THE IMPACT OF JOZSEF TOTH ON UNDERSTANDING AQUATIC ECOSYSTEM GRADIENTS

Many aquatic ecosystems, such as streams, lakes, and wetlands, are in direct contact with ground-water flow systems. In most cases, the chemical characteristics of the water in aquatic ecosystems reflect this interaction. For example, aquatic ecosystems near recharge areas that have little or no ground-water input generally have large variations in water stage and relatively fresh water. In contrast, aquatic ecosystems that receive ground water from regional flow systems, or large local or intermediate flow systems, generally have more stable water levels and more mineralized water, and, in some cases, different major-ion water chemistry compared to wetlands in recharge areas. Biological organisms living in and using the various surface-water bodies respond to the water permanence (hydroperiod) and chemical characteristics of the water. As a result, in some areas such as the prairie pothole region of North America, aquatic ecosystems are very different depending on where they are located in the landscape. Generally, gradients in the hydrological, chemical, and biological characteristics of aquatic ecosystems reflect their position within local, intermediate, and regional ground-water flow systems. In addition, climate variability further drives the hydrological characteristics of both ground water and surface water. Observations of the hydrological, chemical, and biological characteristics and processes of a wetland complex within a regional ground-water flow system during a period of extreme climate variability in North Dakota has resulted in the concept of the Wetland Continuum. This concept makes it possible to predict the hydrological, chemical, and biological response of wetlands to climate variability if their position within ground-water flow systems is known. In general, the Wetland Continuum concept is a model not only for prairie pothole wetlands but for aquatic ecosystems of all types. The key is to place aquatic ecosystems in the context of their position within ground-water and surface-water flow paths.