Agriculture has changed the amount and composition of dissolved organic matter in Central European headwater streams

► Agriculture can be an important source of dissolved organic matter (DOM) to headwaters. ► Export of DOM from agriculture is structurally complex and exhibits a low redox state. ► Land-use related patterns of DOM amount and composition are consistent across seasons. ► In headwaters, the degree humification of DOM is strongly related to DOC concentration. ► Export of DOM from agriculture may affect metabolism and health of aquatic ecosystems.