What Caused The Brown Tide in The Great South Bay in 2013? SCERP Has The Answer in One Graphic

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From SCERP (Stony Brook Southampton Coastal and Estuarine Research Program)’s Facebook Page.  Give them a WELL DESERVED LIKE for their outstanding research!



The outbreak of the brown tide caused by Aureococcus in Great South Bay during late June and early July came as a surprise to citizens and scientists alike as it ended nearly eight months of what some had deemed “gin-clear” water facilitated in part by the new ocean inlet created by Hurricane Sandy. An analysis of environmental data (see accompanying graphic; salinity and chlorophyll data courtesy of Dr. C. Flagg) during June provides some clear signs as to the cause of this brown tide. During the second week of June, eight inches of rainfall fell across Long Island – the equivalent of two months’ worth of rain. This super-saturation of the ground lead to a large input of freshwater from land via surface runoff, but even more so via groundwater underflow into the Bay. This groundwater is highly enriched in nitrogen – derived primarily from septic tanks (more on this in a future post). Nitrogen is the ‘limiting element’ in marine waters and thus stimulates the growth of algae. Brown tide is different from other algae, as it is a poor competitor for the ‘first flush’ of nitrogen (which is mostly nitrate). Hence, immediately following the rains, another group of algae grew rapidly (see first increase in chlorophyll), but also died off in a week. When the algae died off, it released the nitrogen it contained as recycled / organic nitrogen, a form the brown tide uses better than most other algae. With temperatures in the bay being perfect, the stage was set for an intense brown tide that began in mid-June had persisted to date (see first second in chlorophyll). In good news, history shows this week’s heat wave should lead to the demise of this summer’s brown tide. In bad news, this sequence of events demonstrates that, even with a new inlet, current nitrogen loading and flushing patterns leave Great South Bay vulnerable to similar events in the future.

Where is all of the nitrogen in GSB coming from? What is the status of the new inlet? This will be covered in future posts.