The Toxic Takeover Most Lake Reports Can’t Detect
We’ve explained why it is so important to Measure What Matters in your lake, – measuring oxygenation in detail because that is the initial factor that starts eutrophication, measuring sediment nutrient stockpiles and recycling because that is the fuel that drives it, and in this video we are going to talk about Measuring What Matters with regard to phytoplankton in your lake.
We’ll cover:
And I’ll wrap up by telling you about the critical test that should always be done if ever you resort to using algaecides in your lake – that hardly any vendor ever does – because if you don’t, you’ll stand a good chance of being blind-sided by a nasty surprise.
So let’s start with why measuring phytoplankton in detail is so important and why chlorophyll-a is not a meaningful parameter to measure.
If we go back about 60 years when the phenomenon of eutrophication – the process that degrades our lakes – was first identified and studied, certain correlations were noticed.
Eutrophic lakes had elevated levels of phosphorus, a key nutrient for algae growth, which meant they had elevated levels of algae, and all that algae made the water murky and opaque.
So a simple technique was developed to classify the degree of eutrophication that a lake had progressed to, called the Trophic State Index which measured:
Then these three measurements were put through an algorithm that gave a score or index called the Trophic State Index or TSI, and these were categorized in 4 levels – oligotrophic, mesotrophic, eutrophic and hypereutrophic.
All good.
Until veterinarians began to report that animals were being found dead around watering holes that were eutrophic and full of bright green algae. That was puzzling because algae cannot produce toxins.
About 10 years later, Professor Wayne Carmichael showed that it wasn’t algae that were producing the toxins that were killing animals drinking the water – it was cyanobacteria.
Both cyanobacteria and algae are photosynthesizing phytoplankton.
So what’s the difference between them? – It gets a little technical but basically in the stages of evolutionary development, you got bacteria, some of which can produce toxins, then bacteria that could photosynthesize – that’s cyanobacteria – but some of them retained the ability to produce toxins, then algae, which are not bacteria, and cannot produce toxins, but which photosynthesize. Algae are the precursors of all the plant life we have today.
So cyanobacteria are bacteria that photosynthesize like algae, but they can also produce toxins, like pathogenic bacteria do, which algae do not do.
Professor Carmichael’s discovery that cyanobacteria can produce lethal toxins fundamentally changed the meaning, significance and consequence of eutrophication.
Initially it was about noticing the correlation that increased phosphorus levels led to increased algae levels which reduced water clarity.
But now it became clear that there was a lot more to it, because the process somehow progressed to a point where cyanobacteria displace algae by dominating the uptake of available nutrients, and cyanobacteria blooms were potentially toxic – and could make your whole lake toxic.
The consequences of that have become more and more significant as it has happened to more and more rivers, lakes and reservoirs over the past 20 or 30 years – pets have died, beaches are closed, lakes are shut down, the whole lake lifestyle is threatened, property values plummet, the production of safe drinking water becomes impossible and ultimately national water security is threatened.
So that is why it is so important to measure the phytoplankton in detail – so you know how close you are to that tipping point when toxic cyanobacteria take over and so that you can take proactive, preventive measures early to save your lake before it’s too late.
We know there are three key drivers of the overall process that need to be measured:
So let’s dig into that that last part – measuring the shift to toxic cyanobacteria, that we are focusing on today.
The Trophic State Index measures Chlorophyll-a – so let’s start by understanding why measuring chlorophyll-a can be misleading and is futile as our lakes, reservoirs and rivers begin that dangerous shift toward cyanobacteria dominance.
Chlorophyll-a is a substance that algae use to photosynthesize.
Cyanobacteria have relatively lower levels of chlorophyll-a because they also use phycocyanin to photosynthesize. So as the levels of cyanobacteria increase, and the levels of algae decrease, the level of chlorophyll-a decrease as well.
So while chlorophyll-a is a good proxy measure of beneficial algae, it’s not a good measure for cyanobacteria, so it can be misleading if your lake is losing beneficial algae and has rising levels of cyanobacteria.
So how do we Measure What Matters with regard to phytoplankton balance?
There’s three key metrics we need to track:
The first two are about balance – and too many people ignore them until its too late and balance has been lost. That was one of the main criticisms that the GAO report made about conventional monitoring protocols – they wait for HABs to occur and balance to be lost – and then test for toxins – which confirm it’s too late and your lake management program has failed.
We identify what types of phytoplankton are present by identifying the different taxonomic classifications – or taxa.
That tells us how many different types of phytoplankton we have. As I said, there are two broad categories – algae and cyanobacteria – but we need to drill down into more detail to see how many different species and diversity there are of each.
It’s important to have diversity in phytoplankton populations – what you want to see is lots of different kinds of beneficial algae available to compete against cyanobacteria and keep them in check.
Often, by the time we are called in to fix a lake, this is what we see – only a handful of different taxa or species of phytoplankton, and all of them are toxic cyanobacteria.
That was the case here – you can see what the problem is – the only type of phytoplankton found were cyanobacteria so they have no competition. They have free reign to dominate nutrient uptake and shut out beneficial algae.
That data is from Indian Lake Missouri in September 2021, when there were 7 different types of cyanobacteria present and not a single strain of algae identified.
What you want to see is something more like this, which is the change we had achieved in at Indian Lake by September 2022 – 18 different types of algae competing against the cyanobacteria.
Increasing the biodiversity of the phytoplankton is a critical first step in delivering a solution, but we are not going to go into solutions today.
The point is, once you have built up that biodiversity of algae and have some competition against the cyanobacteria, you need to know how well the algae are actually competing.
We measure that by measuring the relative or proportional phytoplankton biovolume by taxa. In other words – what proportion of the total phytoplankton is beneficial algae and what proportion is cyanobacteria?
At Indian Lake, in September 2021, 100% of the phytoplankton biovolume was cyanobacteria because that was the only type of phytoplankton there. By September 2022, although as I showed you, we had 18 different types of algae present, only about 30% of the phytoplankton biovolume was algae – because it takes time and they need biological support to compete effectively, so this is what the proportional profile looked like – still 70% cyanobacteria. But by June 2024 the relative proportion cyanobacteria had turned around and the balance was strongly in favor of the beneficial algae.
The last thing we need to measure is the total biovolume of phytoplankton. In other words, is your lake still overwhelmed with excessive phytoplankton, have we just switched from too much cyanobacteria to too much algae? – or is the phytoplankton under control?
For Indian lake, here is the data for May 2022, when the total phytoplankton biovolume clocked in at 80 million units, by August 2023 that was down to about 10 million and by June 2024 it was about 1,4 million, or less than 2% of what it had been. So the total phytoplankton biovolume is a tiny fraction of what it had been.
So to summarize:
We helped beneficial algae come back into the lake, – and measured that in diversity, we helped them compete and become the majority in the phytoplankton demographics and so restored balance, and we reduced the total phytoplankton populations to an acceptable level by suppressing sediment nutrient recycling and increasing nutrient clearance via a restored food web.
And we can confirm that food web restoration by checking zooplankton populations.
Cyanobacteria are poor nutrition for zooplankton and hypoxia means that the whole food web from zooplankton up becomes constrained.
Here is the zooplankton data from Indian Lake 2022, the first year of the restoration program.
And here is the zooplankton numbers from 2023 and 2024 – about a 400% increase at that foundation level of the food web.
What about chlorophyll-a? We didn’t use that as a measure at all. Why not?
As I said earlier, Chlorophyll-a is a substance that algae use to photosynthesize.
So chlorophyll-a is a good proxy measure of beneficial algae, but it’s not a good measure for cyanobacteria because although cyanobacteria use chlorophyll-a, they also use phycocyanin.
There are two consequences of that:
Firstly chlorophyll-a levels will be lower as cyanobacteria dominate phytoplankton populations, and beneficial algae levels decrease,
and secondly, phycocyanin actually interferes with the fluorescence of chlorophyll-a which is how chlorophyll-a is measured. So when cyanobacteria and phycocyanin are present, the lower levels of chlorophyll-a register even lower measurements with the fluorometers because they under-read the chlorophyll-a.
In the early stages of eutrophication, chlorophyll-a levels will tend to increase as algae levels increase – which is the correlation that the Trophic State Index is based upon.
But as eutrophication progresses and cyanobacteria begin to dominate, beneficial algae populations decrease, so chlorophyll-a levels decrease. So if you are measuring chlorophyll-a to track phytoplankton when cyanobacteria are moving in, you risk being blinded to what is really happening.
Lower or flat-lined chlorophyll-a levels may be due to cyanobacteria taking over and beneficial algae being wiped out – and if you are unaware that is happening – that is a real problem.
This was the case at Indian Lake Missouri, where a statewide lake monitoring program that measured chlorophyll-a reported that the lake’s chlorophyll-a levels were in line with most other lakes in the state and all was good.
In reality, when detailed phytoplankton samples were analyzed, they didn’t show a single cell of beneficial algae over 33 different samples tested during the summer of 2021. The lake was in crisis!
To remediate the lake and restore balance, beneficial algae populations had to be restored, and as this was achieved, the levels of chlorophyll-a measured were increasing.
A consultant on the project actually expressed concern at the fact that chlorophyll-a levels had increased – and was confused at how chlorophyll-a could increase as water clarity improved.
But if you understand how to Measure What Matters, – it is easily understood
So what is that critical test that you should be doing if ever you use algaecides in your lake?
Let me explain three things that algaecides do, and then you will probably be able to figure it out for yourself.
Firstly, most algaecides are more effective against beneficial algae than they are against cyanobacteria – so the net effect is to make it easier for cyanobacteria to become dominant.
Second scientific studies have shown that cyanobacteria build resistance and tolerance to algaecides, but beneficial algae don’t – so again, cyanobacteria gain the upper hand.
Third – algaecides kill all phytoplankton, so that dead biomass sinks down into the sediment, causing hypoxia and recycling nutrients at the bottom where cyanobacteria can get down to them but beneficial algae can’t.
All three of these consequences of using algaecides make life easier for cyanobacteria and more difficult for beneficial algae – so you are actively creating a situation where cyanobacteria stand to benefit.
Here’s some data that shows it
At this 150 acre lake annual algaecide treatments started in May. By June, the lake was hypoxic below 32 feet. Analysis of the bathymetric data showed that meant that 30% of the sediment surface area and 14% of the water volume was hypoxic.
By August, the water was hypoxic at 16 feet – meaning that 60% of the surface area and 35% of the water volume were hypoxic.
If we look at the phytoplankton analysis we find this:
In June about 5% of the biovolume is made up of cyanobacteria – but almost 50% of the cells are cyanobacteria.
Think about that for a minute – I just said that research had shown that cyanobacteria cells that develop resistance to algaecides are much smaller.
And here we have 50% of the cells only making up 5% of the biovolume – so those are very small cyanobacteria cells – and potentially developing tolerance to the algaecide.
Let’s look at what happened as the year progressed.
The number of cyanobacteria cells soared, and they took over completely.
And that was not surprise because that is exactly what the research said would happen if you use algaecides.
So if you ever use algaecides in your lake, be sure to do detailed analysis of what it is doing to your phytoplankton demographics so that when you end up having to test for toxins and put a sign up, it doesn’t come as a surprise.
We’ve had a lot of emails asking us to drill down on some subjects in more detail on some subjects, so we are going to be answering as many of those questions as we can in the next few videos.
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See you next time.
