Interactive Data

We have been collecting data on the health of our freshwater lakes for over 50 years. Here’s just one example of how we can use our unparalleled dataset to understand critical threats to freshwater supplies.

What did we set out to discover?

In the late 1960s, large, harmful algal blooms had taken over many lakes and rivers across North America, but the exact cause of the problem was unclear.

At what was to ultimately become IISD Experimental Lakes Area, scientists kicked off an experiment on a real lake in Canada’s boreal forest (now called Lake 226) to determine which nutrient was the key cause of algal blooms.

They installed a vinyl curtain to separate the lake’s north and south basins. In the north basin, known concentrations of carbon, nitrogen, and phosphorus were experimentally added while in the south basin, only carbon and nitrogen were added. 

Long story short, the north basin received phosphorus, while the south basin did not.

You can learn more about algal blooms here or watch the short video below to discover the algae research that took place at the world’s freshwater laboratory.

What happened next?

Over the course of the experiment, scientists frequently collected samples from both lake basins. Samples were collected at various depths and were used to measure concentrations of phosphorus, nitrogen, and algae in the water column.

The graphs you see below include a subset of the data collected during 3 critical years of the experiment—from 1978 to 1980.

In particular, the visualizations below focus on chlorophyll-a, a pigment that is produced by nearly all plants and is commonly used as an indicator of algal biomass (that is, the size of the algal bloom).

Put simply, the greater the amount of chlorophyll-a, the bigger the algal blooms.

Algal blooms formed in the north basin

The graph below shows data collected during the summer months (between June and September) of 1979 and 1980. 

On average the north basin (with added phosphorus) shows higher concentrations of chlorophyll-a than the south basin (with no added phosphorus)

This is not, however, true of each individual sample; even in a controlled experiment, lake conditions vary over time, and no two samples are identical.

How did the algal bloom formations vary over the course of a year?

In the interactive visualizations below, you will see how concentrations of chlorophyll-a varied over the course of the year across the two study basins. Each year is different, and the timing and strength of the algal blooms can vary, but a general profile stands out when we average across all 3 years.

Lake scientists strive to collect large amounts of data across extended periods so that trends in the data will stand out from other random variations.

What caused the algal blooms to form?

Algal blooms need phosphorus and nitrogen to develop.

The optimal ratio of nitrogen to phosphorus is approximately 7 to 1 by mass. This is called the Redfield Ratio. When a water body has a ratio of over 22 to 1 in favour of nitrogen, it is said to be phosphorus deficient, or P-deficient.

N.B. In the graph below, point size corresponds to algal bloom intensity (chlorophyll-a concentration).

Sometimes, accidents happen!

In 1978, the curtain separating the two lake basins leaked, and phosphorus made its way from the north into the south basin.

The data below show some measurements of chlorophyll-a, nitrogen, and phosphorus for the spring and summer months.

Do you think the data from 1978 is still useful?

Does the leak invalidate the conclusions of the experiment?

N.B. In the graph below, point size corresponds to algal bloom intensity (chlorophyll-a concentration).

This image—showing the vinyl curtain that separated Lake 226’s two basins and the impact phosphorus had on algal bloom growth—is commonly considered the most impactful image in the history of limnology, or freshwater science.