The impact of river stage variability on mixing depth and patterns of biogeochemical processing in the hyporheic zone
Abstract
The zone of groundwater and surface water mixing in the streambed, sometimes called the hyporheic zone, is a region characterised by steep chemical and biological gradients. At this interface, the dynamic flux of oxygen, carbon and nutrients, increased microbial activity, and elevated water temperatures (relative to the groundwater); can create biogeochemical 'hotspots' in the streambed where nutrient attenuation and/or release can occur. The location of these biogeochemical zones is dependent on streambed hydrological connectivity and patterns of hyporheic exchange flow (vertical, lateral, longitudinal) that control the mixing of redox-sensitive species in the hyporheic zone. Much research has focused on hyporheic mixing in the upper few centimetres of the riverbed; our work suggests mixing is deeper and is influenced by groundwater vertical and lateral gradients. Here, utilising multivariate statistical techniques, we examine the role of stage in influencing mixing depth and concurrent biogeochemical cycling in the hyporheic zone. A 250m reach of the River Eden, Cumbria, UK, has been instrumented with a dense network of 88 piezometers, allowing the measurement of both subsurface water fluxes and pore water biogeochemistry. The goal is to test whether variability in the hydrologic flow regime (specifically river stage) has the capacity to influence nitrogen cycling processes in the hyporheic zone.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.B33A0422B
- Keywords:
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- 0414 BIOGEOSCIENCES / Biogeochemical cycles;
- processes;
- and modeling;
- 0469 BIOGEOSCIENCES / Nitrogen cycling;
- 1830 HYDROLOGY / Groundwater/surface water interaction