Jean-Louis Janeau

Runoff and soil erosion under rainfall simulation of Andisols from the Ecuadorian Páramo: effect of tillage and burning

Abstract In northern Ecuador, soils of high altitude grasslands (paramos) are mainly non-allophanic Andisols developed on Holocenic volcanic ash. These soils have a high water retention capacity and are the “water tank” of central Ecuador. To assess the effect of land use (burning and tillage) on soil hydrodynamic properties, rainfall simulation was conducted at two different sites. At Pichincha near Quito, the simulation was conducted on a recent volcanic ash soil comparing natural, tilled and burned plots. At El Angel, the simulation was conducted on a mature non-allophanic Andisol comparing natural, recently tilled and formerly cultivated plots. On natural plots, the infiltration rate was very high and sediment loss very low. Results for infiltration rate and runoff indicated that land use change on paramos increased runoff flow and reduced saturated hydraulic conductivity. Superficial reorganisation of the soil surfaces occurred on tilled plots at both sites. This crusting process was fast and resulted in surfaces with very low conductivity at Pichincha. The same processes seemed to be slower at El Angel. The soil surface of recent Andisols at Pichincha was prone to crusting whereas the mature Andisol, at El Angel, with a lower bulk density, was compacted when the kinetic energy of raindrops was high. Water repellency occurred after burning at Pichincha and following long natural air drying after tillage in the non-allophanic A horizon at El Angel. Water repellency combined with the low bulk density of soil aggregates explain the intensity of sediment losses in the abandoned soils after cultivation (Bare fallow plots). Erosion occurred in these areas through floating hydrophobic and stable aggregates.

Impact of compost, vermicompost and biochar on soil fertility, maize yield and soil erosion in Northern Vietnam: A three year mesocosm experiment

Compost, vermicompost and biochar amendments are thought to improve soil quality and plant yield. However, little is known about their long-term impact on crop yield and the environment in tropical agro-ecosystems. In this study we investigated the effect of organic amendments (buffalo manure, compost and vermicompost) and biochar (applied alone or with vermicompost) on plant yield, soil fertility, soil erosion and water dynamics in a degraded Acrisol in Vietnam. Maize growth and yield, as well as weed growth, were examined for three years in terrestrial mesocosms under natural rainfall. Maize yield and growth showed high inter-annual variability depending on the organic amendment. Vermicompost improved maize growth and yield but its effect was rather small and was only significant when water availability was limited (year 2). This suggests that vermicompost could be a promising substrate for improving the resistance of agrosystems to water stress. When the vermicompost-biochar mixture was applied, further growth and yield improvements were recorded in some cases. When applied alone, biochar had a positive influence on maize yield and growth, thus confirming its interest for improving long-term soil productivity. All organic amendments reduced water runoff, soil detachment and NH₄(+) and NO₃(-) transfer to water. These effects were more significant with vermicompost than with buffalo manure and compost, highlighting that the beneficial influence of vermicompost is not limited to its influence on plant yield. In addition, this study showed for the first time that the combination of vermicompost and biochar may not only improve plant productivity but also reduce the negative impact of agriculture on water quality.

Grass competition is more important than seed ingestion by livestock for Acacia recruitment in South Africa

Although grazing livestock may have direct negative effects on woody species through herbivory and trampling, (heavy-)grazing is often associated with woody plant encroachment. Two main mechanisms can explain the positive effects of grazers on woody cover: (1) Grazers reduce the interspecific competition with trees and may reduce fuel load, and (2) gut passage through livestock increases seedling establishment by scarification (increased germination) and fertilization by dung (higher survival and growth of seedlings). We tested the effects of fire, grass, cattle ingestion (transit) and dung on germination, seedling height and survival as well as on recruitment of Acacia sieberiana in a sub-humid grassland of South Africa. About 8,000 seeds were planted in the field in a randomized block design. The removal of grass by grazing and/or fire had the most important effect on Acacia recruitment in savanna. Our findings highlight the hierarchy of the main factors affecting Acacia recruitment, which provides new insights to the understanding of woody plant encroachment.

Effect of land use and hydrological processes on Escherichia coli concentrations in streams of tropical, humid headwater catchments

Lack of access to clean water and adequate sanitation continues to be a major brake on development. Here we present the results of a 12-month investigation into the dynamics of Escherichia coli, a commonly used indicator of faecal contamination in water supplies, in three small, rural catchments in Laos, Thailand and Vietnam. We show that land use and hydrology are major controlling factors of E. coli concentrations in streamwater and that the relative importance of these two factors varies between the dry and wet seasons. In all three catchments, the highest concentrations were observed during the wet season when storm events and overland flow were highest. However, smaller peaks of E. coli concentration were also observed during the dry season. These latter correspond to periods of intense farming activities and small, episodic rain events. Furthermore, vegetation type, through land use and soil surface crusting, combined with mammalian presence play an important role in determining E. coli loads in the streams. Finally, sampling during stormflow revealed the importance of having appropriate sampling protocols if information on maximum contamination levels is required as grab sampling at a fixed time step may miss important peaks in E. coli numbers.

Seasonal variability of faecal indicator bacteria numbers and die-off rates in the Red River basin, North Viet Nam

The Red River is the second largest river in Viet Nam and constitutes the main water source for a large percentage of the population of North Viet Nam. Here we present the results of an annual survey of Escherichia coli (EC) and Total Coliforms (TC) in the Red River basin, North Viet Nam. The objective of this work was to obtain information on faecal indicator bacteria (FIB) numbers over an annual cycle and, secondly, to determine the die-off rates of these bacterial indicators. Monthly observations at 10 stations from July 2013–June 2014 showed that TC and EC reached as high as 39100 cfu (colony forming units) 100 ml−1 and 15300 colonies 100 ml−1, respectively. We observed a significant seasonal difference for TC (p < 0.05) with numbers being higher during the wet season. In contrast, no significant seasonal difference was found for EC. The FIB die-off rates ranged from 0.01 d−1 to a maximum of 1.13 d−1 for EC and from 0.17 d−1 to 1.33 d−1 for TC. Die-off rates were significantly higher for free bacteria than for total (free + particle attached) bacteria, suggesting that particle attachment provided a certain level of protection to FIB in this system.

Heavy Metals Contamination in the Ecosystem of Mae Thang Reservoir in Northern Thailand

One critical concern for Thailand reservoirs which are used for irrigated agriculture (mainly paddy rice) and aquaculture is the lack of information on contamination from trace metal element (TME) in waters and biological compartments of the reservoirs. TME are both from natural and anthropogenic origins and may affect the quality of lake waters and food chain. The goal of this study was to evaluate the contamination in TME and study their transfer between the different compartments in and downstream of the reservoir. Fourteen TME have been measured in water column (dissolved phase), fishes, and sediments of the Mae Thang Reservoir (northern Thailand) as well as soil and rice grains of irrigated area. Analyses were performed by inductively coupled plasma-mass spectrometer (ICP-MS). This 2-year study showed that TME concentrations in water were lower than standards for irrigation and aquatic life. However, localized values of Fe and Mn were higher than the standard in the bottom of the reservoir in dry season. TME in sediments were relatively high compared to pristine lakes. Two species of fish were contaminated in As and Ni. Soils exceeded standard values for Cr, Ni, and Cu, while rice grains showed contamination in Ni that indicated a transfer between soil and rice grain. The accumulation of TME in sediments showed that upstream cultivated areas may have contributed to bring TME in the reservoir. TME concentrations in fishes were thus affected and should be controlled. Accumulation of TME in soils of paddy field due to the use of pesticides and fertilizer may increase contamination of rice in the long term.