Quantitative and qualitative assessment of collector-drainage waters in Aral Sea Basin: trends in Jizzakh region, Republic of Uzbekistan

Reintroduction of highly mineralized Collector-Drainage Waters (CDW) enhances the salinity of inland waterbodies and limits water suitability for downstream users. Detailed quantitative and qualitative research based on the inter-annual and multiyear generation trends of CDW in Central Asia could help to improve the irrigation system for agriculture and furthermore in determining opportunities for reutilization and biodiversity protection. This is the first long-term research designed to study the discharge, salinity, and ionic composition of CDW in the Jizzakh region (Uzbekistan). A database of field measurements of salinity gathered during the field expeditions from 2000 to 2017 was used in the study. Spring season showed highest CDW discharge where April showed maximum while lowermost was recorded for summers, especially during August. All main collectors showed continuous increments in salinity over the last two decades. This was neither in correlation with CDW discharge nor salinity changes from the irrigation water source (Syrdarya river). A considerable increase of collectors' salinity within the range of 18%-37% was observed from upstream to downstream. The highest salinity values were observed during spring and lowest for summer with even lesser degree for the winter season. Among anions, sulfates were predominant followed by chlorides and bicarbonates; among cations, sodium was predominant followed by calcium and magnesium, which is different from the ionic composition of the water source. The study revealed that increased CDW discharge has not always resulted in low salinity and that high water years have not always caused a decline in CDW salinity showing that CDW discharge and salinity had differential dependence on each other.