Impacts of effluent from Carlsbad Desalination Plant on the coastal biology and chemistry - a in-situ study of pre- and post-discharge.

The Carlsbad Desalination plant located by Carlsbad Beach in Southern California is currently under construction, estimated for operation in late 2015. This study is conducting in-situ measurements of the effects of the effluent discharge. Effluent will be mixed with power plant cooling water. Both pre- and post-discharge measurements of salinity, temperature, Chl a, nutrients (NO₃, PO₄ and silica), δ¹³C and δ¹⁵N stable isotopes, DOC, radioisotopes, organic pollutants, sediment sorting, algae diversity and benthic organisms’ diversity are collected and compared. This allows for a real-time comparison of the effect of discharge. Pre-discharge sampling was done in the winter and summer seasons to capture seasonal variability.

The first baseline results of the water chemistry pre-discharge suggest homogenous water chemistry in this coastal region at the time of sampling due to wave and tidal mixing. The outflow plume has a relative higher water temperature but other than that samples collected around the discharge site are not statistically different than around a control site. The biological samples, however, shows that the high water flow rate at the discharge channel seems to disturb benthic organisms from settling on the bottom (larger grain size and lower benthic organisms’ abundance). The most abundant organisms in the area were the tube-forming worms in the genus Polychaeta. An algae count showed that at all sites sampled the diatom Pseudo-Nitzschia sp. (a known toxic alga that forms large algae blooms) is the most abundant phytoplankton.

Based on the first pre-discharge data it is concluded that, beside differences in water temperature, the water chemistry is relatively uniform and corresponds to conditions expected for coastal seawater in this region at the time of sampling. However, because of the heavy water flow from the outflow channel the benthic community shows decreased abundance in the vicinity of the outflow.