Optical nitrate sensor (10, 10') for sampling a confined volume of water within a prescribed region of a sampling chamber comprising: an UV LED combination configured to generate a first UV LED signal centered at 229 nm and a second UV LED signal centered in a range of 250-275 nm that traverse the confined volume of water within the prescribed region of the sampling chamber in order to sense nitrates in the water with first UV LED signal and dissolved organic matter in the water with the second UV LED signal; a reference photodiode configured to respond to part (L R) of the first UV LED signal and the second UV LED signal, and provide photodiode reference signaling containing information about the part (L R) of the first UV LED signal and the second UV LED signal received; a measuring photodiode configured to sense the first UV LED signal and the second UV LED signal (L M) that pass through the confined volume of water within the prescribed region of the sampling chamber, and provide photodiode measured signaling containing information about a nitrate absorption of the water related to the first UV LED signal and a DOM absorption background related to the second UV LED signal; a transimpedance amplifier configured to respond to the photodiode reference signaling and the photodiode measured signaling, and provide transimpedance amplifier signaling containing information about a photocurrent to voltage reference signaling conversion of the photodiode reference signaling without interaction with the water and also a photocurrent to voltage measured signaling conversion of the photodiode measured signaling after interaction with the water; and a signal processor or signal processing module configured to: receive the transimpedance amplifier signaling, and determine corresponding signaling containing information about a DOM background corrected concentration of nitrates dissolved in the water by determining the nitrate concentration dissolved in water with the nitrate absorption sensed in the water at 229 nm compensated by the DOM background absorption sensed in the water in the range of 250-275 nm, based upon the transimpedance amplifier signaling received, and wherein the signal processor or signal processing module is further configured to implement a compensation algorithm for correcting the concentration of the nitrate by correcting the measurement by making a temperature correction using an internal or external temperature sensor. an UV LED combination configured to generate a first UV LED signal centered at 229 nm and a second UV LED signal centered in a range of 250-275 nm that traverse the confined volume of water within the prescribed region of the sampling chamber in order to sense nitrates in the water with first UV LED signal and dissolved organic matter in the water with the second UV LED signal; a reference photodiode configured to respond to part (L R) of the first UV LED signal and the second UV LED signal, and provide photodiode reference signaling containing information about the part (L R) of the first UV LED signal and the second UV LED signal received; a measuring photodiode configured to sense the first UV LED signal and the second UV LED signal (L M) that pass through the confined volume of water within the prescribed region of the sampling chamber, and provide photodiode measured signaling containing information about a nitrate absorption of the water related to the first UV LED signal and a DOM absorption background related to the second UV LED signal; a transimpedance amplifier configured to respond to the photodiode reference signaling and the photodiode measured signaling, and provide transimpedance amplifier signaling containing information about a photocurrent to voltage reference signaling conversion of the photodiode reference signaling without interaction with the water and also a photocurrent to voltage measured signaling conversion of the photodiode measured signaling after interaction with the water; and a signal processor or signal processing module configured to: receive the transimpedance amplifier signaling, and determine corresponding signaling containing information about a DOM background corrected concentration of nitrates dissolved in the water by determining the nitrate concentration dissolved in water with the nitrate absorption sensed in the water at 229 nm compensated by the DOM background absorption sensed in the water in the range of 250-275 nm, based upon the transimpedance amplifier signaling received, and wherein the signal processor or signal processing module is further configured to implement a compensation algorithm for correcting the concentration of the nitrate by correcting the measurement by making a temperature correction using an internal or external temperature sensor. receive the transimpedance amplifier signaling, and determine corresponding signaling containing information about a DOM background corrected concentration of nitrates dissolved in the water by determining the nitrate concentration dissolved in water with the nitrate absorption sensed in the water at 229 nm compensated by the DOM background absorption sensed in the water in the range of 250-275 nm, based upon the transimpedance amplifier signaling received, and wherein the signal processor or signal processing module is further configured to implement a compensation algorithm for correcting the concentration of the nitrate by correcting the measurement by making a temperature correction using an internal or external temperature sensor.