The Algal Bowl by David Schindler and John Vallentyne - A Comment

I have read with great interest, The Algal Bowl, a book which provides an in depth scientific perspective on the problems of algae on lakes like Lake Winnipeg and Killarney Lake in Manitoba. It is a really good book and recommended reading for anyone interested in decreasing the algal problems in Manitoba's lakes. I have several comments.



1) David Schindler and John Vallentyne make the very important point that we need to focus on reducing the amount of phosphorous getting into our lakes. They also indicate strongly that we do not need to reduce nitrogen going into our lakes, because the most problem causing algae can get the nitrogen they need from the air. While there may be a few exceptions - possibly hot weather marine river delta environments - the critical need in almost all circumstances is to reduce phosphorous only. I have been pushing for several years now for a change in Winnipeg, to remove phosphorous but not nitrogen from our City's sewage and waste-water. It is good to have strong support for this approach in The Algal Bowl.



2) David Schindler and John Vallentyne present elegantly the role of fish species in influencing algal blooms. When because of overfishing, or for other reasons, large fish-eating fish like pickerel or pike are depleted in numbers, there is an increase in the fish species which eat small planktonic crustacea called daphnia and as a result reduce daphnia populations. Because daphnia feed on algae, conditions which reduce pickerel and pike and lead to a reduction in daphnia can lead to increases in algae. For Lake Winnipeg this does not appear to be a problem at the moment as populations of pickerel have been abundant in recent years. Lake Winnipegosis which has seen a major depletion of pickerel has not had algal problems, but this is likely because the phosphorous concentrations in Lake Winnipegosis are very low. This is further discussed on page 173 of The Algal Bowl.



3) More attention should have been given to the influence of flow on phosphorous content of water bodies. Increasing evidence suggests that high flow situations are associated with increased phosphorous transport to Lake Winnipeg. This may happen for a variety of reasons. High flow situations, in the spring run off or at the extreme during floods, are often those in which phosphorous is washed from the land into the waterways. This may be due to phosphorous applied as fertilizer or manure to the land, or it may just be that high flow is associated with increased washing of organic matter (grasses, leaves, crop residue etc) into the waterways, or due to high flow producing more erosion of the banks of the waterways. Erosion of soil from banks, along rivers or along the shores of Lake Winnipeg can contribute to the amount of phosphorous, as there is phosphorous bound to the soil and erosion of the soil into the water increases the phosphorous content of the water. It would have helped to have a chapter on the impact of flow conditions on phosphorous levels in the waterways.

In understanding flow conditions, it is noteworthy under low flow conditions phosphorous bound to particles sediments out of the water. Interestingly, when a dam is built, whether small or large, phosphorous settles out of the water. Thus downstream from a dam, the phosphorous content of the water is much lower after a dam is put in a stream or a river. For example, the Saskatchewan River, even though it drains a lot of agricultural land in Alberta and Saskatchewan, provides a relatively small amount of phosphorous into Lake Winnipeg because much of the phosphorous settles out of the water behind the large Gardiner, Squaw Rapids and Grand Rapids dams. Similarly, the Winnipeg River does not contribute as much phosphorous as it might probably because of settling behind the dams along it. Small dams, along the South Tobacco Creek have been also been shown, I understand, to reduce peak flows and phosphorous levels downstream.


4) I also felt there could have been a more in depth understanding of the role of marshes and how to manage marshes to reduce phosphorous in the water. Schindler and Vallentyne do emphasize the important of marshes in denitrification - releasing nitrogen in the air, and lowering the amount of nitrogen in the water. But, managing marshes optimally to reduce phosphorous is important for lakes like Killarney Lake in southern Manitoba where there are major concerns about algal blooms. It would have been helpful to have a chapter specifically on marsh management to reduce algal blooms.


5) Lastly, there could have been much more discussion on the role of surface and sub-surface drainage as it affects phosphorous levels in waterways. Increased drainage achieved by increasing surface drainage, and surface run-off will tend to increase the amount of phosphorous going into the waterways. In contrast, when sub-surface drainage like tile drainage is used, the water flows through the soil before entering the waterways and much of the phosphorous can be bound by the soil during this process thus dramatically reducing the phosphorous going into the waterways. A caution is necessary here, though, because if the phosphorous levels in the soil are very high, the phosphorous binding sites can become saturated and the soil can no longer bind additional phosphorous and is not effective in removing phoshorous. Fortunately, for most of the agricultural areas of Manitoba, the amount of phosphorous in the soils is low and this is not a problem, with the exception of locations with feedlots.

For example, in 1982, Bengtson showed that tile drainage could reduce phosphorous run off by 48%. For more on this see http://www.manitobaliberals.ca/2005_09_18_archive.html.