The influence of the North Atlantic Oscillation on the physical, chemical and biological characteristics of four lakes in the English Lake District

Abstract

1. Thirty-six years of winter meteorological and limnological measurements from four lakes in the English Lake District are analysed and related to variations in the North Atlantic Oscillation (NAO). Winter weather conditions were strongly influenced by the NAO with mild, wet winters being associated with strongly positive values of the NAO index (NAOI). 2. Lake surface and bottom temperatures were strongly positively correlated with the NAOI, with the highest correlations being recorded in the shallower lakes. 3. Variations in the NAOI also had a significant effect on the winter concentration of nitrate. In all the lakes, there was a significant negative correlation between the NAOI and the detrended winter concentration of nitrate. The key driving variable was the local air temperature, which appeared to limit the quantity of nitrate reaching the lake by increasing the amount assimilated in the surrounding catchment in mild winters. 4. Dissolved reactive phosphorus (DRP) concentrations were not significantly correlated with the NAOI in the two larger basins but significant positive correlations were recorded in the two smaller lakes. The key driving variable was the local rainfall with higher DRP concentrations being recorded after heavy rain in the lakes with a short retention time. 5. The NAOI-related changes in rainfall also influenced the phytoplankton. In wet winters the concentration of chlorophyll in the two smaller lakes with the shortest retention time was lower and the spring growth of Asterionella formosa was delayed in the smallest lake. 6. These differential responses demonstrate how the large-scale effects associated with the NAO can be 'filtered' by the physical characteristics of a particular site.

Effects of the North Atlantic Oscillation on water temperature in southern Baltic coastal lakes

“…The effects of the North Atlantic Oscillation Index on the temperature were most pronounced in lower-lying lakes where ice cover is not frequent and persists for a short time. Significant correlations between water temperature and NAO Index have also been reported from other lakes of the northern hemisphere (George et al, 2004b;Maher et al, 2005). Water temperature trends in some lakes of the northern hemisphere were described by Peeters and Livingstone (2002), Livingston (2003), and Arhonditsis and Brett (2004).…”

“…Those parameters in turn affect the chemistry and biology of aquatic ecosystems. The strong influence of the winter NAO Index on meteorological conditions, physical, and subsequently on chemical conditions of lake waters has also been reported by George et al (2004b) and by Weyhenmeyer (2004). The relationship between the NAO and variations in surface temperature, storms and precipitation, as well as variations within ecosystems and how this affects the economy has been described by Hurrell et al (2003), and also by George et al (2004a).…”

“…The correlation coefficient (x0.54) between the NAO Index and the annual maximum ice extent in the Baltic (Omstedt and Chen, 2001) lies within that range as well. Stronger associations between the ice parameters mentioned and the NAO Index were found for shallow lakes (George et al, 2004b), and also for shallow sheltered areas of the southern Baltic coast. Correlation coefficients calculated for areas off river mouths and shallow coastal lagoons may exceed x0.70 and in coastal lakes may even exceed x0.80 (Girjatowicz, 2003), particularly with respect to the number of days with ice.…”

Consequence of altered nitrogen cycles in the coupled human and ecological system under changing climate: The need for long-term and site-based research

“…Coherent patterns of variation in NO 3 -leaching are sometimes evident over large spatial scales and across catchments covering wide altitudinal gradients and land-use classes (e.g., Rogora et al 2008;Evans et al 2010). In the UK, winters when NO 3 -leaching to remote surface waters have been strongly associated with negative excursions in the winter North Atlantic Oscillation (NAO) Index, most likely due to low winter temperatures, lower than average rainfall and larger contributions from more polluted air masses originating from the European continent (Monteith et al 2000;George et al 2004). However, as soil temperature is a dominant driver, opposing inter-annual patterns in NO 3 -leaching may be observed in regions normally blanketed by snow in winter when they lack snow cover, since snow cover insulates the uppermost soil layer from the atmosphere (Groffman et al 2009;Makoto et al 2013).…”

“…However, as soil temperature is a dominant driver, opposing inter-annual patterns in NO 3 -leaching may be observed in regions normally blanketed by snow in winter when they lack snow cover, since snow cover insulates the uppermost soil layer from the atmosphere (Groffman et al 2009;Makoto et al 2013). Consequently, relationships between NO 3 -leaching and the NAO index in the UK and in northern Europe may vary regionally (George et al 2004;Blenckner et al 2007;de Wit et al 2008).…”