Assessment of hydrological pathways in East African montane catchments under different land use

Conversion of natural forest (NF) to other land uses could lead to significant changes in catchment hydrology, but the nature of these changes has been insufficiently investigated in tropical montane catchments, especially in Africa. To address this knowledge gap, we aimed to identify stream water (RV) sources and flow paths in three tropical montane sub-catchments (27–36&thinsp;km2) with different land use (natural forest, NF; smallholder agriculture, SHA; and commercial tea and tree plantations, TTP) within a 1021&thinsp;km2 catchment in the Mau Forest complex, Kenya. Weekly samples were collected from stream water, precipitation (PC) and mobile soil water for 75 weeks and analysed for stable isotopes of water (δ2H and δ18O) for mean transit time (MTT) estimation with two lumped parameter models (gamma model, GM; and exponential piston flow model, EPM) and for the calculation of the young water fraction. Weekly samples from stream water and potential endmembers were collected over a period of 55 weeks and analysed for Li, Na, Mg, K, Rb, Sr and Ba for endmember mixing analysis (EMMA). Solute concentrations in precipitation were lower than in stream water in all catchments (p&thinsp;&lt;&thinsp;0.05), whereas concentrations in springs, shallow wells and wetlands were generally more similar to stream water. The stream water isotope signal was considerably damped compared to the isotope signal in precipitation. Mean transit time analysis suggested long transit times for stream water (up to 4 years) in the three sub-catchments, but model efficiencies were very low. The young water fraction ranged from 13&thinsp;% in the smallholder agriculture sub-catchment to 15&thinsp;% in the tea plantation sub-catchment. Mean transit times of mobile soil water ranged from 3.2–3.3 weeks in forest soils and 4.5–7.9 weeks in pasture soils at 15&thinsp;cm depth to 10.4–10.8 weeks in pasture soils at 50&thinsp;cm depth. The contribution of springs and wetlands to stream discharge increased from a median of 16.5 (95&thinsp;% confidence interval: 11.3–22.9), 2.1 (−3.0–24.2) and 50.2 (30.5–65.5) % during low flow to 20.7 (15.2–34.7), 53.0 (23.0–91.3) and 69.4 (43.0–123.9) % during high flow in the natural forest, smallholder agriculture and tea plantation sub-catchments, respectively. Our results indicate that groundwater is an important component of stream water, irrespective of land use. The results further suggest that the selected transit time models and tracers might not be appropriate in tropical catchments with highly damped stream water isotope signatures. A more in-depth investigation of the discharge dependence of the young water fraction and transit time estimation using other tracers, such as tritium, could therefore shed more light on potential land use effects on the hydrological behaviour of tropical montane catchments.</p

Age-Related Differences in Socio-demographic and Behavioral Determinants of HIV Testing and Counseling in HPTN 043/NIMH Project Accept

Youth represent a large proportion of new HIV infections worldwide, yet their utilization of HIV testing and counseling (HTC) remains low. Using the post-intervention, cross-sectional, population-based household survey done in 2011 as part of HPTN 043/NIMH Project Accept, a cluster-randomized trial of community mobilization and mobile HTC in South Africa (Soweto and KwaZulu Natal), Zimbabwe, Tanzania and Thailand, we evaluated age-related differences among socio-demographic and behavioral determinants of HTC in study participants by study arm, site, and gender. A multivariate logistic regression model was developed using complete individual data from 13,755 participants with recent HIV testing (prior 12 months) as the outcome. Youth (18–24 years) was not predictive of recent HTC, except for high-risk youth with multiple concurrent partners, who were less likely (aOR 0.75; 95% CI 0.61–0.92) to have recently been tested than youth reporting a single partner. Importantly, the intervention was successful in reaching men with site specific success ranging from aOR 1.27 (95% CI 1.05–1.53) in South Africa to aOR 2.30 in Thailand (95% CI 1.85–2.84). Finally, across a diverse range of settings, higher education (aOR 1.67; 95% CI 1.42, 1.96), higher socio-economic status (aOR 1.21; 95% CI 1.08–1.36), and marriage (aOR 1.55; 95% CI 1.37–1.75) were all predictive of recent HTC, which did not significantly vary across study arm, site, gender or age category (18–24 vs. 25–32 years)

Land use alters dominant water sources and flow paths in tropical montane catchments in East Africa

Conversion of natural forest to other land uses could lead to significant changes in catchment hydrology, but the nature of these changes has been insufficiently investigated in tropical montane catchments, especially in Africa. To address this knowledge gap, we identified stream water sources and flow paths in three tropical montane sub-catchments (27–36 km2) with different land use (natural forest, smallholder agriculture and commercial tea plantations) within a 1 021 km2 catchment in the Mau Forest Complex, Kenya. Weekly samples were collected from stream water, precipitation and soil water for 75 weeks and analysed for stable water isotopes (δ2H and δ18O) for mean transit time estimation, whereas trace element samples from stream water and potential end members were collected over a period of 55 weeks for end member mixing analysis. Stream water mean transit time was similar (~ 4 years) in the three sub-catchments, and ranged from 3.2–3.3 weeks in forest soils and 4.5–7.9 weeks in pasture soils at 15 cm depth to 10.4–10.8 weeks in pasture soils at 50 cm depth. The contribution of springs and wetlands to stream discharge increased from 18, 1 and 48 % during low flow to 22, 51 and 65 % during high flow in the natural forest, smallholder agriculture and tea plantation sub-catchments, respectively. The dominant stream water source in the tea plantation sub-catchment was spring water (56 %), while precipitation was dominant in the smallholder agriculture (59 %) and natural forest (45 %) sub-catchments. These results confirm that catchment hydrology is strongly influenced by land use, which could have serious consequences for water-related ecosystem services, such as provision of clean water

Application of hydraulic geometry to high gradient rivers in southern Ecuador

Using hydraulic geometry (HG) theory, we investigated three rivers typical of the Ecuadorian mountainous region with longitudinal slopes ranging from 0.8% to 10% and coarse bed material with d50 ranging from 3 to 54 mm and values of d90 up to 908 mm. Extensive field measurements were performed to characterize geometric and hydraulic properties at 33 sites. Using these field data, at-a-station HG relationships were obtained for top width, average flow depth, and average flow velocity. Dimensional and dimensionless downstream HG relations were obtained for these parameters as well as the channel bed slope using the bankfull discharge estimated with at-a-station HG. The correlation coefficients indicate that the dimensionless equations adequately represent the observed data for all quantities with the exception of slope. In addition to a low correlation coefficient, the exponent on non-dimensional discharge was small in the downstream HG relation for slope. This small exponent indicates that slope is not dependent on discharge. Based on this finding, the non-dimensional HG relations were reformulated using both dimensionless discharge and bed slope as independent variables. These new relations show improved correlation coefficients and demonstrate the role of slope in determining channel width, flow depth, and average velocity in high gradient river

Validation of an experimental procedure to determine bedload transport rates in steep channels with coarse sediment

The current study presents an experimental procedure used to determine bedload sediment transport rates in channels with high gradients and coarse sediment. With the aim to validate the procedure for further investigations, laboratory experiments were performed to calculate bedload transport rates. The experiments were performed in a laboratory tilting flume with slopes ranging from 3% to 5%. The sediment particles were uniform in shape (spheres). The experiments were divided into four cases based on sediment size. Three cases of uniform sizes of 10 mm, 15 mm and 25 mm and a case with a grain size distribution formed with the uniform particle sizes were considered. From the experimental results a mathematical bedload transport model was obtained through multiple linear regression. The experimental model was compared with equations presented in the literature obtained for gravel bed rivers. The experimental results agree with some of the models presented in the literature. The closest agreement was seen with models developed for steep slopes especially for the highest slopes considered in the present study. Therefore, it can be concluded that the methodology used can be replicated for the study of bedload transport rates of channels with high gradients and coarse sediment particles to study more general cases of this process such as sediments with non-uniform shapes and sizes. However, a simplified model is proposed to estimate bedload transport rates for slopes up to 5%

Using a statistical efficiency methodology for predictors’ selection in the bedload transport problem: a high gradient experimental channel case

Bedload transport rates for high-gradient gravel bed rivers has been studied through a physical model that replicated the typical features of these channels. A stepwise regression was performed to identify the best predictors from a set of independent variables. As independent variables channel slope, the ratio of area occupied by large particles to the total plan area, flow discharge, mean flow depth, mean flow velocity, water surface velocity, boundary shear stress, and shear velocity were considered. Different characteristic diameters (d16, d50, d84, and d90) were used to nondimensionalize the variables as well as to test the influence of grain size. A linear and a potential model were obtained for each characteristic diameter. Based on the correlation coefficients (R2) with the data used to build the models, the d50 and d84 linear and potential models were selected to perform further analysis. A set of independent data was used to verify the selected models. Better performance was observed for the potential models with 96% of the data falling within ½ order of the magnitude bands both for d50 and d84. R2 for the d50 and d84 potential models were 0.63 and 0.76, respectively. Therefore, the d84 potential model can be selected as the present study representative model

Understanding and addressing socio-cultural barriers to medical male circumcision in traditionally non-circumcising rural communities in sub-Saharan Africa

Given the success of recent clinical trials establishing the safety and efficacy of adult medical male circumcision in Africa, attention has now shifted to barriers and facilitators to programmatic implementation in traditionally non-circumcising communities. In this study, we attempted to develop a fuller understanding of the role of cultural issues in the acceptance of adult circumcision. We conducted four focus group discussions with 28 participants in Mutoko in Zimbabwe, and 33 participants in Vulindlela, in KwaZulu-Natal, South Africa, as well as 19 key informant interviews in both settings. We found the concept of male circumcision to be an alien practice, particularly as expressed in the context of local languages. Cultural barriers included local concepts of ethnicity, social groups, masculinity, and sexuality. On the other hand, we found that concerns about the impact of HIV on communities resulted in willingness to consider adult male circumcision as an option if it would result in lowering the local burden of the epidemic. Adult medical male circumcision promotional messages that create a synergy between understandings of both traditional and medical circumcision will be more successful in these communities

Effects of streamflow isotope sampling strategies on the calibration of a tracer‐aided rainfall‐runoff model

Leverhulme Trust (GrantNumber(s): RPG-2018 -375) European Research Council VeWa project (GA335910) (GrantNumber(s): GA335910) Open access via Wiley AgreementPeer reviewedPublisher PD