Groundwater contributions and sources of salinity to Oso Bay in south Texas were investigated using multivariate
statistical analysis of geochemical data and multitemporal electrical resistivity tomography surveys. Both analysis
of geochemical data and subsurface imaging techniques identified two commonalities for the investigated system:
1) hypersaline water occurs near the groundwater/surface water interface during wet conditions creating
reverse hydraulic gradients due to density effects. The development and downward movement of these fluids
as continuous plumes deflect fresher groundwater discharge downward and laterally away from the surface;
and 2) more pronounced upwelling of fresher groundwater occurs during drought periods when density inversions
are more defined and are expected to overcome dispersion and diffusion processes and create sufficiently
large-enough unstable gradients that induce density-difference convection. Salinity mass-balance models derived
from time-difference resistivity tomograph and in-situ salinity data reaffirm these findings indicating
that groundwater upwelling is more prominent during dry to wet conditions in 2013 (~545.5 m3
/d) and is less
pronounced during wet to dry conditions in 2012 (~262.7 m3
/d) for the 224 m2 area surveyed. Findings show
that the highly saline nature of water in this area and changes in salinity regimes can be attributed to a combination
of factors, namely: surface outflows, evapoconcentration, recirculation of hypersaline groundwaters, and
potential trapped oil field brines. Increased drought conditions will likely exacerbate the rate at which salinity