TU Berlin

Chair of Water Resources Management and Modeling of HydrosystemsAbstract

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Abstract

Detention ponds can be used for storage, treatment and reuse of agricultural drainage water as one alternative for freshwater in irrigation. Generally, ponds' hydraulic problems such as dead zones, short - circuiting and swirling and, particularly, water salinity and scarcity in arid!semi - arid areas are challenges facing the ponds' applieability. The purpose of Ihis work is to investigate the potential of duckweeds (Lemnaceae) for salt and nutrient uptake under different
salinities as weil as the methods for optimization of detention ponds.

lnvestigations under controlled c\imate conditions and under natural humid climate conditions with different water salinities showed a significant growth inhibition by salinily, but with a promoted growth up to 1.6 gll. Sall - removal was a first - order kinetic and ranged from 0.5 - 12 % per day dependent on water salinity and duckweeds' biomass. K+, Mg+2 , Na+, er, and NH/ have been removed independent on water salinity, but NO)' and Ca+' removal decreased significantly by salinity inerease. Duckweeds saved up 10 25 % of the water volume lost by evaporation.

Numerical simulations of an actual detention pond in thc State of Brandenburg, Germany with the modelling system TELE MAC 2D showcd that the pond inlet design, turbulent viscosity, and tlood intluenced both, the tlow and transport processes. Design modification by baftles improved the performance. Four baftles of 70 % of pond width aehieved the best performance.
In conclusion, detention ponds can be, generally, more effective, sustainable and, particularly, applicable in aridlscmi ~ arid areas, if duckweeds' species are cultivated with intensity higher than 260 glm', harvesting of duckweeds is done regularly, and numerieal simulation of every pond is undertaken individually.

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