Evaluating Soil Carbon as a Proxy for Erosion Risk in the Spatio-Temporal Complex Hydropower Catchment in Upper Pangani, Northern Tanzania

Abstract

Land use conversion is generally accompanied by large changes in soil organic carbon (SOC). SOC influences soil erodibility through its broad control on aggregate stability, soil structure and infiltration capacity. However, soil erodibility is also influenced by soil properties, clay mineralogy and other human activities. This study aimed to evaluate soil organic carbon as proxy of soil erosion risk in the Nyumba ya Mungu (NYM) catchment in Northern Tanzania. Soil organic carbon (SOC) was measured by an AgroCares scanner from which the soil organic matter (SOM) was derived using the conversional van Bemmelen factor of 1.72. A regression analysis performed between the measured loss on ignition (LOI) values and SOM from the AgroScanner showed a strong positive correlation in all land use classes (LOIFL R2 = 0.85, r = 0.93, p < 0.0001; LOICL R2 = 0.86, r = 0.93, p = 0.0001; LOIGL R2 = 0.68, r = 0.83, p = 0.003; LOIBS R2 = 0.88, r = 0.94, p = 0.0001; LOIBL R2 = 0.83, r = 0.91, p = 0.0002). This indicates that SOC from the soil scanner provided a good representation of the actual SOM present in soils. The study also revealed significant differences in the soil aggregate stability (WSA) and SOM stock between the different land use types in the Upper Pangani Basin. The WSA decreases approximately in the following order: grassland > forest land > bare land > cultivated > bush land. Land use change can thus potentially increase the susceptibility of soil to erosion risk when SOC is reduced. Since WSA was directly related to SOM, the study indicates that, where formal measurements are limited, this simple and inexpensive aggregate stability test can be used by farmers to monitor changes in their soils after management changes and to tentatively assess SOC and soil health.

Novel use of portable gamma sensors to rapidly assess soil status and recovery in degraded East African agro-pastoral land

“…• Principle components analysis (left) of NORM data and basic soil properties, determined by Near Infra Red Spectroscopy (NIRS; Amasi et al, 2021;Kelly et al, 2022), supports modification of NORM signal in this landscape by SOM wherein influence of other factors needs exploring. • Negative correlation (centre and right) between specific radioisotopes and soil properties suggest that in this context the closest proxy to SOM/SOC is negative correlation with Th-232, which is also closely correlated to cps.…”

Assessing the Impacts of Land Use and Climate Changes on River Discharge towards Lake Victoria

“…This study used an ensemble of GCM models (ACCESS1.3, MIROC5 and CNRM.CM5) and three representative concentration pathways (RCPs 4.5, 6.0 and 8.5) to understand the impact of future climate change on the Simiyu river discharge (Figures 3 and 9). Different GCM models have shown discrepancies over regional climate change [79,80], e.g., due to differences in the spatial domains and predictor variables, downscaling with dynamic and statistical downscaling methods [79,81,82] or even within different statistical downscaling methods [83,84]. However, this was overcome by locally validating the models and selecting the one with the lowest inaccuracies for discharge modelling.…”

Soils, Science and Community ActioN (SoilSCAN): a citizen science tool to empower community-led land management change in East Africa

“…To complement visual assessments, the development of portable instrumentation has enabled high spatial resolution data to be obtained for important soil health parameters, including SOC (Visser et al 2020). Near infrared (NIR) spectroscopy has been shown to be an effective tool for measuring SOC in African soils (Recha et al 2021), with portable NIR devices capable of providing rapid, in situ data to inform soil management decisions (Amasi et al 2021). Access to these data would enable smallholder farmers to implement more complex sustainable soil management actions and potentially achieve higher yields alongside protecting their land against soil erosion.…”

“…Novel agricultural technologies, such as portable soil scanners, provide opportunities to address these soil health challenges in partnership with citizen science participatory approaches (Van Beek et al 2018, Visser et al 2020. The ability of portable soil scanners to quickly deliver in-situ data on multiple soil health indicators allows farmers to measure, report and verify sustainable land management outcomes for wider community and regional benefit (Amasi et al 2021).…”

“…Guided by the associated mobile phone app, and following manufacturers guidance, the scanner was calibrated by putting it on a yellow cap (once a day) and a white reference cap (after every sample), both supplied with the scanner. For each selected sample location, a composite sample (10× top 5 cm) was collected with a hand trowel in a bucket following (Amasi et al 2021). Stones and vegetation were removed, and the sample was mixed.…”