Marine monitoring at seawater desalination brine discharge sites: The challenge of doing it right

Seawater desalination produces freshwater and brine that is discharged into the marine environment along with chemicals used in the process. Usually, planning of a desalination plant includes modeling the brine’s dispersion and a baseline survey of the local marine environment. Regular long-term environmental monitoring starts once the plant becomes operational. In here we try to show, using actual monitoring data, the challenges of an effective program set up to pinpoint environmental impact of brine discharge.

Monitoring shows, not surprisingly, excess salinity at the outfall’s vicinity. However, the dispersion of the brine differs from modelling results and among surveys, depending on hydrographic conditions and plant production. Moreover, hypersalinity affected sea grasses and changed benthic community structure in some areas while no effects were detected in others. Basic monitoring of the water column (oxygen, turbidity, nutrients, chlorophyll-a, others) were rarely affected by the brine. Co-discharge of brine with cooling waters of power stations, and additional stressors often confounded the results.

To improve the effectiveness of the monitoring programs we suggest the stations to be dynamically set up based on the conditions during each survey, with excess salinity connecting among them. At regions with significant brine discharge, permanent, continuous data collection stations are recommended. Conflicting benthic responses to brine may be overcome by focusing on specific key species, and if not feasible, by long-term monitoring with suitable references to account for natural variability. Novel chemical and biological measurements, identified in laboratory research, should be incorporated into monitoring. Continuous communication with plant operators is strongly advised, since production, identity and quantity of the chemicals discharged and marine work, are frequently changing. Those may lead to erroneous conclusions of the monitoring results.