An approach to understanding hydrologic connectivity on the hillslope and the implications for nutrient transport

Abstract

[1] Hydrologic processes control much of the export of organic matter and nutrients from the land surface. It is the variability of these hydrologic processes that produces variable patterns of nutrient transport in both space and time. In this paper, we explore how hydrologic ''connectivity'' potentially affects nutrient transport. Hydrologic connectivity is defined as the condition by which disparate regions on the hillslope are linked via subsurface water flow. We present simulations that suggest that for much of the year, water draining through a catchment is spatially isolated. Only rarely, during storm and snowmelt events when antecedent soil moisture is high, do our simulations suggest that mid-slope saturation (or near saturation) occurs and that a catchment connects from ridge to valley. Observations during snowmelt at a small headwater catchment in Idaho are consistent with these model simulations. During early season discharge episodes, in which the mid-slope soil column is not saturated, the electrical conductivity in the stream remains low, reflecting a restricted, local (lower slope) source of stream water and the continued isolation of upper and mid-slope soil water and nutrients from the stream system. Increased streamflow and higher stream water electrical conductivity, presumably reflecting the release of water from the upper reaches of the catchment, are simultaneously observed when the mid-slope becomes sufficiently wet. This study provides preliminary evidence that the seasonal timing of hydrologic connectivity may affect a range of ecological processes, including downslope nutrient transport, C/N cycling, and biological productivity along the toposequence. A better elucidation of hydrologic connectivity will be necessary for understanding local processes as well as material export from land to water at regional and global scales.

Seasonal and hydrologic drivers of dissolved organic matter and nutrients in the upper Kuparuk River, Alaskan Arctic

“…Interannual variability, sparse precipitation datasets at high latitudes, and challenges associated with quantifying winter precipitation have made it difficult to diagnose the exact causes of changes in Arctic river discharge to date (Rawlins et al 2009). However, tight linkages between hydrology and biogeochemistry in watersheds (Creed et al 1996;Creed and Band 1998;Burns 2005;Hinzman et al 1991;Steiglitz et al 2000Steiglitz et al , 2003 make changes in the export of river-borne materials inevitable as river discharge increases. Export of inorganic nutrients (N, P, Si) and DOC and DON are of particular interest because they serve as important resources for downstream ecosystems (Amon and Meon 2004;Post et al 2009).…”

Hydrologic similarity among catchments under variable flow conditions

“…During low flow conditions, typically in summer when the ET demand is high (Fig. 8), water fluxes are predominantly vertical (Tromp-van Meerveld and McDonnell, 2006;James and Roulet, 2007), and the spatial patterns of soil moisture are unorganized and strongly influenced by the local terrain (Grayson et al, 1997;Stieglitz et al, 2003). At these low flow conditions, disparate regions within a catchment are hydrologically disconnected (due to a lack of lateral water movement) and the catchment discharge is most likely controlled by the geologic factors such as the intricacies of landscape micro-topography, subsurface structure, soil texture and structure, etc.…”

Runoff generation in a pre-alpine catchment: A discussion between a tracer and a shallow groundwater hydrologist

“…10a, nr III (Stieglitz et al, 2003;Ocampo et al, 2006;Jencso et al, 2009;Detty and McGuire, 2010;van Meerveld et al, 2015). (Bachmair et al, 2012).…”