Phytofences and Algae Harvesting as Control Strategies for H₂S Emissions from Saline Ponds

ABSTRACT

Excessive atmospheric H₂S (hydrogen sulfide) emissions from large salt evaporation ponds in San Francisco Bay, California, and the effectiveness of possible remedies have been studied since 1989. These emissions are caused by filamentous algae (Cladophora spp., Enteromorpha spp.) which accumulate on the downwind shores, and decay under anoxic conditions. On-site pilot experiments were used to test the effectiveness of two methods of controlling H₂S emissions: harvesting the shoreline accumulation of filamentous algae and the use of a barrier (“phytofence”) to prevent accumulation of algae onshore. Replicate experimental plots were set up along a portion of the downwind (east) shore. Atmospheric H₂S concentrations above the phytofence plots were significantly lower than above both control and harvest plots. In addition, total dissolved sulfide was significantly lower and dissolved oxygen significantly higher in the phytofence plots than in control and harvest plots. Thus, a phytofence may be a viable method for reducing H₂S emissions. Harvest plot H₂S emissions, total dissolved sulfide, and dissolved oxygen concentrations were not significantly different from control plots. Removal of filamentous algae to significantly reduce the H₂S emissions is impractical early in the season due to large amounts of algae involved and the difficulty of harvesting; it is impossible later in the season because of the decomposed state of the algae. Harvesting is not a viable method for reducing H₂S emissions from these evaporation ponds.

Key Words:

• hydrogen sulfide
• filamentous algae
• harvesting
• phytofence