Because the Chesapeake Bay Watershed Agreement goals and outcomes were originally set to be reached in the year 2025, we at Phillips Wharf thought this year might be a good time to do a monthly deep dive into water quality.
Each month, we’ll discuss a different measurement of water quality, exploring what it is and how it is measured, what the current water quality parameters are for our area and the Chesapeake Bay (where that data is available), and discussing what the goal measurement is for the given parameter.
We’re especially interested in this topic right now as restoration projects AND major development are occurring side by side here on Maryland’s Eastern Shore. Monitoring water quality can help us understand the impacts of both of these types of projects on the Chesapeake Bay.
This month, we want to start off with a water quality parameter that is almost always measured but often not thought of when it comes to the health of an aquatic ecosystem – temperature.
Water temperature is going to be variable throughout the year as it changes with air temperature. However, it takes a lot more energy to change the temperature of water than air, so water temperatures change more slowly than daily changes in air temperature. This is why areas surrounded by the Bay have milder weather compared to further inland. Water temperatures in the Chesapeake Bay are typically warmest in August and coldest in February.
Water temperature is important because it dictates what living organisms can be found in a given area and when. Many animals use the Chesapeake Bay seasonally, visiting in warmer months of the year and then heading south when waters start to cool. This includes dolphins, sea turtles, and even the occasional manatee. There are other seasonal visitors (such as waterfowl) but we’re going to focus on aquatic species here.
We also have Chesapeake Bay animals that spend the winter months in a form of hibernation due to cold water temperatures. These include blue crabs and some species of turtles, both of which bury in the mud and slow their metabolism so that they don’t need to feed until the water begins warming up in the spring. We also know that oysters stop growing below certain water temperatures.
Currently, there are no specific Chesapeake Bay Watershed Agreement goals regarding water temperature but there are goals concerning climate change.
Again, because water temperature and air temperature are closely connected, we do see the impacts of climate change on water temperature. Over the last 30 years, the average water temperature of the Chesapeake Bay has increased by 1°C (1.8°F), roughly matching the average increase in global air temperatures seen over the same time period.
We only know that these changes are occurring due to weather, climate, and water monitoring performed by the National Oceanic and Atmospheric Administration. Thanks to their system of water quality monitoring buoys, we can look at real time water quality data and observe long term trends, including for water temperature.
But what are the impacts of changing water temperatures and climate change in the Chesapeake Bay? While these impacts are still being studied, we are possibly seeing this play out with some organisms already.
As winter gets shorter and/or warmer, on average, we will see shifts in when aquatic organisms become active again in the spring. Phytoplankton, the tiny floating plants that are the base of the Chesapeake Bay food web become active earlier, meaning that animals that depend on them for food will also need to be active earlier or they will miss the spring bloom and starve.
This may even be what is causing the current decline in striped bass populations. One study found that cold, wet winters led to better overlap of prey populations for juvenile striped bass, meaning that with warmer winters, there may be a disconnect between when juvenile striped bass food is present and when the juvenile fish are actually feeding.
Because many aquatic animals are temperature dependent, we are also seeing shifts in the geographic range of some species. Lobster fishermen in Maine are beginning to catch blue crabs as they push north due to warming waters. Here in Maryland, the state is testing a commercial shrimp fishery because these tiny crustaceans are coming farther north in summer months than in previous decades.
In addition to climate change, other factors that affect water temperatures can include waste water discharge, rainfall and runoff, and solar radiation. Wastewater treatment plants and other facilities that discharge large volumes of water (such as nuclear power plants) can lead to warmer water over a small area. Scientists often observe very different ecological systems in discharge areas due to warmer water temperatures. For the Calvert Cliffs Nuclear Power Plant, those impacts are observed within approximately 2km of the discharge point and are considered relatively minimal. However, it has been observed that shellfish grow faster in that area and that fish and waterfowl congregate in that region, likely due to increased phytoplankton populations throughout the year due to the warm water. While this impact is relatively benign, it is not negligible.
Overall, water temperature can help us understand the dynamics of an aquatic system within a given season, can help explain changes in animal behavior, and can help us understand long term trends in changing climates. Even if there’s not much we can do on an individual level to change water temperature, it is still an important piece of the picture that water quality monitoring can provide.