Diversification of the hydromorphological state an

Authors: Małgorzata KijowskaStrugała Łukasz Wiejaczka Judith Lekach Anna BucałaHrabia

Publish Date: 2017/01/23

Volume: 76, Issue: 3, Pages: 99-

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Abstract

The hydromorphological state and habitat quality of the selected streams in the Negev Desert was taken under consideration in the paper Field studies were conducted in September 2014 on selected 500 m sections of streams Nahal Be’er Sheva Nahal Hebron characterized by noticeable anthropopressure as well as on streams Nahal Sansana Nahal Yatir Nahal Hatira without visible human pressure The survey of the hydromorphological state of selected streams was carried out using a British method the River Habitat Survey RHS The hydromorphological state and habitat quality of the tested streams based on the habitat naturalness indicator HQA as well as the habitat modification indicator HMS places the analysed streams of weak anthropopressure in class III—moderate Nahal Yatir Nahal Hatira and IV—poor Nahal Sansana Bad hydromorphological state class V is the characteristic of the Nahal Hebron and Nahal Be’er Sheva streams with significant human pressure However it is important to verify RHS method and the classification of a hydromorphological state especially the HQA index and adapt them to the reference conditions in arid and semiarid areasThe hydromorphological state of a river is dependent on the features of the natural environment of the drainage basin and particularly on the lithology and geomorphology climatic conditions hydrological regime the type and density of the vegetation cover as well as the anthropopressure Due to the above rivers from different climatic zones are characterized by a diversified hydromorphological state The extant literature devotes most of its attention to the hydromorphology of rivers in temperate and subtropical climate areas eg Balestrini et al 2004 Raven et al 2005 Kamp et al 2007 Urošev et al 2009 Wiejaczka et al 2014 Wiejaczka and KijowskaStrugała 2015 There is a lack of studies focussed on the hydromorphological state of rivers in arid and semiarid regions Due to the specificity of the natural environment these areas are characterized by a small degree of vegetation cover and limited infiltration which promotes surface runoff Laronne et al 1992 Runoff generated on slopes is concentrated into the channels network to create flash floods Within minutes the flood rise from dry channel bed to its peak discharge and can last few hours or days Flood waters infiltrated into the alluvial channels support therophyte hemicryptophyte and phanerophyte vegetation between floods a time span that can last days months and even few years Such extreme conditions that characterize the desert flow regime conduct a challenge to test the RHS in desert areasThe determination of the hydromorphological state makes up an integral part of research on the abiotic and biotic diversity and serves for a better understanding of the functioning of the fluvial ecosystems Elosegi et al 2010 River regime of ephemeral streams is characterized by extreme diversity of flow dynamics over the year which makes the subject matter of the hydromorphology of these areas a particularly problematic issue The disrupting factor with regard to the natural morphology of the rivers is human activity An example of human activities that directly change the river habitat is inter alia flow regulation fragmentation of the riverbed with water structures stabilization of the banks and the exploitation of aggregates among many others Wohl 2006 Elosegi et al 2010 state that human activity leads to the transformation of the natural environment into a more homogenous and less diversified oneThe habitat quality of rivers is a reflection of their hydromorphological state Generally the greater the number and diversity of natural features the better the conditions for a river habitat is However the appearance of anthropogenic components indicates modifications to the river habitat eg Raven et al 1998 Environment Agency 2003 Szoszkiewicz et al 2006An attractive area to carry out research on the hydromorphological state of rivers of arid and semiarid regions is the Negev Desert in Israel The research on the rivers of the Negev Desert conducted thus far concerned inter alia the course effects and predictions of floods Greenbaum et al 1998 Kahana et al 2002 2004 Bergman et al 2014 sediment yield Reid et al 1995 1998 Schick et al 1997 Clapp et al 2000 the human impact on the morphology of ephemeral streams Hassan and Egozi 2001 as well as the properties of rocks and soils as the most important factor affecting the spatial diversification of plant occurrence OlsvigWhittaker et al 1983 Hoffmann et al 2012The basic purpose of the undertaken research was to evaluate the hydromorphological state and quality of the habitat the degree of naturalness and transformation by human activity of selected streams of the Negev Desert based on the River Habitat Survey method RHS Field studies were conducted in September 2014 on selected 500 m lengths of streams distinguished by noticeable human interference Nahal Be’er Sheva Nahal Hebron as well as on lengths without visible human pressure Nahal Sansana Nahal Yair Nahal HatiraThe Negev Desert has undergone an urban and agricultural development during the last 70 years and it continues intensively nowadays Such intensive development causes a great interference in the drainage network of the streams especially to protect human infrastructures from flash floods Therefore assessment of the hydromorphological state of rivers in areas with visible anthropopressure is important to monitor the quality of the environment and determine the direction of hydromorphological changes

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