Increasing concentrations of organic matter (OM) in surface waters have been noted over large parts of the boreal/nemoral zone in Europe and North America. This has raised questions about the causes and the likelihood of further increases. A number of drivers have been proposed, including temperature, hydrology, as well as SO 2À 4 -and Cl À deposition. The data reported so far, however, have been insufficient to define the relative importance of different drivers in landscapes where they interact. Thirty-five years of monthly measurements of absorbance and chemical oxygen demand (COD), two common proxies for OM, from 28 large Scandinavian catchments provide an unprecedented opportunity to resolve the importance of hypothesized drivers. For 21 of the catchments, there are 18 years of total organic carbon (TOC) measurements as well. Despite the heterogeneity of the catchments with regards to climate, size and land use, there is a high degree of synchronicity in OM across the entire region. Rivers go from widespread trends of decreasing OM to increasing trends and back again three times in the 35-year record. This synchronicity in decadal scale oscillations and long-term trends suggest a common set of dominant OM drivers in these landscapes. Here, we use regression models to test the importance of different potential drivers. We show that flow and SO 2À 4 together can predict most of the interannual variability in OM proxies, up to 88% for absorbance, up to 78% for COD. Two other candidate drivers, air temperature and Cl À , add little explanatory value. Declines in anthropogenic SO 2À 4 since the mid1970s are thus related to the observed OM increases in Scandinavia, but, in contrast to many recent studies, flow emerges as an even more important driver of OM variability. Stabilizing SO 2À 4 levels also mean that hydrology is likely to be the major driver of future variability and trends in OM.

Running water comprises just over one millionth of the world's water. The importance of those streams and rivers as a resource for human welfare and biodiversity, however, is far out of proportion to that minuscule fraction. This explains why protecting running waters (the flow regimes, water quality and biota) is such a vital concern for society. Yet for all the focus and concern, how much do we actually know about these running waters, and the lotic habitat they comprise?Consider what would happen if one asked any national environmental authority to assess the basic chemical and ecological status of running waters. At the river mouths, there would be enough information to make a reasonable assessment of the status. But somewhere on the way upstream, available data would run dry, long before most stream channels did (in non-arid regions).In Sweden, with an ambitious programme for monitoring and assessing surface waters, it came as a surprise several years ago to realize that the length of all perennial streams on the country's maps was not known. When that was modelled in the form of a 'virtual network' from a 50 m × 50 m digital elevation model, the total length turned out to be 530 000 km (ca 1 km/km 2 ), which was double the previous estimates. The length was independently confirmed by another group using remote sensing data (Esseen et al., 2004). Further analysis of the virtual network revealed that over 90% of the stream length had catchment areas under 15 km 2 . Although this might seem merely of academic interest, 15 km 2 is the lower limit for what has been surveyed on a national scale in Sweden. Does this mean that we have missed something important in our assessment of water resources?When the chemistry of all flowing headwaters in a single 78 km 2 catchment was compared to the 2000 Swedish national survey of running waters, there was as much variability within the headwaters of that forested catchment as could be found in a statistically representative sample of over 260 000 km 2 of Sweden's boreal forest waters (Temnerud and Bishop, 2005). Other studies on biota have not just found such headwaters to be teeming with biodiversity, but also found species that are endemic to headwaters (Meyer et al., 2007). Discrete inquiries were made to see if national agencies in other countries of North America and Europe had come further in the documentation and assessment of headwaters. The answer was 'no'. There are, however, some significant efforts (e. g. Hutchins et al., 1999; Smart et al., (2006). But since many first and second order streams are not on the US maps, and the assessment went up to fifth order streams, headwaters are likely to be seriously underrepresented even in that landmark survey. 2001; Likens and Buso, 2006). The most notable is the US Environmental Protection Agency's (EPA's) 'Wadeable Stream AssessmentIn most regions, the overwhelming majority of stream length lies beyond the frontiers of any systematic documentation and would have to be represented as a blank space on the assessment m...

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For more than 50 years, scientific insights from surface water monitoring have supported Swedish evidence-based environmental management. Efforts to understand and control eutrophication in the 1960s led to construction of wastewater treatment plants with phosphorus retention, while acid rain research in the 1970s contributed to international legislation curbing emissions. By the 1990s, long-time series were being used to infer climate effects on surface water chemistry and biology. Monitoring data play a key role in implementing the EU Water Framework Directive and other legislation and have been used to show beneficial effects of agricultural management on Baltic Sea eutrophication. The Swedish experience demonstrates that well-designed and financially supported surface water monitoring can be used to understand and manage a range of stressors and societal concerns. Using scientifically sound adaptive monitoring principles to balance continuity and change has ensured long-time series and the capability to address new questions over time.

In the north-western European countries Norway, Sweden, United Kingdom (UK) and Ireland, variability in the forms, amounts and timing of phosphorus (P) loss from agricultural land is related to national differences in climate, soil, hydrological conditions and agricultural production. The dissolved form of P constitutes 9-93% of the total phosphorus (TP) in water, subsurface drainage can contribute 12-60% and surface erosion 40-88% of TP transfer. TP export in small agricultural streams is generally in the range 0.3-6 kg ha )1 year )1 , with the highest losses in Norway and UK. All four countries are complying with the EU Water Framework Directive and developing a range of measures based on P source with transport controls over P losses. A decreasing trend in TP losses has been detected in agricultural streams following the introduction of measures to reduce erosion in Norway. Average P concentrations in Swedish streams have shown a reduction of nearly 2% per year since 1993 as a result of measures introduced in southern Sweden. However, in two large rivers in agricultural regions of Sweden, the concentrations of suspended solids (SS) and TP were shown to increase by 0.4% and 0.7% per year, respectively, over the period 1975-2004, possibly as a result of climate change. It is too early to detect trends in agricultural contributions to P in surface waters as a result of catchment-sensitive farming (CSF) in the UK and Ireland.

We present an analysis of long-term (1988-2013; 26years) total phosphorus (TP) concentration trends in 81 Swedish boreal lakes subject to minimal anthropogenic disturbance. Near universal increases in dissolved organic carbon (DOC) concentrations and a widespread but hitherto unexplained decline in TP were observed. Over 50% of the lakes (n=42) had significant declining TP trends over the past quarter century (Sen's slope=2.5%y). These declines were linked to catchment processes related to changes in climate, recovery from acidification, and catchment soil properties, but were unrelated to trends in P deposition. Increasing DOC concentrations appear to be masking in-lake TP declines. When the effect of increasing DOC was removed, the small number of positive TP trends (N=5) turned negative and the average decline in TP increased to 3.9%y. The greatest relative TP declines occurred in already nutrient poor, oligotrophic systems and TP concentrations have reached the analytical detection limit (1μgL) in some lakes. In addition, ongoing oligotrophication may be exacerbated by increased reliance on renewable energy from forest biomass and hydropower. It is a cause of significant concern that potential impairments to lake ecosystem functioning associated with oligotrophication are not well handled by a management paradigm focused exclusively on the negative consequences of increasing phosphorus concentrations.

The volume and depth of a lake are basic properties that greatly affect a wide array of its physical, chemical, and biological properties. Nevertheless, volume and depth data are scarce in lake-rich regions of the world. We coupled the Swedish lake register to GIS-derived geographical and topographical parameters, attempting to predict the volume and depth of 6943 lakes from map-derived parameters only. Lake area and the maximum slope in a 50 m wide zone outside of the lake shoreline were the most important predictors of both lake volume and depth, explaining 92% of the variance in lake volume but ˂40% of the variance in both maximum and mean depth. Regression parameters of regional submodels of lake volume were similar across geographically and topographically different regions, indicating that the model probably is applicable for glacially formed lakes in general. Despite the high degree of explanation for lake volume, the uncertainty in predicted volume for a single lake is considerable (relative standard deviation, ±57%). However, the mean or cumulative lake volume of catchments containing several lakes (n > 15) is predictable from map-derived parameters with a greatly reduced uncertainty.

Abstract. Long term data series (1996 through 2009) for trace metals were analyzed from a large number of streams and rivers across Sweden varying in tributary watershed size from 0.05 to 48 193 km 2 . The final data set included 139 stream sites with data for arsenic (As), cobalt (Co), copper (Cu), chromium (Cr), nickel (Ni), lead (Pb), zinc (Zn), and vanadium (V). Between 7 % and 46 % of the sites analyzed showed significant trends according to the seasonal Kendall test. However, in contrast to previous studies and depositional patterns, a substantial portion of the trends were positive, especially for V (100 %), As (95 %), and Pb (68 %). Other metals (Zn and Cr) generally decreased, were mixed (Ni and Zn), or had very few trends (Co) over the study period. Trends by region were also analyzed and some showed significant variation between the north and south of Sweden. Regional trends for both Cu and Pb were positive (60 % and 93 %, respectively) in the southern region but strongly negative (93 % and 75 %, respectively) in the northern region. Kendall's τ coefficients were used to determine dependence between metals and potential in-stream drivers including total organic carbon (TOC), iron (Fe), pH, and sulphate (SO 2− 4 ). TOC and Fe correlated positively and strongly with As, V, Pb, and Co while pH and SO 2− 4 generally correlated weakly, or not at all with the metals studied.