My current research seeks to establish better links between groundwater depletion measured from GRACE, land subsidence from InSAR, and numerical groundwater models.
As groundwater is pumped from an aquifer, sediment grains rearrange in response. Finer, clay-like sediments, often suspended in water before pumping, tend to lay flat as water depletes. This causes compaction of the aquifer that is often irreversible and inelastic. This causes surface deformation and land subsidence that is detectable via InSAR (interferometric synthetic aperture radar) and GPS.
With this project, we seek to better understand the linkages between geologic properties and patterns of subsidence, at depth and over time, using GRACE, InSAR, and a groundwater model. Final deliverable of the initiative will aid Groundwater Sustainability Agencies in sustainable use of groundwater across California’s Central Valley, in compliance with the 2014 Sustainable Groundwater Management Act.
Beach aquifers are hosts of dynamic mixing zones between fresh groundwater and saline seawater. Seawater, driven up the beachface by waves and tides, infiltrates into the aquifer and meets the seaward-discharging fresh groundwater, creating and maintaining a reactive intertidal circulation cell. The intertidal circulation cell is highly dynamic and has been shown to respond to hydrologic, geologic, and topographic changes over various time scales (waves, tides, and seasons).
Spatial patterns of groundwater reactivity in an intertidal beach aquifer
Within the cell, land-derived nutrients delivered by fresh groundwater are transformed or attenuated. We investigated the relationship between physical flow and mixing processes with porewater samples and incubation experiments. Biogeochemical reactions within the circulation cell were highly related to flowpaths, with heightened oxic respiration near the infiltration zone and progressive dominance of denitrification near the discharge zone. The results of this project were published in JGR Biogeosciencesand selected for anEOS Research Highlight.
Migration of beach aquifer reaction zones : Transient seasonal patterns of organic carbon and chemical reactions
Extensive characterization of porewater and sediments spanning two years revealed the seasonal migration of reaction zones. While oxic respiration closely followed the changes to groundwater flowpaths indicated by salinity patterns, spatial locations of denitrification was more variable. This was partially attributed to the heterogeneous distribution of reactive organic carbon within the beach, due to the filtration effect of beach sediments. An article detailing the outcomes were published in JGR Biogeosciences, with data separately published here.