An aquaponics model for growing lettuce (Lactuca sativa) was tested as a means to remediate the Tancheon River, a nutrient-rich urban stream flowing through Seoul, South Korea. The Tancheon today is a modern ecological marvel considering its Korean war-era history as the “tar” river with a black color from heavy charcoal manufacturing along its banks. It has since been revitalized into a highly biodiverse greenbelt. Nutrients and fecal coliforms are the only remaining known pollutants in the river. Because excess nutrients can quickly cause algal blooms, creative ways of remediating nutrient-impaired streams are needed, and “river-ponics”, an in-situ adaptation of aquaponics to a lotic ecosystem, could prove viable.
Phase 1 included a feasibility study where floating PVC platforms were constructed on which seedlings were secured. The platforms were placed in the Tancheon, tethered to shore, and monitored weekly for growth. Similar seedlings were grown in potting soil in a greenhouse as a control. With the success of Phase 1, Phase 2 tests for nutrient reduction from plant growth were run in the greenhouse using the same type of seedlings. Plants-only (no soil) were suspended in different solutions: (1) tap water, (2) water fertilized with compost tea, and (3) Tancheon water.
Results/Conclusions
Phase 1 showed that after 14 days on the river, the plants not only survived, but thrived when compared to the plants grown indoors. Significantly, the river water had 0.03 mg/L total phosphorus and 11.3 mg/L nitrate due to croplands, pet parks, and golf courses located near the river’s edge. The plants in the Tancheon grew approximately 25% larger than the control plants grown in the greenhouse. Phase 1 clearly showed that the river-ponics concept could work.
During Phase 2, the seedlings in the Tancheon water out-grew the seedlings in the fertilized water and the tap water by 15% and 20%, respectively. Assuming that nitrate and phosphate ions are the majority of ions absorbed by the plants, specific conductivity was used as a measure of absorbed nutrients. Specific conductivity was reduced by 5.6%, 5.2%, and 4.3% in each solution, respectively.
With these results, further testing of the in-situ, river-ponics model is clearly warranted. Low nutrient levels are vital to preserve the Tancheon ecosystem. Growing profitable crops to minimize nutrient pollution could prove to be an efficient and responsible way to maintain or improve the health of this urban setting.