Dinitrous oxide (N2O) is a potent greenhouse gas some 354 times stronger than carbon dioxide (CO2) in the atmosphere. Recent studies show that lake denitrification contributes to a considerable part of the global N2O emissions. Despite this, lake-N2O emissions are not being accounted for in global greenhouse gas modeling because it has not yet been accurately understood and quantified. The aim of this study was to assess how denitrification varies between and within boreal lakes and how it is controlled by nitrate- (NO3) and carbon (C) availability and temperature. Studies on denitrification were performed using the acetylene inhibition technique on sediments from three lakes in northern Sweden (February to August, 2014). Results showed that denitrification was correlated (linear regression, r2=0.71) with NO3 concentrations in the hypolimnion water at ambient conditions and that additions of NO3 up to a concentration of 50 µg NO3-N L-1 increased denitrification. Temperature increased denitrification in all lakes, at all sites except in one lake in July, when nutrient concentrations were at its lowest. The spatial and temporal variation in denitrification was small at ambient conditions (1-3 µmol N2O m-2 h-1)but the variation in the response to nutrient additions and temperature increase was very high. This was in part attributed to differences in dissolved organic C (DOC). These findings have important implications for future denitrification research and how lake-N2O production is included in greenhouse gas modeling and contributes to our knowledge on how northern boreal lakes may respond to enhanced nutrient loadings and global warming.

The overall goal of this study was to examine the hydrological and geochemical linkages between the contributing landscape and small tundra lakes affected by shoreline retrogressive thaw slumping (SRTS) in the upland region north east of Inuvik, NT. In 2007, 2008, and 2009, detailed hydroclimatological and geochemical data were obtained from a pair of representative tundra lake catchments (Lake 5A: Control; Lake 5B: Affected by SRTS). This was supplemented with less detailed data obtained from 10 regional small tundra lake catchments (control and affected by SRTS). The hydrology and geochemistry of Lake 5A and Lake 5B exhibited strong seasonal variability that was characterized by spring snowmelt. For the three study years, Lake Level (LL) peaked during spring snowmelt, when the addition of melt water from the contributing landscape led to a rapid rise in LL that was enhanced by snow and ice damming the outlet channel. The addition of this relatively dilute runoff water led to a decrease in the concentration of most major ions and nutrients in the study lakes over the spring months. Notably, the concentration of nutrients increased at the beginning of spring snowmelt, due to the mobilization of surficial organic materials by runoff, before decreasing as runoff to the lake became more diluted. Recent changes in key hydroclimatic factors have likely affected the hydrology and geochemistry of the study lakes. The examination of a suite of hydroclimatic indicators, derived from historical climate data, indicated that the annual May 1st snowpack in Tuktoyaktuk has been increasing at a significant rate over the past half century. Furthermore, detailed snow survey data suggested that the capture of snow by SRTS-affected terrain increases the snowmelt contributions to small tundra lakes. An increase in the contribution of snowmelt inputs to the lake water balance could lead to a higher peak LL and more dilution of lake water. In addition to hydro-climatic drivers, the geochemistry of the study lakes was also driven by SRTS. SRTS-affected lakes had significantly higher concentrations of major ions than unaffected study lakes, due to the addition of relatively ion-rich runoff from SRTS-affected terrain during the spring and summer months. The outlet channels draining the SRTS-affected study lakes also had significantly higher concentrations of major ions than that of the unaffected study lakes, due to the addition of relatively ion-rich lake water, which suggests that SRTS-affected lakes could be a source of major ions to downstream lakes. / Graduate

No description available.

Coastal and shallow lakes are often subjected to eutrophication due to nutrients from catchment farming activities. Lake Ellesmere (Te Waihora) is a hyper-eutrophic lake which has gained recent attention because of concerns over its ecological health and fishery status. This study investigated the benthic ecology of the lake by extensive spatial and temporal sampling. Eight littoral sites were sampled on a single occasion, and 20 benthic sites were sampled once per season for one year. Water chemistry conditions, substrate and invertebrate communities varied significantly around the lake. Salinity, pH, DO and seston were primarily affected by freshwater inputs from inflow streams and salt water intrusion due to the lake opening to the sea. On these occasions, salinity reached 32 ‰ at the lake outlet. The lake invertebrate community was depauperate, comprising of only two species of invertebrate predators restricted to the littoral zone and eight benthic invertebrate taxa, dominated by oligochaetes, amphipods and chironomids. Benthic invertebrate abundances also reflect the dominant local substrate, where oligochaetes and chironomids preferred areas of silt substrate, whereas Potamopyrgus preferred harder substrate. Stable isotope and gut analysis determined that the primary food sources within the lake were phytoplankton and algae. Macrophytes provided a minimal contribution to the food web, possibly relating to the change in status from a clear water, macrophyte dominated lake to a turbid, phytoplankton dominated condition since the Wahine Storm in 1968. Isotope analysis also showed that the lake food web was markedly different in its carbon values from food webs of its inflow streams and nearby marine source. However the lake food web did show a marine-derived carbon signature. A mesocosm experiment testing the effect of common lentic predators on the abundance of the lake chironomid Chironomus zealandicus, showed that if invertebrate predators were present in the lake they could markedly reduce the abundance of the pest prey species. This study highlights that the frequent re-suspension of bottom sediments, lake level fluctuation resulting in wetting and drying of littoral zones, and the management of the lake opening to the sea all have an effect on the benthic ecology of Te Waihora.

Thesis (M.S.)--University of North Carolina Wilmington, 2007. / Includes bibliographical references (Leaves: 58-63)

Thesis (M. Phil.)--University of Hong Kong, 2008. / Also available in print.

Diss. (sammanfattning). Umeå : Sveriges lantbruksuniv., 2003. / Härtill 4 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2003. / Härtill 4 uppsatser.

Thesis (Ph.D. - Hydrology and Water Resources)--University of Arizona. / Includes bibliographical references (leaves 219-230).

Thesis (Ph. D.)--University of New South Wales, 2003. / Also available online.