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Loss of coastal marine habitats by wuyunyi


									                           Tideflat Reclamation: a Global Comparison

                                Jennifer Ruesink1 and Jiaping Wu2
             Department of Biology, University of Washington, Seattle, WA 98195, USA
           Department of Natural Resources, Zhejiang University, Hangzhou, 310029, China

         Humans co-opt about a third of the earth’s net primary production, use half of its
available freshwater, and have created a new biome – the world’s second largest – associated
with agriculture (Vitousek et al., 1986; Pauly et al., 1995; Postel et al., 1996). This heavy
footprint on the earth also leads to pressure for more land, and one response has been to extend
the margins of terrestrial habitat into the nearshore ocean. Termed “reclamation”, this process
fills intertidal or subtidal habitat to provide space for agriculture, industry, transportation, or
residences. While coastal ecosystems are widely recognized as under threat (Beach, 2003), little
is know about how the pace of change varies internationally, and what governance, economic,
and geography factors impinge on decisions. These understandings emerge from a comparison of
representative regions of the world to determine the timing and extent of reclamation.
         In the English language, to reclaim is “to recover… or to bring back to a preferable
manner.” As such, it rarely applies literally to coastal development that extends terrestrial area
through diking and filling into the marine realm. In the Chinese language, this activity is referred
as “Wei-Ken”, which means “to build a dike and then to cultivate”. Clearly, the Chinese term
aptly describes the method and one purpose for the creation of land. We do not consider all types
of shoreline modification as reclamation. For instance, armoring (bulkheads) is widely used to
protect shoreline from erosion, but it involves a relatively small amount of conversion from
marine to terrestrial area.
         The transformation of marine to terrestrial habitat occurs when humans exceed available
space. Space along coastlines is particularly valuable because land is often flat, there is ready
access to shipping routes, and most cities occur there, so human populations are especially dense.
We have identified four major drivers of coastal reclamation.
     1. Agricultural expansion led to early reclamation. For instance, as early as the 6th century,
         rice paddies were created on the marshes of Osaka Bay, Japan. The sheer flatness of tidal
         flats likely appealed to farmers, in addition to the productivity of moist, rich sediments.
     2. Industrial development prompted reclamation as large factories were built. The coast was
         a convenient location for industrial reclamation, close to trade routes for materials and
         exports. Labor was readily available from nearby cities, and waste from industrial
         processes was simply released in effluent.
     3. Industrial reclamation was often accompanied by reclamation for transportation,
         especially shipping ports. More recently, however, roads between islands or entirely new
         islands have been built in areas that were formerly marine. Transportation infrastructure
         represents a third driver of reclamation.
     4. Finally, population density can become so high in some coastal areas that tideflats are
         converted to new towns.
The major drivers are likely to vary over time, with agricultural expansion giving way to
industrial and transportation needs. Also, if most rapid reclamation occurs during industrial
development, the timing of tideflat conversion should vary among countries, depending on when
they industrialized.
         Reclamation inevitably slows as shallow marine areas become filled up. However, two
other factors may serve as brakes on reclamation while some tideflat habitat still remains. First,
economic development may shift away from manufacturing towards service or information, with
many of the industrial processes outsourced. In this case, the pace of reclamation may slow due
to economic change. Second, environmental concerns about loss of habitat or coastal productivity
may arise that resist continued reclamation. This sort of resistance should leave a political imprint
either in terms of coastal zoning legislation or in terms of local protests against dredging and
filling. In this paper we compile information on reclamation of tidal flats in 4 regions that we
consider representative of different patterns of population growth and economic development.
We focus on the magnitude and timing of development, but also on its causes and, when relevant,
political and economic changes that led to some preservation of coastal marine habitats.

        The estuary of the Ouse River, in the United Kingdom, has been used for agriculture for
centuries (Gray, 1976) and continues to be highly productive. Reclamation has produced a steady
increase in land available for cultivation since the 17th century (Figure 1). This time series shows
no evidence of accelerated reclamation during industrialization, likely because agriculture
remains the economic base in the region. The time series of reclamation for the Wash shows that
about 30% of the land was reclaimed by the 17th century, with new pieces added steadily through
1974 (at which point the data source ends).


   Proportion reclaimed





                           1650   1700   1750   1800   1850   1900   1950   2000

Figure 1. Proportion of land reclaimed in the Wash, River Great Ouse, UK (Gray 1976).

       Agricultural reclamation also occurred rather early in Japan, perhaps as far back as the 6th
century for rice paddies. Prior to 1800, 3600 ha were reclaimed for agriculture (Deguchi, pers.
comm., 2004). This area remained essentially constant through WWII, with just 1900 additional
ha over a few centuries. Then, post-WWII, industrial development occurred rapidly, and the
reclaimed area doubled in less than 25 years (to 10800 ha). At that point, however, industrial
needs relaxed because manufacturing jobs were outsourced to other countries. Some reclamation
continues in Osaka Bay, for instance a new island was created to hold Kansai airport. But
economic pressure for land has eased somewhat.
        The Republic of Korea shows much the same time pattern of reclamation as Japan, except
that the pace has not yet slowed. In fact, the largest reclamation efforts on the globe are ongoing
there, during a 20-year project to construct a 30-km dike linking offshore islands. This project
will add tens of thousands of hectares of terrestrial land to Korea.

         Hangzhou Bay is just south of Shanghai City, China. This is among the most developed
regions in the country and has been occupied by humans since ancient times. The tidal flats were
used for paddy rice cultivation some 7000 years ago, during the period known as the He-Mu-Du
Culture [Chen, 1980; Editorial Committee of Bays in China; 1992]. Large scale reclamation was
recorded about one thousand years ago, during the Bei-Song-Dynasty (Table 1) (The Office of
Tideflats Resources Inventory, 1988; Wang pers. comm., 2004). Reclaimed land had high soil
fertility and easy access to nearby fresh water, which made the land very productive. This large
scale reclamation activity continues throughout today, but the pace has varied during different
historical periods.
         Generally, more tideflats were reclaimed when the country was at peace and economic
conditions were good. For example, from 1725 to 1734 in the Cixi region of the Bay, a total of
10,750 ha were reclaimed (Table 1), moving the shoreline towards the ocean about 100 m
annually. Significant activity emerged after WWII and the Chinese civil war, with annual
increase of about 40 m toward the ocean. The reclamation process was clearly visible and
interpretable from Landsat remote sensing image (Figure 2). The white lines, delineated with the
reference data (The Office of Tideflats Resources Inventory, 1988) and image interpretation
technique, showed the boundaries of the areas reclaimed in varied periods. The image is a false
color photo that recorded the spectral reflectance of ground objects from green, red, and infrared
bands. Since this image was acquired on July 19, 2004 when it was in the peak growing season
for plant, densely-forested low mountains showed in red. Farming land was in red-pinkish, varied
with crop-density and growing conditions. Clean fresh water body, for example the reservoir
between low mountains, appeared to be dark, because this water absorbed the green, red, and
infrared magnetic waves. However, shallow ocean, with salt and suspended particles that reflect
visible light, presented cyanine. Residential areas and roads were in blue-grayish.

Table 1 Area reclaimed in Cixi region, Hangzhou Bay, China (ha)
  Year       1047 1472 1725 1735 1797 1862 1909                       1970    1980    1990
               -        -       -       -     -      -       -          -       -       -
             1471 1724 1734 1796 1861 1908 1959                       1979    1989    2001
            12400 10750 9860 6810 4120 11970 7260                     3290    2160    6230
Figure 2. Landsat Thematic Mapper (TM) Image and reclaimed land in Cixi region, Hangzhou
Bay, China. This image was acquired on July 19, 2004 by Landsat. The white lines show the
boundaries of the areas reclaimed in varied periods.

        In another area of Hangzhou Bay (Qian-tang region), conversion activity showed a
different pattern. Strong tides occur monthly in the Qian-tang region, which makes reclamation
activity more demanding and expensive. Therefore, major reclamation did not occur until after
1950’s (Figure 3) (Wang pers. comm., 2004). The pace of the reclamation has accelerated in
both regions. This trend will likely to be continued in the short run, as the demand for land
increases. Most of the reclaimed areas are used for agriculture, based on field observations, even
on newly-converted lands. Many industrial plants have also been built, since they are close to
Shanghai and Ninbo, the two largest ports in China. This proximity to ports allows easy transport
of products worldwide.





















            Figure 3 Area reclaimed in Qian-tang region, Hangzhou Bay, China

        The dramatic expansion of human population has led to strong demand for more space.
The reclamation of tideflats has been a huge success in this regard. It provides highly productive
land for agriculture, good environment for building human shelter, and excellent conditions for
industry. However, we must be aware of the cost (negative side) of the reclamation. This activity
causes the shrinking or disappearance of tideflats or even some inter-tidal zone, causing the
biological loss of coastal marine habitats and species that live there. Some of those species are
highly desirable products for human consumption (e.g. clams, crabs, nearshore fishes).
Reclamation also reduces the buffer zone between the continent and the ocean, an area of
marshes that can act as a biological filter. Without this filter, nutrients from farmland or
pollutants from industry release directly into the ocean. The resulting eutrophication has been a
severe problem in many regions worldwide. For example, ocean eutrophication is the most
important driver on the outbreaks of toxic phytoplankton (red tide). Red tides have occurred more
frequently in the Eastern Sea of China since 2000 (Figure 4), causing catastrophic losses to
fisheries as well as the environment in the nearby region.
   Number of Occurrence





                               2000   2001          2002          2003

Figure 4 The number of occurrence of phytoplankton (red-tide) in Eastern Sea of China (Du,

        The regions explored here are broadly representative of trends that we believe are
happening worldwide. Reclamation in both Europe and Asia has a long history stretching back
centuries or millennia to meet demands for agricultural land. Interestingly, modern acceleration
of rates of reclamation can be driven by agriculture (e.g. in Hangzhou Bay, China) or by
industrialization (e.g. in Osaka Bay, Japan). Where does it end? We suspect that the economic
benefits of reclamation will trump the value of marine resources, simply because land values are
much greater for factories or even fields than for fisheries and aquaculture. However, some of the
value of tideflats is difficult to measure, for instance their role in nutrient recycling, water
purification, and aquatic biodiversity. These goods and services generally are not taken into
consideration unless regulations require it. So, for instance, U.S. law encodes protection for
wetlands and marshes, making further reclamation of these wet areas more difficult. It is our
belief that a careful and comprehensive study of the environment, ecology, marine biology, and
hydrology would slow the move towards reclamation in many regions worldwide. This could
minimize the negative aspects of reclamation.


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