Incorporating ecological costs and benefits into environmental flow recommendations: Ecosystem services provided by freshwater mussels

Background/Question/Methods

Determining the ecological costs and benefits of in-stream flow regimes requires quantifying real, measurable ecological characteristics of rivers and determining how these change under various flow scenarios.  Rivers in southeastern Oklahoma are known for their relatively pristine and abundant water and high biological diversity, including multiple endangered species.  Water from these rivers also is in high demand to meet regional, human water needs.  These rivers contain abundant freshwater mussels, which are filter feeders that move water over their large gills as they feed. They provide important ecosystem services in rivers, particularly water filtration and nutrient recycling.  Further, the ability of mussels to provide these services changes with different in-stream flows because water volume partially governs water temperature, and water temperature determines mussel filtration and nutrient recycling abilities.  We are combining information on (1) discharge and water temperature under various in-stream flows in different seasons with (2) information on how mussels perform the ecosystem services of water filtration and nutrient recycling under those conditions to (3) produce an empirical, predictive model of the ecosystem services provided by mussels under various flow and atmospheric conditions. 

Results/Conclusions

We are modeling the Kiamichi River because we already have rigorous data on where mussels occur, their identity and abundance, and the physical, hydraulic characteristics of river reaches containing them.  In addition, this river is under the most pressure for regional water diversions.  We are conducting laboratory experiments to obtain data on how filtration and nutrient recycling rates of different mussels species change with temperature.  We are recording discharge and temperature throughout the river on a daily basis via automatic loggers.  We will create a GIS-based model that uses incoming solar radiation, topographic and riparian shading, and flow and hydrographic data to create water temperature rating curves.  We will compare these rating curves with mussel ecosystem service data to produce environmental flow recommendations.   We will also provide ranges of optimal flows so that other factors, such as costs of dam releases, can be accounted for in determining flow recommendations.