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. comm.).

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 & O’Reilly, 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.