Predicting Riparian Zone Hydrological and Biogeochemical Functioning Using Easily Measurable Landscape Attributes

In order to efficiently use riparian zones to improve water quality, we need to conceptualize our knowledge of riparian zone hydrology and biogeochemistry. We evaluate two conceptual models developed for riparian zones in southern Ontario, Canada that link landscape hydrogeological characteristics (topography, soil depth, soil texture) to riparian hydrological functioning (water table fluctuations, groundwater fluxes) and nitrate removal efficiency (nitrate removal rate, nitrate fluxes, riparian zone width required for 90% nitrate removal). Data from a range of riparian sites in the USA and Europe suggests that the riparian zone types identified in the models are consistent with patterns of riparian hydrology and nitrate flux and removal in many humid temperate landscapes. These data also support the view that a riparian width of < 20 m is often sufficient for effective nitrate removal unless riparian sediments are coarse-grained or nitrate transport occurs mainly in surface-fed groundwater seeps. We assess the possibility of using topographic, soil, surficial geology and vegetation maps to determine landscape attributes linked by the models to riparian zone hydrological functioning and nitrate removal efficiency. Although mappable data can help in determining broad classes of riparian hydrological and biogeochemical functioning, field visits are necessary to determine non-mappable riparian attributes such as seeps, narrow organic horizons and permeable sediment depth in the riparian zone. We suggest that these conceptual models can be used for landscape management purposes in most temperate landscapes with minor modifications and that they could be adapted for contaminants other than nitrate.