Review Articles

Dredged Soils and Sediments

Environmental Impacts of Abandoned Dredged Soils and Sediments Available Options for their Handling, Restoration and Rehabilitation Elijah I. Ohimain 1., Wim Andriesse 2 and Martinus E.E van Mensvoort 3 1Rohi Biotechnologies Ltd, 104D Airport Road (by Okumagba Avenue Junction), P. O. Box 4517 Warri, Delta State, Nigeria 2Aherra Environmental Sciences, Wageningen University and Research Center, P.O. Box 47, 6700 AA Wageningen, The Netherlands ([email protected]) 3Laboratory of Soil Science and Geology, Department of Environmental Sciences, Wageningen University and Research Center, P O Box 37, 6700 AA Wageningen, The Netherlands ([email protected]) * Corresponding author ([email protected]) Introduction

In the Niger Delta of Nigeria (Fig. 1), the petroleum industry has installed and operates a large stock of oil-related infrastructure such as flowlines, pipelines, trunk lines, manifolds, oil wells, flow stations, compressor stations, gas plants, export terminals, base camps and waste-treatment facilities. While preparing the sites for this infrastructure, soil, sediment and vegetation are removed or dredged. The resultant, dredged spoils are typically deposited along the edges of canals beyond tidal influence and then abandoned. In the mangrove zone, these canals are typically fringed by Rhizophora racernosa (tall red mangrove), which are often killed though burial, smothering and direct removal by the dredger. Dredging and unconfined creek bank spoil deposition has been reported to be extensive (World Bank 1995, Human Rights Watch 1999), but little information is available on the exact extent of the problem. In Nigeria, both Government and the petroleum industry carry out dredging to facilitate marine transportation. Hence, the extent of impacts can be estimated from the activities of the oil companies. For instance, one major oil producing company in the Delta has Oil Mining Leases (OML) that cover an area of over 31,000 sq km. It produces nearly half of Nigeria's oil (2.2 Million bbl/d), and uses 220 sq km to operate its extensive network of over 1000 oil and gas-producing wells, 6000 km of oil and gas flow lines, 100 flow-stations and gas plants, and over 1500 km of trunk lines through which the oil flows to two export terminals in the mangrove zone (Environment Australia 2001). Other oil companies probably operate similar infrastructures in the Delta. Each of these activities is associated with vegetation clearance, dredging, or both. The resultant dredged spoils are usually dumped along the canal banks and abandoned. Over half of these activities take place in the mangrove zone. Recent estimates suggest that about S00 ha of mangroves are lost annually through human impacts (Ainodion et al. 2002) and that about 50% of the Nigerian mangrove vegetation may have already been lost in the process (UNEP 1999). Data on the volume and extent of the spoils do not abound. However, a major oil producing company generated approximately 20 million cubic meters of spoils between 1990 and

JSS - J Soils & Sediments 4 (1) 59 - 65 (2004) 9 ecomed publishers, D-86899 Landsberg, Germany and Ft, Worth/TX | Tokyo 9 Mumbai ~ Seoul, Melbourne * Paris

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Niger Delta 5~

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National boundary M a j o r rivers . Oil wells 5~ / 7 0 i l pipeline

f N 4~ W

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Fig. 1 : Map showing oil wells, pipelines, and related infrastructure in the Niger Delta

1996 (Ade Sobande & Associates 1998). It is estimated that the amount of spoils has increased substantially since the nearly 50 years of such operations in the delta. The high sedimentation rates in the canals constructed necessitate frequent maintenance dredging. The placement of unconfined spoils adjacent to the canals predisposes these areas to erosion which, in turn, often accelerates their siltation. Likewise, most of the spoils have not been characterized and are often abandoned to natural weathering processes, which often cause environmental degradation. The practice of dumping and abandoning sulfidic dredged spoils along canal banks triggers a series of environmental problems leading to habitat degradation which prevent the re-colonization of the site by native species. This paper therefore focuses on the environmental consequences of abandoned sulfidic dredged spoils and options available for their handling, restoration and rehabilitation. 1

1.1

E n v i r o n m e n t a l I m p a c t s of E x p o s e d a n d A b a n d o n e d Sulfidic Sediments Direct burial and destruction of fringing m a n g r o v e s and associated fauna

In the mangrove zone, the tall red mangrove species, Rhizophora racemosa, fringes the banks of rivers and creeks. Deposited dredged spoil destroys several hectares of such mangroves through direct burial (by smothering the pneumatophores) or by forming a barrier to water transport (IUCN 1993). The major potential impacts on animal species from the discharge of dredged material include covering or direct killing of species and impairment or destruction of the habitat to which these species are limited. The discharge of

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dredged material has variously affected populations of fish, crustaceans, mollusks and other food web organisms through the release of contaminants which adversely affect adults, juveniles, larvae, or eggs, or which result in the establishment or proliferation of an undesirable competitive species of plant or animal at the expense of the desired resident species. Suspended particles settling on attached or buried eggs can smother the eggs by limiting or sealing off their exposure to oxygenated water (USEPA/USACE 1998). 1.2

C h a n g i n g t o p o g r a p h y and h y d r o l o g y

The mangroves are located in the mud flats of the intertidal zones. Topographic surveys of the Niger Delta mangrove zone revealed that these areas are 0.8-1.8 m above the mean sea level (Nwilo and Onuoha 1993, Ojo et al. 1993). Canalization is quite extensive and has resulted in the alteration of the hydrology of the Delta. The concomitant dredged spoils are mostly dumped adjacent to the canals on the naturally almost-flat land. This causes a significant height differentiation at the dumpsites, and consequently, the land surface becomes strongly undulating. The heights of the various dump sites in the Delta vary considerably, ranging from 0.5 to 3.4 m as related to the high tide. Along several kilometers of pipeline right of way (ROW), spoils are usually deposited continuously, forming a barrier against tidal inundation. While spoil heaps at the pipeline ROW could be narrow, i.e. less than 5 m, the spoils bordering well heads are often wider than 10 m. Spoil dumps close to major oilfield infrastructures such as flow stations, gas plants, compressor stations, terminals, etc. are quite extensive, covering over 20 hectares in some cases. The undulating terrain impedes surface drainage and prevents the periodic inundation of the spoil dumpsite

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Review Articles by tidal water. Because of the altered topography and hydrology, resurgence and/or re-vegetation of the site by the native mangrove (Rhizophora sp) becomes impossible due to the absence of tidal inundation. After several years of dumping, most of the spoils remain bare and freshwater swamp forest communities frequently develop in the basins formed. 1.3

Dredged Soils and Sediments Table 1: Chemical characteristics of dredged spoils from Warri River, Niger Delta

Increased erosion and siltation

The change in topography and hydrology caused by dredging, spoil disposal and related activities coupled with the impairment of surface drainage causes widespread erosion of the delta (Ebisemiju 1985, Ibe 1988, Awosika et al. 1993, Asangwe 1993, Moffat and Linden 1995). This has resulted in further damage to the entire coastline including the mangroves. In an area where rainfall exceeds 3000 mm annually, the presence of unconfined and un-vegetated creek bank spoils several meters above mean sea level predisposes the spoils to erosion. Erosion washes fine particles from the unvegetated spoils into the canals, thus resulting in accelerated canal siltation. Regular maintenance by dredging leads to additional spoil deposition, thus repeating the cycle to the detriment of the estuarine ecosystem.

pH (1:5, Sample: water)

2.80 + 0.20

Conductivity, pS/cm

5204.35 • 826.85

TOC (%)

3.85 • 1.95

Organic matter (%)

6.59 • 3.39

Total Nitrogen (%)

0.04 • 0.01

Sulfate {mg/kg)

3947.00 • 1873.00

Chloride (mg/kg)

4264.00 • 762.00

Copper (mg/kg)

107.20 • 13.90

Chromium (mg/kg)

119.10 • 23.90

Manganese (mg/kg)

273.70 • 22.30

Total Iron (mg/kg)

1841.50 • 32.00

Nickel (mg/kg)

115.75 _+22.75

Zinc (mg/kg)

124.80 • 6.70

Cadmium (Cd), mg/I

126.40 • 4.40

Source: Ohimain (2001)

Table 2" pH, sulfate and selected heavy metal concentrations of dredged spoil leachates from Warri River, Niger Delta

1.4

Excessive flooding and ponding of the backswamp

The creation of spoil banks along canals, creeks and rivers has led to the establishment of artificial levees in the mangrove tidal mudflats. The resultant backswamp often remains permanently flooded due to the presence of these levees. This prevents the usual tidal water from inundating the site, thus forming an artificial dam/pond. Mangroves are known to be tolerant to periodic flooding, but they are highly sensitive to excessive and continuous flooding (Kathiresan and Bingham 2001). The result is the destruction of mangrove forest fringing the canals. Ponded water soon becomes a breeding site for mosquitoes and noxious algae. The problem even becomes compounded when acidic leachates from the spoils are trapped in the backswamp. 1.5

Estuarine acidification and heavy metal pollution

Another major problem associated with dredged spoils in coastal wetlands is sulfate acidity. Worldwide, mangrove sediments generally contain reduced forms of sulfur, mainly as pyrite (FeS2), which upon exposure to the air is transformed into hydrogen sulfate, thus rendering the soil extremely acidic. Pyrite is present in the sediments of the Niger Delta as well (Anderson 1966) and indeed along the entire West African coast (Sylla and Andriesse 1994, Sylla et al. 1996). The chemical properties of dredged spoils obtained from the Warri River, Niger Delta (Table 1) show that they are extremely acidic with high concentrations of sulfate, iron and other heavy metals. Prior to dredging, the sediments were anoxic and therefore contained reduced forms of sulfur (i.e. sulfides), with pH ranging from slightly acidic to neutral and heavy metals present in unavailable forms mostly as metal sulfides. But exposure to the air through dredging and spoil disposal, leads to acidification, as typified by low pH and high sulfate concentrations as shown in Table 2.

JSS - J Soils & Sediments 4 (1) 2004

pH

2.34 • 0.17

Sulfate, mg/I

2329.42 • 107.12

Copper, mg/I

50.23 • 0.17

Cadmium, mg/I

57.18 • 0.20

Chromium, mg/I

13.97 • 0.17

Nickel, mg/I

26.58 • 0.43

Manganese, mg/I

75.99 • 0.47

Zinc, mg/I

49.80 • 0.59

Source: Ohimain (2001)

Microbial oxidation processes catalyze these conversion processes (Sammut and Lines-Kelly 2000). Ohimain (2001) isolated some known acid-forming and acid-tolerant bacteria from the dredged spoil, e.g. Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Acidithiobacillus acidophilus. The high acidity contributes to the slow or lack of natural re-vegetation in most of the dredged spoil dumpsites, causing canopy gaps and, later on, vast wastelands devoid of vegetation in the otherwise sheltered mangrove ecosystem. Known environmental and socio-economic impacts of estuarine acidification are listed below, whereas Table 3 presents impacts (short- and long-term) on fish and aquatic resources; furthermore, the multi-million-dollar oilfield infrastructure in the delta may be at a risk of corrosion: 9 9 9 | 9 9 9 9 9 9 9

Irreversible loss of soil resources Heavy metal pollution Vegetation loss Plant productivity reduction Animal productivity reduction Corrosion of steel, concrete, and other engineering structures Property abandonment Water quality degradation Groundwater pollution Estuarine biota mortality Pollutant bioaccumulation

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Table 3: Short- and Ionq-term effects of acidic water on fish and fish habitat

In mangrove ecosystems, heavy metals are known to associate with sedimentary pyrite and are mostly trapped in nonbioavailable forms (Kathiresan and Bingham 2001). The acidity resulting from the oxidation of pyrite often causes the dissolution of these soil-metal complexes and the subsequent release of potentially-toxic heavy metals (Delaune and Smith 1985). Available data suggests that concentrations of heavy metals in leachates draining abandoned spoils are high (see Table 2). Trace metals, which are common contaminants of natural water, sediments, and dredged spoils in mangrove ecosystems, may adversely affect flora and fauna of the area, thus making a re-colonization of the spoil impossible. Organisms such as mudskippers and crabs survive, but often exhibit signs of stress, thus posing the risk of bioaccumulation along the food chain. 1.6

People find abandoned dredged dumps attractive for the establishment of houses, fishing camps and home gardens (Fig. 2}. Fruit trees such as pawpaw (Carica papaya), mango (Magifera indica), avocado pear (PerseaAmericana), c o c o n u t (Cocos nucifera), and pineapple (Ananas comosus) are commonly cultivated on matured spoils close to human dwellings. Vegetables and other food crops such as okra (Abelmoschus esculenta), bitterleaf (Vernonia amygalina), flutted pumpkin (Telfaria ocidentalis), cassava (Manihot sp.), c o c o y a m (Colcasia esculenta), and plantain (Musa sp.) are also cultivated here. Some of these crops are tolerant to acid sulfate soils and have been successfully cultivated on elevated beds from sulfidic spoils in other countries (Minh et al. 1997, Stevenson et al. 1999).

Succession to freshwater vegetation

Typically, the abandoned dredged spoils are left to weather naturally. After several cycles of rainfall and acid drainage, some spoils develop scalds while others become less acidic. Because tidal water does not reach the elevated spoil heaps, natural mangrove re-succession becomes impossible. The weathered spoil (i.e. those without acid scalds) may favor the introduction of undesirable plant and animal species at the expense of native species and communities. Usually, grasses and sedges are the first to re-colonize the spoil and, after several years (<10 years), other upland species become established. 1.7

Positive impacts

The availability of suitable land for housing and farming is a major challenge in the mangrove zone. The major o c c u p a t i o n of the native population in the Niger Delta is fishing.

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Fig. 2: Fishing camps and home garden on abandoned spoil

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Management of Abandoned Sulfidic Spoil Dump

Because of the environmental problems associated with exposed sulfidic sediment and the increasing scales at which sulfidic spoil banks are being generated in the delta, it is expedient to properly handle these materials. Options available for the management of these acidic and metal laden spoils are proper handling (to prevent pollution), site restoration (back to pristine conditions or pre-existing conditions) or rehabilitation (to be put into sustainable alternative). 2.1

Proper handling of sulfidic spoils

Environmental factors, which control the growth of acidithiobacilli, also influence spoil acidification (Rose and Cravotta 1998). Such factors include water, air and the presence of pyrite. Proper handling of spoils to prevent or control their acidification needs to be focused on techniques which prevent either air or water from reaching the spoils, neutralize acidity or inhibit acid-forming bacteria (Ohimain 2002). The primary purpose of proper handling is to selectively isolate sulfidic spoils/pyrites in such a way as to minimize or prevent acid production and transport (Perry et al. 1998). Commonly used spoil handling techniques and their mechanism of action are compiled in Table 4. These techniques have been applied in both pilot and large-scale projects with a varying level of success (Sutherland et al. 1996). A technique such as pyrite separation makes use of the physical properties of the spoil. It is known that pyrite commonly associates with the fine fraction of sediments, <75 micron (Bowman 1993). Large-scale pyrite separation has been achieved with the use of mineral processing equipment such as hydrocyclones and other gravity-related equipment. Dredged spoil fractionation has the advantage of reducing the quantity of contaminated materials and thereby reducing the cost of treatment considerably. In Australia, pyrite separation has been applied in situ during dredging, while the non-contaminated sand fractions were discarded; the contaminated, finer fractions were returned into the riverbed (Saffigna et al. 1996). Submergence has the advantage of creating anaerobic conditions that inhibit the growth of the acidithiobacilli (Perry et al. 1998). This has been exploited in the construction of wetlands for the purpose of handling sulfidic wastes (Fennessy and Mitsch 1989). Other techniques that have been successfully used for spoil handling involve capping or burial to prevent oxygen and/or water from reaching the spoils (Bowman 1996, Perry et al. 1998). Sometimes, the spoils are dewatered and selectively placed above the antici-

Dredged Soils and Sediments pated surface and groundwater levels to prevent contact with water (Saffigna et al. 1996, Perry et al. 1998). Finally, both lime and other alkaline reagents and bactericides have been incorporated into dredged spoils to inhibit acid-forming bacteria and prevent acidification. Some of the widely used bactericides include sodium dodecyl sulfate (SDS), calcium fluoride (Schippers et al. 1996), sodium lauryl sulfate, sodum benzoate, sorbic acid (Dugan and Ape11983, Onysko et al. 1984) and iron 8-hydroxyquinoline (Lan et al. 2002). It has been reported that lime, SDS and calcium fluoride have the added advantage of being able to stabilize heavy metals (Schippers et al. 1996). Lime and bactericides have been successfully used in the mining industry for the large-scale control of acidification of sulfidic mine spoils (Rastogi 1996, Schippers et al. 2001) and should be effective for dredged spoils as well. For better efficiency, it is advisable to apply more than one spoil handling technique. 2.2

Mangrove restoration on spoil banks

In this paper, restoration refers to the act of regenerating the mangrove ecosystem. It has been well documented worldwide that mangrove can self repair over a period of 15-30 years if suitable seeds/propagules are available under 'normal' hydrological conditions (Lewis 1982). In order to forestall pollution arising from sulfidic spoils, there is the need to re-vegetate spoil heaps with native mangrove species. This will serve the dual purpose of managing hazardous spoils and restoring the habitat. The various methods/techniques of mangrove restoration can be found elsewhere (Field 1996, Kaly and Jones 1998, Stevenson et al. 1999, Lewis and Streever 2000). Prior to re-vegetation, elevated spoil heaps may be re-graded by backfilling into derelict canals/depressions in order to allow tidal inundation. Owing to the high buffering capacity of the Niger Delta brackish and seawater, tidal inundation will neutralize and flush the hitherto trapped acidic [eachates from the backswamps and allow the return of anoxic conditions. This will suppress further acidification (Ohimain 2003) because of the reducing conditions that are created in the process (van Breemen, 1976, Moore et al. 1999). Tidal buffering has been applied successfully in Australia to counter acidification (Indrarata et al. 2002). Canal backfilling has been used to mitigate large-scale wetland dredging in Louisiana coastal marshes (Nell and Turner 1987). Using the method of hydrologic restoration, about 1.5 ha of degraded mangroves spoil banks have recently been restored in the delta (Ainodion et al. 2002) (Fig. 3).

Table 4: Special techniques for handling sulfidic spoils

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Dredged Soils and Sediments

Review Articles Government should encourage restoration efforts by granting incentives such as tax reduction to companies embarking on mangrove restoration. Furthermore, as a matter of urgency, the government should promulgate laws banning the disposal of spoils in mangrove areas without long-term monitoring and restoration plans. Finally, it is only when spoil management issues are incorporated into site preparation and drilling plans that sustainable development can be achieved in the Niger Delta.

References Fig. 3: Mangrove restoration efforts in the Niger Delta 2.3

Spoil bank rehabilitation to alternative use

According to Stevenson et al. (1999), restoration to the original habitat may not always be the best option, especially in situations where restoration to mangrove is considered inappropriate, technically difficult, or too expensive. They can alternatively be used in a beneficial manner once their geotechnical, chemical and biological properties are determined and found to be suitable. Processed spoils can be used in upland, wetland, and aquatic environments (USACE/WES 1998). Eroding shorelines is one of the major problems facing the entire 900 km Nigerian coastline (Ibe 1988); abandoned dredged spoils can be used to protect such areas. Cultivable land is practically unavailable in the usually lowlying mangrove swamp; hence, the presence of abandoned spoils becomes attractive to farmers and fishermen alike who often travel long distances to fish in the highly productive mangrove swamp. The local people often use abandoned spoils for farming and the establishment of fishing camps/ settlements. This is encouraged, provided the toxicological aspects of using sulfidic spoils are adequately addressed, since crops growing on spoils have been reported to bioaccumulate heavy metals (Bramley and Rimmer 1988). 3

Conclusion and R e c o m m e n d a t i o n s

In the Niger Delta, dredging is often carried o u t to gain access to prolific h y d r o c a r b o n bearing zones. T h e dredged sediments, w h i c h are often deposited a l o n g the sides of the canals, develop into highly acidic spoils t h a t c o n t a i n high concentrations of heavy metals. E n v i r o n m e n t a l impacts arising from p o o r m a n a g e m e n t of d r e d g e d spoil are varied a n d complex; either singly or in c o m b i n a t i o n , a n d result in the deterioration of the m a n g r o v e ecosystems a n d in the d e a t h of estuarine biota. To forestall further impacts, spoils s h o u l d be selectively h a n dled to prevent, or at least to m i n i m i z e acidification, while encouraging restoration a n d r e h a b i l i t a t i o n of despoiled areas. Spoils can alternatively be used in a beneficial m a n n e r once their geotechnical, engineering, chemical a n d biological properties are determined. Processed spoils c a n be used in upland, wetland, a n d aquatic e n v i r o n m e n t s . T h e y are particularly useful for shoreline protection, w h i c h the delta urgently needs in order to counter the rapidly e r o d i n g coastlines.

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Dredged Soils and Sediments [37] Rose AW, Cravotta CA (1998): Geochemistry of coal mine drainage. In: Brady KBC, Smith MW, Shueck J (Eds.): Coal Mine Drainage Prediction and Pollution in Pennsylvania, pp. 1-1 to 1-22. Department of Environmental Protection, Pennsylvania, USA [38J Saffigna PG, Smith DJ, Holland GL, Brown GA, Carstens LW, Brown WJ (1996): Separation and remediation of saline Tween River sediments at Chinderah. In: Proceedings of 2nd National Conference on Acid Sulfate Soils, Smith RJ, Smith HJ (Eds.), pp. 206-214. Robert J. Smith and Associates and ASSMAC, Australia [39] Sammut J, Lines-Kelly R (2000): An Introduction to Acid Sulphate Soils. Natural Heritage Trust, Australia Seafood Industry and Environment Australia [40] Schippers A, Jazsa PA, Kovacs ZM, Jelea M, Sand W (2001): Large scale experiments for microbiological evaluation of measures for safe guarding sulfidic mine waste. Waste Management 21:139-146 [41] Schippers A, yon Rege H and Sand W (1996): Impact of microbial diversity and sulphur chemistry on safeguarding sulfidic mine waste. Minerals Engineering 9:1069 - 1079. [42] Smith MW, Brady KBC (1998): Alkaline Addition. In: Brady KBC, Smith MW, 8hueck J (Eds.): Coal Mine Drainage Prediction and Pollution in Pennsylvania, pp. 13-1 to 13-13. Department of Environmental Protection, Pennsylvania, USA [43] Southerland NM, Scott PA, Morton WK (1996): Field Practicalities of treating acid sulphate soils In: Proceedings of 2nd National Conference on Acid Sulfate Soils, Smith RJ, Smith HJ (Eds.). Robert J Smith and Associates and ASSMAC, Australia 221-226 [44] Stevenson NJ, Lewis RR, Burbridge PR (1999): Disused shrimp pond and mangrove rehabilitation. In: Steever W (Ed.): An International Perspective on Wetland Rehabilitation. Kluwer Academic Publications, The Netherlands 277-297 [45] Sylla M, Andriesse W (1994): An agro-ecological characterization of mangrove ecosystems in West Africa, with special emphasis on rice cultivation. In: Sylla M: Soil salinity and acidity: Spatial variability and effects on rice production in West Africa's mangrove zone. PhD thesis Wageningen Agricultural University, Wageningen, The Netherlands. pp. 19-50 [46] Sylla M, Stein A, Van Mensvoort MEF, Van Breemen N (1996): Spatial variability of soils actual and potential acidity in the mangrove agroecosystems of West Africa. Soil Science Society of America Journal 60, 219-229 [47] UNEP (1999): Regional overview of land based sources and activities affecting the coastal African region. UNEP/GPA Co-ordination Office & West and East African Plan [48] USACE/WES (United States Army Corps of Engineers/Waterways Experiment Station) (1998): Dredged material testing for beneficial use suitability. Tech. Note DOER-C2. USACE / WES, Vicksberg [49] USEPA/USACE (1998): Evaluation of Dredged Material Proposed for Discharge in Waters of the US. Inland testing manual report No .EPA823-398-004, 391 pp. [50] van Breemen N (1996): Genesis and solution chemistry of acid sulphate soils in Thailand. Agricultural Research Report 848. Centre for Agricultural Publishing and Documentation, Wageningen. The Netherlands [51] World Bank (1995): Defining an Environmental Development strategy for the Niger Delta. Volume 1. West Central Africa Department, Washington DC [52] World Conservation Union (IUCN) (1993): Oil and gas Exploration and Production in Mangrove Areas. IUCN, Gland, Switzerland, 47 pp. Received: December 12th, 2002

Accepted: October 9th, 2003 OnlineFirst: November 10th, 2003

About the Authors Dr. Elijah I. Ohimain is an environmental/petroleummicrobiologist whose main focus is on anthropogenic activities affecting the Niger Delta mangroves,.particularly dredging, spoils management, drilling, oil spills, soil acidification, hyper-salinization, modification of topography and hydrological regimes. He is also looking at developing low cost and locally adaptable biotechnologies for mangrove restoration and management of acidic and metal laden spoils. Although he holds a PhD degree in environmental microbiology, his research is now tending towards microbial/heavy metal/ mangrove biogeochemistty ([email protected]). Dr. Wim Andriesse is a tropical soil scientist]agro-ecologist by training (Wageningen University, 1973) who, among other assignments, has been in charge of the Survey Component of the joint Indonesia-Netherlands' Acid Sulphate Soils Project in Kalimantan, Indonesia (1987-1992), and of a regional agro-eeological characterization project for West Africa, including the region's coastal lowlands and mangrove zones (1989-1995). He is presently employed as Senior Manager of International Relations/Africa with Wageningen University and Reseamh Centre ([email protected] Dr. Martinus (Tini) E.F. van Mensvoort is a soil scientist (Wageningen 1973) who worked 5 years in West Africa (1974-1979) and managed a series of projects (1980-1996) dealing with the problems of acid sulfate soils in the Mekong delta, Vietnam, with emphasis on the development and improvement of land use systems. He now (1996 - present) manages a project on environmental management of the coastal resources in the same Mekong delta of Vietnam. He is presently employed as a lecturer at the Wageningen University ([email protected]).

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