characteristics and status of chalk streams

• High fertility and productivity (4)
• Diverse communities of macroinvertebrate fauna
  (4)
• Diverse communities of aquatic plants (4)
• - Clear water and good light penetration
• Numerous conservation designations for habitats
  and species
• (4) Berrie, 1992

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Human impacts and interventions

• Contemporary problems chalk stream malaise
• Historical management and exploitation
• Energy sources and anthropogenic change

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Centre for Environmental Sciences
Chalk stream malaise

• Reduced water clarity
• Declines in fish (salmonids and coarse fish)
• Declines in macroinvertebrates (mayfly, stonefly
  caddis fly)
• Siltation of gravel streambeds
• Proliferation of filamentous algae (benthic and
  smothering of e.g. water crowfoot)

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Blanket weed
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Chalk stream malaise

• Reduced water clarity
• Declines in fish (salmonids and coarse fish)
• Declines in macroinvertebrates (mayfly, stonefly
  caddis fly)
• Siltation of gravel streambeds
• Proliferation of filamentous algae (benthic and
  smothering of e.g. water crowfoot)

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Chalk stream malaise causal factors?

• Reduced discharge and associated reduction in
  flow rates
• Agricultural activities (e.g. soil run-off,
  pesticides fertilizers)
• - Broad agreement between the scientific research
  community and the angling community. (5)
• (5) Frake Hayes, 2001

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Historical management and exploitation
What we have now is a product of past and
continuing human intervention, including -
Deforestation - Water abstraction -
Irrigation - Waste water disposal - Flood
control - Hydropower - Fisheries -
Agriculture See (1) Mainstone,1999
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Energy sources and anthropogenic change

• A densely wooded catchment would provide
  predominantly allochthonous energy.
• By removing tree cover, growth of in-stream plant
  life has been opened up nutrients in river water
  can be exploited and the system becomes
  underpinned by autochthonous energy.
• In a catchment naturally rich in nutrients,
  supplementary nutrients from agriculture further
  increase the potential for plant growth.

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Ecological perspectives habitat food

• Key aspects of habitat
• Water quality and composition
• Discharge, flow velocities, flow structure
• Geomorphology
• Niches and refugia
• Disturbance and variability
• Diversity and connectivity

• Key aspects of food resources
• Quality
• Quantity
• Palatability
• Supply variability
• Competition for food resources
• Predation

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Focal points for chalk stream headwaters

• How do animals (macroinvertebrates) and plants
  interact?
• What is the role of nutrients in chalk stream
  ecology?

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Macroinvertebrate plant interactions
Plants in chalk streams provide both food and
habitat structure, but herbivory is a threat.
Plants such as watercress have a natural chemical
defence (phenylethyl isothiocyanate PEITC) which
is released when plant tissue is physically
broken down. PEITC is a natural pesticide which
is produced at artificially high levels by
handling of watercress and similar plants when
plant tissue is damaged.
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PEITC and impacts on freshwater shrimp

• High concentrations lead to high mortality in
  gammarids (toxicological response)
• Water containing PEITC will be avoided by
  gammarids (behavioural response)
• PEITC breaks down by about 50 in 30 minutes
• Gammarids live in watercress beds themselves
• Gammarid abundance downstream of watercress farms
  is reportedly lower than is typical for chalk
  streams

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• The presence of gammarids downstream of
  watercress farms infers that toxicological
  responses and effects may be sub-lethal
• Feeding?
• Breeding?
• Exposure frequency
• and intensity?
• Gaps in knowledge prevail research is
  ongoing.

http//www.shef.ac.uk/aps/apsrtp/harkness-jo/gamma
rus.bmp
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Centre for Environmental Sciences
Nutrients in chalk rivers

• Chalk catchments tend to be naturally fertile.
• Human activity adds to natural fertility (6,7)
• Agriculture livestock, fertilizer use
• Waste water discharge
• Soil particles in run-off
• Six-fold nitrate rise in 100 years(6) (Dorset)
• (6) Limbrick, 2003
• (7) DEFRA, 2003

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• Nutrient impacts depend on
• Quantity of nutrients
• Speciation, availability, and interaction with
  sediments (8)
• Incident light availability water clarity
• In-stream recycling remobilisation (9)
• The balance of nutrients and nutritional needs of
  plants (limiting nutrient concept)
• (8) House, 2003
• (9) Bowes et al., 2005

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Impacts of nutrients in chalk rivers
there is no conceptual understanding of how
eutrophication develops in rivers. (10) Hilton
et al., 2006 But Proliferation of filamentous
algae (7) may be due to high levels of nutrients,
i.e. weeds outcompeting other, beneficial
macrophytes (e.g. Ranunculus water crowfoot).
(7) DEFRA, 2003 ).
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Contemporary future management

• What is our vision for chalk streams?
• Do we know what our vision comprises functionally
  and structurally?
• Can our vision be achieved?

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Wetlands
Historical changes can be considered to have
disconnected chalk streams from their
floodplains what have we lost by doing this? Is
there a case for reconnecting chalk streams with
their floodplains by reinstatement or
construction of wetlands?
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Centre for Environmental Sciences
Wetlands potential benefits
Reduce nutrient content via plant uptake and
growth Reduce suspended sediment content by
settling Reduce pesticide content by settling
out particles with which pesticides
associate Hold up the throughflow of water to
allow sufficient time for short-lived compounds
to decay.