ABSTRACT
Mangrove deforestation and degradation through anthropogenic activities accelerates climate change process. Carbon capture and storage in mangroves is about 3-5 times more per unit area than any vegetated ecosystem. Studies which experimentally determine differential emissions are globally limited and completely non-extent in Kenya. This study sought to establish the contribution of human activities on carbon emissions from mangrove ecosystems along the Kenyan coastline using two heavily impacted peri-urban creeks: Tudor and Mwache in Mombasa Kenya as a case study. Anthropogenic and natural drivers have subjected mangroves to wanton degradation. Stratified random sampling along intertidal transect with 10x10m plots laid 100m apart were used to collect vegetation and soil data.
The data was analyzed using EXCEL and STATISTICA version 8.0 software. The statistical analyses included descriptive data analysis, linear comparisons, ANOVA, and means comparisons using Tukey test. There were significant differences in ecosystem carbon (p=0.005) between highly degraded and less degraded sites within the creeks. Carbon emissions were estimated at 261.96t.ha-1yr-1 and 335.13t.ha-1yr-1 CO2 equivalents for Mwache and Tudor respectively. The unprecedented high degradation rates, which exceed by far the national, mean and probably the global mean shows that the mangroves are highly threatened due to the discussed pressures. There is need to strengthen the governance regimes through enforcement and compliance and more capacity in mandated institutions e.g. NEMA, KFS, and community involvement e.g. CFAs to curb illegal logging and distilleries. Initiating restoration activities where natural regeneration has failed, providing residents with alternative and cheap sources of energy and building materials and enforcing a complete moratorium on wood extraction will allow recovery.
CHAPTER ONE
INTRODUCTION
Background Information
Mangrove ecosystems are located at the sea – land interface. Globally, there are at least 68 species of mangroves restricted to approximately 25°N and 25°S of equator and estimated to cover an area of between 180,000 and 200,000 km2 (Spalding et al.,2010; Giri et al., 2011). Although spatially limited, (covering 0.7% of the total tropical forests of the world) (Giri et al., 2011), mangroves are keystone coastal ecosystems. They offer a considerable array of ecosystem goods and services. They offer critical ecological functions (Duke et al., 2007), are centers of rapid C cycling (Bouillon et al., 2008; Kristensen et al., 2008) and have recently been found to rank among the most C-dense forests in the tropics due to deep organic-rich soils (Donato et al., 2011; Kauffman et al., 2011).According to Alongi (2012), mangroves sequester 14% of C in the oceans despite occupying less than 0.5% of the coastal ocean. This is mainly captured in the above ground and below ground vegetation components.
The biggest part which is up to 90% is captured and stored in the sediments (Bouillon et al., 2008; Donato et al., 2011; Kauffman et al., 2011) showing that mangrove sediments have carbon storage potential. The rate of C storage in the sediments is approximately 10 times the rate observed in temperate forests and 50 times the rate observed in tropical forests per year (Laffoley, 2009). Overall, mangroves have a far greater capacity (per unit surface area) than terrestrial habitats to achieve long-term C sequestration in sediments, arising in part from the extensive below ground biomass burying approximately 18.4 Tg C per year (Laffoley, 2009).
Mangroves are being degraded at rapid rates globally with 1-2 % per year loss (Duke et al., 2007; FAO, 2007). Primarily this degradation is due to over-exploitation and land conversion affecting organic soils to deep layers. As land use affects soils to deeper layers, the large C stores generate large GHG emissions when disturbed (Donato et al., 2011).Since reducing C emissions will be a global concern for centuries, long-term C sequestration capacity must be accounted for in the benefits associated with mangrove restoration and protection.The large C- stores of mangroves end up generating large amount of GHGs (Donato et al., 2011). Improved estimates of mangrove C storage have recently been obtained at global scales (Donato et al., 2011; Kauffman et al., 2011), but to date estimates of C emissions following degradation in Kenya are less studied hence the need for this study.
Despite its relatively small overall concentration in the atmosphere, CO2 is an important component of Earth's atmosphere because it absorbs and emits infrared radiation thereby playing a role in the greenhouse effects. Naturally CO2 in the atmosphere is re-absorbed by vegetation and therefore deforestation and land conversion reduces the valuable natural C sinks which helps to maintain a balance in the Earth's atmosphere. According to IPCC (2007), about 20% of global C emissions is directly contributed by deforestation and since mangroves store about 3-5 times more C per unit area than all known forest ecosystems, their continued degradation whose rates far exceeds that of tropical rainforests significantly contributes to elevated C emissions.
The effect of all this extra CO2 in the atmosphere is that the overall temperature of the planet is increasing (global warming) on a day-to-day basis but the climate is changing in unpredictable ways (from floods and hurricanes to heat waves and droughts). Rising CO2 concentrations are also likely to have profound direct effects on the growth, physiology, and chemistry of plants, independent of any effects on climate (Ziska, 2008). According to UNEP- WCMC (2006), 35% loss of mangroves over the past two decades resulted in release of large quantities of C aggravating global warming phenomenon. Unfortunately, studies monitoring C losses over longer periods, or the emission of other GHGs, are lacking (Bouillon, 2011).The forecasted consequences of climate change on ecosystems will be more severe if conservation is not given an upper arm as a strategy to mitigate GHGs emissions.
In Kenya, nine (9) identified mangrove species (Spalding et al., 2010), distributed in six families and eight genera occur along the coastline (Kirui et al., 2012). This is only 3% of the forest area in Kenya, or 1% of the total area of the country; which makes mangroves a scarce and very valuable resource (Kokwaro, 1985; Dahdouh-Guebas et al., 2000).Over the years, Kenyan mangroves have been subjected to ever-increasing human population and economic pressure and degradation, which are directly reflected in increased coastal erosion, shortage of building material and firewood and reduction in fisheries (Kairo et al., 2001). As forests are removed, the organic C built up over decades to millennia is subject to increased re-mineralization and erosion, and therefore to release to the atmosphere as CO2 (Bouillon, 2011).
Recent detailed studies have indicated that some mangrove forests have suffered the highest ever-recorded losses of mangroves globally. Specifically, Mombasa mangroves comprising of Tudor and Mwache Creeks have suffered between 46 and 87% cover loss between 1992 and 2009 translating to annual loss rates of 2.7 – 5.1% (Adewole, 2012; Bosire et al., 2014;
Kaino, 2012) far exceeding the global mean of 1 – 2%.The high degradation rates documented for Mombasa mangroves provided an opportunity to quantify C emissions due to unprecedented cover loss.
Statement of the problem
Mangroves sequester 14% of C in the oceans despite occupying less than 0.5% of the coastal ocean in the world. However, they are being deforested and degraded at rapid rates globally with 1-2% per year loss. Primarily this degradation is because of over-exploitation and land conversion which disturbs and exposes carbon stored in sediments leading to generation of large quantities ofGHGs.Information on deforestation, degradation, land-use change, and how they contribute to global anthropogenic CO2 emissions is available. Past studies quantified total ecosystem C stocks but did not specifically assess the impact of deforestation on C emissions. Carbon emissions from these ecosystems are uncertain; due to lack of broad-scale data on C emissions thus the need for this study.The study sites (Tudor and Mwache) are facing pressures due to increased population and dependence on mangroves for life sustenance and effects of climate change, which have led to some of the highest globally recorded rates (2.7 – 5.1% p.a.) of mangroves loss.
Broad objective
To estimate C emissions from mangrove forests resulting from degradation in Tudor and Mwache creeks for mangroves management and conservation.
Specific Objectives
1. To estimateC stocks resulting from mangrove degradation within and between the two creeks.
2. To estimate C emissionsfrom mangrove degradation in Tudor and Mwache creeks.
Hypotheses
Ho1: There is no significant difference in C stocks within and between Tudor and Mwache creeks.
Ho2: There is no significant difference in C emission due to mangroves degradation in Tudor and Mwache creeks.
Justification
Mangroves offer a considerable array of ecosystem goods and services and critical ecological functions. Mangroves sequester 14% of C and store 3 – 5 times more C than any vegetated ecosystem. Mangroves have experienced the highest degradation rates, which are times more than the tropical forests. Globally mangroves are degraded at 1 – 2% p.a. whileTudor and Mwache creeks have recorded the highest degradation rates of 2.7 – 5% p.a. (Adewole, 2012; Kaino, 2012). Carbon emissions from land-use change in mangroves are also not well understood. The fate of the below ground C is also understudied.While data exists on C stocks for different sites globally (Donato et al., 2011; Kauffman et al., 2011) and for the study sites (Adewole, 2012; Kaino, 2012; Mwihaki, 2012), data on differential emissions due to severe degradation is very limited and completely lacking in the Kenyan situation. The rate of C emissions following mangrove degradation will elucidate the impact of this loss in aggravating global warming and associated climate change effects. Estimating C emission is paramount as it gives a detailed analysis of C emissions and shows a linkage between anthropogenic activities, C emissions and climate change. The information is useful to mangroves managers, conservationists, and climate change experts, among others. It assists in forecasting and predicting the trends and addressing adverse environmental challenges facing the world concerning GHGs.
Scope and Limitations
The study was carried out in the mangrove forests of Tudor and Mwache creeks. The sites were selected based on the presence of widespread mangroves, die back areas due to natural process like El-Niño and high anthropogenic pressures due to the ever-increasing population from the adjacent informal settlements. The study focused on the assessment of the differences in C stocks in three carbon pools between the highly degraded and relatively less degraded sites and consequently estimated Cemissions. Although there was limited access to equipment for accurate field assessment of CO2 emissions, general standardized protocol were used in estimation of CO2 emissions.
Definition of terms
Anthropogenic – the human impact (influences) on the environment. It is the effect or the object on the environment resulting from human activity (IPCC, 2003).
Carbon sink – this is a natural or an artificial reservoir that accumulates and stores some carbon containing chemical compounds for an indefinite period.
Deforestation- The conversion of forest to other land uses, e.g. agriculture, and typically involves release of GHGs from loss of biomass and disturbance of the soil, dead wood and litter (Dargusch et al., 2010).
Degradation - refers to changes within a forest, which negatively affect the structure or function of the forest, and its GHG storage capacity. Forest degradation practices include unsustainable commercial logging and over-harvesting of fuel wood and degradation is commonly a precursor to deforestation (FAO, 2006).
Global warming - the rise in the average temperature of Earth's atmosphere and oceans mainly by increasing concentrations of greenhouse gases produced by human activities such as the burning of fossil fuels and deforestation.
Greenhouse effect- a phenomenon whereby atmospheric gases with special physical properties (like carbon dioxide, methane and water vapour) help trap heat received from the sun, making the earth to be warmer than it could be otherwise.
Highly Degraded - The changes within the forest which negatively affect the structure or function of the stand or site, and thereby lowering the canopy to less than 40% (FAO, 2009) Relatively Less Degraded - The changes within the forest which negatively affect the structure or function of the stand or site, and thereby lowering the canopy to about 80% (FAO, 2009).
Peri-urban- according to Hartel (2005), this is the transition zone, or interaction zone, where urban and rural activities are juxtaposed, and landscape features are subject to rapid modifications, induced by anthropogenic activities.
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Item Type: Kenyan Topic | Size: 48 pages | Chapters: 1-5
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