Sentence:  This kind of longitudinal sampling location is referred to as <WSD>micro-location</WSD>. <WSD>Micro-location</WSD> should take place in a reach of river in which the water is completely mixed — that is, where the concentration of water quality variables is independent of lateral location and depth in a cross-section. 
Meaning of the word marked with <WSD> tags:  (countable) A location of something within a larger area or region, such as a part of a city or a section of a river.