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The water quality in headwater streams depends on the groundwater origin and its transport pathways before it eventually discharges as surface water. In this case study, we present the Ce anomaly of over 100 hemiboreal headwater streams in Sweden and discuss the potential of the Ce anomaly to define two stream end members as proxies for the stream origin. The data show a relation between topography and the Ce anomaly, with more negative values (−0.8 to −0.4) in hilly catchments with distinct slopes, defined as an oxidized groundwater end member. The second end member is dominated by groundwater discharge from reduced, organic-rich riparian and wetland soils (reduced groundwater) having small Ce anomalies (−0.3 to zero). Element concentrations show a wide range, depending on the end member of the stream. For example, redox elements (Fe, Mn, S and N) show concentrations up to five times in streams with small negative Ce anomalies (reduced groundwater) compared to the concentrations in streams with large negative Ce anomalies. While element concentrations (of the classic redox elements Fe, Mn, S, N) show seasonal variations due to a summer drought period and the resulting reduced conditions, the Ce anomaly is constant, offering an excellent indicator of the dominant groundwater flow paths regardless of seasonal variations.

There is a growing societal demand to increase the use of forest biomass for substitution of fossil fuels. The production of this biomass must be sustainable and an indicator for critical biomass harvesting (CBH) has been suggested in order to sustain forest soil fertility and mitigate soil acidification at whole-tree harvesting. The CBH indicator is based on an acidity mass balance approach in line with the critical load of acid deposition (CL) concept. Countries like Sweden, the Netherlands and the state of Quebec, Canada apply such mass balance approaches for developing forest biomass harvesting guidelines. The implementation of this type of policy instrument may restrict the use of harvest residues for bioenergy and thereby the substitution of fossil fuels. It may as well affect the forestry sector revenue negatively. To maintain credibility for enforced limitations, it is important that the risk assessment and suggested policy implications are based on solid scientific methods and assumptions. The mass balance approach have been criticized for being too uncertain and not sufficiently validated for being used to guide ecosystem management. In this paper we use published Swedish data on soils, acid deposition, forest production and information from international scientific literature to critically examine the CBH indicator. We conclude that the CBH indicator 1) does not account for all relevant processes 2) it exaggerates the sensitivity and correlates poorly to actual forest soil acid-base status and edaphic conditions and 3) data availability does not allow the indicator to be calculated at a high enough spatial resolution for advice on management for forest owners. The concerns for the mass-balance approach and CBH indicator are discussed in an international perspective.