Nutrient removal in natural swimming pools A mass balance analysis

Natural swimming pools, (NSPs) are constructed bodies of water, with an impermeable liner between the soil and water, a designed, intentional hydraulic and skimmer system and a complex ecological community as a filter. This technology relies on biological filtration, the interaction of a balanced system including bog vegetation, bacteria and substrate, to reduce nitrogen and phosphorus levels in the NSPs water to less than 30 mg/l NO3 and 0.01 mg/l P.;Water from three NSPs in central PA were sampled through a 5 month period and inputs and outputs estimated. Aboveground plant biomass of bog vegetation was harvested and analyzed for N and P concentrations. Results indicated the need for additional research conducted in a controlled setting to improve estimation of inputs and output compartments and allow measurement of the substrate compartment. None of the NSPs sampled could explain all nutrient removal through direct uptake and storage by biomass.;Subsequently, research was conducted estimating phosphorus and nitrogen inputs, outputs and storage in two greenhouse studies. Outputs consisted of nutrients contained in harvested biomass while nutrient storage compartments were defined as plant biomass and substrate. Plant direct uptake proved insufficient to remove all nutrient inputs, and substrate type was significant in nutrient storage.;In an experiment testing four substrates planted with Saururus cernuus and Iris versicolor, haydite/clay was the only substrate able to lower phosphorus levels of the mesocosm water to 0.01mg/l. All substrate treatments reduced mesocosm water NO3 to target levels of 30 mg/l. Iris produced significantly higher biomass than the lizards tail, and biomass was positively correlated with NO3 removal.;A subsequent experiment testing the removal capabilities of treatments consisting of Canna x generalis and Iris versicolor planted in a substrate consisting of calcined clay and activated alumina, showed vegetated treatments removed more NO3 and P than the unvegetated control. Canna x generalis produced higher biomass and removed more NO3 and P than Iris versicolor. Again, biomass production and NO3 removal were highly correlated. The substrate of calcined clay/activated alumina proved very effective at removing P from the mesocosm water, PO4 levels were below 0.01 mg/l when measured using the Murphy-Riley method for both the Canna x generalis, Iris versicolor and unvegetated treatments.