Coastal Marine Environment Sustainability - Sustainable Practices in Geoenvironmental Engineering - page 297

suspended sediments are then pumped from the water and iltered. Recently a pilot test in
Japan was evaluated in an area of 3000 m 2 with a high organic content (30% loss on ignition)
with hydrogen sulide production. About 11 tonnes of wet resuspended solids were removed
during the resuspension pilot test. In the test, 50 cm of the bottom sediment layer was resus-
pended and 3% of the organic and smaller particles were removed Analyses showed that full
scale implementation would enable the removal of about 10% of the resuspended solids, and
reduce COD by 95%, T-P by 50%, T-N by 100%, and sulide by 75% for the redeposited sedi-
ments compared with the untreated sediments. Further tests were performed in Canada on
samples obtained from a harbor. In total, 17 samples (surface and core samples) were taken
at selected stations near the dock and the breakwater area. Sediment size distribution, water
content, and loss of ignition were determined and the concentrations of the heavy metals
were measured before and after the tests. Final results indicate an improvement in sediment
quality. Aeration reduced the concentration of pollutants (mostly organic), and by removing
the ine sediments, the heavy metal concentrations were decreased for some metals.
8.6 Creation of a Natural Purification System
8.6.1 Creation of Sand Beaches and Tidal Flats
Artiicial sand beaches and tidal lat are created for one of the following purposes:
a. Formation of clean beach for resort areas and parks
b. Farming for shellish
c. Recovery of beach following reclamation
d. Rehabilitation of coastal marine environment
Sand beaches and tidal lats possess natural capabilities for cleaning seawater under
repeating waves and tides. This capability arises from a combination of their ability to il-
ter a large amount of suspended solids (mostly organic matter), and the dissolution of the
suspended solids by microorganisms. Although the organic matter entrapped in the sand
pores is food for microorganisms and benthic animals, there are no easy means to quan-
tify the process and its beneits. Evaluation of the impacts arising from construction of the
tidal lats and beaches cannot be readily performed. In part, this is due to the dynamic
processes initiated by the actions of currents and waves. Stabilization of the new beaches
and tidal lats will be a long-term process. The use of breakwaters on beaches brings prob-
lems of decreasing redox in the region due to the dead organisms and excrements. Figure
8.18 shows one of the three tidelands (Kansai Rinkai Park, 270,837 m 2 ), created artiicially
by the Tokyo Metropolitan Government in 1965, at a time when Tokyo Bay was losing its
valuable natural environment. The area incorporates vast tidelands, which were once the
breeding areas for birds and were also once abundant with ish and shellish.
8.6.2 Creation of Seaweed Swards
Eelgrass ( Zostera marina ) is a water plant with long grasslike leaves. Figure 8.19 shows a
dense sward of eelgrass. There are many different species of eelgrass. Shallow intertidal