A study was conducted to assess the impacts of elevation, tree species and management on carbon stock on the slopes of Rungwe Mountain in Tanzania. Twenty 15 m radius plots with trees of DBH >10 cm were used to collect trees measurements as well as soil samples at depths of 10 cm, 20 cm and 30 cm. Tree data collected were calculated and analyzed for tree biomass and carbon by using the Tree Biomass Equations (TBE) while soil samples were analyzed for total soil carbon using oxidative reduction method in which soils were combusted at about 600°C in a muffle furnace to released CO<sub>2</sub> and SO<sub>2</sub> gases carried by the oxygen flow into cells. The results showed that aboveground carbon content increased with altitude ranging from 9.2 t/ha at 2031 m to 561.7 t/ha at 2312 m.a.s.l due to little forest disturbance at high altitudes. However, the trend changed drastically at 2312 m.a.s.l. Soil carbon content tended to increase down the slope ranging from 3.8 t/ha at 2.312 to 4.7 t/ha at 2031 m.a.s.l, respectively. In general, there is limited awareness on sustainable management of forest resource in the study area. It is necessary to empower local communities to monitor and manage their forest resources so that they can contribute to climate change mitigation and income generation through carbon trade under REDD initiative
International audienceCharacteristic trends in landuse and climate highlight critical challenges in future resource management along the tropical topoclimosequence (TCS) of the Rungwe Volcanic Province (RVP), a major headwater biodiversity and food reservoir of Tanzania. The RVP orography supports a coherent distribution of agroecosystems and livelihoods, from hot irrigated lowlands to endangered afromontane forests above 1500 m.a.s.l. Recent increases in deforestation, land fragmentation and soil denudation/compaction in the densely populated TCS were combined with a strengthened need and consumption of water in the lower, warmer and drier end-member. Consistent with a regional decline of the long rains, a considerable (up to 30%) decrease in annual rainfall and a pervasive decline of the Lake Masoko (LM) aquifer testifies to a strong aridification trend. We suggest here that current landuse and demographic trends likely amplified the hydrological response of the TCS to regional and global warming. Testing such a hypothesis, however, requires improved local monitoring, to allow scaling and quantification of local hydrological budgets associated with landuse impacts, and evaluation of the contribution of trees and agroforestry systems to mitigating the aridification trend
The carbon (C) stored in the living biomass of trees is typically the largest C pool of the forest ecosystem which is directly impacted by deforestation and degradation. With the global efforts to combat climate change through a forestation and reforestation to reduce carbon emissions in the atmosphere, natural forests conservation and tree planting programmes are highly emphasized in developing countries for both commercial purposes and carbon emissions reduction. Though most of the trees planted are exotic trees especially Pinus patula, Eucalyptus saligina and partly Cypress sp. with some fruit and shade trees in towns. When comparing survival and carbon content of exotic and indigenous trees grown, exotic trees have high initial biomass and growth rate while indigenous trees perform better in survival rates; also indigenous forest sequesters more above ground biomass (C) and soil carbon than exotic plantations. Hence embarking on clearance of forest's indigenous trees for plantation of commercial exotic trees slightly slows down the efforts of carbon emission reduction and mitigation of climate change through enhancement of carbon sequesters. Therefore, this calls for the need to assess how individual tree planting programs lead into natural forest's encroachment. The study was conducted at Mbeya One ward lying between Mporoto and Rungwe forest reserves in Mbeya rural district, in the Southern highlands of Tanzania. The main objective was 1) to assess the indigenous tree biomass variation between Mporoto and Rungwe forest reserves; 2) to assess the exotic tree biomass variation between the two forest reserves; and 3) to assess the human implication on aboveground biomass variation between the two forest reserves. The findings indicated significant decrease in indigenous trees biomass in residential and crop land areas with a hasty increase in biomass when just reaching Mporoto forest reserve indicating little human encroachment in the forest re- serve. There was the same trend towards Rungwe forest reserve; however, there was a slight increase in indigenous tree biomass when reaching forest reserve signing presence of human encroachment in the forest reserve. The main human activities observed in the reserve were: timber harvesting and commercial exotic trees planting (especially the commercial trees, Pinus patula). The trend was opposite for the exotic trees especially for Pinus patula and Eucalyptus sp. in the study area. Hence the study concludes that there is a significant variation between indigenous and exotic trees in the study area, hence the variation in the tree biomass. There is also a massive human encroachment for indigenous trees clearance in expense of exotic trees plantations towards and in Rungwe forest reserve. Therefore, the study would like to call for an urgent intervention especially in the east side of the study area (Rungwe forest reserve) stopping exotic tree plantation penetrating into the forest reserve which intensifies cutting down of indigenous trees in the forest reserve...
Sediment and macrobenthic fauna distribution at Dar es Salaam harbour channel were investigated to attest the influence of sediment grain size distribution and total organic carbon contents on benthic macrofauna dominance and diversity. Sampling campaign was conducted from January to April, 2019 in 25 sampling stations along the channel. Sediment grain sizes ranged between 0.7405 and 0.00273 mm with an average of 0.0804 mm classified as medium silt. Sediment distribution showed an onshore-offshore pattern consisting of fine dark clay-silt sediments in the southern part of the harbour close to Mwalimu Nyerere Bridge, medium (sandy) at the harbour and coarse sandy offshore. Five classes of macrofauna were identified with sedentary Polychaetes (Diopatra cuprea) found in tubes and free forms being dominant in most of the sediment types, however more abundant in clay-silt. High species diversity index values were encountered in sediments with medium total organic carbon (TOC) and sediment grain sizes (sand-silt). Apparently, low species similarity indices were observed in all sediment type indicating significant dissimilarities in species composition among sediment grain sizes. Thus, the distribution of benthic macrofauna species along Dar es Salaam harbour channel is strongly influenced by the sediment grain sizes and organic carbon contents in sediments.
Investigation of heavy metal contamination along Dar es Salaam harbour channel was carried out in order to determine their current concentrations, sources and potential ecological risks to benthic biota. Sampling was carried out from January to May 2019 and samples analysed using ICP-OES and C-H-N-S analyser. Analysis of heavy metal relationships showed that, Cu, Zn, Cr, As, Ni, Co, Fe, Cd had strong relationships with each other, while Pb only related to Zn. Principal component analysis partitioned metals into two groups; PC1: Ni, Cr, Fe, Co, As, Cu, Cd, and Zn explaining 73.6% variance and PC2: Pb, Zn, and Cd with 13.7% variance. Similarly, Cd, Pb and Zn had severe to very high enrichments (Cd > Pb > Zn) showing serious anthropogenic contamination of these metals in sediments along Dar es Salaam harbour channel. Degree of contamination and potential ecological risks varied from low, moderate, to high; indicating that sediments were considerably contaminated with heavy metals. Levels of contamination varied in space and according to the type of heavy metal Higher contamination and ecological risks were revealed at the harbour area probably due to the observed high concentrations of Cd, Pb and Zn. Monitoring of metals should be emphasized in order to control contaminants release into this area from their sources. Keywords: Dar es Salaam harbour channel, Heavy metals, Contamination, Sediments, Degree of contamination, Ecological risks
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