## 1 Introduction  
Outgassing of carbon dioxide (CO\({}_{2}\)) from rivers has been identified as a significant piece of the carbon cycle [1; 2; 3]. The process has been attributed to an oversaturation of dissolved CO\({}_{2}\) in the water column, resulting in diffusion of CO\({}_{2}\) into the atmosphere. The two primary inputs of CO\({}_{2}\) into the water column of large river systems are (1) in-situ respiration of organic material and (2) flushing of CO\({}_{2}\) produced in soil pores from terrestrial and wetland environments via decomposition of organic material and root respiration [4]. The principal removal mechanism of aqueous CO\({}_{2}\) is in-situ primary production, or photosynthesis [4]. Many of the world's largest rivers are supersaturated in CO\({}_{2}\) with respect to the atmosphere, resulting in a large flux of CO\({}_{2}\) from the water surface [1; 5; 6]. Current estimates of global CO\({}_{2}\) flux from rivers to the atmosphere vary largely from 230 to 1800 Tg yr\({}^{-1}\)[2; 3; 7], calculated using partial pressure estimates of dissolved CO\({}_{2}\) (\(p\)CO\({}_{2}\)), many of which are derived from low-time resolution (i.e., weekly or monthly) measurements of river alkalinity,pH, and water temperature. This method of \(p\)CO\({}_{2}\) calculation has been scrutinized for its great degree of uncertainty in temperate and tropical freshwaters due to the potential of significant contributions of organic acids to total alkalinity and low pH systems greatly over-estimating calculations [8]. The higher range of outgassing estimates is much greater than global estimates for the export of dissolved organic (200-360 Tg yr\({}^{-1}\)) and inorganic carbon (381-410 Tg yr\({}^{-1}\)), as well as particulate organic (180-240 Tg yr\({}^{-1}\)), and inorganic carbon (170 Tg yr\({}^{-1}\)) to the oceans [9; 10; 11; 12]. Variation in estimates stem largely from differences in methods and data availability and resolution. One of the pioneering attempts in calculating total CO\({}_{2}\) outgassing from rivers by [PERSON] and others [2] estimated 230 Tg yr\({}^{-1}\) based on data from approximately 80 rivers. Several years later, [PERSON] and others [3] estimated an annual outgassing of 1800 Tg yr\({}^{-1}\) from rivers, globally incorporating data collected from all stream orders with little requirements of data resolution. The most recent estimates by [PERSON] and others [7] excluded first order stream measurements and only included rivers with multiple samples collected across varying seasons, resulting in a global average riverine \(p\)CO\({}_{2}\) value 700 \(\upmu\)atm less than [PERSON] et al. (i.e., 2400 vs. 3100 \(\upmu\)atm) and an annual outgassing flux nearly one-third of the [PERSON] and others. Great strides have been made to improve freshwater CO\({}_{2}\) outgassing calculations and models through refining gas transfer velocities and \(p\)CO\({}_{2}\) calculations based on regional hydrologic, climate, and atmospheric conditions. Yet, it is clear based on the large discrepancies in outgassing estimates stemming from the difference in spatial and temporal data resolution, that the lack of high resolution \(p\)CO\({}_{2}\) data is a limiting factor on the accuracy of calculations. Aquatic \(p\)CO\({}_{2}\) can fluctuate both spatially and seasonally due to differences in land-use, discharge, water temperatures, and rates of biological respiration and photosynthesis [13; 14; 15; 16; 17]. Furthermore, aquatic respiration and photosynthesis rates can vary greatly over the span of a day due to a change in temperature and sunlight availability [18], resulting in a significant variability of \(p\)CO\({}_{2}\) in water bodies between night and day [19; 20; 21]. A few recent studies have highlighted the importance of diel variation of \(p\)CO\({}_{2}\) and CO\({}_{2}\) evasion from lakes and reservoirs. In a study conducted in Lochaber Lake in eastern Nova Scotia, Canada, Spafford and Risk [22] found that 65-95% of the total CO\({}_{2}\) release in a 24-h period occurred during the nocturnal period.