6533b7d6fe1ef96bd126675b

RESEARCH PRODUCT

Interlake variation and environmental controls of denitrification across different geographical scales

subject

description

Denitrification in lakes significantly reduces the nitrogen (N) load from land to oceans, but the factors controlling it remain poorly under- stood. Therefore, interlake variation of denitrification in sediments of small to medium-sized lakes (from 0.03 to 17.8 km 2 ) was studied across different geo- graphical scales. At the local scale, the denitrification rates and sediment microbial communities were studied in 4 boreal lakes in close proximity (within 20 km) using the isotope pairing technique (IPT) and molecular methods. These local scale data were com- bined with previously published data on denitrifica- tion rates from 10 other European lakes to extend the analysis to the regional (boreal area) and continental (boreal and temperate areas) scales. Denitrification varied considerably among lakes, ranging from ~50 to ~600, ~0 to ~600 and ~0 to ~12900 µmol N m �2 d �1 at the local, regional and continental scales, respec- tively. This variation was primarily due to nitrate availability. The structure of the denitrifier commu- nity studied at the local scale was independent of the denitrification rates but varied among lakes correlat- ing with nitrate availability and sediment organic content. Removal of nitrate and total N load by deni- trification was less efficient in boreal than in temper- ate lakes. In addition, a meta-analysis of published N mass balance data indicates that the total N retention (denitrification + N sedimentation) is less efficient in boreal than in temperate lakes. Anaerobic ammo- nium oxidation (anammox) was studied at the local scale but was not detected, although (based on molecular markers) several anammox genera were present in the sediments.