Harmful algal blooms (HABs) are a major environmental problem inall 50 states. HABs are defined as the excessive growthof various species of phytoplankton, including protists, cyanobacteria, andmacro and benthic algae whose proliferation negatively impacts water quality,aquatic ecosystem stability, animal and human health.
They can produce toxins and create conditions that kill fish andother animals. The ecological stress from HAB’s can also create areas in waterwith little or no oxygen where aquatic life cannot survive, called dead zones. Thetourism industry loses about $1 billion each year due to HAB’s, mostly throughlosses in recreational fishing and boating activities. Moreover, commercialfisheries lose 10’s of millions of dollars due to fish kills and contaminatedshell fish. Nitrogen availability is believed to be one of the leading causesof the proliferation of HAB’s in coastal marine environments. In Long Island,New York, nitrate levels in the Upper Glacial and Magothy Aquifers (groundwater) have increased by 40% and 200% respectively since 1987.
Roughly 90% offresh water entering the coast is from ground water. This paper willinvestigate the hydrology in Nassau and Suffolk counties and the nitrogen fluxthroughout the watershed.Description ofLong IslandLong Island is a densely populated island off the East Coast of theUnited States, beginning at New York Harbor just 0.35 miles (0.56 km) fromManhattan Island and extending eastward into the Atlantic Ocean. The islandcomprises four counties in the state of New York: Kings and Queens Counties(which comprise the New York City boroughs of Brooklyn and Queens,respectively) in the west, and Nassau and Suffolk counties in the east. Thispaper will focus on the eastern side of Long Island (Nassau/Suffolk).
Thecompletion of the Long Island Rail Road to Greenport in 1844 enabled the islandto become a major market-gardening center whose produce could be shipped to NewYork City. Fishing, whaling, and oystering also remained important, but duringthe second half of the 19th century the island became an attractiverecreational area for New York’s wealthy elite. Great estates and mansions werebuilt along the northern shore, and hotels that attracted thousands of summervacationers were constructed along the southern shore eastward from New YorkCity. Nassau and Suffolk Counties with close to 3 million people were and stillare completely dependent on groundwater for all of their freshwater needs. Hydrology ofLong Island The topography of Long Island is related to the last ice age, whichended roughly 10,000 years ago (Franke 1972).
The bedrock deposits of LongIsland are end products of the advance and melting of several ice sheets duringthe Pleistocene Epoch. The lowermostformation of Pleistocene age on Long Island is the Jameco Gravel, acoarse-grained outwash deposit. Above the Jameco is the Gardiners Clay, a fossiliferousmarine interglacial formation composed mostly of beds of silt and clay (Buxton1992).
The beds above the Gardiners Clay consist of several sequences of outwashand till. The unconsolidated materials that overlie the bedrock constitute LongIsland’s groundwater reservoir. Three major aquifers can be identified: theUpper Glacial aquifer at the top, the Magothy aquifer in the middle and a deepless accessible Lloyd aquifer lying just above the Paleozoic metamorphicbasement rocks. There are two major confining units.
The Pleistocene Gardiners Clay isfound mainly on the southern part of the island and provides some restrictionof flow between the Upper Glacial and the Magothy aquifers. The other confiningunit is the Raritan confining unit which is quite thick and restricts the flowbetween the Lloyd and the Magothy aquifers. The flow of water is dominantly to the north or to the south of theground water divide along the center of the island west of William FloydHighway (Buxton 1992). Therefore, thereis little east-west mixing of the groundwater.
On the east side of WilliamFloyd Highway there is significant flow eastward associated with the PeconicRiver. The water moves laterally in the Upper Glacial aquifer to streams andshoreline or moves downward through the Upper Glacial aquifer to the lowerunits. Some of the water from the Magothy circulates downward and then flowsupward toward the shoreline and then into the Long Island Sound or AtlanticOcean (Böttcher et al., 1990). The rest mixes at depth with salt water underthe Long Island Sound and Atlantic Ocean.
A very small percentage of the waterpenetrates the Raritan confining unit and enters the Lloyd aquifer. At the top of the Magothy, the water is about 10 years old. Near thecenter of the Magothy it is 100 years old. Near the base of the Magothy thewater is about 500 years old. The Magothy is the source of much of LongIsland’s drinking water. Within the Lloyd aquifer the water is much moreancient. Near the top the water is 1000 years old and as thefreshwater-saltwater interface it is approached beneath the Atlantic Ocean thewater is some 8000 years old (Buxton 1992).
The ages of water help to conceptualizethe amount of time it would take to naturally flush out any pollutants.Sources ofNitrogen to GroundwaterTypically, the amount of nitrate in groundwater isrelated to land use, where the greatest concentrations are observed inagricultural regions. Nitrogen percolates easily into the groundwater throughthe soil along with rainwater recharge or irrigation water.
As a result, theshallow aquifers are more likely than deeper ones to initially suffer fromcontamination problems. Previous research has demonstrated that ?15Nnitrate and isotopic composition of groundwater nitrates can be used to helpdistinguish among different nitrate sources (Kendallet al., 1997).
In addition, the oxygen isotopes can be used to identifyprocesses, such as denitrification, that may alter the concentration andisotopic composition of nitrate (Amberger andSchmidt, 1987). It was shown that the main sources of nitrate in groundwater indeveloped areas of Suffolk County are turfgrass fertilizers and wastewater viaseptic tank/cesspool systems and discharge from sewage treatment plants (Flipseet al., 1984; Kimmel, 1984).Farming was extensive on Long Island before WorldWar II but since then development has spread eastward from New York City, and ahigh proportion of the land is now used for residential purposes. In 1981turfgrass occupied 25% of Suffolk County (Koppelman et al., 1984), either asgolf courses, parks and residential or commercial lawns.
Suffolk County WaterAuthority estimates 21 million gallons/day, or 30% of the water pumped is usedfor the sole purpose of lawn irrigation (Wayland, K.G, 2003). Nitrogen is amajor nutrient needed to keep turfgrass healthy and green but has a consequenceof groundwater pollution. Table 1: Groundwater recharge in Long Island Infiltration Source Million Gallons per day Precipitation 1,130 Septic tank/cesspools 84 Sewage treatment plants 24 Water used for irrigation 21 Most of Suffolk County is not sewered. Instead mosthomes have septic tank systems that discharge their waste water back to thegroundwater system. As a result a relatively small percentage of the groundwaterrecharge in Suffolk County is lost, about 10%, compared to 55% for NassauCounty.
The most serious problem when using septic tanks is the introduction ofnitrates into the ground water. When sewage is discharged to a septic tank orcesspool, some nitrogen is lost as ammonia or nitrogen gases and about half isoxidized to nitrate. On Long Island, ?18O for nitrates produced bynitrification of ammonium would be expected to range from approximately +2.5 to+ 3.2‰ assuming an isotopic composition of +23.5‰ for atmospheric oxygen (Ambergerand Schmidt, 1987) and -7 to -8‰ for Long Island groundwater U. S. GeologicalSurvey Waterstore data.
The ?18O nitrate values in the publicsupply wells indicate that most nitrate is derived from nitrification ofammonium. Moreover, the ?15N isotope signature of the septicaffected waters were distinguishably heavier than the fertilizer ?15N signature. In a recent interview, Dr. ChrisGobler, a professor at Stony Brook University’s School of Marine andAtmospheric Sciences and a nitrogen pollution expert says, “High levels ofnitrogen – associated with residential septic tanks and cesspools andfertilizer runoff from agricultural lands – in the groundwater has led to thedegradation of local drinking water supplies as well as Long Island’s coastalecosystems”(Rabin 2012).Effect of Nitrogenin Ground WaterSix percent of the wells in Nassau exceed 10 mg perliter of nitrate that is the EPA maximum allowed for drinking water.
Such wellsare either abandoned or the water from the well is blended with that from awell that has a lower nitrate content. Drinking water with elevated nitratelevels is detrimental to human health and is associated with respiratory andreproductive system illness, some cancers, thyroid problems and even “bluebaby syndrome.” From an ecological standpoint, too much nitrogen andnitrate runoff can cause eutrophication, or nutrient loading in surface andmarine waters that result in algal blooms that create those notoriousoxygen-starved “dead zones” and “red tides” that kill offaquatic life. Long Island has experienced annual harmful algae bloom since thespring of 2004. These events result in a huge loss in revenue for fisheries andcoastal real estate due to un-pleasurable conditions. Among other things, excess nitrogencontributes to two notable problems in coastal Long Island waters: theproliferation of macroalgae (specifically Ulva, or “sea lettuce) and extensivedamage to the marsh grasses and their sub structures that, in turn, areintegral to maintaining natural shoreline protection against coastal stormsurge and waves. MitigationStrategiesSome people are concerned about drinking water quality and others aboutwaste and surface water.
Nonetheless, more emphasis should be placed ondeveloping preventative measures to water pollution instead of remediationefforts. Groundwater contamination with nitrate is a prime example of thedifficulties in addressing nonpoint source pollution (where there is no singlesource of attributable pollution but many contributors). With numerous sourcescovering a widespread area, nonpoint source pollution makes it difficult totrack. Many ideas are being put forward to solve long islands nitrate water problems.
I tend to favor the plans that include management of sources, but someremediation techniques can be useful. Treatment of ground water for nitrates can be done inside the ground(in-situ) or outside the ground (ex-situ). Pump-and-treat, a type of ex situremediation, refers to the extraction of contaminated water from the subsurfacefollowed by treatment with denitrifying bacteria and subsequent discharge oftreated water to groundwater or surface water (King 2012). Water that ispumped from the subsurface comes from the highly conductive materials,while water within areas of low conductivity is removed much more slowly.
Thus,reinjected, clean water will mix with untreated water and diffusion of nitratefrom more concentrated to the less concentrated waters will prolong remediationefforts. This technique is a lengthy process, with high cost (construction andenergy) and diminishing returns (King 2012). The same dilution factor wouldresult with less expense if nitrate sources were reduced. A similar techniqueis used by drinking water municipalities in Long Island. To reduce nitratelevels, connections are created such that the contaminated well water can mixwith cleaner well waters, thereby reducing nitrate levels by dilution (source).
These techniques can reduce the symptoms ofnitrate loading but do not address the source.An emerging technique in the field of groundwater nitrate removal is thepermeable reactive barrier (PRB). PRBs can be used inside the groundwater layerto remove nitrate from groundwater through biological denitrification orchemical denitrification.
Denitrification, a process by which nitrate is reducedto nitrogen gas, is one of the only ways to remove nitrate from water. Thisprocess can be facilitated by bacteria or by metals such as zero valent iron(ZVI). Nano particles of ZVI are coated onto sand and then used on PRBs toreduce nitrate as it interacts with its surface (King 2012). There is no energycost to operate it because it works with the flow of groundwater. This is auseful method for nitrate sequestration because it can last for up to 10 years.The biggest limitation of this technique is expense at plume depths greater than30 ft.
I suggest that this method be expanded for use in domestic wastewatertreatment systems. The reactive barrier can convert and remove nitrate fromseptic effluent before it can contaminate surrounding water bodies. Given the fact the septic systems are identified as a source of nitrate pollution,a significant effort should be made towards the development of septic systemscapable of denitrification. The Long Island Nitrogen Action Plan recommends thedevelopment of denitrifying septic systems but there has not yet been a modelagreed upon. Since the contaminant of interest is nitrate, an ideal systemshould include a drain field capable of supporting two conditions, aerobic andanaerobic. The septic effluent is released with ammonium and must undergonitrification and then denitrification to be completely removed of dissolvedinorganic nitrogen. This can be achieved by increasing water retention time inthe soil matrix, unlike the current drain fields that are built for rapid drainage.The cycling of nitrogen in soil is driven by microbial metabolism and plantuptake processes.
A prolonged interaction between the effluent and the soilwill enhance the amount of nitrogen uptake. The dissolved carbon in the septic effluentwill react with oxygen and create an anaerobic layer during retention that is conducivefor denitrification. Moreover, the PRB technology can be integrated into thesoil matrix of septic drain fields in order to maximize nitrogen removal.
A mixof strategies will need to be applied to accomplish the overall goal ofnitrogen management. Septic drain fields are the dumping ground for dissolvednitrogen. The system would benefit from maintaining the appropriate soilcontent, vegetation, water level and retention time necessary for optimumnitrate removal.