PARENT SESSION
PW3 - In Situ Bioassays Using Transplanted Aquatic Organisms
Wednesday, 20 November 2002
8:00 AM to 6:30 PM
Exhibit Hall
(P752) Effects of ammonia on in situ survival and growth of juvenile unionids.
Bartsch, Michelle*,1, Newton, Teresa1, Allran, John2, O'Donnell, Jonathan2, Richardson, William1, 1 U.S. Geological Survey, Upper Midwest Environmental Sciences Center, La Crosse, WI, USA2 University of Wisconsin-La Crosse, La Crosse, WI, USA
ABSTRACT- Unionids have been used as in situ biomonitors of contaminant exposure, however, there is uncertainty regarding their use as indicators of contaminant effects. We conducted 4, 10, and 28 d in situ tests to evaluate the effects of pore water ammonia on juvenile Lampsilis cardium in the St. Croix River. This River contains an abundant unionid population, but due to its proximity to Minneapolis-St. Paul, MN, threats to the River, including ammonia, have accelerated in recent years. We deployed 6 chambers, each containing 20 juveniles, into sediments at 8 sites and randomly removed 2 chambers at each exposure to assess survival and growth. Mean pore water ammonia concentrations ranged from < 1 to 62 
g NH3-N/L in core samples, < 1 to 33 g NH3-N/L in pump samples, and < 1 to 107 g NH3-N/L within chambers. Ammonia concentrations declined at least 3-fold between consecutive years–presumably due to a record flood in the River during the second year. Survival (mean, 45% at 4 d, 28% at 10 d, and 41% at 28 d) and growth (range, 3 to 45 um/d) of juveniles were highly variable and were generally unrelated to NH3-N concentrations. Although unionids are often used as biomonitors of contaminant exposure, the large variance associated with measuring survival and growth of juveniles in the present study suggests that more sensitive effects-level endpoints need to be found in this imperiled faunal group.
Key words: freshwater mussels, ammonia, in situ, juveniles