Effekten av återvätning av dikespåverkad skog på torv undersöktes här med modellberäkningar för hela Sverige för att se om markfuktighet, grundvattennivå samt nedströms flöden och koncentration av näringsämnena kväve, fosfor och organiskt kol väsentligt kunde påverkas. Studien utfördes genom att införa förbättrad information om diken i den hydrologiska modellen S-HYPE och sedan beräkna flöden och transport av näringsämnen med modellen, med och utan återvätning. För diken hämtades information om placering från en ny kartläggning. Det antogs här att samtliga diken hade ett djup av 0,7 m och att grundvattnet kunde påverkas inom 20 m från dikena. I den hydrologiska modellen utfördes beräkningar inom ca 40 000 delavrinningsområden som täcker hela landet. Dessa har en genomsnittlig storlek av ca 10 km2. Information gällande andel markyta som täcks av olika kombinationer av markanvändningar och jordarter, samt information om flöden och koncentration av ämnen i vattendrag och sjöar beräknades och representeras på denna skalan. Modellresultat för till exempel grundvattennivåer och markfuktighet finns dock för respektive markklass, såsom skog på torv.

Enligt beräkningarna höjdes grundvattennivån i dikespåverkad skog på torv vid återvätning oftast upp till ca 14 cm, vilket motsvarar i genomsnitt ca 2 cm höjning för skog på torv där även odikad torv räknas in. Förändringar av markfuktighet samt av flöden (låg-, medel- och högflöden) och koncentrationer av kväve, fosfor och organiskt kol vid utloppet från varje delavrinningsområde i landet, var under 2 % när all dikespåverkad skog på torv återvättes. Effekten i vattendrag på skalan av delavrinningsområden blev alltså liten.

Den största orsaken till att påverkan blir så liten på skalan av delavrinningsområden är den lilla andelen dikespåverkad skog på torv av totala arean i delavrinningsområden enligt implementeringen av information om diken, oftast mindre än 1 %. Dock finns faktorer somskulle kunna öka påverkan nedströms och som inte varit med i beräkningarna, till exempel tillrinning från omgivande mark till dikespåverkad torv, och möjlighet att ha djupare diken än 0,7 m. Effekten av detta skulle kunna undersökas genom modellutveckling och känslighetsanalys. Det finns också osäkerhet i simulering av organiskt kol där processer i ytvatten inte ingick i denna studie, och där processer i bäcknära zon kan vidareutvecklas. Fler observationer av flöden och ämneskoncentrationer före och efter dikesblockering skulle också vara av stort värde för att öka kunskapen om de viktiga processerna och gesäkrare beslutsunderlag.

The effect of re-wetting ditch-affected forest on peat was investigated here with model calculations for the whole of Sweden to see if soil moisture, groundwater level as well as downstream flows and concentration of the nutrient nitrogen, phosphorus and organic carbon could be significantly affected. The study was carried out by introducing improved information about ditches in the hydrological model S-HYPE and then calculating flows and transport of nutrients with the model, with and without re-wetting. For ditches, information about placement was collected from a new survey. It was assumed here that all the ditches had a depth of 0.7 m and that groundwater could be affected within 20 m of the ditches. In the hydrological model, calculations were carried out in about 40,000 subcatchment covering the whole country. These have an average size of about 10 km2. Information on the proportion of land area covered by different combinations of land uses and soil types, as well as information on flows and concentrations of substances in watercourses and lakes were calculated and represented on this scale. However, model results for e.g. groundwater levels and soil moisture exist for each soil and land use class, such as forest on peat. 

According to the calculations, the groundwater level in drained forest on peat during re-wetting was usually raised up to about 14 cm, which corresponds to an average of about 2 cm increase for forest on peat where even peat with no ditching is included. Changes in soil moisture as well as in flows (low, medium and high flows) and concentrations of nitrogen, phosphorus and organic carbon at the outlet of each sub-basin in the country, were below 2% when all drained forest on peat was rewetted. The effect in watercourses on the scale of sub-catchment areas was thus small. 

The main reason why the impact is so small on the scale of sub-catchments is the small proportion of drained forest on peat on this scale according to the implementation of information on ditches, usually less than 1%. However, there are factors that could increase the impact downstream and that have not been included in the calculations, such as runoff from surrounding soil to ditch-affected peat, and the possibility of having deeper ditches than 0.7 m. The effect of this could be investigated through model development and sensitivity analysis. There is also uncertainty in the simulation of organic carbon where processes in surface water were not included in this study, and where processes in the riparian zone can be further developed. More observations of flows and substance concentrations before and after rewetting would also be of great value in increasing knowledge about the important processes and providing better support for decision-making. 

Kort sammanfattning av rapporten till webbplatsen där den laddas upp:

SMHI har under 2018–2020 arbetat i projekt med ett regeringsuppdrag om att förbättra informationen om Sveriges vattenuttag. Arbetet är beskrivet i rapporten ”Ökad kunskap om vattenuttag i Sverige” som i sin tur bygger på en rad delrapporter som är bilagor till rapporten. Under arbetets gång har SMHI haft ett stort samarbete med andra myndigheter och branschorganisationer.

I dagsläget finns viss information om vattenuttag i Sverige, men informationen är långt ifrån heltäckande och det finns ett stort behov av att öka kunskapen. Det är nödvändig i arbetet med klimatanpassning och för planeringen av användningen av vattenresurserna. I förlängningen är det en fråga om att säkra dricksvatten- och livsmedelsförsörjningen, framför allt i de mest utsatta områdena i sydöstra delen av Sverige.

Projektet har bland annat arbetat med att beräkna vattenuttag för bevattning, djurhållning och hushåll med enskilt vatten samt gjort en kartläggning av vattenkraftens uttag och arbetat med frivillig insamling av industriers vattenuttag. Vi har också utrett hur länsstyrelsens tillsyn kan utvecklas för att få in mer vattenuttagsdata samt om det går att införa ett lagkrav på att rapportera vattenuttagsdata.

Detta uppdrag har tagit flera steg mot en bättre kunskap om Sveriges vattenuttag, men det återstår också mycket arbete och det är viktigt att arbetet med vattenuttag får fortsatta resurser de närmaste åren. För att på lång sikt få en bild över Sveriges vattenuttag behöver arbetet fortsätta med länsstyrelsernas tillsyn, lagkrav på rapportering av vattenuttag, beräkningar av bevattningsuttag samt frivillig insamling från industrier. Arbetet behöver utföras i samverkan med berörda samhällsaktörer. Samarbete behövs även kring informationsklassning och datahantering av vattenuttagsdata.

In spite of the great abundance and ecological importance of headwater streams, managers are usually limited by a lack of information about water chemistry in these headwaters. In this study we test whether river outlet chemistry can be used as an additional source of information to improve the prediction of the chemistry of upstream headwaters (size < 2 km(2)), relative to models based on map information alone. We use the concentration of total organic carbon (TOC), an important stream ecosystem parameter, as the target for our study. Between 2000 and 2008, we carried out 17 synoptic surveys in 9 mesoscale catchments (size 32-235 km(2)). Over 900 water samples were collected in total, primarily from headwater streams but also including each catchment's river outlet during every survey. First we used partial least square regression (PLS) to model the distribution (median, interquartile range (IQR)) of headwater stream TOC for a given catchment, based on a large number of candidate variables including sub-catchment characteristics from GIS, and measured river chemistry at the catchment outlet. The best candidate variables from the PLS models were then used in hierarchical linear mixed models (MM) to model TOC in individual headwater streams. Three predictor variables were consistently selected for the MM calibration sets: (1) proportion of forested wetlands in the sub-catchment (positively correlated with headwater stream TOC), (2) proportion of lake surface cover in the sub-catchment (negatively correlated with headwater stream TOC), and (3) river outlet TOC (positively correlated with headwater stream TOC). Including river outlet TOC improved predictions, with 5-15% lower prediction errors than when using map information alone. Thus, data on water chemistry measured at river outlets offer information which can complement GIS-based modelling of headwater stream chemistry.

Factors affecting total organic carbon (TOC) concentrations in 215 watercourses across Sweden were investigated using parameter parsimonious regression approaches to explain spatial and temporal variabilities of the TOC water quality responses. We systematically quantified the effects of discharge, seasonality, and long-term trend as factors controlling intra-annual (among year) and inter-annual (within year) variabilities of TOC by evaluating the spatial variability in model coefficients and catchment characteristics (e.g. land cover, retention time, soil type). Catchment area (0.18-47,000 km(2)) and land cover types (forests, agriculture and alpine terrain) are typical for the boreal and hemiboreal zones across Fennoscandia. Watercourses had at least 6 years of monthly water quality observations between 1990 and 2010. Statistically significant models (p < 0.05) describing variation of TOC in streamflow were identified in 209 of 215 watercourses with a mean Nash-Sutcliffe efficiency index of 0.44. Increasing long-term trends were observed in 149 (70%) of the watercourses, and intra-annual variation in TOC far exceeded inter-annual variation. The average influences of the discharge and seasonality terms on intra-annual variations in daily TOC concentration were 1.4 and 1.3 mg l(-1) (13 and 12% of the mean annual TOC), respectively. The average increase in TOC was 0.17 mg l(-1) year(-1) (1.6% year(-1)). Multivariate regression with over 90 different catchment characteristics explained 21% of the spatial variation in the linear trend coefficient, less than 20% of the variation in the discharge coefficient and 73% of the spatial variation in mean TOC. Specific discharge, water residence time, the variance of daily precipitation, and lake area, explained 45% of the spatial variation in the amplitude of the TOC seasonality. Because the main drivers of temporal variability in TOC are seasonality and discharge, first-order estimates of the influences of climatic variability and change on TOC concentration should be predictable if the studied catchments continue to respond similarly. (C) 2015 Elsevier B.V. All rights reserved.

With the current loss of biodiversity and threats to freshwater ecosystems, it is crucial to identify hot-spots of biodiversity and on which spatial scale they can be resolved. Conservation and management of these important ecosystems needs insight into whether most of the regional biodiversity (i.e. gamma-diversity) can be found locally (i.e. high alpha-diversity) or whether it is distributed across the region (i.e. high beta-diversity). Biodiversity patterns of benthic macroinvertebrates and diatoms were studied in 30 headwater streams in five Swedish catchments by comparing the relative contribution of alpha- and beta-diversity to gamma-diversity between two levels of stream habitat hierarchy (catchment and region level). The relationship between species community structure and local environmental factors was also assessed. Our results show that both alpha- and beta-diversity made a significant contribution to gamma-diversity. beta-diversity remained relatively constant between the two levels of habitat hierarchy even though local environmental control of the biota decreased from the catchment to the region level. To capture most of headwater gamma-diversity, management should therefore target sites that are locally diverse, but at the same time select sites so that beta-diversity is maximized. As environmental control of the biota peaked at the catchment level, the conservation of headwater stream diversity is likely to be most effective when management targets environmental conditions across multiple local sites within relatively small catchments.

Concentrations of nitrogen (N) in surface waters reflect the export of different organic and inorganic forms from terrestrial environments and the modification of these resources within aquatic habitats. We evaluated the relative influence of terrestrial ecosystem state factors, anthropogenic gradients, and aquatic habitat variables on patterns of N concentration in streams and rivers across Sweden. We analyzed data from 115 national monitoring stations distributed along a 1,300 km latitudinal gradient, draining catchments that differed by more than 10 A degrees C in mean annual temperature (MAT), and more than five orders of magnitude in area. Regional trends in total organic nitrogen (TON) and carbon:nitrogen (C:N) were closely linked to broad-scale gradients in state factors (e.g., MAT), reflecting the importance of long-term ecosystem development on terrestrial organic matter accrual and export. In contrast, trends in nitrate (NO3 (-)), the dominant form of inorganic N, were largely unrelated to state factors, but instead were closely connected to gradients related to anthropogenic inputs (e.g., agricultural cover). Despite large differences in drainage size and cover by lakes and wetlands among sites, these descriptors of the aquatic environment had little influence on spatial patterns of N chemistry. The temporal variability in N concentrations also differed between forms: inorganic N was strongly seasonal, with peaks during dormant periods that underscore biotic control over terrestrial losses of limiting resources. Organic N showed comparatively weaker seasonality, but summertime increases suggest temperature-driven patterns of soil TON production and export-temporal signals which were modified by variables that govern water residence time within catchments. Unique combinations of regional predictors reflect basic differences in the cycling of organic versus inorganic N and highlight variation in the sensitivity of these different N forms to environmental changes that directly alter inputs of resources, or indirectly modify terrestrial ecosystems through shifts in species composition, rates of forest productivity, soil development, and hydrologic routing.

Four river basins in southern Sweden, with catchment sizes from 0.3 to 127 km(2) (median 1.9), were sampled in October 2007. The 243 samples were analysed for 26 trace elements (Ag, As, Au, Ba, Be, Bi, Cd, Co, Cr, Cu, Ga, Ge, In, La, Li, Mo, Ni, Pb, Sb, Se, Sn, Tl, Ti, U, V and Zn) to identify spatial patterns within drainage networks. The range and median of each element were defined for different stream orders, and relationships to catchment characteristics, including deposition history, were explored. The sampling design made it possible to compare the differences along 40 stream reaches, above and below 53 stream junctions with 107 tributaries and between the 77 inlets and outlets of 36 lakes. The largest concentration differences (at reaches, junctions and lakes) were observed for lakes, with outlets usually having lower concentration compared to the inlets for As, Ba, Be, Bi, Cd, Co, Cr, Ga, Ge, Ni, Pb, Sn, Ti, Tl, U, V and Zn. Significantly lower concentrations were observed for Cd and Co when comparing headwaters with downstream sites in each catchment. Common factor analysis (FA) revealed that As, Bi, Cr, Ga, Ge, Tl and V co-vary positively with Al, Fe and total organic carbon (TOC) and negatively with La, Li and pH. The strong removal of a large number of trace elements when passing through lakes is evident though in the FA, where lake surface coverage plots opposite to many of those elements. Forest volume does not respond in a similar systematic fashion and, surprisingly, the amount of wetland does not relate strongly to either Fe or TOC at any of the rivers. A better understanding of the quantitative removal of organic carbon and iron will aid in understanding trace element fluxes from landscapes rich in organic matter and iron.

Numerous studies have estimated carbon exchanges at the landatmosphere interface, more recently also including estimates at the freshwateratmosphere interface. Less attention has been paid to lateral carbon fluxes, in particular to the fate of terrestrial carbon during transport from soils via surface waters to the sea. Using extensive datasets on soil, lake and river mouth chemistry of the boreal/hemiboreal region we determined organic carbon (OC) stocks of the O horizon from catchment soils, annual OC transports through more than 700 lakes (OClakeflux) and the total annual OC transport at Sweden's 53 river mouths (OCseaflux). We show here that a minimum of 0.030.87% yr(-1) of the OC soil stocks need to be exported to lakes in order to sustain the annual OClakeflux. Across Sweden we estimated a total OClakeflux of similar to 2.9 Mtonne yr(-1), which corresponds to similar to 10% of Sweden's total terrestrial net ecosystem production, and it is over 50% higher than the total OCseaflux. The OC loss during transport to the sea follows a simple exponential decay with an OC half-life of similar to 12 years. Water colour, a proxy often used for dissolved humic matter, is similarly lost exponentially but about twice as fast as OC. Thus, we found a selective loss of the coloured portion of soil-derived OC during its transport through inland waters, prior to being discharged into the sea. The selective loss is water residence time dependent, resulting in that the faster the water flows through the landscape the less OC and colour is lost. We conclude that increases in runoff will result in less efficient losses of OC, and particularly of colour, if the time for OC transformations in the landscape shortens. Consequently, OC reaching the sea is likely to become more coloured, and less processed, which can have far-reaching effects on biogeochemical cycles.

Specific discharge variations within a mesoscale catchment were studied on the basis of three synoptic sampling campaigns. These were conducted during stable flow conditions within the Krycklan catchment study area in northern Sweden. During each campaign, about 80 individual locations were measured for discharge draining from catchment areas ranging between 0.12 and 67 km(2). These discharge samplings allowed for the comparison between years within a given season (September 2005 versus September 2008) and between seasons within a given year (May 2008 versus September 2008) of specific discharge across this boreal landscape. There was considerable variability in specific discharge across this landscape. The ratio of the interquartile range (IQR) defined as the difference between the 75th and 25th percentiles of the specific discharges to the median of the specific discharges ranged from 37% to 43%. Factor analysis was used to explore potential relations between landscape characteristics and the specific discharge observed for 55 of the individual locations that were measured in all three synoptic sampling campaigns. Percentage wet area (i.e., wetlands, mires, and lakes) and elevation were found to be directly related to the specific discharge during the drier September 2008 sampling while potential annual evaporation was found to be inversely related. There was less of a relationship determined during the wetter post spring flood May 2008 sampling and the late summer rewetted September 2005 sampling. These results indicate the ability of forests to "dry out" parts of the catchment over the summer months while wetlands "keep wet" other parts. To demonstrate the biogeochemical implications of such spatiotemporal variations in specific discharge, we estimate dissolved organic carbon (DOC) exports with available data for the May 2008 and September 2008 samplings using both the spatially variable observed specific discharges and the spatially constant catchment average values. The average absolute difference in DOC export for the various subcatchments between using a variable and using a constant specific discharge was 28% for the May 2008 sampling and 20% for the September 2008 sampling.