Appendix B. Contoured salinity and POM chemistry in the two estuaries.
|FIG. B1. Individual sampling stations and dates are represented by a dot. The freshwater end of each transect is on the left and the marine ends are to the right of each individual plot, along distance transects. The three main data plots represent for Barataria (left colored panel) and Breton Sound (two right colored panels) estuaries. Shown between these panels is the discharge of Mississippi River water (M-R, August 2000 to August 2002) at the diversion structure in Breton Sound, and also the monthly precipitation (August 1999 to August 2002). The names of the largest water bodies along the Barataria Basin transect are abbreviated at the bottoms of left panels and are as follows: LdA = Lake des Allemands, LS = Lake Salvador, and LL = Little Lake, IW = intersection of the Intracoastal Waterway with the transect at the southern margin of Lake Salvador.|
An overview of the salinity dynamics is given here - POM dynamics are discussed more fully in the main paper. Salinity generally increased downestuary, from freshwater to marine ends of the two estuaries. However, elevated salinities in otherwise freshwater areas occurred during a drought period. In 1999, precipitation in southern Louisiana was very low and increasing salinities in the upper estuary could be observed due to saltwater intrusion. Throughout Barataria Basin, no salinities below 1 psu could be observed for almost one year. Heavy rainfall in November 2000 and during tropical storm Allison in June 2001 ended the drought and re-established a large freshwater pool in upper Barataria Basin. In Breton Sound, freshwater dynamics were controlled by a combination of precipitation and freshwater discharge. For the years 2000, 2001, and 2002, precipitation onto the whole watershed was 1.01, 1.94, and 1.75*109 m3, respectively, and freshwater discharge due to the diversion totaled 1.21, 0.98, and 1.24*109 m3, respectively. (Because we considered the area of the whole estuary to calculate the rainfall contribution, our estimate of relative freshwater contribution due to the diversion is conservative, and it would increase two to threefold if calculated only for the mid or upper part of the estuary). Even though total amounts of freshwater from these two sources were in the same range, the timing was quite different. Saltwater intrusion could be observed during the zero-discharge-period between September 1999 and January 2000. High discharge from January to March in 2001 and 2002 resulted in very low salinities mainly in the upper and mid part of the estuary for several weeks, and, after tropical storm Allison in June 2001, salinities were strongly reduced throughout the whole estuary.