Project Goal: To determine the central tendencies of salinity in different parts of the Pensacola Bay System. 

Historically, the Pensacola Bay area receives 65 inches each year¹.  But in the last decade this has increased to 75 inches².  With the current population growth and increased housing development, much of this increased rainfall is falling on impervious surfaces and eventually running off into the bay.  Is this increase in freshwater enough to alter the salinity of the bay to levels that efforts to restore seagrasses, scallops, and oysters could be compromised?

 

The two primary seagrasses that have historically existed in the lower portion of the Pensacola Bay System, turtle grass (Thalassia testidinum), and shoal grass (Halodule wrightii), require salinities be at, or above, 20 parts per thousand (ppt.).  The same is true for bay scallops (Argopecten irradians).  These species were once common in the lower portions of the bay, but all suffered declines in the 1960s and 1970s and there has been interest in trying to restore them.  If the salinities are high enough, and other stressors removed or managed, those seagrasses could return on their own.  Another citizen project led by the University of West Florida and Florida Sea Grant, Eyes on Seagrass, is currently monitoring seagrasses in the bay area to see if this is happening.  Florida Sea Grant also holds The Great Scallop Search each summer to determine where, and how many, scallops still exist there.

 

The salinity project is trying to determine what the current central tendency is for salinity in different parts of the bay system, with a focus on the lower bay.

 

Methods:

Florida Sea Grant trains local residents to use a handheld refractometer to measure salinity of surface water near shore.  Though the seagrasses and scallops grow at depth, higher saline water is more dense and will be found at these deeper locations.  The argument is that the central tendency of salinity in the deeper portions of the bay will be higher than what is found at the surface nearshore.

 

Volunteers take a reading of their assigned/selected beach once a week with the target of 100 readings before they stop.  We calculate the Mean, Median, and Mode of these data to determine the central tendency.

 

 

 

 

 

 

 

 

 

 

 

 

Data:

The following data is cumulative since monitoring began at each site.  Some sites have active monitors and others no longer do.

 

Data as of March 2023

Body of Water	Beach	Number of readings	Mean	Median	Mode
Bayou Grande	Polk Ave	29	20	21	21
	Navy Point SE	32	18	20	20
	Navy Point SW	33	17	18	20
	Bill Dickinson Boat Ramp	8	14	16	16
Bayou Texar	Bayview Park	34	12	12	15
Bayou Chico	Williams Park	7	10	5	5
Big Lagoon	Grand Lagoon	15	23	23	20
	Big Lagoon State Park	63	18	17	27
	Ft. McRee	4	22	22	19
	Siguenza Cove	11	22	21	21
ICW Perdido	Galvez Landing	82	22	22	22
	Kees Bayou	100	20	21	14
Old River	La Serena	36	23	23	25
	Perdido Key State Park	47	22	24	15
Pensacola Bay	Bruce Beach	1	18	18	–
	Hawkshaw Lagoon Memorial Park	37	13	12	15
	Hawkshaw Lagoon 9th Avenue	13	16	15	15
	Sanders Beach	70	18	18	18
Perdido Bay	Lower Perdido Bay	100	16	15	20
Santa Rosa Sound	Big Sabine	68	22	22	22
	Little Sabine	100	23	23	25
	Oriole Beach	68	26	26	30
	Shoreline Park	23	24	23	25
TOTAL		981	19	19	20
Big Lagoon Area		458	21	21	20
Santa Rosa Sound Area		259	24	24	26
Pensacola Bay Area		256	16	15	16

Results:

There are currently 22 stations that have been monitored since the project began.

3 of these (14%) have completed their 100 readings target – Lower Perdido Bay, Kees Bayou, and Little Sabine. 

12 of them (54%) are still actively being monitored.

7 of them (32%) – are not actively being monitored.

 

A total of 981 readings have been taken at these 22 sites.

Mean – 19 ppt

Median – 19 ppt

Mode – 20 ppt

 

In the Big Lagoon area there are 2 sites that have reached their 100 reading target.

Lower Perdido Bay – Mean, Median, Mode = 16 ppt, 15 ppt, 20 ppt.

Kees Bayou – Mean, Median, Mode = 20 ppt, 21 ppt, 14 ppt.   

3 stations continue to monitor – Big Lagoon State Park, Galvez Landing, and Perdido Key State Park

4 stations are currently inactive – Grand Lagoon, Ft. McRee, Siguenza Cove, and La Serena

The salinity for all stations is Mean 21 ppt, Median 21 ppt, Mode 20 ppt.

 

In the Santa Rosa Sound area there is 1 site that has reached the 100 reading target.

Little Sabine – Mean, Median, Mode = 23 ppt, 23 ppt, 25 ppt. 

3 stations continue to monitor – Big Sabine, Oriole Beach, and Shoreline Park

The salinity for all stations is Mean 24 ppt, Median 24 ppt, Mode 26 ppt.

 

In the Pensacola Bay area no stations have reached the 100 reading target.

6 stations continue to monitor – Hawkshaw Lagoon at Memorial Park, Hawkshaw Lagoon at 9^th Ave, Navy Point SE, Navy Point SW, Bill Dickinson ramp on Bayou Grande, and Bayou Texar.

3 stations are currently inactive – Sanders Beach, Bayou Grande at Polk Ave, and Bayou Chico.

The salinity for all stations is Mean 16 ppt, Median 15 ppt, Mode 16 ppt. 

 

Discussion:

 

Since the project began the central tendency for salinity in the bay system has been 19-20 ppt.  NOTE: only 14% of the stations being monitored have reached the 100 reading target.  Based on this, the salinity is at the “line” needed for those specific species of seagrass and scallops to survive.  When you break the bay system down, Santa Rosa Sound has the highest salinities and is most suitable for these species.  Big Lagoon is a little lower, but high enough.  Pensacola Bay is too low for these species of seagrass and for scallops.  But it is not believed that historically had them.

 

Of the 19 stations that have not reached the 100 reading target, 5 of them have 50 or more readings (Big Lagoon State Park, Sanders Beach, Galvez Landing, Big Sabine, and Oriole Beach) and 1 of them (Galvez Landing) has over 75.  It should be possible to have a few of these reach that target by the end of 2023 to give us a bigger picture.

 

Though the data is encouraging for the lower portions of the bay system, it is too early to determine what impact, if any, the increased rainfall has had on the bay.  Monitoring will continue.

 

References

 

¹ U.S. Climate Data.  (2023). Pensacola, Florida. https://www.usclimatedata.com/climate/pensacola/florida/united-states/usfl0715.

 

² Temperature and Precipitation Graph for Pensacola, Florida. 2023. National Weather Service. National Oceanic and Atmospheric Administration. Temperature and Precipitation Graph for Pensacola (weather.gov).