Page 69 - Freshwater-Biology-and-Ecology-Handbook

5.7.1 Network of reference sites

In the AQEM project, criteria for the selection of reference condition sites were described as follows:

A reference stream should fulfil all requirements necessary Physical and chemical conditions
to allow a completely undisturbed fauna to develop and There should be:
establish itself. Therefore, reference sites should not only • no point sources of pollution or nutrient input affecting
be characterised by clean water but also by undisturbed the site
stream morphology and near-natural catchment • no point sources of eutrophication affecting the site
characteristics. Though it is impossible to find sites in • no sign of diffuse inputs or factors which suggest that
such a pristine condition for many stream types, AQEM diffuse inputs are to be expected
has defined the following criteria, which should be met by
realistic reference sites: • normal background levels of nutrient and chemical
base load, which reflect a specific catchment area
• no sign of acidification
Basic statements • no liming activities
• no impairments due to physical conditions; in particular,
• The reference condition must be practical, achievable thermal conditions must be close to natural
within a river basin and reasonable.
• no local impairments due to chemical conditions;
• A reference site, or process for determining it, must hold in particular, no known point-sources of significant
or consider important aspects of natural conditions. pollution, all the while considering the near-natural
• The reference conditions must reflect only minimal pollution capacity of the water body
anthropogenic disturbance. • no sign of salinity.
Land use practices in the catchment area Biological conditions

• In most countries there is anthropogenic influence within There must not be any:
the catchment area. Therefore, the degree of urbanisation,
agriculture and silviculture (forestry) should be as low as • significant impairment of the indigenous biota by
possible for a site to serve as a reference site. No absolute introduction of fish, crustaceans, mussels or any
minimum or maximum values have been set for the defining other kind of plants and animals
reference conditions (eg % arable land use, % native forest); • significant impairment of the indigenous biota by
instead, the least-influenced sites with the most natural fish farming.
vegetation are to be chosen.
In many cases, particularly in lowland stream types or larger
River channel and habitats rivers, no reference sites meeting the above criteria are
available. For these stream types, the best available sites,
• The reference site floodplain should not be cultivated.
If possible, it should be covered with natural climax which meet most of the criteria, should only be a starting
vegetation and/or unmanaged forest. point. The description of these reference communities
should be supplemented by an evaluation of historical data
• Coarse woody debris must not be removed (minimum
demand: presence of coarse woody debris). and possibly the biotic composition of comparable stream
types, eg streams of a similar size but located in a different
• Stream bottoms and stream margins must not be fixed.
ecoregion (AQEM consortium, 2002).
• Preferably, there should be no migration barriers (affecting
the sediment transport and/or the biota of the sampling site).
• Only moderate influence due to flood protection measures So, reference values should be based on information
can be accepted. obtained from sites at which the quality element
Riparian vegetation and floodplain concerned is in reference condition (ie at high status).
UK TAG state that this does not mean that at these sites
• Natural riparian vegetation and floodplain conditions must the quality element will be entirely unaffected by human
be retained, making lateral connectivity between the stream activities. However, it does mean that alterations to it
and its floodplain possible; depending on the stream type, are expected to be minor. There are relatively few sites
the riparian buffer zone should be greater or equal to 3x at which all quality elements are in reference condition
channel width.
and from which data suitable for establishing reference
Hydrologic conditions and regulation values are available. Consequently, reference values
can be derived from sites at which the quality element
• No alterations of the natural hydrograph and discharge concerned is estimated to be in its reference condition
regime should occur.
but other elements at the sites may not be so.
• There should be no, or only minor upstream impoundments,
reservoirs, weirs and reservoirs retaining sediment; no effect
on the biota of the sampling site should be recognisable.
• There should be no effective hydrological alterations such
as water diversion, abstraction or pulse releases.

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