Hydrological codes

Hydrology is probably the single most important determinant of the establishment and maintenance of specific wetland types (Mitsch & Gosselink, 2000). The importance of hydrology has been recognised even within classifications that have not specifically linked wetland type to

functioning (Novitzki, 1979, Gilvear et al, 1989, Wheeler, 1994, Semeniuk and Semeniuk,

1995). Any wetland classification that intends to have a functional aspect must have an element within it that takes account of the hydrologie character of the wetland because hydrology is a fundamental structural element that is responsible for ecosystem functioning.

Hydrological studies of any ecosystem or landscape are concerned with inputs and outputs to the system and the resultant changes in storage. For example. Freeze (1978) argued that hillslope

hydrologists try to determine the relationship between the inputs from precipitation, the outputs from hillslope discharge and water storage such as soil moisture content and surface water generation areas. This type of approach considers the hydrology of a system as a water balance. Dyck (1983) indicates that water balance investigations are useful for many types of hydrological and environmental management scenarios as well as usefiil in the derivation of climatic and hydrological classifications. Viewing a system in this way allows an understanding of the hydrologie processes and therefore a direct link to ecosystem functioning.

Within the different wetland classifications developed a number of different approaches to expressing the hydrologie nature of a wetland have been adopted. Turner and Gosselink (1979) introduced the concept of hydrodynamics to the way wetlands are viewed. The hydrodynamic nature of a wetland is represented by a combination of water inputs, water outputs, type of flow and the frequency, duration and extent of inundation. Acknowledging the seasonal and dynamic nature of wetland hydrology is essential if a link to functioning is to be achieved. However, for a rapid and cheap type of assessment, in the form of a functional classification, detailed understanding of the hydrologie behaviour of a wetland is not possible, as this can only be

accomplished using a long term, empirical research project. Therefore, simple and easily

identifiable indicators of wetland hydrodynamic characteristics are needed.

The majority of wetland classifications, with a hydrology component, have concentrated on water

source as a key criteria for classification (Goode, 1977, Novitzki, 1979, Gilvear et a l, 1989,

Lloyd et a l, 1993, Wheeler, 1984, Wheeler, 1994). Water source has a direct impact on the

wetland hydrodynamics and therefore on the genesis and development of a wetland. It is also a useful criterion as it is generally easily identifiable both in the field and from secondary data.

Semeniuk and Semeniuk (1995) developed another classification criterion by identifying the degree of wetness of a wetland rather than the source of water. The degree of wetness is essentially an expression of the hydrodynamic nature of a wetland. As discussed earlier it is essential to address the seasonal and dynamic nature of wetland hydrology if a functional classification is to be developed.

It is clear that a functional classification requires a hydrological element if an expression of fimctioning is to be made. As discussed in section 2.2, a determination of wetland potential functioning is reliant not just on recognition of the geomorphic setting but also the hydrologie character of the wetland. The review of wetland classifications and hydrologie studies revealed two elements that are needed as criteria for a functional classification. These are the water

sources to the wetland and an expression of the hydrodynamic nature of the wetland. In recognition of this the functional classification uses both water source and an indication of whether there is permanent standing water or not, to define the hydrologie nature of a wetland.

The advantages of adopting this approach for wetland classification are;

1. A combination of these criteria describes the hydrologie elements that are essential to wetland development and character.

2. The criteria are an expression of the hydrologie processes that are fundamental to wetland functioning.

3. They are easily recognisable from maps and in the field. 4. They are not complex criteria so ease of use is high. The disadvantages of using these criteria are:

1. There is a lack of detailed understanding of all wetland hydrologie components such as hydrologie outputs.

2. The information contained within these criteria does not give a thorough expression of the hydrologie processes occurring within a wetland.

Although there is a lack of detail from a combination of water source and the presence or absence of permanent standing water, for the purposes of a functional classification the criteria provide enough information for potential functioning to be determined. As discussed earlier, if a more detailed assessment of wetland processes and functioning is needed a different type of assessment is required that identifies actual functioning. The level of detail that these criteria provide, about the hydrologie nature of a wetland, is sufficient to determine whether the wetland has the potential to perform a function or not.

2.3.4. Statements of potential functioning

The functional classification of European wetlands has two purposes, firstly to provide a structure and common language, for the classification of wetlands across Europe, and secondly to provide information for managers and decision makers as to the potential a wetland has to perform an ecosystem function. The determination of the potential for a wetland to perform a function, rather than whether it is actually performing a function, is appropriate within a classification because an assessment of potential functioning gives added information for management beyond just the classification of a wetland. Potential functioning statements can be generated rapidly and cheaply but also provide valuable information that can aid decision making, policy development and management. Utihsing potential functioning information, a manager can

identify areas for further assessment with techniques that assess actual functioning or develop more appropriate management for an area through an identification of potentially key wetland areas for particular functions.

Although the concept of wetland functioning is now widely recognised as a useful approach to

assessing wetlands (Maltby et al, 1996, Mitsch and Gosselink, 2000) the concept of potential

functioning is a new approach developed in conjunction with the functional classification. As discussed in Chapter 1, a classification that can determine potential functioning is useful for wetland management and allows a link to assessment methods that address actual functioning and wetland value.

Section 2.2 defined potential functioning as the possible interaction of ecosystem processes that

can occur as a result of a wetlands hydrologie and geomorphic (hydrogeomorphic) characteristics. The functional classification utilises this concept by classifying wetlands using hydrogeomorphic criteria and drawing on the research conclusions gained from the FAEWE and

PROTOWET projects (Maltby et al, 1996, Hogan & Maltby, 1997). These projects identified

the functional performance of different hydrogeomorphic units, within a wetland, across a range of different hydrological, biogeochemical and ecological functions. The research conclusions drawn are used as the basis for the potential functioning statement generation. Figure 2.2 indicates the developmental progression of research within the FAEWE and PROTOWET projects and the relationship and progression of the original research and conceptual developments within this study.

The functional classification generates two types of statements of potential functioning. The first type is a low level statement that is derived through the classification process itself. Using the hydrogeomorphic information gained during classification a unique statement of potential functioning is generated for each specific wetland. This statement lists the functions the wetland has the potential to perform and the functions it is unlikely to perform.

The second type of statement is a more detailed statement of potential functioning that indicates

whether one of the following cases exist within the wetland; high potential, potential, unlikely to

occur, no potential or insufficient data available. This statement is generated by identifying key hydrogeomorphic units within the wetland itself and therefore provides a more qualified statement of the potential for a wetland to perform a certain function. A key in the form of questions is followed to determine whether certain hydrogeomorphic units are present within the wetland area or not. At present, within the classification, detailed statements of potential functioning are only

Figure 2-2 D evelopm ental process and relationship between FAEW E and PR O TO W E T projects and this study

Process research at European wetland sites

Determination of theoretical ecosystem functions Hydrogeomorphic Unit (HGMU) Concept Functional Assessment Procedures

Development of actual and potential functioning concepts

Full development of Functional Classification for European Wetlands including the following:

a) development of European biogeographical regions

b) development of major and sub-type geomorphic categories for European wetlands

c) development of hydrological codes for European wetlands

d) development of potential functioning keys and statements for European wetlands based on the HGMU concept

Testing of the classification using:

a) existing data from 29 European wetlands investigated during the FAEWE and PROTOWET projects

b) original data collected during this study at test field sites in southern England r FAEWE and PROTOW ET Projects A Proposed Functional Classification of European Wetlands: Development and Testing P a g e 86

available for river marginal wetland types because these are the wetlands that have received the most thorough functional research within Europe. As new functional research is undertaken in other wetland types then this approach can be expanded to cover all European wetland types.

In summary, the advantages of adopting a potential functioning approach, within a wetland classification, are:

1. Provides useful information for the following: • Catchment management

• Site management for either species or habitat types • Land classification / zonation

• Comprehensive wetland evaluation system

2. The information gathered about wetland functioning is cheap and quick to generate.

3. More effective and focused management can take place, as the potential for wetlands to perform different functions can be determined over extensive areas.

4. The information is easy to generate and simple to understand.

Disadvantages of adopting a potential functioning approach, within a wetland classification, are: 1. It does not give accurate information about whether functions are actually occurring or not. 2. The level of detail about within site wetland variation is limited.

Although statements of potential functioning do not provide information about actual functioning, or within wetland functional variation, they remain an important component of a classification system because they provide cheap, rapidly generated information concerning the functional character of a wetland. This type of approach creates a more powerful tool than a traditional classification because as well as providing a structure to wetland classification across Europe, a classification of this type also provides decision makers and managers with pertinent information about the potential of a wetland to perform a range of ecosystem functions.