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Abstract.  When assessing the acidification status for a body of water, a reference value that describes the natural state is often estimated. One way to define this reference is to use the biogeochemical model MAGIC. However, MAGIC requires too many input parameters and modelling skills to use for operational application at a regional scale where hundreds or thousands of objects need to be assessed. Here we explore the possibility of complementing MAGIC with a simpler metamodel. The metamodel, metaMAGIC, was calibrated to 95 lakes with pre-industrial ANC predicted by MAGIC. The lakes constituted a diverse population, spread across a region stretching 1360 km in a N-S direction. MetaMAGIC proved capable of estimating the pre-industrial ANC calculated by MAGIC with a validated median error of 13.2 μeq/L, using contemporary concentrations of base cations, SO4 2- and Cl- as predictors. In comparison with the commonly used SSWC-model, MetaMAGIC reproduces the pre-industrial buffering capacity reconstructed with MAGIC more accurately. An advantageous feature of the metamodel is that it allows the reference value to vary in response to short-term hydroclimatological influences. Hence it provides a more stable assessment when few contemporary measurements of water chemistry are available. This metamodelling approach is suggested as a useful tool for acidification assessment purposes, and more generally, for extending the information from complex biogeochemical models. [ABSTRACT FROM AUTHOR]

Abstract.  The impact of runoff on allochthonous organic carbon was studied in the River Öre, Northern Sweden, using extensive TOC (total organic carbon) and runoff measurements. No relationship existed between TOC concentration and runoff on an annual basis. However, positive correlations between TOC concentration and runoff were found when observations were divided into three different seasons (winter, spring and summer/autumn). During these seasons runoff explained 62–70% of the TOC variation. Differences in these seasonal relationships indicated that the TOC concentration was restricted by the soil TOC pool during snowmelt, while the pool of TOC in the soil or its availability never limited the TOC export during the rest of the year. Two sets of data were used, a detailed study over 2 years and a long-term study over 14 years. Both showed similar results which indicated that the seasonal variation in the relationship between TOC and runoff is similar from year to year. The chemical variation usually decreases downstream in large rivers due to mixing of water from different sources. Our study, however, showed a strong correlation between TOC and runoff even in a large river like the River Öre. This result indicated that the general pattern of the TOC concentrations was to a large extent determined by the hydrology and climate conditions. [ABSTRACT FROM AUTHOR]