Syntaxonomy of steppe depression vegetation of Ukraine

Aims: To revise the syntaxonomy of the vegetation of steppe depressions (pody), in particular (1) to identify the associations and to reveal their environmental, structural and compositional peculiarities; (2) to assign the associations to higher syntaxa; and (3) to correct nomenclatural aspects according to the ICPN. Study area: Steppe zone of Ukraine, Left-Bank of the Lower Dnieper basin. Methods: 641 relevés were included in the final analysis in the PCOrd program integrated into Juice software. Two expert systems (EVC and EUNIS-ESy) were used to assign relevés to vegetation classes and to EUNIS units. Results: The analysis resulted in nine clusters, which were interpreted as Festuco-Brometea (two units), Molinio-Arrhenatheretea (three units), Isoёto-Nanojuncetea (three units) and one derivate community of the Festuco-Puccinellietea. Detailed characteristics of the species composition, structure, distribution, and environmental conditions are provided for each unit. According to the DCA ordination, the leading factors of the syntaxa differentiation are soil moisture and fluctuating water level. Conclusions: We could clarify the placement of steppe depression vegetation in the system of syntaxonomic units of Europe. The previously described syntaxa of the rank of alliance (Myosuro-Beckmannion eruciformis), suballiance (Galio ruthenici-Caricenion praecocis), and six associations are validated. Two associations and two subassociations are described as a new to science. Taxonomic references: Euro+Med PlantBase (https://www.emplantbase.org), except Mosyakin and Fedoronchuk (1999) for Phlomis scythica Klokov & Des.-Shost. and Tulipa scythica Klokov & Zoz. Syntaxonomic references: Mucina et al. (2016) for syntaxa from alliance to class level; Dubyna et al. (2019) for associations. Abbreviations: DCA = Detrended Correspondence Analysis; DES = Didukh Ecological Scales; EUNIS = European Nature Information System; EVC = EuroVegChecklist; GIVD = Global Index of Vegetation-Plot Databases; ICPN = International Code of Phytosociological Nomenclature.

Lake Chad: Fluctuating Water Level and Its Implications for People’s Livelihood in the Area

This study assessed the fluctuating water level of Lake Chad and its consequences on the livelihood of people that depend on it. In terms of depth, Lake Chad is very shallow which makes it vulnerable to climate change and human activities. The study opined that continuous reduction in the volume of water of the lake will lead to negative effects such as forceful migration, resource-induced conflict, loss of biodiversity etc. Insurgency spear-headed by Nigeria based terrorist organization, “Boko Haram”, has killed many people including farmers and fishermen in the riparian countries of Nigeria, Niger, Chad and Cameroun and this has led to a decline in agricultural activities around the Lake Chad area making many to depend on food aid for their survival. The insurrectional activity of the terrorist group around the Lake Chad area also makes trade between communities extremely difficult as they are known to have attacked and killed people inside market. It is recommended that measures such as livelihood diversification through technology, creation of protected area, improved agricultural practices etc. should be adopted to reduce pressure on the lake and its resources. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 9(2), 2020, P 1-8

On a predator-prey system interaction under fluctuating water level with nonselective harvesting

A predator-prey model interaction under fluctuating water level with non-selective harvesting is proposed and studied in this paper. Sufficient conditions for the permanence of two populations and the extinction of predator population are provided. The non-negative equilibrium points are given, and their stability is studied by using the Jacobian matrix. By constructing a suitable Lyapunov function, sufficient conditions that ensure the global stability of the positive equilibrium are obtained. The bionomic equilibrium and the optimal harvesting policy are also presented. Numerical simulations are carried out to show the feasibility of the main results.

On the Seismic Performance of Elevated Water Tanks and their Control Using TLDs

The post-earthquake function of elevated water tank structures so as respond to the civil water requirements is of extreme significance. These structures are, however, extremely vulnerable to seismic conditions and there has been substantial damage/failure of several such structures during major earthquakes. A review of the damage and performance of some elevated water tanks subjected to earthquakes is presented in this paper. An investigation is also made on the seismic vibration control of elevated water tank structures by using Tuned Liquid Dampers (TLDs). A frequency domain formulation for the transfer function of the elevated water tank with attached TLDs is developed. Numerical studies on a reinforced concrete elevated water tank with shaft type support are carried out. The effect of detuning on the performance of the TLDs due to the change in the structural frequencies resulting from the fluctuating water level in the water tank is also examined. Results indicate that it is possible to design a fairly robust and effective TLD system for the seismic vibration mitigation of the considered elevated water tank.