Evaluating nutrient removal efficiency of aquatic plants in pond aquaculture discharges

Semi-intensive common carp ( Cyprinus carpio ) pond aquaculture in Central and Eastern Europe provides valuable ecosystem services, such as water retention and biodiversity hotspots, but may also contribute to nutrient pollution and eutrophication. This study assessed the phytoremediation potential, bioconcentration efficiency, and biomass yield of two aquatic plants—watercress ( Nasturtium officinale ) and duckweed ( Lemna minor )—cultivated using carp farm effluents. Watercress yielded 7.99–11.92 kg m −2 , while duckweed yielded 2.54 kg m −2 . Watercress bioremediated 5.93–8.63% of total nitrogen (TN) and up to 23.43% of total phosphorus (TP), whereas duckweed removed 19.15% of TN and 57.89% of TP. Despite negligible carbon (C) retention, duckweed and watercress systems effectively reduced N (−9.9%) and P (−25.6%) concentrations of the carp pond effluents, with duckweed performing best in terms of nutrient uptake relative to the influx of nutrients. All phytoremediated water met the European Union Water Framework Directive limits for nitrogen concentration; duckweed-treated water also approached compliance with the limits for phosphorus concentration, safe for riverine discharge. Furthermore, both macrophytes remained within food-grade limits for heavy metals, providing safe and marketable biomass. These findings suggest that integrating watercress and duckweed production into carp aquaculture can diversify farm income while mitigating eutrophication through scalable, nature-based bioremediation solutions.