Bathurst caribou on the Barrenland.  Photo:  Catherine Graydon Bathurst caribou on the Barrenland. Photo: Catherine Graydon

Measuring the Zone of Dust Disturbance inside the Bathurst Caribou Range

Both traditional knowledge and scientific studies have observed that barren-ground caribou are very sensitive to changes in their environment.  Disturbances can interrupt caribou feeding, for example, or cause the caribou to move away in response to the disturbance.  These changes in the caribou’s behaviour can use up valuable energy needed for growth, maintaining a healthy condition, and pregnancy–and have other negative effects on caribou.

Researchers are looking at changes on the Bathurst caribou’s range to better understand some of the factors that may be contributing to their declining numbers.  Habitat disturbance, effects from a changing climate, predation, harvest, and forest fires –or any combination of these factors--are examples of the multiple stressors that may be limiting caribou populations.   New features on the landscape such as buildings and other structures, roads, noise, smells, dust and air emissions may also be adding to the “cumulative effects” affecting caribou. 

Our last newsletter looked at a research project that has been measuring how far mining-related disturbances such as noise, the sight of mining structures and activities, and dust reach inside the Bathurst caribou range.  Based at the Ek’atì (Lac de Gras)  mine site and surrounding area, a research team led by Wenjun Chen, Natural Resources Canada, has been conducting field surveys, satellite remote sensing,  and laboratory analyses to learn more about the size of a mining development’s footprint.  Traditional knowledge and scientific research have each reported that caribou tend to avoid areas such as mine sites.  How far away from a mine does a disturbance such as noise affect caribou? What is the Zone of Influence, the distance at which caribou change their behaviour, habitat selection, and distribution, in response to industrial developments such as mines? 

Earlier, we described the work the team has done to study the Zones of Visual Disturbance and Noise Disturbance.  Measuring mining-related dust and its potential effects on caribou food –the lichens and plants they browse on—is another challenge the researchers have undertaken. 

What is Dust and the Zone of Dust Disturbance?

Dust –both dust that has fallen on the ground and dust that is in the air—is a third kind of disturbance. Community members have often commented on the dust they have observed on caribou food.  Dust is made up of bits of dirt and other tiny solid particles scattered or suspended in the air, and can be stirred up by passing vehicles or be carried on the wind.   Larger dust particles will fall out of the air almost right away, often on ground vegetation, and relatively close to the source.   Finer particles tend to stay in the air the longest and fall further away.  How far away from mining operations can dust reach? What is the Zone of Dust Disturbance (ZODD)?

Figure 1. A photo of dirty vegetation near the busy Misery Road as a road dust plume passes by (Photo by Wenjun Chen).       

A number of different research strategies were used to estimate the Zone of Dust Disturbance.  How did the researchers measure the distance dust could be detected from the mine site? First, they had to consider the design of their research project.  There is always “natural variation” to consider.  Dust can come naturally from the environment itself, from the gravel and rock on eskers, for example.  How do you know that the dust you’re measuring comes from the mining?  As a next step, the team limited their study areas to places with one “class” of vegetation—dwarf shrub vegetation, which includes bearberry, blueberry and cranberry shrubs, mosses and lichens.  By examining only plant sites, they removed the “rock effect”, and the chance that the dust they measured came from sources other than mining activities, such as from rocks and eskers.

Reading a Map of Dust

The amount of dust at a location can be estimated by measuring the amount of dust on leaves.  Researchers picked leaves, washed them, and then measured the turbidity—or cloudiness—of the water, which created a “map of dust” that could be read and measured.  Alternatively, the amount of dust on leaves can also be detected using hyperspectral remote sensing imagery. Hyperspectral remote sensing can extract information about subtle (or extreme) colour changes to help us examine a scene, much the same way we do every day with our eyes when we admire the shades of colour in a landscape.Their results showed that the amount of dust on birch leaves collected within 1 km from the Misery Road was 2 to 8 times higher than the background value.

Figure 2. Charlotte Kelly of NRCan measuring the amount of dust on leaves using a LaMotte LTC3000we Benchtop Turbidity and Chlorine Meter inside the DDEC Environment Laboratory in 2016 (Photo by Wenjun Chen).

Detecting Dust Using pH

Looking at changes in the pH of soil is another way to detect dust.  pH is a measure of how acidic or alkaline something is.  On a scale from 0 to 14, substances with a pH below 7 are considered acidic.  An example is orange juice with a pH of 3.5.  Substances with a pH above 7 are considered alkaline or basic.  Hand soap is alkaline, usually in the 9-10 pH range. Pure water, with a pH of 7, falls right in the middle and is considered neutral.  Dust changes the pH of the soil, tending to turn it more alkaline. 

The research team found that soil pH changed significantly near the busy mining road and showed hardly any change near a new road that was not well used.  The soil pH near mining roads turned out to be strongly alkaline (pH 9) and became less alkaline the further away until it registered as slightly acidic (pH 5) at about 1 km distance.

Figure 3. Soil pH measurement using a HACK H135 Advanced Compact WaterPR Soil pH and Conductivity Meter by Cole-Parmer Canada inside the DDEC Environment Laboratory in 2016. The sample on the left hand side yellow colour was collected from a site near the busy Misery Road, while that on the right hand side with dark colour from a site 1.5 km away from the road (Photo by Wenjun Chen).

Does Dust Affect Lichens and Other Vegetation?

Lichens

Many plants thrive best in soils with a pH range between 5.5 and 7.5.  Some plants will grow in a more acidic soil and some at a more alkaline level.  Spruce trees, blueberries, and lichens, for example, grow well in acidic soils.  Lichen, an important part of the caribou’s diet, absorbs substances in the air and is sensitive to pollution.  Did the researchers notice any changes in the abundance or health of lichen and other vegetation that caribou feed on?

Using remote sensing and visual surveys on the ground, the research team measured the amount of foliage and the heights of various types of vegetation at different distances from the Misery Road. To study the effect of dust on lichens, they calculated the percent of land cover that was made up of lichen at different locations.  In other words, how much of a particular area was covered in lichen?  When they graphed the results, they saw that there were fewer lichens close to the road.  The lichen percent cover increased the further away they sampled until it reached a number that was typical in the landscape –at about 1 km away.  So, in the case of lichens, these initial observations indicated that the effects of dust reached about as far as 1 km away from the mine site. 

Using their measurements of soil pH at different distances from the mine, the team then graphed the relationship between soil pH and lichen percent cover.  Their preliminary findings showed that lichens were most abundant (with the highest percent cover) when the soil pH was between 4 and 6 (slightly acidic).  They were far less abundant at soil pH over 6 and down to zero percent cover when the soil pH was over 8 (alkaline). 

Figure 4. A photo from above looking over a background site 11 km away from any mining infrastructure, with abundant lichen cover (Photo by Wenjun Chen).

What about plants like dwarf birch and blueberries?  Does dust affect them?

The team also looked at the percent cover of vascular plants at different distances from the Misery Road.  Vascular plants like trees, shrubs, grasses, and flowering plants use roots and stems to take in water and nutrients.  Similar to the case with lichen, there were few vascular plants very close to the road, but the percent cover increased rapidly as they sampled further away.  What was different from the lichens survey results was the fact that the number of vascular plants increased more quickly, coming back to their usual numbers much closer to the road.  This suggests that vascular plants may be more resilient to dust than lichens are. 

Just as they did with lichen, the researchers graphed the relationship between soil pH and the percent cover of vascular plants.  Most of the vascular plants were found in soil with pH of between 4 and 7.  Their numbers dropped steeply when the soil was more alkaline, falling to zero plants recorded at pH over 8. 

All the data together—dust deposition, dust on leaves, soil pH and lichen percent cover—suggest that the extent of dust from mining operations is about 1 km, but the research team wants to collect and add more observations to confirm the Zone of Dust Disturbance.

Looking further ahead, Wenjun said, “My hope for future phases is some kind of integration to see if what we have been monitoring has made sense to understand why caribou are declining.”

Fact Box:  Hyperspectral Remote Sensing

  • Much of traditional remote sensing uses structure to help identify features, such as the size of a lake, or the breadth of a forest habitat.  In optical remote sensing, colour is also useful, but there are only a limited number of colours available.  In more advanced optical remote sensing, such as hyperspectral, there are often over 200 colours used to image the Earth’s surface, from the visible to the infrared regions of the spectrum.
  • With this increased range of colours, researchers can now model more directly such things as regions exhibiting stressed vegetation or regional foliage distribution.
  • In the case of mining disturbances, researchers are planning to evaluate the use of hyperspectral remote sensing to help detect the "spectral signature" of waste rock dust throughout the area, as well as to detect areas of stressed vegetation within the zone of influence of the mine.
  • Researchers see the potential benefits of using this new technology to contribute information to better understand mining impacts on the surrounding environment.  They are looking forward to advancing the research to turn that potential into a reality.