An estuary is a unique body of water that can be found all along the eastern coast of the U.S., most notably between the barrier islands and the mainland. The reason it is so unique is because it is a mix of fresh water and salt water. Salt water enters the estuary from the ocean with the incoming tides. Fresh water enters from the rivers and streams flowing downstream towards the ocean.
The salt marsh is a primary nursery for most of the species that inhabit it. There are several natural factors that are important to their growth and survival including temperature, salinity (amount of salt dissolved in water), tides, and seasonal changes. Tides can be beneficial to smaller prey species avoiding larger predators and they also bring in valuable nutrients from the ocean.
When an natural disaster, such as a tropical storm or hurricane, hits the coastline, it will bring a lot more salt water into the estuary. As the storm moves inland, it can bring with it gallons of rainwater (fresh water). As this rainwater fills water basins and rivers, that fresh water will make its way through the watershed, down to the estuary. So during a storm event, the estuary will be flushed with salt water and then flushed with fresh water.
The issue with this type of flushing is that it could be detrimental to the species so special to this ecosystem. Their bodies are designed to withstand a small increase or decrease of temperature and salinity. Anything outside of this range and their bodies will expire. An increase of salinity may not have the same effect as a decrease, though. Since these species are used to a slight increase of salt water twice a day, every day with the tides, when a storm hits the coast, it's not going to bring that much more salt water than it would every day. The rivers and rain water, by contrast, will bring enough fresh water to inundate the marsh hammocks and mudfluts with no salt in it at all. This complete flushing could wipe out whole species throughout the estuary.
One of our first responses during a natural disaster is always to the people. We want to make sure our homes, our businesses, our roads, and our neighbors are standing, undamaged, and healthy. What we fail to respond to is the health of the ecosystems that are damaged by these storms. Fresh water can also bring wastewater that is untreated, roadside pollution, and eroded sediment, all of which can suffocate the lungs of fish and poison filter-feeding species such as oysters and clams.
Being that it is National Estuaries Week, let's give a little more attention to this valuable ecosystem to the coast. Our estuaries need a delicate balance of fresh and salt water to survive.