ABSTRACT
Most ecological assessments often focus on one ecosystem without investigating the integrity of contiguous ecosystems and implications thereof on the habitat of interest. From a conservation perspective, ignored ex situ processes may counteract management interventions in an ecosystem of interest if the former aren’t taken into account. This study sought to assess land-use cover change and its potential relationship or impact on the integrity of contiguous mangroves downstream. Carbon stocks data was collected from 36 systematically established 10 x 10 plots set along stratified transects. Biomass carbon was estimated based on general allometric equations applicable globally and wood densities derived within WIO region. Soil carbon estimation was done using soil samples extracted from the 36 plots. Loss on ignition procedure was used to get %SOM then calorimetric equation from adjacent creek was applied to get soil organic carbon. Mangrove cover and land use changes within Mtwapa system in Kenya was assessed using multi-temporal medium resolution Landsat TM (1992) and SPOT images taken in 2000 and 2009. Maximum likelihood classification method was used in ERDAS 9.1 and ArcGIS 10.0 softwares. Land-cover changes around the creek from 1990 to 2009 revealed a high rate of upland deforestation (3.85% yr-1) and an increase in agricultural land (13.9% yr-1). Between 1992 and 2009 the mangrove forest lost 21% of the cover, translating to 1.2% cover loss per annum which fell within the global mean of 1 – 2%. The stocking rates of mangroves in Mtwapa were estimated at 2870±295 stems/ha. The mean biomass carbon for the study area was 49.46±8.49 Mg C ha-1, with no significant variation between sites (p>0.5). Mean SOC of the study area was 196.09±19.31Mg C ha-1 giving a total ecosystem carbon of 245.54±20.95Mg C ha-1. This was quite low compared to in-country and off-shore carbon stocks and is likely due to poor forest structure in Mtwapa creek associated with anthropogenic disturbance as noted by high stump count 2,425±423 stumps/ha. There was a highly positive correlation between land use cover change (agricultural expansion – R2 = 0.70) and mangrove cover Although these mangroves recorded high stocking densities, high degradation rates and observed sedimentation due to poor land-use practices upstream have led to poor stand structure hence low carbon stocks. A landscape approach which combines sound land husbandry upstream and mangrove conservation is recommended.
CHAPTER ONE
Introduction
This chapter provides the general introduction to the mangrove ecosystem, emphasizing on the motivation for the thesis. It highlights both global and local environmental and socio-economic importance of this habitat and threats compromising the integrity of the system that necessitated need for current research with scientific justification based on available information. Statement of problem, aims and objectives of the research are well spelt out, with clear statement of research hypotheses. At the close of this chapter, scope of the study is stated.
Background of the Study
Mangroves are woody inter-tidal trees up to medium height and shrubs growing in saline coastal sediment habitats occurring along the sheltered coastlines, mudflats and riverbanks between land and sea in tropical and subtropical regions (Neukerman et al., 2008). They sustain a wide bio- diversity of flora and fauna and provide many ecosystem services such as coastal protection from storms, reduction of shoreline and riverbank erosion, stabilizing sediments and absorption of pollutants (Duke et al., 2007; IUCN, 2006).
Globally, mangroves are disappearing at alarming rates throughout the world, mainly owing to anthropogenic activities (Ong and Khoon, 2003). With recent changes in global climate and related effects, over the last 50 years, about one-third of the world’s mangrove forests have been lost (Alongi, 2002). Projections suggest that mangroves in developing countries are likely to decline by more than 25% in the next three decades (Ong and Khoon, 2003).
Traditionally mangroves in Kenya have served the local communities with a number of goods and services such as resources for building huts, for boat construction, fencing, making fish traps, source of fuel as firewood, medicine, insecticides and even fodder for livestock (Kairo, 1995). Up to date mangrove forest ecosystems have considerable economic potential in terms of timber, wood products, fisheries and tourism (UNEP, 2003a). Although economic valuation of mangroves in Kenya is still scanty (Kaino, 2012), available information indicates estimates of US$3000/ha/yr in Gazi Bay for a 12-year plantation (Kairo et al., 2009).
Recently, mangroves have been found to play an important role of sequestering and storing carbon more than any other forest ecosystem on Earth (Donato et al., 2011). However, anthropogenic activities and climate change related impacts continue to accelerate degradation of these ecosystems.
Research studies on mangrove biodiversity and conservation have increased the understanding of values, functions and attributes of mangrove ecosystems (IUCN, 2006). Mangrove in Mtwapa creek is capable of providing sustainable economic and ecological benefits to its residents (Kairo, 2002). However it is located in a peri-urban setting with close proximity to settlements and hotels (Okello et al., 2013). Studies on peri-urban mangrove forests have reported human activities as the main cause of mangrove forest degradation, (Omar et al., 2009 and Kaino, 2012).
Mtwapa creek is subjected to problem related to land use effects like urbanization, Aquaculture and agricultural activities from surrounding areas, besides unsustainable indiscriminate deforestation and pollution from raw sewage from nearby hotels, residential quarters and a government prison, (Okello et al., 2012).
Statement of the Problem
Mangrove forests sequester and store large amounts of carbon especially due to the fact that mangroves can store large amounts of carbon in the sediments besides its biomass making it very important within the frameworks of mitigating climate change. However, these ecosystems are threatened by overexploitation, conversion, land use changes and sea-level rise. About 1-2% of global mangrove cover is lost annually (Giri et al., 2011). In Kenya peri-urban mangroves have recorded higher loss rates of about 2.7% annually (Olagoke, 2012). Loss of mangroves means loss of ecosystem services.
Despite that, a lot of gaps still exist as most of the mangrove carbon stocks are unaccounted for. Spatio-temporal cover change dynamics are limited owing to complexity associated with availability and analysis of past cover change data which can only be derived remotely using satellite images and past aerial photographs. Furthermore these are complex wetland ecosystems that have been for long neglected and degradation having immensely taken place over the years.
Mtwapa mangroves are peri-urban systems subjected to a lot of anthropogenic pressure from deforestation and degradation due to upland activities. This study was carried out to estimate carbon stocks and determine the temporal cover change dynamics in order to add information on status of mangrove degradation in Mtwapa creek besides the general effects related to 1997 ENSO events.
Broad Objective
To assess carbon stocks and status of temporal cover change dynamics of peri urban mangroves of Mtwapa creek, for enhanced conservation and better management of mangrove forest resource
Specific Objectives
1. To estimate below ground and above ground carbon stocks in Mtwapa creek
2. Determine spatio-temporal changes in mangrove cover and Land cover changes between 1990 and 2009 in Mtwapa Creek
3. To establish spatio-temporal relationship between mangrove cover change and land use changes in Mtwapa creek
Research hypothesis
Ho1 There is no statistically significant variation in carbon stocks between the study sites in Mtwapa Creek.
Ho2 There is no statistically significant changes in mangrove cover and land use changes between 1990 and 2009 in Mtwapa Creek.
Ho3 There is no relationship between spatio-temporal mangrove cover change and land use changes in Mtwapa Creek.
Justification/ Significance of the Study
There is a recent information need on area, biomass and carbon entities of the coastal and marine ecosystems (Rabiatul et al., 2012). The carbon stored in a hectare of mangroves contribute to emissions as three to five hectares of other tropical forest (Murray et al. 2011) and halting current rates of mangrove deforestation would lead to mitigation of approximately 170 – 490 million tCO2e per year (Murray et al. 2011). Therefore, quantification of carbon and cover trends will highlight the importance of these ecosystems in carbon capture and storage, hence providing the basis for its conservation.
Mangroves also play a crucial role to the coastal ecosystem among them: breeding ground for fisheries, habitats for wildlife, sources of livelihood to people in the tropics and sub-tropics and provides coastal protection from storm surges (Kairo, 2001). However, degradation from unsustainable harvesting, conversion to other uses, coastal urban development, household and industrial pollution and sedimentation continue to be a threat (Giri, 2010, Bosire, 2010, Rabiatul et al., 2012 and Duke et al., 2007).
Studies on Mangrove forest cover change in Mombasa Kenya, (with satisfactory levels of accuracy at (87.5%)) estimated forest cover loss rate at 0.7% per annum (Kirui et al., 2012). Site specific forest cover assessment, in Mwache and Tudor Creeks indicates 2.7% annual loss of mangrove cover. However, spatial and temporal variations exist possibly because of legislative inadequacies and difference in habitat alteration pattern, calling for a site specific study.
Mtwapa creek mangrove forest is a peri-urban system that prompted for assessment of cover changes to ascertain threats facing this ecosystem. Because of the complexity associated with coastal fringe ecosystems, the management of these regions requires an integral view. Hence this study employed both Field survey and satellite Imagery in analyzing the Spatio-temporal dynamics of land cover and land use changes in order to provide a synoptic view which incorporates the time scale and allows a comprehensive spatial analysis of change.
Scope of the study
This study was conducted in Mtwapa creek located in the Northern Coast of Mombasa, Kenya. It focused on estimating the carbon stocks within the mangrove ecosystem and assessing surrounding spatio-temporal cover change between 1990 and 2009.
This study applied generic allometric equations and species specific wood densities for biomass estimation and analysis of carbon for above and below ground biomass. Generic allometric equations were sourced from general equations derived in Palau Micronesia (Komiyama et al., 2008). Wood densities derived from a study in Mozambique were used. This is because it falls within Western India Ocean (WIO) region, and lack of local mangrove species specific wood densities. Soil carbon was calculated based on lab analysis results and calorimetric equations derived from the analysis of soils from adjacent Tudor creek.
Image analysis was done using Landsat of April 1990, SPOT of May 2000 and SPOT of Jan 2009 which fairly falls within the dry season of between January and April. Low rainfall season in Mombasa falls between January and April, although in the year 2000 SPOT image of May had least cloud obscurity despite being captured in May and hence its inclusion in the study.
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Item Type: Kenyan Topic | Size: 66 pages | Chapters: 1-5
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