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Excess nitrogen (N) from terrestrial landscapes poses environmental challenges as it moves via surface runoff and groundwater flows into aquatic ecosystems. Managing and anticipating the environmental challenges associated with these altered N inputs from terrestrial to aquatic ecosystems requires a deep understanding of how N is biogeochemically transformed, retained, and/or transported in streams and rivers. Here, I used long-term data on surface stream and groundwater chemistry as well as discharge to determine the main sources of N and estimate the N mass balance of a 1.4 km boreal stream reach. The goal was to evaluate daily net uptake or production rates of different N forms (ammonium - NH4-N, nitrate NO3-N and dissolved organic N - DON) throughout the seasons, and assess physical and chemical factors that may drive changes in net processing. The mass balances analysis revealed distinct patterns in net uptake among N forms. Notably, there was clear evidence of NH4-N and DON uptake (removal) in the stream, while NO3-N processing patterns showed neither clear uptake nor production. Further, variation in net uptake for NH4-N and DON was positively related to stream DOC, DOC:DIN, and C:N ratios, indicating that carbon rich conditions promoted greater N demand in this ecosystem. By comparison, variations in net NO3-N uptake or production at the reach scale were only weakly correlated with these carbon rich conditions. Finally, I assessed these patterns within the nutrient processing domains (NPDs) framework to characterize the behavior/character of the study reach. Accordingly, during the open water season, the stream reach acted mostly as a consumer for both NH4-N and DON, while on many dates it acted as a weak enhancer for NO3-N. These findings contribute to the broader understanding of N dynamics in boreal stream ecosystems and emphasize the complex interplay among organic and inorganic N forms, carbon dynamics, and nutrient processing in these environments. Thi

With widespread increases in air temperature, it is expected that the temperature of aquatic ecosystems will also increase, especially at high latitudes. Warmer streams and rivers could have severe, direct impacts on cold-adapted aquatic fauna but may also indirectly influence species by reducing the amount of suitable habitat. Yet, increases in air temperature alone ara potentially insufficient to cause stream warming, which is also influenced by a range of other factors that govern the energy balance of individual stream reaches. Here, I used long-term water temperature data from seven streams in the Krycklan Catchment Study (KCS) to ask whether there are recent trends in warming, and to evaluate how catchment properties regulate the sensitivity of streams to air temperature change during summer. Mann Kendall trend analysis at one headwater site showed that there has indeed been a warming trend in the KCS, but only during a brief time-window in early summer. Across, KCS sites, air temperature-water temperature regressions highlighted notable variation in the thermal sensitivity of streams depending on their catchment features. Finally, observations during extreme warm and dry years did not indicate strong responses in terms of stream temperature. In fact, extreme low-flow conditions seem to reduce the downstream propagation of warm lake water during these events. Collectively, my results suggest that ongoing climate changes in the boreal region have not had dramatic influences on stream temperature, although future changes occurring around the snowmelt season are likely.

Hydrological drought at high latitudes represents a rising environmental hazard induced byglobal climate change. Yet, we still know little about how drought events influence thebiogeochemistry of boreal streams. Here, I used 15 years of data from eight streams withinthe Krycklan Catchment to test how interannual variability in summer low flows influencesstream water chemistry. My analysis focused several key biogeochemical indicators in thesestreams, including concentrations of dissolved organic carbon (DOC), dissolved organicnitrogen (DON), nitrate (NO3) and ammonium (NH4), as well as the total C/N and NH4/NO3ratios. Overall, results revealed widespread declines in summer average DOC concentrationsand C/N ratios with greater drought severity. These responses likely reflect shifts in thebiogeochemical properties of soils that feed streams during high- versus low-flow summers.By comparison, nitrogen-based parameters were less clearly influenced by drought, exceptfor in mire-dominated headwaters, where NH4 and DON both increased during the lowestflow periods. Overall, the strong effects of flow variability drove a high degree of interannualsynchrony for DOC and C/N across all sites in the drainage system. This synchrony was morevariable overall for nitrogen-based parameters, with several sites having unique year-to-yearchanges in concentrations and ratios. However, strong temporal coherence for NH4 acrossforested streams suggest other broad-scale factors (e.g., related to forest processes) mayregulate interannual patterns for this nutrient. Collectively, results provide insight into howincreases in drought frequency and severity may alter boreal streams and rivers in the future.

Few environmental issues have resulted in such a heated policy-science controversy in Sweden as the 1990s acidification debate in the north of the country. The belief that exceptionally high stream acidity levels during hydrological events was caused by anthropogenic deposition resulted in a governmentally funded, multi-million dollar surface-water liming program. This program was heavily criticized by a large part of the scientific community arguing that the acidity of northern streams was primarily caused by naturally occurring organic acids. Here, we revisit the acid deposition legacy in northern Sweden two decades after the culmination of the controversy by examining the long-term water chemistry trends in the Svartberget/Krycklan research catchment that became a nexus for the Swedish debate. In this reference stream, trends in acidic episodes do show a modest recovery that matches declines in acid deposition to pre-industrial levels, although stream acidity continues to be overwhelmingly driven by organic acidity. Yet there are legacies of acid deposition related to calcium losses from soils, which are more pronounced than anticipated. Finally, assessment of these trends are becoming increasingly complicated by new changes and threats to water resources that must be recognized to avoid unnecessary, expensive, and potentially counterproductive measures to adapt and mitigate human influences. Here we make the argument that while the acidification era is ending, climate change, land-use transitions, and long-range transport of other contaminants warrant close monitoring in the decades to come.

The ongoing pressures of climate change, as expressed by the increased intensity, duration, and frequency of temperature and precipitation events, threatens the storage of carbon in northern latitudes. One key concern is how these events will affect the production, mobilization, and export of dissolved organic carbon (DOC), the main form of aquatic carbon export in these regions. In this study, we retrospectively show contrasting effects of climate extremes over 23 years on two adjacent boreal catchments, one dominated by forest cover and the other draining a mire (wetland), despite experiencing the same extreme climate events. During the peak snowmelt, DOC concentrations ranged from 20 to 33 mg l(-1) in the forest catchment and 10-28 mg l(-1) in the mire catchment respectively, highlighting large inter-annual variation in the springtime hydrologicCexport at both sites. Weused climate and discharge variables to predict this variation, and found that DOC from the forested catchment, which is derived largely from riparian soils, had the highest concentrations following cold summers, dry autumns, and winters with high precipitation. By contrast, in the mire outlet, where DOC is primarily derived from decomposing peat, the highest DOC concentrations in the spring followed cold/dry winters and dry summers. Our results indicate that processes regulating stream DOC concentrations during spring in both catchments were dependent on both temperature and precipitation in multiple seasons. Together, these patterns suggest that DOC responses to climatic extremes are complex and generate variable patterns in springtime concentrations that are strongly dependent upon landscape context.

Community assembly results from a combination of deterministic and stochastic mechanisms, whose relative effects can vary in response to environmental heterogeneity, connectivity, disturbance regimes and anthropogenic stressors. Understanding how community assembly mechanisms vary in response to environmental changes and connectivity is crucial for the management and conservation of river ecosystems. In this thesis, I tested the effects of connectivity and natural flow disturbances on riverine invertebrate communities by assessing assembly mechanism changes in response to (I) habitat connectivity, (II) seasonal flow intermittency and (III) inter–annual hydrological variability. I also conducted a field experiment to test for (IV) the effects of human–induced nutrient enrichment on community assembly of microorganisms (diatoms and aquatic fungi) and stream ecosystem functioning under different environmental settings. Invertebrate community assembly changed gradually with habitat connectivity. While limited dispersal resulted in higher community variability in the most isolated streams, mass effects caused community homogenization in the most connected ones. Natural and human induced disturbances lead to changes in the relative importance of deterministic and stochastic factors but often through different, or even opposite, mechanisms depending on the natural background of the ecosystem and organism type considered. For instance, seasonal drying and high–flow periods in intermittent Mediterranean rivers promoted deterministic and stochastic assembly processes respectively, whereas environmental sorting and stochastic processes respectively dominated during high and low flow years in boreal streams. Diatom and fungal communities responded differently to nutrient enrichment, with detrital processes and fungal communities responding more in naturally acidic than in circumneutral streams. The results of this thesis highlight the complexity of community assembly m, Tiivistelmä Eliöyhteisöjen koostumus heijastelee determinististen ja stokastisten mekanismien vuorovaikutusta. Niiden suhteellinen merkitys vaihtelee suhteessa yhteisöjen kytkeytyneisyyteen sekä luontaisiin ja ihmisen aiheuttamiin häiriöihin. Yhteisöjen säätelymekanismit vaihtelevat jokiverkoston eri osissa ja tietoa tästä vaihtelusta tarvitaan jokiekosysteemien hoidon kehittämiseksi. Tässä tutkielmassa testasin elinympäristöjen kytkeytyneisyyden ja luontaisten häiriöiden (virtaamavaihtelut) vaikutuksia jokien selkärangatonyhteisöihin. Suoritin myös kenttäkokeen, jossa testattiin ihmisen aiheuttaman rehevöitymisen vaikutuksia mikro–organismeihin (piilevät, mikrobit) ja ekosysteemitoimintoihin erilaisissa ympäristöoloissa (luontaisesti happamat vs. neutraalit purot). Selkärangattomien yhteisökoostumus muuttui asteittain jokiverkostossa. Yhteisökoostumuksen vaihtelu oli suurinta eristäytyneimmissä latvapuroissa, kun taas isommissa, uomaston keskivaiheilla sijaitsevissa koskissa voimakas levittäytyminen eri suunnista (ns. massatekijät) aiheutti yhteisöjen rakenteen homogenisoitumista. Kuivuusjaksot ja niitä seuraavat korkean virtaaman jaksot edistivät determinististen prosessien merkitystä Välimeren alueen joissa, kun taas boreaalisissa puroissa Pohjois–Suomessa äärevät virtaamaolot, erityisesti poikkeuksellisen kuivat kesät, edistivät satunnaismekanismien vaikutusta. Perustuottajat (piilevät) ja hajottajat (akvaattiset sienet) vastasivat eri tavoin ravinnelisäykseen. Sienten hajotustoiminta nopeutui ravinnelisäyksen myötä, mutta vain luontaisesti happamissa puroissa. Tämän opinnäytetyön tulokset korostavat yhteisön kokoonpanomekanismien monimutkaisuutta: ne ovat usein erittäin tilanneriippuvaisia ja ajallisesti vaihtelevia. Siksi jokien ekologisen tilan arvioinnissa tulisi huomioida tutkimuspaikkojen kytkeytyneisyys jokimaisemassa.

Although flow regime is a key element in determining the structure and function of lotic ecosystems, little is known about the variation of natural flow regimes and its relation to biological communities in highly seasonal northern boreal rivers. Temperature and precipitation patterns at northern latitudes are predicted to change drastically in the future causing severe effects on stream ecosystems. Interactions between climate change impacts and land use might further create unpredictable environmental stress. In this thesis, I first assessed the relationship of natural flow regimes of northern boreal rivers with taxonomic and functional structure of stream macroinvertebrates. Second, I combined hydrological, climate and biological models to study how climate change will alter northern flow and thermal regimes, how macroinvertebrates will respond to these changes and where these changes are going to be most pronounced. Third, I experimentally studied how different stream organisms are responding to flow change, sedimentation and their possible interaction. The role of hydrology in structuring macroinvertebrate assemblages was evident. Streams were predicted to lose much of the flow seasonality in the future, causing drastic changes that even exceeded the effect of future warming on macroinvertebrates. Especially communities within small seasonal streams were predicted to change, highlighting the importance of focusing conservation actions on these systems. Different organism groups exhibited highly variable responses to different stressors. For instance, aquatic fungi, which have been used less in climate change research, responded more strongly to flow change than traditionally used macroinvertebrates. The interactive effects of flow and sand were all antagonistic (i.e. less than the sum of the individual effects), which could be reassuring for management, although it means that both stressors may need to be removed to produce true ecological recovery. Th, Tiivistelmä Joen virtaamaolosuhteet ja niiden vaihtelu ovat tärkeimpiä jokiekosysteemien rakenteeseen ja toimintaan vaikuttavia tekijöitä. Tästä huolimatta pohjoisen havumetsävyöhykkeen jokien luonnollisia virtaamaolosuhteita ja niiden yhteyttä virtavesieliöihin on tutkittu vähän. Ilmastonmuutoksen on ennustettu aiheuttavan voimakkaita muutoksia pohjoisten alueiden ilman lämpötilassa ja sadannassa, ja nämä muutokset tulevat mitä todennäköisimmin aiheuttamaan vakavia seurauksia myös jokiekosysteemeissä. Ilmastonmuutoksen ympäristövaikutukset voivat lisäksi aiheuttaa jo olemassa olevien ihmistoiminnasta aiheutuvien ympäristövaikutusten kanssa haitallisia ja vaikeasti ennustettavia yhdysvaikutuksia. Väitöskirjassani arvioin ensin pohjoisten virtavesien luonnollisten virtaamaolosuhteiden suhdetta pohjaeläinyhteisöjen taksonomiseen ja toiminnalliseen rakenteeseen. Tämän jälkeen tarkastelin yhdistämällä erilaisia ilmastonmuutoksen skenaarioita hydrologisen ja biologisen mallin kanssa, miten ilmastonmuutos saattaa tulevaisuudessa vaikuttaa jokien virtaamaolosuhteisiin ja niissä eläviin pohjaeläinyhteisöihin. Lisäksi arvioin missä ja minkälaisissa jokityypeissä ilmastonmuutoksen vaikutukset tulevat esiin kaikkein voimakkaimmin. Lopuksi tutkin kokeellisesti, miten virtaamavaihtelu ja hienojakoinen sedimentti ja näiden mahdolliset yhdysvaikutukset vaikuttavat eri virtavesieliöihin. Tulokset osoittivat, että vuodenajasta riippuvat virtaamavaihtelut vähenevät ilmastonmuutoksen myötä, minkä seurauksena pohjaeläinyhteisöissä tapahtuu voimakkaita muutoksia. Erityisesti pienten jokien pohjaeläinyhteisöjen monimuotoisuus ja koostumus muuttuivat verrattaessa tämän päivän lajistoa tulevaisuuden ennustettuun lajistoon. Eri virtavesieliöryhmät vastasivat hyvin eri tavalla virtaamavaihtelun ja hiekoittumisen aiheuttamaan elinympäristön muutokseen. Esimerkiksi akvaattiset sienet, joita on aikaisemmin harvoin käytetty ilmastonmuutostutkimuksissa, vastasivat voimakkaammin virtaamamuutoksiin

The aim of this study is to evaluate the relative importance of N and P as limiting factor to aquatic fungi growing on leaves in boreal streams in northern Sweden. The study focused on aquatic hyphomycetes (fungi) growing on Betula pendula litter in enclosed containers within a climate controlled room. Water for experiments was collected from five different streams spanning a range of nutrient and total organic carbon (TOC) concentrations and each site had replicate containers with either added nitrogen, phosphorous, nitrogen + phosphorous or ambient. At the end of a three-week incubation period, litter was removed, and microbial activity measured in terms of respiration on leaf discs. In all containers there was a decrease in total N and almost all of the experimentally added inorganic N was consumed by the end of the experiment. In N+P containers most of the added P was used, but only a smaller fraction was used in only P treatments. Concentrations of TOC increased during the experimental period in all containers. There were no significant differences in leaf disc respiration between sites (F=1.483, p=0.571 or sites*treatment (F=2.588, p=0.245). There were, however, significant differences between nutrient treatments (F=4.711, p=0.004).When performing multiple comparisons between different nutrient treatments there was a significant difference in respiration between NP and ambient (p= 0.003) and NP and P (p=0.002) treatments. There were close to significant differences in respiration rate between N and P (p=0.053) and N and ambient (p=0.08) treatments. Overall, results from this experimental study suggest that N is the key limiting nutrient for aquatic hyphomycetes in the system. However, it is not only the availability of nutrients that affect the respiration and decomposition by aquatic microbes such as aquatic hyphomycetes, there are also other factors such as temperature, pH, macroinvertebrates and other environmental factors.

Knowing which factors govern variation in community structure is crucial for assessing and conserving biodiversity. Two main processes structuring biological communities are selection by environmental conditions and dispersal between sites. In this thesis, I studied the potential importance of these two processes in structuring stream metacommunities (i.e. a set of local communities that are connected by the dispersal of individuals). I used altogether four datasets collected from three different drainage basins located in northern Finland. For small species, such as stream diatoms, bryophytes and macroinvertebrates, measuring dispersal directly and for all the species in a community, is very difficult. Thus, I used three kinds of spatial proxies to represent the potential effects of dispersal: (1) the size of species pool, (2) spatial locations of the sample sites and (3) distances between sites. In general, local environmental characteristics explained the variation in community structure better than any of the spatial proxies. The results suggested that stream diatoms, bryophytes and macroinvertebrates should not be dispersal limited at within-basin scale. However, in some cases spatial proxies explained a relatively larger proportion of community variation. One major difficulty when using such proxies is that high and limiting dispersal rates produce similar patterns. Here, I also present and test a novel hierarchical metacommunity approach for differentiating if a significant spatial signal is produced by high or limiting dispersal rates. This approach seemed promising. The results suggested that, at very small spatial scales (i.e. within a stream section) the community composition of stream macroinvertebrates is possibly influenced by high dispersal rates. I also used the so-called deconstructive approach and assigned the whole community into smaller groups of species based on their traits (i.e. feeding mode, dispersal mode and body size). This approa, Tiivistelmä Eliöyhteisöjen rakenteeseen vaikuttavien tekijöiden tunteminen on välttämätöntä luonnon monimuotoisuuden hoidon ja suojelun kannalta. Kaksi merkittävää tekijää yhteisörakenteen säätelyssä ovat ympäristötekijöiden aiheuttama valinta ja levittäytyminen. Tutkin väitöskirjassani näiden kahden tekijän suhteellista merkitystä puroeliöiden metayhteisöjen rakentumiselle. Metayhteisöllä tarkoitetaan joukkoa paikallisia yhteisöjä, joiden välillä yksilöt kykenevät levittäytymään. Käytin neljää aineistoa, jotka oli kerätty yhteensä kolmelta valuma-alueelta Pohjois-Suomesta. Pienille lajeille, kuten piileville, sammalille ja pohjaeläimille, levittäytymisen mittaaminen suoraan ja kaikille yhteisön lajeille vertailukelpoisella tavalla on hyvin vaikeaa. Tässä väitöskirjassa tavoitteeni oli selvittää, kuinka hyvin epäsuoria menetelmiä voidaan käyttää levittäytymisen merkityksen selvittämisessä. Käytin kolmea erilaista niin sanottua spatiaalista muuttujaa kuvaamaan levittäytymisen potentiaalisia vaikutuksia: (1) alueellisen lajipoolin kokoa, (2) tutkimuspaikkojen spatiaalista sijaintia ja (3) paikkojen välisiä etäisyyksiä. Yleisesti ottaen tulokset osoittivat, että paikalliset ympäristötekijät selittivät yhteisörakenteen vaihtelua paremmin kuin mikään spatiaalisista muuttujista. Saadut tulokset viittasivat siihen, että valuma-alueen sisällä purojen piilevien, sammalten ja pohjaeläinten yhteisörakenteen ei pitäisi olla rajoittuneen levittäytymisen muokkaamaa. Joissain tapauksissa jokin levittäytymistä kuvaava muuttuja kuitenkin selitti suhteellisesti suuremman osuuden yhteisörakenteen vaihtelusta. Tämä tulos tuo esille yhden spatiaalisten muuttujien käyttöön liittyvän merkittävän haasteen: samankaltaiseen tulokseen voi johtaa sekä voimakas että rajoittunut levittäytyminen. Väitöskirjassani esittelen ja testaan myös uudenlaista lähestymistapaa, jonka tavoitteena on erottaa, onko merkitsevä spatiaalinen signaali voimakkaan vai rajoittuneen levittäytymisen aiheuttamaa. Tämä u

Gaining knowledge about what factors determine benthic algal biomass and productivity is vital for understanding food webs in aquatic systems, especially in woodland streams with naturally low rates of primary productivity. The aim of this study was to investigate what factors determine algal growth in Swedish headwater streams. Nutrients, in terms of nitrogen (N) and phosphorus (P), and light are factors known to affect algal growth. By using nutrient diffusing substrate (NDS) and different gradients of light, it was possible to test the importance of these factors. To determine the effect of the experiment, the study was carried out in a forested reference stream, which is largely shaded with extreme low nutrient levels, and in a stream running through a clear-cutting plantation with high nutrient levels and incident light. In the forested reference stream it became clear that algal growth increased by experimentally adding N (P<0.005), although light did not affect the productivity. In the stream running through the clear-cut, algal productivity increased significantly with higher levels of light (P<0.005), regardless of nutrient addition. The results from this study suggest that light only becomes the depending factor when sufficient amounts of nutrients are available. However, it is still unclear at what nutrient levels this shift occur, and therefore future research is recommended.

Intresset för vattenfrågor har ökat efter införandet av EU:s ramdirektiv för vatten (vattendirektivet, 2000/60/EG) och inneburit att vattenvård och hänsynstagande till vatten inom skogsbruket fått större fokus. Målet med vattendirektivet är att alla vatten inom EU (Europeiska Unionen) ska erhålla en god kemisk och ekologisk status innan år 2015 samt att ingen försämring får ske. Skogsbruket kan i vissa fall ha negativa effekter på vattenmiljöer. NPK+ och Blå målklassning är två skogliga vattenplaneringsverktyg som har utvecklats för att öka vattenhänsynen i skogen. Verktygen utgörs av ett inventeringsprotokoll som bedömer vattenmiljöns naturvärde (N), påverkan (P), känslighet för skogsbruk (K) samt plusvärden (+). Med stöd av NPK+-protokollet utförs sedan en subjektiv indelning av Blå målklasser. Blå målklasser hjälper skogsägare att optimera hänsynen till vatten och visar också vilka åtgärder som bör göras för att utveckla eller bibehålla ekologiska värden i vattendraget. Huvudsyftet med denna studie var att (1) utvärdera verktygens förmåga att fånga in vattenkvalitet med avseende på vattenkemi och (2) undersöka hur väl verktygen bidrar till vattendirektivets mål. För ändamålet inventerades 173 skogskällvattendrag, belägna i Dalarna och sydvästra Sverige, med hjälp av verktygen NPK+ och Blå målklassning. Bedömningen av vattenkvalitet med NPK+-protokollet och Blå målklasser jämfördes med kemisk analys av vattenprover och vattenkemisk status av försurning och övergödning enligt EUs vattendirektiv genom parvisa korrelationer och multivariat statistik. Resultatet pekade på att vattenkemin i de två regionerna skiljde sig åt, med mindre mänskligt orsakad försurning, lägre nivåer av TOC, totalkväve, totalfosfor, absorbans, turbiditet och slamhalt samt högre pH i Dalarna, vilket också fångades upp av många parametrar i NPK+-protokollet. Variationen inom respektive region var dock liten, vilket gjorde att skillnader i vattenkemiskt tillstånd var svårare att avgöra med hjälp, The interest in water related issues has increased after the introduction of the Water Framework Directive (WFD, 2000/60/EC) and more attention has been given to water management in forestry. The objective of the WFD is that all waters within the EU (European Union) should achieve a good chemical and ecological status before 2015 and also that no degradation of water quality should occur within the timeframe. Forestry can sometimes have adverse effects on aquatic environments. BIS+ and Blue targets are two water planning tools that have been developed to facilitate water consideration in forestry. BIS+ consist of a simple checklist that assesses a stream section’s biodiversity (B), human impact (I), sensitivity for forestry (S) and added values (+). With support from the BIS+ checklist a subjective classification of Blue targets is performed. The Blue targets should help forest owners to optimize environmental considerations to forest streams and also show the actions needed to develop or maintain ecological values in the stream. The main purpose of this study was to (1) evaluate the tools' ability to assess water quality regarding water chemistry and (2) examine how well the tools contribute to WFD objectives. For the purpose 173 headwater streams, located in Dalarna and southwestern Sweden, were assessed using the tools BIS+ and Blue targets. The assessment of water quality and water chemistry with the checklist were compared with chemical analyzes of water samples and surface status of acidification and eutrophication according to the WFD using pairwise correlations and multivariate statistics. The results indicate that the water chemistry in the two regions differ, with less anthropogenic acidification, lower levels of TOC , total nitrogen, total phosphorus, absorbance, turbidity and suspended solids and higher pH in Dalarna. This is also shown in the assessment of many characters in the BIS+-checklist. However, the variation within each region is small and the

The goal of the society to increase the proportion of renewable energy has led to an increased demand of bioenergy e.g. forest biomass. However, there are concerns that removal of biomass will lead to decreased base cation concentrations in the soils and acidification of streams. In order to find in which types of landscape removal of branches and tops could have such negative effects, this study aims to analyse the relations between pH-sensitivity and landscape variables in the Bothnia Bay water district. GIS and digital geographical data were used to analyse the landscape in subcatchments. This data were analysed together with stream water chemistry data by using principal component analysis. The results indicate differences between the north and south parts of the district. In the northern subcatchments, pH-sensitivity was positively correlated to water surfaces and coarse quaternary deposits with Scots pine forests. In the south, pH-sensitive streams were positively correlated to till soils and the concentrations of total organic matter (TOC). In both areas, alkalinity and ANC were the most important factors indicating that the buffering capacity primarily was due to weathering.

There is no scientific consensus about how dissolved organic carbon (DOC) in surface waters is regulated. Here we combine recent literature data from 49 catchments with detailed stream and catchment process information from nine well established research catchments at mid- to high latitudes to examine the question of how climate controls stream water DOC. We show for the first time that mean annual temperature (MAT) in the range from -3 degrees to +10 degrees C has a strong control over the regional stream water DOC concentration in catchments, with highest concentrations in areas ranging between 0 degrees and +3 degrees C MAT. Although relatively large deviations from this model occur for individual streams, catchment topography appears to explain much of this divergence. These findings suggest that the long-term trajectory of stream water DOC response to climate change may be more predictable than previously thought. Citation: Laudon, H., J. Buttle, S. K. Carey, J. McDonnell, K. McGuire, J. Seibert, J. Shanley, C. Soulsby, and D. Tetzlaff (2012), Cross-regional prediction of long-term trajectory of stream water DOC response to climate change, Geophys. Res. Lett., 39, L18404, doi: 10.1029/2012GL053033., 011BH Times Cited:0 Cited References Count:45

There is no scientific consensus about how dissolved organic carbon (DOC) in surface waters is regulated. Here we combine recent literature data from 49 catchments with detailed stream and catchment process information from nine well established research catchments at mid- to high latitudes to examine the question of how climate controls stream water DOC. We show for the first time thatmean annual temperature (MAT) in the range from -3 to +10 degrees C has a strong control over the regional stream water DOC concentration in catchments, with highest concentrations in areas ranging between 0 and +3 degrees C MAT. Although relatively large deviations from thismodel occur for individual streams, catchment topography appears to explain much of this divergence. These findings suggest that the long-term trajectory of stream water DOC response to climate change may be more predictable than previously thought.

The transport of elements by streams from headwater regions to the sea is influenced by landscape characteristics. This thesis focuses on the influence of landscape characteristics (e.g. proportion of wetland/forest coverage) on temporal and spatial variations of Fe, Mn, S and trace elements (As, Co, Pb) in streams located in northern Sweden, a boreal region characterized by coniferous forests and peat wetlands. Water samples from a network of 15 streams revealed a different hydrogeochemistry in forested catchments compared to wetland catchments. The temporal variation was dominated by spring flood, when concentrations of Fe, Mn and trace elements increased in forested headwaters. However, in streams of wetland catchments concentrations decreased, but Pb concentrations were higher in comparison to other streams. Both Fe and Pb showed positive correlations with wetland area, while Co correlated with forest coverage. The anthropogenic contribution of As and Pb appear to be larger than the supply from natural sources. During spring flood SO42- decreased in most streams, although concentrations increased in streams of wetland catchments. Concentrations of SO42- were higher in streams of forested catchments than in wetland dominated streams, the former being net exporters of S and the latter net accumulators. Isotope values of stream water SO42- (δ34SSO4) were close to that of precipitation during spring flood, indicating that the major source of S is from deposition. The results show that, although emissions of anthropogenic S have been reduced, there is still a strong influence of past and current S deposition on runoff in this region. In conclusion, wetlands are key areas for the hydrogeochemistry in this boreal landscape. The findings emphasize the importance of understanding stream water chemistry and element cycling from a landscape perspective. This may be important for predicting how boreal regions respond to environmental disturbances such as climate change.

The transport of trace metals (TM) and dissolved organic carbon (DOC) from headwater streams to the sea is influenced by various landscape elements. Our focus was to investigate the influence of major landscape elements on observed concentrations of dissolved metals (e.g. As, Cd, Co, Fe, Pb), DOC, sulphate, and sulphur isotope composition in streams, north- eastern Sweden, a coastal region characterized by peat wetlands and coniferous forests. Stream water samples collected from 10 streams (0.13 to 67 km2) in a boreal stream network reveal that landscape type (i.e. coverage of wetland and forest) is significant for river chemistry. Streams with different catchment characteristics responded differently to hydrological episodes. In forested streams, concentrations of TM, Fe and DOC increased, while they decreased in wetland influenced streams. Furthermore, Fe and Pb correlated positively with wetland coverage. Moreover, significantly lower average sulphate concentrations, but higher isotope values, were observed in wetland streams. This study emphasises the importance of understanding stream water chemistry from a landscape perspective in order to identify potential environments where climate change may induce enhanced metal mobilization in the future.