|The source of water for an aquaculture facility is very important and sources are manifold. Water sources can be from underground (groundwater), on the ground (surface waters), or above the ground (rain). Each source has unique water-quality parameters associated with it. An evaluation of a potential site for aquaculture should at least include a basic testing for the following water quality parameters as shown in Table 1. If a sample were taken from a natural surface water and evaporated it would contain organic matter in addition to the usual salts. Organic matter consists of living material, it excretions or decomposing dead material. This is usually only a small percentage of a residue. Organic matter can have a great effect on water chemistry by requiring oxygen for living processes as the complex organic matter is built up from and torn down into simple compounds.|
more extended summary of the sources of water and associated parameters relevant
to aquaculture is presented in Table
Recommendations for safe reuse of wastewater in aquaculture is given in Table
3. This basic information given here is intended to provide an overview of water
sources and a framework from which to judge their suitability for
refers to water that is contained in subsurface geological formations.
It is brought to the surface either by pumping from a well or flowing
naturally from a spring or artesian well. Water has a mass of about
1000-1028 kg/m3 (62-64 lb/ft3) depending on salinity and temperature. To
move a large mass of water needed for fish culture any great height or
distance requires energy. Water sources that are located deep in the
earth or at great distance from the farm will always be more costly than
water that is free flowing or shallow (2). The impact that this will
have on the economic viability of the farm depends on many factors
related to species and site selection.
groundwater is contained far from the surface and can remain underground
for millions of years, the water takes on characteristics that are
related to the rock formations that the water is in contact with.
Alkalinity, hardness, pH, dissolved minerals, and dissolved gasses in
groundwater can all be at very different levels from water that is in
contact with the atmosphere. Oxygen and biological processes are limited
underground, so ground water typically contains few pathogens and little
oxygen, although carbon dioxide and argon gasses can be supersaturated.
temperatures below 10 m (33 ft) are quite stable in a given location
relative to surface waters. Temperature is moderated by the thermal mass
of the earth, so groundwater tends to have a relatively minor seasonal
temperature change. Groundwater varies with latitude, being warmer near
the equator and colder away from the equator.
In general, the average annual temperature of groundwater is a
degree or two (°C) higher than the mean annual air temperature. In
addition, groundwater temperature increases 1-5 °C (average about
2.5'C) per 100 m depth (4). Higher increases may be due to local
geothermal activity. If the groundwater is in proximity to volcanic
activity, then it may be naturally heated by a geothermal source.
is usually fresh, but saltwater aquifers also exist. Saltwater aquifers
are common near the coasts, but can also extend for hundreds or
thousands of miles inland. The salinity of the groundwater is variable.
Discharge into freshwater canals or streams may be problematic if the
site is located very far inland or in agricultural areas.
waters include streams, rivers, canals, ponds, lakes, seas, and oceans.
Because they are exposed to the atmosphere and typically support diverse
and abundant biological ecosystems, surface waters have different
characteristics from groundwater. Surface waters can be fed either by
rain or groundwater or both. Water quality parameters such as alkalinity,
hardness, pH, dissolved minerals, and other factors will be somewhat
dependent on the source. In addition, biological processes tend to
change water quality and add competing organisms, pathogens, and
predators. Biological processes tend to add acids to water, there by
lowering pH and depleting alkalinity. They also tend to reduce dissolved
compounds in water and lower the oxidative-reductive potential (ORP) of
the water. Water temperature follows seasonal and local weather patterns,
therefore surface water is more variable than groundwater.
Rain is not usually a reliable source of water for aquaculture; however, in certain regions it can be. Rainwater may also be a useable supply for makeup in recirculation systems or other systems where a continuous high volume supply is not needed. Since rainwater contains almost no buffer and can be affected by airborne pollution, careful consideration must be given to its quality and dependability as a primary source of supply. In some cases, it may help reduce demand on other sources.
water can originate from groundwater, surface water, or rainwater
sources. While it may be convenient to simply hook up to a
municipal-water source, there are two drawbacks. First of all, municipal
water is treated to make it safe for human consumption. Typically, this
includes treatment with strong oxidizers, such as chlorine or ozone, `to
kill human pathogens. These compounds are lethal to fish and need to be
removed or treated to make the water safe for fish. Second, municipal
water is expensive and a limited resource in most areas. The use of
municipal water for aquaculture is largely limited to
amounts of seawater can be made from salt mixtures and freshwater. This
might be sufficient for inland holding facilities, aquariums, or small
research re-circulation systems, but due to the expense and labour
needed to prepare seawater, high-flow production aquaculture will likely
need a large body of natural saltwater nearby. The advantage of making
up seawater from salts is that very clean water can be made. This might
be important for algae, zooplankton, egg, and larval culture, no matter
where the facility is located.
as recycling of paper and plastic can reduce the use of trees and
petroleum resources, water re-circulation technologies can reduce the
demand on the water supply. Water re-circulation can increase the flow
to the culture units by 10-1000 times the flow of new water (9). The
downside is the high capital cost of the treatment components.
requirements may be greater or lesser than a single-pass system,
depending on the amount of water that needs to be pumped in each system
and the need for temperature adjustment. Temperature and other water
quality parameters can be adjusted in a re-circulation system to suit
the species and life stage of interest. This is a major advantage and
may or may not offset high capital and energy costs and may offer higher
growth rates. This advantage is particularly important with photoperiod
and temperature-manipulated broodstock, egg incubation, and larval
MICHAEL B. RUST, JOHN COLT
Northwest Fisheries Science Center Seattle, Washington
Encyclopedia of Aquaculture, 2000.
Created by B. Ueberschär, 25.01.2003