Effects of floating covers used for evaporation suppression on reservoir physical, chemical and biological water quality parameters

Abstract

Increasing demand for freshwater in arid regions with chronic water shortage calls for expansion of water storage for drought periods while protecting storage from evaporative losses. A cost‐effective and scalable method for evaporation suppression uses floating elements; however, little is known regarding biochemical and water quality effects under these covers. Two identical reservoirs with area of 25 m2 and depth of 2 m were used to investigate the influence of floating covers on water quality parameters for a period of one year (2019–2020). One of the reservoirs was covered with Styrofoam discs, and results were compared with the uncovered one. Results showed that the evaporation suppression efficiency of floating discs gradually decreased from 80% in spring to about 60% in winter. The comparison between reservoirs revealed that the presence of floating covers decreased pH, electrical conductivity (EC), total dissolved solids (TDS) and dissolved oxygen by 11%, 11%, 15% and 36%, respectively. We observed an increase in nitrate (30%), phosphate (27%) and ammonia (95%) concentrations in the covered reservoir. Results also demonstrated more concentration of biological populations such as algae and protozoa in the uncovered reservoir. The findings highlight improvement of certain water quality parameters in covered reservoirs such as EC and TDS with potential impacts on irrigation systems and soil health and salinity constraints.

Evaporation Loss From Small Agricultural Reservoirs in a Warming Climate: An Overlooked Component of Water Accounting

“…Considerable evaporation from small agricultural reservoirs calls for enhancing the efficiency of the on‐farm water storage infrastructure. Depending on the environmental conditions and reservoir characteristics, common measures for suppressing evaporative losses include deepening the reservoirs, covering the surface, or deploying wind breakers (Aminzadeh et al., 2018; Bakhtiar et al., 2022; Lehmann et al., 2019; Maestre‐Valero et al., 2011; Rezazadeh et al., 2020). Among different techniques, modular floating covers offer an efficient and scalable solution for suppressing evaporative losses from small reservoirs.…”

“…Future investigations may benefit from high resolution satellite products such as Sentinel‐2 (available from 2015) with the spatial resolution of 10 m to quantify spatio‐temporal extent of water reservoirs with different sizes. The dynamic changes in physical, chemical, and biological characteristics of a water body (e.g., water depth, turbidity, algae growth) could change thermal and radiative properties of reservoirs and consequently affect water evaporation (Bakhtiar et al., 2022). Considering the lack of such detailed information for individual reservoirs in the scale of the present study, our theoretical calculations tacitly ignore such inherent variations to retain model applicability for estimating evaporative losses from water reservoirs.…”

“…Among different techniques, modular floating covers offer an efficient and scalable solution for suppressing evaporative losses from small reservoirs. Mechanistic modeling accompanied by laboratory and field measurements indicate that floating covers may suppress evaporative losses by Earth's Future 10.1029/2023EF004050 more than 80% while supporting multiuse applications (e.g., fish cultures and floating photovoltaic plants) and maintaining water quality for certain purposes (e.g., drip irrigation) (Aminzadeh et al, 2018;Bakhtiar et al, 2022;Jin et al, 2023;Lehmann et al, 2019;Pourmand et al, 2022).…”

Towards Sustainable Water Resources Management Considering Climate Change in the Case of Saudi Arabia

“…However, it is crucial to acknowledge that the use of chemicals or physical covers on water bodies may affect the aquatic ecosystem [130,132,140,[143][144][145]. Therefore, the applicability of some of these techniques in the KSA environment needs to be further investigated.…”