Discovering Dissolved Oxygen

Discovering Dissolved Oxygen

We all know how important oxygen is to all life.  It is an element with the atomic number of 8, meaning it has eight protons and eight electrons.  It has an atomic mass of 16 indicating that it also has eight neutrons.  Oxygen is a gas at room temperature indicating that 70°F is VERY hot for this element.  It is a diatomic molecule, meaning that it likes to combine with other elements and will combine with itself if need be.  Oxygen is not actually O, it is O2 in nature.  There is a triatomic form of this element, O3, which is called ozone – but that is another story.

Again, we know oxygen is much needed by living organisms.  Well… by most living organisms – there are some microbes that can survive with little or no oxygen, but for the majority of the creatures we are familiar with, it is a must. 

I have asked students why oxygen was so important to life.  I usually get the answer “that we will die without it”.  I respond by asking again – “but WHY do we need it?  What does it DO?”  And the response usually does not change – “we must have it or we will die”.  There is no doubt that it is important.  Being in an atmosphere with little or no oxygen sends our bodies into a “stress mode” gasping – but what DOES the element actually do for us? 

Life is abundant on this planet due to the presence of oxygen. Photo: Rick O’Connor

Oxygen is needed to complete the reaction we call respiration.  For most, the term respiration means “breathing” and this would be correct – but it is more than that.  It is an oxygen demanding reaction we all need to remain alive.  In this reaction the sugar molecule glucose (C6H12O6) is oxidized to produce Adenosine triphosphate (ATP – C10H13N5O13P3).  ATP is the “energy” molecule needed for cells to function – our gasoline.  It fuels all metabolic reactions needed to sustain life.  ATP cannot be consumed in food, it must be made in the cell and, as the reaction below shows, it requires sugar (which we get from food) and oxygen (which we inhale from the atmosphere) to work.

C6H12O6 + O2 –> CO2 + H2O + ATP

This reaction will produce 36 of the much-needed molecules of ATP with each cycle.  It is known that in anaerobic respiration (the break down of glucose without oxygen) it will also produce ATP but not as much – only 2 molecules of it instead of 36.  So, for most creatures’ aerobic respiration (with oxygen) is preferred and needed.  

The primary source of oxygen on our planet is plants.  This suggest that before plants existed there may have been little, or no, oxygen on in our atmosphere and scientists believe this was the case.  When you look at the fossil records it suggests that prior to plants existence there was life (anaerobic life) but after plants the diversity and abundance of life exploded.  Aerobic respiration seems to be the way to go. 

As most know, plants produce oxygen in the process known as photosynthesis.  This chemical reaction is used by the plants to produce the other needed respiration molecule glucose.  Plants produce their own glucose and so are called producers, while other creatures, including animals, are consumers – consuming glucose in their food.  The reaction for photosynthesis is –

CO2 + H2O –> C6H12O6 + O2

The excess oxygen produced in this reaction is released into the atmosphere by the plants.  It makes up 20% of our atmosphere and this allows life as we know it to exist.  Note… almost 50% of the oxygen in our atmosphere comes from single celled algae called phytoplankton that grow and exist at the surface of our oceans.    

Single celled algae are the “grasses of the sea” and provide the base of most marine food chains. Photo: University of New Hampshire

But what about aquatic creatures who do not breath the atmosphere you and I do?  How do they obtain this much needed oxygen drifting in our atmosphere? 

The answer is in dissolved oxygen.  Oxygen, being a gas, is released into the atmosphere.  Even the oxygen produced by submerged aquatic plants, like seagrasses and algae, release their oxygen as a bubble of gas which floats to the surface, pops, and is released to the atmosphere.  To get that back to the creatures in the water who need it as much as we do, you have to “dissolve” it into the water. 

To do this you must break the hydrogen bonds that connect water molecules to each other.  Water is a polar molecule, and each molecule connects to each other like magnets using hydrogen bonds.  These hydrogen bonds are weak and easy to break, but you must MOVE the water in order to do this. 

The water molecule. Image: Florida Atlantic University

Water movement, such as waves, currents, and tides, will do it.  The more movement you have the more oxygen will dissolve into it.  Waterways such as the rapids of mountain rivers and waterfalls will have high concentrations of dissolved oxygen – usually over 10 µg/L.  For some creatures this could be too high – like an oxygen rush to the head – but for others, like brook trout, it is perfect.  They do not do well in water with dissolved oxygen (DO) concentrations less than 10. 

For most waterways the DO concentrations run between 4 and 10 µg/L.  Most systems run between 5-7.  Waterways with a DO concentration less that 4 µg/L are termed hypoxic – oxygen deprived – and many creatures cannot live at these levels.  They are literally gasping for air.  I have seen fish at the surface of our local waterways when the DOs are low gasping for much needed oxygen through the atmosphere.  It is also the primary reason the great crab jubilees of Mobile Bay occurs.  Low levels of DO in the bay will trigger many creatures to leave seeking higher DO in the open Gulf.  But for some benthic creatures – like stingray, flounder, and blue crabs – they will literally run onto the beach gasping for oxygen.  The fish known as menhaden are particularly sensitive to low DOs and are one of the first to die when concentrations begin to dip below 4.  When you see the surface of a waterway littered with dead menhaden it typically means there is a DO problem. 

Slick calm water diffuses/dissolves less oxygen. Photo: Molly O’Connor

That said, some creatures, like catfish, can tolerate this and do not become stressed until the concentrations get below 2 µg/L.  If they ever reach 0 µg/L (and I have seen this twice – once in Mobile Bay and once in Bayou Texar) the waterway is termed anoxic – NO oxygen.  This is obviously not good.  Some are familiar with the “Louisiana Dead Zone”.  An area of the open Gulf of Mexico south of the Mississippi River where DO levels decline in the summer to levels where most benthic species, particularly shrimp, are hard to find.  It seems “dead” – void of marine life.  This is also a DO issue. 

How – or why – do dissolved oxygen levels get that low?

There are three basic reasons to this answer. 

  1. The surface is still, and little atmosphere oxygen is being “dissolved”.  We have all seen calm days when the water is as slick as glass.  On days like these, less oxygen is being dissolved into the system and the DO concentrations begin to drop.  But how low will they go? 
  2. The water is warm.  Higher water temperatures hold less oxygen.  As the water warms the oxygen “evaporates” and the DO concentrations begin to decline.  If it is a warm calm day (like those during a high-pressure system in summer) you have both working against you and the DO may drop too low.  Most fish kills due to DO concentrations occur during the hot calm summer days. 
  3. What is called biological oxygen demand.  All creatures within the system demand oxygen and remove it from the water column.  However, in most cases, atmospheric dissolved oxygen will replace for a net loss of zero (or close to it).  But when creatures die and sink to the bottom the microbes that decompose their bodies also demand oxygen.  If there is a lot of dead organic material on the bottom of the waterway that needs to be broken down, the oxygen demanding microbes can significantly decrease the DO concentrations.  This dead organic material is not restricted to fish and crabs that die but would include plant material like leaves and grass clippings from our yards, organic waste like feces, food waste, the carcasses of cleaned fish, any organic material that can be broken down can trigger this process. 

Now picture the perfect storm.  A hot summer day with no wind and high humidity over a body of water that has heavy organic loads of leaves, dead fish carcasses, and waste.  BAM – hypoxia… – low DO… fish kill… which would trigger more oxygen demanding decomposition and – more dead fish – a vicious cycle.   

You have probably gathered that low dissolved oxygen concentrations can occur naturally – and this is true – but they can also be enhanced by our activity.  Allowing organic material from our yards (grass clippings, leaves, and pet waste) to enter a body of water will certainly enhance the chance of a hypoxic condition and a possible fish kill – which would in turn fuel lower DO and poor water quality state for that body of water.  The release of human waste (food and garbage, sewage, etc.) will also trigger this.  And throwing fish carcasses after cleaning at the boat dock will too. 

But there is another process that more people are becoming familiar with that has been a problem for some time.  The process of eutrophication.  Eutrophic indicates the waterway is nutrient rich.  These nutrients are needed by the plants in order to grow – and they do.  Particularly the single celled algae known as phytoplankton.  These phytoplankton begin to grow in huge numbers.  So, abundant that they can color the water – make it darker.  As mentioned above, they produce a lot of oxygen, but at night they consume it, and with SO much phytoplankton in the water they can consume a large amount of DO.  The DOs begin to drop as the evening wears on and before sunrise may reach concentrations low enough to trigger a fish kill.  These phytoplankton will eventually die and with the large mass of organic matter sinking to the bottom, the oxygen demand to decompose them can trigger larger fish kills.  These fish kills in turn demand more oxygen to decompose and the process of eutrophication can create a waterway with very poor water quality and a habitat unsuitable for many aquatic creatures.  It is not good.  This is the process that causes the Louisiana Dead Zone each summer.  The nutrients are coming from the Mississippi River. 

One of 39 stormwater drains into Bayou Texar that can introduce a variety of organic compounds that can fuel eutrophication. Photo: Rick O’Connor

So, is there anything we can do to help reduce this from happening?

Well, remember some hypoxic conditions are natural and they will happen.  But there are things we can do to not enhance them or trigger them in waterways that would otherwise not have them. 

  1. When raking your yard, place all leaves in paper bags for pick up.  This keeps the leaves from washing into the street during rain events (and we are getting plenty of those) and eventually into a local waterway.  The problem with using plastic bags is that the local utility who collects them can no longer compose this into mulch.  You might consider using your leaves and grass clippings for landscaping yourself. 
  2. Watch fertilization of your yard.  Many over fertilize their yards and the unused fertilizer is washed into the street and eventually into the local waterway.  These fertilizers will do to phytoplankton what they were designed to do with your lawn – make them grow.  Of course, not fertilizing your yard would be best, but if you must place only the amount, and type, your lawn needs.  Your extension office can help you determine what that would be. 
  3. Pick up pet waste when you take your pets out to go to the bathroom. 
  4. If you have a septic tank – maintain it.  You can also look into converting to a sewer system. 
  5. If you are on sewer – watch what you pour down the drain.  Many products – such as fats, oils, and grease – can create clogs that cause sanitary sewage overflows when we have heavy rains (and we will have heavy rains).  Our local utility in the Pensacola area offers the FOG program (Fats, Oils, and Grease).  In this program you can pick up a clean 1-gallon plastic container to pour your fats, oils, and grease into.  Once full, you bring it back and switch for a clean empty.  To find where these containers bins are located near you visit the ECUA website – https://ecua.fl.gov/live-green/fats-oils-grease.
1-gallon container provided free to dispose of your oil and grease. Photo: Rick O’Connor

Dissolved oxygen concentrations naturally go up and down, and sometimes low enough to trigger a natural fish kill but following some of the suggestions above can help reduce how frequently these happen and can help to make our estuary healthier. 

Come on in… The Water Is Fine!

Come on in… The Water Is Fine!

Well… It’s Better 

When I joined Florida Sea Grant in 2012 my advisory committee told me water quality was one of their major concerns.  Makes sense really.  Some members were from the tourism and boating industry.  Some were from commercial and recreational fishing.  Others were homeowners.  ALL had concerns.  ALL depended on clean water for the success of their business and for the quality of their own lives.  It is a big concern. 

Since that time, we have been training volunteers to monitor nutrients and salinity.  We just recently added harmful algae monitoring and we report fecal bacteria data collect by the Department of Health.  All to (a) get people out there so they can see what is happening themselves, and (b) provide information we share with the members of the community. 

Local bayous in the Pensacola Bay area have experienced fish kills due excessive nutrients in the past. The Lakewatch Program trains volunteers to monitor nutrients in these waterways today. Photo: Rick O’Connor

Lakewatch is a program where volunteers use their boats to monitor nutrients at three locations in a particular waterway within the bay system.  Excessive nitrogen and phosphorus can lead to agal blooms, which in themselves can be a problem, just ask the folks in south Florida.  But when these organisms die, they form dense mats of organic matter that sink and decay.  The decaying process is oxygen demanding and the dissolved oxygen in the system decreases to levels where fish kills can happen.  Many may remember the large fish kills our bayous experienced in the 1960s and 1970s. 

Their samples are analyzed by the Lakewatch lab in Gainesville for total nitrogen, total phosphorus, and total chlorophyll a (which is a proxy for phytoplankton in the water column – algae).  The volunteers also measure the water clarity using a secchi disk.  Water clarity decreases with increase algal blooms and this can be a problem for submerged seagrasses.  The lab provides us with the salinity when they analyze the samples. 

Below is a table of data since sampling began in 2007.  However, some locations are JUST getting started. 

Table 1. Nutrients in the Pensacola Bay Area

All values are the geometric means.

Body of WaterTotal Phosphorus (µg/L)Total Nitrogen (µg/L)Total Chlorophyll a (µg/L)Water Clarity (Feet)Salinity (parts per thousand)
Pensacola Bay
Station 1     
Station 21527557.3 
Station 3     
Bayou Texar
Station 11780363.58
Station 21867383.810
Station 31759283.810
Bayou Chico
Station 129533163.27
Station 227548131.07
Station 32235384.17
Bayou Grande
Station 11531144.514
Station 21529045.515
Station 31731255.416
Big Lagoon
Station 11325238.918
Station 2     
Station 312213210.08
Lower Perdido Bay
Station 11532756.415
Station 21532455.415
Station 31532855.815

Pensacola Bay was only sampled for one year (2019-2020).  These three stations extend from the near the mouth of Bayou Texar, along the east side of the 3-Mile Bridge to the middle where the “hill” is in the bridge.  This site is open and in need a volunteer.  If interested, contact me.  You will notice as you glance at the data table there is very little information on this location.  The data provided in this table is the geometric means over the period of monitoring.  Only data from station #2 was enough to report on and the values for nutrients are on the lower side.  The water clarity is one of the better locations at 7.3 feet and there is insufficient data to report on the salinity. 

Again, this site was not monitored for long and there is not enough to see short- or long-term trends here.  But based on the little information provided, there does not appear to be nutrient issue here. 

Bayou Texar has been monitored the longest in this Lakewatch program.  One volunteer monitored from 2000-2002 before stopping.  A second volunteer began in 2007 and monitored until 2013 when a third volunteer took on these sites.  There is a current need for a new volunteer to continue monitoring this location beginning in 2023 – contact me if interested.  The Lakewatch data is provided in two sections, one covering the 2000-2002 monitoring period, and the other the 2007-present.  The data provided in this report are those collected between 2007-present.  The sample stations run north to south with #3 being closest to the mouth near Cervantes Bridge. 

A quick glance at the data shows significantly high nitrogen values, particularly at station #1 (near the 12th Avenue Bridge).  Most bodies of water monitored in this project have nitrogen values running between 200-400 µg/L (Bayou Chico being an exception – more on that next).  The total nitrogen in Bayou Texar runs between 600-800 µg/L – MUCH higher than the others.  Though the total nitrogen is higher, the total phosphorus and chlorophyll numbers are not much above other locations (again, Bayou Chico is an exception).  Water clarity, between 3-4 feet, is low for most locations.  The salinity is also lower than most. 

Since 2007 there have been significant improvements in total phosphorus at stations #2 and #3 – meaning improvements as you go from the 12th Avenue Bridge to the Cervantes Street Bridge.  Water clarity has significantly improved at all locations.  This is all good news.  However, the total nitrogen numbers have not changed significantly over that time and are much higher than other bodies of water sampled.  When you look at the number of health advisories issued for Bayou Texar it tends to be around 30% of the samples collected.  Much better than Bayou Chico but higher than other bodies of water monitored by the Health Department. 

Bayou Texar does have a total nitrogen problem and the closer you get to the 12th Avenue Bridge, the worse it becomes.  Sources of nitrogen can come from leaf litter, fertilizers, animal waste, and leaky septic tanks, or sanitary sewage overflows.  Identifing which source is the problem will be difficult.  Some suggest the issues may be coming further upstream in Carpenters Creek.  It is recommended that local residents and businesses along the creek and bayou use some of the management practices listed at the end of this report to help reduce this problem.  There is a large effort currently to try and improve conditions in and around Carpenters Creek.  Many of the properties along the bayou might consider the BMPs listed at the end of the report.  Based on the chlorophyll data, Bayou Texar is border lined eutrophic (excessive nutrients).  Reduction of nitrogen would help. 

There are records of seagrass growing in Bayou Texar as well as active ospreys, dolphins, and even manatee sightings. 

Bayou Chico has been sampled since 2014.  The stations run from west to east with station 3 being the closest to the mouth of the bayou (near the bridge).  As you glance across the numbers you will notice the nutrient data is slightly higher than the other bodies of water.  The other bodies of water have total phosphorus between 10-20 µg/L.  However, Bayou Chico has the highest values running between 20-30 µg/L.  Other than Bayou Texar, the total nitrogen values are between 200-400 µg/L.  Though lower than Bayou Texar, Bayou Chico is high running between 300-600 µg/L.  The same is true for the third nutrient parameter chlorophyll.  At most locations, excluding again Bayou Texar, the chlorophyll values are less than 5 µg/L.  Bayou Chico has the highest values running between 8-16 µg/L.  Along with Bayou Texar it has the lowest water clarity between 3-4 feet and has the freshest water in our sample locations with salinities running at 7 ppt. 

Though most parameters have improved slightly since 2014, there have been no significant changes in water quality.  There has been a slight increase in nitrogen at two stations – but again, not significant. 

These values do classify Bayou Chico as eutrophic (nutrient excessive).  The lower water clarity and salinity suggest more freshwater input – possibly from stormwater runoff.  The low water clarity could be from small algal blooms but could also be attributed to shore-based sediments entering the system via stormwater runoff.  These excessive nutrients could be linked to the excessive health advisories issued here due to fecal bacteria entering the waters.  Based on data from the Department of Health, over the years Bayou Chico has required a health advisory be issued 50-60% of the time they sampled – significantly more than the other bodies of water monitored.  Since 2010, this is the only body of water currently being monitored that has experienced a large fish kill – though this fish kill was attributed excessive warm water (which, like algal blooms, is oxygen demanding).  It is a body of water that has seen problems for decades and is the only body of water in our area that requires a state Basin Area Management Plan (BMAP). 

There are records of seagrass growing in Bayou Chico – and this is good news.  There are also reports of ospreys, dolphins, and manatee sightings here as well.  The state has deployed oyster reefs to help remove nutrients.  There is an invasive species present (giant salvinia – Salvinia molesta) that is of concern.  The state is currently managing this plant.  It prefers high nutrient, low energy (calm) freshwater water.  The salinities of the other bayous may be too high for this plant, but we are trying to education residents about the situation and help monitor/remove it if it appears.  You can contact the county extension office for more information on this plant if interested.    

Bayou Grande has been monitored since 2012.  The stations also run west to east with station #3 closest to the mouth near NAS main side bridge.  As you glance across the numbers you will notice values at, or below, average for the areas sampled.  Total phosphorus runs close to 15 µg/L.  Total nitrogen values run close to 300 µg/L.  Total chlorophylls are some of the lowest running close to 4 µg/L.  Water clarity is the clearest of all three of the bayous running between 4.5-6 feet and is also the saltiest with salinities running around 15 ppt. 

All though all parameters have shown improvement in water quality since 2012, most are not significant improvements.  The one exception is water clarity at station #1 – it has shown significant improvement during this time. 

In general Bayou Grande is in the best shape of the three bayous and compares well with the open bay stations being monitored.  It is classified as mesotrophic – meaning nutrients are middle range (where you expect an estuary to be).  The health advisory reports are usually between 20-30% of the samples taken and fish kills have not occurred here since we began monitoring.  There have been improvements on septic to sewage conversions in these communities, as well as efforts to build living shorelines (which can help reduce nutrient runoff to the bayou coming directly from properties in lieu of storm drainpipes).  It is also a larger bayou (hence its name) with less development along the southern shoreline.  There are more efforts planned to try and improve sewage issues and in planting living shorelines using filter feeding oysters.  Residents along Bayou Grande could also incorporate Florida Friendly Landscaping principals to help reduce nutrients further as well as incorporate clean boating practices.  Information on these programs can be found at your county extension office. 

Big Lagoon has only been monitored since 2020.  Thus, there are gaps in the data table where there are insufficient data to calculate a geometric mean.  The sample stations run from east to west with #1 being closest to Ft. McRee and the mouth of the Pensacola Bay system itself.  Glancing at the data where a geometric mean was able to be determined you will see that nutrient values are some of the lowest in the bay area.  The total phosphorus runs between 12-13 µg/L, total nitrogen between 200-250 µg/L, and the total chlorophyll between 2-3 µg/L.  The water clarity data are the clearest in the bay area, running from 9-10 feet.  The salinity is interesting.  At station #1 (near Ft. McRee) the geometric mean for salinity is 18 ppt, but at station #3 (near Big Lagoon State Park) it is only 8 ppt. 

Since sampling only began two years ago, it has not been long enough to determine any long-term trends. 

 The chlorophyll numbers are actually low enough to classify Big Lagoon as oligotrophic (nutrient poor).  This is unusual for an estuary, which are typically bodies of water with moderate amounts of nutrients due to natural runoff.  But remember (a) Big Lagoon does not have a lot of natural runoff and (b) we have only been collecting samples there for two years. 

The interesting thing about the salinity is how low it is.  Station #3 (near Ft. McRee) is 18 ppt and being so close to the mouth of Pensacola Bay, and the Gulf of Mexico, you would expect this to be higher – maybe between 25-30 ppt.  The fact that there are thick beds of turtle grass (Thalassia testdidnium) suggest that the actual mean is probably higher than the 18 ppt reported here.  The opposite side of Big Lagoon is interesting as well.  Station #3 reports a geometric mean of 8 ppt.  This is equivalent to the upper end of Bayou Texar (near the 12th Avenue Bridge) and most of Bayou Chico.  This too seems very low for this body of water.  The Department of Health samples for fecal bacteria near Big Lagoon State Park and it does, at times, get high enough (> 70 colonies/100ml) for a high bacteria reading.  DOH usually takes a second sample to confirm the reading and most often the second reading is lower, and a moderate classification is given for that week.  That said health advisories have been given in this region, albeit less than 10% of the samples taken.   All of this suggest that there may be some runoff issues at the west end of the Lagoon.  Obviously more sampling is needed. 

This body of water does support plenty of seagrass, ospreys, dolphins, and an increase in manatee reports.  There are diamondback terrapins and horseshoe crabs both reported here as well.  But it was also a location where bay scallops once thrived and no longer do.  Scallop searches have been ongoing here for six years and only one live animal has been found.  There are several possible reasons for their decline, decrease in salinity maybe one of them.  Monitoring will continue.  It is also a location where the state has measured a decline in seagrass – also concerning.  Sea Grant is currently partnering with the University of West Florida to monitor both seagrass abundance and water quality within Big Lagoon. 

Lower Perdido Bay has been monitored since 2014.  The three stations run from south to north.  Station #1 is near Innerarity Point and station #3 is near Tarkiln Bayou.  Glancing across the numbers of the lower Perdido you will see that they are similar to most of the other bodies of water being monitored.  The total phosphorus is 15 µg/L.  The total nitrogen is between 320-330 µg/L.  And the total chlorophyll is 5 µg/L classifying this area of Perdido Bay as mesotrophic.  Being an open bay, the water clarity is higher, running between 5-6 feet, and the salinity is reported at 15 ppt.  As with Big Lagoon, the salinity seems lower than one would expect but historic records suggest that Perdido Bay in general may have been lower than most other open bays.  Historically the mouth of the bayou open and closed frequently giving the Spanish the reason to name it Perdido (“Lost Bay”).  This closer may have made it more of a freshwater system – similar to the dune lakes of Walton County and the historic Choctawhatchee Bay – and may play a role in the lower salinity of Big Lagoon. 

The trends over time show that most parameters have improved but not significantly.  The one exception is total nitrogen.  The total nitrogen in lower Perdido Bay has significantly decreased over the period Lakewatch has been monitoring – and this is good news. 

Perdido Bay has had a history of poor water quality, but this is due more to industrial compounds being released through the tributary creeks.  These compounds did cause other problems, including some species of fish altering sex, and whether these are still an issue cannot be determined by these data – this project is monitoring for nutrients.  The nutrient driven algal blooms and fish kills found in the bayous 50 years ago were not as common in this body of water and these data suggest that the system is mesotrophic as most estuaries are.  As with most of the other bodies of water, ospreys, dolphins, and manatees have all been recorded here.  Seagrasses are present but being a less saline system than Big Lagoon and Santa Rosa Sound, the species composition is different and abundance is less.  There have been efforts to survey for bay scallops in the lower portions of Pensacola Bay, but no efforts have been made in the lower Perdido due to salinities currently, and historically, not being high enough.  Again, the lower salinity is thought to be more natural than from heavy development and urban runoff. 

Summary

In summary, these data suggest that the nutrient problems area waterways experienced in 1960s and 1970s have improved.  Algal blooms and fish kills are no longer common.  But there still could be dissolved oxygen (DO) issues at the bottom of our bays and bayous that reduce biodiversity.  This is not monitored by Lakewatch and we are not aware of any long term monitoring of DO to know how things have changed in the last 50 years. 

Anecdotal reports suggest the coverage of seagrasses in these systems are improving.  Though there are seagrasses in Big Lagoon, some reports suggest there has been a decline in recent decades.  There is a current citizen science project entitled Eyes on Seagrass where Sea Grant and the University of West Florida train volunteers to monitor both coverage and species composition.  Data from this project will presented in a separate report later in the year.  There are also separate citizen science efforts monitoring the presence of bay scallops, horseshoe crabs, and diamondback terrapins in the bay area.  Horseshoe crabs are being encountered more often, as are terrapins, but bay scallops seem to still be missing.  As with the seagrass monitoring, these reports will be coming later this year. 

There are still concerns with both Bayou Chico and Bayou Texar – these being the only two nutrient eutrophic systems in this monitoring project (based on chlorophyll data).  Efforts to better understand the sources of nutrients, and enact better management practices, should be considered for these waterways.  Things such as reducing fertilizer use, mitigating fertilizer runoff with living shorelines, converting from septic to sewers, better maintenance of septic systems, and reduction of sanitary sewage overflows are all actions that citizens can take now to help improve these waterways.  For information on how to do these, contact your county extension office and we will be glad to assist.   

Lakewatch is a citizen science volunteer supported by the University of Florida IFAS

Panhandle Outdoors Live! at St. Joseph Bay Rescheduled for September 28th

Panhandle Outdoors Live! at St. Joseph Bay Rescheduled for September 28th

The University of Florida/IFAS Extension faculty are reintroducing their acclaimed “Panhandle Outdoors LIVE!” series. Conservation lands and aquatic systems have vulnerabilities and face future threats to their ecological integrity.  Come learn about the important role of these ecosystems.

The St. Joseph Bay and Buffer Preserve Ecosystems are home to some of the one richest concentrations of flora and fauna along the Northern Gulf Coast. This area supports an amazing diversity of fish, aquatic invertebrates, turtles, salt marshes and pine flatwoods uplands.

This one-day educational adventure is based at the St. Joseph Bay State Buffer Preserve near the coastal town of Port. St. Joe, Florida. It includes field tours of the unique coastal uplands and shoreline as well as presentations by area Extension Agents.

Details:

Registration fee is $45.

Meals: breakfast, lunch, drinks & snacks provided (you may bring your own)

Attire: outdoor wear, water shoes, bug spray and sun screen

*if afternoon rain is in forecast, outdoor activities may be switched to the morning schedule

Space is limited! Register now! See below.

Tentative schedule:

All Times Eastern

8:00 – 8:30 am  Welcome! Breakfast & Overview with Ray Bodrey, Gulf County Extension

8:30 – 9:35 am Diamondback Terrapin Ecology, with Rick O’Connor, Escambia County Extension

9:35 – 9:45 am  Q&A

9:45- 10:20 am The Bay Scallop & Habitat, with Ray Bodrey, Gulf County Extension

10:20 – 10:30 am Q&A

10:30 – 10:45 am Break

10:45 – 11:20 am The Hard Structures: Artificial Reefs & Marine Debris, with Scott Jackson, Bay County Extension

11:20 – 11:30 am Q&A

11:30 – 12:05 am The Apalachicola Oyster, Then, Now and What’s Next, with Erik Lovestrand, Franklin County Extension

12:05 – 12:15 pm Q&A

12:15 – 1:00 pm Lunch

1:00 – 2:30 pm Tram Tour of the Buffer Preserve (St. Joseph Bay State Buffer Preserve Staff)

2:30 – 2:40 pm Break

2:40 – 3:20 pm A Walk Among the Black Mangroves (All Extension Agents)

3:20 – 3:30 pm Wrap Up

To attend, you must register for the event at this site: 

https://www.eventbrite.com/e/panhandle-outdoors-live-at-st-joseph-bay-tickets-404236802157

For more information please contact Ray Bodrey at 850-639-3200 or rbodrey@ufl.edu

Mercury Contamination in Local Fish

Mercury Contamination in Local Fish

Imperiled (verb) – put at risk of being harmed, injured, or destroyed.

 

In 2021 the Florida Department of Environmental Protection classified 44 area waterways in the Pensacola Bay System as imperiled.  Such designations are based on an environmental parameter making it unhealthy for one reason or another.  When we think of an unhealthy body of water, many times we think of sewage.  There are nine bodies of water in the Pensacola Bay System classified as imperiled due to the fecal bacteria concentrations within.  There are another seven for bacteria levels high enough to close them for shellfish harvesting.  This is a total of 16 bodies of water having bacteria issues (36% of the 44 designations).

Closed due to bacteria.
Photo: Rick O’Connor

 

Low dissolved oxygen and fish kills is another parameter we think of.  There are four waterways designated imperiled due to high nutrients (a cause of hypoxia and fish kills), and one for low dissolved oxygen readings itself.  This is a total of five (11% of the 44 designations).

Dead redfish on the eastern shore of Mobile Bay.
Photo: Jimbo Meador

 

But you may be surprised to learn that 23 of the 44 imperiled water bodies (52%) are designated based on the mercury content of the fish sampled there.

 

Most people are aware of the mercury issue in fish.  Many of those living in the Pensacola Bay area are aware of this issue locally, but they may not be aware that with the 2021 designations, it is the primary reason for many listed.  To be fair, it is not that mercury issues are increasing, it may be more that there are 97 waterways in the Pensacola Bay System being considered for delisting in 2021 and those are listed for a variety of other issues.  What it is stating is that with the 44 that remain imperiled, mercury is the primary cause.

 

We have all heard of mercury in fish, but where is it coming from?  What health problems does it cause?  And is there anything that can be done to make these bodies of water healthier?

 

Mercury is a naturally occurring element on the periodic table.  It is element #80, meaning it has 80 protons and electrons, one of the larger naturally occurring elements.  It is a silver-colored liquid at room temperature, one of only two naturally occurring elements in the liquid phase at these temperatures – the other being bromine.  It is sporadically found throughout the earth’s crust, usually combined with other elements.  There are two forms of mercury – mercury (I) and mercury (II) – indicating the number of cations available for sharing or transferring in compound bonding.  Mercury (II) is more common in nature.

 

 

The element has been of interest to humans for centuries.  There are records of it buried beneath the Mayan pyramids, though we are not sure how it was used, and it was used in Chinese medicine centuries ago.  The Spanish used it to help extract silver from mines during their colonial period around the world.  It was also used in separating fir from skin in felt hat making in the 19th century.  Hatters who used this method eventually had neurological problems and became known as “mad hatters”, an idea used in Lewis Carol’s Alice’s Adventures in Wonderland.

 

In more modern times it has been used in fillings for tooth cavities (including my own) and preserving specific vaccines.  Being a good conductor of electricity and not of heat, it is used in numerous electrical components, fluorescent lighting, and batteries.  Some cultures used it to help “whiten their skin” and a common use is in the processing and production of certain industrial chemicals.  Today, due to the toxic properties of mercury, many of these uses are no longer.

Fluorescent lighting contains mercury.

 

Mercury is obtained for these uses by mining their ores.  The most sought after ore is cinnabar, a red-colored rock found around the world.  Mercury (II) sulflide (HgS) is a common compound found in cinnabar.  When heated and oxidized it will produce sulfur dioxide and elemental mercury.

 

HgS + O2 à Hg + SO2

 

Cinnabar is the most common ore mined for mercury.
Photo: Classic Crystal

 

 

The problem with mercury is that it is toxic, and some forms of mercury are more toxic than others.  The element is known to cause brain, kidney, and lung issues.  It also can weaken the immune system.  It is most known for the neurological problems it causes.  Sensory impairment, lack of motor skill coordination, psychotic reactions, hallucinations, tremors and spasms have all been connected to exposure to mercury.  There are concerns with the neurological development within the fetus if exposed to mercury and many of the health advisories target women of childbearing age who are pregnant or considering it.  They have included the very young and the very old in their recommendations that these members of the population do not eat more than 6 ounces of fish (or shellfish) that have high mercury contamination.

 

Mercury contamination in fish.
Image: BBC

 

 

The organic forms of mercury, dimethylmercury and methylmercury, are the more toxic forms.  These are introduced to the environment both naturally and from human activity.  Once in the aquatic environment they are absorbed by the phytoplankton (microscopic plants in aquatic environments).  Methylmercury accumulates in lipids (fats) within the cell at relatively low concentrations (phytoplankton are not large).  However, they are not passed by the creature.  The slightly larger zooplankton (microscopic animals) feed on the phytoplankton and accumulate the mercury they have stored.  Feeding on a lot of these, they accumulate even more mercury.  The zooplankton are consumed by small fish, who eat a lot and accumulate even more mercury.  Then the mid-sized fish consume them, and the larger fish consume those, and on and on.  The top predators have accumulated enough methylmercury to be hazardous to human health IF they are consumed by people.  This process of increasing the concentration of mercury through the food chain is known as biomagnification – “magnifying the problem”.

 

So, which fish are of concern?

 

Based on the Florida Department of Health for freshwater systems in Escambia County.

  • Bluegill, Channel catfish, Largemouth bass, Long-eared sunfish, Red-eared sunfish, Spotted sunfish and Warmouth from the Escambia River system – you should not eat more than one/week.
  • Do not eat chain pickerel or largemouth bass – and do not consume more than two red-eared sunfish from Crescent Lake.
  • Lake Stone near Century FL – no more than two bluegill and sunfish per week and no more than one largemouth bass each week.
  • From the Perdido River do not eat more than two bluegill or sunfish each week and do not eat largemouth bass from the Perdido River.
  • The same species and regulations apply for the Yellow River system as well.

The following marine species are of concern….

Almaco jack, Atlantic spadefish, Atlantic croaker, Weakfish (trout), Black drum, Black grouper, Blackfin tuna, Bluefish, Cobia, Dolphin, Pompano, Gafftop catfish, Gag, Greater amberjack, Gulf flounder, Hardhead catfish, King mackerel, Ladyfish, Lane snapper, Bonito, Mutton snapper, Pigfish, Red grouper, Red snapper, Sand seatrout, Scamp, Shark, Sheepshead, Snowy grouper, Southern flounder, Southern kingfish, Spanish mackerel, Spot, Striped mullet, Vermillion snapper, Wahoo, White mullet, Yellow-edge grouper, and Yellowfin tuna.

 

In each case it is not recommended eating more than two servings a week.  For a few, it is recommended that the most vulnerable people mentioned earlier not at ANY… Those would include Blackfin tuna, Cobia, King mackerel, Bonito, and Shark.

 

It is recommended that NO ONE eat king mackerel over 31 inches and any shark species over 43 inches in length.

 

I guess as you look at this list, you see fish species that you like.  This list can lead folks to think… “I am just not going to eat seafood”.  This would be a mistake.  The Department of Health has found there are essential vitamins and nutrients provided be seafood that are missing if you do not eat them.  They found additional problems in fetal development when seafood protein was left out of the mothers’ diet.  So, the response would be… eat other seafood species you do not see on this list… or, if you see something you do like, no more than 1-2 6-ounce servings per week.

 

So, is there anything we can do about the mercury issue in our bay system?

 

Well, to have the biggest impact you will need to determine the biggest source.  33% of the mercury in our environment comes from natural sources, such as volcanic eruptions.  We can do nothing about volcanic eruptions, or other natural sources, so we will need to look at anthropogenic (human) sources.

 

The larger sources would be anthropogenic, which account for 67% of the known mercury in the environment, focusing on these can make a large impact.  Coming in at No.1 – producing electricity by burning coal.  This accounts for 65% of the anthropogenic sources.  Moving away from burning coal would make a huge difference.  But that is easier said than done.  Mining and burning coal are important for the economy of many communities.  It is one of the cheaper methods of producing much needed electricity.  But in addition to producing mercury compounds during the heating process, many other toxic compounds are produced and released as well – not to mention the amount of greenhouse gases produced during this process.  Hence the name “dirty coal”.  There are other methods of producing electricity and the solution would be to convert not only the power plants to these methods, but the coal dependent communities to this line of work.  This one step would make a big difference.

Power plant on one of the panhandle estuaries.
Photo: Flickr

 

At a much smaller scale, mining for gold produces 11% of the mercury from the mine tailings, cement production (7%), and incinerating garbage (3%).  Though not a large player in this game, reducing the amount of solid waste burned each year would help reduce the mercury issue.

 

The takeaway here is that the number of imperiled waterways in the Pensacola Bay System have been reduced over recent years and we will look at this in another article.  But for those that remain, mercury is the prime reason.  It is also important to understand that mercury is a naturally occurring element and can not be broken down, so we have what we have – but, we can stop adding to the problem.  Third, eating some seafood each week is good for you.  You will just need to select species that are not problems or watch how much you eat if you prefer some of the listed species.

 

For more information on the 2021 imperiled waterways list visit

https://floridadep.gov/dear/watershed-assessment-section/content/final-lists-impaired-waters-group-4-cycle-2-basins

 

For more on the seafood safety species lists visit

https://dchpexternalapps.doh.state.fl.us/fishadvisory/

 

Other sources for this article included:

 

Wikipedia – https://en.wikipedia.org/wiki/Mercury_(element)

 

Miller, G.T., Spoolman, S.E. 2011. Living in the Environment. Brooks and Cole Cengage Learning. Belmont CA. pp. 674.

The Recent Fish Kill Near Pensacola Was Due to Stratification… Say What?

The Recent Fish Kill Near Pensacola Was Due to Stratification… Say What?

This began with a call from one of my volunteers who was checking salinity at Shoreline Park.  She reported the salinity, but also reported to smell of dead fish – though she could not see them.  I visited Shoreline Park the following day on another project and could smell it as well.  There was a large amount of dead seagrass washed ashore from a recent storm and I thought this may be the cause of the smell because I did not see the dead fish either.

 

When I got home, I checked the FWC fish kill database.  It reported a redfish kill in Pensacola Bay.  It is unusual to see a kill of only one species.  Many times, these are releases from fishing activity, particularly bait, and thought this must be the case – FWC did not mention the cause.  I let the volunteer know and asked to keep an eye out.

 

I reported this to the Escambia County Division of Marine Resources to (a) let them know, and (b) to find out if they had any idea of cause.  They replied that the location was incorrect.  The kill was actually near Galvez Landing on Innerarity Point.  He (Robert Turpin) had visited the site and did find any dead fish.  I have a lot of volunteers over that way so asked each to take a look.  They did not see any dead fish.  I asked them to keep an eye out and collect a dead fish if they saw one for testing.  Often when a large fish kill occurs, and it is only one species, the suspect cause is disease.  Tissue samples could confirm this.

 

And then came another call.

This time it was from one of our Master Naturalist who lives on the eastern shore of Mobile Bay.  He wanted to know what was up with all of the dead redfish along the shore of the bay.  He sent photos and his beach was littered with them.  I reached out to Mississippi/Alabama Sea Grant to see if they knew what was going on.  They had heard about the situation and knew the Alabama Department of Natural Resources was collecting samples.  The Gulf Islands National Seashore then reported large numbers of dead redfish along the National Shores property in Mississippi, something was up.

Dead redfish on the eastern shore of Mobile Bay.
Photo: Jimbo Meador

I eventually got word from Dr. Marcus Drymon at the Dauphin Island Sea Lab.  They had a team working on this.  Their team reported that stratification of the Gulf had created a hypoxic (low dissolved oxygen) layer on the bottom and the male “bull redfish” had gathered for breeding and died.

 

So, we are back to our title – what is stratification and how did this cause the fish kill?

 

Stratification is the layering of the water.  Less dense water will sit atop the more dense.  Water temperature or salinity can cause this density difference and layering.  Colder and/or saltier water is denser and will form the bottom layer.  If you have high winds, it will mix the water and the stratification disappears.  Tides and currents can affect this as well.

 

What they believe happened recently was excessive amounts of rainfall created a large layer of freshwater to move from Mobile Bay into the open Gulf.  The combination of tides and wind allowed a stratified layer to form.  The oxygen that marine life uses is dissolved into the water at the surface and referred to as dissolved oxygen (DO).  If the system is stratified, then the oxygen dissolved at the surface will not reach the bottom and hypoxia (low DO) can happen.  They this is what happen.  It just so happens that the large male redfish (bull reds) had congregated just offshore for breeding.  They are more sensitive to low DO than the smaller females and any juveniles.  So, the males died.  To answer the question as to why other fish did not die (what you typically see in a DO related fish kill) – the numbers were not mentioned by there was one reference to 4.0 ppm.  This is the high threshold of hypoxia.  Many fish can tolerate at this concentration, but the male redfish could not.

 

So, that is what we think happened.  The perfect storm of the demise of a group of male redfish just off of Mobile, and the carcasses drifted to other locations.

Maintaining your septic system: Should you use additives?

Maintaining your septic system: Should you use additives?

A conventional septic system is composed of a septic tank and a drainfield, where most of the wastewater treatment takes place. Image: US EPA

Why do you need to maintain a septic system?

Conventional septic systems are made up of a septic tank (a watertight container buried in the ground) and a drain field, or leach field. In the septic tank, solids settle on the bottom (the sludge layer), and oils and grease float to the top and form a scum layer. The liquid wastewater, which is in the middle layer of the tank, flows out through perforated pipes into the drainfield, where it percolates down through the ground. Most wastewater treatment takes place in the drainfield.

Solids settle to the bottom of a septic tank (sludge), oils and greases float to the top (scum) and wastewater (effluent) flows out of the tank into the drainfield for further treatment. Image: Soil and Water Science Lab, UF GREC.

Although bacteria continually work on breaking down the organic matter in your septic tank, sludge and scum will build up, which is why a system needs to be cleaned out periodically. If not, sludge and scum can flow into the drainfield clogging the pipes and sewage can back up into your house. Overloading the system with water also reduces its ability to work properly by not leaving enough time for material to separate out in the tank, and by flooding the system.

Should you use additives in your septic system?

Septic systems do not need any additives to function properly and treat wastewater. Although there are many commercial microbiological and enzyme additives sold on the market that claim to enhance bacterial populations and reduce the time between septic system pumping, there really isn’t any peer-reviewed scientific literature that shows that these additives are effective in doing what they claim.

In Florida, the Department of Health (DOH) reviews commercially sold additives to ensure that they are safe to use in septic systems. DOH clearly states that although products are approved, it does not mean that this is an endorsement or a product recommendation. Approval simply means that as required by Florida law, the additive doesn’t interfere with septic system function and that when an additive is used, the effluent (wastewater) leaving the septic system meets Florida’s water quality standards. Only products in compliance with this law can be sold or used in septic systems in Florida. You can find a list of approved products and more information regarding additives on the Florida Department of Environmental Protection (FDEP) septic system website. Access the list of products directly here (updated 10/18/2021).

How can you properly care for your septic system?

The best way to keep your system functioning properly is to follow some common-sense practices.

  1. Only flush human waste and toilet paper down the toilet. Wet wipes do not break down in the septic system even though the packaging labels them as septic-safe!

    Be mindful of what you put down sinks and flush down toilets. All drains in your home lead to the septic tank. Image: A. Albertin

  2. Think at the sink. Avoid pouring oil and fat down the kitchen drain. Avoid excessive use of harsh cleaning products and detergents which can affect the microbes in your septic tank (regular weekly cleaning is fine). Prescription drugs and antibiotics should never be flushed down the toilet.
  3. Limit your use of the garbage disposal. Disposals add organic matter and additional water to your septic system, which results in the need for more frequent pumping.
  4. Take care at the surface of your tank and drainfield. Don’t drive vehicles or heavy equipment over the system. Avoid planting trees or shrubs with deep roots that could disrupt the system or plug pipes.
  5. Conserve water. Reduce the amount of water pumped into your septic tank through water conservation practices like (1) repairing leaky faucets, toilets, and pipes, (2) installing, low-flush toilets, low-flow showerheads and faucet aerators, and (3) only running the washing machine and dishwasher when full.
  6. Have your septic system pumped by a certified professional. The general rule of thumb is every 3-5 years, but it will depend on household size, the size of your septic tank, how much wastewater you produce and what you flush down your toilet.

Even when conventional septic systems are well maintained, they are still a source of nutrients, particularly nitrogen, to groundwater. They were designed from a public health perspective to remove pathogens, not nutrients.

For more information on septic systems, visit the UF/IFAS septic system website and FDEP’s septic system website.