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Surface water quality data are available from many public and private agencies across the United States. But, how can they be effectively utilized to help resolve the complex biogeochemical relationships of surface waters? The present study examined available stream and reservoir water quality, stream discharge, and meteorological time-series datasets for the Upper and Lower Scioto watersheds in central Ohio. The focus was on the fate and transport of nutrients, specifically nitrate and total phosphorus, in the streams and surface water reservoirs of these predominantly agricultural watersheds. The study area is composed of seven sub-watersheds, five of which contain major surface water reservoirs. Mean nitrate values for the more “riverine” J. Griggs and O’Shaughnessy reservoirs were more than double those for the more “lacustrine” Hoover and Alum Creek Lake reservoirs, and were at least partially due to the different reservoir morphometries and resultant residence times. Nitrate concentrations have gradually decreased over the periods of record in all four reservoirs. Phytoplankton populations in Hoover and Alum Creek Lake reservoirs are ecologically driven, while populations in O’Shaughnessy and J. Griggs reservoirs are weather and stream flow dependent. The Big Darby Creek contains no major reservoirs or stream impoundments. From 1973 to 2008, annual-mean discharge ranged from 6.8 m3s-1 to 26.8 m3s-1 with an average of 16.1 m3s-1. Fall months were periods of lowest discharge, with spring to mid-summer months typically having highest discharge values. Nitrate and total phosphorus concentrations exhibited a wide range with means closely similar to the values in O’Shaughnessy and J. Griggs reservoirs. Nitrate concentrations have slowly increased in the Big Darby Creek study area from 1973 to 2010. Quadratic model regression analysis showed nitrate concentration had a strong positive relationship with corresponding daily-mean discharge, but total phosphorus concentration was uncorrelated. Seasonal nitrate and daily-mean discharge trends were positive and similar except for fall, which could have been biased by a lack of concentration data for low flows. An analysis of stream flow dynamics suggests that chloride is primarily associated with ground water and is negatively related to stream discharge. Nitrate concentration is predominantly associated with precipitation generated surface runoff or tile-drained discharges from crop lands. The nitrate reservoir in the soil horizon of the Big Darby Creek watershed is gradually depleted from winter to fall. A conceptual model for the prediction of nitrate concentration at the USGS gaging station at Chillicothe, terminus of all study area surface water, is the sum of the calculated nitrate concentrations of all seven sub-watersheds. Main components of the model are the calculation of daily discharge and nitrate concentrations for the individual sub-watersheds. The model is specifically designed to capture the effect widespread precipitation events have on individual sub-watershed areas, and can be modified for the prediction of other watershed nutrient concentrations. This study has provided an important first step in the quantitative interpretation of the origin of complexity in the development of understanding of nutrient distribution in large watersheds.