Linking river sediment physical properties to biofilm biomass and activity

River sediments are composed by a variety of grain sizes which determine their permeability and biogeochemistry. The aim of this thesis was to test whether differences in river sediment physical characteristics generate differences in biofilm biomass and metabolic activity in a Mediterranean river. To this aim, formulae for estimating hydraulic conductivity were reviewed, and the relationship between sediment grain-size distribution and microbial biomass, and microbial metabolism depth gradients were analyzed. Results suggest selecting the Kozany-Carman formula to estimate hydraulic conductivity for Tordera sandy sediments. Sediment physical properties affected accumulation of organic matter, chlorophyll-a and bacteria but this effect was different depending on hydrological events and microbial group considered; bacteria being the most affected. Microbial activities in sediment depth were regulated by the permeability of streambeds through organic compounds contributing to microbial activities. Hydraulic conductivity is among the most important physical factors driving biogeochemical dynamics and microbial processes at Tordera riverEls sediments fluvials es component d’una varietat de mides de gra que determinen la seva permeabilitat i biogeoquímica. L’objectiu d’aquesta tesi era testar si les diferències en les característiques físiques del sediment generen diferències en la biomassa i l’activitat metabòlica del biofilm en un riu mediterrani. Per aquest objectiu, es revisaren diverses fórmules per a estimar la conductivitat hidràulica i s’analitzà: la relació entre la distribució de mides de gra del sediment amb la biomassa microbiana i, el metabolisme microbià en un gradient de profunditat del sediment. Els resultats suggeriren seleccionar la fórmula de Kozany-Carman per a estimar la conductivitat hidràulica dels sediments sorrencs del riu Tordera. Les característiques físiques del sediment afectaren l’acumulació de matèria orgànica, clorofil·la i bacteris però aquest efecte fou diferent en funció del període hidrològic i del grup microbià, sent els bacteris els més afectats. Les activitats microbianes en profunditat eren regulades per la permeabilitat del sediment. La conductivitat hidràulica és un dels factors físics més importants afectant els processos microbians al riu Torder

WATER QUALITY AND POLLUTION CONTROL IN PHNOM PENH, CAMBODIA

The urban infrastructure, particularly water supply and drainage systems, have deteriorated severely in the past two decades in Phnom Penh, the capital city and the economic center of Cambodia. Water pollution caused by untreated wastewater is one of the serious problems that confront most developing countries (Kwai et al.1991). In Phnom Penh City, all kinds of wastewater are discharged to rivers, lakes and wetlands throughout the city without proper treatment causing serious surface water pollution. Water testing is an essential factor to control water pollution. However, water quality data and water quality testing systems are still poorly developed in Cambodia due to lack of facilities and technical expertise. Therefore, there is no information available on sewage water quality in Phnom Penh City. That’s why the work is aimed at collating basic information about the situation of water supply, waste water system and solid waste. The present information will provide the basis for targeting further field research. This is included the overview of sources and activities that may lead to pollution, with an appreciation of type of water pollutants involved, their magnitude and movement. Types of waste and effluent disposal including sanitation, liquid and solid waste management systems are described. After reviewing all the available, we found that the distribution of water has been well organized by the Phnom Penh Water Supply Authority while the managements of the wastewater, storm water and solid waste are poor due to the rapid urbanisation and industrialisation

Flood mapping under an extreme event in a large shallow lake influenced by flood pulse in Southeast Asia

Tonle Sap Lake (TSL) in Cambodia is the largest shallow lake in Southeast Asia. Influenced by flood pulse system of the Mekong River, TSL provides diverse benefits including ecosystem services, ecological functioning, and flood water storage in the floodplains. However, extreme events (e.g., flooding) due to rising water level caused by dam break and/or heavy rainfall in the Mekong River Basin could threaten the ecosystems of the lake, community health and economic growth in the region. Flood mapping under such extreme event could be informative in the flood risk and emergency management. In this study, we aim to develop a flood risk boundary map in TSL using an existing 2D hydrodynamic model (Caesar-Lisflood, CL) with rising water levels estimated by Gumbel distribution. As a result, the extreme water level of 1% chance (or 100-year flood return period) exceeding the annual maximum water level at Prek Kdam station was approximately 11.38 m resulting in the largest inundation area of 15193 km2. Overall, the employed method and flood risk mapping are useful for the decision makers to manage flood risks and emergency in the lake. This is to anticipate the consequences of a possible rising water level by an extreme event

Impact of Biochar from Rice Husk on Nutrient Distribution and Rice Growth and Yield: A Soil Column Experiment

peer reviewe

Evaluating the Effect of Biochar on Nutrient Leaching and Rice Growth in Disturbed and Undisturbed Soil Columns

editorial reviewedThis article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).Integrated approach of precise irrigation and sustainable Soil management to improve crop water productivity in Cambodia through ITC soil laboratory development: the focus on rice farmin

Termite constructions as patches of soil fertility in Cambodian paddy fields

(IF 4.20; Q2)In Cambodia, termite mounds are commonly used by farmers as amendments to increase the fertility of their paddy fields. However, despite their utilization, their chemical and physical properties have not been described yet. Therefore, the aim of this study was to analyze the chemical and physical properties of two termite constructions commonly found in paddy fields: (a) termitaria built and occupied by the fungus-growing termite Macrotermes gilvus and (b) lenticular mounds that are initially built by termites but host a large diversity of other invertebrates and plants. This study shows that these biogenic structures have very specific properties. Termitaria were characterized by higher clay, phosphorus and electrical conductivity than the surrounding soil. However, their effect on carbon dynamics was limited to a modification of the interactions between soil organic matter and minerals and to the presence of carbonates. At the same time, lenticular mounds appeared as patches of nutrients in paddy fields because they were always enriched in carbon, nitrogen, and phosphorus in comparison with the surrounding cultivated soil. Lenticular mounds were also enriched in clay, although this effect was only measured when the sand content in the surrounding environment was >60%. Together with these changes, lenticular mounds were characterized by a lower bulk density, higher saturated hydraulic conductivity (Ksat), and higher water holding capacity. In conclusion, this study shows that termite constructions can be considered fertility and biogeochemical hotspots in paddy fields, thus explaining their use by farmers for improving the fertility of their lands

Termite mounds in Cambodian paddy fields. Are they always kept for improving soil quality?

International audienceThe utilization of termite mounds for the improvement of soil fertility is a worldwide practice and usually explained by the specific properties of this biogenic material. In Cambodia, farmers also use termite mound soils as amendments with the aim to improve the fertility of paddy fields. The first objective of this study was, therefore, to describe the physical and chemical properties of this material and, consequently, to determine its potential for improving soil fertility. A second objective was to consider farmer’s perception and to quantify the diversity of services provided by termite mounds. We confirmed the specific soil properties of termite mounds but showed that their positive influence on soil chemical fertility and water retention are only significant in very sandy soil (-40-80% sand) while they remain limited in less sandy soil (~40 and 60% of sand). However, termite mounds are considered useful by farmers independently of the soil condition, mostly because this soil material is considered to positively increase soil fertility but also because they host a specific biodiversity which can be used for medicinal purposes or because consumed, then increasing population livelihood. Our work shows the discrepancy between the perception of farmers and the real impact of termite mounds on soil fertility as well as the diversity of services delivered by biodiversity in paddy fields

Abundance, perceptions and utilizations of termite mounds in Cambodia

International audienceIn the Lower Mekong Basin, paddy fields often appear as mosaics, with soil mounds covered by trees or other plants in a spotty distribution. These soil mounds are commonly named termite ‘lenticular mounds’ because termite bioturbation is considered to be at their origin. Termite mounds host a large diversity of animals and plants, increasing landscape patchiness. Because the preservation of these islands of biodiversity is threatened by modern agricultural practices, the aim of this study was to quantify their abundance and the services they provide to the local population. The abundance of mounds and their use by the population were quantified in a catchment in Cambodia. We found that mounds density reached ~2 mounds ha−1. Interviews carried out within the catchment showed that most of the interviewees used mounds for increasing the fertility of their field and for the cultivation of rice and other plants (e.g. sponge gourd and pumpkin). In addition to their potential to increase plant productivity, the survey revealed that animals (rats and snakes), mushrooms and 13 plant species found on or in mounds were consumed by the population. In addition to potentially contributing to an increase in food diversity, mounds also impacted farmers' health by allowing access to 20 medicinal plant species and indirectly via a reduction in pesticide use. In conclusion, this study is the first attempt to quantify the large number of services provided by termite mounds in Cambodia. This increase in the knowledge of the diversity of environmental and socioeconomic services provided by termite mounds is likely to contribute to their preservation and provide a basis for the sustainable management of biodiversity in paddy fields in the Lower Mekong Basin regio

The impact of termites on soil sheeting properties is better explained by environmental factors than by their feeding and building strategies

International audienceTermites are key soil bioturbators in tropical ecosystems. Apart from mound nests constructed by some advanced lineages, most of the species use their faeces, oral secretions, debris, or soil aggregates to protect themselves from predators and desiccation when they go out to forage. Although this soil ‘sheeting’ is considered to play a key role in soil functioning, the properties of this termite-made material has been poorly studied. The few available data showed that sheeting properties are highly variable with positive, neutral or negative impacts on soil C and clay content, and consequently on soil aggregate stability. Therefore, the objective of this study was to determine the factors controlling the physical (particle size fractions and structural stability) and chemical (pH, electrical conductivity and carbon content) properties of soil sheeting produced by termite species encompassing all feeding and building categories using a dataset representative of an important diversity of biotopes coming from 21 countries from all continents colonized by termites. We showed that sheeting properties were explained by the properties of their environment, and especially by those of the bulk soil (linear relationships), followed in a lesser extent by the mean annual precipitation and biotope. Classic hypotheses related to termite feeding and building strategies were not hold by our analysis. However, the distinction of termites into fungus-growing and non-fungus growing species was useful when differentiating the impact of termites on soil electrical conductivity, C content, and structural stability. The large variability observed suggests the need to redefine termite functional groups based on their impacts on soil properties using a trait-based approach from morphological, anatomical and/or physiological traits