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Nutrients Still a Problem in Some Pensacola Area Waters – 2021 Report

In the world of water quality, many experts agree that excessive nutrients are one of our larger problems.  Organic and inorganic compounds that “feed” plants help complete the food cycle, but in excess can generate algal blooms which can eventually decrease the dissolved oxygen content in the water and, depending on the species of phytoplankton, can release toxins – both of which can cause fish kills.

Lakewatch is a UF IFAS citizen science volunteer program.

The University of Florida IFAS Extension Program trains local volunteers to monitor for these nutrients in their local waterways.  Along with their training, each volunteer is given a kit of supplies needed to sample three stations in their assigned body of water as well as filtering the water for chlorophyll analysis.  Analysis of samples for nutrients and chlorophyll are conducted by the UF IFAS LAKEWATCH lab in Gainesville.  In addition to collecting and filtering water, volunteers measure water clarity using a secchi disk provided in the kit.     

 

Total phosphorus and nitrogen are the two nutrients monitored in this project.  High concentrations of these could potentially trigger algal blooms (measured here with chlorophyll a concentrations), which could in turn lower dissolved oxygen and trigger fish kills.  This was a common occurrence in the bay system in the 1960s and 1970s.   As algal blooms increase, water clarity decreases – though water clarity can also decrease during stormwater events due to excessive sediments in the water – another pollutant of concern.

 

In the Pensacola Bay area, we have six bodies of water we are currently monitoring.  Those include the three larger bayous – Bayou Texar, Chico, and Grande – as well as Lower Perdido Bay, Upper Pensacola Bay, and Big Lagoon.  Volunteers sample their three stations every other month.  Below are the results over the time of monitoring.  All data goes through Dec 9, 2020.

 

Body of Water No. Years Sampling Period Station Total Phosphorus (µg/L) Total Nitrogen (µg/L) Total Chlorophyll a (µg/L) Secchi (feet) Salinity (‰)
Geometric Means
Bayou

Chico

7 2014 – 2020 1 28 530 14 0.9 6
2 26 575 12 3.3 9
3 20 351 7 4.5 8
Bayou Grande 7 2012 – 2019 1 15 315 4 4.3 14
2 15 298 5 5.4 16
3 17 319 5 5.3 17
Bayou Texar 3 2000 – 2002 1 22 360 6 2.7 3
2 26 406 9 2.4 6
Bayou Texar 14 2007 – 2020 1 17 800 6 3.5 8
2 17 677 7 3.8 9
3 17 677 7 3.8 9
Lower Perdido Bay 7 2014 – 2020 1 15 335 5 6.4 14
2 15 330 5 5.4 15
3 16 336 5 5.9 14
Big Lagoon 1 2020 – 2020 1 10 240 3 8.8
2 13 220 2 8.9
3 15 260 2 9.3
Pensacola Bay 2 2019 – 2020 1 10 298 4 7.5
2 15 275 5 7.3
3 14 236 6 7.4

 

Trends Over Time

 

Body of Water Metric Station Trend Notes
Bayou Chico Phosphorus 1 Decreasing Phosphorus is decreasing but not significantly
2 Decreasing
3 Decreasing
Nitrogen 1 Increasing Nitrogen is overall stable
2 Stable
3 Stable
Chlorophyll 1 Decreasing Chlorophyll is decreasing but not significantly
2 Decreasing
3 Decreasing
Water Clarity 1 Increasing Water clarity is improving, but not significantly
2 Increasing
3 Stable
Bayou Grande Phosphorus 1 Decreasing Phosphorus decreasing but not significantly
2 Decreasing
3 Decreasing
Nitrogen 1 Decreasing Nitrogen is decreasing but not significantly
2 Decreasing
3 Decreasing
Chlorophyll 1 Decreasing Chlorophyll is decreasing but not significantly
2 Decreasing
3 Decreasing
Water Clarity 1 Increasing SIGNIFACNTLY Water clarity is improving and significantly at station 1
2 Increasing
3 Increasing
Bayou Texar Phosphorus 1 Decreasing Phosphorus is decreasing significantly
2 Decreasing SIGNIFACNTLY
3 Decreasing SIGNIFICANTLY
Nitrogen 1 Stable Nitrogen has remained stable since 2007, but is much higher than it was in 2000
2 Stable
3 Stable
Chlorophyll 1 Decreasing Chlorophyll is decreasing
2 Decreasing SIGNIFICANTLY
3 Decreasing
Water Clarity 1 Increasing SIGNIFICANTLY Water clarity is improving significantly
2 Increasing SIGNIFICANTLY
3 Increasing SIGNIFICANTLY
Lower Perdido Bay Phosphorus 1 Increasing Phosphorus is increasing slightly
2 Stable  
3 Increasing  
Nitrogen 1 Declining Nitrogen is declining and significantly at station 2
2 Declining SIGNIFCANTLY  
3 Declining  
Chlorophyll 1 Declining Chlorophyll is declining but not significantly
2 Declining  
3 Declining  
Water Clarity 1 Increasing Water clarity has been increasing
2 Decreasing  
3 Increasing  
Big Lagoon Due to 1 year reported, there are no trends in Big Lagoon at this time
Pensacola Bay Due to 2 years reported, there are no trends in Pensacola Bay at this time

 

 

RESULTS

 

In this UF IFAS Lakewatch project, the bayous have been monitored more than the bays have; Bayou Texar being surveyed 17 of the 21 years since 2000.  The range of geometric means comparing the bayous and the bays indicates that the bayous have higher levels of nutrients, higher levels of chlorophyll a, and lower water clarity.

 

Bayous

Geometric means           Phosphorus range:          15-28                   µg/L

Nitrogen range:               298-800              µg/L

Chlorophyll range:          4-14                     µg/L

Water clarity range:       0.9-5.4                feet

 

Bays

Geometric means           Phosphorus range:          10-16                   µg/L

Nitrogen range:               220-336              µg/L

Chlorophyll range:          2-6                       µg/L

Water clarity range:       5.4-9.3                feet

 

In the Bayous

  • The phosphorus has decreased over time, though not significantly
  • The nitrogen has remained stable in Texar and Chico, but has decreased in Grande. The data submitted from Bayou Texar in 2000-2002 and 2007-2020 has shown that the nitrogen concentrations DOUBLED during that time period.  It is particularly high at station 1 in Bayou Texar.
  • The chlorophyll a has decreased over time
  • The water clarity has improved over time. Significantly improving in Bayou’s Texar and Grande.
  • Between the bayous, Bayou Grande is doing better overall

In the Bays

  • ONLY LOWER PERDIDO BAY HAS ENOUGH DATA TO COMPARE
  • Interestingly, the phosphorus in lower Perdido Bay has been slightly increasing over time.
  • Nitrogen has been decreasing, and has so significantly at station 2
  • Chlorophyll a has been decreasing slightly
  • Water clarity has been improving

 

DISCUSSION

 

As you glance at the data it is apparent that the bayous have larger nutrient issues than the bays.  It is true that the bayous have been monitored for a longer period of time, but there is a difference.

 

As you glance at the bayous it is apparent that Bayou Chico has a higher problem with nutrients than the others.  However, the total nitrogen concentrations in Bayou Texar (particularly at station #1) are much higher than the others.  In fact, when you compare the samples collected from Bayou Texar from 2000-2002 to those collected from 2007-2020 the total nitrogen concentrations have doubled.

 

This is a bit concerning during a period when most communities are working hard to reduce nutrients in our waterways.  With the highest geometric mean being at station 1 the question becomes are these nutrients coming from nearby sources, or from Carpenter’s Creek.  Either way this is an area where the community should try to identify the source(s) and mitigate them.

 

Reviewing the trend data for many of the metrics the graph is moving the right direction.  Most of the nutrients and chlorophyll’s are decreasing and the water clarity is increasing, but only slightly.  Certainly the community should continue what they have been doing to reduce these problems, but more data is needed to determine true long term trends.

 

One trend of interest is the increase in phosphorus in lower Perdido Bay.  This is a nutrient that has not concerned many because we do not have the source of phosphorus as water bodies in central and south Florida do.  So, to see this increase (albeit a slight increase) is worth further monitoring.

 

Overall, the nutrient picture is not too bad – and fish kills are not common any longer.  The team will continue to monitor and we will continue to report.  If you would like to read the full UF IFAS Lakewatch report for this area, contact Rick O’Connor (roc1@ufl.edu).