Carbon dioxide dynamics in an agricultural headwater stream driven by hydrology and primary production

Headwater streams are known to be hotspots for carbon dioxide (CO2) emissions to the atmosphere and are hence important components in landscape carbon balances. However, surprisingly little is known about stream CO2 dynamics and emissions in agricultural settings, a land use type that globally covers ca. 40% of the continental area. Here we present hourly measured in situ stream CO2 concentration data from a 11.3 km(2) temperate agricultural headwater catchment covering more than 1 year (in total 339 d excluding periods of ice and snow cover). The stream CO2 concentrations during the entire study period were generally high (median 3.44 mg C L-1, corresponding to partial pressures (pCO(2)) of 4778 mu atm) but were also highly variable (IQR = 3.26 mgC L-1). The CO2 concentration dynamics covered a variety of different timescales from seasonal to hourly, with an interplay of hydrological and biological controls. The hydrological control was strong (although with both positive and negative influences dependent on season), and CO2 concentrations changed rapidly in response to rainfall and snowmelt events. However, during growing-season base flow and receding flow conditions, aquatic primary production seemed to control the stream CO2 dynamics, resulting in elevated diel patterns. During the dry summer period, rapid rewetting following precipitation events generated high CO2 pulses exceeding the overall median level of stream CO2 (up to 3 times higher) observed during the whole study period. This finding highlights the importance of stream intermittency and its effect on stream CO2 dynamics. Given the observed high levels of CO2 and its temporally variable nature, agricultural streams clearly need more attention in order to understand and incorporate these considerable dynamics in large-scale extrapolations

Intra-annual variability of natural organic matter in boreal streams

Natural organic matter (NOM) is a key component in aquatic ecosystems. It influences for example acidity, mobility and toxicity of metals and organic pollutants, energy input to aquatic food webs, weathering, and water light conditions. There are also considerable costs associated with removing NOM in drinking water production. Furthermore, NOM is an integral part of the carbon cycle with possible indirect effects on climate. During recent decades, there have been observations of increasing concentrations of NOM in surface waters in parts of North America and Europe. The causes of these trends are not fully understood, but are thought to be related to climate change and recovery from anthropogenic acidification. This thesis presents results from studies on intra-annual NOM cycling in more than 130 boreal streams and rivers. It also presents developments of the Riparian flow-concentration Integration Model (RIM). Detailed studies on five forested headwater catchments revealed that stream discharge and soil temperature were the main drivers of NOM variability. In addition, a small headwater catchment at the Swedish West Coast was substantially influenced by sea-salt deposition, which suppressed NOM mobilization. A modified version of RIM with discharge and soil temperature as variables could successfully simulate NOM dynamics in all five catchments. Riparian soil organic matter content and distribution was hypothesized to be the underlying control on NOM response to discharge and soil temperature. Catchments where NOM was sensitive to discharge displayed stronger gradients in soil NOM concentrations than did catchments with weak discharge sensitivity. A large scale study of 136 streams and rivers indicated common relationships among NOM, discharge and temperature. Conversely, there was no geographical pattern in NOM trends. Relative trends were weakly related to NOM response to flow and temperature. There were also clear relationships among intra-annual NOM dynamics, temperature, flow, and catchment landscape characteristics, indicating that catchments can be classified based on NOM dynamics. Taken together, this implies that NOM dynamics could change in ways not reflected in inter-annual trends due to climate change

The social order in the 12th-15th century christian Iberia

Bakalaura darba “Sociālā kārtība kristīgajā Ibērijā 12. gs. - 15. gs.” mērķis bija izpētīt kristiešu, jūdaistu un musulmaņu sociālo mijiedarbību un minēto reliģisko minoritāšu statusu kristīgo monarhu pārvaldītajā Ibērijas pussalas daļā 12.-15. gadsimtā. Galvenie izpētes fokusa punkti bija reliģisko minoritāšu grupu tiesiskais statuss, ikdienas starpkonfesionālie kontakti un vispārējā dzīve starp kristiešiem. Izpētes gaitā tika secināts, ka reliģisko minoritāšu dzīvi no 12. līdz 14. gadsimta sākumam raksturoja tiesiska līdztiesība un vispārēja iecietība, kristiešiem saglabājot dominanci daudzos dzīves aspektos. 1391. gada grautiņi pret Seviļas jūdaistiem bija lūzumpunkts, pēc kuriem reliģisko minoritāšu stāvoklis degradējās līdz šīs kopienas tika vai nu fiziski iznīcinātas, vai arī piespiestas pāriet kristietībā 15. gadsimta gaitā.The aim of the bachelor’s work “The social order in the 12th-15th century christian Iberia” was to research social interaction between christians, judaists and muslims and the status of religious minorities in the christian part of the Iberian peninsula from the 12th to the 15th century. The main focus of the resarch was the legal status, interconfessional contact and the life of these minorities among christians. In the research it was concluded that the life of religious minorities from the 12th until the 14th century was characterized by legal equality and an overall tolerance, with christians remaining dominant most cases. The riots of 1391 against the judaists of Seville was the breaking point, after which the status of these minorities degraded until they were destroyed or forced to convert to christianity in the 15th century

Why monitor carbon in high‐alpine streams?

In this short communication, we report on dissolved organic and inorganic carbon concentrations from a summer stream monitoring campaign at the main hydrological catchment of the Tarfala Research Station in northern Sweden. Further, we place these unique high-alpine observations in the context of a relevant subset of Sweden's national monitoring programme. Our analysis shows that while the monitoring programme (at least for total organic carbon) may have relatively good representativeness across a range of forest coverages, alpine/tundra environments are potentially underrepresented. As for dissolved inorganic carbon, there is currently no national monitoring in Sweden. Since the selection of stream water monitoring locations and monitored constituents at the national scale can be motivated by any number of goals (or limitations), monitoring at the Tarfala Research Station along with other research catchment sites across Fennoscandia becomes increasingly important and can offer potential complementary data necessary for improving process understanding. Research catchment sites (typically not included in national monitoring programmes) can help cover small-scale landscape features and thus complement national monitoring thereby improving the ability to capture hot spots and hot moments of biogeochemical export. This provides a valuable baseline of current conditions in high-alpine environments against which to gauge future changes in response to potential climatic and land cover shifts

Reviews and syntheses : Carbon use efficiency from organisms to ecosystems - definitions, theories, and empirical evidence

The cycling of carbon (C) between the Earth surface and the atmosphere is controlled by biological and abiotic processes that regulate C storage in biogeochemical compartments and release to the atmosphere. This partitioning is quantified using various forms of C-use efficiency (CUE) - the ratio of C remaining in a system to C entering that system. Biological CUE is the fraction of C taken up allocated to biosynthesis. In soils and sediments, C storage depends also on abiotic processes, so the term C-storage efficiency (CSE) can be used. Here we first review and reconcile CUE and CSE definitions proposed for autotrophic and heterotrophic organisms and communities, food webs, whole ecosystems and watersheds, and soils and sediments using a common mathematical framework. Second, we identify general CUE patterns; for example, the actual CUE increases with improving growth conditions, and apparent CUE decreases with increasing turnover. We then synthesize > 5000CUE estimates showing that CUE decreases with increasing biological and ecological organization - from uni-cellular to multicellular organisms and from individuals to ecosystems. We conclude that CUE is an emergent property of coupled biological-abiotic systems, and it should be regarded as a flexible and scale-dependent index of the capacity of a given system to effectively retain C

Riparian soil temperature modification of the relationship between flow and dissolved organic carbon concentration in a boreal stream

Discharge is often strongly correlated to the temporal variability of dissolved organic carbon concentrations ([DOC]) in watercourses. One recently proposed way to model this is the riparian flow-concentration integration model (RIM) concept that accounts for the role of flow pathway control on [DOC] dynamics in streams. However, in boreal systems, there is also commonly a seasonal pattern, which cannot be explained by variability in discharge alone. The objectives with this study were to (1) demonstrate RIM as a tool for studying variability in stream water chemistry, (2) investigate factors related to stream water DOC variability, and (3) modify RIM to account for these factors. RIM was used with 14 years of daily discharge and almost 500 stream measurements of [DOC] from a forested boreal headwater stream. We used the calibrated RIM to account for discharge influences and then investigated variables that could be related to DOC variability (air and soil temperature, soil moisture, precipitation, antecedent flow and stream sulfate). Five alternative formulations of RIM, with temporally varying soil concentration profiles based on the variability in soil temperature and/or antecedent flow, were evaluated. The model where only the effects of riparian soil temperature on dynamics in DOC depth profiles were included performed best overall. This dynamic RIM improved the Nash-Sutcliffe to 0.58 compared to 0.42 for the flow-only formulation and reduced the median absolute error from 3.0 to 2.1 mg L−1. This study demonstrates that RIM is a simple way of modeling stream DOC and exploring controls on stream water chemistry