Carbon dioxide and methane exchange between a boreal pristine lake and the atmosphere

Lakes serve as sites for terrestrially fixed carbon to be remineralized and transferred back to the atmosphere. Their role in regional carbon cycling is especially important in the Boreal Zone, where lakes can cover up to 20% of the land area. Boreal lakes are often characterized by the presence of a brown water colour, which implies high levels of dissolved organic carbon from the surrounding terrestrial ecosystem, but the load of inorganic carbon from the catchment is largely unknown. Organic carbon is transformed to methane (CH4) and carbon dioxide (CO2) in biological processes that result in lake water gas concentrations that increase above atmospheric equilibrium, thus making boreal lakes as sources of these important greenhouse gases. However, flux estimates are often based on sporadic sampling and modelling and actual flux measurements are scarce. Thus, the detailed temporal flux dynamics of greenhouse gases are still largely unknown. ----- One aim here was to reveal the natural dynamics of CH4 and CO2 concentrations and fluxes in a small boreal lake. The other aim was to test the applicability of a measuring technique for CO2 flux, i.e. the eddy covariance (EC) technique, and a computational method for estimation of primary production and community respiration, both commonly used in terrestrial research, in this lake. Continuous surface water CO2 concentration measurements, also needed in free-water applications to estimate primary production and community respiration, were used over two open water periods in a study of CO2 concentration dynamics. Traditional methods were also used to measure gas concentration and fluxes. The study lake, Valkea-Kotinen, is a small, humic, headwater lake within an old-growth forest catchment with no local anthropogenic disturbance and thus possible changes in gas dynamics reflect the natural variability in lake ecosystems. CH4 accumulated under the ice and in the hypolimnion during summer stratification. The surface water CH4 concentration was always above atmospheric equilibrium and thus the lake was a continuous source of CH4 to the atmosphere. However, the annual CH4 fluxes were small, i.e. 0.11 mol m-2 yr-1, and the timing of fluxes differed from that of other published estimates. The highest fluxes are usually measured in spring after ice melt but in Lake Valkea-Kotinen CH4 was effectively oxidised in spring and highest effluxes occurred in autumn after summer stratification period. CO2 also accumulated under the ice and the hypolimnetic CO2 concentration increased steadily during stratification period. The surface water CO2 concentration was highest in spring and in autumn, whereas during the stable stratification it was sometimes under atmospheric equilibrium. It showed diel, daily and seasonal variation; the diel cycle was clearly driven by light and thus reflected the metabolism of the lacustrine ecosystem. However, the diel cycle was sometimes blurred by injection of hypolimnetic water rich in CO2 and the surface water CO2 concentration was thus controlled by stratification dynamics. The highest CO2 fluxes were measured in spring, autumn and during those hypolimnetic injections causing bursts of CO2 comparable with the spring and autumn fluxes. The annual fluxes averaged 77 (±11 SD) g C m-2 yr-1. In estimating the importance of the lake in recycling terrestrial carbon, the flux was normalized to the catchment area and this normalized flux was compared with net ecosystem production estimates of -50 to 200 g C m-2 yr-1 from unmanaged forests in corresponding temperature and precipitation regimes in the literature. Within this range the flux of Lake Valkea-Kotinen yielded from the increase in source of the surrounding forest by 20% to decrease in sink by 5%. The free water approach gave primary production and community respiration estimates of 5- and 16-fold, respectively, compared with traditional bottle incubations during a 5-day testing period in autumn. The results are in parallel with findings in the literature. Both methods adopted from the terrestrial community also proved useful in lake studies. A large percentage of the EC data was rejected, due to the unfulfilled prerequisites of the method. However, the amount of data accepted remained large compared with what would be feasible with traditional methods. Use of the EC method revealed underestimation of the widely used gas exchange model and suggests simultaneous measurements of actual turbulence at the water surface with comparison of the different gas flux methods to revise the parameterization of the gas transfer velocity used in the models.Sisävesien merkitys hiilenkierrolle on huomattava pohjoisella havumetsävyöhykkeellämme, missä järvien osuus maapinta-alasta voi paikoin olla jopa yli 20%. Järviimme kulkeutuu suuria määriä orgaanista hiiltä ympäröiviltä valuma-alueilta, mutta toisaalta epäorgaanisen hiilen määrä hiilen kokonaiskuormassa on pitkään ollut arvoitus. Osa metsien tuottamasta orgaanisesta hiilestä muuntuu järvien biologisissa prosesseissa metaaniksi ja hiilidioksidiksi, mistä johtuen järvet ovat pääsääntöisesti näiden tärkeiden kasvihuonekaasujen lähteitä ilmakehään. Kaasujen vaihto järven ja ilmakehän välillä on kuitenkin suurin epävarmuustekijä, kun määritetään järvien roolia alueellisessa hiilenkierrossa. Tämä johtuu siitä, että perinteiset tutkimusmenetelmät ovat niin työläitä, että edustavan mittausaineiston kerääminen on hankalaa. Yleisesti käytetyt menetelmät voivat myös muuttaa luonnollista kaasujen vaihtoa ja siten vääristää tuloksia. Tutkin työssäni pienen, luonnontilaisen metsäjärven metaani- ja hiilidioksidipitoisuuksien, sekä järven ja ilmakehän välisen kaasujen vaihdon ajallista vaihtelua. Käytin hiilidioksidimittauksissa järvitutkimuksessa uusia jatkuvatoimisia mittausmenetelmiä ja testasin niiden käyttökelpoisuutta suhteessa perinteisiin menetelmiin. Tulosten perusteella arvioin tutkimusjärveni roolia alueellisessa hiilenkierrossa. Järven lämpötilakerrostuminen sääteli kasvihuonekaasujen pitoisuuksien ajallista vaihtelua. Keskimäärin pitoisuudet kohosivat jääpeitteisenä aikana, kuten myös alusvedessä kesäkerrostuneisuuden aikaan. Päällysvedessä pitoisuudet olivat kesällä lähes tasapainossa ilmakehän kanssa. Metaanipitoisuudet olivat koko ajan tasapainopitoisuutta suuremmat, hiilidioksidilla havaittiin kesällä ajoittain myös alikyllästystilanteita eli järvi toimi hiilidioksidin nieluna. Metaanin biologinen hapetus vesipatsaassa oli tehokasta keväällä ja kesällä, ja suurimmat päästöt ajoittuivatkin syksyn täyskiertoon. Hiilidioksidipäästöt ilmakehään olivat suurimmillaan keväällä heti jäiden lähdettyä ja syksyn täyskierron aikana. Korkeita päästöjä mitattiin hetkellisesti myös kesällä, kun lämpötilakerrostuneisuus murtui, ja alusveden hiilidioksidirikas vesi sekoittui päällysveteen. Kesäaikaiset hiilidioksidipäästöt jäivät kuitenkin kokonaisuudessaan alhaisiksi. Vuositasolla metaanipäästö järvestä oli pieni eli vain 0,11 mol m-2 yr-1. Vuotuiset hiilidioksidipäästöt olivat keskimäärin 77 g C m-2 yr-1. Järven hiilidioksidipäästöt olivat arviolta noin 10% koko valuma-alueen vuotuisesta tuotannosta, eli periaattessa 10% metsän sitomasta ilman hiilidioksidista palautui järven kautta takaisin ilmakehään. Tutkimuksessa kokeiltu metsien hiilidioksidimittauksissa yleisesti käytetty ns. suora vuonmittaus toimi hyvin myös järven ja ilmakehän välisen hiilidioksidin vaihdon mittauksessa. Suojainen metsäjärvi osoittautui kuitenkin haastavaksi tutkimuskohteeksi, koska olosuhteet eivät aina olleet menetelmälle suotuisat, ja suuri osa mittausaineistosta jouduttiin hylkäämään. Tutkimusaineiston tarkan seulonnan jälkeen saatiin kuitenkin luotettava aineisto kuvaamaan järven ja ilmakehän välisen hiilidioksidin vaihdon ajallisesta vaihtelua ja vuotuista tasoa. Viisi avovesikautta kattava aikasarja on nyt maailman pisin. Kun tutkimukseen yhdistettiin jatkuvatoiminen veden hiilidioksidipitoisuuden mittaus havaittiin, että yleisesti käytössä oleva kaasunvaihtomalli aliarvioi järven ja ilmakehän välistä kaasunvaihtoa. Työssä esitetty jatkuvaa hiilidioksidipitoisuuden mittausta ja metsäekologisessa tutkimuksessa käytettyä laskentamallia hyödyntävä menetelmä järven perustuotannon ja yhteisöhengityksen määrittämiseksi osoittautui lupaavaksi. Menetelmä vaatii kuitenkin lisää testausta ja tarkempaa tietoa hiilidioksidin kulkeutumisesta järven vesipatsaassa. Tämä tutkimus antaa aiempaa tarkempaa tietoa järven metaani- ja hiilidioksidipitoisuuksista sekä järven ja ilmakehän välisestä kaasujenvaihdosta. Tutkimus myös vahvistaa käsitystä siitä, että järvillä on tärkeä rooli alueellisessa hiilenkierrossa. Se myös luo pohjaa uusien menetelmien käytöönotolle järvien hiilenkiertotutkimuksessa

Vallankäyttöä vai strategista politikointia? Öljyn ja maakaasun merkitys Venäjän ulkopolitiikassa

Pro gradu -tutkielmani käsittelee öljyn ja maakaasun merkitystä Venäjän ulkopolitiikassa. Olen tutkinut miten öljy ja maakaasu määrittävät Venäjän ulkopolitiikkaa ja sen tavoitteita,miten globaalitalous vaikuttaa öljyn ja maakaasun politisoitumiseen ja miten öljyn ja maakaasun on tulkittu vaikuttavan Venäjän ulkopolitiikkaan. Venäjän on tulkittu käyttäneen energiaa poliittisena vallankäytön välineenä useissa naapurivaltioidensa kanssa käymissään kiistoissa. Tämän toiminnan taustalla on nähty olevan maan pyrkimyksen palata globaaliksi suurvallaksi. Tutkielman teoreettisena viitekehyksenä toimii uusrealismin,energiaturvallisuuden ja geopolitiikan teknologia- ja resurssimallien keskinäiselle vuorovaikutukselle.Työn punaisena lankana Venäjän harjoittama politiikka Euraasian reuna-alueilla,jotka kuuluvat sekä öljyn ja kaasun tuotantoalueisiin että niiden siirron kannalta strategisiin kauttakulkualueisiin. Valtiot perustelevat osallistumistaan energiapolitiikan ohjaamiseen ja kontrollointiin laaja-alaisen energiaturvallisuuden käsitteellä. Tutkielmani metodina on hermeneuttinen kehä,jota käytän väljänä tutkielman tekoa ohjaavana menetelmänä korostaen tekstien ja puheiden funktionalisuutta sekä sosiaalista ja materiaalista todellisuutta rakentavaa luonnetta.Aineisto koostuu pääosin Venäjän ulko- ja energiapolitiikkaa käsittelevistä strategioista sekä Vladimir Putinin ja Dimitri Medvedevin energiaa käsittelevistä puheista vuosilta 2000 - 2011. Tutkielmassa tarkasteltiin Venäjän energia- ja ulkopolitiikan välistä suhdetta arktisella alueella, Keski-Aasiassa ja Kaukasuksella sekä Itä-Aasian ja Tyynenmerenalueilla. Tutkielmassa havaittiin että, tutkituilla alueilla Venäjän energiapolitiikka on ollut dynaamista. Muutoksen nopeuteen ja suuntaan vaikuttaa öljyn maailmanmarkkinahinnan kehitys

Long-Term (2001–2020) Nutrient Transport from a Small Boreal Agricultural Watershed: Hydrological Control and Potential of Retention Ponds

Agriculture contributes significantly to phosphorus and nitrogen loading in southern Finland. Climate change with higher winter air temperatures and precipitation may also promote loading increase further. We analyzed long-term nutrient trends (2001–2020) based on year-round weekly water sampling and daily weather data from a boreal small agricultural watershed. In addition, nutrient retention was studied in a constructed sedimentation pond system for two years. We did not find any statistically significant trends in weather conditions (temperature, precipitation, discharge, snow depth) except for an increase in discharge in March. Increasing trends in annual concentrations were found for nitrate, phosphate, and total phosphorus and total nitrogen. In fact, phosphate concentration increased in every season and nitrate concentration in other seasons except in autumn. Total phosphorus and total nitrogen concentrations increased in winter as well and total phosphorus also in summer. Increasing annual loading trend was found for total phosphorus, phosphate, and nitrate. Increasing winter loading was found for nitrate and total nitrogen, but phosphate loading increased in winter, spring, and summer. In the pond system, annual retention of total nitrogen was 1.9–4.8% and that of phosphorus 4.3–6.9%. In addition, 25–40% of suspended solids was sedimented in the ponds. Our results suggest that even small ponds can be utilized to decrease nutrient and material transport, but their retention efficiency varies between years. We conclude that nutrient loading from small boreal agricultural catchments, especially in wintertime, has already increased and is likely to increase even further in the future due to climate change. Thus, the need for new management tools to reduce loading from boreal agricultural lands becomes even more acute

Infections after intramedullary fixation of trochanteric fractures are uncommon and implant removal is not usually needed

Background and purpose. Infections after intramedullary fixation of trochanteric femoral fractures are rare, but potentially life-threatening complications. There are limited data available to support decision making in these cases. Patients and methods. A retrospective study of 995 consecutive operatively treated trochanteric fractures was made to find out different risk factors for infection and to describe the results of treatment. Results. 28 patients developed a surgical site infection (2.8%) after intramedullary fixation of trochanteric fracture. 15 patients (1.5%) had a deep and 13 patients (1.3%) a superficial surgical site infection. Cigarette smoking ( p < 0.05) and prolonged operative time ( p < 0.05) were significant risk factors for an infection. 15 of 28 patients needed revision surgeries. Implant removal or exchange was needed only for 4 of 28 patients: 1 exchange of the blade, 1 removal of additional cable used to assist reduction and 2 removals of distal locking screws. None of the patients needed additional surgeries for problems with fracture healing. Mortality was not increased among patients with an infection. Interpretation. Infection after intramedullary fixation of trochanteric fractures can be successfully treated without removal or exchange of the fixation material. (c) 2020 Elsevier Ltd. All rights reserved.Peer reviewe

Effects of pH on phosphorus form transformation in lake sediments

The pH value of lake water varies with the lake environment, which has an effect on the form of phosphorus in sediment, and then the release of sediment phosphorus. The form of phosphorus in sediments was analyzed using field sampling. The environmental conditions with pH values of 4.0, 7.0 and 10.0 were simulated indoors to estimate the effects of pH on phosphorus release from sediments and the content change of various forms of phosphorus was studied. The results showed that in Wuliangsuhai Lake, Ca-P accounted for 54.3%, which was the largest portion of the TP. Phosphorus release was favored under acidic and alkaline conditions, and the alkaline condition was more favorable. The proportion of Fe/Mn-P and Fe/Al-P in the TP decreased with an increase in the pH, while the proportion of Ca-P in the TP increased with an increase in the pH. Under the alkaline condition (pH = 10), Ca-P in the sediment increased significantly, with an increase of 22.5%. However, Fe/Mn-P and Fe/Al-P decreased significantly, with drops of 37.3% and44.9%, respectively. Under the acidic condition (pH = 4), Fe/Mn-P and Fe/Al-P in the sediment increased significantly, and the increases were 63.1% and 37.1%, respectively. However, Ca-P decreased significantly, with a drop of 39.2%. In general, low pH promoted the release of Ca-P, and a high pH promoted the release of Fe/Mn-P and Fe/Al-P. Wuliangsuhai Lake water is characterized by weak alkaline characteristics throughout the year, and biological available phosphorus accounts for 13.3%-20.9% of the TP, with Fe/Mn-P being the dominant form. This study revealed that the risk of phosphorus release from sediments to the overlying water was greater under alkaline conditions.Peer reviewe

Denitrifying microbial communities along a boreal stream with varying land-use

Streams have an important role in regulating nitrogen (N) transportation from terrestrial ecosystems to downstream waters. Here, we examined how catchment land-use affects potential denitrification rates and the function and composition of denitrifier communities in boreal stream sediments, using stable isotope incubations and qPCR and 454-pyrosequencing targeted on nirS, nirK and nosZ genes. Although land-use influenced the water chemistry as higher nitrite+nitrate (NOx)-concentration at the agriculture-affected sampling point, sediment organic matter content was found to be the key factor in regulating potential denitrification rates. However, the abundance as well as the diversity and community composition of denitrifying microbes, and genetic N2O production potential (the ratio between nirS+nirK and nosZ gene abundances) were connected to both NOx- and sediment quality. Overall, our results suggest that catchment land-use-driven changes in N and carbon availability affect the denitrification rates, and possibly N-2:N2O production ratio, in boreal streams, through altering denitrifier abundance and community composition.Peer reviewe

Water Balance Analysis of Hulun Lake, a Semi-Arid UNESCO Wetland, Using Multi-Source Data

Hulun Lake is the largest lake in northeastern China, and its basin is located in China and Mongolia. This research aims to analyze the dynamic changes in the water volume of Hulun Lake and to estimate the groundwater recharge of the lake during the past 60 years. Multi-source data were used, and water-level-data-interpolation extrapolation, water-balance equations, and other methods were applied. The proportion of the contribution of each component to the quantity of water in Hulun Lake during the last 60 years was accurately calculated. Evaporation loss was the main component in the water loss in Hulun Lake. In the last 60 years, the average annual runoff into the lake was about 1.202 billion m3, and it was the factor with the largest variation range and the leading factor affecting the changes in the quantity of water in Hulun Lake. There was groundwater recharge in Hulun Lake for a long period, and the average annual groundwater recharge was about 776 million m3 (excluding leakage). The contribution ratio of the river water, groundwater, and precipitation to the recharging of Hulun Lake was about 5:3:2. The changes in the quantity of water in Hulun Lake are affected by climate change and human activities in China and Mongolia, especially those in Mongolia

Laboratory-scale x-ray absorption spectroscopy of 3d transition metals in inorganic thin films

In this paper we present laboratory-scale X-ray absorption spectroscopy applied to the research of nanometer-scale thin films. We demonstrate the Cu K edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) of CuI and CuO thin films grown with atomic layer deposition. Film thicknesses in the investigated samples ranged from 12 to 248 nm. Even from the thinnest films, XANES spectra can be obtained in 5-20 minutes and EXAFS in 1-4 days. In order to prove the capability of laboratory-based XAS for in situ measurements on thin films, we demonstrate an experiment on in situ oxidation of a 248 nm thick CuI film at a temperature of 240 degrees C. These methods have important implications for novel and enhanced possibilities for inorganic thin film research.Peer reviewe

Solar radiation transfer for an ice-covered lake in the central Asian arid climate zone

Spectral albedo and light transmittance through snow, ice, and water were measured in Lake Wuliangsuhai (40 degrees 36 '-41 degrees 30 ' N, 108 degrees 43 '-108 degrees 70 ' E), Inner Mongolia, China, during winter 2016. Data on the weather, structure of lake ice, and geochemistry of water were also collected during the 60-day field program. The study lake is shallow (mean depth 1.0-1.5 m) with a large wetland area. Compared with polar lakes, solar elevation is higher, snow accumulation is much lower, and the ice has more sediment. The ice was all congelation ice with a mean thickness of 36.6 cm, corresponding to a mean air temperature of -9.6 degrees C. The mean daily broadband albedo and photosynthetically active radiation (PAR) band transmittance were 0.54 and 0.08 (bare ice), 0.74 and 0.04 (new snow), and 0.30 and 0.12 (melting period), respectively. The level of light allowed photosynthesis to occur to the bottom of the lake. The ice acted as a grey filter for the sunlight with a mean attenuation coefficient of 2.1 m(-1). These results expand our knowledge of the evolution of light transfer through ice and snow cover and its role in the ecology of lakes in temperate and arid areas.Peer reviewe