Agricultural ditches and stream networks are overlooked hotspots of carbon emissions

Boxplots showing variation of CH4 flux among different types of ditches (Agriculture (ndiffusive = 41, nebullusive = 9), Forest (n = 24), Urban (n = 10), Wetland (n = 5)), streams (ndiffusive = 321, nebullusive = 27), rivers (Strahler stream order > 4, ndiffusive = 157, nebullusive = 20), and lakes (ndiffusive = 631, nebullusive = 144). (c) Boxplots showing variation of CO2 flux among different types of ditches (Agriculture (n = 40), Forest (n = 26), Urban (n = 12), Wetland (n = 5)), streams (n = 311), rivers (n = 170), and lakes (n = 7250). Abbreviations: DO (dissolved oxygen), OC (organic carbon), SOC (soil organic carbon), TP (total phosphorus), TOC (total organic carbon), TN (total nitrogen), n (number of samples). Carbon emission flux data of ditches was obtained from Silverthorn, Audet [16], streams and rivers from [17], lakes from [18]. Stream and river represent rivers with Strahler stream orders 1-2 and > 5 in the Global River Methane Database of concentrations and fluxes (non-targeted sites were used), respectively.