No. 01–The Beginning
This is the first in a continuing series of columns intended to better acquaint Lowcountry residents and visitors with the unique estuarine (es-tyou-reen) environment we live, work and play within.
OK, so what’s an estuarium you may wonder? Well, The Lowcountry Estuarium is an aquarium like learning center located on the corner of 14th St and Paris Ave. in the Old Village section of Port Royal. It’s called an estuarium because its focus is on the creatures and habitats of the greater estuarine salt marsh eco system stretching from marshes and creeks of Port Royal, Lady’s and St Helena islands to the Savannah River.
To begin with, an estuary may be a costal bay, sound, delta or even a fjord where fresh water from a land mass meets and mixes with salt water from the ocean. The term brackish is used for the mixed water which is half the salinity of the ocean or less. Salinity is measured in parts per thousand (ppt) with fresh water at zero ppt and sea water at 35 ppt.
The concept of parts per thousand is easily understood if you envision a large container into which you pour 965 cups of fresh water to which you add and stir into solution 35 cups of sea salt. Voila, you have water at 35 ppt salinity.
The literature I’ve researched on the topic states without exception that estuaries have brackish water. What the literature fails to tell you is that the Port Royal Sound system is unique in that it is a high salinity estuary averaging between 29 and 32 ppt. The implications of this fact will be addressed in future columns.
Present day estuaries came into being with the rise in sea level at the end of the last ice age and fall into four major classifications. Coastal plain estuaries are drowned river valleys like Chesapeake Bay. Fjords are flooded glacial valleys found in Canada, New Zealand and Norway. San Francisco Bay is an example of a tectonic estuarine system. The two estuaries (ACE Basin and Port Royal Sound), between Charleston and Savannah, while technically not bar built estuaries more closely fit that classification than the others.
There are also four classifications regarding the dynamics of mixing fresh and salt water in an estuary. They are described as, vertically mixed, highly stratified, slightly stratified and salt wedge. Local waters are vertically mixed throughout most of the estuary. That means that salinity is virtually the same from top to bottom of the water column. Salt wedge effects may be observed at the mouths of our two small fresh water rivers where one may fish for bass and bream at the surface and flounder on the bottom.