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Sediment Mobilization

Rehabilitation and Remediation

Rehabilitation is defined as the act of partially or completely replacing structural or functional characteristics of an ecosystem that have been diminished or lost. It is also the substitution of alternative qualities or characteristics than those originally present with the proviso that they have more social, economic value than existed in the disturbed or degraded form.

Determinants influencing extent of habitat rehabilitation benefit are described in the table below.

Factors	Descriptors
1. Site Location and Description	Accessibility
	Remoteness
	Links and corridors to other and similar habitats
	Variety and abundance of species present
	Quantity and quality of surrounding habitat
2. Utilization of site: current and potential	Residential population of people
	Potential use by locals
	Potential use by visitors
3. Rehabilitation of site	Magnitude of the operation
	Type of habitat to be rehabilitated
	Rate of development of the required habitat

The key issues to be researched for rehabilitation management plans to be formulated are important where pollutants are concerned. Many pollutants are chemically bound to geological sediments and are, thus, always a prime concern. Aspects of pollutants to be addressed are:

Residence times of pollutants in the marine environment;
Rate of accumulation of pollutants;
Distribution patterns of the pollutants.

In order to determine residence times in water, see table below:

Key issues in pollution and sedimentation analysis	Features of analysis	Descriptors
1. Mode of discharge	Geology	Rock types determine ground water transmissivity of water and, thus, pollutants. Non-transmissible rocks such as igneous (versus sedimentary limestone) confine outflow to surface streams and rivers.
2. Potential for retention	Geomorphology	Coastal geomorphology is also basis for the retentive capacity of the area well as determining the distribution of habitats.
	Climate and geomorphology	Tidal range determines the residence times and transfers of pollutants.
3. Dispersal from the coastal zone	Climate	Dispersal is dependent on wind and wave energy.
	Geology and geomorphology	Intertidal shores and creeks: which are sheltered, including those with mangroves, provide sinks for sediments and pollutants. Narrow shelves are effective in allowing mixing and dispersal of pollutants.

Rehabilitation studies should involve the following particular aspects of research:

� Ecological parameters of affected systems, their response to rehabilitation and the time taken for recovery

� Lessons learnt from individual rehabilitation projects, both successful and unsuccessful

� Criteria for measuring success

� Identify which functions of degraded ecosystems may be rehabilitated and which cannot.

Geological studies of wave action of shoreline sedimentation are also effective. Methods for stabilizing coasts such as crenulate shaped bays, headland control and barrier beach have proved to be effective in reducing shore erosion.

A species of seagrass, Posidonia oceanica, has been found to absorb sea swells and currents and the planting/ protection of this species is a valid potential rehabilitation tool. The living leaves absorb currents while the dead leaves accumulate on beaches, forming a matt and reducing shore erosion. The rhizomes of the plant form interlacing structures which reduce sediment removal. Further research is required to determine the degree of effectiveness of shoreline protection.

For appropriate remediation strategies to be formulated, integrated studies are required to quantify the flux of sediments into coastal waters and ascertain their long term effects on organisms. Qualitative and quantitative studies need to be conducted on the direct cause and effect of sedimentation. These studies are lacking and are key to formulating governmental policies around the issue.

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