25 Years of Water Quality Change in Rhode Island Lakes and Ponds.
Citation:
Shivers, S., Jeff Hollister, D. Kellogg, B. Kreakie, E. Herron, L. Green, AND A. Gold. 25 Years of Water Quality Change in Rhode Island Lakes and Ponds. New England Association of Environmental Biologists, Saratoga Springs, New York, February 26 - March 01, 2019.
Impact/Purpose:
Lakes are critical ecosystems that respond to not only local but also large-scale environmental influences. Therefore, to understand how and why a lake is changing, long-term monitoring data is often required. Yet these data are difficult and expensive to collect. When this type of data is available, it is typically for a single lake. We used a rare long-term lake data set (25 years for approximately 170 Rhode Island lakes) to examine trends in water quality. Our results show that most lakes in Rhode Island are growing warmer with increased algae. The broader impacts of this study are that 1) we are seeing regional drivers impacting lakes in RI and 2) long term data are necessary to come to these conclusions.
Description:
The University of Rhode Island’s Watershed Watch Volunteer Monitoring Program has been collecting water quality data on dozens of Rhode Island lakes and ponds for over 25 years, allowing exploration of long-term trends in common water quality parameters. Not all lakes and ponds in the study area were sampled across the full time period and lakes were often added in geographic clusters (e.g. in urbanized northern Rhode Island). Similar to how long-term temperature records are analyzed, we centered and scaled (i.e., the z-score) water quality measurements on a per-station basis. This provides a robust and commonly scaled measurement to explore this data for long-term trends. State-wide aggregation of all lakes showed increasing temperature, chlorophyll a, and total nitrogen. Interestingly, total phosphorus is showing a decline, perhaps reflecting the management focus on phosphorus reductions. While yearly trends are useful, they do mask month-to-month variability differences across sites. Additionally, while most sites track the yearly trend in decreasing water quality, there are bright spots with a few sites improving over the 25 years. Contrary to previously reported analyses that show relatively stable water quality at the regional scale, our analysis shows that long-term water quality trends within Rhode Island show some parameters improving while others are in decline. Importantly, this analysis also points out the value and importance of data from long-term monitoring programs, like Watershed Watch, for identifying trends in environmental condition.