What
affects the quality of surface and groundwater?
Many
factors affect the quality of surface and groundwater. Water moving over or
under the land surface can undergo physical and chemical changes. These changes
may be caused by either natural factors or human activities.
Contaminants
can impair water quality and affect water use. A contaminant is an undesirable
substance in water that either is not normally present or is a naturally
occurring substance at an unusually high concentration.
Contaminants can be
divided into four general classes:
-
Bacteria
These
contaminants can contribute to water by either point or non-point sources.
Point sources contribute contaminants at a discrete site, such as the outflow
from a pipe, ditch, tunnel, well, concentrated animal-feeding operation, or
floating craft. These sources can be controlled to some degree by
treatment at or before the point of discharge.
Non-point sources contribute contaminants from a broad area; as a result, such sources are not as easily identified or controlled as point sources. Non-point sources include the atmosphere, agricultural areas, golf courses, residential developments, roads, parking lots, and contributions from groundwater along lengthy reaches of streams.
Sediment
is defined as particles derived from soil, rock, or organic matter that have
been, or are being, transported by water or wind. Natural organic materials
include plant debris, and human and animal wastes. The erosion of land surfaces
and stream banks produces sediment.
Erosion occurs naturally, but human
activities, like farming, logging, or road construction can increase sediment
transport to and within streams. Sediment deposited in streams can restrict
navigation. Sediment can also increase the potential for floods by decreasing
reservoir storage and stream-channel capacity.
Suspended sediments contribute
to the reduction of water clarity and quality. Fine sediments can severely
alter aquatic communities by clogging fish gills and suffocating fish eggs and
aquatic insect larvae.
Harmful materials such as heavy metals and toxic
chemicals can attach to sediments and move with them down the stream system.
Sediment is a major water quality issue in most places.
Nutrients
are any organic or inorganic compound needed to sustain life. Examples include
carbon, nitrogen, phosphorus, and potassium. Nutrients are contributed to
waters from the atmosphere, agricultural lands, golf courses, lawns, septic
systems, wastewater treatment plants, and factories.
An excess amount of
nutrients in water can result in a disproportionate amount of aquatic
vegetation. The decomposition of this excess vegetation can remove oxygen
from water and cause fish and other aquatic life to die. An overabundance of
aquatic vegetation can also interfere with recreation. High nitrate or ammonia
concentrations can impact drinking water or kill fish. Nitrate and ammonia are
forms of nitrogen.
Some
bacteria are disease-causing organisms that may be delivered to surface water
and groundwater by sewer overflows, leaking septic tanks, and runoff from
animal feedlots or pastures. Some bacteria are a threat to humans, and
indicator organisms such as fecal coliform are used to determine their
presence.
Indicator bacteria are found in great numbers in the intestines of
humans and other warm-blooded animals. When water tests confirm the presence of
the indicator bacteria, the water body may be contaminated by untreated sewage
and other more dangerous organisms may be present.
In
sufficient quantities, toxic substances, such as cleaning solvents, pesticides,
and certain metals, can cause sickness, genetic disorders, and even kill
organisms. Toxic chemicals can enter waters through direct discharge from
industry or by improper disposal of industrial, mining, farm, and household
wastes.
Contaminants contributed from industrial uses of water include toxic
substances produced from cleaning solvents, acids, and alkalis.
The over
application of pesticides can result in the excess entering waters through
runoff to surface water and infiltration into groundwaters.
Even
extremely low concentrations of some chemicals are hazardous to humans and
aquatic life. Toxic substances also can affect an organism’s growth,
metabolism, reproduction, or behavior.
The potential dangers of many toxic
substances are only now being recognized. Assessing the environmental dangers
of these substances has been enhanced as our ability to detect smaller
concentrations has improved and our understanding of their effects on the
environment has increased.
http://www.americangeosciences.org/critical-issues/faq/what-affects-quality-surface-and-groundwater
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