Chlorophyll-a (chl-a) concentration is an indicator of the trophic status and is extensively used as a measurement of the algal biomass which affects the level of eutrophication in aquatic systems. High concentration of chl-a may indicate high biomass of phytoplankton which can decrease the quality of water or eliminate important functional groups in the ecosystem. Predicting chl-a concentrations is desirable to understand how great impact chl-a may have in aquatic systems for different scenarios during long-time periods and seasonal variation. Several models of predicting annual or summer chl-a concentration have been designed using total phosphorus, total nitrogen or both in combination as in-parameters. These models have high predictive power but are not constructed for evaluating the long-term change or predicting the seasonal variation in a system since the input parameters often are annual values or values from other specific periods. The models are in other words limited to the range where they were constructed. The aim with this thesis was to complement these models with other methods and models which gives a more appropriate image of how the chl-a concentration in an aquatic system acts, both in a short as well as a long-time perspective. The results showed that with a new method called Statistically meaningful trend the Baltic Proper have not had any change in chl-a concentrations for the period 1975 to 2007 which contradicts the old result observing the p-value from the trend line of the raw data. It is possible to predict seasonal variation of median chl-a concentration in lakes from a wide geographically range using summer total phosphorus and latitude as an in-parameter. It is also possible to predict the probability of reaching different monthly median chl-a concentrations using Markov chains or a direct relationship between two months. These results give a proper image of how the chl-a concentration in aquatic systems vary and can be used to validate how different actions may or may not reduce the problem of potentially harmful algal blooms. / Koncentrationen av klorofyll-a (chl-a) är en indikator på vilken trofinivå ett akvatiskt system har och används som ett mått på algbiomassa som påverkar övergödningen i akvatiska system. Höga koncentrationer av chl-a i sjöar kan indikera hög biomassa av fytoplankton och försämra kvalitén i vattnet eller eliminera viktiga funktionella grupper i ett ekosystem. Det är önskvärt att kunna prediktera chl-a koncentrationer för att förstå hur stor påverkan chl-a kan ha för olika scenarier i akvatiska system under längre perioder samt under säsongsvariationer. Flera modeller har tagits fram som predikterar årsvärden eller sommarvärden av chl-a koncentrationer och i dessa ingår totalfosfor, totalkväve eller en kombination av båda som inparametrar. Dessa modeller har hög prediktiv kraft men är inte utvecklade för att kunna utvärdera förändringar över längre perioder eller prediktera säsongsvariationer i ett system eftersom inparametrarna ofta är årsmedelvärden eller värden från andra specifika perioder. Modellerna är med andra ord begränsade till den domän som de togs fram för. Målet med denna avhandling var att komplettera dessa modeller med andra metoder och modeller vilket ger en bättre förståelse för hur chl-a koncentrationer i akvatiska system varierar, både i ett kortsiktigt och ett längre perspektiv. Resultaten visade att med en ny metod som kallas för Statistiskt meningsfull trend så har egentliga Östersjön inte haft någon förändring av chl-a koncentrationer under perioden 1975 till 2007 vilket motsäger tidigare resultat då p-värdet tas fram från en trendlinje av rådata. Det är möjligt att prediktera säsongsvariationer av median chl-a koncentrationer i sjöar från en bred geografisk domän med totalfosfor från sommar och latitud som inparametrar. Det är även möjligt att beräkna sannolikhetenav ett predikterat värde för olika månadsmedianer av chl-a koncentrationer med Markovkedjor eller ett direkt samband mellan två månader. Dessa resultat ger en reell förståelse för hur chl-a koncentrationer i akvatiska system varierar och kan användas till att validera hur olika åtgärder kan eller inte kan reducera problemet av de potentiellt skadliga algblomningarna.

Due to perceived shortcomings in some aspects of hazard assessment for chemicals administered to aquatic systems, experiments were conducted to determine the effects of copper on various ecological parameters in artificial streams and microcosms. Effects investigated were colonization and growth of periphyton communities in artificial streams, community composition and nutritional content of periphyton in these streams, leaf conditioning and nutritional content in laboratory microcosms, and nutritional suitability of these leaves to a shredding macroinvertebrate. Main effects observed in periphyton growth experiments were significant reduction in substrate colonization due to copper treatment, which led to significantly lower standing biomass in treated streams. Observed growth rates were generally similar between control streams and copper treated streams. Light treatments did not affect periphyton responses to copper. Community composition of the periphyton was affected by 2.5 μg/L copper. Periphyton phosphorus and nitrogen contents were not affected by copper treatment. Conditioning rate of leaves was significantly decreased by 50 μg/L copper treatments in some cases. Leaf phosphate and nitrogen contents were not significantly affected by copper treatment. Significant differences in nutritional suitability of copper-treated leaves to a shredding macroinvertebrate were not detected. These experiments suggest that aquatic primary producers are more sensitive to copper than heterotrophs. Additionally, adverse effects on periphyton were observed at concentrations well below measures of chronic toxicity to organisms dependent on periphyton as a trophic resource and the chronic criteria for copper. As such, greater emphasis should be placed on the sensitivities of periphyton communities in future copper criteria determination. / Ph. D.

No description available.

No description available.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Endocrine disrupting contaminants (EDCs) coming from households, industrial parks, wastewater (sewage) treatment and agricultural areas have been shown to pollute our freshwater systems. These contaminants may disrupt early development and reproductive systems in freshwater organisms (fish, frogs and crocodile species) as well as humans. Agricultural pesticides are shown as a large contributor to endocrine disruption activity in water catchment areas through spray drift, runoff, and/or groundwater leeching. Although South Africa is recognized as the largest consumer of agricultural pesticides in Africa, few studies have been undertaken to assess the prevalence and impact of endocrine disorders activities of pesticides in local freshwater systems. Recent studies have suggested that various agricultural pesticides, especially fungicides, might have adverse effects on the male endocrine system. There is therefore a need to test for a wider range of endocrine disrupting activities (mechanisms) in environmental waters other than conventional estrogenic (feminising) activities. Furthermore, there is a need to establish biomarkers in endemic species (bio-indicators) to show endocrine disruption in vertebrates (therefore also apply to humans). The specific objectives of the study were to: (1) describe and confirm the use of androgen-controlled breeding glands in male African clawed frogs (Xenopus laevis) as a biomarker for (anti)androgenic endocrine disruption activity (Chapter 2), (2) to investigate the premature development of breeding glands in X. laevis tadpoles (pre-metamorphic) and young froglets (post-metamorphic) (Chapter 2), (3) to investigate the disruption of male reproductive traits in adult X. laevis frogs by exposure to substances disrupting two different anti-androgenic endocrine disruption pathways (Chapter 3), (4) screen for (anti)androgenic activity of individual and binary mixtures of pesticides, which are regularly used in agricultural areas in the Western Cape Province of South Africa (Chapter 4), and (5) to test for (anti)androgenic and estrogenic endocrine disrupting activities by making use of in vitro assays as well as adult male X. laevis frogs collected from selected ponds surrounded by vineyards and fruit orchards in the Stellenbosch Winelands. The present study confirmed that male breeding glands can serve as biomarkers for (anti)androgenic endocrine disruption and that male reproductive and secondary sexual characteristics can be disrupted through two different biochemical control pathways. The study also confirmed that the expression of androgen-regulated breeding glands can be stimulated in pre-metamorphic tadpoles and immature, post-metamorphic frogs, and can thus be used for (anti)androgenic testing. The rapid testing and predictive value of an in vitro recombinant yeast screen for androgen receptor binding inhibition of selected individual or binary mixtures of pesticides was also confirmed. However, the current study showed that the predicted in vitro (anti)androgenic activity did not always correspond with in vivo (anti)androgenic biomarker outcomes. This It also confirmed that single-cell in vitro assays can be used as a first-level prediction for (anti)androgenic activities of individual or mixtures of agricultural pesticides. This study provides a better understanding for potential mixture interactions of commonly used agricultural pesticides, the hormonal control of secondary sexual characteristics in male frogs and the use of reproduction biomarkers to study long-term effects of endocrine disruptors in local water supplies. / AFRIKAANSE OPSOMMING: Endokriene versteurings-kontaminante (EVKe) wat vanaf huishoudings, industriële parke, afvalwater(riool)-behandeling en landbougebiede kom, besoedel ons varswaterstelsels. Hierdie kontaminante mag versteuring van vroeë ontwikkeling- en voorplantingstelsels in varswater-organismes (vis-, padda- en krokodil-spesies) sowel as die mens inhou. Landbou-plaagdoders word uitgesonder as ’n bydraer van endokriene versteuring-aktiwiteite in wateropvangs-gebiede deur spuitnewel, afloop-water en/of grondwater-deurvloei. Hoewel Suid-Afrika erken word as die grootste verbruiker van landbou-plaagdoders in Afrika, word min studies onderneem om die voorkoms en impak van endokriene versteurings-aktiwiteite van plaagdoders in plaaslike varswaterstelsels te ondersoek. Onlangse studies het voorgestel dat verskeie landbou-plaagdoders, veral swamdoders, nadelige uitwerkings kan hê op die manlike endokriene stelsel. Daar bestaan dus 'n behoefte om te toets vir 'n wyer verskeidenheid van endokriene versteurings-aktiwiteite (meganismes) in omgewingswater anders as konvensionele estrogeniese (vervroulikings) aktiwiteite. Verder bestaan daar ’n behoefte om biomerkers in endemiese spesies te gebruik as bio-indikators van endokriene versteuring in werweldiere (daarom ook van toepassing op die mens). Die spesifieke doelwitte van die studie het ingesluit om: (1) die gebruik van androgeen-beheerde parings- velkliere (“breeding glands”) in manlike platannas (Xenopus laevis) as 'n biomerker vir (anti)androgeniese endokriene versteuring-aktiwiteit te beskryf en bevestig (Hoofstuk 2); (2) ondersoek in te stel na die voortydige ontwikkeling van parings-kliere in X. laevis paddavisse (pre-metamorfose) asook jong paddas (post-metamorfose) as biomerkers van androgeniese (vermanlikheids) aktiwiteite (Hoofstuk 2); (3) ondersoek in te stel na die versteuring van manlike geslags-eienskappe in volwasse X. laevis paddas deur middel van blootstelling aan stowwe wat twee verskillende androgeniese endokrien reaksie-weë verteenwoordig (Hoofstuk 3); (4) toets vir (anti)androgeniese aktiwiteit van individuele en binêre mengsels van landbou-plaagdoders wat gereeld in die Westelike Provinsie van Suid Afrika gebruik word (Hoofstuk 4) en (5) te toets vir (anti)androgeniese en estrogeniese endokriene versteurings aktiwiteite deur gebruik te maak van in vitro toetse asook volwasse manlike X. laevis paddas wat uit geselekteerde damme (omring deur wingerde en vrugte boorde in die Stellenbosch wynland distrik) versamel was. Die huidige studie het bevestig dat die manlike parings-velkliere as biomerkers vir (anti)androgeniese versteuring kan dien en dat manlike voortplanting en sekondêre geslagskenmerke deur twee verskillende biochemiese beheer-weë ontwrig kan word. Die studie het verder bevestig dat die uitdrukking van androgeen-gereguleerde parings-velkliere voortydig gestimuleer kan word in pre-metamorfose paddavissies asook onvolwasse, post-metamorfose paddas. Die vinnige toetsing en voorspellingswaarde van 'n rekombinante in vitro gis toets om binding-inhibisie van die androgeen reseptor deur geselekteerde individuele of binêre mengsels van plaagdoders aan te toon is ook bevestig. Alhoewel, die huidige studie het getoon dat die voorspelde in vitro (anti)androgeniese aktiwiteit nie altyd ooreenstem met in vivo (anti)androgeniese biomerker uitkomstes nie. Hierdie studie bevestig dat enkel-sel in vitro toetse aangewend kan word as eerste vlak- en voorspelling-toetse vir (anti)androgeniese aktiwiteite van enkel of mengsels van landbou-plaagdoders. Sodoende is 'n beter begrip verkry vir potensiële mengsel-interaksies van algemeen-gebruikte landbou plaagdoders, die hormonale beheer van sekondêre geslagskenmerke in manlike paddas asook die aanwending van voortplantingsbiomerkers om langtermyn effekte van endokriene versteurders in plaaslike waterbronne te ondersoek.

In Asia, the recent rapid growth in production of higher value, more pesticide intensive, horticultural crops and inland aquatic foods in linked agri-aquatic systems poses numerous environmental, health and wider livelihood threats in these often multi-use aquatic systems. ‘Green Revolution’ technologies have enhanced food security and pesticides have been promoted, however, the sustainability of prolonged pesticide use from a functional, environmental and socio-economic perspective is increasingly questionable. Further, despite international pesticide trade agreements and country-specific legislation, illegal practices still prevail. In Thailand and Sri Lanka the influence of pesticide marketing and regulation on pesticide use and hazards was investigated. Community livelihood relationships with three very different agri-aquatic systems (in Central and Northeast Thailand and Northwest Sri Lanka), pesticide use and associated aquatic and health hazards were explored with respect to surface water use and well-being status. Quantitative and qualitative data collection methods utilised participatory community appraisals, household surveys, pesticide fate in surface waters and dietary risk assessment and modelling, key informant semi-structured interviews and stakeholder workshops, to assess these relationships. Enhanced environmental and human pesticide hazards were contributed by pesticide sales incentives and weak regulation allowing illegal practices to prevail. Preliminary risk assessments found greater aquatic and human dietary pesticide hazards within communities, with the poorest at greatest vulnerability from applying pesticide and higher dependency on threatened natural aquatic food resources. The poorest in communities were most likely to overuse pesticide in Sri Lanka and were most vulnerable to illegal practices in the pesticide industry that are often linked with unauthorised traders and credit arrangements. Most horticultural production is for fresh wholesale markets with no food safety controls, and despite growing demand for safer horticultural produce, most farmers perceive pesticides as necessary, the associated hazards low and have little knowledge of safe food production and markets. These circumstances help sustain pesticide use. Some unofficial certification and misleading labelling in the ‘safe’ fruit and vegetable sector in Thailand potentially misinforms consumers and undermines trust that may threaten pesticide reduction efforts. Good Agricultural Practice (GAP) and vegetable Integrated Pest Management (IPM) are evolving practices and techniques of producing horticultural crops with less or no pesticide, the latter sometimes through Farmer Field Schools (FFS), however, evidence of success varies. Teaching through lectures and more lengthy and costly participatory methods is evident, with the former more successful on GAP and higher educated farmers and the latter with IPM and worse-off farmers, particularly when addressed within livelihood issues as a whole. However, production scale, farmer enthusiasm, produce marketing and facilitator expertise all influence outcomes, particularly with IPM, whilst proper evaluation could improve progress. Growing rural consumer interest in organic produce offers further incentives for small to medium scale farmers to implement IPM and reduce pesticide use and hazards. As value of aquatic resources was an incentive to reducing pesticide use, particularly the most dangerous products, exploration of this component of agri-aquatic systems is another exciting prospect for empowering farming community livelihoods over established and failing fear based chemical practices. Such new practices may lead the way towards affordable and trustworthy agri-aquatic systems produce with ethical certification. Greater pesticide use savings on a wider scale come from use of efficient flat fan spray nozzles compared with conventional pesticide spray nozzles. Complementary policies and stakeholder co-operation could aid pesticide use and hazard reduction efforts. A number of recommendations arose from the research.

Methods were developed for the determination of methylmercury in natural waters and sediments based on steam distillation and aqueous phase ethylation followed by gas chromatography-atomic fluorescence spectrometry. The methods were shown to be free from measurable artefactual methylation of inorganic mercury and offered improved sample throughput over existing methods. Improvements were made to existing methods for the determination of total mercury in biota, sediments and natural waters and dissolved mercury species in natural waters. These methods were applied to the study of mercury cycling in two remote field sites. The cycling of mercury species was studied in Lake Murray in Western Province, Papua New Guinea, which has been historically noted as a region of high mercury concentrations in fish. Concentrations of methylmercury and total mercury in the water column were found to be variable and consistent with non-contaminated lake systems. Concentrations of methylmercury and total mercury in the sediments were also found to be low, except for in the south of the lake, which was influenced by an intermittent supply of water and sediments with elevated mercury concentrations from the Strickland River. Methylmercury concentrations in the sediments were generally higher in the backwater areas due to littoral processes. The low concentrations of methylmercury in the sediments and waters were inconsistent with other systems previously studied in the northern hemisphere, showing a link between high mercury concentrations in fish and high concentrations of methylmercury in waters or sediments. Therefore, the biota of Lake Murray were studied in order to account for the differences between this and other systems. A study was conducted of the stable isotope ratios of carbon and nitrogen in biota from Lake Murray to elucidate key food-web interactions. This study revealed that the dominant carbon source for fish in the lake is plankton, although algae and macrophytes may also be involved in the food-web. The methylmercury bioaccumulation factors between trophic levels were similar to those measured in temperate systems of the northern hemisphere. The high concentrations of methylmercury, observed in piscivorous fish, were shown to be a consequence of the complex food-web and the number of trophic levels in the food-chains. The cycling of mercury species was studied in Lake Gordon and Lake Pedder in southwest Tasmania, which has recently been identified as being in a region of high mercury concentrations in trout and eels. The concentrations of total mercury were found to be reasonably uniform in the waters of both lakes, spatially and temporally. The concentrations of methylmercury in the waters were seasonally variable, and were consistently lower in Lake Pedder than in Lake Gordon. Dilution of methylmercury concentrations by precipitation direct to the lake surface, probably accounts for the most of the difference in methylmercury concentrations between the lakes. Owing to the long residence time of water in Lake Gordon, this reservoir mixes inputs of water with varying methylmercury concentrations. Concentrations of total mercury and methylmercury in submerged soils were low and depth profiles of mercury species in the water column did not show evidence of a gradient of mercury concentrations due to releases from the sediments. The concentrations of methylmercury observed in the water column are consistent with the concentrations observed in the fish. A budget of the mercury inputs and outputs to Lake Gordon showed that in-lake processes and sources in the catchment areas both contributed significantly to the concentrations of methylmercury in the lake. The methylation of mercury in Lake Gordon appeared to mainly occur in the surface waters (< 10 m) and was not consistent with processes leading to the methylation of mercury at the oxic/anoxic boundary observed in seepage lakes in Wisconsin. The concentrations of total mercury and methylmercury in bogs in the catchment areas of Lakes Gordon and Pedder, were high and governed by the concentration of organic matter in the sediments. The processes involved in the supply of mercury species from the Lake Gordon and Lake Pedder catchments appear to be similar to those in drainage lakes in the temperate and boreal regions of the northern hemisphere. The formation of the Lake Gordon and Lake Pedder reservoirs appears to have had little impact on the mean annual concentrations of methylmercury released to the downstream environment.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / The contamination of surface water bodies due to antropic action has made water ever more scarce. Knowledge of the water quality is essential to determine instruments for it's management . Monitoring water quality in huge areas requires a high number of saimples for water quality control. This fact, allied to the high costs of water analysis, limits the evaluation that can be made of continental waters. Even though in later years geoprocessing and remote sensing techniques have been developed with important results in water quality studies, these techniques have yet to be applied in the study of aquatic systems in semiarid regions. Therefore, it was attempted to develop a methodology based on the spectral characteristics of water as a support method for the evaluation of water quality in semiarid regions. Water samples were collected in seven points from 2008 to 2010 (every two months) and in 20 points from 2011 and 2012 (every three months) . The campaigns for radiometric data acquisition occurred in 2011 and 2012, alongside the water sampling. The determinant factors and water similarity were identified by the multivariable analysis. Data from orbital and insitu remote sensing correlated with limnologic data were used. The determinant indicators for water quality in the Oros were defined mainly by the following factors: the geologic components of the soil; sediment transport by surface flow and organic pollution. The Cluster Analysis formed three distinct groups. The water similarity was defined by natural conditions and by the land use around the reservoir and along the basin. The models developed for limnologic variables, suspended inorganic solids, turbidity, transparency and electric conductivity, showed themselves to be trustworthy, indicating that these variables can be quantified remotely through remote sensing data. The models developed for the clorophile - a fitted well, indicating that this variable can be quantified accurately through in situand orbital remote sensing data. The general three banded model presented a better efficiency to that of the two band model. According to the developed model and the image use of the MERIS sensor, the Oros waters, as far as trophic state is concerned, presented 61.15% of it's water bater classified as eutrophic for the month of February, 2010. For the MERIS image of August 2011, 95.77% of it's waters were classified as eutrophic. Therefore, through remote sensing data it is possible to elaborate a water resources management at a lower cost, generating a usefull information for decision making by managers, vital for the implementation of public policies at county, regional, state and federal levels. / Com a contaminaÃÃo de corpos hÃdricos pela aÃÃo antrÃpica, a disponibilidade de Ãgua torna-se cada vez menor. O conhecimento da qualidade das Ãguas à essencial à proposiÃÃo de instrumentos de gestÃo das mesmas. O monitoramento em Ãreas extensas requer um elevado nÃmero de amostras para o controle da qualidade da Ãgua; este fato, aliado aos altos custos das anÃlises, limita a avaliaÃÃo do processo de degradaÃÃo das Ãguas interiores. Apesar do desenvolvimento, nos Ãltimos anos, das tÃcnicas de geoprocessamento e sensoriamento remoto, com a obtenÃÃo de informaÃÃes relevantes em estudo de qualidade de Ãguas, elas nÃo tÃm sido exploradas em estudos de sistemas aquÃticos de regiÃes semiÃridas. Com isso, objetivou-se desenvolver uma metodologia baseada nas propriedades espectrais da Ãgua como suporte a avaliaÃÃo de sua qualidade em ambientes semiÃridos. As amostras de Ãgua foram coletadas em sete pontos de 2008 a 2010 (bimestralmente) e em 20 pontos de 2011 a 2012 (trimestralmente). As campanhas para aquisiÃÃo de dados radiomÃtricos ocorreram em 2011 e 2012, concomitantes Ãs coletas das amostras de Ãgua. Os fatores determinantes e a similaridade das Ãguas foram identificados pelo emprego da anÃlise multivariada. Foram usados dados de sensoriamento remoto orbital e in situ, correlacionando com os dados limnolÃgicos. Os indicadores determinantes da qualidade das Ãguas do OrÃs sÃo definidos principalmente pelos seguintes fatores: processo natural de intemperismo dos componentes geolÃgicos do solo; carreamentos dos sÃlidos suspensos atravÃs do escoamento superficial das Ãguas e poluiÃÃo orgÃnica. A anÃlise de agrupamento formou trÃs grupos distintos. A similaridade das Ãguas foi definida pelas condiÃÃes naturais e pelas atividades antrÃpicas exercidas nas proximidades do reservatÃrio e ao longo da bacia. Os modelos desenvolvidos para as variÃveis limnolÃgicas, sÃlidos inorgÃnicos suspensos, turbidez, transparÃncia e condutividade elÃtrica, mostraram-se confiÃveis, indicando que essas variÃveis podem ser quantificadas remotamente a partir dos dados de sensoriamento remoto de campo. Os modelos desenvolvidos para a variÃvel clorofila-a sÃo confiÃveis, indicando que esta variÃvel pode ser quantificada remotamente a partir dos dados de sensoriamento remoto de campo e orbital com elevado grau de confiabilidade. O modelo geral de trÃs bandas apresentou desempenho superior ao modelo de duas bandas. De acordo com o modelo desenvolvido e com uso de imagens do sensor MERIS, as Ãguas do reservatÃrio OrÃs, quanto ao estado trÃfico, apresentaram 61,15% da sua bacia hidrÃulica classificadas como eutrÃfica, para o mÃs de fevereiro de 2010. Para a imagem MERIS de agosto de 2011, 95,77% das Ãguas foram classificadas como eutrÃficas. Portanto, com o uso do sensoriamento remoto à possÃvel elaborar um gerenciamento dos recursos hÃdricos de menor custo, gerando informaÃÃes Ãteis à tomada de decisÃes pelos gestores, vital para a implantaÃÃo de polÃticas pÃblicas em Ãmbito municipal, regional, estadual e federal.

Monomethylmercury, MeHg, is formed under anoxic conditions in waters, sediments and soils and then bioaccumulated and biomagnified in aquatic food webs, negatively effecting both human and wildlife health. It is generally accepted that precipitation of mercury, Hg, and adsorption of Hg to e.g. organic matter and mineral surfaces are important processes limiting the reactivity of Hg mobilized in the environment by natural and anthropogenic activities. However, knowledge concerning the role of different solid and adsorbed chemical forms of Hg for MeHg formation, evasion and bioaccumulation is missing. Such information is vital for the understanding of environmental processes controlling MeHg formation and bioaccumulation, as well as for predicting how changes in e.g. loading rates of atmospheric Hg and the outcome of climate change scenarios and anthropogenic land use could alter Hg concentrations in biota. In this thesis, a novel experimental approach, using isotopically enriched solid and adsorbed phases of inorganic Hg, HgII, as tracers, was developed. Using this approach, we successfully determined rates of MeHg formation from solid and adsorbed Hg species in sediment slurries and in mesocosm systems under conditions closely resembling those in field. We conclude that the solid/adsorbed phase speciation of HgII is a major controlling factor for MeHg net formation rates. Microcosm experiments revealed that newly formed MeHg was a major contributor to the evasion of MeHg from the water‒sediment system, emphasizing the importance of MeHg formation rate, rather than MeHg concentration, in the sediment for this process. From mesocosm systems, we provide experimental evidence, as well as quantitate data, for that terrestrial and atmospheric sources of HgII and MeHg are more available for methylation and bioaccumulation processes than HgII and MeHg stored and formed in sediments. This suggests that the contribution from terrestrial and atmospheric sources to the accumulation of Hg in fish may have been underestimated. As a consequence, in regions where climate change is expected to further increase land runoff, terrestrial MeHg sources may have even higher negative effects on biota than previously thought. Data and concepts presented in this thesis lay the basis for unprecedented in-depth modeling of processes in the Hg biogeochemical cycle that will improve our understanding and the predicting power on how aquatic ecosystems may respond to environmental changes or differences in loading rates for atmospheric Hg. / Monometylkvicksilver, MeHg, bildas under anoxiska förhållanden i naturliga vatten, sediment och jordar och bioackumuleras och magnifieras därefter i den akvatiska näringskedjan med negativa effekter på djur och människor som följd. Det är generellt vedertaget att utfällning av Hg och adsorption av Hg till exempelvis organiskt material och mineralytor begränsar tillgängligheten för biogeokemiska reaktioner av Hg som mobiliserats i miljön via naturliga och antropogena processer. Kunskap om betydelsen av speciationen av Hg i fasta och adsorberade faser för bildning, avgång och bioackumulering av MeHg är dock bristfällig. Denna information är kritisk för att förstå vilka processer som kontrollerar bildning och bioackumulering av MeHg samt för att kunna prediktera hur olika ekosystem kan förväntas svara på exempelvis ändrad deposition av atmosfäriskt Hg eller hur klimatförändringar kan påverka koncentrationerna av Hg i fisk. I denna avhandling har en experimentell metod utvecklades, där isotopanrikade fasta och adsorberade kemiska former av oorganiska tvåvärt Hg, Hg II används som s.k. "tracers". Denna metod användes för att bestämma MeHg bildningshasigheter i homogeniserade sediment prover samt i mesokosmsystem där förhållandena efterliknar de som förväntas i naturliga ekosystem. Från dessa drar vi slutsatsen att speciationen av HgII i fast/adsorberad fas är en viktig kontrollerande faktor som begränsar nettobildningen av MeHg. Mikrokosmexperiment visade att i första hand nyligt bildad MeHg avgick till gasfas vilket understryker betydelsen av MeHg bildningshastighet, snarare än koncentration, i sedimentet för denna process. Från mesokosmexperimenten visar vi, med kvantitativa data, att terrestra och atmosfäriska källor av HgII och MeHg är mer tillgängliga för bildning och bioackumulering av MeHg än HgII och MeHg lagrat eller bildat i sedimenten. Orsaken till detta är framförallt skillnad i speciationen av Hg i fasta/adsorberade faser. Detta innebär att bidraget från MeHg från terrestra och atmosfäriska källor till koncentrationen av Hg i fisk kan ha underskattats, samt att de negativa effekterna på MeHg exponering i områden där exempelvis klimat-förändringar förväntas leda till ökad terrest avrinning kan bli mer allvarliga än vad som tidigare predikterats. Data som presenteras i denna avhandling möjliggör modellering av Hg’s biogeokemiska cykel på en ny detaljnivå samt möjliggör säkrare prediktioner av hur olika ekosystem kan förväntas svara mot miljöförändringar eller ändrad deposition av atmosfäriskt Hg. / <p>Till Finansiärer skall också följande läggas till: Kempe stiftelsen (SMK-2942, SMK-2745, JCK-2413).</p>

No description available.