Large, unsightly manifestations of algae have been prevalent across the surface of the Georgica Pond during the past week. The algae seemed to intensify as the temperatures have warmed. This year, there have been reports of algae in Georgica Pond that are green, yellow, brown, at the surface in front of their home one day but gone the next and then reappearing once again. What are these algae and how are they moving? Last year the algae was identified via DNA testing as Cladaphora vagabunda, a globally distributed algae known for its ability to form dense ‘bloom’ in regions over-enriched in nutrients. Despite all the different shapes, sizes, colors, and locations of algae in Georgica Pond this year, all signs suggest this is all Cladophora. Cladaphora exist and grows at the bottom of Georgica Pond where they attach to the bottom by means of a structure called a holdfast. Beneath the surface, the algae can range in color from brownish to bright green. As it grows upward and reaches the surface, it can begin to bleach by the sun at which point it turns a yellowish color and as it begins to die, and can turn brown or even black. Once at the surface, the algae can break loose from the holdfast and then be transported by winds. For example, on Thursday, a front moved through (recall the two low humidity days on Thursday and Friday) and shifted the typical mild, south winds to stronger north winds (gusts up to 25 MPH). This event pushed much of the surface algae accumulated on the east bank of Georgica Pond to the west side (note geographically, Georgica Pond does not sit north-south but rather northwest-southeast). Our recent survey show the macroalgae covering much of the bottom of the Pond (see graphic below), meaning it has the potential to re-grow to the surface again in regions from which is has broken off from. Importantly, the Gobler Lab has initiated conversations with the NYSDEC and East Hampton Town Trustees aimed toward developing a comprehensive plan to remove these macroalgae on a regular basis for the purpose of both aesthetics and nutrient mitigation. This will be discussed further at the August 1st presentation.
As the data continues to come in, there are three observations this week that are hopeful.
1. The coverage of macroalgae in Georgica Pond is quantitatively decreasing. As of this week, the surface coverage is significantly lower in the north, Eel Cove, and Georgica Cove (see below).
2. The salinity remains relatively high at over 18 as of today as compare to 7 a year ago (see below); remember the blue-green algae like low salinity.
3. The oxygen levels in Georgica Pond are high. A year ago, oxygen levels were dropping to near zero at night. At 10 mg/L (see below), Georgica Pond has higher oxygen levels than more than 30 sites the Gobler laboratory is currently monitoring across Long Island. One year ago, low oxygen conditions were killing fish in Georgica Pond.
The data below illustrates these trends. For the maps, brown is bottom coverage of the algae, green is surface coverage of the algae, and blue is clear of algae.
Until two weeks ago Georgica Pond was open and exchanging with the Atlantic Ocean bringing in high salinity water. While this salty water has not deterred the macroalgae that are presently overgrowing parts of Georgica Pond, it may discourage the other, more dangerous type of algae in the Pond, blue-green algae. Blue-green algae are microscopic, but more dangerous than macroalgae as they synthesize biotoxins that can poison animals including pets and even humans. In perhaps some good news, these blue-green algae have a love of freshwater and are generally found in freshwater lakes and ponds. In 2014, blue-green algae emerged in Georgica Pond only once the salinity dropped to 7 grams per kilogram of water (See figure below). One year ago today, when the Pond had been closed for months, the salinity was less than 9 (See figure below). Today, after months of being open, the salinity in Georgica Pond is 20 (See figure below). As a point of reference, ocean salinity is about 31. The salinity will drop further in the coming weeks as natural groundwater and stream flow slowly fills the Pond. The questions will be, how long will that take and how low will the salinity get? Because there are no prior salinity records of the Pond being opened as long as it has been in 2015, we are entering some uncharted territory. We can eagerly watch the buoy in the coming weeks to see what happens: https://you.stonybrook.edu/georgicapond/buoy/
Your questions and comments to this site are welcome.
Macroalgae. Seaweeds. The visible overgrowth of fleshy plants in aquatic environments. Macroalgae are an important component of any aquatic ecosystem serving as an important food sources and habitat for many animals. Their overgrowth, however, is problematic. When macroalgae begin to take over an ecosystem, they can shade out other important habitats, lead to dangerously low oxygen levels at night, and can release large quantities of nutrients and organic matter when they die, an occurrence that can trigger further problems with low oxygen or microalgae blooms. Georgica has been historically prone to macroalgae ‘blooms’ and the bloom this year has been exceptionally large. In fact, these macroalgae blooms are precisely why the Georgica Pond Project was initiated: To determine the cause of the blooms and the most likely solutions. Toward that end, last week (June 18), we completed our most recent survey of the macroalgae across the Pond and here are the results:
Blue regions are free of macroalgae, green regions have macroalgae growing up to the surface of the Pond, brown regions have macroalgae growing on the bottom of the Pond, with dark brown representing full coverage and blends indicating partial coverage. In short, there are macroalgae nearly everywhere, with nearly full coverage in Georgica Cove and the northern half of the Pond but little to no coverage to the south near where the cut had been open. This distribution confirms some of the prior hypotheses regarding the macroalgae: They prefer lower salinity water and are promoted by nutrient loading from land as the regions where they are most abundant have lower salinity which means a higher level of nutrients from streams and groundwater.
As stated above, the Georgica Pond Project has been specifically designed to determine the steps needed to remediate these macroalgae blooms. Here is what is being done: 1. Surveys like the one above are being done biweekly so we can continue to understand the temporal and spatial dynamics of these events, 2. Experiments to determine the specific nutrient or nutrients that are promoting the growth of the macroalgae began in May and continue biweekly, 3. Five nutrient source quantification models for Georgica Pond have been constructed and are being refined. These models will indicate where the nutrients are coming from and what needs to be done to cut-off the supply of nutrients to the macroalgae to limit their proliferation, 4. Water quality monitoring and bathymetric surveys of the Pond will indicate the extent to which other water quality parameters and flushing may be promoting these blooms, and 5. The macroalgae are be analyzed for elemental content and DNA content. On this later point, DNA sequencing of the algae from last year has revealed that the genus and species of the macroalgae in Georgica Pond is Cladophora vagabunda, not Sago pondweed or other types some had speculated it to be. While this may seem like a simple scientific nuisance, this knowledge will greatly alter how remediation will proceed given the preferred habitats of Cladophora vagabunda and Sago pondweed are entirely different.
As all of the above information is progressively gathered, any efforts to remove the macroalgae, specifically the dead and dying part which float on the surface of the Pond, would be beneficial to Georgica Pond. In 2014, these macroalgae eventually died off and may have contributed to later problems such as toxic blue-green algae and low oxygen.
Stay tuned for more updates and you can always watch the data stream in from the buoy!
As our research continues, we are beginning to recognize we may be entering some uncharted territory for Georgica Pond, as least in recent memory. Specifically, while the inlet or cut in Georgica Pond has been traditionally opened to the ocean twice annually, in the spring and fall and closing shortly thereafter, this year it has been more or less open all year. Specifically, the Trustees opened the cut in January and it remains open today. Since January, the cut to the ocean has meandered, shrunk, closed temporarily, and re-opened several times. The most recent iteration of this metamorphic process occurred in late May and was recorded by our water quality buoy. Specifically, with the cut temporarily closed, the salinity of the Pond was dropping below 20 and a microalgae bloom was developing in the Pond as chlorophyll levels were rising (see buoy figure below). During a series of storms that occurred on June 2nd and 3rd, the cut re-opened, causing the microalgae to be flushed out of the Pond by ocean water (see buoy figure below). This version of the inlet permitted strong flushing of the Pond this month as, according to our buoy, the salinity in the southern extent of the Pond is the same as the ocean (31), there is no accumulation of microalgae, and oxygen levels in the Pond are high (see buoy figure below). Then, suddenly this weekend, the cut closed again, and the salinity is now dropping once again (see figure). While this closure could remain through the fall, only time will tell if this is indeed the case. Given that two of the problems that have plagued Georgica Pond, microalgae (blue-green algae) blooms and low oxygen, have been in check this year, having the cut open has had benefits. As I am sure many of you have seen, there is a downside to this ‘inlet open’ status, specifically the Pond is so shallow as to be partly unnavigable for boats and the current conditions have been favorable for the proliferation of macroalgae (seaweeds) which are presently wide-spread through much of the Pond. In 2014, the growth of macroalgae increased through the early summer and began to dissipate in July. Because of the extended ‘inlet open’ status and higher salinity this year, it is difficult to know if the macroalgae patterns will parallel 2014. As was done last year, we are surveying the macroalgae on a regular basis. Later this week, we will review what we know about the macroalgae in Georgica Pond.
The Georgica Pond Project is in high gear and in fact has been for five months. With the first indications that The Georgica Pond Project would be a reality, the Gobler Lab commenced its activities to address the major research questions of this project. Some important progress to date is as follows:
1. In January, before the Pond froze over, a research team performed a comprehensive survey of water entering Georgica Pond from groundwater, streams, and tributaries along the north, east, and west boarders of the Pond. These samples have been analyzed to assess the levels of nutrients in them as well as the source of nitrogen in differing regions of the Pond.
2. When the Pond thawed in March, regular monitoring of the Pond commenced, including both discrete, grab sampling and continuous monitoring of surface waters via research vessels.
3. Nutrient budgets have been constructed to quantify the amounts of nitrogen and phosphorus entering the Pond. These calculations assess where these nutrients are coming from both geographically and with regard to their ultimate source. Calculations also consider how the nutrients are delivered (i.e. via groundwater, streams, run-off, or the atmosphere). This information will be presented this summer.
4. Our water quality monitoring buoy was ordered, delivered, and installed in May. See the ‘Water Quality Buoy’ to see up-to-the-minute changes in parameters such as temperature, salinity, dissolved oxygen, blue-green algae, and more. In less than two weeks we have already learned a lot from this device!
5. We are continuing our weekly monitoring of all regions of the Pond as well as the performance of experiments to determine the role of nitrogen and phosphorus in controlling the growth of algae in the Pond.
Future updates will provide information on the status of the Cut and what it means for the near term health of Georgica Pond.