Science Inventory

Analyzing long-term water quality of lakes in Rhode Island and the northeastern United States with an anomaly approach

Citation:

Hollister, Jeff, K. Dorothy, B. Kreakie, S. Shivers, W. Milstead, E. Herron, L. Green, AND A. Gold. Analyzing long-term water quality of lakes in Rhode Island and the northeastern United States with an anomaly approach. Ecosphere. ESA Journals, 12(6):e03555, (2021). https://doi.org/10.1002/ecs2.3555

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 is a focus of lake management. Controlling phosphorus and nitrogen can mitigate these impacts, but determining management effectiveness requires long-term datasets. Recent analysis of the LAke multi-scaled GeOSpatial and temporal database for the Northeast (LAGOS-NE) United States found stable water quality in the northeastern and midwestern United States; however, sub-regional trends may be obscured. We used the University of Rhode Island’s Watershed Watch Volunteer Monitoring Program (URIWW) dataset to determine if there were sub-regional (i.e., 3000 km2) water quality trends. URIWW has collected water quality data on Rhode Island lakes and reservoirs for over 25 yr. The LAGOS-NE and URIWW datasets allowed for comparison of water quality trends at regional and sub-regional scales, respectively. We assessed regional (LAGOS-NE) and sub-regional (URIWW) trends with yearly median anomalies calculated on a per-station basis. Sub-regionally, temperature and chlorophyll a increased from 1993 to 2016. Total nitrogen, total phosphorus, and the nitrogen:phosphorus ratio (N:P) were stable. At the regional scale, the LAGOS-NE dataset showed similar trends to prior studies of the LAGOS-NE with chlorophyll a, total nitrogen, and N:P all stable over time. Total phosphorus did show a very slight increase. In short, algal biomass, as measured by chlorophyll a in Rhode Island lakes and reservoirs increased, despite stability in total nitrogen, total phosphorus, and the nitrogen to phosphorus ratio. Additionally, we demonstrated both the value of long-term monitoring programs, like URIWW, for identifying trends in environmental condition, and the utility of site-specific anomalies for analyzing for long-term water quality trends.