We need to talk! It's about water.

Is the “water cycle” we learned in grade school still accurate, or have human activities fundamentally changed it?

The water cycle works the same way it always has. The energy of the sun and the power of gravity cause water to evaporate, condense and fall as precipitation, travel overland as run-off, and seep through soils to enter the groundwater, among other processes and transformations. What has changed, however, is the amount of water in each pool and the rates of the transformations.

For example, the amount of groundwater has generally declined in many parts of the world. This is due to extraction by humans, but also because the paving of land in cities produces much more run-off than non-developed land. Urbanization reduces the amount of water that ultimately descends to groundwater. Warming temperatures, due to climate change, increase evaporation rates, which can lower water levels. This is especially common in already hydrologically stressed regions like the prairie provinces. And of course, the damming of surface water holds more water on land and lengthens the time it takes for freshwaters to reach the sea.

A “thin ice advisory” was issued in Manitoba this winter; what happens to fish and plants when a body of water does not freeze over as long as it used to?

Loss of ice is definitely something to be concerned about. Across the northern hemisphere, lakes are generally losing ice. Lakes are freezing for shorter periods of time, and the ice that does form may be thinner than average. The entire effects of these changes are not well understood yet, but it appears that shorter ice-cover can result in changes in food-web structure in the spring. Changes in ice duration and thickness may also affect the under-ice light environment, which can alter primary production, but this is also an area of active investigation.

The more important aspect of this problem is its mirror. Less ice in winter generally means that the growing season was longer, warmer, and more productive than previously. These changes in climate can lead to stronger, lengthier, and more frequent algal blooms, less oxygen due to longer periods of thermal stability (wherein the water column of a lake becomes stable and does not mix well), as well as disruptions to the natural annual rhythms of other organisms, such as fish.

What is the importance of algal blooms in the context of Manitoba?

Beyond being aesthetically displeasing with bad-smelling scums that foul beaches, many algal blooms can be highly toxic. While rarely directly threatening human health, they have led to the deaths of pets, livestock, and aquatic organisms and can possibly lead to changes in the health of commercial fisheries.

Many of Manitoba’s lakes are severely affected by these algal blooms. Famously, Lake Winnipeg experiences very large blooms due to incredibly high levels of agricultural and urban nutrients (phosphorus and nitrogen) coming into the lake primarily from the Red River. Many other lakes in the agriculturally developed southern and western areas of the province also experience blooms, with incidences becoming generally worse over time.

All that algal growth must go somewhere, and it usually ends up dead at the bottom of the lake. The decay of all that organic material consumes a lot of oxygen in deep waters (which is already declining in many lakes due to climate change). Here in Manitoba, much of this decay happens under the ice when there is no chance of getting more oxygen into the water from the atmosphere. This can, and has, led to under-ice fish kills in some lakes in the province. This loss of oxygen can also release nutrients from the sediment back into the water column, leading to more blooms, which leads to more organic deposition and deoxygenation, in a self-reinforcing feedback loop.

What are the biggest contributors to the impacts we see on aquatic systems?

This will be different from lake to lake, or watershed to watershed. But generally and in simple terms, the biggest problem, closest to the lake, is the biggest contributor to environmental stress. Major local disturbances like mining, logging, and urbanization will be very important in modifying aquatic ecosystems, if the stressors are intense. If those local stressors are not occurring, then broader-scale regional effects like agricultural development become very important.

However, these stressors often interact at different magnitudes and spatial or temporal scales, which can reinforce or counteract each other in interesting and sometimes unexpected ways. These compounding factors make understanding how and why aquatic ecosystems are changing challenging, particularly in areas like Manitoba, where we have multiple, long-term, and broad-scale environmental stressors.

Which of those is more prevalent in our province?

Climate change is an expansive and pervasive threat that is constantly applying stress to aquatic ecosystems. This is true in Manitoba as our winters are getting milder, summers are getting hotter, and precipitation patterns are changing. We know that some lakes in Manitoba are being pushed into new states by these climate changes. These lakes are typically in areas far away from the agriculturally dominated southern and western regions of the province. The widespread agricultural development of these regions is a major source of nutrients to lakes across southern Manitoba, with Lake Winnipeg being impacted by these nutrients, as mentioned before.

Beyond these climate and land-use threats, Manitoba is now the front line of the zebra mussel invasive that has been occurring across North America for the last 40 or so years. These invaders have rapidly spread across the province and will likely have serious consequences for our lakes and the organisms that live in them.

Could you talk to us about the impacts of data centres water consumption?

As I understand it, the extremely high water use by these data centres is for evaporative cooling systems. Essentially, water is drawn into the data centre and used to cool the computing infrastructure, which produces a lot of heat. The water is heated in this process, which can result in a lot of water being lost through evaporation. This reduces the amount of water returned to the ecosystem, and for regular municipal, agricultural, or industrial use. Returning heated water to the environment (if it is not sufficiently cooled back to ambient temperatures) could also have negative impacts on aquatic organisms. It takes a lot of energy to heat and cool water (much more so than the air), which means that aquatic organisms are relatively sensitive to changes in temperature, especially if it happens quickly.

What is a “hidden threat” to freshwater systems that the public and policymakers are not paying enough attention to?

It’s hard to say that there are “hidden” or “secret” threats to freshwater systems. There is still a lot of work to be done in fully understanding their function, but we have really solid evidence about these environmental drivers of change. For instance, we know that excessive nutrients entering freshwaters are a major driver of algal blooms, but preventing them is a greater challenge. It is an unrealistic expectation to totally stop agricultural fertilization, for example. People need to eat. The question, in my opinion, is how we keep these nutrients in the soil and crops and out of the water. I like to frame this problem with the understanding that every molecule of phosphorus or nitrogen that is put on the land as fertilizer but ends up in the water represents a financial loss to the farmer. They paid for that fertilizer, and it is not doing its job of growing food if it is growing algae in a lake.

When we look at the problems this way, everyone has the incentive to improve the system, though some stressors represent greater challenges than others. Sustainable management of livestock manure could certainly be improved in Manitoba, for example. And of course, reducing the effects of climate change is going to take a massive number of resources and effort by industrialized, high-emitting countries, Canada included.