Applying continuous-cover forestry on drained boreal peatlands; water regulation, biodiversity, climate benefits and remaining uncertainties

Continuous-cover forestry (CCF) is increasingly argued as an alternative to clear-cut harvesting in managed boreal forests to improve water quality and quantity, biodiversity, and carbon sequestration. We review the empirical evidence for the potential benefits of CCF on drained forested peatlands in boreal ecosystems as an alternative to conventional clear-cut harvesting. We also discuss possible risks and uncertainties that need further consideration and highlight unanswered questions that need to be resolved before large-scale implementation. In general, we found that the ability to maintain forest production on drained forested peatlands pri-marily depends on water regulation of the groundwater (GW) table. Currently, the problem with high GW is typically solved using ditch cleaning, but if CCF is adopted, it could be an alternative approach to manage GW without the need of disturbing this already extensive artificial channel network. Implementation of CCF could lower the risk of extreme flooding and droughts, in addition to maintaining water quality and potentially enhancing the carbon sequestration conditions. Furthermore, it could provide a compromise between industrialized forestry and peatland restoration to better meet these targets. However, several important uncertainties remain regarding the potential for natural regeneration in northern latitudes, the net effect of different types of soil damage due to repeated use of heavy machinery, and consequences of climate change that could result in enhanced storm felling. We primarily focus on Swedish conditions, but also evaluate implications in an international context and propose ways to close remaining knowledge gaps

Influence of the Landscape Template on Chemical and Physical Habitat for Brown Trout Within a Boreal Stream Network

We used the distribution of stream-dwelling brown trout (Salmo trutta) in a 67 km(2) boreal catchment to explore the importance of environmental organizing factors at a range of spatial scales, including whole-catchment characteristics derived from map data, and stream reach chemical and physical characteristics. Brown trout were not observed at any sites characterized by pH < 5.0 during the spring snowmelt episode, matching published toxicity thresholds. Brown trout distributions were patchy even in less acidic regions of the stream network, positively associated with glaciofluvial substrate and negatively associated with fine sand/silty sediments. A multivariate model including only whole-catchment characteristics explained 43% of the variation in brown trout densities, while models with local site physical habitat characteristics or local stream chemistry explained 33 and 25%, respectively. At the stream reach scale, physical habitat apparently played a primary role in organizing brown trout distributions in this stream network, with acidity placing an additional restriction by excluding brown trout from acidic headwater streams. Much of the strength of the catchment characteristics-fish association could be explained by the correlation of catchment-scale landscape characteristics with local stream chemistry and site physical characteristics. These results, consistent with the concept of multiple hierarchical environmental filters regulating the distribution of this fish species, underline the importance of considering a range of spatial scales and both physical and chemical environments when attempting to manage or restore streams for brown trout

The emerging role of drought as a regulator of dissolved organic carbon in boreal landscapes

One likely consequence of global climate change is an increased frequency and intensity of droughts at high latitudes. Here we use a 17-year record from 13 nested boreal streams to examine direct and lagged effects of summer drought on the quantity and quality of dissolved organic carbon (DOC) inputs from catchment soils. Protracted periods of drought reduced DOC concentrations in all catchments but also led to large stream DOC pulses upon rewetting. Concurrent changes in DOC optical properties and chemical character suggest that seasonal drying and rewetting trigger soil processes that alter the forms of carbon supplied to streams. Contrary to expectations, clearest drought effects were observed in larger watersheds, whereas responses were most muted in smaller, peatland-dominated catchments. Collectively, our results indicate that summer drought causes a fundamental shift in the seasonal distribution of DOC concentrations and character, which together operate as primary controls over the ecological and biogeochemical functioning of northern aquatic ecosystems.Long-term records from boreal streams indicate strong seasonal redistributions of dissolved organic carbon concentrations and quality linked to the severity of summer drought condition

Evaluating the effects of alternative model structures on dynamic storage simulation in heterogeneous boreal catchments

Estimating dynamic storage as a metric can be used to make an overall assessment of catchment resilience to extreme weather events such as droughts and floods. Because of the complexity of direct empirical measurements, bucket-type hydrological models can be a suitable tool to simulate the catchment storage across a broad range of scales as they require minimal input data. However, these models consist of one or more conceptual structures based on several linear or nonlinear reservoirs and connections between these reservoirs. Therefore, choosing the most appropriate model structure to represent storage-discharge functioning in catchments is difficult. To bridge this gap, this study evaluated the performance of three different HBV model structures on 14 heterogeneous boreal catchments classified into four distinct catchment categories. The results showed that the three-bucket structure performed better in larger catchments with deeper sediment soils. In contrast, a single reservoir structure is sufficient to predict the storage-discharge behavior for a lake-influenced catchment with lower elevation above the stream network. Moreover, our results indicate that while the estimates of mean catchment storage varied between the different model structures, the ranking between the catchments largely agreed for the different structures. Hence, our results suggest that instead of a single model structure, using an ensemble averaging approach would not only better address the structural uncertainty but also facilitate further storage comparison between different catchments. Finally, based on Spearman rank correlation results, we found that catchment size and sediment soil were positively correlated with dynamic storage estimation

Using isotopes to constrain water flux and age estimates in snow-influenced catchments using the STARR (Spatially distributed Tracer-Aided Rainfall-Runoff) model

Acknowledgements. This work was funded by the NERC/JPI SIWA project (NE/M019896/1) and the European Research Council ERC (project GA 335910 VeWa). Numerical simulations were performed using the Maxwell High Performance Computing Cluster of the University of Aberdeen IT Service, provided by Dell Inc. and supported by Alces Software. The isotope work in Krycklan is funded by the KAW Branch-Point project together with SKB and SITES. We would like to thank Marjolein van Hui- jgevoort for her help with the STARR code, and Masaki Hayashi and two anonymous reviewers for their insightful suggestions that significantly improved the paper. The Supplement related to this article is available online at https://doi.org/10.5194/hess-21-5089-2017-supplement.Peer reviewedPublisher PD

From legacy effects of acid deposition in boreal streams to future environmental threats

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

Krycklan: markanvändning från forntid till nutid

Kring vattendraget Krycklan i Vindelns kommun, Västerbottens län, finns en unik forskningsinfrastruktur, anlagd och underhållen av Sveriges Lantbruksuniversitet, SLU. Där kan hydrologiska, biogeokemiska och ekologiska processer studeras i ett sammanhang. Nutida förhållanden är emellertid alltid ett resultat av historiska skeenden. Utan att förstå historien kan det vara svårt att tolka nutiden. Under åren 2017–2019 har därför ett projekt bedrivits för att ta fram historiska fakta om markanvändningen inom Krycklans avrinningsområde. En mängd data har samlats in, varav en liten del presenteras i denna skrift

Surstötar i norra Dalarna 1994-2002

Institutionen för miljöanalys, SLU har på uppdrag av länsstyrelsen i Dalarna utvärderat vattenkemin i 13 bäckar (16 mätstationer) i norra Dalarna under 51 olika flödesepisoder 1994- 2002. Totalt omfattar utvärderingen 46 surstötar i samband med snösmältning och 5 surstötar i samband med höstregn. Syftet med utvärderingen har varit att med hjälp av Episodmodellen, BDM (Boreal Dilution Model), söka fastställa i vilken omfattning svaveldepositionen gjort surstötarna i de studerade bäckarna ännu surare än vad de skulle ha varit naturligt. Dessutom har det undersökts hur olika egenskaper i de studerade avrinningsområdena påverkat surstötarnas omfattning