Topographic controls on shallow groundwater dynamics: implications of hydrologic connectivity between hillslopes and riparian zones in a till mantled catchment

Abstract

Abstract:Hydrologic connectivity is regarded as one of the key controls in determining catchment rainfall-run-off response and has been linked to the export of solutes from uplands to streams. We sought to identify the patterns of hydrologic connectivity within a small forested watershed by monitoring the shallow groundwater fluctuations of simple topographically defined landform sequences (footslope-backslope-shoulder). A spatially distributed instrument network was employed to continuously measure hydrometric responses of the shallow subsurface during seasonal wet-up from summer through winter in a small till mantled research catchment. We demonstrate that the spatial patterns of shallow water table extent and duration, and therefore hydrologic connectivity, had a strong seasonal signature. During the low antecedent soil moisture conditions typically associated with the growing season, water tables were patchy, discontinuous, and only the wettest near-stream footslope areas were consistently hydrologically connected with the stream network. During the dormant season, footslopes and backslopes maintained water tables that persisted between storm events and were almost continuously connected with the stream network. In the largest storm events, the typically driest landforms (shoulder slopes) established shallow transient water tables, suggesting that nearly the entire catchment was temporarily hydrologically connected with the stream network. In addition, we found significant differences (p < 0Ð05) in the magnitude and duration of groundwater responses to rainfall among landform groups both seasonally and during events. These results have implications for using a similarity approach in representing characteristic hydrologic responses of topographically defined watershed elements, determining hydrologic connectivity between watershed elements, as well as for understanding solute transport in catchments.

Isotopic signals of summer denitrification in a northern hardwood forested catchment

“…Spodosols of sandy loam to loamy sand texture comprise ∼80% of catchment soils, and Inceptisols and Histosols make up the rest (45). The C horizon occurs at ∼70 cm depth and has variable although generally lower hydraulic conductivity compared with the overlying B horizon (40). A shallow groundwater system with a transient saturated zone develops within the solum throughout the catchment (45).…”

“…A shallow groundwater system with a transient saturated zone develops within the solum throughout the catchment (45). A more consistent saturated zone is present in the near-stream region that is typically hydrologically connected to surface water in perennial stream reaches and is at or near the surface beneath ephemeral and intermittent stream reaches (40). WS3 is drained by Paradise Brook, a second-order perennial stream fed by several ephemeral and intermittent tributaries, which together comprise 79% of the stream length within the catchment (45).…”

“…Sampling encompassed 11 locations along Paradise Brook and 8 locations on tributaries, along with 1 seep and 9 shallow groundwater wells selected from >30 wells installed previously in WS3 (34,40,41), and chosen for their tendency to provide water during midsummer (40) and ease of repeated sampling. The wells included three wells in or within 2 m of the perennial channel of Paradise Brook and forming a transect across it (R12 on the east, R13 in-stream, and R14 on the west).…”

“…This study provides evidence of the widespread but fragmented nature of denitrification in saturated soil and shallow groundwater in a temperate forested watershed. The existence of transient, perched patches of saturation in the soil that are poorly connected to streams (40,41), where N then recycles rapidly (31)(32)(33), may explain why previous dual isotope studies based on streamwater samples alone-at HBEF and elsewherehave shown little to no denitrification signal (Table S1). That is, even as denitrification occurs in saturated patches, these hotspots are connected poorly to surface streamwater (40,41), which contains NO 3 − produced by local nitrification (Fig.…”

Índices topográficos aplicados à modelagem agrícola e ambiental

“…Áreas em branco representariam áreas com maior risco, devido à menor capacidade de armazenamento de água pelos solos, sendo então recomendadas para culturas resistentes a secas. Os limites sugeridos para as classes da figura 3 poderiam ser validados com o acompanhamento da análise da umidade do solo após eventos de chuva e durante estiagens, conforme se verifica nos trabalhos de CHAPLOT & WALTER (2003), CHANG & LEE (2008) e DETTY & MCGUIRE (2010).…”