Summer weather effects on Narragansett Bay
By Mackensie duPont Crowley, content & digital media specialist & Save The Bay’s Waterkeepers
Narragansett Bay faces unique challenges during the hot summer months. High temperatures affect water quality and cause issues like algal blooms and fish kills. Lack of precipitation can quickly lead to drought, which has an impact on both water quality and availability around the watershed. There’s also the threat of a hurricane or tropical storm and associated storm surge and coastal damage.
Drought
Generally speaking, a “drought” is a prolonged period of dry weather caused by a lack of precipitation and resulting in a serious water shortage for some activity, population, or ecological system. At the end of July, the US Drought Monitor, a national list, described all of Rhode Island as generally in a moderate drought (level 2 out of 5), which eventually turned into an extreme drought (level 3 out of 5) in August.
Rainfall is not the only factor that officials consider when declaring a drought. This summer, streamflow in the northern part of Rhode Island was well below normal summertime flows in the northeast. Some streams naturally dry up in summer; however, many small rivers that typically don’t dry up have done so. Groundwater is a factor, as well. People who use wells for water should be aware that groundwater is a finite resource that can run dry just like rivers and reservoirs do.
By contrast, Massachusetts has clearer descriptions of drought levels. As of the end of August, the regions in which the Blackstone River watershed and Taunton River watershed are located were in a level 3 Critical Drought. If you live in an affected region, there are things you should do to conserve water.
Hypoxic Conditions
An annual trend of high water temperatures in late July and August contributes to hypoxic conditions, particularly in the Seekonk and Providence rivers and parts of the Upper Bay. “Hypoxia” refers to a condition in which there is not enough oxygen in the water for animals to survive.
How do high water temperatures lead to hypoxic conditions? Warmer weather can lead to different water temperatures in the Bay; surface waters can become warmer than deeper waters. Where there are differences in temperature, density or salinity (“saltiness”) between deeper and shallower waters, the layers of different kinds of water can become pronounced, and poor circulation can occur. When this phenomenon—known as a “stratified water column”—occurs, the oxygenated surface water struggles to mix in with the deeper waters.This frequently leads to isolated fish kill events around the Bay as fish find themselves trapped in areas without the oxygen they need to survive.
Last summer, we witnessed an abundance of blue crabs at the surface of Green Hill Pond in Charlestown struggling with these kinds of conditions. Based on feedback from biologists at the DEM Division of Marine Fisheries, we believe that many blue crabs survived the mild winter and were then driven to the pond’s surface because hot summer weather was causing hypoxic conditions near the bottom. They may have been clustering on rocks near the surface because greater flow and oxygen were present in the water there!
Algal Blooms
Warmer surface water and a prolonged period of stratification can also lead to harmful algal blooms. The hot summer months can provide the perfect conditions for algae to thrive, especially when pollution leads to too many nutrients- like nitrogen and phosphorus- in the Bay. Too many nutrients plus warm weather conditions can create what is sometimes called a “red tide,” or a large algal bloom. These blooms can cause additional problems, like a decline in water quality and the emission of hydrogen sulfide odors. Algal blooms also contribute to hypoxia, because when algae dies, oxygen is consumed in the decomposition process.
Learn more about Save The Bay’s efforts to improve water quality in Narragansett Bay.
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