Several policies have therefore sought to develop or adapt this policy principle to support wise
use more effectively. This is a complex matter as it is generally acknowledged to be easier to apply
no net loss policies to area than to functions or values: valuation techniques for known wetland
values are in their relative infancy, whilst new values may still remain to be identified. There is also
uncertainty as to which wetland functions are most important for the sustainability of wetland
ecosystems (less well documented than values beneficial to human interests).38
Nevertheless some
recent policies do incorporate some measure of wetland extent or quality and/or specify criteria by
which the no net loss principle is to be applied. Two examples are given below.