While we were conducting some dives during the scientific dive training on Bali I was pretty sure I stumbled upon a source of SGD right in front of our doorstep. But before I get overly excited I would to confirm this information somehow. Unfortunatly, as of now, we have no equipment available on site to conduct any sort of analyis. So I was wondering if there are any biological indicators or other signs which I could observe, before have to take more drastic measures and get my wiggle stick.
Marine exploration is not my specialty. The importance of such a find may depend on the quantity, reliability and quality of the freshwater discharge. There may or may not be important ecological connections or adding diversity of conditions where obvious changes could be found. One of the simplest tests is water conductivity of the discharge waters and then swimming around the vicinity of the discharge to see if you can determine the extent of the area affected with significantly lower salinity. Many aquatic flora and fauna are sensitive to salinity changes, but unless the freshwater volume of discharge is high, or the underwater topography has some way to collect, detain or capture this flow or reduce the mixing rate, or the flow is substantial discharge with regularity, the lighter freshwater would tend to rise toward the surface, and mix in the process. I know of a few circumstances where these were developed into drinking water sources, when close to the shore.
It would seem to me that temperature would be the first and simplest thing to measure. I'd expect the discharge temperature to equal the local air temperature averaged over the year as would be typical of spring water.....I did a review several years back: https://www.researchgate.net/publication/236596705_Biological_communities_in_springbrooks
I don't do marine work, but I'm sure that sea water temp varies over the course of the year.....so measure at the high or low sea water temp for maximum difference from ground water temp. Ground water temp remains quite constant year round....9 degrees C in PA USA......5 degrees in VT USA etc
Next I'd use a syringe grab a sample along with a sea water sample. Dye both with different food colors and allow them to equilibrate to room temp. Put the sea water in a graduated cylinder; layer the discharge in on top......if it floats as a distinct layer then you know it is lower density than sea water.
Good luck.
Chapter Biological communities in springbrooks
Sorry for the late reply - I seem to have missed your question... If you suspect a substantial freshwater proportion, as e.g. indicated by a blurry mixing zone coming from a submarine spring, you could also try to take a sample right at the spring and try to taste the salt content. Conductivity would be a major parameter to look out for in order to identify freshwater contents. Until now, I do not know of any "indicator-species" for SGD. Can you take a picture?
Sorry for my lateness in seeing this interesting post. At least in freshwater floodplain (off-channel & tributary) habitats, I can infer spring-fed conditions based on thermal differences from the mainstem across seasons. I.e., the nearby mainstem shows more thermal variability than do spring-fed, floodplain habitats. I suspect that the seafloor, freshwater inputs would show thermal differences from the nearby water column.
-Bob
- Badges
- Science method
- Similar topics
- Biological Science
- Ecology