The NOAA Chesapeake Bay Office’s (NCBO) seasonal summaries use data collected from CBIBS buoys, satellites, and other data sources to assess water conditions. NCBO scientists investigate whether current conditions differ from averages over the past roughly 20 years, and, if so, explore how these differences might affect certain Bay species. Here are some elements noted in the Fall 2024 Seasonal Summary. For more information, graphs, and figures, you can access the full scientific document.
Water Temperature
Overall, water temperature was near normal in fall 2024. Satellites observed that temperatures were slightly above the long-term average in the southern and northern portions of the Bay and slightly below the long-term average in areas of the Potomac and Choptank rivers and Tangier Sound.
Sea surface temperature anomalies observed by NOAA satellites September–November 2024 relative to the average of this seasonal period 2007–2023.
Data from CBIBS buoys show water temperatures overall steadily declining from 80°F to near 50°F from September to November as expected. This graph of water temperature at the Gooses Reef CBIBS buoy shows temperature bouncing around either side of, but remaining close to, average for the fall.
Surface water temperatures at the Gooses Reef CBIBS buoy September–November 2024 relative to the long-term average (2010–2023).
Precipitation and Freshwater Flow
Rainfall, and resulting freshwater flow into the Bay, were lower than usual. In southern Maryland, rainfall amounts were the lowest since 2007.
Figure 11. Precipitation data from 2007–2024 for September–November for Tidewater Virginia. Data from NOAA Centers for Environmental Information.
Salinity
Lower freshwater flow leads to higher salinity in Bay waters. Observations from CBIBS buoys, including the Gooses Reef CBIBS location, show that salinity increased from below the long-term average in early and mid-September to average or slightly above average.
Salinity observations at the Gooses Reef CBIBS buoy September–November 2024 (blue line) relative to the average at each buoy over this seasonal period 2010–2023 (red line).
Dissolved Oxygen
NCBO added a new discussion section in this edition of the seasonal summary: Data from hypoxia monitoring buoys that NCBO deployed in three locations (Lower Choptank, Lower Potomac, and Sharps Island) in 2024. All stations measure dissolved oxygen (DO) at 2m, 5m, and 8m depths every 10 minutes. Stations located in deeper water have sensors at additional depths. For the seasonal summaries, daily averages from the hypoxia monitoring buoys are compared to monthly ranges from the long-term monitoring record that is maintained by the Chesapeake Bay Program.
In general, fish avoid water with less than 4 mg/L of DO. Low DO in bottom waters affects benthic and bottom-dwelling organisms that are unable to move, including oysters.
DO levels were below average for much of the fall. However, DO levels remained above 4 mg/L at all stations from the surface down to 5 meters. DO measured at or below 8 meters dropped under 4 mg/L several times at the Lower Choptank and Lower Potomac stations throughout the fall, and DO was below 4mg/L from September until mid October in deeper waters at the Sharps Island location.
Dissolved oxygen (DO) daily averages at the Lower Choptank buoy for September to November 2024 compared with long-term averages (1984-2023) from a nearby monthly monitoring station.
Effects on Living Resources
While water conditions discussed in the Fall 2024 Seasonal Summary were not dramatically different from average, even small anomalies can cause different species to react. For example, lower salinities can negatively affect oyster reproduction and spat sets. Scientists will look to the to-be-published data from the fall oyster survey to see if lower salinity did affect oysters.
And while temperature and salinity conditions likely had little effect on blue crabs, the low DO that lasted into the fall in some parts of the Bay may have affected blue crab movement and habitat use.