Reduced chlorophyll to phosphorus ratios in nearshore Great Lakes waters coincide with the establishment of dreissenid mussels

• Published in: Canadian journal of fisheries and aquatic sciences 1999-01, Vol.56 (1), p.153-161
• Main Authors: Nicholls, KH, Hopkins, G J, Standke, S J
• Format: Article
• Language: English
• Subjects: chlorophylls; North America, Great Lakes; phosphorus
• ISSN: 0706-652X; 1205-7533
• DOI: 10.1139/cjfas-56-1-153

The establishment of zebra and quagga mussels (Dreissena spp.) in the Great Lakes has coincided with dramatic decreases in chlorophyll a to total phosphorus (Chl/TP) ratios in nearshore waters of Lake Erie, western Lake Ontario, and the Detroit River, but not in Lake Superior, southern Lake Huron, central and eastern Lake Ontario, or the upper St. Lawrence River. May-October average Chl/TP ratios in samples collected weekly (1976-1995) from five Lake Erie municipal water supply intakes were two to six times higher during the pre-Dreissena time period than during the post-Dreissena period. The pre-Dreissena logarithmically transformed Chl and TP data (May-October averages at all Great Lakes sampling locations) were highly correlated, with 75% of the log-transformed Chl variance explained by log-transformed TP. The post-Dreissena regression of May-October average Chl on TP was statistically significant, but only 14% of the variance in the Chl data could be explained by TP. We suggest that this has important implications for Great Lakes basin P management because changes in lake water TP resulting from further changes in TP loading will (post-Dreissena) have far less impact on Great Lakes phytoplankton growth potential than during pre-Dreissena times.