Arriving at a Framework for Classification of Representative Aquatic Ecosystems in Ontario

To develop an aquatic ecosystem classification for Ontario, we review characteristics and approaches used to classify flowing waters and lakes around the world. Classifications can be abiotic, biotic, or both. There are at least four different types of abiotic classifications that attempt to describe the physico-chemical characteristics of different species’ habitat at a variety of spatial scales: geoclimatic, geomorphic, hydrologic, and chemical. Biotic classifications make groupings predominantly on the basis of the presence of various taxa such as game fish. Many European and North American classifications developed between 1911 and 1987 ordered stream sections into longitudinal zones based on fish distributions. Recent aquatic classifications incorporate hierarchy theory by creating nested, multi-level classifications based on variables designed to match ecological processes at different scales. Some classifications use available data on the zoogeographic patterns of fishes to create regionalizations. These zoogeographic patterns are partially the result of post-glacial dispersal limitations, and they do not necessarily reflect abiotic differences among system typology. An icthyocentric view may prove inadequate for interpreting regional life history variation if taxa dependent on riparian, wetland, or floodplain habitats are under consideration.

Ontario has nearly six times the land area of Washington State and is unique in several respects: large parts of the north are sparsely populated and poorly sampled, and the Province has over 35,000 lakes and inter-connecting streams. Our classification system will need to include these features and focus on abiotic variables that capture lake, wetland, and river network flows in addition to geoclimatics. Landscape-scale network topology is just beginning to be incorporated into stream ecological theory. We propose an aquatic ecosystem classification framework for Ontario that incorporates measures of aquatic network topology. Four hierarchical levels are proposed. Levels one and two will capture broad- and medium-scale ecosystem variability based on bedrock geology, physiography, climate, and network topology (at scales equivalent to terrestrial ecozones and ecoregions). Levels three and four will capture stream segments (100 m to 10 km in length), catchment areas, whole lake and wetland systems and finer site-scale details such as pools and riffles. Each level in the hierarchy represents a separate hypothesis that captures current understanding about the key ecological processes that shape aquatic networks. We hope that these hypotheses can then be put to the test with field data.