University of Iowa and Iowa State University researchers are reviewing the history of mussels to help chart changes in Iowa’s rivers. Scott Carpenter of the University of Iowa’s geological science department is reviewing mussels that a world-famous U-of-I botanist collected from Iowa rivers from 1875 through 1933. Carpenter says those specimens are housed at the Smithsonian in Washington, D.C. Carpenter’s analyzing the mussels, using a small dental drill to take samples from each.. Carpenter says they are hoping to estimate nitrogen content so they can analyze if and when fertilizer started changing the state’s rivers. In addition to the old mussels collected in the past, Carpenter and his research partner will collect present-day mussels from Iowa rivers. Carpenter says mussels are essentially freshwater clams. Carpenter says mussels are a “sentinel organism” so that if a stream has problems like silt or lots of pesticide, the mussels don’t fare well. Carpenter says if the mussels in a stream are in decline, then the overall health of the stream is “not good.” Carpenter says by going back to evaluate mussels collected in the 1800s, their goal is to find long-term trends in the state’s rivers.