This chapter introduces basic concepts connected to river systems. It explains the concept of a water cycle in connection to a river system. At the end, it explains the upstream-downstream concepts in river systems.
Our goal is to introduce the hydro-morphological context of river quality (good hydro-morphological status) and connect it to the habitats of aquatic biota. It is necessary to preserve or restore the natural shape of a river with its natural water-flow, self-purification, as well as the riparian area for the quality of water and life in it.
This chapter introduces the biological context of river quality or good biological status, mainly through microorganisms (bacteria), zoobenthos, phytobenthos, and periphyton. This aquatic community is responsible for the self-purification of a river system. Fish, at the top of the aquatic food chain, are not considered in detail here.
This section aims to explain how water quality is assessed in rivers in the European Union. The ecological status (in natural and semi-natural rivers) or ecological potential (in heavily modified water bodies) is evaluated based on biological, hydro-morphological, and chemical quality.
This chapter explains what self-purification ability of a water system is, what happens when we add pollution to the biological cycle in a river, what physical, chemical, and biological processes are important, and what kind of pollution a water system can clean by itself.