Sea level is projected to rise by 1 m or more by 2100. A common concern for rapidly growing coastal communities is storm-driven inundation of coastal zones, but another subtle and potentially more critical impact will be changes to drinking water resources from salt water intrusion into aquifers along the coasts. These negative impacts from sea level rise could increase with the growth in coastal populations and their elevated demand for groundwater. Impacts will include both salinization of available water resources as well as changes to coastal ecosystems that rely on discharge of fresh water. Fresh water flows from coastal aquifers in a spectrum of ways, ranging from widely distributed discharge from sandy sediments to discharge from springs in limestone areas that contain water-filled conduits and caves. Moreover, the intrusion of salt water is likely to change the microbial communities living underground. Because these microbes are important for controlling the water chemistry, changes in the communities could also lead to a change in the water quality of the aquifers.

Specific questions to be addressed with this project include:

  • how will changing coastal demographics and sea level rise impact the sustainability of coastal water resources?
  • what are the relative magnitudes of salt intrusion if coastal aquifers discharge diffusely from sand or from springs?
  • how does salinization change microbial communities?
  • will these changes in microbial communities affect the quality of water in coastal aquifers and hence the cost of water supplies?
  • what strategies can be proposed to improve the sustainability of these water resources?

These questions will be addressed in two locations: Puerto Morelos Lagoon on the east coast of the Yucatan peninsula, which is characterized by numerous spring discharges from limestone and Indian River Lagoon on the east coast of Florida, which is characterized by diffuse flow from sandy sediments. Two field trips to the Yucatan and three to Florida will allow collection of human demographic information, measurements of the exchange of salt water following extremely large tides and storms, and measurements of changes in microbial communities and water quality following these events. The work will be carried out collaboratively by investigators with expertise in multiple disciplines including urban and regional planning, coastal hydrodynamics, microbial ecology, and aqueous geochemistry.

Non-technical Explanation of the Projects Broader Significance and Importance
The sustainability of coastal water resources in the face of rising sea levels should depend on how quickly coastal aquifers are intruded by salt water and how the water quality changes as a result of salt water intrusion and the effects on the microbial communities from that intrusion. Results from this project should aid in general planning for potential impacts related to changes in the coastal water resources, regardless of whether the intruding flow of water originates at springs or across broad areas of sand. Both of the field sites to be studied for this work have important regional impacts; Indian River Lagoon is designated an estuary of national importance by the National Estuaries Program, and Puerto Morelos Lagoon is the site of a national park. Findings from this work will be incorporated into regional water planning through collaboration with local water management districts.

1. The impacts of human activities on water demand and underground water recharge
2. The integrated impacts of sea level rise and human activities on saltwater intrusion and water resources
3. The impacts of sea level rise are closely related to the local environmental characteristics

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