Understanding biotic interactions is important to illustrate ecological functions of stream environments. The purposeof this study is to compare the ecological functions of natural and artificial streams. For linking species, we used bioticinteraction databases and made food-webs for species lists of 18 streams in Seoul, Korea. We conducted species removalanalysis of networks and compared network beta-diversity between watersheds. The results showed that natural streamswere more affected by a removal of keystone species than artificial streams. The cheonggye watershed including artificialstreams had high dissimilarities among streams, presenting that artificial streams had different functions from natural streams.

Among the functions of ecosystem, nutrients cycle is the most important for sustaining natural system. But in modernized and industrialized countries, the product consumes the resources and make wastes. This means that valuable resources are turning to waste through product. Waste water is one of the product from the valuable resources, so waste water is no more waste and it can be used as valuable resources for other process by using natural ecosystem. By the conventional wastewater treatment systems, the “zero discharge” could not be achieved by several factors. Shortage of resources is one of the reasons. Secondly, by the environmental engineering, the pollutants are only transformed from one medium to another. Thirdly, for eliminating the pollutants, fossil fuel must be used, which means another pollution. Self-designed and solar energy based ecotechnology could be an alternative method which solve the local, regional and global environmental problems properly should be found out. Already ecotechnology was defined as “the design of human society with it natural environment for the benefit of both”. By using the functions of ecosystem, such as food web, energy flow, nutrients cycles and homeostasis, pollutants can be eliminated, concentrated and transformed to nature. The major purpose of mechanical wastewater treatment systems is focused on the large quantity of domestic wastewater. But, small quantity of domestic wastewater is not concerned by public treatment because economic and technical difficulty. However, for improvement of water quality of streams and rivers, the small quantity of domestic wastewater must be purified. Here, some eco-technologies for water quality improvement installed in Korea are introduced. The artificial wetland, artificial food web and artificial vegetation island are installed in polluted and ecologically disturbed areas. These methods are not perfectly solving the environmental problems, and they are acting as alternative methods for clean up of polluted and restoration of disturbed ecosystems.