Excess nutrients are causing dramatic ecosystem changes in Cape Cod’s Waquoit Bay; The bay is a harbinger of estuaries worldwide, researchers say – ScienceDaily

When the 2020 Covid-19 pandemic hit with its attendant travel restrictions, Matthew Long thought his students could relocate their research projects abroad to study the seagrass beds ecosystem at Waquoit Bay instead. It is a shallow micro-tidal estuary on the south side of Cape Cod, Massachusetts, near the Woods Hole Oceanographic Institution (WHOI), where Long is an Associate Scientist in the Department of Marine Chemistry and Geochemistry.

However, when Long and his students searched for seagrass beds where he had seen them in previous years, there were only a few dying shoots Marina Zostera seaweed, a type of seaweed.

This prompted Long and Jordan Mora, an ecologist for Cape Cod’s restoration, to analyze decades of local environmental monitoring data to find out what happened to the estuary. They found that human causes, including excessive input of nutrient pollution along with climate change, have transformed Waquoit Bay from a benthic to a pelagic-dominated ecosystem.

This disruption to Waquoit Bay’s ecosystem raises serious concerns about the fate of coastal estuaries around the world, the researchers said.

In addition, the researchers note the importance of using and analyzing long-term monitoring data to better understand changes in Waquoit Bay and potentially other estuaries.

Estuary water quality and overall health continue to deteriorate due to excess nutrients from depleted sewage systems, agricultural runoff and other anthropogenic sources, the researchers note. Additionally, warming water temperatures due to climate change, particularly in the Northeastern United States, are exacerbating the problem of nitrogen pollution by reducing dissolved oxygen levels and accelerating microbial metabolism, further reducing oxygen levels.

“This shift toward pelagic dominance in Waquoit Bay may indicate that other eutrophic and warming estuaries may also shift to pelagic dominance in the future as the US Northeast warms most rapidly,” states Deoxygenation, Acidification and Warming in Waquoit Bay”. , USA, and a Shift to Pelagic Dominance,” an article co-authored by Long and Mora, published in estuaries and coasts, the journal of the Coastal and Estuarine Research Federation. “The range of nitrogen loading in the Waquoit Bay watersheds is comparable to the range of nitrogen loading in 90% of the world’s estuaries, making it an ideal site for studying the effects of eutrophication.”

The scientists note that their research in Waquoit Bay “cannot unravel the contributions of global change or eutrophication to estuarine decline. However, they point to a possible combined effect that could result in other similar estuaries being dominated by pelagic metabolism in the future. and the resulting deleterious effects of harmful algal blooms, hypoxia, and loss of biodiversity and ecosystem function.

The researchers’ analyzes showed recent and unexpectedly large increases in chlorophyll A Concentrations, an indicator of microalgal blooms, in the water column throughout the estuary, coinciding with a sustained decrease in macroalgal density at the bottom of the estuary. In addition, the analyzes showed, among other things, an increase in temperature over the last 20 years and a significant decrease in oxygen and pH values.

The analyzes drew on long-term monitoring data collected over decades from two monitoring programs coordinated by the Waquoit Bay National Estuarine Research Reserve, including the reserve’s system-wide monitoring program and the Waquoit BayWatchers, the latter of which is a citizen science water quality monitoring program.

One of the main goals of the current study, according to the paper, was to apply time-series analysis techniques and extensive knowledge of the history of monitoring programs to uncover long-term trends in water quality. ‘These methods can be applied to other monitoring data to expand knowledge gained from similar monitoring programs, improve our understanding of estuary biogeochemistry, and study estuary responses to long-term changes,’ the paper states.

According to Long, seagrass provides a number of ecosystem benefits, including stabilizing sediments and providing habitat for a variety of organisms. In addition, seagrass is a good indicator of good water quality in estuaries and also serves as a carbon sink.

“Carbon storage is extremely important globally and we are actively trying to find ways to store and sequester carbon. Seagrass beds represent a really important and efficient carbon sink,” Long said. “Let’s not lose the seagrass beds and carbon sequestration that we have already established, and let’s actively conserve and restore the seagrass beds. With the loss of seagrass beds like the one we saw at Waquoit Bay, we’re actively releasing that carbon back into the atmosphere.”

Long added that the use of environmental monitoring data helped piece together the history of the shift from a seagrass-dominated system to a macroalgae-dominated system from the 1980s to the present in Waquoit Bay. Without the long-term data, gradual changes in the system are harder to spot, he said.

“This paper is significant not only because it shows that the estuaries of southern Cape Cod and more generally the northeastern United States are entering a new stage of degradation where not even macroalgae or algae can survive, but also because it is clear Providing evidence that long-term monitoring programs are extremely important and worth maintaining,” said Mora, who worked at the Waquoit Bay National Estuarine Research Reserve for 10 years, working with visiting scientists, volunteers and other collaborators to collect data on water quality and underwater vegetation and witness the incremental First-hand evidence of decline in habitat quality.

“My hope is that by showing the impact of rising temperatures on already degraded systems, this paper will help facilitate local and regional management discussions and speed up the decision making needed to mitigate nutrient overload in our estuaries,” added Mora added.

The paper notes that “there is an urgent need to address sanitation to improve the estuary, especially in light of global changes.”

However, Long said if local stressors, including nutrient pollution, can be addressed and if we can reduce carbon emissions and slow global warming and the amount of carbon that diffuses into the ocean, “we could reverse this situation before it happens many.” Similar estuary systems around the world, preserve the valuable ecological functions of seagrass beds and enable their carbon storage potential.

Funding to support the Marine Biology Laboratory’s macrophyte data collection was provided by the Woods Hole Sea Grant. This research was funded by an independent research and development grant from WHOI.?

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