THE UTILIZATION OF WATERCRESS IN A CONSTRUCTED NATURALISTIC STREAM TO TREAT HATCHERY EFFLUENT

The efficient treatment of hatchery effluent is a critical concern of the aquaculture industry, government regulatory agencies and the public. An effective effluent elimination system must not only meet discharge permit requirements, but be cost effective as well.

The Fisheries and Aquaculture Program at the State University of New York at Cobleskill has developed a low maintenance, low cost method of reducing the discharge of solids and nutrients from the campus 40,000 gallon recirculating trout hatchery. Primary solids removal is accomplished with a 3000 gallon settling tank. Hatchery effluent is then discharged at 20+ gal/min into a 65 m long, rubber lined excavated stream channel.  The stream channel is filled with cobbles and 7 waterfalls are utilized to help maintain high oxygen levels. The heavy reliance on cascades and riffles, resulted in a much more limited reduction in total dissolved solids and biological oxygen demand than the previous design with equal proportions of pools and riffles. In this study, watercress was added to the constructed artificial stream to determine if nutrient removal could be improved.

Water quality parameters (discharge, temperature, dissolved oxygen, ammonia, nitrite, phosphorus, total suspended solids, total dissolved solids and BOD) were sampled throughout the year from 2014 to 2016. Samples were collected at the beginning and end of the constructed naturalistic stream. The addition of watercress substantially improved the effectiveness of the constructed artificial stream by increasing dissolved oxygen levels and reducing levels of ammonia, nitrite and BOD. For example, the presence of watercress reduced nitrite discharges by 91% compared to a 45% reduction in the absence of watercress.  On the other hand, contrary to expectations, the addition of watercress had little impact on the treatment of suspended and dissolved solids.  

Increasing effluent regulations have put pressure on the aquaculture industry to develop new strategies for treating hatchery effluent.  A constructed naturalistic stream planted with watercress and coupled with a settling basin has the potential of effectively controlling nutrients and solids year round, without the capital and resource requirements of mechanical filters.