Dividing the transit wind speeds into intervals as a favorable methodology for analyzing the relationship between wind speed and the aerodynamic impedance of vegetation in semiarid grasslands

In grassland ecosystems,the aerodynamic roughness(Z0)and frictional wind speed(u*)contribute to the aerodynamic impedance of the grassland canopy.Thus,they are often used in the studies of wind erosion and evapotranspiration.However,the effect of wind speed and grazing measures on the aerodynamic impedance of the grassland canopy has received less analysis.In this study,we monitored wind speeds at multiple heights in grazed and grazing-prohibited grasslands for 1 month in 2021,determined the transit wind speed at 2.0 m height by comparing wind speed differences at the same height in both grasslands,and divided these transit wind speeds at intervals of 2.0 m/s to analyze the effect of the transit wind speed on the relationship among Z0,u*,and wind speed within the grassland canopy.The results showed that dividing the transit wind speeds into intervals has a positive effect on the logarithmic fit of the wind speed profile.After dividing the transit wind speeds into intervals,the wind speed at 0.1 m height(V0.1)gradually decreased with the increase of Z0,exhibiting three distinct stages:a sharp change zone,a steady change zone,and a flat zone;while the overall trend of u*increased first and then decreased with the increase of V0.1.Dividing the transit wind speeds into intervals improved the fitting relationship between Z0 and V0.1 and changed their fitting functions in grazed and grazing-prohibited grasslands.According to the computational fluid dynamic results,we found that the number of tall-stature plants has a more significant effect on windproof capacity than their height.The results of this study contribute to a better understanding of the relationship between wind speed and the aerodynamic impedance of vegetation in grassland environments.

Effects of Different Cations on the Flocculation and Sedimentation of Static Fine-Grained

Natural water bodies mostly contain cations,and the type and content of these cations are the main factors affecting the flocculation of fine-grained cohesive sediments and the floc sedimentation rate at the interface between clear and turbid water.From the microscopic aspect,this study examined the changing patterns of porosity and the fractal dimension of the flocs of fine-grained cohesive sediments.Sedimentation experiments under different sediment contents and electrolyte conditions were conducted,and microscopic images of the flocs were analysed using Image-Pro Plus(IPP)and MATLAB based on the fractal theory.From the macroscopic aspect,this study experimentally investigated the flocculation and sedimentation of fine-grained cohesive sediments and proposed a sedimentation rate equation by introducing an ion concentration-related parameter into an existing sedimentation rate equation(stagnation zone)based on the adsorption isotherm equation.The equation proposed in this study was validated with measured data.The calculated values were in good agreement with the measured values,with a relative error of 16%.The findings of this study provide a reference for further research on the flocculation and sedimentation of fine-grained cohesive sediments in different water bodies.

Study of a Toposequence of West Mayo-Kani Soils (Far North Cameroon)

The soils of Gadas, object of the present study, are identified on the macromorphological, physico-chemical level and the indices of erodibility are related to their physico-chemical properties. The physico-chemical analyzes were carried out by standard methods. The macromorphological analysis of a toposequence made it possible to identify five types of soils: the lithosols which occupy the high zones of the landscape, the colluvial soils (arenosols, regosols) which are located high on the piedmont, alluvial soils (fluvisols) which are located at the bottom of the slope in the alluvial plain and are the most extensive, topomorphic vertisols, and brown soils formed on granite are located either between a colluvial soil and alluvial soil. Physico-chemical analyzes of the soils of Gadas show that these soils are weakly acidic to neutral, sandy to sandy-clayey, saturated, low in nitrogen and organic matter and characterized by average proportions of exchangeable bases. The study of soil erodibility, based on the use of erodibility indices, showed that alluvial soils and brown soils formed on granites are the most susceptible to erosion, whereas vertisols and colluvial soils are the least vulnerable to erosion.

Physico-Chemical Features of the Kpassa Reservoir, Northern Benin, with Emphasis on Its Trophic State: A Preliminary Study

This work presents recent data on the physico-chemical properties and the trophic status of Kpassa reservoir at eighteen locations from August 2014 to February 2015. Seventeen physico-chemical parameters were measured and data obtained were statistically analyzed. The descriptive statistics showed their variations (minima-maxima) as follows: pH (4.65 - 7.30), temperature (25.1°C - 29.9°C), dissolved oxygen (1 - 5.79 mg/L), oxydability (0.32 - 10.88 mg O2/L), electrical conductivity (55 - 77 μS/cm𕒵), TDS (76 - 94 mg/L), turbidity (15.70 - 274.40 NTU), transparency (0.24 - 1.55 m), suspended matter (3 - 92 mg/L), total phosphorus (0.25 - 1.90 mg/L), orthophosphate (0.08 - 0.61 mg/L), nitrate (undetected 5.50 mg/L), nitrite (undetected 0.79 mg/L), ammonia (undetected 0.36 mg/L), chlorophyll a (7.20 - 2334.6 μg/L), silica (4.34 - 15.67 mg/L) and N/P ratio (0.08 - 42.62). These parameters were mainly influenced by agricultural activities and climatic conditions. The restriction or the removal of the use of chemical fertilizers in agricultural activities in Kpassa reservoir basin was recommended. The highest values of Pearson and Spearman correlations were observed across TDS and conductivity (0.967;0.951), turbidity and oxydability (0.924;0.665), turbidity and chlorophyll a (0.884;0.663), turbidity and suspended matter (0.982;0.793), suspended matter and transparency (𕒴.781;𕒴.819), suspended matter and nitrate (𕒴.813;𕒴.839), suspended matter and oxydability (0.919;0.602) and suspended matter and chlorophyll a (0.879;0.656). Carlson’s trophic state index (TSI) values varied between 36 and 66 showing that Kpassa reservoir was eutrophic in August and mesotrophic to oligotrophic during the other months of the sampling period. ANOVA and Kruskal-Wallis test indicated that there were no significant differences between sampling stations.

Nitrogen addition and mowing alter drought resistance and recovery of grassland communities

Nitrogen enrichment and land use are known to influence various ecosystems,but how these anthropogenic changes influence community and ecosystem responses to disturbance remains poorly understood.Here we investigated the effects of increased nitrogen input and mowing on the resistance and recovery of temperate semiarid grassland experiencing a three-year drought.Nitrogen addition increased grassland biomass recovery but decreased structural recovery after drought,whereas annual mowing increased grassland biomass recovery and structural recovery but reduced structural resistance to drought.The treatment effects on community biomass/structural resistance and recovery were largely modulated by the stability of the dominant species and asynchronous dynamics among species,and the community biomass resistance and recovery were also greatly driven by the stability of grasses.Community biomass resistance/recovery in response to drought was positively associated with its corresponding structural stability.Our study provides important experimental evidence that both nitrogen addition and mowing could substantially change grassland stability in both functional and structural aspects.Our findings emphasize the need to study changes across levels of ecological organization for a more complete understanding of ecosystem responses to disturbances under widespread environmental changes.

Greenhouse gas emissions from Daihai Lake,China:Should eutrophication and salinity promote carbon emission dynamics?

Greenhouse gases(GHGs)emitted or absorbed by lakes are an important component of the global carbon cycle.However,few studies have focused on the GHG dynamics of eutrophic saline lakes,thus preventing a comprehensive understanding of the carbon cycle.Here,we conducted four sampling analyses using a floating chamber in Daihai Lake,a eutrophication saline lake in Inner Mongolia Autonomous Region,China,to explore its carbon dioxide(CO_(2))and methane(CH_(4))emissions.The mean CO_(2)emission flux(FCO_(2))and CH_(4)emission flux(FCH_(4))were 17.54±14.54 mmol/m^(2)/day and 0.50±0.50 mmol/m^(2)/day,respectively.The results indicated that Daihai Lake was a source of CO_(2)and CH_(4),and GHG emissions exhibited temporal variability.The mean CO_(2)partial pressure(p CO_(2))and CH_(4)partial pressure(p CH_(4))were 561.35±109.59μatm and 17.02±13.45μatm,which were supersaturated relative to the atmosphere.The regression and correlation analysis showed that the main influencing factors of p CO_(2)were wind speed,dissolved oxygen(DO),total nitrogen(TN)and Chlorophyll a(Chl.a),whereas the main influencing factors of p CH_(4)were water temperature(WT),Chl.a,nitrate nitrogen(NO_(3)^(-)-N),TN,dissolved organic carbon(DOC)and water depth.Salinity regulated carbon mineralization and organic matter decomposition,and it was an important influencing factor of p CO_(2)and p CH_(4).Additionally,the trophic level index(TLI)significantly increased p CH_(4).Our study elucidated that salinity and eutrophication play an important role in the dynamic changes of GHG emissions.However,research on eutrophic saline lakes needs to be strengthened.