statements of potential functioning
LISTENING FOR WATER I
A month without rain
and the river is a blemish of innards a seam of clotting amber.
Nettles bare their ovum, the skeins of marsh grass hush distance,
alders pant
under a scraped out husk of sky.
He listens for water trying to find its depth, somewhere beneath the feet of cattle,
who mark the potion of air with flicks of spittle firom jerked up heads. He listens again, scribing numbers on his clip board as if they were
the broken parts of god.
4.1. Introduction
This chapter discusses the rationale used for the selection of field sites needed for further testing of the functional classification. Within these field sites a detailed examination of wetland hydrology was undertaken. Hydrological information from these sites, was used to test the detailed statements of potential functioning generated by the functional classification. This chapter also provides a detailed description of the study area catchment and the individual sites where field monitoring took place. In particular the site descriptions focus on the factors which influence wetland ecosystem functioning.
4.1.1. Site selection
Complete testing of the classification is beyond the scope of this study. Potentially there are 1496
distinct wetland types that can be generated using the classification. To test the detailed
statements of potential fimctioning, within the classification, accurate functional information is needed for a wetland. Although there are a number of wetlands throughout Europe that have undergone some type of detailed research and/or monitoring, very few have had research undertaken using a functional approach. As a result many wetlands have a number of years of data related to flora and fauna or hydrological regime but these have not been collected corresponding to wetland functioning or to the hydrogeomorphic variability within a wetland. Therefore, to test each wetland type a wetland functional monitoring campaign would have to be undertaken at one or more examples of every type. Testing of each individual wetland type would be a major undertaking, beyond the constraints of this study. Therefore, in order to undertake detailed testing only one wetland sub-type was chosen. Although testing of just one wetland sub-type would not prove the accuracy of the entire classification it was assumed that it would be able to test the linkages, relationships and usabihty of the classification. Testing of one wetland sub-type would also develop a methodology for future testing of the other classification sub-types.
The statements of potential functioning, generated by the classification are directly related to the presence or absence of key hydrogeomorphic units within a wetland. Within the functional classification the detailed statements of potential functioning have thus far been developed for riverine wetlands. Riverine hydrogeomorphic units have the potential to be located within all three of the riverine wetland sub-types. Therefore it was assumed that focusing on one riverine wetland type would illustrate the validity of the functional classification approach because the
suite of hydrogeomorphic units and their relationship with wetland functioning is broadly similar in all riverine wetlands. Therefore, detailed testing within one wetland sub-type, that has a variety of hydrogeomorphic units, will allow general conclusions to be drawn about the accuracy of such statements for other riverine wetlands on the basis of the hydrogeomorphic units that are present.
The testing of the detailed statements of potential functioning for even one wetland sub-type would still be a massive task as detailed information about all processes contributing to wetland functions would have to be monitored to provide empirical data against which predictions of functioning can be compared. To test the detailed statements of potential functioning the two
hydrological functions of Floodwater retention and Groundwater discharge were chosen.
Hydrological processes controlling these functions contribute greatly to other wetland functions and are responsible for shaping the unique character of wetlands. Focusing on these two functions in detail allows a thorough testing of the detailed statements of potential fimctioning, within the classification, because the relationship between hydrogeomorphic type and the two functions is key to all wetland functioning. It can be assumed that if the classification does not work for these two functions then it will not work for the other wetland functions. Using these two functions also affords testing of the hydrogeomorphic / functioning relationship itself. Detailed study of the floodwater retention and groundwater discharge characteristics of different hydrogeomorphic units allows a determination of whether hydrogeomorphology is a good indicator of functioning or not.
The wetland sub-type that was chosen for study was the Unconfined channel wetland as it is
characteristic of riverine wetlands and found m all biogeographical regions. This is perhaps the most common riverine wetland sub-type found in Europe although the extent of this wetland type has diminished greatly through factors such as the intensification of agriculture, water abstraction
and dredging for navigation (Treweek et al, 1997). Unconfined channel wetlands often exhibit
the characteristic profile of channel, floodplain and slope presenting the fiiU range of riverine hydrogeomorphic units. For the testing of the detailed statements of potential functioning a wetland sub-type was needed that contains many different hydrogeomorphic units, in relative close proximity, so that as much hydrogeomorphic variation could be studied as possible. The variation in hydrogeomorphic units will allow the full variation in functioning to be tested and therefore the detailed statements of potential functioning.
Much attention has been given to large wetland complexes throughout Europe because these have often been viewed as the most important for rare species and large bird populations (Carp, 1980).