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Groundwater flowing from hillslopes through riparian (near stream) soils often undergoes chemical transformations that can substantially influence stream water chemistry. We used landscape analysis to predict total organic carbon (TOC) concentrations pro- files and groundwater levels measured in the riparian zone (RZ) of a 67 km² catchment in Sweden. TOC exported from 13 riparian soil profiles was then estimated based on the riparian flow-concentration integration model (RIM). Much of the observed spatial variability of riparian TOC concentrations in this system could be predicted from groundwater levels and the topographic wetness index (TWI). Organic riparian peat soils in forested areas emerged as hotspots exporting large amounts of TOC. Exports were subject to considerable temporal variations caused by a combination of variable flow conditions and changing soil water TOC concentrations. From more mineral riparian gley soils, on the other hand, only small amounts with relatively time-invariant concentrations were exported. Organic and mineral soils in RZs constitute a heterogeneous landscape mosaic that controls much of the spatial variability of stream water TOC. We developed an empirical regression-model based on the TWI to move beyond the plot scale to predict spatially variable riparian TOC concentration profiles for RZs underlain by glacial till. [ABSTRACT FROM AUTHOR]

A physically based SVAT-model was tested with soil and snow physicalmeasurements, as well as runoff data from an 8600 m2 catchment in northern Sweden in order to quantify the influence of soil frost on spring snowmelt runoff in a moderately sloped, boreal forest.The model was run as an array of connected profiles cascading to thebrook. For three winter seasons (1995-98) it was able to predict theonset and total accumulation of the runoff with satisfactory accuracy. Surface runoff was identified as only a minor fraction of the total runoff occurring during short periods in connection with ice blocking of the water-conducting pores. Little surface runoff, though, doesnot mean that soil frost is unimportant for spring runoff. Simulations without frost routines systematically underestimated the total accumulated runoff. The possibility of major frost effects appearing in response to specific combinations of weather conditions were also tested. Different scenarios of critical initial conditions for the winter, e.g. high water saturation and delayed snow accumulation leading to an increased frost penetration, were tested. These showed that under special circumstances there is potential for increased spring runoff due to soil frost. [ABSTRACT FROM AUTHOR]

To determine how soil frost changes flowpaths of runoff water along a hillslope, a transect consisting of four soil profiles directed towards a small stream in a mature forest stand was investigated at Svartberget, near Vindeln in northern Sweden. Soil temperature, unfrozen water content, groundwater level and snow depth were investigated along the transect, which started at the riparian peat, and extended 30 m upslope into mineral soils. The two, more organic-rich profiles closest to the stream had higher water retention and wetter autumn conditions than the sandy mineral soils further upslope. The organic content of the soil influenced the variation in frost along the transect. The first winter (1995-96) had abnormally low snow precipitation, which gave a deep frost down to 40-80 cm, whereas the two following winters had frost depths of 5-20 cm. During winter 1995-96, the two organic profiles close to the stream had a shallower frost depth than the mineral soil profile higher upslope, but a considerably larger amountof frozen water. The fraction of water that did not freeze despite several minus degrees in the soil was 5-7 vol.% in the mineral soil and 10-15 vol.% in the organic soil. From the measurements there were no signs of perched water tables during any of the three snowmelt periods, which would have been strong evidence for changed water flowpaths due to soil frost. When shallow soil layers became saturated duringsnowmelt, especially in 1997 and 1998, it was because of rising groundwater levels. Several rain on frozen ground events during spring 1996 resulted in little runoff, since most of the rain either froze in the soil or filled up the soil water storage. [ABSTRACT FROM AUTHOR]

Quantitatively separating the anthropogenic and natural contributions to acid neutralisation capacity (ANC) depression during spring flood is complicated by the many factors which contribute to this depression. Besides anthropogenic sulphate and nitrate, there are natural influences which include dilution, organic acids, sea salts, as well asstrong mineral acid anions from bedrock and/or sediment. This paper presents a model for separating and quantifying the effects of dilution, organic acids and strong mineral acids on the ANC for five streams in Nothern Sweden during the spring floods of 1994 and 1995. The basis of the model is that the baseflow prior to and following the event is essentially unaffected by acid deposition and hence can act as the chemical baseline for the episode. The relative contribution of different factors to the spring flood ANC depression are calculated with reference to the dilution of a conservative hydrological tracer. The most important contributor to the ANC decline was found to be dilution of baseflow and organic acids in this remote region of Europe with relatively low acid deposition levels. [ABSTRACT FROM AUTHOR]

Conifer needles are an important link in the cycling of Total Mercury (THg) and Methylmercury (MeHg) in the boreal ecosystem due to the high THg and MeHg concentrations in litterfall. Translocation within the tree of Hg from soils to the crown canopy has been assumed to be aminor source of the Hg in litterfall. This paper, however, is the first to present direct observations of THg/MeHg transport from the soil via xylem sap. Xylem sap concentrations of THg and MeHg were measured in sap drained from different levels along the boles of freshly cut 100 year old Norway spruce (Picea abies) and Scots pine (Pinus sylvestris). The trees came from a mixed stand growing on podzolized tillsoils at the Svartberget Forest Research Station in N. Sweden. Soil solution concentrations of THg and MeHg at different levels in the soil profile were measured for comparison. Concentrations of THg in xylem sap ranged from 10--15 ng L-1 in both the Scots pine and Norway spruce. Concentrations of MeHg varied from 0.03 ng L-1 to 0.16 ng L-1 with higher values in Scots pine thanNorway spruce. If these concentrations are representative of the transport from soils to needles in xylem sap at this site, then only 3% of the MeHg in litterfall (0.12 mg ha- 1 yr-1) and 11% of the THg (26 mg ha-1 yr-1) can originate via this pathway. The upward transport via xylem sap is larger relative to the open field inputs (84% of THg and 17% of MeHg). Comparison of soil solution and xylem sap THg/MeHg suggested some degree of THg exclusion during water uptake in Scots pine and Norway spruce, but MeHg exclusion only in Norway spruce. [ABSTRACT FROM AUTHOR]

The input and output flux data of total Hg (THg) and methylmercury (MeHg) from three catchments located in different geographical regionsin Sweden and one catchment in southern Finland were compared to elucidate the role of current atmospheric Hg/MeHg deposition with regardto waterborne Hg/MeHg output. There was a negative co-variation between the open field THg inputs and the ratio of THg output to open field input. The highest ratio (and lowest input) occurring in N. Swedenand S. Finland, while the lowest output ratio (and highest inputs) occurred in southwest Sweden. A much larger variation was found in theratio of output to open field input for MeHg (14 to 160%). Examinations of MeHg input/output data in relation to catchment characteristics suggest that riparian peat, mires and wet organic soil contributed to the large MeHg output from certain catchments, probably due to in situ production of MeHg. This finding is consistent with other studies which have found that catchment characteristics such as wetland area, flow pathways, seasonal temperature and water flow are important in controlling the output of MeHg. These catchment characteristics govern the fate of the contemporary input of Hg and MeHg as well as the mobilization of the soil pools. [ABSTRACT FROM AUTHOR]

TOPMODEL was calibrated to a small catchment using precipitation andrunoff data. Acceptable fits of simulated and observed runoff were obtained during both the calibration and validation periods. Predictions of groundwater levels using this calibration did not agree well with observations at the 37 points within the catchment where groundwater levels were measured, including three locations with continuous recordings. Groundwater level observations at one single point in time,however, sufficed to calibrate new topographic--soil indices that improved the prediction of the local groundwater levels at the observedtubes. This suggests that spatially distributed calibration data arenecessary to exploit reliably TOPMODEL's ability to predict spatially distributed hydrology. The mean or recalibrated transmissivity values at these 37 points differed from the catchment mean as determined by the precipitation--runoff calibration. Thus, while groundwater information can help in predicting groundwater levels at specific locations, increasing the number of local groundwater level measurements isnot sufficient to improve the spatially distributed representation of subsurface flow by TOPMODEL for the catchment as a whole, as long as the groundwater information is not integrated in the precipitation-- runoff calibration. [ABSTRACT FROM AUTHOR]

Short-term increases in soil solution nitrate (NO(3)(-)) concentration are often observed after forest harvest, even in N-limited systems. We model NO(3)(-) leaching below the rooting zone as a function of site productivity. Using national forest inventories and published estimates of N attenuation in rivers and the riparian zone, we estimate effects of stem-only harvesting on NO(3)(-) leaching to groundwater, surface waters and the marine environment. Stem-only harvesting is a minor contributor to NO(3)(-) pollution of Swedish waters. Effects in surface waters are rapidly diluted downstream, but can be locally important for shallow well-waters as well as for the total amount of N reaching the sea. Harvesting adds approximately 8 Gg NO(3)-N to soil waters in Sweden, with local concentrations up to 7 mg NO(3)-N l(-1). Of that, ∼3.3 Gg reaches the marine environment. This is ∼3% of the overall Swedish N load to the Baltic., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Previous studies at the Svartberget catchment in northern Sweden have identified potential terrestrial sources of methylmercury (MeHg) and total mercury (THg) in runoff as well as processes controlling MeHg/Hg transfers from soil to runoff water. This paper considers whether the concepts based on a few seasons of observations are consistent with catchment budgets of MeHg/THg over half a decade. Inter-annual and seasonal variations in the input and output fluxes of THg/MeHg, in open field wet deposition (OF), litterfall (LF) and runoff water are evaluated together with more recently measured concentrations that include the throughfall water (TF) data. The input and output flux data of THg and MeHg from the Svartberget catchment are also compared to those from the Gårdsjön Catchment. The average annual MeHg input fluxes in OF, TF and LF are 0.08, 0.17 and 0.3 g km(-2) year(-1), respectively. The comparable inputs for THg are 7, 15 and 17 g km(-2) year(-1). Thus, LF is as important as TF for THg inputs, while LF is twice as important as TF for MeHg inputs. The annual output flux of MeHg varied between 0.05 and 0.14 g km(-2) year(-1). The annual output flux of THg varied between 1 and 3.4 g km(-2) year(-1). The large inter-annual variations in catchment output did not follow the smaller variations in atmospheric input. This suggests that changes in climate can effect terrestrial outputs of THg/MeHg to surface water more than atmospheric deposition. These data do not contradict the earlier findings that it is the hydrological and biogeochemical processes in the riparian zone that have a central role in determining the amount of MeHg reaching surface waters from forested catchments. The juxtaposition of major flow paths and organic-rich soils in the riparian zone may create the locations of most importance for net MeHg production, runoff export and a larger pool of MeHg.