Agricultural sediment reduction using natural herbaceous buffer strips: a case study of the east African highland

Buffer strips are permanently vegetated areas situated immediately adjacent to streams and provide an efficient and economical way to reduce nutrient loads from agricultural areas, but no studies exist of their effectiveness from the East African highlands. We thus evaluated the sediment filtering capabilities of natural herbaceous buffer strips under tropical highland climatic conditions. Overland flow samples were collected at field edges and at various positions in herbaceous buffers and tested for total suspended sediment, nitrate‐nitrogen and total phosphorus. There was a significant effect (P < 0.05) of distance from field edge on the mean values of nutrients. On average, a 10.0 m herbaceous buffer reduced the total phosphorus by 99%, total suspended sediment by 94% and nitrate‐nitrogen by 85%. Altogether, the results suggest that herbaceous buffer strips are important to include in watershed management in agriculturally dominated tropical highlands in order to control sediment loss, stream siltation and the washout of nutrients.     

The state of play regarding the social sustainability of the construction industry: a systematic review

The social dimensions of sustainability’s three bottom lines are often overlooked in the construction industry. This is despite attempts to find optimal trade-offs between economic growth, environmental impacts, human health and well-being, as well as social considerations. This study reviews the literature on social sustainability (SS) within the construction arena, identifies research gaps and proposes a forward-looking research agenda. This critical review employes the ‘Preferred Reporting Items for Systematic Reviews and Meta-Analyses’ (PRISMA) technique to retrieve secondary data on SS from available academic, government and industry documents. The literature analysis focuses on seven themes: (1) definition of SS, (2) the theoretical dimensions of SS, (3) primary stakeholders, (4) policy and guidelines, (5) major SS performance indicators, (6) barriers to SS uptake in the construction industry, and (7) SS drivers in the construction industry. The review identifies primary stakeholders and proposes a list of assessment criteria that can be used by the construction industry in measuring progress towards SS. The study proposes a conceptual model that maps out key stakeholders, the major barriers, and enablers of SS in construction projects. The findings will support the development of SS guidelines specific to the construction industry in Australia as well as overseas.

     

Static and cyclic properties of clay subgrade stabilised with rice husk ash and Portland slag cement

In the present study, clay soil collected from new Banda, Uttar Pradesh, India has been treated with rice husk ash (RHA) and Portland slag cement (PSC). Based on unconfined compressive strength test results, the optimum mix obtained is of 82.5%Soil+7.5%PSC+10%RHA. The increase in strength of the optimum mix is about 29.8%, 37.2% and 48.55% for a curing period of 7, 14 and 30 days, respectively. The soaked California bearing ratio (CBR) test gives about 91.75% higher values as compared to unsoaked CBR test for a curing period of 30 days. Strain-controlled cyclic triaxial tests were conducted to study the variation of degradation index, shear modulus and damping ratio of the optimum mix with number of cycles for strain amplitudes of 0.4%, 0.6%, 0.8% and 1% and for frequencies of 0.2 and 1 Hz at an effective confining pressure of 100 kPa. It is observed that the degradation index decreases at a fast rate for the first 25–50 cycles. From the study, it is concluded that the aforementioned mix may be suitable for pavement subgrade material.