Evasion of gaseous carbon (C) from streams is often poorly quantified in landscape C budgets. Even though the potential importance of the capillary network of streams as C conduits across the land-water-atmosphere interfaces is sometimes mentioned, low-order streams are often left out of budget estimates due to being poorly characterized in terms of gas exchange and even areal surface coverage. We show that evasion of C is greater than all the total dissolved C (both organic and inorganic) exported downstream in the waters of a boreal landscape. In this study evasion of carbon dioxide (CO2 ) from running waters within a 67 km(2) boreal catchment was studied. During a 4 year period (2006-2009) 13 streams were sampled on 104 different occasions for dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC). From a locally determined model of gas exchange properties, we estimated the daily CO2 evasion with a high-resolution (5 × 5 m) grid-based stream evasion model comprising the entire ~100 km stream network. Despite the low areal coverage of stream surface, the evasion of CO2 from the stream network constituted 53% (5.0 (±1.8) g C m(-2)  yr(-1) ) of the entire stream C flux (9.6 (±2.4) g C m(-2)  yr(-1) ) (lateral as DIC, DOC, and vertical as CO2 ). In addition, 72% of the total CO2 loss took place already in the first- and second-order streams. This study demonstrates the importance of including CO2 evasion from low-order boreal streams into landscape C budgets as it more than doubled the magnitude of the aquatic conduit for C from this landscape. Neglecting this term will consequently result in an overestimation of the terrestrial C sink strength in the boreal landscape.

No abstract

[1] The purpose of this study was to quantify the effects of clear-cutting and site preparation on dissolved organic carbon (DOC) concentrations and export in four boreal headwater streams in northern Sweden. The data set included intensive stream water monitoring from 2 years of pretreatment conditions (2004)(2005), a 2 year post-clear-cut period (2006)(2007), and a 2 year period after site preparation (2008)(2009). To investigate differences in [DOC], an analysis of variance on ranks was performed on the data sets. Clear-cutting increased the median DOC concentrations significantly from 15.9 to 20.4 mg L À1, which represents a net increase (treatment versus control) of 3.0 mg L À1 in the 2006-2007 period. Site preparation had an even more profound effect on DOC levels; an increase from 20.4 to 27.6 mg L À1 was found in the site-prepared catchments, whereas the control sites increased slightly from 17.4 to 21.4 mg L À1 during the wetter years of 2008-2009. Riverine C fluxes increased significantly by 100% after clear-cutting and by 79% after site preparation (92% and 195%, respectively, if compared to pretreatment conditions). When comparing these yearly C fluxes (183 kg C ha À1 yr À1 after clear-cutting; 280 kg C ha À1 yr À1 after site preparation) to the net ecosystem exchange (NEE) of a forest in the region, the DOC flux represented 10% of NEE before harvest, increased to 18% after the clear-cut, and increased to 28% after site preparation. These results underline the large impact of forestry operations on stream water quality as well as DOC exports leaving managed boreal forests.Citation: Schelker, J., K. Eklöf, K. Bishop, and H. Laudon (2012), Effects of forestry operations on dissolved organic carbon concentrations and export in boreal first-order streams,

It is well established that stream dissolved inorganic carbon (DIC) fluxes play a central role in the global C cycle, yet the sources of stream DIC remain to a large extent unresolved. Here, we explore large-scale patterns in δ13C-DIC from streams across Sweden to separate and further quantify the sources and sinks of stream DIC. We found that stream DIC is governed by a variety of sources and sinks including biogenic and geogenic sources, CO2 evasion, as well as in-stream processes. Although soil respiration was the main source of DIC across all streams, a geogenic DIC influence was identified in the northernmost region. All streams were affected by various degrees of atmospheric CO2 evasion, but residual variance in δ13C-DIC also indicated a significant influence of in-stream metabolism and anaerobic processes. Due to those multiple sources and sinks, we emphasize that simply quantifying aquatic DIC fluxes will not be sufficient to characterise their role in the global C cycle.

Improving the understanding of how stream flow dynamics are influenced by landscape characteristics, such as soils, vegetation and terrain, is a central endeavor of catchment hydrology. Here we investigate how spatial variability in stream flow is related to landscape characteristics using specific discharge time series from 14 partly nested subcatchments in the Krycklan basin (0.12 – 68 km2). Multivariate principal component analyses combined with univariate analyses showed that while variability in landscape characteristics and specific discharge were strongly related, the spatial patterns varied with season and wetness conditions. During spring snowmelt and at the annual scale, specific discharge was positively related to the sum of wetland and lake area. During summer, when flows are lowest, specific discharge was negatively related to catchment tree volume, but positively related to deeper sediment deposits and catchment area. The results indicate how more densely forested areas on till soils become relatively drier during summer months, while wet areas and deeper sediment soils maintain a higher summer base flow. Annual and seasonal differences in specific discharge can therefore be explained to a large extent by expected variability in evapotranspiration fluxes and snow accumulation. These analyses provide an organizing principle for how specific discharge varies spatially across the boreal landscape, and how this variation is manifested for different wetness conditions, seasons and time scales.

Low-order streams are suggested to dominate the atmospheric CO 2 source of all inland waters. Yet, many large-scale stream estimates suffer from methods not designed for gas emission determination and rarely include other greenhouse gases such as CH 4 . Here, we present a compilation of directly measured CO 2 and CH 4 concentration data from Swedish low-order streams (> 1600 observations across > 500 streams) covering large climatological and land-use gradients. These data were combined with an empirically derived gas transfer model and the characteristics of a ca. 400,000 km stream network covering the entire country. The total *Correspondence: marcus.wallin@geo.uu.se Author Contribution Statement: MBW brought the idea and compiled the concentration data. MBW and TG designed the study, analyzed the data and conducted the modelling component. AC, JA, DB, KB, JK, HJ, EL, SL, SN, SB, CT and GAW provided data, ideas and catchment/region specific information. MBW wrote the manuscript with great support from all co-authors.Data Availability Statement: Data are available in the Uppsala University data repository at http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-332472.Additional Supporting Information may be found in the online version of this article.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. This article is part of the Special Issue: Carbon cycling in inland waters Edited by: Emily Stanley and Paul del Giorgio Scientific Significance StatementStreams have been identified as disproportional emitters of CO 2 to the atmosphere across all inland waters. Despite their suggested importance, reliable large-scale stream C emission data are often lacking which makes current estimates uncertain. Here, we show that Swedish low-order streams emit much higher amounts of C to the atmosphere than previously reported, corresponding to 21% of the estimated terrestrial C sequestration. We also show that local scale spatiotemporal variability in stream gas concentrations often exceeds variability across regions, and that stream surface area matters. Without such fundamental information, large-scale stream C emission estimates will always be associated with a large degree of uncertainty.1

No abstract

Mercury (Hg) levels are alarmingly high in fish from lakes across Fennoscandia and northern North America. The few published studies on the ways in which silviculture practices influence this problem indicate that forest operations increase Hg in downstream aquatic ecosystems. From these studies, we estimate that between one-tenth and one-quarter of the Hg in the fish of high-latitude, managed forest landscapes can be attributed to harvesting. Forestry, however, did not create the elevated Hg levels in the soils, and waterborne Hg/MeHg concentrations downstream from harvested areas are similar to those from wetlands. Given the current understanding of the way in which silviculture impacts Hg cycling, most of the recommendations for good forest practice in Sweden appear to be appropriate for high-latitude regions, e.g., leaving riparian buffer zones, as well as reducing disturbance at stream crossings and in moist areas. The recommendation to restore wetlands and reduce drainage, however, will likely increase Hg/MeHg loadings to aquatic ecosystems.