Economic value and management of mangrove forests in Cameroon

Mangrove forests constitute a pantropical ecosystem that has been much misused and mismanaged, without regard for actual and potential value to coastal resources. This paper uses primary and secondary data sources to assesses the economic value and pollution problems affecting a mangrove ecosystem. It concludes that this fragile ecosystem is under increasing biological stress resulting from industrial, agro-industrial, fishing and urban activities because both the private and public sector regard this ecosystem as wasteland. The paper concludes that, in order to achieve sustainability of the remaining forest, there is need for financial evaluation of the potentials of this ecosystem. Finally, the study identifies sustainable development and management options for mangrove forest and challenges scientists, researchers, natural resource managers and mangrove biologists to provide government authorities and society with evidence of the true potentials of mangrove ecosystems.     

Sediment-associated trace and major metals in the headwaters of a tropical reservoir

Bed sediment samples of the two headwaters of a tropical reservoir in Southwestern Nigeria were analysed for some metal concentrations using ICP-OES for a period of one year. Sediment samples were collected bi-monthly from both the lower and upper reaches of the streams from May 2013 to March 2014. Sediment samples were microwave-digested and analysed using ICP-OES. Concentrations of metals were higher in the lower reach than in the upper reach, and wet season concentrations were higher than in the dry season with the exception of Fe and Mn. The annual mean metal concentrations were as follows: Fe (121.72?±?6.82?µg/g); Mn (9.34?±?2.57?µg/g); Na (6.20?±?2.29?µg/g); K (0.65?±?0.57?µg/g); Mg (8.07?±?1.36?µg/g); Ca (13.92?±?2.85?µg/g); Ba (0.17?±?0.17?µg/g); Al (106.54?±?5.55?µg/g); and Se (0.6?±?0.19?µg/g). These values were lower in comparison with the baseline concentrations of elements on the earth’s crust. Contamination assessment of all the metals investigated in this study showed that metals in the bed sediments of the two headstreams had not reached pollution status with the exception of Se.     

International standardized procedures for in vivo evaluation of multi-walled carbon nanotube toxicity in water

The classical approach in ecotoxicological evaluation of chemical substances consists of conducting standardized bioassays on organism models. In this work, the potential impact of industrial multi-walled carbon nanotubes was investigated by ecotoxicological standardized procedures using aquatic organisms of different trophic levels, namely bacteria, green algae, invertebrates, fish, and amphibians. The results indicated (1) inhibition of growth in amphibians at 50 mg L^?1 and higher, and (2) no effects on daphnia and fish up to 100 mg L^?1. With the exception of algae (for which Fe deficiency is measured), it seems that the observed toxicity may be due to physiological effects in relation to the ingestion of carbon nanotubes not necessarily related to their intrinsic effects.     

Self-contamination of aquaculture cages in shallow water

Fish farms, which initially colonized quiet and protected natural coastal areas, are now frequently installed in open flow zones, due to the lack of space along coasts and to the emergence of new environmental constraints. For the past two decades, a salmon fish farm has been located inside the roadstead of Cherbourg (France) to benefit from both sea protection and tide currents which regularly refresh the water. In spite of these favourable environmental conditions, periods of non-negligible fish mortalities have been observed to occur without clear evidence of their origin. This motivated the turbidity measurements and the numerical simulations presented in this paper. Firstly, it is shown that high turbidities in the farm site under study are mainly due to the flow acceleration under the cages, which causes the re-suspension of sediments and bio-deposits. Secondly, particles which enter the fishnet can have different origins (external source, bottom, or the net itself). Numerical simulations, based on the Reynolds equations and on the discrete random walk model for particle dispersion, suggest that the rear area of the net can be reached by particles emerging from below the net. It is observed that turbulent dispersion is a key ingredient for such a behaviour, as it can lead particles towards a large recirculation cell behind the net. Dispersion by realistic unsteady vortices has also been analysed by means of a Lattice-Boltzmann model. Though these computations involve smaller Reynolds numbers, they confirm qualitatively the observations of the random walk model. In addition, they suggest that vortex shedding and unsteady recirculation cells near the bottom can force particles from the sand bed to be lifted up and reach the rear of the net.     

Reduced n-3 highly unsaturated fatty acids dietary content expected with global change reduces the metabolic capacity of the golden grey mullet

In this study, we hypothesised that a reduction in n-3 HUFA availability for higher consumers, as expected with global change, would negatively impact the physiological performances of fish. The aim was to experimentally evaluate the effect of n-3 HUFA dietary content on cardio-respiratory performances of the golden grey mullet (Liza aurata), a microalgae grazer of high ecological importance in European coastal areas. These performances were evaluated in terms of critical swimming speed U _crit, associated oxygen consumption MO₂, post-exercise oxygen consumption and calcium fluxes in cardiomyocytes. Two replicated groups of fish were fed on a rich (standard diet, SD diet: 1.2 % n-3 HUFA on dry matter basis, DMB) or a poor n-3 HUFA (low n-3 HUFA diet, LD diet: 0.2 % n-3 HUFA on DMB) diet during 5 months and were called SD and LD groups, respectively. The results showed that the LD diet reduced growth rate as well as the aerobic capacity of L. aurata at 20 °C, suggesting that fish may have to save energy by modifying the proportion of energy allocated to energy-demanding activities, such as digestion or feeding. In addition, this LD diet induced higher levels of haematocrit and plasma osmolality, indicating a stress response at the second and third levels in that group. However, the LD diet caused a massive increase in swimming efficiency. This should improve the capacity of L. aurata to migrate and to forage over a wide area. In turn, these could then compensate for the reduction in growth rate and aerobic metabolism.     

Discussion of “Tang,H., Zhang,H., & Yuan,S. (2018). Hydrodynamics and contaminant transport on a degraded bed at a 90-degree channel confluence. Environmental Fluid Mechanics, 18(2), 443–463”

The authors measured and computed the hydrodynamics and passive scalar dispersion in 90-degree open channel confluences over flat and degraded beds with a dominant upstream or tributary inflow. The present discussion essentially deals with the direction of rotation of the secondary currents, reported for the flat bed configuration with dominant tributary inflow. This rotation direction is indeed surprisingly opposite to the ones reported in the literature, both from calculations and measurements, even if present geometry slightly differs from literature geometries.     

Spatial-Scale Effects on Relative Importance of Physical Habitat Predictors of Stream Health

A common theme in recent landscape studies is the comparison of riparian and watershed land use as predictors of stream health. The objective of this study was to compare the performance of reach-scale habitat and remotely assessed watershed-scale habitat as predictors of stream health over varying spatial extents. Stream health was measured with scores on a fish index of biotic integrity (IBI) using data from 95 stream reaches in the Eastern Corn Belt Plain (ECBP) ecoregion of Indiana. Watersheds hierarchically nested within the ecoregion were used to regroup sampling locations to represent varying spatial extents. Reach habitat was represented by metrics of a qualitative habitat evaluation index, whereas watershed variables were represented by riparian forest, geomorphology, and hydrologic indices. The importance of reach- versus watershed-scale variables was measured by multiple regression model adjusted-R² and best subset comparisons in the general linear statistical framework. Watershed models had adjusted-R² ranging from 0.25 to 0.93 and reach models had adjusted-R² ranging from 0.09 to 0.86. Better-fitting models were associated with smaller spatial extents. Watershed models explained about 15% more variation in IBI scores than reach models on average. Variety of surficial geology contributed to decline in model predictive power. Results should be interpreted bearing in mind that reach habitat was qualitatively measured and only fish assemblages were used to measure stream health. Riparian forest and length-slope (LS) factor were the most important watershed-scale variables and mostly positively correlated with IBI scores, whereas substrate and riffle-pool quality were the important reach-scale variables in the ECBP.     

Notions of environment and environmental management in Akwa Ibom State, Southeastern Nigeria

In the study of environmental degradation, there has not been sufficient attention paid to the perceptions of the local inhabitants. The importance of traditional beliefs and practices has often been overlooked. This paper looks at traditional and Christian beliefs in Akwa Ibom State in South Eastern Nigeria. Interviews, observations and focus group discussions were used to collect the data. The data analysis shows that knowledge and attitudes are somewhat linked to tradition but also influenced by Christian ideas concerning genesis. There are a number of recommendations made.     

Grass–legume mixtures can yield more nitrogen than legume pure stands due to mutual stimulation of nitrogen uptake from symbiotic and non-symbiotic sources

Concerted use of legumes and of functional diversity in grassland forage systems can provide major contributions to the challenges of agricultural systems being productive yet environmental friendly. Acquisition and transformation of nitrogen (N) resources by legumes and grasses were studied in a temperate grassland experiment near Zurich (Switzerland) to investigate mechanisms driving effects of functional diversity in mixed swards and to optimise mixtures for efficient resource use.Grass–legume interactions and N availability were varied by manipulating legume percentage of the sward (0–100%) and N fertiliser application (50, 150 or 450 kg of N ha^?1 year^?1). ¹⁵N technology quantified N derived from symbiotic (Nsym) and non-symbiotic (Nnonsym) sources.Generally, acquisition of Nsym by the entire mixture was stimulated by grasses. As a result, strong overyielding of Nsym occurred (e.g. 75 and 114% for year 1 and 2 at N150) and mixtures with only 60% and 37% legumes (year 1 and 2) already attained the same Nsym yield as pure legume stands. Legumes stimulated Nnonsym acquisition by the entire mixture, largely via increased uptake by the grass component. Thus, overyielding of Nnonsym of 31% occurred in year 1 (N150).Mutual grass–legume interactions stimulated acquisition of Nsym, acquisition of Nnonsym and efficient transformation of N into biomass compared to either monocultures. These effects of functional diversity can substantially contribute to productive and resource efficient agricultural grassland systems and were maximised in mixtures with 40–60% legumes.     

Effect of metallic cations on the sorption of pesticides on soil

We studied the adsorption and desorption of two pesticides, namely isoproturon and dimetomorph, onto a model soil sample. We first show that the adsorption of isoproturon depends on pH, from 1 mg g⁻¹ at pH 4 to 2 mg g⁻¹ at pH 10, contrary to the adsorption of dimetomorph (5.8 mg g⁻¹). We also studied the influence of metallic cations, copper(II), iron(III), manganese(II), and chromium(III), on the sorption of isoproturon and dimetomorph. We found that in the case of isoproturon, the presence of metallic cations does influence the retention capacity of the soil sample. The sorption becomes very weak in the presence of copper and chromium, whereas in the case of iron and manganese the sorption properties are slightly modified.