2008/5/28 frank theriault <[EMAIL PROTECTED]>: > What I've heard is that global warming is thought to be a major > contributor to algal bloom in some Canadian lakes. Since loons hunt > fish by sight, if they can't see to catch fish, they won't populate > those lakes with algal bloom, thus squeezing them out of longtime > habitats.
hmmm... This is rather complex... Algal blooms are most likely to occur after the springtime full-circulation (in temperate/boreal regions, at least, which includes most of Canada and Norway) because the water mixing brings up fresh nutrients from the sediments and bottom water. To simplify things a bit, let's consider that the amount of nutrients redistributed in the water column is constant irrespective of temperature. In most lakes where loons would be able to hunt in the first place, it is also reasonable to assume that the amount of nutrients is the limiting factor for algal growth irrespective of temperature. Even with these factors held constant, many things can happen when the temperature goes up. One is that the full-circulation happens earlier in spring, and thereby shifts the bloom to a different time relative to the nesting season. Another thing is that you actually increase the algal production _rate_. But this also means the algae will run out of nutrients more quickly. So effectively the algal bloom will become more intense, and thus reduce visibility more than with lower temperatures, but be of shorter duration. Yet another effect of increased temperature will be a shift of behaviour in the loon's prey species. Most of the charr species, for example, prefer cold water and will move to deeper waters when the temperature rise. As will the graylings and other salmonids. This effect may be just as significant as the blooming, at least in salmonid-dominated lakes. On the whole, I think you may be right that global warming (or local warming) could affect the loons. But some observational data on loon distribution would be nice... :-) Anyway I think Ken has a good point too, that the nutrients required for blooming may well have been supplied by human activity in the first place. I know there's a campaign going on towards farmers to stop them from plowing their fields in the autumn. By waiting until spring, they reduce the run-off of nutrients significantly. This is both beneficial for the recipient water system and for the farmer himself because it reduce the need for artificial fertiliser in the growth season. Jostein -- http://www.alunfoto.no/galleri/ http://alunfoto.blogspot.com -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
