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Hydrological versus biogeochemical controls on catchment nitrate export: a test of the flushing mechanism
Author(s) -
Ocampo Carlos J.,
Oldham Carolyn E.,
Sivapalan Murugesu,
Turner Jeffrey V.
Publication year - 2006
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/hyp.6311
Subject(s) - flushing , biogeochemical cycle , environmental science , hydrology (agriculture) , streamflow , drainage basin , antecedent moisture , discharge , surface runoff , groundwater , catchment hydrology , groundwater discharge , aquifer , groundwater flow , geology , ecology , geography , medicine , geotechnical engineering , cartography , runoff curve number , biology , endocrinology
Deciphering the connection between streamflows and nitrate (NO − 3 ) discharge requires identification of the various water flow pathways within a catchment, and the different time‐scales at which hydrological and biogeochemical processes occur. Despite the complexity of the processes involved, many catchments around the world present a characteristic flushing response of NO − 3 export. Yet the controls on the flushing response, and how they vary across space and time, are still not clearly understood. In this paper, the ‘flushing response’ of NO − 3 export from a rural catchment in Western Australia was investigated using isotopic (deuterium), chemical (chloride, NO − 3 ), and hydrometric data across different antecedent conditions and time‐scales. The catchment streamflow was at all time‐scales dominated by a pre‐event water source, and the NO − 3 discharge was correlated with the magnitude of areas contributing to saturation overland flow. The NO − 3 discharge also appeared related to the shallow groundwater dynamics. Thus, the antecedent moisture condition of the catchment at seasonal and interannual time‐scales had a major impact on the NO − 3 flushing response. In particular, the dynamics of the shallow ephemeral perched aquifer drove a shift from hydrological controls on NO − 3 discharge during the ‘early flushing’ stage to an apparent biogeochemical control on NO − 3 discharge during the ‘steady decline’ stage of the flushing response. This temporally variable control hypothesis provides a new and alternative description of the mechanisms behind the commonly seen flushing response. Copyright © 2006 John Wiley & Sons, Ltd.