Coastal Marine Environment Sustainability - Sustainable Practices in Geoenvironmental Engineering - page 266

but also because many substances required for the preservation of the sea environment are
transported with the circulation of water.
Nutrients, such as phosphorus, nitrogen, silicate, etc., are produced during the decom-
position of plants by the actions of organisms and are transported into the sea by water.
Phosphorus and nitrogen are produced from the decomposition of withered leaves, while
silicate originates primarily from inorganic soils. These nutrients are essential to the organ-
isms in the sea, and are basic elements of the ecosystems in the sea. In general, there are
fewer nutrients in shallow coastal zones, in comparison to deep seawater. This makes deep
seawater more attractive for ish farming and for creating ishing grounds. To increase the
amount of nutrients in the ishing grounds, ishermen have begun to plant broad-leaved
trees in mountainous areas as a means to increase production of phosphorous and nitro-
gen as decomposition products for eventual rainfall (land surface low) transport into the
sea. Recognition of the high mineral and nutrient values that can be obtained from deep
seawater has led to harvesting of deep seawater for extraction of salt and other products.
8.2.2 Sedimentation
The sea bottom is the interface between the seawater as the hydrosphere and the sedi-
ments and rock as the geosphere. Sediments are formed from substances deposited in the
hydrosphere or produced in the hydrosphere itself. Because of the concentration of cations
in seawater, suspended clay particles can aggregate more easily and settle faster than in
freshwater. In addition, most sediment solids have a speciic gravity greater than that of
seawater—which explains why most of the nonaggregated solids will inally settle to the
bottom of the sea. The settlement or sedimentation of solids is probably one of the stron-
gest agents responsible for the puriication of seawater because
1. Various (harmful and noxious) substances sorbed or attached to the sedimenting
substances (particles) will be sedimented with the particles—resulting in a mea-
sure of puriication of the seawater
2. Turbidity is reduced and transparency is promoted
8.2.3 Eutrophication
In some closed sea areas, increased concentration of nutrients can be found. This phenom-
enon is called eutrophication. This can happen naturally. More often than not, this phenom-
enon is developed as a result of the input of additional nutrients due to anthropogenic
sources. This is sometimes called anthropogenic eutrophication. The main sources of these
nutrients are sewage efluents, nutrients washed out of farm land, golf courses, lawns, and
deposition of nitrogen from nitrous oxide emissions. Low to moderate eutrophication is
beneicial because it enhances production of microscopic plants called phytoplankton that
live in the ocean. Because they (phytoplankton) are bait for zooplankton, they are the basis
for the marine food chain, and their increased presence means a better food supply for
the ish that rely on them as their source of food. However, when eutrophication is high,
an excess amount of phytoplankton will be produced, and the resultant phytoplankton
bloom will contribute to the reduction in the amount of dissolved oxygen in the immedi-
ate region—creating problems for the ish population as explained later in this section as
red tide.
Resuspension of decayed algae and inorganic and organic particles will contribute to
the turbidity of water, adding to the sunlight shading effect. Turbidity affects growth of