Thank you.
I'm going to start with a list of issues, not because I'm going to cover them all, but rather because I want to emphasize that most of the Great Lakes issues we're concerned about are related, both in terms of their ultimate causes and also in terms of possible management solutions. The problems are not independent.
As Dr. Bruce started out saying that the Great Lakes Water Quality Agreement in 1972 set targets for the nutrient concentrations in the Great Lakes to remediate the effects of eutrophication. To achieve those targets, they worked out loadings with models whose thrust the figure 2 graph illustrates, to achieve those concentrations. Loadings were adopted, and management actions were put in place to achieve those loadings.
What happened was that at the same time the Great Lakes were suffering from eutrophication there was a great excess of small fish. Some of you who are my age and who grew up in the Toronto area might remember that they washed up on the shoreline in massive amounts in the spring and were cleared by bulldozers into dump trucks, there were so many of them. But with an aggressive stocking campaign of exotic fishes from the Pacific and with control of the sea lamprey, which devastated the population of the native lake trout, those small fish were brought under control, and instead we had a valuable recreational fishery in its place. That is a pretty good success story.
I threw in the next slide to make the point that when phosphorus goes into a lake, it does feed algae—it is first assimilated by algae and bacteria—but it also moves up the food web and nourishes a whole chain of organisms, from those algae through invertebrates and ultimately to the large fish that we find valuable and want to preserve.
A problem with too much algae can arise because there are too many nutrients, and that's commonly the case; but it also can arise if the flow of nutrients up the food web isn't happening properly and efficiently, so that it's accumulating where we don't want it, either in algae, in the water, or on the shoreline. There is a food web aspect to this problem that we need to keep in mind.
Also keep in mind that when we measure phosphorus in the water, we're not measuring all of the phosphorus in the system. We're only measuring in a water sample the small organisms at the base of the food web, whereas just as much phosphorus can in fact be in the larger organisms that we're not including in our measurements. When we say total phosphorus, we really should be saying total phosphorus in the small organisms and not the total amount of phosphorus that's out there.
To return to the management actions that were undertaken, which Dr. Bruce already mentioned, targets for P loading were achieved. I've shown some data on my sixth slide for several of the lakes. The loadings fell as phosphates in detergents were banned and sewage treatment plants were improved. All the lakes met their target loadings, or in fact loadings became lower than the target amount set.
I've chosen Lake Ontario as an example on the next slide, because those preceding are pretty small to look at. The phosphate concentration through time fell, again below the targets that we thought would be necessary to achieve good water quality in the lakes.
What's interesting about this slide is that it shows the trend through time. The circles are all the actual data points of phosphorus in the lake year by year. The black line is the line predicted by the model that was used to set the loadings.
You can see that it over-predicts in recent years. In fact, the model has to be altered to make it fit the data now. That's the blue line. It reflects that the food web and the fate of phosphorus in the lakes has changed since the model was developed. The lakes have changed. It's very obvious when you look at the fish community that this has changed, but the important point is that the lakes are changing, and phosphorus no longer behaves as it did when we set out to manage it.
As we've heard, we have a resurgence of problems in the near shore. These are extreme pictures that I've chosen in the next three slides, but these problems are widespread around the Great Lakes.
The first picture shows the northern shore of Lake Erie in the eastern part, in Ontario, and a massive fouling event with shoreline algae. Clearly you don't want your cottage there. The next shows the infamous algal bloom of 2011 that started in the western basin of Lake Erie and gradually spread and covered a good part of the lake.
Despite achieving our targets for loading and concentration we see a resurgence of these problems. It is very distressing.
One of the hypotheses that is in the literature as to what has changed in the lake concerns invasive species, the zebra and quagga mussels that came from Europe.
In the following picture you can see the bottom of the lake in a shallow area of Lake Ontario. It is covered with these mussels, and this fouling algae, Cladophora, is growing on the mussels in a high-nutrient environment that is created by the excretion of the mussels.
This nearshore shunt hypothesis suggests that the phosphorus is coming into the lake and, instead of distributing over the lake, is being held in the nearshore zone where it is feeding this food web composed of organisms new to the lakes.
We're also pretty sure that non-point source pollution is part of the problem. You have been introduced to this already. The next slide is an illustration from a recent paper on this problem. This shows the southern shore of Lake Ontario between Hamilton and Niagara Falls, illustrating that along the shoreline in areas that are being developed there are small tributaries and other outlets producing high concentrations of algae right against the shore, while the offshore waters are still clean and clear. Nonetheless, right at the shoreline where these small storm sewers and small streams flow in, we see high levels of algae. It's a local problem, but certainly important to the people who live there.
The next slide shows the algal blooms in western Lake Erie for the different years, relating the intensity of the algal bloom, the cyanobacterial index or CI, to the spring loading of phosphorus. You can see there is good evidence in the intensity of the summer algal bloom and that it is directly related to the amount of phosphorus that comes in between March and June.
In particular, that massive 2011 bloom occurred when there was a thunderstorm in June which took a lot of phosphorus off the land at a time before the crops had really started to grow and assimilate that phosphorus, or were dense enough to hold back the soil. Those extreme rain events are becoming more frequent.
There are management options, as the next slide shows, to decrease phosphorus loading into the lakes. We could ban phosphorus from dishwashing detergent and lawn fertilizer and we could continue to improve sewage treatment plants. For non-point sources, we could regulate fertilizer application by farmers or we could push the implementation of best management practices or even more radically, retire farmland. There are management options, if we're confident that reducing phosphorus loading is the right thing.
What about the fishery? The graphs on the next slide show what's going on in Lake Huron. Lake Huron has very low levels of nutrients in the offshore, lower levels than we intended to create. The top graph shows the forage fishes, and they are almost gone. The salmon are getting few and skinny. The number of species of fish that are caught in the survey trials has dropped remarkably as well. We are losing biodiversity, because even though there is a fouling issue at the near shore, there is not much in the way of nutrients in the offshore waters.
We're left with what to do. If the changes in the distribution of phosphorus are due to mussels, we don't really have a management strategy that could deal with the mussels, so it's not clear what we might do there. We could legislate or somehow reduce phosphorus loadings even further, but we are interfering with farmers making a living and with what consumers want to purchase and do with their homes. There is room to question whether these are really no regrets actions that aren't without consequence.
I would submit that in fact what we really need to do is start managing the Great Lakes as ecosystems and manage them more holistically, including managing the fishery as well as the water quality at the same time, and the land use. It really takes a much more complex approach to the problem than just more or less phosphorus than what we are currently allowing in.
Thank you.