Harmful due to fish kills and contaminated shell fish.

Harmful algal blooms (HABs) are a major environmental problem in
all 50 states. HABs are defined as the excessive growth
of various species of phytoplankton, including protists, cyanobacteria, and
macro 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 and
other animals. The ecological stress from HAB’s can also create areas in water
with little or no oxygen where aquatic life cannot survive, called dead zones. The
tourism industry loses about $1 billion each year due to HAB’s, mostly through
losses in recreational fishing and boating activities. Moreover, commercial
fisheries lose 10’s of millions of dollars due to fish kills and contaminated
shell fish. Nitrogen availability is believed to be one of the leading causes
of the proliferation of HAB’s in coastal marine environments. In Long Island,
New York, nitrate levels in the Upper Glacial and Magothy Aquifers (ground
water) have increased by 40% and 200% respectively since 1987. Roughly 90% of
fresh water entering the coast is from ground water. This paper will
investigate the hydrology in Nassau and Suffolk counties and the nitrogen flux
throughout the watershed.

Description of
Long Island

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Long Island is a densely populated island off the East Coast of the
United States, beginning at New York Harbor just 0.35 miles (0.56 km) from
Manhattan Island and extending eastward into the Atlantic Ocean. The island
comprises 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. This paper will focus
on the eastern side of Long Island (Nassau/Suffolk). The completion of the Long
Island Rail Road to Greenport in 1844 enabled the island to become a major
market-gardening center whose produce could be shipped to New York City.
Fishing, whaling, and oystering also remained important, but during the second
half of the 19th century the island became an attractive recreational area for
New York’s wealthy elite. Great estates and mansions were built along the
northern shore, and hotels that attracted thousands of summer vacationers were
constructed along the southern shore eastward from New York City. Nassau and
Suffolk Counties with close to 3 million people were and still are completely
dependent on groundwater for all of their freshwater needs.

Hydrology of
Long Island

The topography of Long Island is related to the last ice age, which
ended roughly 10,000 years ago (Franke 1972). The bedrock deposits of Long
Island are end products of the advance and melting of several ice sheets during
the Pleistocene Epoch. The lowermost
formation of Pleistocene age on Long Island is the Jameco Gravel, a
coarse-grained outwash deposit. Above the Jameco is the Gardiners Clay, a fossiliferous
marine interglacial formation composed mostly of beds of silt and clay (Buxton
1992). The beds above the Gardiners Clay consist of several sequences of
outwash and till. The unconsolidated materials that overlie the bedrock
constitute Long Island’s groundwater reservoir. Three major aquifers can be
identified: the Upper Glacial aquifer at the top, the Magothy aquifer in the
middle and a deep less accessible Lloyd aquifer lying just above the Paleozoic
metamorphic basement rocks.

There are two major confining units in long island aquifers. The
Pleistocene Gardiners Clay is found on the southern part of the island and
provides some restriction of flow between the Upper Glacial and the Magothy
aquifers. The other confining unit is the Raritan confining unit which is thicker
than the Gardiners Clay. This layer restricts the flow between the Lloyd and
the Magothy aquifers. The flow of water is
dominantly to the north or to the south of the ground water divide along the
center of the island west of William Floyd Highway (Buxton 1992). Therefore, there
is little east-west mixing of the groundwater. The Peconic river is recharged
by the eastward flow on the east side of the William Floyd Highway. The water
moves laterally in the Upper Glacial aquifer to streams and shoreline or moves
downward to the lower units. Some of the water from the Magothy circulates
downward and then flows back upward toward the shores of Long Island Sound or
Atlantic Ocean (Böttcher et al., 1990). The rest mixes at depth with salt water
under the Long Island Sound and Atlantic Ocean. A very small percentage of the
water penetrates the Raritan confining unit and enters the Lloyd aquifer.

The Magothy is the source of much of Long Island’s drinking water. At
the top of the Magothy, the water is about 10 years old. Near the center of the
Magothy it is 100 years old. Near the base of the Magothy the water is about
500 years old. Within the Lloyd aquifer the water is much more ancient at 1000
years old. Moreover, the freshwater-saltwater interface that  is beneath the Atlantic Ocean is some 8000
years old (Buxton 1992). The ages of water help to conceptualize the amount of
time it would take to naturally flush out any pollutants.

Sources of
Nitrogen to Groundwater

Typically, the amount of nitrate in groundwater is
related to land use, where the greatest concentrations are observed in
agricultural regions. Nitrogen percolates easily into the groundwater through
the soil along with rainwater recharge or irrigation water. As a result, the
shallow aquifers are more likely than deeper ones to initially suffer from
contamination problems. As shown in table 1, septic effluent is the greatest
load to groundwater outside of precipitation. Previous research has
demonstrated that ?15N nitrate and isotopic composition of
groundwater nitrates can be used to help distinguish among different nitrate
sources (Kendall et al., 1997). In addition, the
oxygen isotopes can be used to identify processes, such as denitrification,
that may alter the concentration and isotopic composition of nitrate (Amberger and Schmidt, 1987). It was shown that the main
sources of nitrate in groundwater in developed areas of Suffolk County are
turfgrass fertilizers and wastewater via septic tank/cesspool systems and
discharge from sewage treatment plants (Flipse et al., 1984; Kimmel, 1984).

Farming was extensive on Long Island before World
War II but since then development has spread eastward from New York City, and a
high proportion of the land is now used for residential purposes. In 1981
turfgrass occupied 25% of Suffolk County (Koppelman et al., 1984), either as
parks and residential or commercial lawns or golf courses. Suffolk County Water
Authority estimates 21 million gallons/day, or 30% of the water pumped is used
for the sole purpose of lawn irrigation (Wayland, K.G, 2003). Nitrogen is a
major nutrient needed to keep turfgrass healthy and green but has a consequence
of 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 most
homes have septic tank systems that discharge their waste water back to the
groundwater system. As a result a relatively small percentage of the groundwater
recharge in Suffolk County is lost, about 10%, compared to 55% for Nassau
County. The most serious problem when using septic tanks is the introduction of
nitrates into the ground water. When sewage is discharged to a septic tank or
cesspool, some nitrogen is lost as ammonia or nitrogen gases and about half is
oxidized to nitrate. On Long Island, ?18O for nitrates produced by
nitrification of ammonium would be expected to range from approximately +2.5 to
+ 3.2‰ assuming an isotopic composition of +23.5‰ for atmospheric oxygen (Amberger
and Schmidt, 1987) and -7 to -8‰ for Long Island groundwater (U. S. Geological
Survey Waterstore data). The ?18O nitrate values in the public
supply wells indicate that most nitrate is derived from nitrification of
ammonium. Moreover, the ?15N isotope signature of the septic
affected waters were distinguishably heavier than the fertilizer ?15N
signature. In a recent interview, Dr. Chris Gobler, a professor at Stony Brook
University’s School of Marine and Atmospheric Sciences and a nitrogen pollution
expert says, “High levels of nitrogen – associated with residential septic
tanks and cesspools and fertilizer runoff from agricultural lands – in the
groundwater has led to the degradation of local drinking water supplies as well
as Long Island’s coastal ecosystems”(Rabin 2012).

Effect of Nitrogen
in Ground Water

Six percent of the wells in Nassau exceed 10 mg per
liter of nitrate that is the EPA maximum allowed for drinking water. Such wells
are either abandoned or the water from the well is blended with that from a
well that has a lower nitrate content. Drinking water with elevated nitrate
levels is detrimental to human health and is associated with respiratory and
reproductive system illness, some cancers, thyroid problems and even “blue
baby syndrome.” From an ecological standpoint, too much nitrogen and nitrate
runoff can cause eutrophication, or nutrient loading in surface and marine
waters that result in algal blooms that create those notorious oxygen-starved
“dead zones” and “red tides” that kill off aquatic life. Long
Island has experienced annual harmful algae bloom since the spring of 2004.
These events result in a huge loss in revenue for fisheries and coastal real
estate due to un-pleasurable conditions. 
Among other things, excess nitrogen contributes to two notable problems
in coastal Long Island waters: the proliferation of macroalgae (specifically
Ulva, or “sea lettuce) and extensive damage to the marsh grasses and their sub
structures that, in turn, are integral to maintaining natural shoreline
protection against coastal storm surge and waves. 

Mitigation Strategies

Some people are concerned about drinking water quality and others about
waste and surface water. Nonetheless, more emphasis should be placed on
developing preventative measures to water pollution instead of remediation
efforts. Groundwater contamination with nitrate is a prime example of the
difficulties in addressing nonpoint source pollution (where there is no single
source of attributable pollution but many contributors). With numerous sources
covering a widespread area, nonpoint source pollution makes it difficult to
track. 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 some
remediation 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 situ
remediation, refers to the extraction of contaminated water from the subsurface
followed by treatment with denitrifying bacteria and subsequent discharge of
treated water to groundwater or surface water (King 2012). Water that is
pumped 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 nitrate
from more concentrated to the less concentrated waters will prolong remediation
efforts. This technique is a lengthy process, with high cost (construction and
energy) and diminishing returns (King 2012). The same dilution factor would
result with less expense if nitrate sources were reduced. A similar technique
is used by drinking water municipalities in Long Island. To reduce nitrate
levels, connections are created such that the contaminated well water can mix
with cleaner well waters, thereby reducing nitrate levels by dilution (source). These techniques can reduce the symptoms of
nitrate loading but do not address the source.

An emerging technique in the field of groundwater nitrate removal is the
permeable reactive barrier (PRB). PRBs can be used inside the groundwater layer
to remove nitrate from groundwater through biological denitrification or
chemical denitrification. Denitrification, a process by which nitrate is reduced
to nitrogen gas, is one of the only ways to remove nitrate from water. This
process 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 to
reduce nitrate as it interacts with its surface (King 2012). There is no energy
cost to operate it because it works with the flow of groundwater. This is a
useful 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
than 30 ft. I suggest that this method be expanded for use in domestic wastewater
treatment systems. The reactive barrier can convert and remove nitrate from
septic 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 systems capable of denitrification. The Long Island Nitrogen Action Plan
recommends the development of denitrifying septic systems but there has not yet
been a model agreed upon. Since the contaminant of interest is nitrate, an
ideal system should include a drain field capable of supporting two conditions,
aerobic and anaerobic.

The septic effluent is released with ammonium and must undergo
nitrification and then denitrification to be completely removed of dissolved
inorganic nitrogen. This can be achieved by increasing water retention time in
the 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
plant uptake processes. A prolonged interaction between the effluent and the
soil will enhance the amount of nitrogen uptake. The dissolved carbon in the
septic effluent will react with oxygen and create an anaerobic layer during
retention that is conducive for denitrification. Moreover, the PRB technology
can be integrated into the soil matrix of septic drain fields in order to
maximize nitrogen removal. A mix of strategies will need to be applied to
accomplish the overall goal of nitrogen management. Septic drain fields are the
dumping ground for dissolved nitrogen. The system would benefit from maintaining
the appropriate soil content, vegetation, water level and retention time
necessary for optimum nitrate removal. 

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