Observation of Less-mobile Porosity Dynamics in an Urban Stream
Abstract
Groundwater-surface water (GW-SW) interactions affect a diverse range of hydrologic and geochemical processes, including contaminant transport, nutrient cycling and greenhouse gas production. GW-SW interactions can be particularly complex in the presence of natural sediment heterogeneity, with increased complexity in urban streams due to the anthropogenic impacts. Electrical geophysical techniques have shown great potential to investigate solute exchange between pores with different connectivity that can be classified as mobile zones (well-connected pores) and less-mobile zones (poorly-connected pores). Simultaneous measurements of fluid electrical conductivity (EC) via fluid sampling and bulk EC via geoelectrical measurements allow for quantitative analysis of less-mobile porosity dynamics. Many factors can impact the less-mobile porosity dynamics, some of which have been overlooked in previous studies, including the effects of flow rate on the creation of less-mobile porosity. Our previously reported numerical simulations show that the less-mobile porosity dynamics are flow-dependent. Here, we experimentally assess the flow effect on less-mobile porosity fraction and residence time by manipulating downwelling flux across the GW-SW of an urban stream that has been affected by road sand. We apply constant-head EC tracer injections using a newly developed dual-domain porosity apparatus (DDPA) to quantify the less-mobile exchange parameters at different experimental flux rates. These experiments confirmed the simulated flow dependence of less-mobile parameters, with the strongest effect on less-mobile residence time, and hence, the rate coefficient governing mobile/less-mobile exchange. Additionally, our observations show the capability of the DDPA approach in field settings to quantify centimeter-scale changes in sediment properties.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.H34E..04M
- Keywords:
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- 0408 Benthic processes;
- BIOGEOSCIENCESDE: 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 1806 Chemistry of fresh water;
- HYDROLOGYDE: 1830 Groundwater/surface water interaction;
- HYDROLOGY