Aspects of Nitrogen Transport and Transformation in Headwater Streams

Water in a stream and time are alike, both keep moving. It has been aptly remarked, though in a different context, that today is yesterday’s tomorrow (Vallentyne, 1978). Just as yesterday’s events interact with today’s conditions and these together with tomorrow’s, similarly a given stretch of a stream, because of water flow, is a reflection of its own and upstream conditions and, in turn, influences what lies downstream from it. Water flow is thus an important factor that complicates studies on nitrogen transformation in streams. To this, one may add the fact that nitrogen occurs in various forms ranging from nitrate, the most oxidized state, to ammonia, the most reduced form. In addition, nitrogen can enter into streams from point sources as well as from surface and subsurface diffuse sources. All these factors compound the situation and make it extremely difficult to carry out nitrogen budget and transformation studies in streams. It is, therefore, not surprising that although nitrogen is important to biological systems, as a constituent of proteins, in the eutrophication process, in oxygen depletion caused by oxidation of its compounds, in the development of conditions toxic to fish (caused by ammonia) and for incidences of methemoglobinemia in humans and animals (Shuval and Gruener, 1977), the processes that control the transport and transformation of nitrogen in streams have rarely been studied in detail.