Quantitative Change Levels in the management of intertidal sand and mudflats and
subtidal mobile sandbanks
Surveillance assesses the state and changes in features of a biotope whereas monitoring
implies testing against pre-defined and agreed standards or limits (i.e. compliance
monitoring). As a trigger to determining whether further action and management decisions
are required for Intertidal Sand and Mudflats and Subtidal Mobile Sandbanks, the Country
Nature Conservation Agencies have proposed the use of Change Levels (Dr K Hiscock, pers.
Change Levels can be regarded as synonymous with numerical standards for which
compliance is derived (Elliott, 1996). Environmental Quality Standards have been long used
for chemical and microbiological determinants in quality assessment and the control of
human impacts. However, only recently have Ecological Quality Standards been proposed for
macrobiology, especially community-based features (MAFF, 1993). In essence, these are
suggested as a means of defining the standards against which compliance monitoring (as
opposed to surveillance) is carried out.
It is considered impractical, because of the wide and undefined variability in the
systems (Elliott & OReilly, 1991), at present to derive well-defined and
numerical limits as standards for use in monitoring. If poorly-defined limits are given
without adequate testing these will be unsuitable for use by 'non-experienced' monitoring
staff to determine quality and the magnitude of anthropogenic changes. Thus, the
determination of action or trigger levels will require further research.
Despite this, further work is required to give Environmental and Ecological Quality
Objectives which may be regarded as statements against which any assessments can be
carried out (Elliott, 1996). However, the concept of 'naturalness' of a biotope, as
defined by an experienced ecologist, may be the most appropriate means of defining and
describing unacceptable change. The uncertainty and high degree of variability dictate
that exceedence of any level of acceptable change should act as a trigger for further
study prior to, and/or rather than, management action such as prohibition of an activity
suspected of causing the change. In this case, it is not necessary to separate man-induced
or natural changes as long as there is some response to change, although such a separation
is important for practical and financial management.