Monthly monitoring reveals highs and lows of Great Bay water quality
JEL staff demonstrating the use of SWMP data sonde.
Weather in 2024 caused fluctuations in water quality and nutrient content throughout the seasons. Findings such as these are explored in the recently published 2024 Great Bay Estuary Weather and Water Quality 2024 Trends report, aka the SWMP report. SWMP, or System-Wide Monitoring Program, is a set of common protocols, or methods, that all 30 National Estuarine Research Reserves across the country conduct in order to collect and compare weather and water quality data across time and geographies. Included in the SWMP protocol are continual water quality and weather measurements taken every 15-minutes by sensors placed in Great Bay, the Oyster River, the Lamprey River, and the Squamscott River, and a weather station in Greenland, NH. In addition, monthly water sample grabs located at the same sites as the data sensors are analyzed for nutrient concentration. From this year-round sampling, researchers can analyze trends in weather, water quality, and nutrient content and compare these results to past years.
The 2024 SWMP report focuses on the seasonal differences in precipitation, and how an influx of freshwater, or lack thereof, can impact water quality metrics such as salinity, and nutrients such as ammonium, nitrate and nitrite, and dissolved inorganic phosphorus. A heavy winter precipitation (Jan-March) decreased salinity in the Bay throughout the spring, and a prolonged drought throughout the summer and fall resulted in a high saline estuary environment, with measurements peaking at a high 31ppt in October (the ocean averages at 35ppt). Seasonal fluctuations similarly affected nutrient concentrations, but in the reverse manner, with high concentrations recorded throughout the spring, and historic low concentrations recorded in the summer and late fall.
These intra-annual fluctuations are important to measure in order to capture how water quality can fluctuate to extreme highs and extreme lows throughout the seasonal cycle within a year. If these highs and lows were averaged out to a single yearly value, the nuances of seasonal extremes may be lost. Understanding when and how extreme water quality metrics spike or plummet throughout a year is important so we can track the effects on Bay inhabitants’ phenology and survivorship, especially as the ecosystem is enduring stressors such as frequent precipitation fluctuations and increasing water temperatures.
To access the 2024 SWMP report, and past reports through 2019, please visit the monitoring section of our website.
JEL staff collecting water samples.
