role of organic-matter-bound chlorine in the chlorine cycle: a case study of the Stubbetorp catchment, Sweden

The objective of this study is to construct a balanced chlorine budget for a small forested catchment, focusing on the interaction between chloride ($\text{Cl}_{\text{inorg}}$) and organic-matter-bound chlorine ($\text{Cl}_{\text{org}}$). Data from the actual catchment are combined with secondary data from other sites to elucidate more clearly which parts of the cycle are fairly well known and which are more or less unknown. The budget calculations show that the principal input and output fluxes of Cl in the catchment are inorganic but that the main pool is$\text{Cl}_{\text{org}}$in the soil. In addition, the budget calculations suggest that a considerable portion of$\text{Cl}_{\text{inorg}}$in soil is transformed to$\text{Cl}_{\text{org}}$and subsequently leached to deeper soil layers, that net mineralization of$\text{Cl}_{\text{org}}$takes place in soil, preferably in deeper soil layers, and that degrading organic matter is a major source of$\text{Cl}_{\text{inorg}}$in runoff. The loss of$\text{Cl}_{\text{org}}$through runoff is small to negligible in relation to other fluxes. It appears as if dry deposition of$\text{Cl}_{\text{inorg}}$is at risk of being underestimated if$\text{Cl}_{\text{inorg}}$is assumed to be conservative in soil. The pool of organic-matter-bound chlorine in soil is considerably larger than the annual flux of chloride through the system. The estimates suggest that the amount of$\text{Cl}_{\text{org}}$in the upper 40 cm of the soil at the investigated site is approximately twice as large as the$\text{Cl}_{\text{inorg}}$. Furthermore, the amount of$\text{Cl}_{\text{org}}$biomass is small in relation to the occurrence of$\text{Cl}_{\text{org}}$in soil. Finally, the estimates indicate that the transport of volatile$\text{Cl}_{org}$from the soil to the atmosphere may influence the chlorine cycle.