Early Wet Season Research Articles

Farmers’ perceptions and management of risk in rice-based farming systems of south-west coastal Bangladesh

Farmers in coastal Bangladesh face significant production and market risks as well as uncertainty about trends in the farming environment. Understanding farmers’ perceptions of the risks they currently experience and the farming and livelihood strategies they adopt to mitigate risk is important to inform policies designed to safeguard coastal livelihoods in the future. In this paper, we draw on a case study of typical village in the coastal zone to explore (1) farmers’ perceptions of the cropping risks they face, (2) the implications of risk for the choice of cropping strategies within different farm types, and (3) the role of other farm and non-farm activities in mitigating risk to household livelihoods. Quantitative and qualitative farm-level data were collected through a reconnaissance survey, a village census, a household survey, and household case studies. Farmers saw the shortage of irrigation water in the dry season and uncertain weather patterns as the major sources of production risk. The main source of market risk was the fluctuation in farm-gate demand and prices for dry-season cash crops. Representative budgets were constructed for the major cropping systems practised by small, medium, and large farm households. The riskiness of these systems was simulated, based on farmers’ estimates of yield and price variability, and a stochastic efficiency analysis was undertaken. The current systems appeared economically viable given the typical range of yields and prices. While some were riskier than others, farm households were largely able to balance their livelihood portfolios to offset the risks. Major risk management strategies included adoption of stress-tolerant rice varieties, staggering the sale of rice, using early wet season rice as a buffer, switching from rice to non-rice crops in the dry season, and undertaking off- or non-farm employment within and outside the village. The dominant trend was to farm and livelihood diversification, contributing to household resilience. However, at the village level, public policy to safeguard the agricultural environment will be crucial to sustaining household risk management strategies.

Studies on parasitic contamination of soil and local drinking water sources, Doma Local Government Area, Nasarawa State, Nigeria

Water is essential to all living things on earth, however if contaminated, can be injurious to human health when consumed. This study evaluates the parasitic contamination of potable water sources and surrounding soil in Doma Local Government Area of Nasarawa State. Forty-eight soil and water samples from different sources (wells, streams and boreholes) were collected from March to July 2017. Water samples were analyzed using the Calcium carbonate (CaCO 3 ) floatation method while a modified Baermann Technique was used to microscopically examine soil samples for the parasitic presences. 32 water samples were parasitized including 2 protozoans ( Entamoeba histolytica , and Giardia lamblia) 3 nematodes ( Trichuris trichiura , Ascaris lumbricoides and hookworm), and Fasciola hepatica a trematode. The nematodes were most contaminated 19(59.38%) while trematodes were least 1(3.13%). The most contamination was in stream water sources for late dry and early wet season (69.23% and 94.74%) while the boreholes had no contamination for both seasons. Prevalence of parasites in relation to water sources showed a high significant difference ( p = 0.0000001), while there was no significant difference in relation to late dry and early rainy seasons ( p = 0.1258). Geohelminths was highest around the boreholes 15(35.71%) but least in the streams 13(30.95%). However, there was no significant difference ( p = 0.6221) in the prevalence rate of geohelminths in relation to sources of water. Result indicated a high rate of parasitic contamination of soil and drinking water sources in the study=area. Hence there is need for advocacy and enlightenment on the importance of proper drinking water treatment. Keywords: Geohelminths; parasitic contamination; water

Why did the buffalo cross the park? Resource shortages, but not infections, drive dispersal in female African buffalo (Syncerus caffer).

Dispersal facilitates population health and maintains resilience in species via gene flow. Adult dispersal occurs in some species, is often facultative, and is poorly understood, but has important management implications, particularly with respect to disease spread. Although the role of adult dispersal in spreading disease has been documented, the potential influence of disease on dispersal has received little attention. African buffalo (Syncerus caffer) are wide‐ranging and harbor many pathogens that can affect nearby livestock. Dispersal of adult buffalo has been described, but ecological and social drivers of buffalo dispersal are poorly understood. We investigated drivers of adult buffalo dispersal during a 4‐year longitudinal study at Kruger National Park, South Africa. We monitored the spatial movement of 304 female buffalo in two focal areas using satellite and radio collars, capturing each buffalo every 6 months to assess animal traits and disease status. We used generalized linear mixed models to determine whether likelihood of dispersal for individual female buffalo was influenced by animal traits, herd identity, environmental variables, gastrointestinal parasites, or microparasite infections. The likelihood and drivers of buffalo dispersal varied by herd, area, and year. In the Lower Sabie herd, where resources were abundant, younger individuals were more likely to disperse, with most dispersal occurring in the early wet season and during an unusually dry year, 2009. In the resource‐poor Crocodile Bridge area, buffalo in poor condition were most likely to disperse. Our findings suggest that dispersal of female buffalo is driven by either seasonal (Lower Sabie) or perhaps social (Crocodile Bridge) resource restriction, indicating resource limitation and dispersal decisions are tightly linked for this social ungulate. We found no direct effects of infections on buffalo dispersal, assuaging fears that highly infectious individuals might be more prone to dispersing, which could accelerate the spatial spread of infectious diseases.

Qualitative identification of hydrologically different water sources used by plants in rock-dominated environments

Sources of water used by plants in rock-dominated environments are far less clear than those in relatively homogeneous soils, largely because plants in rocky environments normally expose to more complex substrate conditions and their potential water sources are hard to locate and sample. In the current study, potential water sources for plants growing on cliff-face (a typical kind of rock-dominated environment) were roughly separated into two water pools based on their hydrological differences. A variable pool that is composed of water derived from recent precipitation that has rapid fluctuations in water content due to recharge by precipitation and depletion by transpiration, and a constant pool that is characterized by slower changes in water status because it can only be recharged by precipitation under certain conditions and depleted by transpiration of deep-rooted species. This study was conducted in a typical karst catchment of Northwest Guangxi, Southwest China. Stem water samples for the most common dominant tree species of cliff-faces and rainwater for each rain event were consecutively collected throughout the growing season. A co-occurring shrub species, which was identified to have a shallow root system, was further selected as a reference species. The reliance on different water pools was qualitatively identified based on the deviation of stem water isotope values between current and last sampling times, as well as its relationship to the isotope values of rainfall between these two sampling times. Our results showed that the shrub species continuously relied on water from the variable water pool, which was consistent with its shallow root system. While the dominant tree species shifted from the constant pool during the early wet season to the variable pool during the mid-wet season, then back to the constant pool during the early dry season. Moreover, the divergent reliance on different water pools by the two species was further supported by the species-specific dynamics in the efficiency in water use by various plants (reflected by leaf carbon isotope ratio). Our results provide new insights into the linkages between plant transpiration and hydrologically different water pools, which would be helpful in understanding the hydrological importance of different plant species.

Trends and seasonal variability of atmospheric NO2 and HNO3 concentrations across three major African biomes inferred from long-term series of ground-based and satellite measurements

In the framework of the INDAAF (International Network to study Deposition and Atmospheric chemistry in AFrica) programme, part of the ACTRIS European Research Infrastructure for the long-term observation of Aerosols, Cloud, and Trace gases, this paper aims to study trends and seasonal variability of surface atmospheric NO2 and HNO3 concentrations, and OMI (Ozone Monitoring Instrument) NO2 over 6 sites in tropical Africa. Sites are located in west and central Africa to represent the major African biomes: dry savanna (Banizoumbou, Niger and Katibougou, Mali), wet savanna (Djougou, Benin and Lamto, Côte d’Ivoire) and forest (Bomassa, Republic of Congo and Zoétélé, Cameroon). Ground-based NO2 and HNO3 concentrations were obtained over the period 1998–2015 using INDAAF passive samplers at a monthly basis, and NO2 Vertical Column Densities (VCDs) from OMI for a 1° grid cell around each sites were obtained from 2005 to 2015. Mean annual NO2 concentrations ranged from 2.3 ± 1.2 to 0.9 ± 0.4 ppb from dry savannas to forests, representing a north south gradient. In dry savannas, we observe two concentration peaks of NO2 appearing at the beginning and the end of the wet season both for ground-based and satellite measurements, whereas at wet savannas and forest sites, NO2 concentrations are highest in the dry season. The seasonality of surface NO2 observations provide further evidence for a large role of microbial soil NOx emissions in dry savannas and of biomass burning NOx emissions in wet savanna and forest sites. Mean annual HNO3 concentrations ranged from 0.4 to 0.5 ppb in dry and wet savannas to 0.2–0.3 ppb in forest. In dry ecosystems, higher HNO3 concentrations are measured in the early wet season, consistent with NO2 results. The analysis of a long-term dataset of surface O3 concentrations indicates that HNO3 production can mainly be explained by the photooxidation of NOx. Mann-Kendall and Seasonal Kendall statistical tests showed that NO2 surface concentrations have a significant decreasing seasonal and annual trends at multiple sites (p-value < 0.05) ranging from −2.96% yr−1 (at Zoétélé) to −0.64% yr−1 (at Banizoumbou). HNO3 results indicate no trends except at Bomassa (1.07% yr−1). The decreasing NO2 ground-based concentration trends observed in wet savannas sites are correlated with OMI NO2 decreasing trends at these sites. Trends obtained for NO2 concentrations in wet savanna and forest ecosystems are consistent with trends of NOₓ biomass burning emissions.

Evaluation of parasitic contamination of local potable water sources in Doma Local Government Area of Nasarawa State, Nigeria

The health and well-being of individuals in a nation absolutely depends on the quality of water available for consumption. Therefore, this study evaluated parasitic contaminants of drinking water sources in Doma Local Government Area of Nasarawa State, Nigeria. A total of 48 water samples were collected from different sources (boreholes, wells and streams) from March to July 2017. The water samples were analyzed using the Calcium Carbonate (CaCO3) floatation method and the samples were examined microscopically for the presences of parasites. A total of 32 (66.67%) water samples were parasitized by a trematode (Fasciola hepatica), two protozoans (Entamoeba histolytica, and Giardia lamblia) and three nematodes (Trichuris trichiuria, Ascaris lumbricoides and Hookworm). The nematode group had the highest contamination rate 19 (59.38%) followed by the protozoan group 12 (37.50%) while trematode was the least with 1(3.13%). The stream source was the most contaminated in late dry and early wet seasons having 69.23% and 94.74% respectively, followed by wells which had 30.77% and 5.26% in late dry and early wet seasons respectively while boreholes had 0% contamination in both seasons. Therefore, prevalence of parasites in relation to sources of water showed a very high significant association (X2= 49.741, df = 2, P < 0.0001), while there was no significant association with seasons (X2 = 2.3438, df = 1, P = 0.1258).Result indicated high rate of parasitic contamination of drinking water sources in the study area. Hence, the need for advocacy and enlightenment of the inhabitants of the area on the importance of proper treatment of potable water.Key words: Parasites, potable water sources, seasons

Restoring historical fire regimes increases activity of endangered bats

BackgroundFire suppression has altered ecological communities globally. Prescribed fire regimes strive to restore function to these fire-dependent ecosystems by mimicking natural fire regimes. Although fire frequency is a widely acknowledged component of fire regimes, the importance of fire seasonality for biodiversity is less clear but appears to play a critical role for a variety of taxa, particularly in the North American Coastal Plain. In subtropical Florida, USA, fire historically occurred primarily at the transition from the dry to wet season (early wet season: April to June) when dry fuel accumulation coincides with a high incidence of lightning. We investigated the effects of fire frequency and season on endangered Florida bonneted bats (Eumops floridanus [G.M. Allen, 1932]), a species endemic to a region that evolved with frequent fires.ResultsWe surveyed bat activity acoustically in 149 sites in fire-dependent vegetation communities (pine flatwoods and prairies), and evaluated the effects of fire frequency and seasonality, using burn records from the previous 18 years. Variation in bat activity was best explained by both fire frequency and season: bat activity decreased with early wet season (April to June) burn interval and increased with dry season (November to March) burn interval. Bat activity and foraging activity were highest in sites burned at > 3- to 5-year intervals during the early wet season.ConclusionFires during the historic fire season at a moderate frequency (> 3 to 5 yr) appear to optimize habitat for bats in both pine flatwoods and prairies, likely through increases in roosts, flight space, and insect prey availability. It appears that Florida bonneted bats are fire-adapted and benefit from prescribed burn programs that closely mimic historical fire regimes. We encourage consideration of both fire frequency and seasonality when managing ecosystems with fire.

A diagnostic on-farm survey of the potential of seed drill and transplanter for mechanised rice establishment in Central Laos and Southern Cambodia

ABSTRACTDue to labour shortages in rural areas, traditional manual transplanting is often no longer feasible and alternative rice establishment methods are required in Central Laos and Southern Cambodia. The work reported here evaluated the potential of a seed drill and transplanter by comparing yield of over 200 crops established by different methods including broadcasting in farmer’s fields under their management in 3 seasons in Laos. In Cambodia, yield of rice established by drill planting was compared with farmers’ practice by broadcasting in two early wet seasons. When mechanised and manual establishment methods were compared in each of 10 farms in the same season in Laos, drilled crops produced slightly higher yield compared with manual planting. Similarly in Cambodia, the technology package including drill produced slightly higher yield and higher gross margin despite lower plant density than that of the farmer practice based on broadcasting. On the other hand, mean yield established using drill was 26% lower than manually transplanted crops across all seasons and villages in Laos, indicating that possibly drills were used in fields unsuitable to them. Mean yield established using transplanter across all fields was 16% lower than manually transplanted crops. Hill density of crops established from transplanter was lower than that from manual transplanting, and yield increased with increased hill density. The labour requirement and hence establishment cost were greatly reduced compared to manual transplanting. The results show the economic advantage of mechanised rice establishment particularly of seed drills.Abbreviations: WS: wet season; DS: dry season.

Tropical summer induces DNA fragmentation in boar spermatozoa: implications for evaluating seasonal infertility.

Summer infertility continues to undermine pig productivity, costing the pig industry millions in annual losses. The boar's inefficient capacity to sweat, non-pendulous scrotum and the extensive use of European breeds in tropical conditions, can make the boar particularly vulnerable to the effects of heat stress; however, the link between summer heat stress and boar sperm DNA damage has not yet been demonstrated. Semen from five Large White boars was collected and evaluated during the early dry, late dry and peak wet seasons to determine the effect of seasonal heat stress on the quality and DNA integrity of boar spermatozoa. DNA damage in spermatozoa during the peak wet was 16-fold greater than during the early dry and nearly 9-fold greater than during the late dry season. Sperm concentration was 1.6-fold lower in the peak wet than early dry whereas no difference was found across several motility parameters as determined by computer-assisted sperm analysis. These results demonstrate that tropical summer (peak wet season) induces DNA damage and reduces concentration without depressing motility in boar spermatozoa, suggesting that traditional methods of evaluating sperm motility may not detect inherently compromised spermatozoa. Boar management strategies (such as antioxidant supplementation) need to be developed to specifically mitigate this problem.

The Mekong's future flows under multiple drivers: How climate change, hydropower developments and irrigation expansions drive hydrological changes

The river flow regime and water resources are highly important for economic growths, flood security, and ecosystem dynamics in the Mekong basin – an important transboundary river basin in South East Asia. The river flow, although remains relatively unregulated, is expected to be increasingly perturbed by climate change and rapidly accelerating socioeconomic developments. Current understanding about hydrological changes under the combined impacts of these drivers, however, remains limited. This study presents projected hydrological changes caused by multiple drivers, namely climate change, large-scale hydropower developments, and irrigated land expansions by 2050s. We found that the future flow regime is highly susceptible to all considered drivers, shown by substantial changes in both annual and seasonal flow distribution. While hydropower developments exhibit limited impacts on annual total flows, climate change and irrigation expansions cause changes of +15% and −3% in annual flows, respectively. However, hydropower developments show the largest seasonal impacts characterized by higher dry season flows (up to +70%) and lower wet season flows (−15%). These strong seasonal impacts tend to outplay those of the other drivers, resulting in the overall hydrological change pattern of strong increases of the dry season flow (up to +160%); flow reduction in the first half of the wet season (up to −25%); and slight flow increase in the second half of the wet season (up to 40%). Furthermore, the cumulative impacts of all drivers cause substantial flow reductions during the early wet season (up to −25% in July), posing challenges for crop production and saltwater intrusion in the downstream Mekong Delta. Substantial flow changes and their consequences require careful considerations of future development activities, as well as timely adaptation to future changes.

Land Use‐Dependent Preferential Flow Paths Affect Hydrological Response of Steep Tropical Lowland Catchments With Saprolitic Soils

AbstractForested catchments in Central Panama can produce more base flow during the dry season compared to pasture catchments—the so‐called “forest sponge effect.” During rainfall events, peak storm runoff rates and storm runoff coefficients can be lower for forested catchments than pasture catchments, even when they have similar topographic characteristics, underlying geology, and soil texture. The internal mechanism of these differences in hydrological response due to land use is yet to be fully understood. A distributed model explicitly simulating preferential flow paths (PFPs), which is referred to as “PFPMod,” is used to explain the hydrological response caused by land use using data from three catchments with distinct land covers in Central Panama. Input parameters of forest and pasture land covers were identified using field observations and literature values. Multiple satisfactory objective criteria demonstrate that the two end‐member land cover parameter sets are adequate to explain the observed difference in dry‐season base flow and storm runoff coefficients. Field measurements of matrix infiltrability using soil cores and plot‐scale infiltration capacity enabled estimating the number of vertical macropores that fully penetrate the root zone. Model simulation results demonstrate that fast drainage through lateral PFPs in the early wet season and high flow in vertical PFPs to recharge deep groundwater in the late wet season contribute to the observed differences in peak storm runoff and the “forest sponge effect” during the dry season. This study provided insights to the mechanism by which reforestation may help to restore ecosystem services and water security in tropical settings.

FENOLOGIA DE &lt;i&gt;Astronium graveolens&lt;/i&gt; Jacq. EM FLORESTA ESTACIONAL DECIDUAL EM VITÓRIA DA CONQUISTA, BAHIA

O presente trabalho teve como objetivo estudar a fenologia da espécie arbórea Astronium graveolens Jacq. e correlacioná-la com a precipitação, umidade relativa e temperatura da região de estudo. Os estudos foram conduzidos em um fragmento de Floresta Estacional Decidual, no campus da Universidade Estadual do Sudoeste da Bahia em Vitória da Conquista, Bahia, Brasil. Os indivíduos foram visitados quinzenalmente de setembro de 2010 a dezembro de 2014, quando foram registradas as características fenológicas referentes a desfolhamento, brotamento, floração e frutificação. A análise dos dados fenológicos foi feita através de testes de normalidade, utilização de estatística circular para testar a sazonalidade das fenofases e teste de correlação de postos de Spearman, para verificar com qual intensidade e sentido os eventos climáticos se relacionavam com as fenofases. A espécie apresentou uma queda foliar com padrão decíduo de alta sincronia com concentração no período de seca, seguido pelo brotamento altamente sincrônico que se iniciou no começo da estação úmida. A floração e frutificação apresentaram um padrão bianual, sendo um evento que se manifestou como sendo de baixa sincronia a assincrônico.

Future Precipitation Projections over Central and Southern Africa and the Adjacent Indian Ocean: What Causes the Changes and the Uncertainty?

Future projections of precipitation at regional scales are vital to inform climate change adaptation activities. Therefore, is it important to quantify projected changes and associated uncertainty, and understand model processes responsible. This paper addresses these challenges for southern Africa and the adjacent Indian Ocean focusing on the local wet season. Precipitation projections for the end of the twenty-first century indicate a pronounced dipole pattern in the CMIP5 multimodel mean. The dipole indicates future wetting (drying) to the north (south) of the climatological axis of maximum rainfall, implying a northward shift of the ITCZ and south Indian Ocean convergence zone that is not consistent with a simple “wet get wetter” pattern. This pattern is most pronounced in early austral summer, suggesting a later and shorter wet season over much of southern Africa. Using a decomposition method we determine physical mechanisms underlying this dipole pattern of projected change, and the associated intermodel uncertainty. The projected dipole pattern is largely associated with the dynamical component of change indicative of shifts in the location of convection. Over the Indian Ocean, this apparent northward shift in the ITCZ may reflect the response to changes in the north–south SST gradient over the Indian Ocean, consistent with a “warmest get wetter” mechanism. Over land subtropical drying is relatively robust, particularly in the early wet season. This has contributions from dynamical shifts in the location of convection, which may be related to regional SST structures in the southern Indian Ocean, and the thermodynamic decline in relative humidity. Implications for understanding and potentially constraining uncertainty in projections are discussed.

Hot temperatures during the dry season reduce survival of a resident tropical bird.

Understanding how climate change will shape species distributions in the future requires a functional understanding of the demographic responses of animals to their environment. For birds, most of our knowledge of how climate influences population vital rates stems from research in temperate environments, even though most of Earth's avian diversity is concentrated in the tropics. We evaluated effects of Southern Oscillation Index (SOI) and local temperature and rainfall at multiple temporal scales on sex-specific survival of a resident tropical bird, the rufous-and-white wren Thryophilus rufalbus, studied over 15 years in the dry forests of northwestern Costa Rica. We found that annual apparent survival of males was 8% higher than females, more variable over time, and responded more strongly to environmental variation than female survival, which did not vary strongly with SOI or local weather. For males, mean and maximum local temperatures were better predictors of survival than either rainfall or SOI, with high temperatures during the dry season and early wet season negatively influencing survival. These results suggest that, even for species adapted to hot environments, further temperature increases may threaten the persistence of local populations in the absence of distributional shifts.

Exotic grass invasion alters microsite conditions limiting woody recruitment potential in an Australian savanna

Andropogon gayanus Kunth. is a large African tussock grass invading Australia’s tropical savannas. Invasion results in more intense fires which increases the mortality rate of adult woody plants. Invasion may also affect community structure by altering the recruitment potential of woody plants. We investigated the effects of A. gayanus invasion on ground-level microclimate, and the carbon assimilation potential and recruitment potential of two Eucalyptus species. We compared microclimatic variables from the early wet-season and into the mid-dry season to coincide with the period of growth of A. gayanus. We assessed Eucalyptus recruitment by monitoring seedling establishment, growth and survival of experimentally sown seed, and estimating seedling density resulting from natural recruitment. A. gayanus invasion was associated with increased grass canopy height, biomass and cover. Following invasion, the understorey microclimate had significantly reduced levels of photon flux density, increased air temperatures and vapour pressure deficit. The conditions were less favourable for woody seedling with aboveground biomass of seedlings reduced by 26% in invaded plots. We estimated that invasion reduced daily carbon assimilation of woody seedlings by ~30% and reduced survivorship of Eucalyptus seedlings. Therefore, A. gayanus invasion reduces recruitment potential, contributing to the transformation of savanna to a grassland ecosystem.

Bio-economic evaluation of cropping systems for saline coastal Bangladesh: I. Biophysical simulation in historical and future environments

Climate change, increased climate variability, extreme weather events, and increasing salinization pose a serious challenge to the sustainability of crop production in coastal Bangladesh. This study assessed yield performance of rice and non-rice crops under farmers' current practices across five climate and three salinity scenarios in the south-western coastal zone. Representative village case studies in Khulna District were used to obtain data on current cropping practices and yields. A validated biophysical crop simulation model (APSIM) was used to simulate performance of crops within 10 cropping systems, representing both existing and potential future cropping patterns. The salinity impact on rice crops was simulated directly using an improved APSIM model, capable of simulating both soil salinity dynamics and the resulting rice crop response. The salinity impact on maize, wheat and sunflower was assessed by developing crop salinity response functions and applying these post-simulation to the crop yields simulated in the absence of salinity. The future performance of some existing crops, namely, watermelon, and pumpkin were extrapolated from data available in the literature and expert knowledge. Climate change is projected to have both positive and negative impacts on crop yields but growing salinity is projected to have substantial negative effects. Allowing for uncertainties inherent in the modelling process, the results indicate that loss of crop production would be negligible under projected 2030 conditions for climate and salinity, even with farmers' current practices. Under 2060 conditions, the adverse impacts on wet-season rice, dry-season rice, and wheat remained negligible, while sunflower experienced notable yield decline. However, the effects of 2060 conditions on early wet season rice and dry-season maize were positive. Climate change in itself does not pose a major risk to crop production and aquaculture in south-west coastal Bangladesh over the next 15–45 years but increasingly salinity will have an unambiguously negative influence.

Estuarine Turbidity Maxima and Variations of Aggregate Parameters in the Cam-Nam Trieu Estuary, North Vietnam, in Early Wet Season

This study aims at exploring the characteristic parameters of the Estuarine Turbidity Maxima (ETM) and at investigating their tidal variations within the Cam-Nam Trieu estuary (North Vietnam) during the early wet season. Six longitudinal river transects were performed at spring tide. Two types of ETM were observed: an upper well mixed ETM with high Suspended Particulate Matter (SPM) concentrations up to the surface at low salinity (0.11 to &lt;1 psu), and a lower ETM confined in a bottom layer over stratified waters at salinities between ~1 psu and 15 psu. Their length depended on the longitudinal salinity gradient and was highest at low tide than at high tide. D50 of the flocs varied between 35 and 90 μm, their excess of density between 60 and 300 kg m−3 and their settling velocity ranged from 0.07 to 0.55 mm s−1 with values between 0.12 and 0.40 mm s−1 in the core of ETMs. The average fractal dimension of flocs was estimated to vary between 1.93 (at high tide) to 2.04 (at low tide).

Aspects of reproductive biology of the red gobyTrypauchen vagina(Gobiidae) from the Mekong Delta

This study provides knowledge on reproductive traits of Trypauchen vagina, a target fish for catching, based on data analysis of 701 individuals collected in the Mekong Delta from January to December 2015. The species is a multiple spawner depositing eggs in early wet season (June–August) since gonadosomatic index reaches a high point during this period, supported by the appearance of ripe and spent gonads at that time. Male and female fish matures firstly at 16.59 and 16.81 cm in total length respectively. The species displays high batch fecundity (4,000–12,750 eggs/female). Knowledge of length at first maturity and spawning season is essential for local authorities to set the suitable fish length and time for fishing. The results provide fundamental information on the reproductive biology and contributed to knowledge for fish population sustainable management.

Effect of Techniques and Time of Sowing, Seed Rate, and Weed Management on Selcted Herbaceous Legumes Establishments in East Nusa Tenggara, Indonesia

&lt;p&gt;A series of experiments on techniques and time of sowing, and weed management of legumes &lt;em&gt;Clitoria ternatea&lt;/em&gt; cv Milgarra, &lt;em&gt;Centrosema pascuorum&lt;/em&gt; cv Cavalcade and cv Bundey, and &lt;em&gt;Lablab purpureus&lt;/em&gt; cv Highworth, was conducted in East Nusa Tenggara (in the islands of Timor, Flores, and Sumba) in order to determine proper technique and time of sowing and weed management, which would be efficient in labor use and sufficient biomass production. Treatments of sowing techniques included dibble, furrow (covered and not covered), and broadcast (harrowed and not harrowed); while sowing time consisted of early wet season (December-January), mid of wet season (February-March) and the end of wet season (April-May), while weed managements consisted of weeded and unweeded treatments. The experiments employed block randomized design with four replications using plot sizes of 3 x 4 m to 4 x 5 m, depending on the availability of land for the experiments. The results of the experiments showed that the best sowing technique with the highest plant population at 4 weeks after planting was dibbling (42 plants/m²), followed by furrow, while the lowest plant population was obtained at the broadcast technique (9-20 plants/m²). Similarly, the highest biomass production was obtained in the dibbling technique (1.75 to 2.5 tons DM/ha per harvest at 12 weeks after planting in Ende, and 4-5 ton DM/ha in Nagekeo), followed by furrow technique covered or not covered (1-1.3 tons DM/ha in Ende and 3.5-4 tons DM/ha in Nagekeo), and the lowest in broadcast technique (0.3-1 ton DM/ha in Ende and 2-2.5 ton DM/ha in Nagekeo). However, considering the labor requirement and cost, it was recommended that furrow technique to suit the small farmer practices in the region. Weed management showed that weeded treatment (keep legume cleaned of weeds) gave significantly better (P&amp;lt;0.05) biomass production compared with to that of unweeded treatment. It can be seen also that weed had more suppressing effects on &lt;em&gt;Clitoria ternatea&lt;/em&gt;, compared to that of &lt;em&gt;Lablab purpureus&lt;/em&gt;, especially when the plants were sown in the early wet season.&lt;/p&gt;

Carbon balance of a grazed savanna grassland ecosystem in South Africa

Abstract. Tropical savannas and grasslands are estimated to contribute significantly to the total primary production of all terrestrial vegetation. Large parts of African savannas and grasslands are used for agriculture and cattle grazing, but the carbon flux data available from these areas are limited. This study explores carbon dioxide fluxes measured with the eddy covariance method for 3 years at a grazed savanna grassland in Welgegund, South Africa. The tree cover around the measurement site, grazed by cattle and sheep, was around 15 %. The night-time respiration was not significantly dependent on either soil moisture or soil temperature on a weekly temporal scale, whereas on an annual timescale higher respiration rates were observed when soil temperatures were higher. The carbon dioxide balances of the years 2010–2011, 2011–2012 and 2012–2013 were −85 ± 16, 67 ± 20 and 139 ± 13 gC m−2 yr−1, respectively. The yearly variation was largely determined by the changes in the early wet season fluxes (September to November) and in the mid-growing season fluxes (December to January). Early rainfall enhanced the respiratory capacity of the ecosystem throughout the year, whereas during the mid-growing season high rainfall resulted in high carbon uptake.