Dr. Janet Reimer, a postdoctoral research associate at University of Delaware, describes how regular coastal ocean monitoring provides clues about the sources of acidification in nearshore waters. When she’s not at work on the high seas, Dr. Reimer enjoys camping, taking trips to the beach, gardening and spending time with her family in land-locked Lancaster, Pennsylvania.
My job as a scientist could be described as part detective, part adventurer and part cleanup crew. My nemesis? Coastal ocean acidification, also known as “COA,” is affecting some of our nation’s largest estuaries and important marsh habitats. Plants and animals in these ecosystems don’t thrive in lower pH conditions, where acidity is high. Here at the University of Delaware, we have joined the effort to combat COA by monitoring the partial pressure of carbon dioxide (CO2), the primary factor that influences marine pH.
Our monitoring resources include two NOAA-funded systems that measure CO2 in the mouth of the Chesapeake Bay and just off the coast of Savannah, Georgia. Logistical support and man (or woman) power is provided through partnerships with the University of Georgia, the University of Delaware, the Gray’s Reef National Marine Sanctuary, Caribbean Wind, LLC., MARACOOS, and SECOORA. The systems also monitor sea surface temperature and salinity. The amazing thing about these monitoring systems is that they measure all the parameters on their own, or autonomously, every three hours and then send data back to NOAA on shore through satellite communication. Here’s where the detective work comes in. Monitoring temperature changes allow us to determine the effects of small changes like day-night heat and cooling, as well as changes due to larger seasonal variations in temperature. In the coastal oceans, monitoring salinity gives us insights into CO2 changes due to the influences of rivers and precipitation.
Many processes affect CO2 at any given time. So, on top of the temperature influence, local river and freshwater inputs carry nutrients that fuel phytoplankton blooms that initially remove CO2 from the water through photosynthesis. But as the bloom decays, bacteria digest organic material and release CO2 back to the water. Our monitoring work helps identify which processes are driving the COA signals we detect. If nutrient runoff is a big cause of COA during particular times or in specific places, nearby communities can reduce the amount of nutrients, typically from fertilizer runoff and sewage treatment, in river water and runoff. This will then decrease the amount of plant material created, and subsequently the amount of decay in our coastal bodies of water.
In April of 2018, the newest NOAA-funded coastal autonomous CO2 monitoring system was installed near the mouth of the Chesapeake Bay, in the northern part of the channel just east of the Bay Bridge and Tunnel. The Chesapeake sampling system, pictured above with the Principal Investigator of the project Dr. Douglas Wilson, along with Bay-wide water sampling will be key for determining the long-term changes in acidification of waters both in the Bay, as well as the impacts of discharge on the coastal ocean. Each month we scrub any biological growth off the sensors and take water samples as part of validation studies, sometimes referred to as ground-truthing, conducted regularly at monitoring sites like this across the globe. The project ensures not only that the system is functioning well, but it allows us to compare results of water samples collected elsewhere in the Bay to the levels of CO2 at the moored time-series.
Perhaps the most telling results from a coastal moored CO2 time-series are those from the Gray’s Reef mooring, just off the coast of the Altamaha River and Savannah, Georgia. Recently I visited the Gray’s Reef mooring for validation sample collection while on the NOAA-funded East Coast Ocean Acidification cruise this past August, pictured right. Using almost a decade of CO2 observations from the moored time-series, with an additional 26 years of validated ship-based measurements within the South Atlantic Bight, we determined that pH is decreasing, making the water more acidic. pH in the coastal waters of the South Atlantic Bight is decreasing because there is an increase in the nutrients that fuel plant and phytoplankton growth. Therefore, increased bacterial digestion of organic matter puts more CO2 back into the water than is being removed. Farther offshore in the South Atlantic Bight, however, temperature increases drive up the partial pressure of dissolved CO2 in the water, which drives pH down as well.
Over the last decade or so, our detective work has suggested that stronger regulation of inland water quality has decreased the amount of dissolved CO2 in the Altamaha River in the South Atlantic Bight. This means that less CO2 is being transported to the coast, and by process of elimination, which eliminates rivers as the source of large amounts of CO2 to Georgia marshes, it tells us that CO2 is likely coming from the marsh itself. Furthermore, because the overall health of the Chesapeake Bay is also improving because surrounding states have sharply decreased nutrient runoff in recent years, we expect this will also slow the progress of COA and give the Chesapeake Bay a chance at an even fuller recovery from COA and excessive nutrients. Historically, the Chesapeake Bay has been plagued by excessive nutrients, or eutrophication, which can lead to large amounts of plant production, then decay; bacterial decay consumes oxygen during respiration, thus removing vital oxygen from the water. Stronger regulation of sewage treatment has also been found to reduce the nutrients discharged into coastal waters, thus decreasing fuel for plants and ultimately limiting decay.
Fighting COA can be done from the local level (city, municipality, etc.) to the regional (individual to several states) level. For example, the Chesapeake Bay watershed is influenced by the states of Delaware, Maryland, Pennsylvania, and Virginia; however, not all of these states have equally stringent river water quality regulations. It should also be noted that freshwater also has a much lower buffering capacity, or total alkalinity, than seawater. Therefore, coastal regions already have an intrinsically more acidic pH than the adjacent seawater. Nevertheless, several states, including Washington, Delaware, California, and Virginia, to name a few, have already come up with their own plans to combat COA. This shows that despite its complexity, COA is an issue that can be fought on local levels as well as at the Federal level.