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Nadir — Refers to a low or the lowest point, as the lowest point of a lake or other body of water attained of a certain period of time (period of record). Natant — Floating or swimming in water. Nappe, also Nap — A sheet or curtain of water flowing over a dam or weir or similar structure. National Environmental Policy
Act (NEPA) — A 1970 Act of Congress that requires all federal
agencies to incorporate environmental considerations into their
decision-making processes. The act requires an Environmental Impact
Statement (EIS) for any “major federal action significantly affecting
the quality of the human environment.” Nitrate — An ion consisting of nitrogen and oxygen (NO3-). Nitrate is a plant nutrient and is very mobile in soils. Nappe, also Nap — A sheet or curtain of water flowing over a dam or weir or similar structure. Narrow — Natant — Floating or swimming in water. National Environmental Policy
Act (NEPA) — A 1970 Act of Congress that requires all federal
agencies to incorporate environmental considerations into their
decision-making processes. The act requires an Environmental Impact
Statement (EIS) for any “major federal action significantly affecting
the quality of the human environment.” National Flood Insurance Program
(NFIP) — National Oceanic and Atmospheric
Administration (NOAA) — An agency of the U.S. Department of
Commerce, the National Oceanic and Atmospheric Administration was
formed in 1970, but its origins may actually be traced as far back
as 1807 when President Thomas Jefferson ordered a survey of the
new nation’s coastline. Today, NOAA has translated the United States’
geographic, atmospheric, oceanic, and meteorological informational
needs into an organization concentrating in the following principal
areas: National Pollutant Discharge Elimination System (NPDES) — The program established by the Clean Water Act (CWA) that requires all Point Sources (PS) of pollution discharging into any “waters of the United States” to obtain a permit issued by the U.S. Environmental Protection Agency (EPA) or a state agency authorized by the federal agency. The NPDES permit lists permissible discharges and/or the level of cleanup technology required for wastewater. National Priorities List (NPL) — A list of the hazardous waste disposal sites most in need of cleanup. The list is updated annually by the U.S. Environmental Protection Agency (EPA) based primarily on how a site scores using the Hazard Ranking System. A site must be on the NPL to receive money from the trust fund for remedial action. Also referred to as the Superfund List. National Secondary Drinking Water
Regulations (NSDWR) — Regulations governing the operation of
public water supply systems under the Safe Drinking Water Act (SDWA).
The regulations define secondary maximum contaminant levels, the
maximum concentrations of certain substances in drinking water that
affect its aesthetic quality. While the NSDWR set aesthetic standards
for drinking water, i.e., color, odor, taste, etc., the National
Primary Drinking Water Regulations (NPDWR) set standards protective
of the public health. National Stream Quality Accounting Network (NASQAN) — A data system operated by the U.S. Geological Survey (USGS) that compiles measurements of water pollutants concentrations taken at the downstream ends of all major water basins in the United States. Native Species — A species
that is a part of an area’s original fauna or flora. Natural Attenuation — The process of Microbiological Anaerobic Degradation in which hazardous wastes and toxic compounds are treated while not involving the addition of foreign microbes to the site but rather using naturally occurring microbes already present. Natural Flow — The rate of water movement past a specified point on a natural stream from a drainage area for which there have been no effects caused by stream diversion, storage, import, export, return flow, or change in Consumptive Use caused by man-controlled modification to land use. Natural flow rarely occurs in a developed county. Natural Recharge — The replenishment of groundwater storage from naturally-occurring surface water supplies such as precipitation and stream flows. Natural Resources Defense Council (NRDC) — A private American environmental organization emphasizing the proper management of natural resources. The NRDC has been an active participant in numerous precedent-setting lawsuits concerning national environmental policies. Natural Sink — A habitat
that serves to trap or immobilize chemicals such as plant nutrients,
organic pollutants, or metal ions through natural processes. For
example, a river that enters a swamp may carry a substantial amount
of dissolved plant nutrients. The natural biological activity of
the swamp may remove these nutrients to such an extent that the
water exiting the swamp is relatively low in nutrient concentrations.
The swamp has then served as a sink to trap the nutrients that are
no longer available for subsequent plant growth downstream from
the swamp. Also referred to as a Nutrient Sink. Natural Substrate — Any naturally occurring immersed or submersed solid surface, such as a rock or tree, upon which an organism lives. [The] Nature Conservancy — An international conservation organization incorporated in 1951 in the District of Columbia for scientific and education purposes. The mission of The Nature Conservancy is to preserve plants, animals and natural communities that represent the diversity of life on earth by protecting the lands and waters they need to survive. Current resource conservation efforts cover Canada, the United States, Latin America, and the Caribbean. Through private donations, The Nature Conservancy purchases lands and then either retains ownership or transfers ownership for management to other conservation groups, both public and private. Nauplius — The free-swimming microscopic larval stage characteristic of many crustaceans, barnacles, etc. Navigable — Capable of being navigated; deep enough and wide enough to afford passage to vessels. In the United States, for the purpose of defining the rights of ownership, some states have adopted the common-law test of flow of the tide, others that of actual navigability. For determining the right of the public to the use of a body of water as a public highway, however, the test in the U.S. is as to whether the water is navigable in fact or not. And waters are navigable in fact when they are used, or are susceptible of being used, in their ordinary condition as highways for commerce, over which trade and travel are or may be conducted in the customary modes of trade and travel on water. In truth, the law has a number of different and frequently confusing definitions of “navigable” rivers and lakes, although agreement exists that all tidal areas are considered navigable. For purposes of determining state title to the beds of rivers and lakes, they must have been capable of carrying commerce at the time the state entered the union. “Commerce” for this purpose includes more than boats carrying persons and cargo. The courts have found streams to be “navigable” where they have carried saw logs or shingle bolts. For purposes of some federal regulatory programs, a waterway must have carried, or be capable of carrying, interstate commerce. Other federal regulatory programs, for example, the Federal Power Act, include waterways which could carry interstate commerce with reasonable modifications. And finally, the Clean Water Act (CWA) defines “navigable” waters to include all waters of the United States which may affect or be affected by interstate commerce. Consequently, this encompasses most water bodies in the nation. Neap Tide — A tide that occurs when the difference between high and low tide is least; the lowest level of high tide. Neap tide comes twice a month, in the first and third quarters of the moon. Nekton — Nephelometer — A device which
measures the intensity of light scattered at right angles to its
path through a sample. It is used to measure turbidity, and the
results are expressed in Nephelometric Turbidity Units (NTUs). Nephelometric Turbidity Unit
(NTU) — Neritic — Of the shallow
regions of a lake or ocean that border the land. The term is also
used to identify the biota that inhabit the water along the shore
of a lake or ocean. Neritic Zone — The relatively
shallow water zone that extends from the high tide market to the
edge of the Continental Shelf. May also refer to such shallow water
regions of lakes. Net Consumptive Use — The Consumptive Use decreased by the estimated contribution by rainfall toward the production of irrigated crops. Net consumptive use is sometimes called the Crop Irrigation Requirement. Net Depletion — The total
water consumed by irrigation, or another use in an area, which is
equal to the water withdrawn minus the return flow. Net Duty of Water — The amount of water delivered to the land to produce a crop, measured at the point of delivery to the field. Net Precipitation — Neuston — New Source Performance Standards
(NSPS) — Effluent limitations set by the U.S. Environmental
Protection Agency (EPA) for new Point Sources (PS) of water pollution.
The standards are applied to industry categories (Standard Industrial
Classification [SIC] Codes), such as petroleum refineries and phosphate
manufacturers. Nick Point (Bedscarp) — Nitrates — Nitrates represent
a class of chemical compounds having the formula NO3 –. Nitrate
salts are used as fertilizers to supply a nitrogen source for plant
growth. Nitrate additions to surface waters can lead to excessive
growth of aquatic plants. The presence of nitrates in groundwater
occurs from the conversion of nitrogenous matter into nitrates by
bacteria and represents the process whereby ammonia in wastewater,
for example effluent discharges from septic tank systems, is oxidized
to nitrite and then to nitrate by bacterial or chemical reactions.
High groundwater nitrate levels can cause methemoglobinemia in infants. Nitrification — The conversion
of nitrogenous matter into Nitrates by bacteria; the process whereby
ammonia in wastewater is oxidized to nitrite and then to nitrate
by bacterial or chemical reactions. Nitrogen — Nitrogen Cycle — (Ecology) The circulation of Nitrogen in nature, consisting of a cycle of chemical reactions in which atmospheric nitrogen is compounded, dissolved in rain, and deposited in the soil, where it is assimilated and metabolized by bacteria and plants, eventually returning to the atmosphere by bacterial decomposition of organic matter. Also, a model illustrating conversion of nitrogen from one form to another through a combination of biological, geological, and chemical processes. The process is continuous, with atmospheric nitrogen, N2, being converted to forms usable by biota and then ultimately returning to the atmosphere as N2. Nitrogenous BOD — (Water
Quality) The amount of molecular oxygen required for the microbial
oxidation of ammonia and nitrite contaminants in a specified volume
of wastewater. This type of oxygen demand can complicate the interpretation
of data obtained from the determination of the Biochemical Oxygen
Demand (BOD) of treated sewage, although a chemical can be added
to the BOD test to prevent ammonia oxidations. Ammonia and nitrite
are oxidized by Chemoautotrophic Bacteria. Nitrogenous Waste — (Water
Quality) Wastewater that contains inorganic forms of nitrogen, including
ammonia and nitrite. Nitrogen Supersaturation — A condition of water in which the concentration of dissolved nitrogen exceeds the saturation level of water. Excess nitrogen can harm the circulatory systems of fish. Non-Consumptive Water Use — Nonconsumptive water use includes water withdrawn for use that is not consumed, for example, water withdrawn for purposes such as hydropower generation. This also includes uses such as boating or fishing where the water is still available for other uses at the same site. The terms Consumptive Use and Nonconsumptive Use are traditionally associated with water rights and water use studies, but they are not completely definitive. No typical consumptive use is 100 percent efficient; there is always some return flow associated with such use either in the form of a return to surface flows or as a ground water recharge. Nor are typically nonconsumptive uses of water entirely nonconsumptive. There are evaporation losses, for instance, associated with maintaining a reservoir at a specified elevation to support fish, recreation, or hydro-power, and there are conveyance losses associated with maintaining a minimum streamflow in a river, canal, or ditch. Non-Conventional Pollutants
— Under the Clean Water Act (CWA), water pollutants not listed as
conventional pollutants, toxic pollutants, or thermal discharges.
These include chloride, iron, ammonia, color, and total phenols. Non-Degradation Policy —
An environmental policy which disallows any lowering of naturally
occurring quality regardless of preestablished health standards. Nondestructive Testing (NDT)
— In geophysical surveying, methods used to detect subsurface
water, subsurface containers, or the areal extent of groundwater
contamination without soil borings. The testing involves the use
of acoustic soundings, infrared radiation, x-rays, magnetic field
perturbations, and electrical resistivity, among other Nondischarging Treatment Plant — A treatment plant that does not discharge treated wastewater into any stream or river. Most are pond systems that dispose of the total flow they receive by means of evaporation or percolation to groundwater, or facilities that dispose of their effluent by recycling or reuse, for example spray irrigation or groundwater discharge. Nonfull-Cost Entitlement (USBR) — Maximum acreage, whether held directly or indirectly, that a landholder may irrigate with Reclamation irrigation water at less than the Full-Cost Rate. Nonpersistent Emergents —
Emergent Hydrophytes whose leaves and stems break down at the end
of the growing season so that most above-ground portions of the
plants are easily transported by currents, waves, or ice. The breakdown
may result from normal decay or the physical force of strong waves
or ice. At certain seasons of the year there are no visible traces
of the plants above the surface of the water; e.g., wild rice (Zizania
aquatica), arrow arum (Peltandra virginica). Nonpoint source — A pollution source that cannot be defined as originating from discrete points such as pipe discharge. Areas of fertilizer and pesticide applications, atmospheric deposition, manure, and natural inputs from plants and trees are types of nonpoint source pollution. Non-Potable — Used to describe
water that is not suitable for drinking because it contains pollutants,
contaminants, minerals, or infective agents. Nonstructural Measures —
Measures for managing, utilizing, or controlling water and related
lands without structural development to achieve the desired objective.
Such measures include best management practices, flood plain zoning,
flood warning systems, education and legal restraints, and preservation,
as well as the more common land management measures. Nonstructural Flood Control Measures — Measures such as zoning ordinances and codes, flood forecasting, flood proofing, evacuation and channel clearing, flood fight activities, and upstream land treatment or management to control flood damages without physically restraining flood waters. Also see Nonstructural Floodplain Management Measures. Nonstructural Floodplain Management
Measures — Those measures employed to modify the exposure of
buildings to floods, e.g., floodproofing, land use planning, warning
schemes, and insurance, as opposed to structural measures such as
dams, levees, and channel modifications. Non-Threshold Pollutant —
A substance or condition harmful to a particular organism at any
level or concentration. Non-Transient Non-Community Water
System — Nonuniform Flow — (Hydraulics)
Flow in which the mean velocity or cross-sectional area vary at
successive channel cross-sections. If the velocity at a given cross-section
is constant with time, it is referred to as Steady Nonuniform Flow.
If the velocity changes with time at each cross-section, it is known
as Unsteady Nonuniform Flow. Non-Volatile Solids (NVS)
— The quantity of solids in water, wastewater or other liquids,
not lost by ignition of the dry solids at 600EC. Reported in milligrams
per liter (mg/l). Non-Volatile Suspended Solids
(NVSS) — The quantity of solids in a sample which is removed
by filtration but not lost by ignition at 600EC. Reported in milligrams
per liter (mg/l). Non-Velocity Coastal Flood Area
— (FEMA) Any area that is subject to inundation by tidal waters
which has lower velocity or wave components than a Coastal High
Hazard Area. Nonwithdrawal Use — Use which
does not require diversion. Navigation, recreation, waste disposal
and conservation of fish and wildlife are examples of nonwithdrawal
uses. Such uses are typically nonconsumptive uses of water. Also
referred to as Instream Use and In-Channel Use. Noria — A water wheel with
buckets attached to its rim, used to raise water from a stream,
especially for transfer to an irrigation channel. Normal (Hydrologic) — A central
value (such as an arithmetic average or median) of annual quantities
for a 30–year period ending with the first year of a decade, e.g.,
1931–1960, 1961–1990. Normal Annual Precipitation —
Average annual precipitation during a base period. Normal Daily Temperature
— The average daily mean temperature for a given date, computed
for a specific 30–year period. Normal Distribution — (Statistics) A fundamental underpinning of statistical and econometric analysis: that if repeated samples are drawn (observed) from a population, that as the sample size grows then the observed values will centralize around a non-random value, termed the expected value. A normal distribution of observations may be pictured as a “bell-shaped” curve, with a central peak and symmetrical “tails” or either side. In a normal distribution, the (Arithmetic) Mean (the average value of all observations) is also equal to the Mode (the most frequently occurring) and the Median (the middle-most with an equal number of observations appearing below and above). Normal Fault — (Geology)
A Fault in which the hanging wall appears to have moved downward
relative to the footwall. Normal Water Level — For
a reservoir with a fixed overflow, the lowest crest level of that
overflow. For a reservoir whose outflow is controlled wholly or
partly by movable gates, siphons or other means, it is the maximum
level to which water may rise under normal operating conditions,
exclusive of any provision for flood surcharge. Normal Year — A year during
which the precipitation or streamflow approximates the average for
a long period of record. Normalized Demand — The process
of adjusting actual water use in a given year to account for unusual
events such as dry weather conditions, government interventions
for agriculture, rationing programs, or other anomalies. North American Vertical Datum Plane — Elevation datum currently used by the Federal Emergency Management Agency (FEMA) for the determination of flood elevations, replacing the National Geodetic Vertical Datum (NGVD) which had been used previously. Notch — The opening in a
dam or spillway for the passage of water. No Till Farming — Planting
crops without prior seedbed preparation, into an existing cover
crop, sod, or crop residues, and eliminating subsequent tillage
operations. NOX — Oxides of nitrogen,
specifically NO (nitric oxide), NO2 (nitrogen dioxide or nitrogen
peroxide), and NO3, nitrate. Noxious Plant — A harmful
plant species. Also see Noxious Weed. Noxious Weed — A plant species
that possesses one or more of the following attributes: aggressive
and difficult to manage, poisonous, toxic, parasitic, a carrier
or host of serious insect or disease and being native or new to
or not common to the United States or parts thereof. Also referred
to as Noxious Plant. Nucleating Agent — In cloud
physics, any substance that serves to accelerate the Nucleation
of cloud particles. Nucleating agents may themselves be nuclei (silver
iodide, salt, sulfur dioxide, dust) or they may enhance the nucleation
environment (dry ice, propane spray). Nucleation — Any process
by which the phase change of a substance to a more condensed state
(condensation, sublimation, freezing) is initiated at certain loci,
nuclei, within the less condensed state. Nuisance Flooding — Flooding
which causes public inconvenience, but little or no property damage.
Also referred to as Minor Flooding. Also see Major Flooding and
Moderate Flooding. Nutrient — Nutrient Cycle — The cyclic
conversions of nutrients from one form to another within the biological
communities. A simple example of such a cycle would be the production
and release of molecular oxygen (O2) from water (H2O) during photosynthesis
by plants and the subsequent reduction of atmospheric oxygen to
water by the respiratory metabolism of other biota. The cycle of
nitrogen is much more complex, with the nitrogen atom undergoing
several changes in oxidation state (N2, NO3 –, R — NH2, and NH4
+, among others) during the cycling of this element through the
biological community, and into the air, water, or soil, and back. Nutrient Pollution — Contamination
of water resources by excessive inputs of nutrients. In surface
waters, excess algal production is a major concern. Although natural
sources of nutrients exist, major sources are typically Anthropogenic
(caused by man’s activities) and include point sources such as municipal
sewage-treatment plants and industrial outflows, and non-point sources
such as commercial fertilizers, animal waste, and combustion emissions.
Most of the recent legislation to curb nutrient pollution has been
targeted towards such goals as updating sewage-treatment plants
to reduce phosphorus and nitrogen in effluents, bans on phosphorous
in laundry detergents, and controlling agriculture operations to
control the flow of nitrogen and phosphorous from fertilizers entering
natural waters. |
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