A while ago you asked Robert (Robert Burg, LISS Communcations Coordinator) why some zones in the Western LIS have low transfer efficiencies in terms of sewage loading. This question stems from the transfer efficiency rating which is assigned to each wastewater treatment plant in LIS, which roughly approximates how much of each pound of nitrogen released from that plant makes it into Western Long Island Sound, where hypoxia is most severe. This transfer efficiency is used in a nitrogen “trading program” designed to maximize the efficiency of wastewater treatment plant nitrogen loading reductions, with the idea being that a pound of nitrogen released from a wastewater treatment plant here in Stamford (part of zone 6 in the above map), which discharges directly into LIS, has much more impact than a pound of nitrogen discharged at a plant 100 miles up the Connecticut River (zone 2-3 and 1-35 in the map), which has time to be used as food by plankton, broken down by bacteria, and diluted. For more information on this see http://www.ct.gov/deep/cwp/view.asp?A=2719&Q=325572.
Anyway, when you look at the map of transfer efficiencies, you notice that the efficiency generally gets higher from east to west, and from north to south. Plants closer to Western LIS and the Narrows, where hypoxia is worst, have the highest transfer efficiencies. This makes logical sense. However, some of the biggest plants which discharge into LIS are those serving New York City, which when combined, discharge just over 1,000,000,000 (yes, one billion) gallons of treated sewage per day. By volume of discharge and total nitrogen load, the impact of these plants dwarfs the impact of surrounding facilities. However, the transfer efficiencies assigned to these plants is very low. This is because they discharge into the East River, which is not actually a river, but a very fast moving tidal strait which connects Western LIS (often referred to as the Narrows) to New York Harbor. The predominant direction of flow through this strait is out of LIS and into NYH, so much of the effluent discharged by these plants is rapidly removed from LIS through the East River. Because this water is so fast moving, there is not really enough time for phytoplankton blooms to form, and because the water is so turbid (from the combination of pollution and suspended sediment due to its speed) primary productivity is generally limited by light availability, not nutrients, so not much of that nitrogen is used by plankton in LIS in such a way that it might contribute to hypoxia (by dying and settling to the bottom and decaying).
Jason Krumholz, aka Dr., K, is the NOAA liaison to EPA’s Long Island Sound Office. Dr. Krumholz received his doctorate in oceanography at the University of Rhode Island Graduate School of Oceanography.
ASK DR. K!
Send an e-mail to Jason Krumholz.. Dr. Krumholz is a marine scientist working as the NOAA liaison to the EPA Long Island Sound Office. View more of Dr. K’s questions and answers on the Ask Dr. K blog.
Editor’s Note: The opinions expressed in this blog are those of the author. They do not reflect EPA or NOAA policy, endorsement, or action, and EPA or NOAA do not verify the accuracy or science of the contents of the blog.