Why All the Algae Blooms?

Yesterday, Karen and I took our canoe out to Little Cultus Lake along the Cascade Lakes Highway for a late afternoon, escape-the-heat excursion.  Given the drought and heat wave I was not too surprised to see algae starting to form, but it was disappointing.  As anyone who has lived in Central Oregon for any amount of time knows, algae blooms are occurring more frequently.  This excursion reminded me that in April I was given this report on algae in Odell Lake and am way overdue for a post about it.

The report’s lead author is Joe Eilers, a local and highly regarded limnologist who I first got to know from his work analyzing Lake Billy Chinook. The Odell Lake report is lengthy, but the single-page abstract on page 12 sums it up.  Algae blooms in Odell Lake are relatively recent phenomena and can be attributed to increased “sedimentation”.  This is not the sedimentation you might think of, such as debris washed into the lake from logging or following a fire.  It’s sedimentation from “in-lake sources”, specifically kokanee poop (or “excretions” to use the more scientific term) and the increase in other organisms enabled by this poop.

Kokanee are not native to Odell Lake.  They were first introduced in 1932 and extensively stocked from the 1950s through the 1980s.  Kokanee are now prolific in the lake and made up the bulk of the 150 metric tons of fish in Odell in July 2004.

It makes intuitive sense: a dramatic increase in fish population and excretions causes nutrient loading which enables algae blooms.  Not everyone agrees, however.  As I have written about before, algae blooms are happening more frequently and more intensely all over Central Oregon.  No one seems to know why, but global heating is a frequently mentioned culprit.

I emailed Joe about this and he wrote back that higher temperatures play an “additive effect to the internal nutrient cycling”, but you still need an excess of fish poop.  He gave Diamond Lake as an example.

“The same argument was raised with Diamond Lake…namely that climate change was responsible for the blooms.  However, when we removed the tui chub the lake transparency increased from about 1.5 m to 12 m.  Zooplankton populations exploded and cyanos were minuscule.  When they increased fish biomass in Diamond through fish stocking and illegal introduction of cyprinids, productivity once again increased and some cyanos have returned to the lake.  These up & down changes in Diamond were rapid and do not correspond with changes in weather/climate.  It’s the fish.”  (Note: “cyanos” is short for cyanobacteria or blue-green algae.)

So, why the algae blooms all over Central Oregon?  Is it due to a heating planet or because we have planted fish in so many water bodies that previously did not have them?  Are they both factors? Is the “sediment” problem occurring in many lakes?  Joe has been unsuccessfully seeking funding for over a decade to do more research.  Furthermore, what do we do about it?  Stop all fish stocking and get rid of existing non-native species that have successfully colonized a lake?  Is that even possible?  It’s an interesting question and yet another example of how we have altered our environment.

BTW, Little Cultus Lake had no fish prior to stocking.