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BLUE-GREEN ALGAE: HOW THEY STRIVE IN OUR OVERFED, INVADED & WARMING LAKES

Interview with Environment Canada Research Scientist, Sue Watson. - Part 2

Sue Watson is a research scientist at Environment Canada specializing in algal outbreaks and source-water impairment. WaterToday spoke with Dr. Watson over the phone, this is PART 2 of the transcript of that conversation.

Transcription: fiverr.com/andreagordon

WaterToday: What can be done to reduce bloom-forming cyanobacteria?

Dr. Watson: One of the things that Canada and the US are calling for is a reduction in phosphorous input to our surface waters. Around the Great Lakes, most focus is on Lake Erie because it is the lake that's in worst shape. And for several reasons -it is the most heavily populated, it is also the smallest, and shallowest and warmest of the Lakes. Add all those together and the proportion of its basin given over to agriculture and it is very vulnerable to problems with blooms.

WaterToday: Getting farmers to reduce runoff by say 40% is not going to be an easy matter, do you know of other solutions or is that the one?

Dr. Watson: Unfortunately there is no 'free lunch'. For example, if we eat too much we gain weight. And a way to lose weight is to reduce what we're eating. If a person has gained a lot of weight from the intake of too many calories they accumulate a lot of 'excess energy' which is stored in their cells. Their physiology (i.e. metabolism) has changed and they have many more fat cells. In order to lose weight, they need to go on a diet and reduce their calorie intake below their normal required daily intake (humans can also increase their caloric need by e.g. exercise).

If they just reduce their input to their daily basal need, nothing is going to change. Unfortunately, people often find they are very much more susceptible to putting the weight back on - especially if they go on repeated overindulgence and crash diets - because they're basically a different person; famine and feast regimes can lead to a far more efficient (conservative) physiology which becomes more efficient in using everything taken in. Your basic metabolic and physiological makeup has changed and consequently you usually have to be aware of what you're eating for the rest of your life.

Mixed community of bloom-forming cyanobacteria
WaterToday: So lakes are similar?

Dr. Watson: To a certain extent, yes.

WaterToday: That's amazing, how does it work for lakes?

Dr. Watson: What happens is when you push a lake past its normal level of variance, for example if you discharge excessive amounts of something into it whether its nutrients; acid rain or toxic contaminants, you may end up killing off or adversely affecting various parts of the food web which provides stability.

A good healthy lake has a very diverse food web; it's like a pyramid with lots of little blocks, a very, very wide base and fewer top levels. If you remove one or two blocks the whole thing won't fall down. On the other hand, if your base is small, if you take one or two blocks out you've got something that is likely to fall over, or at least have a partial collapse. So the more blocks you have in your pyramid- that is, the more diverse the foodweb - then the more likely it's going to withstand a little bit of push and pull between the natural variants. We have taken these lakes to an extreme and there's been a real change in both the structure of the food web and the way in which nutrients are processed and stored in these waterbodies.

But not just because of nutrients and other contaminants. The other thing that's happened to these Lakes is invasive species. And the species on everyone's list of course is the invasive mussels, which have had far-reaching effects on many aspects of these waterbodies, many of which may have favoured the development of toxic cyanobacterial blooms

Mussel larvae, bloom-forming cyanobacteria


WaterToday: How does that affect cyanobacteria?

Dr. Watson: In two major ways. The mussels first colonized the Lakes by settling on the hard substrate, like the hard rocks, and buoys. These were the zebra mussels. Then a second species arrived, the quagga mussels, which are able to colonize sand and soft areas – and there are now more of these species across the lakes, which are more aggressive feeders and able to withstand colder temperatures. They multiplied rapidly!

The mussels filter the water column to get their food using filtering units that pull the water through a 'sieve'-like apparatus, and remove particles in that water column which they then digest, and like every other organism they excrete what they don't need.

And like every other organism they excrete this food in a far more bio-available form. In other words the food is ingested as particles - organic matter and living cells - and it's excreted as digested solids, along with dissolved phosphate, ammonia and other nutrients liberated from this material which are far more easily taken up y opportunistic cyanobacteria.

So by filtering the water columns the mussels are recycling nutrients, which in many cases would have stayed locked into particles, in cells and so one, and settled to the bottom where this material would possibly be lost or turned over far more slowly.

The mussels are most active during the time when things are happening in the lake, the nice warm sunny season. Instead of material sinking to the bottom, slowly being rotted and then releasing some nutrients, it's being turned over rapidly in the inshore areas where most of these mussels are located.

WaterToday: So these new mussels are essentially creating if you like a drive-through of expedited food for the cyanobacteria.

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Dr. Watson: Sure, a shortcut. But they also have a certain size range that they recycle, their sieve will only allow smaller particles to be ingested; the big cells are left behind. And these larger species are the ones we care about and often form the big nuisance blooms. So in other words it's no longer a level playing field. The mussels are selectively removing 'the competition'. A bit similar to a road race where there are 20 people at the start line, but suddenly half of them are shackled or disabled, the ten left in the race are 'home free'.

WaterToday: So the big cyanobacteria are sort of becoming the top dog in the bacteria game in Lake Erie?

Dr. Watson: Well in the cyanobacteria game. The mussels also filter out some of the natural predators of the algae and cyanobacteria ('zooplankton') which also would help to control the cyanobacteria. And, importantly, by filtering out suspended particles, the mussels change the depth to which the light can travel down through the water column, that is, the water is more transparent. This can shift the species of cyanobacteria that does well in those Lakes.

Microcystis and picocyanobacteria


WaterToday : I've read that climate change plays a role in the proliferation of cynobacteria blooms.

Dr. Watson: It is widely thought that climate change will generally increase the risk of cyanobacteria blooms in these and other lakes, because many of these species are favoured by warmer temperature, more storms and intense runoff from fields and urban centres, less ice cover (and extended growing season), changes in wind, precipitation and other factors that affect water levels, mixing and circulation in lakes.

WaterToday: Can you elaborate a bit on the different species of cyanobacteria?

There are several cyanobacteria we now see blooming in the Great Lakes (there's never just one) – but the species that everyone is really worried about is called Microcystis which dominate many of the present-day blooms in Lake Erie. Some of these can produce microcystin toxins. Microcystis was one of the first cyanobacteria found to produce this group of toxins when we started identifying what it was in water that was killing off cattle.

Bloom-forming Microcystis


There are also lots of different types of microcystins produced by cyanobacteria; some a little bit more toxic than others. One problem with microcystins is that they are in general very, very resilient to chemical treatment, to UV radiation, etcetera. So once released, they can persist in the water long after the cells that produced them have disappeared. And that is one of the biggest problems that faces beach managers and water treatment plant operators.

People are focused on the bloom material - which when living and healthy, keeps most of the toxins inside the cell. But should you break those cells open, for example, as a result of some kind of environmental stress, disease, predation or treatment with chlorine or other chemical treatment, they will release these toxins into the water and the dissolved toxins are very much more difficult to remove,and also tasteless and odourless – in other words, they cannot be detected unless analysed using special kits or lab procedures .

And a lot of times people may think that, “the bloom's gone, no problem.” Or they'll access an area where there's been a bloom and it's disappeared, and they're not aware of this.

WaterToday: Right. I've seen that and at first hand.

Dr. Watson: Yes. There are some agencies, for example Hamilton Health, that use toxin test kits in their beach monitoring program and monitor for the dissolved toxins after the bloom is gone. And they only open the beach when the toxin levels are below levels that present a risk to human health.





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