Browsing by Subject "kasvihuonekaasut"

Purpose of this thesis is to estimate the carbon sequestration potential in eucalyptus plantations in Uruguay. This study also aims to show how beneficial these plantations are for carbon sinks. The aim of this research is calculate total carbon balance in eucalyptus plantations and compare the results to degraded lands. This study is first-of-its-kind study in Uruguay, but not unique globally. The objective was to use a modeling approach to formulate the results. The methodology of this study is based to the dynamic growth model (CO2fix V3.1). Model is developed to calculate and estimate forest carbon fluxes and stocks. In this study the model was utilized for estimating how much carbon is sequestered in eucalyptus plantations and soils. In this thesis the model was used to simulate eucalyptus forest plantations that stem from numerous studies and different data. Ad hoc Excel model was generated to form calculated results from the simulated data. A separate sensitivity analysis is also formulated to reveal a possible different outcome. The framework is based on a stand-level inventory data of forestry plantations provided by the Ministry of Uruguay (MGAP) and companies. Also multiple scientific reports and previous studies were used as guidelines for simulations and results. The forest stand, yield, soil and weather data used for this study are from three different departments. There are over 700 000 hectares of different species of eucalyptus plantations in Uruguay. The theoretical framework was tested computationally with eleven simulations. CO2fix was parameterized for fast-growing eucalyptus species used in different parts of Uruguay. The model gave outputs per hectare and then this result was scaled up to the national level. This study will also estimate how much grassland (Pampa) and former pasture land could sequester carbon. Situation prior to plantation is a baseline scenario and it is compared to the expected carbon sequestration of plantations. The model is also used to calculate the effect of changing rotation length on carbon stocks of forest ecosystem (forest vegetation and soil) and wood products. The results of this study show that currently the 707,674 hectares of eucalyptus plantations in Uruguay have the potential to sequester 65 million tonnes of carbon and reduce 238 million tonnes of CO2. The calculated carbon storage is 38 and simulated 25 million tonnes of C, products are deducted from the equation. During 22 years (1990–2012) the annual carbon sequestration benefit (afforestation-baseline) without products is 1 757 847 Mg C. The results suggest that it is reasonable to establish eucalyptus plantations on degraded, grassland (Pampa) and abandoned pasture land. The implications of the results are that eucalyptus plantations in Uruguay actually enhance carbon sequestration, are carbon sinks and store more carbon than grassland and abandoned pasture land. Plantations have a vast sequestration potential and are important in mitigating of CO2 emission and effects of the climate change. The findings endorse the significance of plantations to increase carbon sinks and this role will broaden in the future. The most relevant findings of this study are that afforestation increases the soil carbon in 10-year rotation plantations by 34% (101.1>75.6) and in 12-year rotation 38% (104.4>75.6 Mg Cha-1) in a 60-year simulation. The net (afforestation-baseline) average carbon stock benefit in the soil is 25.5 Mg C ha?1 in a 60-year simulation. The (CO2Fix) model indicate that the total average carbon sequestration for eucalyptus plantations is 92.3 Mg Cha?1. The average total carbon storage ranges from 25.8–138.5 Mg Cha?1 during a 60-year simulation. The simulations show that the net annual carbon storage in the living biomass is 29.1, 25.5 (soil) and 37.6 Mg C (products) on the average scenario. There is some fluctuation in the sequestration results in other 10 simulations. Previous studies have showed that the average carbon stock for eucalyptus plantations varies from 30–60 Mg C ha-1, when soil and products are deducted. The capacity of forest ecosystems to sequester carbon in the long run could be even more strengthened if a rotation length increases. Extending rotation from 10 to 12 years increased the average soil carbon stock from 25.5 to 28.8 Mg C (by 13%) in 60 year simulation. The results also indicate that mean annual precipitation (MAP) alters the carbon sinks of the forest ecosystem. There are some limitations in this study and they are clearly explained and analyzed. Hence, most of the results are estimations. Ministry and companies need to prolong planting of trees and even intensify annual programs in order to achieve carbon sequestration targets. Further research is needed to get an estimate of the total forest ecosystem carbon storages and fluxes.

Peatlands are a significant carbon and nitrogen reservoirs, making them potential sources of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) emissions. Variations in water table level change the oxygen content of peat, affecting the oxidation-reduction or redox state of the peat, which is known to influence the biochemical processes and thus greenhouse gas (GHG) emissions. The aim of this study was to assess the effect of controlled anoxic redox conditions and inorganic electron acceptors (TEAs) on redox potential (Eh), and N2O, CH4, and CO2 emissions. In this study during an anaerobic incubation experiment, the rates of formation of these GHGs and Eh values as a function of time were measured from drained (D) and undrained (UD) peat of three nutrient levels: mesotrophic (ME), oligotrophic (OL), and ombrotrophic (OM). Redox conditions were controlled to three levels by nitrate (NO3-), ferric iron (Fe3+), and sulphate (SO42-). In addition, measurements were performed on untreated (Ctrl) peat. The peat was in an anoxic state throughout the incubation (Eh < 300 mV) and the values were in the order of TEA reduction, even though they were mainly in the iron and manganese reduction zones, probably due to the naturally high iron content of the peat. As expected, N2O formation was highest in flasks with added NO3-, and N2O formation was weak and ceased without addition. CH4 formation was reduced in flasks with added NO3- or SO42-, and SO42- addition also inhibited CO2 formation on which NO3- addition had no effect. In contrast, the addition of Fe3+ increased both CO2 and CH4 formation compared to Ctrl treatment, and it is possible that methanogens were involved in the reduction of Fe3+. In Ctrl flask, the redox state did not decrease to the lowest level compared to the other treatments as expected, but the Ctrl treated UD ME peat had the highest CH4 formation at the end of incubation. For all treatments, GHG emissions were higher from nutrient-rich peat in the descending order ME > OL > OM. In general, UD peat also had higher gas formation than D peat. All GHGs were formed the most while Eh values were around 0 mV and the value was especially high for CH4 formation, probably due to the linkage between methanogens and iron. The poor ability of the Pt electrode to detect NO3- or oxygen was the most likely reason for the variable and low Eh values of the flasks with NO3- addition. For the same reason, oxygen leakage of the anaerobic chamber was most likely responsible for the varying Eh values measured from Ctrl treated OM peat. This study suggests that Eh measurement is a useful predictor of the redox state and reactions, but it must be considered together with other measurements and analyses such as microbial analysis, nutrient analysis, and GHG measurements to predict redox processes and GHG emissions in anaerobic peatland. In particular, the role of iron on CH4 emissions requires further research.

Environmental factors are important tools in constructing methane flux models and estimations. Among the abiotic factors, plants and their functional groups have been noted to have significant effect on methane fluxes for three reasons. First, the vegetation community compositions express their abiotic environmental factors that affect not only the plants, but also local methanogen and methanotroph communities. Second, the vegetation itself might produce methane emissions and have a direct effect on methane balance. Third, the plant functional groups and species have differences in their chemical and physical properties that support different methanogen communities and therefore have an indirect impact on methane fluxes. In this study, methane fluxes of different plant communities were observed during one growing season in northern boreal catchment area in Muonio. Study focuses to determine the link between methane fluxes and abiotic and biotic environmental factors in different vegetation types. Closed chamber technique was used to measure methane and carbon dioxide fluxes from 23 plots every two weeks in period of June-August. Environmental data, such as moisture, temperature species composition etc. were collected from the plots. Vegetation types for each plot were determined via ordination analysis. Linear mixed-effects regression model and generalized additive model were applied and compared to observe the relationships of methane and environmental factors in different vegetation types. Dataset was divided into four vegetation types in clustering analysis: wet fen, pine bog, spruce swamp and forest. The greatest amount (average 5959 µg/m²/h) and biggest range (standard deviation 5285 µg/m²/h) of methane emissions were observed on wettest fen-like study sites. Peatland types in general acted as net methane sources. The driest, forest-like vegetation type acted as a net methane sink. The amount (average -107 µg/m²/h) and range (standard deviation 117 µg/m²/h) of methane fluxes were very moderate in comparison to peatland types. These effects intensified towards the climax of growing season. The most significant environmental factors were mostly abiotic on driest study sites and the whole plant biomass was more significant biotic methane flux regulating factor than plant functional groups. On wetter study sites, the role of abiotic factors decreased, and plant functional group increased. Graminoids were linked to bigger methane emissions especially on wetter study sites. Forest mosses and different shrub types seemed to have a link with lower methane emissions or methane absorption. The effect of other plant functional groups on methane fluxes varied more, and their role remains unclear. None of the environmental factors could estimate the methane flux alone, and the methane budget seems to be a sum of multiple variables in each vegetation type. The role of plant functional groups varied in different vegetation types and was dependent on surrounding vegetation. More research is needed to get better tools to estimate methane balance and to understand the underlying mechanisms in climate and environmental change.

Maaperän fysikaaliset, kemialliset ja biologiset ominaisuudet tarjoavat lukuisia ekosysteemipalveluja, joista erityisesti haitallisten yhdisteiden, mukaan lukien hiilidioksidin, sidonta on saanut paljon huomiota ilmastonmuutosta hillitsevän potentiaalinsa tähden. Orgaanisten ja epäorgaanisten yhdisteiden varastointi on tärkeää etenkin kaupungeissa, jotka kuuluvat suurimpiin kasvihuonekaasujen päästölähteisiin. Kaupunkien vihermaat kuuluvat tehokkaimpiin sitojiin runsaiden orgaanisen aineen varantojensa ansiosta, minkä lisäksi ne tuottavat useita muita paikallisia ekosysteemipalveluja sekä toimivat virkistysalueina. Vihermaat vähenevät kuitenkin jatkuvan rakentamisen vuoksi, kun niitä peitetään esimerkiksi asfaltilla ja mukulakivillä, minkä seurauksena myös pinnoitetun kaupunkimaaperän merkitystä on alettu tutkia. Selvitysten mukaan pinnoitettu maa on hiili- ja typpivarannoiltaan selkeästi pinnoittamattomia vihermaita niukempi, mikä johtuu fyysisen esteen rajoittavasta vaikutuksesta kaasujenvaihtoon ja veden läpäisyyn. Lisäksi hiilen (C) ja typen (N) sidonnassa ja ravinnekierrossa olennainen pintamaa poistetaan ja korvataan C:n ja N:n osalta niukemmalla rakennusmaalla. On tärkeää selvittää, kuinka nämä muutokset vaikuttavat kaupunkimaaperän kykyyn sitoa ilmakehän hiiltä ja haitallisia yhdisteitä ja ylläpitää ainekiertoja. Tutkimuksessani tarkastelin pinnoitetun kaupunkimaan ominaisuuksia Helsingissä, sillä Suomen kaltaisilla kylmillä alueilla tutkimukseen perustuvaa tietoa ei käytännössä ole. Tätä varten keräsin maanäytteen 11 katutyöojasta kahdelta eri syvyydeltä rakennusmaasta. Näytteistä mitattiin kokonaishiili ja –typpi, hiilen ja typen suhdeluku (C/N), orgaanisen aineen määrä, kosteusprosentti, pH, maahengitys ja tiheys (engl. bulk density). Vertailin maan ominaisuuksia syvyyksien, pinnoitetun ja pinnoittamattoman maan sekä kylmien ja lämpimämpien alueiden välillä, minkä lisäksi laskin tulosten perusteella pinnoitetun ja pinnoittamattoman maan C- ja N-varastot Helsingin keskustassa sekä pinnoitteen osuuden maa-alasta. Aikaisempien tutkimusten perusteella laadin 3 hypoteesia: 1) Pinnoitetun maan C- ja N-pitoisuudet ovat selkeästi pienempiä pinnoittamattomaan maahan nähden. 2) Pinnoitetussa maassa C- ja N-pitoisuuksien erot kahden syvyyden välillä ovat tasaisemmat kuin pinnoittamattomassa maassa, sillä C- ja N-rikas pintamaa on vaihdettu niukempaan rakennusmaahan ja pinnoite estää karikkeen tuomaa C:tä ja N:ä kulkeutumasta ja keskittymästä pintamaahan. 3) Kylmillä alueilla pinnoitteen aiheuttama C- ja N-hävikki on suurempi kuin lämpimämmillä alueilla paksumman rakennusmaakerroksen vuoksi. Odotusten mukaisesti 1) pinnoitetun maan C- ja N-pitoisuudet olivat pienemmät kuin pinnoittamattomassa maassa, 2) pinnoitetun maan C- ja N-pitoisuudet pysyivät tasaisina eri syvyyksillä verrattuna pinnoittamattomaan maahan ja 3) Helsingin C- ja N-hävikki on suurempi verrattuna aiempiin tutkimustuloksiin lämpimämmistä maista. Kaikkien kolmen tarkastelukohdan tulokset ovat yhdistettävissä maanvaihdon ja pinnoituksen aiheuttamiin muutoksiin. Muidenkin muuttujien tulokset vastasivat kirjallisuuden luomia ennakkokäsityksiä. Helsingin C- ja N-varastot ovat myös huomattavasti pienentyneet pinnoitteen lisäännyttyä, mikä heikentää kaupungistuneiden alueiden ekosysteemipalvelupotentiaalia. Tulokset vahvistavat oletuksia pinnoitteen tuomista muutoksista maaperän sitomiskykyyn sekä yleisesti että verrattaessa kylmiä ja lämpimämpiä alueita keskenään.

Improving land management to mitigate climate change is important, especially in agriculture on soils with high organic content. Many studies have found evidence that increasing diversity can help to improve plant biomass production and soil carbon storage. This is attributed to complementarity which consists of more efficient resource use due to niche differences and facilitative interactions. For the total climate impact, the effect of greenhouse gas emissions from the soil needs to be considered. To find out if adding more species to a grass mixture could have similar benefits in boreal zone grass cultivation in Finland, an experiment was set up with four different species mixtures, and three levels of species richness were established under a nurse crop. It was additionally of interest if these effects can counter the emissions of cultivation on organic soils. Biomass samples were collected both before the nurse crop was removed and at the end of the growing season. Both species richness and Shannon diversity index were considered as explanatory factors. Carbon exchange, divided into respiration and photosynthetic capacity, as well as nitrous oxide and methane fluxes, were monitored monthly. There was no strong evidence that species richness affects biomass or greenhouse gas fluxes during the first year. The effect of species richness on the biomass was clearer when the diversity index was considered. These results were significant when the lowest biomass values were excluded from the analysis, probably because complementary resource use needs enough biomass to have an effect. The differences in carbon flux measurements may be sensitive to timing within the growing season since the results closest to significant were obtained at the start of the season. At the time, the measurement conditions were good and the nurse crop biomass was small enough not to obscure the effects of grass mixture. When it comes to other greenhouse gases, species richness had most impact on early nitrous oxide emissions, while methane flux probably needs significantly more time for any changes to appear. Overall, the effect of species richness needs to be studied over the full grass cultivation cycle to find out the full effect. Based on current results, increasing species richness may be an option when other methods cannot be used to reduce emissions and improve carbon sink of agriculture.