Hot and Cold Phenomena In Riparian Zones: It Is Not Just about Nitrate

Many studies have investigated nutrient and to a lesser degree contaminant removal and transformations in riparian systems. These studies have encompassed a variety of hydrogeomorphic and climatic regions and represent a wide range of geographic locations. These studies have demonstrated significant spatial and seasonal variability in riparian zone hydrological and biogeochemical conditions. However, recent research has shown that when certain hydrological and biogeochemical conditions converge, riparian zone functioning can change episodically within seasons and over a variety of spatial scales. This presentation summarizes our current understanding of the variables controlling hot and cold moments in riparian zones, both in terms of transport and biogeochemical transformation. In particular, we discuss the hot/cold moment paradox, i.e. that a riparian zone can serve as both a hot spot for biogeochemical transformations and a cold sport for contaminant transport to streams or vice-versa. We also discuss potential trade-offs associated with riparian zone management and hot/cold moment perception. For instance, reducing conditions within a riparian zone can potentially enhance the denitrification process but those same conditions may also enhance the solubilization of phosphorus and promote the methylation of Hg in some environments. We propose that the presence of cold spots and cold moments within riparian systems represent opportunities where riparian water quality function might be enhanced.