Review of methods for assessing the hydromorphology of lakes
- The European Water Framework Directive (WFD) was adopted on 22 December 2000. This is a major legislative initiative, intended to resolve the piecemeal approach to European water law which has developed since 1975. The WFD stipulates that surface water bodies such as lakes should achieve good ecological and chemical status (pollutant levels) by 2015. Good ecological status requires hydromorphological conditions supporting at worst 'slight changes' in the composition and abundance of key biological quality elements (phytoplankton, macrophytes and phytobenthos, benthic macroinvertebrates and fish fauna) relative to the appropriate natural reference condition (high ecological statuts). The two elements of hydromorphology are hydrological regime and morphological conditions, the corresponding hydromorphological quality elements are:
Hydrological regime: quantity and dynamics of flow, level, residence time, and the resultant connection to groundwaters reflect totally or nearly totally undisturbed conditions.
Morphological conditions: lake depth variation, quantity and structure of the substrate, and both the structure and condition of the lake shore zone, correspond totally or nearly totally to undisturbed conditions.
Standing water designated as Heavily Modified Water Bodies (HMWBs) or Artificial Water Bodies are required to attain Good Ecological Potential by 2015.
- Currently no EU Member States carry out routine assessments of lake hydromorphology. A comprehensive literature review has provided an overview of human pressures on lakes, and the resulting impacts on hydromorphology and biota. A review of methods used to measure the hydromorphology quality attributes of lakes has identified several potential metrics for each. Methods vary in the ease with which they can be adapted for the purposes of the Directive.
- Member states are required to produce a lake typology based on a modeling and/or a reference network of undisturbed water bodies (including development of hydromorphological reference conditions) that define high ecological status. The System A typology is unlikely to prove adequate for UK purposes. A priority need is therefore the development of a UK-specific System B typology, ideally using statistical clustering to determine the most significant optional factors (additional hydrological quality elements) to be included beyond the System A obligatory factors.
- A key milestone in the implementation of the WFD is by 2004 to complete a screening exercise to identify significant pressures acting on water bodies and identify those at risk of failing to achieve good ecological status (inclusive of rivers, lakes, transitional and coastal waters). Many of the pressures operating in the catchment of an individual lake can be assessed by direct observation. However, the scale of the exercise required for WFD implementation is such that it will be expedient to use desk-based information sources as far as possible. An outline scheme is presented, which should take advantage of existing databases, exploiting where possible Geographical Information Systems (GIS) query techniques.
- An important conclusion emerging from the review exercise is that both the quantity and quality of existing aquatic ecology data sets are limited. Clearly the regulatory authorities (e.g. the Scottish Environment Protection Agency or the Environment Agency in England and Wales) need to initiate new measurement and monitoring campaigns. There are also fundamental gaps in the knowledge base regarding the inter-relationships between ecology and hydromorphology. In the absence of fuller ecological data sets, more emphasis much be placed on abiotic approaches to both screening and in guiding the necessary programme of measures needed to raise a failing water body to at least good ecological status. A screening tool is proposed in the form an Abiotic Index based on a combination of the Dundee Hydrological Regime Alteration Method (DHRAM) for standing waters and a newly proposed Lake Habitat Survey (LHS) approach derived from the integration of the Environment Agency's River Habitat Survey (RHS) and the USEPA's Field Operations Manual for Lakes (FOML). Extensive field-testing is required to calibrate such screening tools with ecological data, not only to validate the underlying science, but to ensure that designations and management options are accepted by all stakeholders and user groups.
- In addition to initiating a surveillance (monitoring) exercises, it will be necessary to implement a Programme of Measures to ensure that the hydromorphological quality elements of a standing water body such as a lake are improved to enable the biota to achieve the requirements of good ecological status or good ecological potential in the case of HMWBs. A series of recommendations are made accordingly.
Lakes; Hydromorphology; Water Framework Directive; Monitoring; Assessment; Pressures, Impacts; Typology; Reference Conditions; UK.
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