Are Our Bays Becoming Less Salty? 2022 Annual Salinity Report

Introduction

Historically the average rainfall in the Pensacola Bay is around 60 inches per year.  However, over the past 10 years that has increased to slightly more than 75 inches per year (see Table 1).  The frequency of those levels over the past decade shows that most are between 60 – 80 inches but there have been two years with over 90 inches reported.  In the last decade, nine of the 10 years had total rainfall above the historic mean for the area.

Along with the increase in rainfall has come an increase in development.  This increase reduces the amount of the excess rainfall to percolate into the ground and recharge our aquifer.  Instead, it is directed into stormwater projects to reduce flooding in the community.  Some of this stormwater will eventually find its way to the estuary or the tributaries that feed the estuary.  The question is whether this increase in freshwater run-off is enough to decrease the salinity of the bay system.

There are several restoration projects ongoing within the bay.  Two of them Sea Grant has been involved in.  One is monitoring the status of seagrass and the other is status of bay scallops.  The species of seagrass in lower bay, such as turtle grass (Thalassia testudnium) and shoal grass (Halodule wrightii) require salinities to be at, or above, 20 parts per thousand.  Bay scallops depend on turtle grass for their life cycle and also require the salinity at, or above, 20 ppt.

Citizen volunteers are assisting Florida Sea Grant by monitoring the salinity of the bay on a weekly basis.

Table 1 – Annual Rainfall for Pensacola FL (National Weather Service)

Table 2 – Frequency of Rainfall Amounts in Inches

Method

Volunteers are trained to use a refractometer and asked to monitor their assigned beach once a week, reporting their results to Sea Grant and calibrating their instrument once a month.

We are asking our volunteers to continue to monitor until they have logged 100 readings.

Currently 21 locations around the bay are being monitored.  Nine are in the Big Lagoon area, eight near downtown Pensacola, and four near Pensacola Beach.

12 of these sites are actively being monitored at this time, 3 have reached the 100-reading mark, and 6 have not been monitored in some time.

Note:

Our volunteers are monitoring the water at the surface near the beach due to ease of access.  The seagrass and scallops we are interested in grow at the bottom and at depth.  However, saline water is more dense than fresh, and it is assumed that the water on the bottom at depth is saltier than the data being found at the surface near the beach.

There are other agencies who are monitoring salinity at depth.

Data for Each Site as of the end of 2022

Table 3 – Salinity Mean, Median, and Mode from Around the Pensacola Bay Area

Table 4 – Salinity Mean, Median, and Mode from the Big Lagoon Area

Table 5 – Salinity Mean, Median, and Mode for the Downtown Pensacola Area

Table 6 – Salinity Mean, Median, Mode for the Pensacola Beach Area

Discussion

A glance at Table 3 will show all 21 bodies of water that have been involved in this project.  Three of those, Lower Perdido Bay, Kees Bayou, and Little Sabine have reached the 100-reading mark.

For Lower Perdido Bay the mean salinity was 16 ppt ±5.  The highest reading was 24 ppt and the lowest was 6 ppt.  The median was 15 ppt and the mode was 20.  These data suggest that this body of water would not support turtle grass or bay scallops, but it is not believed that historically lower Perdido Bay did.  We would like to thank Bob Jackson for his effort on collecting these data.

For Kees Bayou the mean salinity was 20 ppt ±6.  The highest reading was 31 ppt and the lowest was 5 ppt.  The median was 21 ppt and the mode was 14 ppt.  These data suggest that turtle grass and bay scallops could survive here.  It is noted that Kees Bayou is a shallow basin located next to a highway and during intense rainfall the salinities could drop drastically to cause a decline of both target species.  We would like to thank Marty Goodman for his effort on collecting these data.

For Little Sabine the mean salinity was 23 ppt ±4.  The highest reading was 30 ppt and the lowest was 12 ppt.  The median was 23 ppt and the mode was 25 ppt.  These data also suggest that both turtle grass and scallops could survive in Little Sabine, and there are records that scallops were once there.  Turtle grass exist there now.  We would like to thank Betsy Walker and Liz Hewson for their efforts on collecting these data.

The Big Lagoon Area

These data suggest that most of the sampled areas could, in fact, support both turtle grass and scallops, and there are records that they have supported both in relatively recent years.  One note of interest is the lower salinities near Big Lagoon State Park.  Most of the sites have data at 20 ppt or higher – except Lower Perdido Bay (understandable) but we are not sure why the numbers are below 20 ppt. at the state park.  We would like to thank our active volunteers in the Big Lagoon area Jessica Bickell, Glenn Conrad, John Williams, and Emogene Johnson for their effort in collecting these data. 

The Downtown Pensacola Area

These data suggest that this area of the bay would not support turtle grass nor bay scallops.  But historically they did not.  Seagrass does exist in these bodies of water but much of it is widgeon grass (Ruppia maritima) which can tolerate lower salinities.  We would like to thank our active volunteers for the downtown area Tim Richardson and Glenn Conrad for their efforts in collecting these data.  

The Pensacola Beach Area

 These data suggest that Santa Rosa Sound could support, and do support, populations of turtle grass and scallops.  During our scallop searches conducted in July we have found one live scallop in Big Lagoon and two in Santa Rosa Sound over the last six years.  Again, these data suggests that all of these locations could do so with the highest salinities in the bay area based on these data.  We would like to thank our active volunteers in the Pensacola Beach area Ann Livingston, Gina and Ingo Hertz, and Holly Forrester for their efforts in collecting these data.

Though we have not reached the targeted 100-readings for most of our sites, these early results suggest the rainfall may not be lowering the salinity.  We will continue to monitor until we do reach the 100-reading for each and have a better idea.

We are seeking new volunteers.  The water bodies needing help are Bayou Chico, Bayou Texar, Big Lagoon, Bruce Beach, and Sanders Beach.  If you are interested contact me at roc1@ufl.edu