A system, comprising: an emissions reduction system configured to treat emissions from a hybrid power plant, wherein the emissions reduction system comprises: a catalyst system comprising an oxidation catalyst assembly and a selective catalytic reduction catalyst assembly; a diesel particulate filter assembly configured to reduce particulates or soot from an exhaust flow from a gas engine and arranged upstream of the catalyst assembly; a first sensor disposed upstream of the catalyst system configured to measure one or more emissions of the exhaust flow of the gas engine prior to flowing into the catalyst system to generate a first signal representative of the one or more emissions; a second sensor disposed upstream of the catalyst system configured to measure one or more emissions of an exhaust flow of a gas turbine engine prior to flowing into the catalyst system to generate a second signal representative of the one or more emissions; a third sensor disposed downstream of the catalyst system configured to measure a one or more emissions of an outlet of the catalyst system to generate a third signal representative of the one or more emissions; a fourth sensor disposed upstream of the DPF assembly and a fifth sensor disposed downstream of the DPF assembly, wherein the fourth and fifth sensors are configured to measure a change in pressure across the DPF assembly and generate a fourth signal and a fifth signal representative of the change in pressure; and a controller communicatively coupled to the catalyst system and the sensors, wherein the controller is programmed to receive the first, the second, the third, the fourth, and the fifth signals to generate a first control signal representative of a reductant injection command to control an amount of reductant injected, via an injection system, into a mixture of the exhaust flows of the gas engine and the gas turbine engine prior to flowing into the catalyst assembly based on at least the first, second, and third signals. a catalyst system comprising an oxidation catalyst assembly and a selective catalytic reduction catalyst assembly; a diesel particulate filter assembly configured to reduce particulates or soot from an exhaust flow from a gas engine and arranged upstream of the catalyst assembly; a first sensor disposed upstream of the catalyst system configured to measure one or more emissions of the exhaust flow of the gas engine prior to flowing into the catalyst system to generate a first signal representative of the one or more emissions; a second sensor disposed upstream of the catalyst system configured to measure one or more emissions of an exhaust flow of a gas turbine engine prior to flowing into the catalyst system to generate a second signal representative of the one or more emissions; a third sensor disposed downstream of the catalyst system configured to measure a one or more emissions of an outlet of the catalyst system to generate a third signal representative of the one or more emissions; a fourth sensor disposed upstream of the DPF assembly and a fifth sensor disposed downstream of the DPF assembly, wherein the fourth and fifth sensors are configured to measure a change in pressure across the DPF assembly and generate a fourth signal and a fifth signal representative of the change in pressure; and a controller communicatively coupled to the catalyst system and the sensors, wherein the controller is programmed to receive the first, the second, the third, the fourth, and the fifth signals to generate a first control signal representative of a reductant injection command to control an amount of reductant injected, via an injection system, into a mixture of the exhaust flows of the gas engine and the gas turbine engine prior to flowing into the catalyst assembly based on at least the first, second, and third signals.