SIMULTANEOUS NITROGEN RELEASES AND REMOVAL FROM EUTROPHIC LAKE SEDIMENTS

Anthropogenic nutrient inputs, especially from agriculture, lead to eutrophication, harmful algal blooms, and biodiversity loss. Nutrient legacies (both nitrogen (N) and phosphorus (P)) accumulate in lake sediments and can later be released into the water column, delaying water quality improvements after external load reductions. Sediments in eutrophic lakes release both N and P, representing internal nutrient loads, which can be used by harmful algae to produce biomass (and toxins). To determine whether sediments in eutrophic lakes Kaiavere and Veisjärv (central Estonia) are a net source or sink for bioavailable N, intact sediment cores were incubated in a continuous-flow system, with and without 15N-ammonium or 15N-nitrate tracers, to measure microbial N transformations, such as denitrification/anammox (N removal), N fixation (N source), and dissimilatory nitrate reduction to ammonium (DNRA) rates and net nutrient fluxes. Low/no anammox or DNRA was detected in either lake, but denitrification was stimulated by 15N-nitrate in both lakes. N fixation consistently exceeded denitrification in unamended Veisjärv sediments, but Kaiavere sediments varied between net N fixation and net denitrification. Bioreactive N (e.g., ammonium and urea) and phosphate were also released from sediments in both lakes, but molar N:P of these sediment nutrient releases was very high, indicating N excess, relative to P. External N loads should thus also be reduced, in addition to P, to minimize internal N loading from legacy N and to effectively manage eutrophication and algal blooms in lakes.

Presentation Preference: Poster

Primary Presenter: Esther Amalachukwu Nwume, Estonian University of Life Sciences (esther_amalachukwu.nwume@emu.ee)

Authors:

Esther Nwume, Estonian University of Life Sciences  (esther_amalachukwu.nwume@emu.ee)

Kadi Palmik-Das, Estonian University of Life Sciences  (kadi.palmik-das@emu.ee)

Triin Hunt, Estonian University of Life Sciences  (triin.hunt@emu.ee)

Mark McCarthy, Estonian University of Life Sciences  (mark.mccarthy@emu.ee)