Citation:

Hollister, J., D. Kellogg, B. Kreakie, S. Shivers, E. Herron, L. Green, W. Milstead, AND A. Gold. Increasing Productivity Amid Stable Nutrient Regimes in Rhode Island Lakes and Reservoirs. 39th International Symposium of the North American Lake Management Society, Burlington, Vermont, November 11 - 15, 2019.

Impact/Purpose:

It is well known that the quality of aquatic ecosystems has degraded and that in extreme cases this can reduce property values, impact human health, and reduce recreational uses. Managers of these ecosystems have many tools at their disposal to help mitigate these impacts. To understand how effective these efforts are requires long-term data, such as the University of Rhode Island's Watershed Watch Volunteer Monitoring program data. We used this data to examine trends in water quality in Rhode Island lake and reservoirs. Since 1993, nutrients (e.g., nitrogen and phosphorus) have been relatively stable. Lake temperature and chlorophyll, a potential indicator of harmful algal blooms, have both increased overtime. This work highlights the role that physical parameters (i.e., temperature) may play in controlling algal growth in lakes, indicates that efforts to control nutrients in Rhode Island have prevented an unwanted increase, and shows that to reduce chlorophyll and related impacts will require additional management efforts. Furthermore, this study is one of the first to utilize the rich, long-term data collected by colleagues and volunteers at the URI Watershed Watch program.

Description:

Addressing anthropogenic impacts on aquatic ecosystems has long been the focus of lake management. Controlling phosphorus and nitrogen can mitigate the impacts of eutrophication, but to determine its effectiveness requires long-term datasets. A recent analysis of the LAke multi-scaled GeOSpatial and temporal database (LAGOSNE), found stable water quality in the Northeast and Midwestern regions of the United States, however, trends at smaller scales may be masked. We address this by analyzing the University of Rhode Island’s Watershed Watch Volunteer Monitoring Program (URIWW) dataset. URIWW has collected water quality data on Rhode Island lakes and reservoirs for over 25 years. These data, included in LAGOSNE, allow for comparison of water quality trends at regional and state extents. We assess for trends with z-scores (i.e. scaled anomalies) calculated on a per-station basis and examine yearly averages. Temperature and chlorophyll *a* are increasing. Total nitrogen shows a weak increasing trend driven by low years in the early 1990s. Total phosphorus and the nitrogen:phosphorus ratio (N:P) were stable. Applying the site-specific z-score approach to LAGOSNE found similar trends to prior studies with chlorophyll *a*, total nitrogen, total phosphorus, and N:P all stable over time. In short, productivity in Rhode Island lakes and reservoirs is increasing, in spite of stable nutrient regimes. Although not causal, this analysis suggests an association between lake temperature and productivity. Additionally, we demonstrate both the value of long-term monitoring programs, like URIWW, for identifying trends in environmental condition, and the utility of site-specific z-scores for analyzing for long-term trends.

Record Details: