The influence of road salts on the salinity and the meromictic stability of Lake Svinsjøen, southeastern Norway

Abstract

Primarily as a result of road salting, the water masses ofLake Svinsjøen, a small meromictic lake in southeasternNorway, have been subject to great changes in salinity duringthe period 1947–1995. The greatest change in saltconcentration has occurred in the upper part of themonimolimnion (depth 10–15 m) where mean conductivityincreased 104.2 per cent, from 143 to 292 μS cm⁻¹. Inthe upper mixolimnion (depth 0-5 m), mean conductivity rosefrom 130 to 238 μS cm⁻¹ during the same period. Theions responsible for the salinity changes were Na⁺ andCl⁻ from de-icing salts, and Ca²⁺ and Cl⁻ fromsalts used to keep down dust from roads. Further sources ofCa²⁺ are the road asphalt and increased weathering andleaching of the lime-rich rocks caused by acid precipitation,the main source of the additional inputs of SO$_{\text{4}}^{{\text{2 - }}}$ tothe lake. The salinity changes caused major changes inmeromictic stability, S$S\prime _c$. In the period1947-1966, S$S\prime _c$ increased by 24 g cm cm⁻²,and the maximum level of meromictic stability, 125 gcm⁻², was found in 1966. As a result of higher rate ofsalt accumulation in the upper part of the monimolimnion andin the mixolimnion, S$S\prime _c$ decreased by 30 g cmcm⁻² during the period 1966-1991, and a simultaneousrise in the chemocline took place. In the period 1991-1995 anadditional decrease of 26 g cm cm⁻² occurred. Continuedectogenic inputs of salts through processes typical of thetime period investigated will in future further weaken thelake's meromictic stability, and may cause the demise ofmeromixis in Lake Svinsjøen, a development which may haveimportant implications for primary productivity of thelake.