Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2008. / Härtill 6 uppsatser.

O objetivo do presente trabalho foi avaliar o desempenho de um reator de leito fixo e fluxo ascendente (RLFFA) em escala de bancada submetido à baixa aeração e recirculação. O reator foi utilizado como um sistema de pós-tratamento do efluente de indústria de fabricação de ração animal (INCOFAP) a partir de resíduos de abatedouro de aves, caracterizado por elevada carga de nitrogênio amoniacal. Para tanto, o RLFFA foi avaliado quanto à remoção da fração remanescente de matéria orgânica e de nitrogênio do efluente do reator UASB instalado na indústria. O RLFFA foi operado em condições mesofílicas (30°C) e tinha volume total de 11,5 L e volume útil de 6,1 L, com leito estruturado composto por 13 estruturas cilíndricas (3 cm de diâmetro) de espuma de poliuretano, dispostas verticalmente no interior do reator. O reator apresentou sistema de recirculação interna, com razão de recirculação igual a 3, suficiente para garantir a mistura completa. O sistema foi operado em três condições distintas, que foram denominadas de fases, todas com tempo de detenção hidráulica (TDH) de 24 horas e concentração de oxigênio dissolvido próxima a 1,0 mg.L-1. Nas fases 1 e 2, o RLFFA foi alimentado com 20% de efluente do UASB diluídos em água, e a alimentação da Fase 3 foi com 10% de efluente. As relações DQO/N para as Fases de 1 a 3 foram de, respectivamente, 0,28, 0,41 e 0,26. Na Fase 1, a alcalinidade foi mantida em concentração estequiométrica para a ocorrência da nitrificação total, enquanto nas fases 2 e 3 a alcalinidade foi adicionada em excesso. As melhores eficiências de remoção de N-total e DQO foram obtidas na Fase 1, com respectivamente, 48 ± 24% e 63 ± 20%, atingindo remoção máxima de N-total de 79% e 92% para DQO. As análises estatísticas demonstraram independência entre a remoção de DQO e a remoção de N-total, e com demanda de doador de elétrons para desnitrificação heterotrófica via nitrato superior à DQO removida, indicando a ocorrência de vias complementares. A desnitrificação via nitrito e a desnitrificação autotrófica foram observadas nos ensaios cinéticos de desnitrificação via nitrito e teste de atividade para desnitrificação autotrófica utilizando sulfeto como doador de elétrons. A modelagem para qualidade da água do rio Chibarro( local de lançamento do efluente da empresa INCOFAP) utilizando uma modificação do modelo de Streeter-Phelps, indicou que o cenário com a adoção do reator estudado no presente trabalho para tratamento do efluente da INCOFAP permitiu reduzir o impacto para a qualidade da água do rio Chibarro ao se comparar ao sistema atual de tratamento do efluente da empresa INCOFAP. Entretando, ainda faz-se necessária a elevação da eficiência de remoção de N-total no sistema, para atingir a concentração máxima de N-amoniacal permitida de 20 mg.L-1 para o efluente para compatibilização com a capacidade de autodepuração do rio Chibarro. / The objective of this study was to evaluate the performance of a bench scale up-flow fixedbed reactor (UFBR) subjected to low aeration and effluent recirculation.The reactor was used as a post-treatment system of effluent from animal food plant (INCOFAP) using poultry slaughterhouse wastes, characterized by high ammoniacal nitrogen load rate.Therefore, the UFBR was evaluated in respect to residual organic matter and nitrogen removal of industrys UASB reactor effluent. The UFBR was operated in mesophilic conditions (30°C) and it had a total volume of 11.5 L and a working volume of 6.1 L, with a structured bed composed by 13 polyurethane foam vertical cylindrical structures (3 cm of diameter) inside the reactor. The reactor was provided with internal recirculation system with recirculation ratio of 3, suficiente to guarantee a complete mixture. The system was operated in three different phases, with hydraulic retention time (HRT)of 24 hours and dissolved oxygen concentration close to 1.0 mg.L-1.On Phases 1 and 2, the UFBR was fed with 20% of UASB effluent diluted in water,and the Phase 3 was fed with 10% of effluent. On phases 1 to 3 COD/N ratios were, respectively, 0.28, 0.41 and 0.26. The alkalinity on Phase 1 was maintained on stoichiometric concentration to total nitrification, while in phases 2 and 3 excess alkalinity was added. The best total nitrogen and COD removal efficiencies were obtained in Phase 1, with respectively, 48 ± 24% and 63 ± 20% , reaching maximum total nitrogen removal of 79% and 92% for COD. Statistical analysis demonstrated independency between COD and total nitrogen removal, and with higher electron donor demand for nitrate denitrification than COD removal, indicating the occurrence of complementary paths. The nitrite denitrification and autotrophic denitrification were noted in kinetics experiments and activity tests for autotrophic denitrification using sulfide as source of electron donors. The modeling for Chibarro river water quality (site of INCOFAPs effluent release) , using a modified Streeter-Phelps model, indicated the scenario with the adoption of the studied reactor on this work for INCOFAP's effluent treatment provided the reduction of the impact on Chibarros water quality in comparison with the current effluent treatment of INCOFAP. However, it is still necessary an increase on system denitrification efficiency to reach the maximum ammoniacal nitrogen concentration allowed of 20 mg.L-1 for the effluent to make compatible with de selfpurification of Chibarro river.

Im Einzugsgebiet der Fassung A des Wasserwerks Thülsfelde wurden in langjährigen Beobachtungen Nitratgehalte an einzelnen Lokationen von bis zu 300 mg/L im oberflächennahen Grundwasser gemessen. Dennoch ist die betrachtete Fassung A des 27 km2 großen Einzugsgebietes weitgehend nitratfrei. In der vorliegenden Arbeit wurde untersucht, welche Prozesse im Untersuchungsgebiet wirken, wie die hierfür in Frage kommenden Abbauprozesse und das für die Prozesse notwendige reaktive Material verteilt sind. Es ist bekannt, dass mikrobielle Reduktionsprozesse die effektivsten Nitratsenken sind. Diese Prozesse benötigen geeignete Reaktionspartner, die im Untergrund auch vorhanden sind, z.B. organischer Kohlenstoff oder Disulfidschwefel. In der vorliegenden Arbeit wurden folgende Teilaufgaben bearbeitet: • Identifikation reaktiver Zonen • Identifikation der Umsetzungsprozesse • Identifikation ihrer räumlichen Lage • Identifikation der Verteilung reaktiven Materials • Aufbau eines Prognosewerkzeuges. Mit den Ergebnissen der Untersuchungen (Gesamtschwefelgehalt, Gesamtkohlenstoffgehalt) an Gesteinsmaterial aus 13 Rammkernsondierungen bis in eine Tiefe von 19 m uGOK sowie einer Bohrung bis in eine Tiefe von 40 m uGOK, konnte im Grundwasserleiter eine vertikale Zonierung des reaktiven Materials abgebildet werden. Bis in eine Tiefe von 20 m uGOK sind nur geringe Gehalte reaktiven Materials gefunden worden (gemessen als Schwefelgesamtgehalte: kleiner 100 [mg/kg]). Erst darunter wurden bis 26 m uGOK Schwefelgesamtgehalte zwischen 100 und 1000 [mg/kg] und in Tiefen bis zu 36 m uGOK bis zu 6400 [mg/kg] Gesamtschwefel gefunden. Die Auswertung der Beschaffenheitsdaten an Vorfeldmessstellen und an der für diese Arbeit projektierten Mehrstufenmessstelle SGM (7 Beprobungshorizonte, bis in 35,6 m uGOK) zeigten, dass genau in den Tiefenbereichen mit ansteigenden Gehalten reaktiven Materials die Redoxgrenze verläuft. Unterhalb von 25 m uGOK ist das Grundwasser praktisch nitratfrei. Untersuchungen zum Grundwasseralter ergaben für den Bereich der Redoxgrenze ein Alter zwischen 15 und 25 Jahren. Dies konnte als Hinweis darauf gedeutet werden, zusammen mit den beschriebenen Erkenntnissen zur Zonierung des reaktiven Materials und der Nitratkonzentrationen in diesem Bereich, dass der Grund für die praktische Nitratfreiheit unterhalb von 20 bis 25 m uGOK Umsatzprozesse im Grundwasserleiter sind. Die durchgeführten Batch-und Säulenversuche zum Abbau von Nitrat an Material aus dem Grundwasserleiter zeigten in ihren Ergebnissen ebenfalls eine vertikale Zonierung über die Tiefe. Mit zunehmender Tiefe wurde eine höhere Abbauleistung (bezogen auf die Ausgangsmassenkonzentrationen von Nitrat in den Versuchsgefäßen) erreicht. Im oberen Grundwasserleiter wurden bis zu 50 % Abbauleistung erreicht, nur in den tiefen Zonen wurden mehr als 50 bis zu 100 % Abbauleistung erreicht. In den Versuchen mit Material aus dem oberen Grundwasserleiter konnten keine vollständigen ablaufenden Reaktionen beobachtet werden. Für die Berechnung des Nitrattransportes wurde ein Grundwasserströmungs- und Transportmodell aufgebaut. Verwendet wurde die Software Modflow und MT3d99. In das Transportmodul MT3d99 wurden für den Abbau von Nitrat aus Feldversuchen ermittelte Geschwindigkeitskonstanten eingebaut. Mit dem Prognosewerkzeug wurden Szenarien unterschiedlicher Nitrateinträge abgebildet. Es konnte gezeigt werden, dass steigende Nitratkonzentrationen im Grundwasserleiter abhängig vom Eintrag und von der reaktiven Kapazität eines Grundwasserleiters sind. Dabei wurde anhand von 3 unterschiedlichen Szenarien deutlich, dass das Vorhandensein z.B. von Disulfidschwefel im Untergrund nur eine Scheinsicherheit darstellt. Der Reaktionspartner wird bei dem mikrobiellen Umsatz aufgebraucht. Es kann innerhalb weniger Jahre zum Ansteigen der Nitratkonzentrationen und zum Nitratdurchbruch kommen. Das aufgebaute Modell ist in der Lage unterschiedliche Szenarien für den Nitrateintrag, z.B. bei Landnutzungsänderungen, unter der Berücksichtigung der Verteilung reaktiven Materials, zu simulieren. Das Ergebnis des Rechenmodells sind Spannweiten von Nitratkonzentrationen für das System Grundwasserleiter. Für die Fassung A bleiben noch Fragen offen: • Wie ist die Verteilung reaktiven Materials im tiefen Grundwasserleiter? • Welche Massen reaktiven Materials sind verfügbar, nicht nur stöchiometrisch? • Wie sind die Reaktionen im tiefen Grundwasserleiter verteilt? • Welche Abbausequenzen existieren im tiefen Grundwasserleiter? (Anlage Rohdaten auf CD-Rom in Printversion 226 MB)

It has been illegal to deposit household waste in Swedish landfills since 2005. The large amount of waste deposited prior to this does however continue to pose an environmental concern, mainly in the form of leachate water. This study focused on enhancing the denitrification process in a leachate water treatment plant through bioaugmentation. The two strains Brachymonas denitrificans and Comamonas denitrificans as well a commercial seed mix from ClearBlu Environmental® (CBE-mix) containing amongst others, Pseudomonas putida AD 21 and Pseudomonas fluorescens, were investigated as candidates. Nitrite, nitrate, and ammonium concentrations were measured in laboratory-, and pilot-scale studies to follow the processes of nitrification and denitrification. The pilot study was conducted for 10 days in the middle of May 2020 with leachate from the treatment plant in an aerated and nonaerated setup in open field conditions. C. denitrificans and B. denitrificans were both shown to be able to adapt to growth in landfill leachate. The addition of these strains led to a higher rate of nitrate reduction compared to the control during the first days of the pilot experiment but showed no difference in the total amount of nitrate reduced. The combined nitrogen concentration of ammonium, nitrate, and nitrite was 6.7% lower than the control when using a culture augmented with the CBE-mix in the aerated setup. This could indicate aerated denitrification. The amount of nitrate reduced during the pilot experiment was increased with 32% when augmenting the community with the CBE-mix in a nonaerated setup. An explanation could be that certain strains in the mix were able to utilize hard to degrade organic carbon present in the leachate or that the mix had a higher ratio of reduced nitrate to consumed organic carbon than the indigenous community. / Det har varit olagligt att deponera hushållsavfall i Sverige sedan 2005, den stora mängd avfall som deponerats innan dess fortsätter dock att utgöra ett miljöproblem, främst genom genereringen av lakvatten. Den här studien fokuserade på möjligheten att förbättra denitrifikationen i ett reningsverk för lakvatten genom bioaugmentation. Två stammar tillhörande Brachymonas denitrificans, och Comamonas denitrificans, samt en kommersiell bakterieblandning från ClearBlu Environmental® innehållande bland andra Pseudomonas putida AD 21 och Psedomonas flourescens, undersöktes som möjliga kandidater. Ammonium-, nitrat- och nitritkoncentrationer mättes i odlingsstudier i labbskala och i en pilotstudie för att undersöka nitrifikation och denitrification. Pilotstudien utfördes i en luftad och en o luftad konfiguration utomhus i mitten av maj 2020, med lakvatten från reningsverket under en 10 dagars period. C. denitrificans och B. denitrificans klarade båda av att anpassa sig till tillväxt i lakvatten. Tillsats av dessa arter ledde till en ökning i nitratreduktionshastighet i början av pilotexperimentet men gav ingen total minskning av nitratmängden. Den sammanlagda slutkoncentrationen av ammonium-, nitrat- och nitritkväve var 6,7% lägre än i kontrollen när en kultur argumenterad med den kommersiella bakteriemixen användes i den luftade konfigurationen. Mängden reducerat nitrat ökade med 32% när en kultur augmenterad med den kommersiella mixen användes i den oluftade konfigurationen. En möjlig förklaring är att vissa stammar i mixen klarade av att tillgodogöra sig svårnedbrytbara kolföreningar i lakvattnet eller att ration mellan reducerat nitrat mot konsumerat organiskt kol var högre än i det ursprungliga microbsamhället.

A pilot scale nitrogen (N) removal system was constructed and operated for approximately 365 days and was designed to remove inorganic total ammonia nitrogen (TAN) from solids-separated dairy manure. An anaerobic fermenter, upstream of the N removal reactor, produced volatile fatty acids (VFAs), to be used as an electron donor to fuel denitrification, and TAN at a COD:N ratio of 18:1. However, sufficient amounts of non-VFA COD was produced by the fermenter to fuel the denitrification reaction at an average NO3- removal rate of 5.3 ± 2 mg/L NO₃--N. Total ammonia N was removed from the fermenter effluent in an N removal reactor where a series of aerobic and anoxic zones facilitated aerobic TAN oxidation and anoxic NO₃- and NO₂- reduction. The minimum dissolved oxygen (DO) concentration allowing for complete TAN removal was found to be 0.8 mg/L. However, TAN removal rates were less than predicted using default nitrifying kinetic parameters in BioWin®, a biological modeling simulator, which indicated the presence of a nitrification inhibitor in fermented dairy manure. Furthermore, an N balance during the aerobic zone indicated that simultaneous nitrification-denitrification (SND) was occurring in the aerobic zone of the N removal reactor and was most apparent at DO concentrations below 1.3 mg/L. A series of nitrite generation rate (NGR) experiments confirmed the presence of an inhibitor in fermented dairy manure. A model sensitivity analysis determined that the most sensitive ammonia oxidizing bacteria (AOB) kinetic parameters were the maximum specific growth rate, , and the substrate half saturation coefficient, . Nitrifying inhibition terms of competitive, non-competitive, mixed competitive, and un-competitive were applied to the growth rate equation in BioWin® but an accurate representation of the observed TAN removal rates in the pilot scale system could not be found by adjusting the kinetic parameters alone. Reducing the default BioWin® hydrolysis rate by approximately 50% produced a more accurate calibration for all inhibition terms tested indicating that the hydrolyization of organic N in dairy manure is less than typical municipal waste water. / Master of Science

Master of Science / Department of Agronomy / Charles W. Rice / Agricultural lands receiving N inputs are considered the primary source of N2O, a potent greenhouse gas. N fertilizer management has shown variable effects on both N2O losses and corn grain yield. The objectives of this study were to assess the impact of N source and placement on N2O emissions, fertilizer-induced emission factor (FIEF), corn grain yield, yield-scaled N2O emissions (YSNE) and N fertilizer recovery efficiency (NFRE). The experiment was conducted from 2013 through 2014 at the Agronomy North Farm located at Kansas State University, Manhattan, KS. The soil was a moderately well-drained Kennebec silt loam. The treatments were broadcast urea (BC-Urea), broadcast urea ammonium nitrate (UAN) (BC-UAN), broadcast coated urea (BC-CU), surface-band UAN (SB-UAN), subsurface-band UAN (SSB-UAN), subsurface-band UAN + nitrification inhibitor (SSB-UAN+I) and a 0 N control. In 2013, SSB- UAN emitted significantly more N2O (2.4 kg N2O-N ha-1), whereas control (0.3 kg ha-1) and BC- UAN (0.6 kg ha-1) emitted the least. In 2014, most treatments emitted between 3.3 and 2.5 kg N2O-N ha-1. Only SSB-UAN+I (1.03 kg ha-1) and control (0.26 kg ha-1) were significantly lower. The use of a nitrification inhibitor decreased N2O emissions by 62% and 55% in 2013 and 2014, respectively. BC treatments had cumulative emissions significantly higher in 2014 compared to 2013. Only SSB-UAN+I had a significantly lower FIEF (0.4%), and 2013 FIEF (0.68%) was significantly lower than that of 2014 (1.38%). In 2013, banded treatments had significantly higher grain yields (from 9.1 to 10.5 Mg ha-1), whereas in 2014 fewer differences among N treatments were observed, ranging from 7.2 to 8.6 Mg ha-1. Banded treatments had significantly lower grain yields in 2014 compared to 2013. Only BC-UAN and SSB-UAN+I had significantly lower YSNE, and 2013 had lower YSNE than 2014. In 2013, SSB-UAN had the greatest NFRE, whereas BC treatments had the lowest. In 2014, N treatments did not differ in NFRE. SSB-UAN and SSB-UAN+I had significantly lower NFRE values in 2014 compared to 2013. Fertilizer source and placement have the potential to mitigate N2O emissions and promote high yields and NFRE in corn, however, the response is dependent on the rainfall pattern after fertilizer application. The option of banding UAN without any additive promoted higher N2O losses on a year when precipitation was well distributed, but also enhanced grain yield and NFRE. On the other hand, under the same precipitation conditions, broadcasting N fertilizer promoted lower N2O losses, grain yield and NFRE, but those were all improved in a wet year. Therefore, the subsurface band placement would be the best option under a normal year, whereas broadcasting fertilizer would be the best option under a wetter year. Further, the use of NI with subsurface band UAN provides the most sustainable option, since the NI decreased N2O losses compared to UAN alone in both years. Further research should evaluate N source and placement combinations under different environments in order to better understand how they impact crop performance and the negative environmental aspects of N fertilization. It is important to test those treatments under different precipitation scenarios and look for trends that indicate the best N management option at the local level.

Thesis (M.Tech.: Biotechnology)-Dept. of Biotechnogy, Durban Institute of Technology, 2005 xvi, 85 leaves : ill. ; 31 cm / Atmospheric nitrogen pollution is on the increase and human activities are directly or indirectly responsible for the generation of the various nitrogen polluting compounds. This can lead to the two major problems of eutrophication and groundwater pollution. Therefore, the removal of nutrients such as nitrogen and phosphorus from wastewater is important. Nitrogen removal from wastewater is achieved by a combination of nitrification and denitrification. Thus, there is a need to identify and characterise heterotrophic denitrifying bacteria involved in denitrification in wastewater treatment systems. The aim of this study, therefore, was to characterise heterotrophic denitrifying bacteria through detailed biochemical and molecular analysis, to facilitate the understanding of their functional role in wastewater treatment systems. Drysdale (2001) isolated heterotrophic denitrifiers to obtain a culture collection of 179 isolates. This culture collection was used to screen for nitrate and nitrite reduction using the colorimetric biochemical nitrate reduction test. The isolates were thereafter Gram stained to assess their gram reaction, cellular and colonial morphology. Based on these results identical isolates were discarded and a culture collection of approximately 129 isolates remained. The genetic diversity of the culture collection was investigated by the analysis of polymerase chain reaction (PCR)-amplified 16S ribosomal DNA (rDNA) fragments on polyacrylamide gels using denaturing gradient gel electrophoresis (DGGE). Thus DNA fragments of the same length but different nucleotide sequences were effectively separated and microbial community profiles of eight predominant isolates were created. Batch experiments were conducted on these eight isolates, the results of which ultimately confirmed their characterisation and placed them into their four functional groups i.e. 3 isolates were incomplete denitrifiers, 2 isolates were true denitrifiers, 2 isolates were sequential denitrifiers and 1 isolate was an exclusive nitrite reducer.

<p>This study was made as a part of a feasibility study on a polishing wetland at Rimbo wastewater plant (wwp) in Norrtälje municipality. The wwp had to decrease the nitrogen discharge to reach the limit 15 mg tot-N/l. The nitrogen in the outlet was mainly in the form of nitrate, hence the wetland mainly ought to support denitrification. The proposed area for the wetland was situated right next to the wwp and was already in the municipalitys posession. One aim of this study was to examine what spieces of plants needed to achieve highest possible denitrification. Some different plant spieces for providing a good and interesting environment for birds and people were also proposed. Furthermore a massbalance model was developed for studying the important exchange processes in a wetland, to study the impact of an uneven streambed on the hyporheic water exchange and for trying to predict the wetlands nitrogen removal capacity. Proposed plants to support denitrification was different reeds such as Common reed (Phragmites australis), Bulrush (Typha), Reed Sweet-grass (Glyceria maxima) och Reed Canry-grass (Phalaris Arundinacea). Common reed is a durable species who can survive in deeper water up to 2 metres while the others need a shallower water about 0,5 m of depth. For the good of the birdlife, different spieces of Sedges (Carex) were chosen due to their ability to produce large amounts of nutrient rich seeds. Measurment in sediment cores from Ekeby wetland in Eskilstuna gave a potential denitrification capacity of 3,31 mg NO3-N m^-3 _sed s^-1. The denitrification capacity was then used in a massbalance model were the theory of advective pumping in an uneven bedsurface also was implemented. Evaluation of the model results showed that an uneven bedsurface did not contribute to an increased nitrogen removal from the wetland, possibly due to a far too low advection and flow of the water. This was also a reason to why the distribution between denitrification from the water- and plant community vs the sediment was unbalanced. The model results showed that less than 1 % of the reduced nitrogen came from the sediment part, in contrast to current knowledge that says about 50%. The model and the participating exchange processes need to be further evaluated before the models prediction of nitrogen removal can be used in design of a wetland. Calculations and comparisons with other wetlands showed that with a well estimated, grown up and maintained wetland, there should be no problems in achieving the goal of nitrogen removal in Rimbo wetland. Such a wetland should also provide a good habitat for birds and animals and also be a good recreationarea for people to visit, properties that were appreciated as important effects in other wetlands studied in this work.</p> / <p>Detta arbete gjordes som en del av en förstudie för anläggande av en efterpolerande våtmark till reningsverket i Rimbo, Norrtälje kommun. Reningsverket behövde sänka sitt utsläpp av kväve till riktvärdet 15 mg tot-N/l. Huvuddelen av kvävet i utloppsvattnet förelåg i nitratform, varför denitrifikationen borde förstärkas genom att anlägga en våtmark. Det tilltänkta området för våtmarken ligger i anslutning till reningsverket och ägs idag av kommunen. I detta arbete undersöktes vilken växtlighet i våtmarken som var lämpligast för syftet att få en så bra denitrifikation som möjligt. Även olika växtarter för att ge en intressant miljö för fåglar och människor togs fram. Dessutom utvecklades en massbalansmodell som användes för att studera de utbytesprocesser som är viktiga i en våtmark, frågan hur en ojämn bottenmorfometri påverkar det hyporheiska vattenutbytet samt om det går att förutsäga reningskapaciteten i Rimbo våtmark. Lämpliga växter för denitrifikationen ansågs vara vassbildande växter, och då främst främst bladvass (Phragmites australis), men även kaveldun (Typha), jättegröe (Glyceria maxima) och rörflen (Phalaris Arundinacea). Bladvass är en mycket tålig växt som klarar stort vattendjup, medan de andra vassorterna behöver en grundare våtmark på ca 0,5 m. För fågellivets bästa ansågs starrväxter (Carex) vara viktiga arter då de producerar stora mängder frön. Mätning av denitrifikationspotentialen i sediment från Ekeby våtmark gav en hastighet för denitrifikationen i sedimentet på 3,31 mg NO3-N m^-3 _sed s^-1. Denitrifikationen från sediment användes sedan i en massbalansmodell där även även teorin om advektivt pumputbyte vid ojämn bottenform implementerades. En utvärdering av modellresultaten kunde avgöra att en ojämn eller vågig bottenmorfometri inte skulle förbättra reningen i våtmarken. Detta beroende på bland annat för låg advektionshastighet och flöde. Detta låga flöde ned i sedimentet bidrog även till att fördelningen av kväveborttag från sediment respektive vatten- och växtdelen blev snedfördelad. Enligt modellen var det mindre än 1% av kvävet som togs bort från sedimentet medan all vetenskap tyder på närmare 50%. Modellen och de ingående utbytesprocesserna bör utvärderas och utvecklas ytterligare innan den kan användas som verktyg för att beräkna kvävereningen från en våtmark. Beräkningar och jämförelser med andra våtmarker visade dock att en väl beväxt, utförd och beskickad våtmark inte skulle ha några problem att sänka nitrathalten till riktvärdet. En våtmark skulle även utgöra en bra uppehållsmiljö för fåglar, djur och människor vilket anses som viktiga mervärden i våtmarker på andra platser i Sverige.</p>

Our understanding of the global marine xed nitrogen budget has undergone rapid growth, and as a result there is debate as to whether or not it is balanced. The Arctic plays a disproportionately large role in the sink terms of this budget. This paper works to understand the role of the Canada Basin in the nitrogen cycle. We utilize two tracers of denitri cation: N2/Ar, a dissolved gas tracer, and N*, a nutrient ratio tracer. We aim to quantify the current state of nitrogen cycling in the Canada Basin, and determine its role in the global cycle. Our paired tracer method provides support for shelf denitri cation rates while providing an estimate of ventilation in the same water mass, and provides an estimate for deep benthic denitri cation rates. We observe a disconnect between N2/Ar and N* in the Paci c Upper Halocline Layer (PUHL), wherein the excess N2/Ar we expect from N* is nearly 250% larger than the excess we observe. Our calculations suggest that an approximate steady state between benthic denitri cation and gas exchange on the Chukchi shelf maintains this disconnect. Our measurements of the PUHL support the shelf denitri cation rates reported from direct measurements, and can predict wind speeds required for ventilation within a factor of two. A 1D diffusion model of the old deep waters of the Canada Basin supports benthic denitri cation rates of 0.095-0.15 Tg N y-1. Benthic denitri cation rates determined from the model are on the low end of rates in other deep basins. Our results suggest additional measurements of these tracers in the Canada Basin and surrounding areas would help to constrain both the physical and biological processes controlling nitrogen cycling. / Graduate / 0425 / jen.l.reeve@gmail.com

La rivière Essonne est influencée quantitativement et qualitativement par la nappe de Beauce. L'eau de cette nappe possède des concentrations en nitrates élevées et qui continuent d'augmenter, représentant ainsi une menace croissante pour la qualité du cours d'eau. Des cressonnières (zones humides artificielles où le cresson de fontaine [Nasturtium officinale R. Br.] est cultivé) étaient autrefois très nombreuses entre ces deux masses d'eau, mais sont aujourd'hui massivement abandonnées. Or, ces zones humides jouent potentiellement un rôle épurateur vis-à-vis des nitrates, et pourraient contribuer au bon état du cours d'eau en limitant les transferts de ces nutriments (zones tampons) de la nappe vers la rivière. Ce travail a donc pour objectif d'étudier l'élimination des nitrates dans les cressonnières, mais également l'évolution de ces zones humides après l'abandon de la culture du cresson, et ses conséquences sur l'épuration. Pour cela, nous nous sommes basés sur l'étude d'un site expérimental (Maisse, 91, France) comprenant plusieurs stades d'abandon et sur des expérimentations en laboratoire (bioréacteurs). Les successions de macrophytes après l'abandon de la culture ont été étudiées sur le site expérimental et dans 14 autres sites de la vallée de l'Essonne. Après l'abandon de la culture, le cresson ne se maintient pas dans les fosses. On observe alors une évolution progressive vers un milieu terrestre, avec la colonisation successive par des hydrophytes pionnières ou invasives (Lemna minuta Kunth.), puis par des hélophytes pionnières (Epilobium hirsutum L., Typha latifolia L., Phragmites australis (Cav.) Steud.). Enfin, il s'établit une roselière avec l'apparition d'espèces arbustives et ligneuses (Salix sp), qui s'accompagne d'un comblement des fosses et qui semble constituer une transition vers une forêt alluviale. Au cours du passage de l'eau dans les fosses du site expérimental, une partie des nitrates a été éliminée. Les fosses cultivées ont été les plus efficaces avec un taux moyen de 1770 mg NO3-/m²/jour au cours des trois années de suivi. En comparaison, les fosses abandonnées ont montré des taux d'élimination largement inférieurs allant de 550 à 750 mg NO3-/m²/jour. Toutefois, ces taux n'ont permis qu'une faible diminution des concentrations (approximativement 44 mg/L en entrée à 42 mg/L en sortie) à cause de temps de séjour trop courts de l'eau dans les fosses. Les taux d'élimination des nitrates ont varié de façon saisonnière, avec un maximum en été et un minimum en hiver. L'ampleur des variations saisonnières a cependant été beaucoup plus forte dans les fosses cultivées que dans les fosses abandonnées. L'estimation des prélèvements par les macrophytes a montré que la dénitrification est la voie majoritaire de l'élimination des nitrates (70 à 85% de l'élimination totale). Des mesures de dénitrification potentielle en bioréacteurs ont montré que ce processus était limité par la disponibilité du carbone organique. Or, le cresson des fosses cultivées représente une source de carbone très disponible, par rapport aux hélophytes (Phragmites australis) qui dominent les cressonnières abandonnées. L'effet des cressonnières sur les concentrations en nitrates de la rivière Essonne est actuellement limité, mais peut être amélioré par la gestion des sources de carbone et des temps de séjour de l'eau dans ces zones humides. / River Essonne is quantitatively and qualitatively influenced by groundwater. Nitrate concentrations of this groundwater are high and are still increasing, threatening the quality of the watercourse. In the past, watercress farms (artificial wetlands where watercress [Nasturtium officinale R. Br.] is cultivated) were numerous between this groundwater and the river, but they are nowadays massively abandoned. These wetlands potentially play the role of buffer zones, and could contribute to maintain the quality of surface water with respect to nitrate. This study aims to assess nitrate mitigation in watercress farms, but also the changes occurring in these wetlands after watercress cropping has been abandoned and their consequences on nitrate removal. This work is based upon the study of an experimental site (Maisse, France) including several stages of abandon, and on laboratory experiments (bioreactors). Macrophytes succession after the abandonment of watercress farms has been assessed at the experimental site and in 14 other abandoned sites of the Essonne valley. After the abandonment of the crop, watercress do not maintain in the beds. The wetlands progressively evolve towards a terrestrial ecosystem, being successively colonized by pioneer or invasives hydrophytes (Lemna minuta Kunth.) and by pioneer helophytes (Epilobium hirsutum L., Typha latifolia L., Phragmites australis (Cav.) Steud.). To finish with, the vegetation consists in reed beds, with the appearance of shrubby and woody species (Salix sp) which seems to indicate an evolution towards an alluvial forest. Nitrates were partially removed from the water between the inflow and the outflow of our experimental site. Cultivated beds were the most efficient with a mean removal rate of 1770 mg NO3-/m²/day during this 3-years survey. In comparison, abandoned beds exhibited lower removal rates ranging from 550 to 750 mg/m²/day. In spite of these rates, the effects on nitrate concentrations in water were limited (approximately 44 mg/L at the inflow and 42 mg/L at the outflow), because the residence times were short. Nitrate removal rates varied seasonally, and were highest in summer and lowest in winter. The amplitude of these variations was higher in cultivated beds than in abandoned beds. The estimate of nitrate uptake by macrophytes revealed that denitrification could account for 70 to 85% of nitrate removal. Measurement of potential denitrification in bioreactors showed that organic carbon availability limited denitrification in watercress farm sediments. Watercress is a readily available source of carbon, in contrast with helophytes which dominate abandoned beds such as Phragmites australis.The effects of nitrate mitigation in watercress farms on nitrate concentrations in the river Essonne are very limited, but can be improved with the management of carbon sources and hydraulic residence time in these wetlands.