Quantifying human impacts on trout streams in Southern basin of Caspian Sea at different spatial scales

Various human impacts are affecting biological components in running waters of Iran similarto other areas of the world. Available studies in Iran exclusively describe impacts (exceptwater quality) at local scale not quantifying all types of impacts at different spatial scales. Forunderstanding response of biota to human activities it is essential to quantify different typesof impacts at appropriate spatial levels. In this study 88 sites from 67 streams of the troutregion in the Southern Basin of the Caspian Sea were chosen and twenty-seven potentialhuman impact variables acting on biological communities at four different spatial scales wereidentified. All impact variables were classified along a five-step graded classification scheme.Overall, seven impact groups (hydrology, morphology, water quality, connectivity, land use,biology and other (non-predicted) impacts) were found to describe the grade of degradationat a specific site. Finally, a regional pressure index was created by taking additive effects ofmultiple pressures into account. Our analysis shows that the most dominating human impactis land use, in particular urbanization and agriculture, followed by water quality. The numberof sites affected by land use was 81%, water quality 70%, morphology 65%, biology 27%,connectivity 18%, hydrology 13% and other impacts 2%. The frequency of impacted sites bya single pressure was 13%, by double and triple pressures each 31% and by quadruple pressure25%. Our results can be applied for better understanding of biological indicators reaction tohuman impacts. The results are particularly important for trout river management andrestoration, as it is necessary to reveal fundamental processes and effects of human impactson aquatic communities.

Keywords:

Human impacts assessment , Trout Rivers , Spatial scale , Southern Basin of Caspian Sea