25 Years of Water Quality Change in Rhode Island Lakes and Ponds
Citation:
Kellogg, D., Jeff Hollister, B. Kreakie, S. Shivers, E. Herron, L. Green, AND A. Gold. 25 Years of Water Quality Change in Rhode Island Lakes and Ponds. Association for the Sciences of Limnology and Oceanography (ASLO) Summer Meeting, Victoria, British Columbia, CANADA, June 10 - 15, 2018.
Impact/Purpose:
We use rare long-term lake data to examine trend in water quality variables. We are able to depict clear trends in TN, TP, temperature, and chlorophyll a. Our analysis shows that lake water quality is not as static as previously thought.
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.