Greenhouse gases (GHGs), including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), are increasing in concentration in the atmosphere. This poses a risk to the planet due to the radiative forcing of these gases which is ultimately leading to climate change. Inland waters across the globe, specifically lakes, rivers, and wetlands, are important sources, and occasional sinks, of GHGs to the atmosphere, due to the natural biogeochemical processes happening in these waterbodies. Understanding the contribution of these systems to the global GHG budget and the processes regulating the GHG emissions is important, as it helps to understand how these systems can contribute to climate change but also how climate change may influence the GHG emissions from these systems. However, relatively little is known about the contribution of GHGs of constructed waterbodies, particularly in agricultural regions receiving large amounts of nutrients (carbon, nitrogen, and phosphorus). This thesis investigates the magnitude and regulating factors of CO2, CH4, and N2O emissions in agricultural reservoirs on seasonal and diel timescales and compares constructed waterbodies to natural wetland ponds located on the same landscape. Applying generalized additive models in this thesis, I analyzed the controlling factors of CO2 (64-88% deviance explained), CH4 (75-86% deviance explained), and N2O (87-96% deviance explained) and the seasonal trends in the three GHGs (37-90% deviance explained) in agricultural reservoirs. In Chapter 2, I explored the concentrations of the GHGs on seasonal and diel timescales, and the regulating factors on GHG concentrations over a seasonal timescale. The GHGs exhibited significant seasonal trends, but no consistent trends on a diel timescale, and were regulated by a combination of biological, chemical, and physical parameters (Ch. 2). In Chapter 3, I contrasted the differences in concentration and regulating factors of GHGs in natural wetland ponds and agricultural reservoirs on the same landscape. Agricultural reservoirs and natural wetland ponds exhibited similar concentrations of all GHGs, however, the factors regulating the concentration of GHGs in these systems are different (Ch. 3). Together, these studies show that natural and constructed waterbodies located on the same landscape are important sources of GHGs, provide insight to how climate change may affect these systems, and potential opportunities to manage these systems to reduce GHG emissions, provided in Chapter 4.