NANFA-- Re: nanfa V1 #1459

Dave McNeely (
Mon, 21 Oct 2002 09:59:50 -0500

> Date: Fri, 18 Oct 2002 05:08:57 EDT
> From:
> Subject: NANFA-- Freshwater/brackish
> Would anyone like to give a cut off point that marks the official
> between freshwater and brackish water in specific gravity?
> Moon
> Date: Fri, 18 Oct 2002 10:29:31 -0400
> From: "Brian" <>
> Subject: Re: NANFA-- Freshwater/brackish
> I looked for a cutoff point when doing water testing with Bridgewater
State College.
> The methods they use are taken from the USGS. I found no such thing.
> We (BCAS/BCNHC) are located on the Taunton River in an area considered
> We are near or at the upper limit of the estuary. At high tide the water
> about 16-18 ppt. At low tide it is below our meager detectable limits.
> aquarium salinity meter) Open ocean is 32 ppt.
> At high tide we can siene up juvi. winter flounder and the occasional
> marine species. At low tide we have caught bluegills and largemouth bass.
> The typical esturine species are always present in varying ratios.
> Brian Bastarache
> Natural Resources Dept.
> Bristol Co. Agricultural School/
> Bristol Co. Natural History Center
> 135 Center St.
> Dighton, MA 02715
McCluskey, D.S. 1989. _The Estuarine Ecosystem 2nd edition_. Blackie and
Son, Ltd., United Kingdom (Chapman and Hall, New York, USA). page 2: "The
salinity of fresh water is always less than 0.5 ppt. Thus the salinity of
estuarine waters is between 0.5 and 35 ppt. This range is generally termed
brackish, as distinct from marine or fresh waters. .................. .
Whereas marine and fresh waters are characterised by stable salinities,
estuarine water is extremely variable in its salinity."

For anyone who wants a complete, yet easily readable by anyone with just a
modest scientific literacy, introduction to estuarine environments, I highly
recommend McClusky's little book.

Dave McNeely

> >--Bruce Stallsmith
> >Huntsville, AL, US of A
> >
> >
> >The difference can be very small; for instance, many freshwater fishes
> >sunfish and shiners can't tolerate more than 2 ppt salinity (or 1.002
> >specific gravity, approximately). But different people will tell you
> >different cutoffs, depending on what processes or organisms you're
> >with.
> >
> >--Bruce Stallsmith
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