Consider rice production activities in three farms located in China, India, and the USA. The runoff of nitrate fertilizer requires the ecosystem service of water quality regulation. The nitrate concentrations in the runoff from the three farms are 14.35, 1.13, and 4.42 mg/L, respectively, and the hydraulic loading rates are 11.41, 8.68, and 7.61 m³/day, respectively. Consider a 50 m wetland that is built to treat each runoff, which can be modeled as a steady-state first-order system using the following equations:

Here, C^ο, and C are the concentrations of nutrients in the outflow and inflow, respectively; Kr is the rate constant with the unit of day^-1, measured at T, which represents the water surface temperature; T can be assumed to be 20 ^οC. A (in m) is the area of wetland; e is the bed porosity (assumed to be 0.42); h (in m) is the wetland bed depth (assumed to be 0.6 m); Q (in m³/day) is the hydraulic loading rate. What are the net nitrate outflow concentrations from each farm?

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Co Ci KT = 1.157-20 = e-KTt Ach 0