Chlorine Distribution in Soil and Vegetation in Boreal Habitats along a Moisture Gradient from Upland Forest to Lake Margin Wetlands

Interactionsbetween plant communities and Cl biogeochemistryalong hydrological gradients across landscapes are fundamental knowledgefor interpreting most Cl-related environmental studies. The assumed dominance of chloride (Cl-) in terrestrialecosystems is challenged by observations of extensive formation oforganically bound Cl (Cl-org), resulting in large soil Clstorage and internal cycling. Yet, little is known about the spatialdistribution of Cl in ecosystems. We quantified patterns of Cl distributionin different habitats along a boreal hillslope moisture gradient rangingfrom relatively dry upland coniferous forests to wet discharge areasdominated by alder. We confirmed that dry habitats are important forCl storage but found that Cl pools tended to be larger in moist andwet habitats. The storage of Cl-org was less important inwet habitats, suggesting a shift in the balance between soil chlorinationand dechlorination rates. Cl concentrations in the herb layer vegetationwere high in wet and moist sites attributed to a shift in plant speciescomposition, indicating plant community-dependent ecosystem Cl cycling.Mass-balance calculations showed that internal Cl cycling increasedoverall ecosystem Cl residence times at all sites and that plant uptakerates of Cl- were particularly high at wet sites.Our results indicate that habitat characteristics including plantcommunities and hydrology are key for understanding Cl cycling inthe environment.