Ionic composition in Norwegian lakes from 1986 to 2014 : dominating processes and trends

• Main Author: Hunskår, Linn Agnethe
• Other Authors: Haaland, Leif Ståle, Riise, Gunnhild
• Format: Master Thesis
• Language: English
• Published: Norwegian University of Life Sciences, Ås 2016
• Subjects: See salt; Acidification; climate change; ionic composition; VDP::Mathematics and natural science: 400; permafrost
• Online Access: http://hdl.handle.net/11250/2398792

In the 70s anthropogenic emissions of sulphur dioxide (SO2) and nitrous oxides (NOx) in Europe and Russia lead to acidification and fish deaths in many lakes in the South and North of Norway. Therefore the Gothenburg protocol with the aim of reducing SO2 and NOx emissions was developed and a monitoring program on the ionic composition in Norwegian lakes was initialized. Different interactions between ions in the catchment area and in the lakes are known to play a crucial role in Lake Acidification. While some ions can become toxic (aluminium), increase the H+ release into the lakes (sodium and chloride), reduce buffer capacities (calcium and magnesium), or act as acids (humus), other ions are important buffers themselves (bicarbonate) and may counteract acidification. Several processes, such as weathering, sea-salt episodes, vegetation changes, or eutrophication, can affect the ionic composition. The current study evaluates whether climate change related processes can lead to lake acidification, in spite of the reduced acid rain during the last 29 years and change the ionic composition. A dataset on the ionic composition of 77 Norwegian lakes from 1986 to 2014 is used to test for time trends in their ionic compositions and buffer capacities. It appears that the lakes are still recovering in the initially most impacted areas in the South and North of Norway. The buffer capacity and pH is increasing and acid based weathering seems to decrease. In less impacted areas, however, weathering seems to increase, as indicated by increased base cation concentrations. My proposed explanations for this increase are climate change related factors, such as increased precipitation and temperature. Another potentially climate change related change is the increased Brownification (TOC concentrations). Besides the increasing pH, thawing permafrost in the north and afforestation are potential explanations. Storm related sea-salt episodes are not increasing, but can be expected for the future. I conclude that the reduction of SO2 ...