Canvasback ducks (Aythya valisineria), wild celery (Vallisneria americana), and phosphorus regulation in large shallow water lakes

Background/Question/Methods:

E.P. Odum’s Strategies of Ecosystem Development provides a framework to compare intact functional ecosystems with under-connected dysfunctional ecosystems.  An important component of the framework suggests nutrient flows in functional ecosystems are regulated through a series of biotic mechanisms which reinforce the functional state.  Likewise, Alternative Stable State theory provides a framework to understand how a change in nutrient regulating biotic mechanisms can trigger a decline in ecosystem integrity causing the functional system to suddenly transition into a dysfunctional system. These two frameworks highlight the importance of biotic regulation over nutrient flows and ecosystem integrity.  If this assumption is correct, then restoration of dysfunctional ecosystems should focus on restoring biotic controls which maintain the functional state.  To test this assumption, I research a large shallow water lake in SW Minnesota that transitioned from a clear water macrophyte dominated system to a turbid water cyanobacteria dominated system nearly a century ago.  The research intends to elucidate potential former biotic controls and model their impact over nutrient regulation and their capacity to reinforce the clear water state.  I use historic documents, loss on ignition analysis, and existing research to identify former biotic controls over phosphorus regulation. 

Results/Conclusions:

Results indicate numerous biotic mechanisms which exported phosphorus from the lake, potentially reinforcing the functional clear water state.  A strong control exists in the relationship between the canvasback duck (Aythya valisineria) and wild celery (Vallisneria americana).  Historic migrating canvasback populations feeding on wild celery annually export 15000 kg of phosphorus out of the lake.  Heavy market hunting of canvasbacks in the late 1800s and early 1900s eliminates the canvasback-wild celery phosphorus export mechanism, and the clear water state is replaced by a turbid water state.  In conclusion, shallow water lake managers seeking to restore the functional clear water state, need to focus on restoration of the biotic controls which regulate in-lake phosphorus levels.  These management techniques include in-lake biomass harvests. The ultimate goal is to restore the canvasback-wild celery relationship, and all else will follow.