Incorporating uncertainty into nitrate concentration-discharge interpretation

Abstract:

Concentration-discharge relationships are increasingly shown to vary through time. Additionally, there is equifinality in concentration-discharge (c-Q) relationships. That is, there are multiple combinations of biophysical mechanisms that can equally explain a given c-Q pattern. Given these patterns change thru time and as a function of temporal resolution of the data, there is substantial uncertainty around their interpretation. A complex systems-based approach to catchment science, with requisite data is required to address the underlying hydrobiogeochemical process uncertainty of c-Q patterns. This is especially true for reactive and biologically-essential solutes such as nitrate. This work seeks to develop mechanistic understanding of coupled ecohydrological and biogeochemical processes that drive nitrate concentration-discharge patterns and advance the application of this information to watershed management. Excess nitrogen has significant effects on downstream aquatic ecosystems and it has proven notoriously difficult to effectively manage, particularly at larger watershed scales. Discrete elements of the landscape (hot spots) and brief moments of time (hot moments) have been shown to control watershed scale processing and export of nitrogen. Despite increasingly higher spatial resolution spatial data and higher temporal resolution water quality data to pinpoint the geographic sources and timing of nitrogen pollution, substantial uncertainty remains. This uncertainty needs to be more carefully examined, especially if concentration-discharge patterns are used to guide watershed management decisions.