635 1. I n t r o d u c t i o n For many years biologists have attempt ed to set up divisions of coastal waters based on salinity ranges corresponding to biotic divisions. The first classification to receive wide acceptance was that of REDEKE (1933). Other schemes were advanced. The history of this movement has been reviewed by REMANE (1948), SEGERSTR~LE (1959) and DEN HARTOG (1960). The latest proposal carries the authority of the Venice Symposium (1958). The part of these proposals that is of particular interest here is the suggested boundary between fresh water and low salinity or oligohaline water. JOHANSEN (1918) set the upper salinity limit of fresh water at O.lO/"; REDEKE (1935) set the limit a t 0.1 g/l of chloride or 0.184Β°/,,0, while KOLBE (1927) and BROCKMANN (1908) set i t a t 0.2Β°/". EKMAN (1953), REMANE (1940), JΓRNEFELT (1940), HALME (1944), HILTER-MANN (1949) and the "Venice System" set the limit a t 0.5Β°/,,0. Thus, generally there seem to be two suggested limits between fresh water and low salinity brackish water, about 0.2Β°/00 and 0.5Β°/00. JOHANSEN'S limit, 0.lo/,,,,, is close to the salinity of soft fresh water (0.065). The limit of BROCKMANN, KOLBE and REDEKE, circa 0.2Β°/,,0, is lower than hard fresh water (about 0. 300Β°/,,,,). On the other hand, it is a little higher than the average salinities for lake and river waters of the Earth (0.146Β°/00) according to CLARKE (1924).
GUNTER and SHELL (1958) stated that a precise definition of the boundary between fresh water and low salinity coastal water had never been given in chemical terms. During the summer of 1962, PRICE, with the help of his students, made several chemical analyses of fresh waters, brackish water and sea water, chiefly in Mississippi. A few samples were taken in Alabama and Louisiana. Part of those data are used here in a discussion of the boundary between fresh water and oligohaline brackish water.