THE COASTAL GROUNDWATER SUSTAINABILITY PARADOX

Coastal groundwater supports life, livelihoods, and ecosystems, yet it is squeezed from pressures of legacy contamination, growing populations, intensifying coastal storms, and sea-level rise. While coastal groundwater may be managed such that it is sustained as a resource for the freshwater needs of future generations, sustainability of coastal groundwater systems as a whole – maintaining the status-quo of land use, ecosystems, and processes they support – is not possible in the face of global change. As sea level rises, the base hydrologic level rises too, drowning roots of trees and crops and causing more extensive and more frequent flooding. If current water tables are artificially maintained, the land-sea balance is upset, and saline groundwater pushes inland. As coastal storms intensify, saline floodwater reaches farther inland, causing marshes to displace forests and farmland. Engineering solutions such as seawalls and tide gates may hold back surface flooding, but saltwater will still intrude through the subsurface, and groundwater tables will still rise. The interconnectedness of coastal systems means that as groundwater rises and salinizes, ecosystems change, and the biogeochemical processes they support shift, ultimately affecting global carbon budgets and land-ocean fluxes. While shifts are inevitable, the feedbacks among system components and the extent to which we manage our systems will determine how quickly changes occur and how well the transformed coastlines will support future generations.