Inland, brackish water r ecirculating aquaculture systems (RAS) face unique challenges with effluent disposal due to high salt content. Water reuse is a research focus and brackish water aquaponics can facilitate nutrient removal from system water, particularly nitrogenous compounds that build up over time in RAS. Mustard is a member of the Brassicaceae family and garden orache belongs to the Amaranthaceae family. Both families contain several halophytic species in addition to showing some tolerance to saline/ sodic growing conditions. Garden orache is a halophyte and is therefore adapted to growing in saline/sodic environments; however, mustard is a glycophyte and although there are limited studies testing the plant's salt tolerance , there are no known studies using brackish water hydroponic or aquaponic systems. Continuing suitability studies examined Brassica juncea 'Green Wave' and Atriplex hortensis 'Copper Plume' for their tolerance to and performance in brackish water conditions.
Trials were conducted in a controlled environment under LED lighting programmed for a 12-hour photoperiod. Randomized, r eplicated treatments in 18 L aerated tanks included 0, 5, 10, 15 and 20 ppt. salinity . Seeds were germinated in perlite and fresh water, and then transplanted to grow grips upon true leaf emergence. Acclimation to salt was accomplished with five biweekly increases in salinity, with the final salinity increase achieved at stocking. Four plants were stocked in each 18 L tank and each tank was fertilized using 50 mL Fox Farm Grow Big Hydroponic fertilizer. Trials were harvested when growth was impeded due to limited space, at which time growth metrics were measured. Water quality parameters were measured twice weekly (temperature, dissolved oxygen (DO), pH and salinity), with weekly monitoring of total ammonia nitrogen (TAN), nitrite-nitrogen and phosphate. Potassium and nitrate-nitrogen were also monitored weekly for the mustard trial. Initial and final water samples were analyzed for an array of elements and dissolved nutrients.
Mustard had 100% survival through 15 ppt. and 66.7% survival at 20 ppt. Orache had 91.7% survival at 0 ppt. and 100% survival at all other salinities. Mustard growth was reduced as salinity increased, with a 51.6% growth reduction in height and a 75% reduction in biomass wet weight from zero to 15 ppt. Orache growth increased with salinity, peaking at 10 ppt. Orache had a 33.3% increase in height and a 246.4% increase in biomass wet weight from 0 to 15 ppt. chlorophyll content index (CCI) levels for both plants peaked at 15 ppt. Nitrate and potassium uptake in mustard decreased as salinity increased , phosphate absorption for both plants was similar regardless of salinity. Foliage on both plants remained healthy at all salinities. Future trials will examine tolerance of both plants to reused shrimp water in addition to full grow-outs in an aquaponics system.