Marginal land use and value characterizations in Lagos: untangling the drivers and implications for sustainability

Lagos, the leading African megacity, is a coastal city located in creeks and riparian environment. In all parts of the city, transactions in marginal lands—riparian or water-logged areas—are increasingly becoming more noticeable. However, while previous studies have focused upon normal land transactions, the dynamics of land uses in marginal regions remain largely unexplained. Information on the dynamics of informal land transactions in the marginal regions of Lagos city is important for urban sustainability. This study therefore interrogates the attributes, uses, values and drivers of marginal land in Lagos using generalized linear model (GLM). Findings show that the predominant land use in marginal areas of Lagos is residential, majority of the lands are less than full plot size, close to river channels and less accessible, and the mean price ranges from NGN 3,156,908 to NGN 4,052,158. The GLM estimations show that distance to river channels/lagoon and buyer’s status have more significant influence on marginal land uses and values in Lagos. These findings have significant policy and practical implications for the city’s land use and sustainability. For urban and environmental sustainability, there is need to stem transactions in coastal marginal environments of Lagos for their obvious implications for climate change, flooding, erosion, sea incursion, building collapse, natural parks and public spaces, river channels and urban greening.     

Anthropogenic impacts on suspended sediment load in the Upper Yangtze river

Climate change and human disturbance drive catchment erosion and increase riverine sediment load sensitively in small and medium-sized watersheds. This is not always true in large basins, where aggregation and buffering effects have dampen the ability to determine the driving forces of sedimentation. Even though there are significant responses to sedimentation in large river basins, it is difficult to get a precise quantitative assessment of specific drivers. This paper develops a methodology to identify driving forces that change suspended sediment load in the Upper Yangtze river. Annual runoff and sediment load data from 1954 to 2005 at the Yichang gauging station in the Upper Yangtze basin, daily precipitation data from 60 meteorological stations, and survey data on reservoir sediment were collected for the study. Sediment load/rainfall erosivity (S/R), is a new proxy indicator introduced to reflect human activities. Since the mid-1980s, S/R in the Upper Yangtze has dramatically declined from 0.21 to 0.03 (×10¹⁰ t ha h MJ⁻¹ mm⁻¹), indicating that human activity has played a key role in the decline of the suspended sediment load. Before the mid-1980s, a higher average S/R is attributed to large-scale deforestation and land reclamation. A significant sediment decrease occurred from 1959 to 1961 during an extreme drought condition, and an increase in sedimentation in 1998 coincided with an extreme flood event, which was well recorded in the S/R curve. This indicates that the S/R proxy is able to distinguish anthropogenic from climate impacts on suspended sediment load, but is not necessarily indicatory in extreme climate events. In addition, typical drivers of riverine sediment load variation including soil conservation projects, reservoirs construction, and land use/cover change are discussed.     

Sedimentation rates and erosion processes in the lagoon of Venice

Since the early 1990s in the lagoon of Venice, especially in the central basin, the surface sediment underwent high re-suspension and sedimentation changes and water turbidity increased both because of the disappearance of the macroalgal coverage and the harvesting of the Manila clam Tapes philippinarum Adams and Reeve, which had rapidly colonised the bottom free of macrophytes. Clams are harvested with hydraulic and mechanical dredges which remove and re-suspend surface sediments causing the transport and loss of the finest materials. Sediment transport and re-deposition in the lagoon have been monitored with sediment traps placed onto the bottoms near the Malamocco mouth (st. A), the Lido watershed (st. B) and the mainland (sts. C and D). From 1989-1993 to 1998-1999 sedimentation rates increased significantly at st. A (from 41 to 228 kg DW m(-2) year(-1)), st. B (from 65 to 760 kg DW m(-2) year(-1)) and st. C (from 140 to 721 kg DW m(-2) year(-1)), while at st. D sedimentation rates increased only by ca. 20%. In parallel sediment grain-size changed with a loss of the finest fraction especially near the mainland. The erosion or sedimentation status, acquired by utilizing sedimentation devices placed onto the bottoms, showed that sts. B, C, D were affected by sediment losses, while st. A, populated by seagrasses and characterised by seasonal variations which depend on the shoot development, did not show any significant bathymetric change on an annual basis. The highest sediment erosion was recorded at st. D (ca. 3.6 cm year(-1)) whereas a loss of ca. 1.5 and 0.5 cm year(-1) was found at sts. C and B, respectively, which accounted for a mean loss in the central lagoon of ca. 1.2 million tonnes year(-1). Those data agree with the previous indirect estimation of sediment loss which was based on the number of fishing boats operating in the lagoon on an annual basis.     

Sediment and carbon accumulation in a small tidal basin: Yuehu,Shandong Peninsula,China

A small sedimentary basin (the Yuehu lagoon), located at the eastern tip of Shandong Peninsula, China, was selected to study its filling by sediment and the vertical flux of particulate organic carbon in response to natural/anthropogenic processes. Surficial and short core sediment samples were collected and analyzed to obtain data sets of grain size, organic carbon content, deposition rates and vertical fluxes of sediment and organic carbon. The analytical results show that the lagoon is covered mainly with fine-grained sediments with high deposition rate and particulate organic carbon content being found from the central part of the mud deposit. The sediment balance of the lagoon indicates high denudation rates of the catchment basin, which may be related to soil erosion in response to farming and land use pattern changes. Furthermore, preliminary analysis of the organic carbon fluxes of the Yuehu lagoon and other embayments of the region shows that these coastal systems make an important contribution to the regional shallow sea carbon burial.     

Present to future sediment transport of the Brahmaputra River: reducing uncertainty in predictions and management

The Brahmaputra River in South Asia carries one of the world’s highest sediment loads, and the sediment transport dynamics strongly affect the region’s ecology and agriculture. However, present understanding of sediment conditions and dynamics is hindered by limited access to hydrological and geomorphological data, which impacts predictive models needed in management. We here synthesize reported peer-reviewed data relevant to sediment transport and perform a sensitivity analysis to identify sensitive and uncertain parameters, using the one-dimensional model HEC-RAS, considering both present and future climatic conditions. Results showed that there is considerable uncertainty in openly available estimates (260–720 Mt yr^?1) of the annual sediment load for the Brahmaputra River at its downstream Bahadurabad gauging station (Bangladesh). This may aggravate scientific impact studies of planned power plant and reservoir construction in the region, as well as more general effects of ongoing land use change and climate change. We found that data scarcity on sediment grain size distribution, water discharge, and Manning’s roughness coefficient had the strongest controls on the modelled sediment load. However, despite uncertainty in absolute loads, we showed that predicted relative changes, including a future increase in sediment load by about 40 % at Bahadurabad by 2075–2100, were consistent across multiple model simulations. Nevertheless, for the future scenarios we found that parameter uncertainty almost doubled for water discharge and river geometry, highlighting that improved information on these parameters could greatly advance the abilities to predict and manage current and future sediment dynamics in the Brahmaputra river basin.     

Spatio-temporal variation of dissolved inorganic nutrients related to hydrodynamics and land use in the mangrove-fringed Segara Anakan Lagoon, Java, Indonesia

Segara Anakan is a mangrove-fringed lagoon in Java, Indonesia, which is affected by human activities in the lagoon and its hinterland. Nutrient and sediment input from the Citanduy River which drains an agriculture-dominated hinterland is thought to be an important factor for ecosystem degradation. From dry and rainy season investigations of dissolved inorganic nutrients between May 2004 and August 2006 we infer that the nutrient inventory of Segara Anakan is controlled by a complex mixture of anthropogenic and natural sources and processes. Maximum inputs into the western lagoon were supplied by the Citanduy during the rainy season while tidal exchange with the Indian Ocean dominated in the eastern lagoon with little freshwater input. During the dry season recycling in mangroves appeared to be an additional source of nutrients to the lagoon. Despite an extremely high population density and intensive agriculture in the hinterland nutrient pollution and eutrophication in the lagoon were low to moderate on a global scale. It is probably due to the short residence time of water in the shallow lagoon which indicates that major part of the land-derived nutrient input is rapidly exported to the sea. Although Segara Anakan is a highly perturbed system for decades, it appears that still natural processes exert major control on the nutrient inventory of the lagoon.     

Quantifying the erosion processes and land-uses which dominate fine sediment supply to Moreton Bay, Southeast Queensland, Australia

In this paper, the contributions from the three major erosion sources in the catchments of Moreton Bay are quantified, specifically for the <10 microm sediment size class. The erosion sources are classified as (i) sheet erosion from cultivated land, (ii) sheet erosion from uncultivated land, and (iii) subsoil erosion from gullies and channels. The catchments were the Brisbane and Logan rivers as well as the coastal catchments. A GIS based analysis of erosion risk was used to define areas of high erosion potential in each of the erosion source types. Radionuclide concentrations of 137Cs and 226Ra were measured on the <10 microm fraction of eroding soils from these areas and then compared to concentrations on the same size fraction on deposited sediments within the rivers. A mixing model was then used to calculate the contributions from the different sources to the sediments. The contributions in the Brisbane and Logan catchments were found to be subsoil erosion (approximately 66 +/- 10%); sheet erosion from cultivated lands 33 +/- 10% and sheet erosion of uncultivated land 1 +/- 10%. Surface and subsoil erosion contributions from the coastal catchments were found to be variable.     

Conflicts between stakeholder groups affecting the ecology and economy of the Segara Anakan region

This study analyses how the conflict potential between different stakeholder groups is affecting the ecology and economy of the Segara Anakan region, a mangrove-fringed lagoon in central Java, Indonesia. The lagoon’s increasing sedimentation/silting up and the area’s expanding population has led to various interest groups conflicting with one another over how the resources of the lagoon and its surrounding area are to be utilized. Conflicts arise between occupational and ethnic groups in the lagoon’s bordering villages in the context of a transformation from fisheries to wetland agriculture. Land and mangrove use is therefore a cause for conflict between multiple groups, including Javanese fishermen, Sundanese farmers from Central and West Java and external shrimp farm owners. A result of the “Segara Anakan Development Project”—an 8-year undertaking that began in 1996—is that the lagoon was frequently dredged. Due to the dredging and resulting contamination of the land, a regional clash was triggered between Sundanese farmers and Javanese fishers. Our study reveals that the conflict potential between the various interest groups in the Segara Anakan Lagoon area could be reduced if the scarcity of natural resources were alleviated. Religious aspects also play a large role in marine resource utilization. Recognizing that the human utilization of natural resources is strongly symbolic and thereby culturally defined, we unravel the resource conflicts in our study area and offer some strategic approaches towards more sustainable outcomes.     

Environmental degradation by mud in tropical estuaries

In wet tropical countries, the intense rainfall and the lack of effective restrictions on human activities in the river catchment leads to increased rates of soil erosion. This has increased the sediment loads many times over from the natural level. As a result, estuarine and coastal waters are becoming increasingly muddy with associated losses for society in terms of increased flooding and a degradation of the environment, the fisheries and the economic use of these waters. It is suggested that science-based models be used to predict the fate of mud in estuaries and coastal waters when planning development in river catchments, particularly in wet tropical countries. This would help integrate land and water management. Modelling technology is demonstrated by a combination of field and model studies in four turbid tropical estuaries, namely the Fly River in Papua New Guinea, the Mekong River in Vietnam, the Cimanuk River in Indonesia, and Hinchinbrook Channel in Australia. The final model is adapted to local conditions and extensively uses data assimilation especially for open boundary conditions. There can be a feedback between the hydrodynamics and the mud dynamics when the system silts; in wet tropical countries this can occur rapidly, sometimes in only 30 years. Electronic Publication     

Regimes of human and climate impacts on coastal changes in Vietnam

Vietnam is a tropical to subtropical country located on the eastern Asian coast where the Red (Song Hong) and Mekong rivers discharge into the sea. The catchments of these two transboundary rivers cover parts of six countries, and their water and sediment discharges greatly influence the coastal seas of Vietnam. The impact of human activities include changes in the supply and distribution of water, sediments, and nutrients; changes in the relationships and balance among dynamically interacting factors and processes; and changes in the quality of the coastal and marine environments due to the increased use and accumulation of pollutants and the loss of habitats. These impacts have resulted in increasing unpredictability and severity of coastal problems such as floods, erosion, sedimentation, and saltwater intrusion; environmental pollution; and the degradation of ecosystems, with accompanying decrease in biodiversity and fishery productivity.     

长江流域水土流失及其防治

对长江流域水土流失现状和分布作了具体分析,指出建国以来水土流失有发展趋势;从土壤资源、土地资源、水资源与生态环境等方面,阐述了水土流失对资源环境的破坏性;着重指出了长江流域的流失物质、泥沙输移比和沉积规律与我国黄土高原流失区有着不同的特点,同时存在着比黄土高原更大的潜在危险;针对长江流域水土流失特点、发生原因并结合兴建三峡工程和长江经济带的开发,从战略高度提出了防治水土流失的策略和措施。     

Present and future environmental impacts on the coastal zone of Berau (East Kalimantan, Indonesia), a deductive scenario analysis

Using the drivers–pressures–state–impact–responses (DPSIR) analytical framework, local stakeholder respondents and experts were interviewed to construct and prioritize a causality network that links ecosystem state of the coastal waters of Berau (East Kalimantan, Indonesia) with societal drivers of change. Particularly on the perceived top priority drivers and pressures, consensus among respondents was considerable. The constructed network was found to be consistent with literature findings from elsewhere in SE Asia. This causality network was then confronted with a local articulation of the SRES scenarios (IPCCs Special Report on Emissions Scenarios: A1, A2, B1, B2), and four plausible trajectories of future change were deduced over a period of 20?years, until 2030. Our scenario articulations differed greatly in the projected immigration influx into the region, in local economic growth and in institutional strength of governance. Under business-as-usual conditions, it is foreseen that fisheries will continue to overexploit the resource, and inland and mangrove deforestation, as well as sediment and sewage loading of the coastal waters, will increase, leading to declines in coral and seagrass extent and depleted fisheries. Scenarios with continued immigration (~A1, A2) will probably aggravate this pattern, whereas those with reduced immigration (~B1, B2) would appear to lead to considerable improvements in the state of the coastal waters of Berau.     

Historical area and shoreline change of reef islands around Tarawa Atoll, Kiribati

Low-lying reef islands on atolls appear to be threatened by impacts of observed and anticipated sea-level rise. This study examines changes in shoreline position on the majority of reef islands on Tarawa Atoll, the capital of Kiribati. It investigates short-term reef-island area and shoreline change over 30 years determined by comparing 1968 and 1998 aerial photography using geographical information systems. Reef islands have substantially increased in size, gaining about 450 ha, driven largely by reclamations on urban South Tarawa, accounting for 360 ha (~80 % of the net change). Widespread erosion and high average accretion rates appear to be related to disjointed reclamations. In rural North Tarawa, most reef islands show stability, with localised changes in areas such as embayments, sand spits and beaches adjacent to, or facing, inter-island channels. Shoreline changes in North Tarawa are largely influenced by natural factors, whereas those in South Tarawa are predominantly affected by human factors and seasonal variability associated with El Niño—Southern Oscillation (ENSO). However, serious concerns are raised for the future of South Tarawa reef islands, as evidence shows that widespread erosion along the ocean and lagoon shorelines is primarily due to human activities and further encroachment onto the active beach will disrupt longshore sediment transport, increasing erosion and susceptibility of the reef islands to anticipated sea-level rise. Appropriate adaptation measures, such as incorporating coastal processes and seasonal variability associated with ENSO when designing coastal structures and developing appropriate management plans, are required, including prohibiting beach mining practices near settlements.     

Regional challenges in tourist wetland systems: an integrated approach to the Ria Formosa in the Algarve, Portugal

Coastal change and coastal erosion have been a long-existing source of environmental changes. Traditionally, regional changes in wetland systems and their relations to agriculture, industry and urbanization are a major cause for concern. Nowadays, coastal distress has reached even global proportions: the problems of coastal change are strongly linked to the loss of fragile ecosystems, eutrophication and loss of biodiversity. Given that over 70 % of all human activity is in coastal areas, it is clear that many environmental and socio-economic changes occur at a local level and manifest themselves in a spatial context. The physical effect on the geographic morphology is evident in the related consequences for land use. A deep understanding of the changes in land use, and simultaneously in coastal erosion, calls for the integrated monitoring of the most relevant effects in fragile regions. The Ria Formosa wetland system is a unique and very special wetland system in the Algarve (Portugal) and has been integrated in the NATURA 2000 network. The strong symbiosis between nature, agriculture and fisheries, as well as tourism, in the Algarve has led to spatial-ecological synergy. By using coastal recession analysis techniques by means of remote-sensed imagery from 1987, 1989, 2000 and 2007 and by combining this information with available data sets on surface erodibility, a cost surface on multitemporal transitions of land-use classes from the CORINE Land Cover data allows us to assess and integrate a decision-making framework by means of GIS. The novelty of this combined approach to land-use management is the blend of spatial analysis and remote-sensing techniques that share important information on ecosystems at risk. Our findings suggest a growing concern to the area brought by anthropogenic activity. This is studied to a spatial accounting of the distribution of land changes and transitions, where (1) a significant loss of coastal area is witnessed along the Ria Formosa, leading in particular to loss of agricultural land. (2) This loss is underpinned by an increase in leisure facilities to respond to the tourism demand of the region of the Algarve, while landscape metrics suggest that these areas are more volatile for coastal erosion. (3) Simulation through Markov chains on the land use and effects of urban, agricultural, forest and wetland dynamics suggests that by 2026, it is expected to continue to have an increase in urban land, leading to an augmented vulnerability of coastal erosion processes brought by the loss of forest areas which protect from erosion given the root system that directly protects from the existing wave energy and helps sedimentation processes. The above methodology and the availability of data that are freely available render such a combined approach interesting for many other regions of the world, where tourism, coastal change and regional balance are of the utmost importance for sustainable development. The advanced research tools presented here are of critical importance for coastal zone degradation management.     

Environmental quality of transitional waters: the lagoon of Venice case study

The health status of European aquatic environments, including transitional waters such as coastal lagoons, is regulated by the Water Framework Directive (WFD), which requires the classification of the water bodies' environmental quality and the achievement of a good ecological status by 2015. In the Venice lagoon, a transitional water body located in the northeastern part of Italy, the achievement of a good ecological status is hampered by several anthropogenic and natural pressures, such as sediment and water chemical contamination, and sediment erosion. In order to evaluate the lagoon's environmental quality according to the WFD (i.e. 5 quality classes, from High to Bad), an integrated Weight-of-Evidence methodology was developed and applied to classify the quality of the lagoon water bodies, integrating biological, physico-chemical, chemical, ecotoxicological, and hydromorphological data (i.e. Lines of Evidence, LOE). The quality assessment was carried out in two lagoon habitat typologies (previously defined on the basis of morphological, sediment, and hydrodynamic characteristics) which were selected taking into account the ecological gradient from sea to land, and the differences in anthropogenic pressure and contamination levels. The LOE classification was carried out by using indicators scored by comparing site specific conditions to reference conditions measured in lagoon reference sites, or provided by local, national or European regulations (e.g. Environmental Quality Standards, EQS, for chemicals). Finally, the overall quality status for each water body was calculated by a probabilistic approach, i.e. by reporting the final result as the frequency distribution of quality classes. The developed procedure was applied by using data and information concerning selected LOE and collected from monitoring programs and research studies carried out in the last 15 years in the lagoon of Venice. A set of sampling stations characterized by spatially and temporally coherent information for each LOE was selected, and among these stations, potential reference sites for each water body typology were identified. The quality assessment highlighted that there are specific lagoon areas, especially those located near the industrially developed area, which are highly affected by anthropogenic activities, and that chemical contamination is one of the main pressures affecting ecological status (e.g. macro-benthonic biodiversity) in the Venice lagoon. The integrated quality assessment procedure that was developed provided a new tool supporting decision making, as well as lagoon assessment and management.     

长江上游不平衡水沙输运对三峡库区泥沙淤积影响

2003～2017年以三峡水库为核心的长江上游水库群运行和联合调度从宏观上改变上游河流泥沙时空分布规律,金沙江已不是三峡入库泥沙最大供沙区;长江上游水沙输运集中在汛期5～10月,1956～2002年水沙峰值基本同步,而三峡水库蓄水后2003～2017年水沙峰值不同步,流量特性曲线由顺时针转为逆时针,出现滞后现象。入库泥沙锐减后并未降低三峡库区细颗粒泥沙淤积率,2014～2017年汛期5～10月淤积率增加至85.2%,其中d0.031 mm的极易发生絮凝的泥沙所占比例最高(63.5%,2009～2013年),典型河段现场观测到大量泥沙絮团,所以三峡库区极可能存在细颗粒泥沙絮凝。入库水沙不平衡也使得朱沱-清溪场河段出现泥沙冲刷。     

Spatio-temporal variation of macrobenthic communities in the mangrove-fringed Segara Anakan lagoon, Indonesia, affected by anthropogenic activities

The benthic macrofauna of the Segara Anakan lagoon, Java, Indonesia and its fringing mangroves were investigated between May 2004 and August 2006. This lagoon has been affected by various human activities for decades, in particular fishing, effluents from agriculture and industry, and illegal deforestation. In total, 163 taxa were identified, including 127 species occurring in the mangrove forest and 59 species in the subtidal. Mean density of macrobenthos was 2.5-fold higher in the central (881.8 ± 1,151.3 ind. m^?2) than in the eastern mangrove site (356.3 ± 218.8 ind. m^?2). Community structures differed significantly between these sites and showed a serial shift during the investigation period. Gastropods dominated the community in the central mangrove location, whereas sipunculids, polychaetes and gastropods had similar densities in the eastern site. Differences in community composition were best explained by three sediment properties: pore water salinity, δ¹³C_org, and C_org/N. It is suggested that small-scale heterogeneity of food availability and quality is a main factor determining the small-scale variability of the community composition. Compared to other Indo-West Pacific mangroves, species richness and densities are high. However, the dominance of specific taxa, especially of opportunistic species and the comparably low species richness in the subtidal of the lagoon may be attributed to the high sediment input by rivers in the central part and to the large-scale cutting of mangroves. Continuous tree logging will probably lead to a further spread of two fast growing understorey plants and thus to an increase of uniform swamp sites and a decrease of micro-habitats for benthic macrofauna. To our knowledge, this is the first detailed study on the spatio-temporal variation of benthic macrofauna in mangroves of Indonesia.     

Impact of dredging in a shallow coastal lagoon: Microtox Basic Solid-Phase Test, trace metals and Corophium bioassay

The aim of this work was to measure survival of the amphipod Corophium insidiosum and luminescence inhibition in the marine bacterium Vibrio fisheri on surface sediment samples collected from a shallow coastal lagoon (Pialassa Baiona, northern Adriatic Italian coast) before execution of dredging operations to deepen the main inner channel of the lagoon and restore the water circulation. Trace metal (Cd, Cu, Cr, Hg, Ni, Pb) concentrations, grain size and organic carbon matter content as loss of ignition were also measured. Toxicity testing with V. fisheri was carried out according to the Microtox Basic Solid-Phase Test (BSPT) protocol. The preliminary outcomes of this work show that: (a) the investigated area can be categorised as moderately degraded; (b) there is no evident spatial pattern in sediment toxicity and trace metal concentrations; (c) Microtox responses are not biased by sediment characteristics such as silt, clay and organic matter content.     

Land use and land cover change affecting habitat distribution in the Segara Anakan lagoon, Java, Indonesia

This study quantifies and spatially characterizes land use and land cover changes in the Segara Anakan lagoon (SAL), Java, Indonesia, from 1987–2006. Classification of four satellite (SPOT) images from the years 1987, 1995, 2004 and 2006 and field ground truth data from 2004 and 2005 were used for map generation. The results show major changes in the western area of the SAL, with large area increases of rice fields, dry land agriculture, aquaculture and rural areas, and decreases in mangrove cover, mud flat and lagoon area. In the eastern area, minor decreases in mangrove area and increase in aquaculture, rural and industrial areas were also observed. Changes are due to the filling of the lagoon with riverine sediments derived from the hinterland and to mangrove conversion and resources exploitation. The results of this study provide basic information which is required for developing measures towards a sustainable management and conservation of the SAL.     

Status, diversity and distribution patterns of mangrove vegetation in the Segara Anakan lagoon, Java, Indonesia

In the Segara Anakan lagoon, Java, 21 tree species and 5 understorey genera have been identified. Average tree density is 0.80 ± 0.99 Ind./m2 with 48.71% seedlings and an average basal area of 9.86 ± 10.54 cm2/m2. Tree density and diversity are high in the eastern part of the lagoon, located near the city of Cilacap. There, the dominant tree species are Aegiceras corniculatum, Nypa fruticans and Rhizophora apiculata, of which the two latter are characteristic for mature forests. By contrast, understorey species and the pioneer species (Avicennia alba, Aegiceras corniculatum and Sonneratia caseolaris) dominate the central lagoon where several rivers discharge. Compared to former studies, seedling density and tree diameter in the central lagoon has declined considerably and tree species dominance has changed. The high sedimentation rates and deforestation are likely to prevent the formation of a mature forest there. Tree communities are more equilibrated in the eastern lagoon which points to a more stable and less disturbed mangrove forest.