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.
![](http://blogs.ifas.ufl.edu/escambiaco/files/2018/08/Lakewatch.jpg)
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).