EFFECTS OF AMMONIA ENRICHMENT ON SURVIVAL AND GROWTH OF JUVENILE MUSSELS IN THE 
ST. CROIX RIVERWAY

Michelle Bartsch1, John O'Donnell 2, Teresa Newton1, LeeAnne Thorson2, and Bill 
Richardson1, 1U.S. Geological Survey, Upper Midwest Environmental Sciences 
Center, La Crosse, WI and 2University of Wisconsin-La Crosse, River Studies 
Center, La Crosse, WI.
										
The St. Croix Riverway contains an extremely rich fauna of unionid mussels.  
This group, which is highly sensitive to habitat changes, is one of the 
Riverways's most significant natural resources.  As the metropolitan area of 
Minneapolis-St. Paul expands into the basin, there is an increased threat of 
contamination to water and sediment quality and its associated biota.  We 
performed a series of tests to examine existing concentrations of sedimentary 
ammonia, and to determine what effects these concentrations were having on 
survival and growth of juvenile mussels.  We conducted a combination of 4, 10, 
and  28 day in situ toxicity tests with Lampsilis cardium at 8 sites in the 
Riverway.  At each site, we deployed 6 chambers in the sediment, each containing 
20 juveniles, and randomly removed 2 chambers to evaluate survival and growth of 
juveniles at each exposure duration.  Sedimentary ammonia was characterized 
using core and in situ pump samples, with concentrations ranging from 0.1 to 
122.4 ug/L and  0.9 to 46.0 ug/L, respectively.  Ammonia was also measured in 
individual chambers and ranged from 0.8 to 80.6 ug/L.  Survival of mussels was 
highly variable (mean, 45% at 4d, 28% at 10d, and 41% at 28d) and our ability to 
predict survival based on sedimentary ammonia was generally poor.  The growth 
rate was highly variable (range, 0 to 45 um/day), but in general, was positively 
correlated with ammonia.  Although we were able to culture, deploy, retrieve, 
and measure survival and growth of juveniles in the 300-1,000 um size range, 
correlating survival or growth to sedimentary ammonia concentrations was 
problematic.

Keywords: mussels, ammonia, St. Croix River, sediments, Lampsilis cardium