Elemental and isotopic compositions of organic carbon and nitrogen of recently deposited organic matter in Empakai crater and its implication for climatic changes in northern Tanzania

A 29 cm long core recovered from a water depth of 5 m in a small closed lake located in the Empakai crater northern Tanzania, is used to document the contents of organic carbon and nitrogen, stable isotopes composition of organic carbon and nitrogen, and C/N ratios and to infer climatic changes from these data. The &#948 13C and &#94815N values for this core, which averages -16.5±2.1l and 11.0±5.6l respectively, show a general downcore decrease below 5 cm. However, within this general trend, two peaks enriched in 13C are observable at about 8 cm and 13 cm. The peak at about 13 cm corresponds also to a zone depleted in 15N values. The general downcore trend can be attributed to systematic changes in relative proportion between C3 and C4 types of organic matter (OM), resulting from climatic changes or nutrient changes and shift between algae and higher plants. The lower most section containing the most depleted values can be attributed either to high input of autochthonous material owing to wetter/humid conditions or high contribution of C3 high land plant materials in response to increase in forest cover. The general downcore decrease in 13C values can also be interpreted to indicate that precipitation and vegetation cover in the area has been declining over time, and occasionally drought has been intense particularly during two zones that are characterized by enrichment in 13C. The upper 5 cm is characterized by near constant values of 13C and 15N with isotope values as high as -13.15‰ and 22.15‰ respectively. High enrichment in 15N in the upper 5 cm could be attributed to denitrification and ammonium volatilization processes, while enrichment in 13C in the upper 5 cm could be attributed to high proportion of C4 type of OM and/or utilization of HCO3- by phytoplankton during synthesis of OM. This site is also characterized by high concentrations of organic carbon (averaging 7.8±2.0%) and nitrogen (averaging 0.8±0.3%). A smell of hydrogen sulfide detected in water samples collected at approximately 20 m, suggest that there is enhanced preservation of OM in the lake under anoxic condition. The C/N ratios values, which average 12.2±2.3, increase downcore to the base of the core owing to preferential loss of nitrogen containing compounds during diagenesis. Tanzania Journal of Science Vol. 30 (2) 2004: pp. 87-9

Stable isotope compositions of organic carbon and contents of organic carbon and nitrogen of lacustrine sediments from sub-arid northern Tanzania

The stable isotope compositions of organic carbon (OC), and contents of OC and nitrogen for four sediment cores recovered from lakes Makat (located in the Ngorongoro Crater), Ndutu and Masek (located in the Serengeti Plains) are used to document sources of organic matter (OM) and climatic changes in sub-arid northern Tanzania during the late Pleistocene-Holocene period. Accelerate mass spectrometer (AMS) 14C ages on total OM for sediments collected from the Ngorongoro Crater Lake indicate that the sedimentation rate is approximately 17 cm/ka. The &#94813C values from the 20 cm long core (short core) show a downcore increase, whereas that of 500 cm long core (long core), show two peaks enriched in 13C and three peaks depleted in 13C. A general downcore increase in the 13C values for the short core suggests changes in the relative proportion of C3 and C4 with C4 fraction increasing downcore. Similarly, low and high peaks in the long core suggest changes in the relative proportion of C3 and C4 with low values having high proportion of C3 type of material, probably indicating changes in precipitation and lake levels in the area. Deposition of OM depleted in 13C took place during periods of high precipitation and high lake levels. Although high content of OC and nitrogen in some core sections are associated with elevated C/N ratio values, diagenetic alteration of isotope signature is unlikely to have caused OC isotope enrichment in sections having high contents of OC and nitrogen. The OC isotope record from Lake Ndutu shows a general downcore decrease in &#94813C values and contents of OC and nitrogen. Furthermore, this general trend is punctuated by a period of above normal enrichment in 13C, with &#94813C values being as high as -6‰. A downcore decrease in &#94813C values and contents of OC and nitrogen could be attributed either to climatic variability or diagenetic effect. Moreover, a peak enriched in 13C probably indicates a period of reduced precipitation, where phytoplankton used dissolved bicarbonate rather than dissolved atmospheric CO2. Lake Mesak record shows two peaks depleted in 13C that are flanked by near constant values of about -20‰. These two peaks (depleted in 13C), which most likely have high proportion of C3 type of OM, are associated with low contents of OC and nitrogen. Generally, the contents of OC and nitrogen for this lake are lowest relative to other lakes. Tanzania Journal of Science Vol. 32 (1) 2006: pp. 61-7

Optimization of Biogas Production Process in Solid State Digesters in Semiarid Areas of Northern Tanzania

Solid state digestion process has received much attention due to its low water requirements, making it preferred in semi-arid areas as well. In this study, the performance of the household solid state digesters was evaluated through monitoring of the feedstock mixing ratios and using the digester gas pressure as a measure of performance. Additionally, a batch study to verify the appropriate and optimal mixing ratio of feedstocks was also done. The mixing ratios of cow dung to water ranged from 2:1, 3:1 and 4:1. Total solids determined were 120, 150 and 170 mg/g for the ratios 2:1, 3:1 and 4:1, respectively. Biogas yield for 2:1, 3:1 and 4:1 mixing ratios in laboratory batch mode were 21.4, 22.7 and 46.4 mL/gVS, respectively. These results from a practical scenario show a promising future of the technology which can be adopted by all solid state digester users living in dry areas. Key words: Cowdung, Biogas, Mixing ratio, Batch solid state anaerobic digeste

Recent trends in accumulation rate, elemental and isotopic composition of organic matter in the Magu bay, Lake Victoria

Stable isotope composition of organic carbon (OC), 14C data, OC and nitrogen content of recently deposited sediments in Magu Bay of Speke Gulf, Lake Victoria are used to document accumulation rates, sources and distribution of organic matter in the bay. The stable isotope values of both organic carbon and nitrogen decrease towards offshore, and this trend is associated with increase in the contents of organic carbon and nitrogen. The isotope results show that the organic material deposited in the bay are generally derived from C4 type of plants and are not transported far from the river mouth. Also the results show that preservation of organic matter is high in open water probably due to high primary productivity owing to high concentration of nutrients and low in turbidity. Low isotope values in offshore sites indicate that the available stock of nutrients far exceeds the demand. Sedimentation rates in the bay are not high and range from 5 to 54 cm/ka. This could be attributed to trapping efficiency by shoreline aquatic macrophyte. Furthermore, the mean accumulation rates of organic carbon and nitrogen for the bay, range from 6.92 to 57.25 gC/m2/yr and 0.51 to 4.37 gN/m2/yr, respectively, and show that Magu Bay is currently experiencing eutrophication. Tanzania Journal of Science Vol. 31 (1) 2005: pp. 23-3

Sediment characteristics and hydrodynamic setting of reef platform sediments of Kunduchi, north of Dar es Salaam harbour

Sediment grain size distribution, carbonate content and current velocities for the Kunduchi area are used to determine its hydrodynamic setting and sediment characteristics. The sediment mean grain size generally decreases northward. The sediments consist of medium to coarse sand south of the Tegeta River and fine sand further north. The sediment sorting values, which lack a north-south trend, vary from moderately well sorted to poorly sorted. The skewness of the sediment vary from near-symmetrical to very negatively skewed while the peakedness (kurtosis) varies from platykurtic to leptokurtic. The carbonate content increases with distance offshore, whereas the siliciclastic component decreases with distance offshore. The siliciclastic/carbonate transition of the investigated area is characterized by a narrow transition with no inter-fingering of the two facies. The lack of inter-fingering of the two facies suggests that there is a limited offshore transport of land-derived sediments. This is further supported by the drogue experiment results, which shows that the predominant surface current flows northward irrespective of the tidal phase Tanzania Journal of Science Vol. 32 (1) 2006: pp. 37-5

Impacts of Emerging Agricultural Practices on Groundwater Quality in Kahe Catchment, Tanzania

This research articles was published in Journals Water Volume 11,Issue 11, 2019This paper assesses the impacts of farmers’ intensive use of agrochemicals (fertilizers and pesticides) on groundwater quality in the Kahe catchment. Samples were collected during the wet and dry seasons of the year 2018 and analyzed for the presence of agrochemicals in the water. Groundwater chemistry was dominated by magnesium-sodium-bicarbonate (Mg-Na-HCO3−). The cations levels were in the trend of Mg2+ >Na+ > Ca2+ > K+, whereas anions were HCO3− > Cl− > SO42− for both seasons. The NO3− had an average value of about 18.40 ± 4.04 and 7.6 ± 1.7 mg/L in the wet and dry season, respectively. Elevated levels of nitrate, sulfate, phosphate, and ammonium were found in water samples collected near the large-scale sugarcane plantation in the catchment. For both seasons, Pb, Cd, Fe, Mn, Zn and Cu concentrations averaged approximately 0.08 ± 0.03, 0.11 ± 0.03, 0.16 ± 0.02, 0.11 ± 0.01, 0.46 ± 0.05, and 0.55 ± 0.02 mg/L, respectively. On the other hand, the concentrations were higher in shallow wells than in the deep boreholes. Pesticides’ residues were below the detection limit in all sampled groundwater. The findings from this study provide important information for intervention in groundwater quality management in Kahe Catchment, Tanzani

A Review of the Late Pleistocene-Holocene Climatic and Paleoecological Records in Tanzania

Climate change is poorly addressed in the developing countries particularly in tropical East Africa such as Tanzania. This paper aimed to reconstruct the late Pleistocene to Holocene Tanzanian climate change using proxies from terrestrial and marine environment. Although data are limited, the inferred major events were found to have a link with global events. In late Pleistocene, during the Last Glacial Maximum (LGM), Tanzania experienced aridity as the other areas in the tropics. This was followed by the humid high precipitation period, highly pronounced between 9-6 ka.  Proxies indicate that the humid period was interrupted by a brief dry Younger Dryas (YD) around 13.0-11.5 ka and a cool dry event at 8.2 ka. Other remarkable events are the cool event in the mid Holocene at 5.2 ka and the global dry event at 4.0 ka. There is a general decrease in precipitation from 5 ka to present with the aridity being pronounced between 3-2 ka and 1.2-0.5 ka. Despite of relatively low precipitation in Late Holocene, wet conditions are inferred between 1.7-1.2 ka (being interrupted by remarkable episodes of aridity) and the late periods of the 19th and 20th centuries. The 20th century which is marked by increased temperature is likely to cause changes in hydrological circle leading to the increase in heavy rainfall and drought periods. Through this study, it is revealed that works are limited and concentrated in some specific areas within the country which exhibit different climatic condition. As a result, some proxies particularly from Eastern Arc Mountains show contradicting records and, in some places, interpretation is partial due to extrapolation of the proxies which are not widely distributed within a specific climate zone

Evidence of climate change impacts on water, food and energy resources around Kilimanjaro, Tanzania

This research article published by Springer Nature Switzerland AG., 2019This review presents research evidence of climate change and anthropogenic impacts on the slopes of Mt. Kilimanjaro and its implications on water, food and energy production (WFE nexus). While there exist divided scholarly opinions on the impacts of climate change on the Mt. Kilimanjaro glacier, consistent decreases in precipitation amounts are evident throughout the existing literature. The 2050 projections indicate increases in the precipitation amounts by approximately 16–18%. However, it is also stated that there will be a concomitant increase in water deficit of about 71%, 27% and 1% in agriculture, hydropower and livestock production respectively. Despite a large number of researches on impacts of climate and anthropogenic pressure on WFE along Mt. Kilimanjaro slopes, there are still limited long-term, good-quality and high-resolution altitudinal precipitation, temperature records and observation network. Moreover, there is limited information on groundwater recharge areas and their stability under changing environment. It is not clear how the interdependence and interaction between climate change, irrigation, vegetation and river discharges affect groundwater recharge process. Also, there is scarce information on future land use/cover changes. Very limited studies focused on fog water deposition for Mt. Kilimanjaro forest and East Africa, despite its relevance as the water tower of the mountain streams. The review further highlights how both climate and anthropogenic impacts may affect ecosystem services in the region. There is a need for developing adaptive strategies for responding to climate change and anthropogenic impacts on the slopes of Mt. Kilimanjaro now and into the future

Origin and mechanisms of high salinity in Hombolo Dam and groundwater in Dodoma municipality Tanzania, revealed

This research article published Springer Nature Switzerland AG.,2017The Hombolo dam (HD), in central Tanzania, is a shallow reservoir characterized by high salinity that limits its use for human activities. The origin of the salinity, mechanisms of reaching and concentrating in the dam remain unclear. These were assessed using hydrogeochemical facies, water type evolutions and mapping. The source of HD salinity was identified to be shallow groundwater (SG) and runoff from a seasonal floodplain with NaCl-rich lithological materails, along Little Kinyasungwe River that feeds the dam. The NaCl-rich lithological units, about 5–7 km upstream of the dam, were highly concentrated with NaCl to the extent that the local community was commercially separating table salt from them. The physicochemical parameters from these NaCl-rich lithological materials were well represented in HD and nearby groundwater sources, which suggests active water interactions. Water type evolution and surface hydrology assessments clearly showed that SG in the salty-floodplain was influenced by evaporation (ET) and was periodically carried to the HD. Clearly; HD water had high chemical similarity with the nearby SG. This agrees with previous studies that HD is partly fed by the local aquifer. However, this is the first attempt at mapping its physical origin. The origin of HD salinity was further supported by the spatial distribution of electrical conductivity (EC), where very high EC (up to 21,230 μScm−1) was recorded in SG within the NaCl-rich lithological unit while water sources far away from the NaCl-rich materials had much lower EC values. Thus, the study disagrees with previous conclusions that HD salinity was sorely due to high dam surface ET but is primarily due to geological reasons. Comparisons of HD with a nearby Matumbulu dam (MD), another earthen dam in climatologically similar settings, reveals that MD water was less saline/mineralised. This further shows that HD high salinity is most likely a geologic phenomenon, but local climatic factors, namely high ET, decreasing rainfall and warming trends are likely to have concentrated the salts further. Although HD is widely/ideally used for grape vine irrigation, it was clearly revealed that its prolonged usage would potentially affect the soil and grape productivity due to high salinity

Statistics in Climate Variability, Dry Spells, and Implications for Local Livelihoods in Semiarid Regions of Tanzania: The Way Forward

This research article published by Springer Nature Switzerland AG., 2016The Dodoma municipality, a semiarid region of Tanzania, is characterized by limited rains, lack of surface water sources, and a high frequency of extreme climate events, particularly droughts and floods. These disadvantaged settings make it vital to study long-term climate trends for signals and patterns of shifting climate regimes for integrity of local livelihood support systems, especially agriculture, recharge, and pasture developments. The area has fairly long climate records, some of which extend to about 100 years. This chapter presents detailed analysis of six climate parameters, namely, rainfall (R), atmospheric relative humidity (ARH), temperature (T), sunshine (S), radiation (RD), wind speed (WS), and evaporation (ET) records from three meteorological stations, namely, Hombolo Agrovet (HMS), Dodoma (DMS), and Makutupora (MMS). The parameters above were statistically and graphically analyzed in four time scales, namely, monthly, seasonal, annual, and time series. The results showed the area is characterized by slight spatial variability in R intensity and T magnitudes with HMS having higher T and rains than DMS and MMS. Further there are clear decreasing trends in ARH and R, while T, S, WS, ET, and RD parameters showed characteristic increasing trends. Thus, except for extreme rain events, particularly El Niño-Southern Oscillations (ENSO), which are characterized by abnormally increased R magnitudes, R intensity has generally decreased in which over the past 91 years, there has been a net R decrease of 54 mm out of annual rains of only about 550 mm/year. Compared to annual time step, however, monthly step reveals more silent features like shortening of the growing seasons. Similarly, the frequency and severity of drought episodes are increasing, all of which adversely impact agriculture, pasture development, and recharge. Similarly, disappearance of R in some months, shifting seasonality, and general declining R intensities and magnitudes are clearly observed. May rains have largely disappeared, while in January, February, March, and April rains have decreased and hence shortening the length of growing season. On the other hand, clear warming trends and declining ARH were also observed. Yet the area is marked by cyclic wetting and drying events where in recent years, drying cycles have been prolonged. However, there is more variability in the mean minimum temperature (MMT) than in mean maximum temperatures (MMMT) in all stations. Between 1961 and 2012, there has been a net 1.13 and 0.778 °C increases in annual MMT and MMMT in DMS, respectively. Like for R trends, silent features are more evident under monthly T data than annual time steps where it is clear that June had the highest increase in MMT (1.54 °C), while April had the least (only 0.662 °C). However, both trends have the potential of affecting major livelihood support systems particularly agriculture and pasture development, but also local groundwater recharge that is vital for the local economy. The study area therefore offers a rare opportunity to understand and manage changing climate regimes including on extent of dry spells and longevity of growing seasons. The changing climate trends consequently call for significant adaptation and mitigation strategies so that local activities adjust to the current climate regimes particularly on onset and end of rainfall seasons and recharge fluxes