CLASSIFICATION OF WATER REGIMES IN SYSTEMS OF FLUCTUATING WATER-LEVEL

Aquatic macrophyte communities have been shown to form sequences along water depth gradients, and water depth has been related to various ty pes of environmental stresses. However, in semi-permanent wetlands, wa ter depth is rarely constant through time; there are large fluctuation s in water level between seasons and years, and the relative lengths o f wet and dry periods may be as important a stress as the average (or maximum) depth of water. This paper presents a method of quantifying w ater regimes on the basis of infrequently sampled water level data and of comparing and defining regime-types within and between semi-perman ent swamps. Time periods per depth class are calculated from water dep th data for each gradient position from the bottom of the swamp to the high-water mark. These data can be represented as a histogram that de scribes the wet/dry pattern of each gradient position. A multivariate clustering is used to compare gradient positions in different swamps o n the basis of depth and period of inundation. Water regime types are then defined on the basis of the groups derived in the clustering. The method is illustrated for the Bool Lagoon system in the south-east of South Australia.