Discrete wetland groundwater discharges revealed with a three-dimensional temperature model and botanical indicators (Boxford, UK)

House, Andrew R.; Sorensen, James P. R.; Gooddy, Daren C.; Newell, Andrew J.; Marchant, Ben; Mountford, J Owen; Scarlett, Peter; Williams, Peter J.; Old, Gareth H.

Discrete wetland groundwater discharges revealed with a three-dimensional temperature model and botanical indicators (Boxford, UK) | Exfiltrations discrètes en zone humide révélées par un modèle thermique tridimensionnel et par des indicateurs botaniques (Boxford, UK) Las descargas de agua subterránea discretas en humedales reveladas con un modelo tridimensional de temperatura e indicadores botánicos (Boxford, Reino Unido) 采用三维温度模型和植物指标揭示分散的湿地地下水排泄(英国,博克斯福德) Descargas discretas de água subterrânea em zonas húmidas identificadas com um modelo tridimensional de temperatura e com indicadores botânicos (Boxford, Reino Unido)

2015

Wetlands provide unique goods and services, as habitats of high biodiversity. Hydrology is the principal control on wetland functioning; hence, understanding the water source is fundamental. However, groundwater inflows may be discrete and easily missed. Research techniques are required with low cost and minimal impact in sensitive settings. In this study, the effectiveness of using a three-dimensional (3D) temperature model and botanical indicators to characterise groundwater discharge is explored at the CEH (Centre for Ecology and Hydrology) River Lambourn Observatory, Boxford, UK. This comprises a 10 ha lowland riparian wetland, designated for its scientific interest and conservation value. Temperature data were collected in winter at multiple depths down to 0.9 m over approximately 3.6 ha and transformed into a 3D model via ordinary kriging. Anomalous warm zones indicated distinct areas of groundwater upwelling which were concurrent with relic channel structures. Lateral heat propagation from the channels was minimal and restricted to within 5–10 m. Vertical temperature sections within the channels suggest varying degrees of groundwater discharge along their length. Hydrochemical analysis showed that warmer peat waters were akin to deeper aquifer waters, confirming the temperature anomalies as areas of groundwater discharge. Subsequently, a targeted vegetation survey identified Carex paniculata as an indicator of groundwater discharge. The upwelling groundwater contains high concentrations of nitrate which is considered to support the spatially restricted growth of Carex paniculata against a background of poor fen communities located in reducing higher-phosphate waters.

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