The isotopic composition of water in the atmosphere is influenced by how the water evaporated, how it was transported, and how it formed in the cloud before falling. Because these processes are temperature dependent, the isotopic ratios stored in glacial ice and other proxy sources have been used as an indicator of pre-instrumental climate. There is uncertainty, however, as to whether isotopic ratios should be interpreted as a proxy of local temperature, or as a broader indicator of changes in how the vapor was transported. To better understand these processes, the NASA GISS general circulation model (GCM) was used to examine two different types of controls on the isotopic composition of moisture. The first control was the large-scale circulation of the atmosphere. Over Europe, it was found that δ18O is strongly controlled by a Northern Annular Mode-like pattern, detected in both the GCM and for Europe’s high-quality precipitation δ18O data. Over the southwest Yukon, it was found that higher δ18O was associated with moisture transport from the south, which led to a re-interpretation of the large mid-19th century δ18O shift seen in the ice cores from Mt. Logan. The second type of control was microphysical, relating to the way precipitation interacts with vapor after it has formed. Using a GCM sensitivity experiment, the effects of ‘post-condensation exchange’ were found to depend primarily on the proportion between the amount of upstream precipitation that fell as rain and the amount that fell as snow, and at low latitudes, on the strength of atmospheric moisture recycling. This led to a partitioning of the well-observed correlation between temperature and precipitation δ18O into its initial and post-condensation components, and a GCM-based interpretation of satellite measurements of the isotopic composition of water vapor in the troposphere.

The isotopic composition of water in the atmosphere is influenced by how the water evaporated, how it was transported, and how it formed in the cloud before falling. Because these processes are temperature dependent, the isotopic ratios stored in glacial ice and other proxy sources have been used as an indicator of pre-instrumental climate. There is uncertainty, however, as to whether isotopic ratios should be interpreted as a proxy of local temperature, or as a broader indicator of changes in how the vapor was transported. To better understand these processes, the NASA GISS general circulation model (GCM) was used to examine two different types of controls on the isotopic composition of moisture. The first control was the large-scale circulation of the atmosphere. Over Europe, it was found that δ18O is strongly controlled by a Northern Annular Mode-like pattern, detected in both the GCM and for Europe’s high-quality precipitation δ18O data. Over the southwest Yukon, it was found that higher δ18O was associated with moisture transport from the south, which led to a re-interpretation of the large mid-19th century δ18O shift seen in the ice cores from Mt. Logan. The second type of control was microphysical, relating to the way precipitation interacts with vapor after it has formed. Using a GCM sensitivity experiment, the effects of ‘post-condensation exchange’ were found to depend primarily on the proportion between the amount of upstream precipitation that fell as rain and the amount that fell as snow, and at low latitudes, on the strength of atmospheric moisture recycling. This led to a partitioning of the well-observed correlation between temperature and precipitation δ18O into its initial and post-condensation components, and a GCM-based interpretation of satellite measurements of the isotopic composition of water vapor in the troposphere.

Freshwater ostracods (crustacea, ostracoda) are sensitive to environmental conditions, and are widely used as biological indicators for past and present environmental changes. The abundance and diversity of ostracods from permafrost areas is currently documented in scattered records with incomplete ecological characterizations. The objectives of the thesis were to determine the taxonomic and ecological range of ostracod assemblages and their habitat conditions in polygon ponds in different landscape units of the Indigirka Lowland (north-east Siberia, Russia). A monitoring approach focused seasonal meteorological and limnological variability of a selected pond site, its ostracod population dynamics, and the geochemical properties of ostracod valve calcite. Shallow, well-oxygenated, and dilute ponds with slightly acidic to circumneutral pH hosted an abundant and diverse ostracod fauna. A total of 4849 identified ostracods from eight species and three taxa represent the first record of the ostracod fauna in the Indigirka Lowland. Fabaeformiscandona krochini and Fabaeformiscandona groenlandica were documented for the first time in continental Siberia. Fabaeformiscandona sp. I and Fabaeformiscandona sp. II were newly found taxa holding a strong indicative potential for hydrochemical parameters. Repeated sampling of a typical low-center polygon pond revealed detailed insights in the population dynamics of Fabaeformiscandona pedata and its reproduction strategy. Substrate properties, physical and hydrochemical conditions in the studied ponds offered largely homogeneous habitats across different landscape units and pond types to ostracods. River flooding and differences in morphology between pond types resulted in variations in sediment, vegetation, hydrochemical and stable water isotope composition of the ponds. Ponds in the river floodplain and intrapolygon ponds hosted the most diverse ostracod fauna while species diversity was lowest in thaw lakes. Air temperature and precipitation were identified as the main external drivers of water temperatures, water levels, ion concentrations, and stable water isotope composition in small periglacial waters on diurnal and seasonal scales. Ostracod valve calcite recorded seasonal variations in stable oxygen isotopes of the ambient waters, but needs to be interpreted carefully with regard to species-specific background knowledge. / POLYGON - Polygons in tundra wetlands: state and dynamics under climate variability in polar regions

Alluvial groundwater systems are an important source of water for communities and biodiverse riparian corridors throughout the arid and semi-arid Basin and Range Geological Province of western North America. These aquifers and their attendant desert streams have been depleted to support a growing population, while projected climate change could lead to more extreme episodes of drought and precipitation in the future. The only source of replenishment to these aquifers is recharge. This dissertation builds upon previous work to characterize and quantify recharge in arid and semi-arid basins by characterizing the intra-annual seasonality of recharge across the Basin and Range Province, and considering how climate change might impact recharge seasonality and volume, as well as fragile riparian corridors that depend on these hydrologic processes. First, the seasonality of recharge in a basin in the sparsely-studied southern extent of the Basin and Range Province is determined using stable water isotopes of seasonal precipitation and groundwater, and geochemical signatures of groundwater and surface water. In northwestern Mexico in the southern reaches of the Basin and Range, recharge is dominated by winter precipitation (69% ± 42%) and occurs primarily in the uplands. Second, isotopically-based estimates of seasonal recharge fractions in basins across the region are compared to identify patterns in recharge seasonality, and used to evaluate a simple water budget-based model for estimating recharge seasonality, the normalized seasonal wetness index (NSWI). Winter precipitation makes up the majority of annual recharge throughout the region, and North American Monsoon (NAM) precipitation has a disproportionately weak impact on recharge. The NSWI does well in estimating recharge seasonality for basins in the northern Basin and Range, but less so in basins that experience NAM precipitation. Third, the seasonal variation in riparian and non-riparian vegetation greenness, represented by the normalized difference vegetation index (NDVI), is characterized in several of the study basins and climatic and hydrologic controls are identified. Temperature was the most significant driver of vegetation greenness, but precipitation and recharge seasonality played a significant role in some basins at some elevations. Major contributions of this work include a better understanding of recharge in a monsoon-dominated basin, the characterization of recharge seasonality at a regional scale, evaluation of an estimation method for recharge seasonality, and an interpretation of the interaction of seasonal hydrologic processes, vegetation dynamics, and climate change.

Ce travail de thèse s’intéresse à deux zones de l’Atlantique Nord : la région subpolaire et la région subtropicale. Cette large couverture permet d’étudier le cycle de l’eau dans des régions hydrologiquement différentes, où des processus variés rentrent en jeu comme l’évaporation, la convection atmosphérique, la formation des précipitations, le cycle saisonnier de la glace de mer, les apports des rivières et des glaciers, et l’advection des masses d’eau et des masses d’air. Dans la région subtropicale, les variations des compositions isotopiques de la vapeur d’eau sont étudiées afin de comprendre le rôle de l’évaporation et du mélange avec la troposphère libre dans le contrôle de l’humidité et des compositions isotopiques à la surface des océans. Ces données innovantes recueillies in situ principalement au cours de l’été 2012 dans le gyre subtropical de l’Atlantique nord (campagne STRASSE) ont offert l’opportunité d’étudier les processus de fractionnement isotopique lors de l’évaporation océanique et le renouvellement de l’air de la couche limite atmosphérique. Aux plus hautes latitudes de l’océan Atlantique nord, la circulation de surface du gyre subpolaire permet le transfert d’eaux froides et dessalées en provenance de la région (sub)arctique vers l’intérieur du gyre. Dans le cadre de cette thèse, un jeu de données a été recueilli sur la période 2010-2014 et porte plus particulièrement sur la région du courant du Labrador et permet de se poser les questions suivantes : Comment le cycle de la glace de mer affecte la salinité de ces courants dessalés ? Comment évolue l’apport en eau météorique dans un contexte de fonte accélérée des glaciers continentaux ? / This thesis focuses on two regions of the North Atlantic: the subtropical gyre and the subpolar gyre. This large coverage allows an investigation of the water cycle in different hydrological regimes, where various processes take place such as sea ice seasonal cycle, rivers runoff, continental ice melt and advection of air and water masses. In the subtropical region, the variability of the isotopic composition of the water vapor is studied to understand the role of evaporation and mixing with free troposphere in humidity and isotopic compositions at the ocean surface. In particular, new data collected during summer 2012 (STRASSE cruise) gave the opportunity to explore kinetic fractionation processes during oceanic evaporation and air renewal in the atmospheric boundary layer. In the subpolar region, the surface circulation is cyclonic and transfers cold and fresh water from the arctic region to the interior of the subpolar gyre. For this thesis, data were collected between 2010 and 2014 from oceanographic cruises and commercial vessels to study the gyre interior and the main coastal currents carrying water from the arctic to lower latitudes. The study is mainly focused on the Labrador Current. There, isotopic measurements are used to identify the freshwater sources and to consider the following questions: How is the salinity of fresh currents affected by the sea ice formation and melting? How is the contribution of meteoric waters changing in a context of an acceleration of the melting of continental glaciers?

No description available.

Near-level Prairie landscapes have received limited attention in hydrological research. For this thesis, hydrometric measurements and four tracing experiments were completed at three “riparian-to-stream” sites in the Catfish Creek Watershed (southeastern Manitoba) to enhance Prairie hydrology understanding. First, hydrologic state variables were examined to infer vertical and lateral water movement. Second, tracer data were analyzed to evaluate the relative importance of surface versus subsurface water movement. Results show that hydrologic state variables can be useful for inferring riparian-to-stream water movement. Tracer data also revealed that subsurface water movement can contribute significantly to streamflow during snowmelt- and rainfall-triggered events in the study watershed. This thesis demonstrated that subsurface flow is a significant runoff generation mechanism in Prairie landscapes, thus challenging surface water-focused conceptualizations and management strategies that are traditionally used. The findings summarized in this thesis will be critical to improve the performance of hydrological models when applied to the Prairies. / February 2017

Climate change is causing larger wildfires and more extreme precipitation events throughout the world. As these ecological disturbances increasingly coincide, they are altering lateral fluxes of sediment, organic matter, and nutrients. Increased lateral flux of nutrients could exacerbate eutrophication and associated harmful algal blooms, and increased sediment and organic matter flux could degrade the water supply. Here, we report the immediate stream chemistry response of watersheds in central Utah (USA) that were affected by a megafire followed by an extreme precipitation event in 2018. The wildfires burned throughout the summer of 2018 until the remnants of Hurricane Rosa released torrential rain on the still smoldering, 610-km2 burn scar. To assess how these multiple stressors affected lateral material fluxes, we collected daily to hourly water samples at 10 stream locations starting immediately before the storm event until three weeks after it finished. We quantified suspended sediment, solute and nutrient concentrations, water isotopes, and the concentration, optical properties, and reactivity of dissolved organic matter. For all land-use types, the wildfire caused substantial increases in sediment concentration and flux, increasing total suspended sediment by over 20-fold, attributable to the loss of stabilizing vegetation and increased runoff. Unexpectedly, dissolved organic carbon (DOC) was 2.1-fold higher in burned watersheds, despite the decrease in plant and soil organic matter, and this DOC was 1.3-fold more biodegradable and 2.0-fold more photodegradable than in unburned watersheds based on 28-day light and dark incubations. However, nitrogen and phosphorus concentrations were higher in watersheds with high anthropogenic influences, regardless of burn status. Likewise, direct human land use had a greater effect than wildfire on runoff response, with rapid storm water signals in urban and agricultural areas and a slow arrival of storm water in unburned areas without direct human influence. These findings indicate how megafires and intense rainfall fundamentally increase short-term sediment flux and alter organic matter concentration and characteristics, confirming previous research. These fluxes of degradable dissolved and particulate organic matter could exert short-term pressure on ecosystems already fragmented by human infrastructure. However, in contrast with previous research, which overwhelming focuses on burned-unburned comparisons in pristine watersheds, we found that the presence of urban and agricultural activity exerted a much greater influence on nutrient status than the wildfire. This novel finding suggests that reducing nutrient fluxes from urban and agricultural areas could make ecosystems more resilient to megafire and extreme precipitation events. Together with reducing anthropogenic climate change to reduce the frequency and extent of large wildfires, improving nutrient management should be a priority in semi-arid regions such as Utah.

High latitude and altitude ecosystems are currently undergoing rapid and unprecedented warming in response to anthropogenically induced climate change. Subarctic, alpine regions are particularly vulnerable to increases in air temperature and changing precipitation regimes, which have caused cascading hydrological and ecological impacts. In addition to changing flow regimes, thawing permafrost, and declining glaciers, widespread changes in vegetation composition, density and distribution have been observed across northern regions. Specifically, treeline is advancing with increasing latitude and altitude and shrubs are increasing in height, extent, and density. Despite widespread documentation of this northern greening, few field-based studies have evaluated the hydrological implications of these changes. Quantification of total evapotranspiration (ET) across a range of vegetation gradients is essential for predicting water yield, yet challenging in cold alpine catchments due to heterogeneous land cover. Direct field-level measurements of transpiration (T) and evaporative partitioning across subarctic, alpine ecosystems and species are rare, yet essential to assess sensitivities and hydrological response to changing climate drivers. This thesis presents six years of surface energy balance components and ET dynamics and two years of sap flux measurements and critical zone stable water isotope sampling at three sites along an elevational gradient in a subarctic, alpine catchment near Whitehorse, Yukon Territory, Canada. These sites span a gradient of thermal and vegetation regimes, providing a space-for-time comparison for future ecosystem shifts: 1) a low-elevation boreal white spruce forest (~12-20 m), 2) a mid-elevation subalpine taiga comprised of tall, dense willow (Salix) and birch (Betula) shrubs (~1-3 m) and 3) a high-elevation subalpine taiga with short, sparse shrub cover (< 0.75 m) and moss, lichen, and bare rock. We utilize both mass flux measurements and stable water isotopes to evaluate the timing, magnitude, sensitivities, and sources of plant water uptake across these vegetation covers. Total ET decreased and interannual variability increased with elevation, with mean May to September ET totals of 349 (±3) mm at the forest, 249 (±10) mm at the tall, dense shrub site, and 240 (± 26) mm at the short, sparse shrub site. The shrub sites exhibited similar ET losses over 6 years despite differences in shrub height and abundance, although daily rates were higher at the tall shrub site in the peak growing season. From May to September, ET:R ratios were the highest and most variable at the forest (2.19 ± 0.37) and similar at the tall, dense shrub (1.22 ± 0.09) and short, sparse shrub (1.14 ± 0.05) sites. In the mid-growing season, mean T rates were greater at the dense shrub site (2.0 ± 0.75 mm d-1) than the forest (1.47 ± 0.52 mm d-1). During this time, T:ET was lower at the forest (0.48) than at the tall, dense shrub site (0.80). During the growing season between the two years, 2020 was considerably wetter and cooler than 2019. At the tall shrub site, during the mid-growing season (July 1-Aug 15), T dropped considerably in 2020 (-26%), as T was suppressed during the short, wet growing season. In contrast, T at the forest was only moderately suppressed (-3%) between years in this same period. Evapotranspiration was more strongly controlled by air temperature during the early and late season at the forest, while ET at the shrub site was more sensitive to warmer temperatures in the mid-growing season. At the shrub sites, ET was energy limited with no observed soil moisture limitation on T. While 2H and 18O of volume weighted precipitation became more depleted with elevation, the opposite was true in xylem water, where 2H and 18O became more enriched with elevation. Plant water uptake was more reflective of snow water at the forest site than both shrub sites, particularly early in the year and during dry periods. Near-surface bulk soil water had more negative lc-excess at the forest throughout the season and with depth, highlighting increased contributions from soil evaporation. This study combined direct measurements of sap flux, ET, and critical zone isotopes to provide new details on multi-year plant-soil-water dynamics, critical zone water cycling, and species-specific plant water uptake patterns in seasonally frozen soils, which have not previously been reported in cold regions. Our results suggest that advances in treeline will increase overall ET and lower interannual variability; however, the large growing season water deficit and stable water isotope signature at the forest indicates strong reliance on soil moisture from late fall and snowmelt recharge and the potential for plant water stress. Differences between the shrub species were apparent in the sap flux and stable isotope measurements, highlighting the need to further evaluate species specific responses and feedbacks when predicting hydrological fluxes across subarctic ecosystems. Overall, our results suggest that predicted changes in vegetation type and structure in northern regions will have a considerable impact on water partitioning and will vary in a complex way in response to changing precipitation timing, phase and magnitude. / Thesis / Candidate in Philosophy

Abstract Groundwater-dependent ecosystems (GDEs) are aquatic or terrestrial ecosystems that rely directly or indirectly on groundwater (GW). Recent European and Finnish legislation requires better consideration of these systems in GW management. The main aim of this thesis was to develop new methods for GDE classification and management, by testing environmental tracer methods in different environments. New information about GW-surface water interactions was obtained and novel methods for GDE classification and management were developed for lakes, peatlands, streams, and springs. Stable water isotopes proved to be an efficient tool for determining the GW dependence of lakes. An iterative isotope mass balance method was applied for 67 lakes situated in the Rokua esker aquifer area. Stable water isotopes also showed potential in determining the GW dependence of a peatland surface horizon. A study conducted in peatlands adjacent to Viinivaara esker aquifer indicated that the GW dependence of peatlands can vary significantly and that GW-dependent areas can extend outside current GW protection areas. Thermal images proved useful in pinpointing clear GW seepage locations in peatlands. For streams, a novel stream tracer index method was developed to evaluate GW dependence based on GW volume in streams, thermal properties of streams, and stream water quality. The method was tested in three streams discharging from Viinivaara and Rokua aquifers and was found to efficiently capture spatial variations in GW dependence. In Oulanka region, hydrological and chemical characterization and statistical methods were used to classify springs into different types. Spring altitude and &#948;2H value were identified as useful proxies for spring water chemistry. The methods developed in this thesis can be helpful when classifying and studying GDEs and applying environmental tracer methods in various environments. Knowing the GW dependence of an ecosystem, the impacts of possible GW table decline caused by e.g., GW abstraction, drainage, and/or climate change can be evaluated. For large-scale applications, GDE classification methods have to be practical, effective, and low-cost. Combined use of stable water isotopes and other tracers can be especially effective for characterizing ecosystem hydrology on different temporal and spatial scales. / Tiivistelmä Pohjavedestä riippuvat ekosysteemit (GDE) ovat vesi- tai maaekosysteemejä, jotka ovat suoraan tai epäsuorasti riippuvaisia pohjavedestä. Euroopan Unionin ja Suomen lainsäädännön mukaan pohjavesien hallinnassa tulisi ottaa paremmin huomioon GDEt. Tämän työn tavoitteena oli kehittää uusia menetelmiä näiden ekosysteemien luokitteluun ja hallintaan. Luonnollisia merkkiainemenetelmiä soveltaen saatiin uutta tietoa pohjavesi-pintavesi vuorovaikutuksesta ja kehitettiin uusia menetelmiä GDE-luokitteluun järville, soille, puroille ja lähteille. Veden stabiilit isotoopit osoittautuivat tehokkaaksi työkaluksi järvien pohjavesiriippuvuuden määrittämisessä. Iteratiivista isotooppimassatase-menetelmää käytettiin 67 Rokuan järven pohjavesiriippuvuuden selvittämiseen. Veden stabiileilla isotoopeilla pystyttiin myös määrittämään suon pinnan pohjavesiriippuvuus. Viinivaaran harjun viereisen suoalueen tutkimus näytti, että suon pohjavesiriippuvuus voi vaihdella merkittävästi ja pohjavedestä riippuvia alueita löytyy myös nykyisten pohjavesirajojen ulkopuolelta. Lisäksi soilla havaittiin selkeitä pohjavedenpurkupaikkoja lämpökamerakuvauksen avulla. Puroille kehitettiin uusi menetelmä, jolla niiden pohjavesiriippuvuutta voidaan arvioida perustuen pohjaveden määrään puroissa, puroveden lämpötilaominaisuuksiin ja puroveden laatuun. Menetelmää testattiin Viinivaaran ja Rokuan harjuista purkautuville puroille ja sillä havaittiin pohjavesiriippuvuuden vaihtelevan purojen eri osissa. Oulangan lähteitä luokiteltiin eri tyyppeihin hydrologisen ja kemiallisen karakterisoinnin ja tilastollisten menetelmien avulla. Lähteiden altitudin ja &#948;2H-arvon havaittiin ennustavan lähdeveden kemiallista koostumusta. Tässä tutkimuksessa kehitetyt menetelmät voivat olla hyödyllisiä GDE-luokittelussa, eri ekosysteemien tutkimisessa ja luonnollisten merkkiainemenetelmien soveltamisessa eri ympäristöissä. Kun ekosysteemin pohjavesiriippuvuus tiedetään, voidaan arvioida pohjavedenotosta, ojituksesta ja/tai ilmaston muutoksesta mahdollisesti aiheutuvan pohjavedenpinnan laskun vaikutuksia. Suuressa mittakaavassa, GDE-luokittelumenetelmien tulee olla käytännöllisiä, tehokkaita ja halpoja. Veden stabiilien isotooppien ja muiden merkkiaineiden yhdistetty käyttö vaikuttaa olevan tähän erityisen tehokas työkalu, jolla voidaan ymmärtää ekosysteemien hydrologiaa eri temporaalisissa ja spatiaalisissa mittakaavoissa.