Assessing the Driving Forces of Submarine Groundwater Discharge

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ABSTRACTOCE-0520723Submarine groundwater discharge (SGD) represents an important, yet largely unquantified pathway for nutrients and other dissolved constituents from land to the coastal ocean. Coastal oceanographers and hydrologists have shown that slow yet persistent seepage of fresh groundwater through sediments occurs wherever an aquifer with a positive head is hydraulically connected to a surface water body. It is now recognized that a considerable amount of seawater is also recirculated through coastal aquifer systems and that both fresh and saline water inputs contribute nutrients and other dissolved solids to coastal waters. However, the relative importance of the driving processes and the extent to which saline water flow is coupled to fresh water discharges is still not well understood and the predictive capabilities are lacking. For this reason, researchers at Florida State University will investigate the forces that drive both fresh and saline groundwater discharges. Since both terrestrial (hydraulic gradient, seasonal recharge cycle) and marine (wave setup, tidal pumping, water level differences) forces drive subsurface fluid flows through coastal aquifers and nearshore sediments, this team of scientists will examine these processes via a cross-disciplinary approach. It is critical to tackle the problem of SGD from both ends (terrestrial and marine), and from both disciplines (hydrology and oceanography) because driving forces overlap in time and space and the resultant fluid flow measured through coastal sediments is often a result of composite forcing. The project will separate and evaluate these forcing functions by a combination of long-term measurements (i.e., isotopic tracers, seepage meters), hydrological/geophysical investigations, and numerical modeling. The goal is to develop a long-term data set on all parameters that are relevant to SGD and its driving forces. Since many SGD drivers have known temporal variations, the frequency of the parameters and the ensuing SGD responses will be measured to deconvolute the influence of the forces.In terms of broader impacts, this study will significantly advance our understanding of the mechanisms controlling SGD. Proposing to carry out the work prior to coastal development at the site will provide a baseline from which to assess the impact of commercial/residential development on coastal aquifers in the future. To disseminate information to coastal zone manager on SGD and its implications, a workshop will be held during the third year of the project. Graduate and undergraduate students will be involved in the field and laboratory studies of the project.