Cintra-Buentrostro, C.E. and Flessa, K.W., 2004.  A thirsty clam on a salty delta: Determining the amount of freshwater needed by Mulinia coloradoensis in the Colorado River delta and estuary.  Gulf of California Conference, Tucson, AZ.


The amount of river water needed for restoration in the Colorado Delta is the amount of freshwater needed for sustainable populations of its inhabitants.  The bivalve mollusk Mulinia coloradoensis is one of the species directly threatened by the diminished flow of river water.  High levels of predatory shell damage indicate that this species was important to species higher in the food web of the delta and estuary.  The good news is that the geochemistry of pre-dam shells can be used to determine the species’ salinity requirements, and thus the amount of river water needed for its restoration.  We used oxygen isotopes to estimate the amount of river water present in four localities where M. coloradoensis used to be abundant.  The deviation of  del
18O in a pre-dam shell from that in a shell growing under fully marine, no flow-conditions today is directly proportional to the amount of freshwater mixing with marine water.  Averaged estimated salinities from del18O values in CaCO3 from M. coloradoensis shells ranged from 35.4 to 32.7‰ yielding an estimated annual river flow of 2.6 to 6.7 million acre-ft.  Although these flows estimate the amount needed to partially restore the estuarine habitats, the timing of the flows remains an open question.