Treatment with Nitrate and Oxygen Improves Water Quality of Contaminated Urban Lakes

The ecological status of two eutrophic urban lakes has dramatically improved following a treatment with calcium nitrate and oxygen-enriched water. These lakes were affected by decades of nutrient and pollutant loading from stormwater runoff. The intervention suppressed the release of legacy phosphorus from sediments and reduced phosphate in the bottom water by over 80% in both lakes within one year. With the start of the treatment, nitrate (NO₃) levels temporarily increased in the bottom water, but returned to drinking water standards within a month when no further NO₃ was added. No leaching of NO₃ to the aquifer below the lake was detected. DOC levels in the pore water declined during the treatment, indicating heterotrophic denitrification took place. Simultaneously, sulfate increased in the bottom water, hydrogen sulfide production was inhibited, and oxygen levels increased throughout the water column, alleviating the anoxic conditions prior to the treatment. Although Microcystis was detected in the sediment of one lake, no microcystin was detected in either lake. This contradicts the concept that reducing phosphorus without reducing nitrogen leads to an increase in microcystin concentrations. Although the sediments contained high concentrations of lead (Pb) and other metals, no increase above drinking water limits was observed during or after the treatment. This is in contrast to previous lab-scale studies, suggesting remediation based on NO₃ and oxygen leads to Pb mobilization. Analysis of the sediment microbial communities reflected a reduction in the relative abundance of sulfate reducers and methanogens induced by the treatment. NO₃ is often considered a pollutant. We show that its controlled addition to lakes resulted in a clear improvement in water quality. The treatment shows great promise as a practical, field-scale tool for remediating lakes impacted by urban pollution and constant inputs of excess nutrient.

Presentation Preference: Oral

Primary Presenter: Robin Burgold, TU Berlin (robin-burgold@web.de)

Authors:

Robin Burgold, Technische Universität Berlin  (burgold@tu-berlin.de)

Roman Klemz, Büro Wassmann  (mail@buero-wassmann.de)

Hartmut Wassmann, Büro Wassmann  (mail@buero-wassmann.de)

Erika Martinez-Ruiz, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB)  (Erika.martinez@igb-berlin.de)

Anne Wagner, Technische Universität Berlin  (aw@boku.tu-berlin.de)

Martin Kaupenjohann, Technische Universität Berlin  (martin.kaupenjohann@tu-berlin.de)

Ulrich Szewzyk, Technische Universität Berlin  (ulrich.szewzyk@tu-berlin.de)

Myriel Cooper, Technische Universität Berlin  (myriel.cooper@tu-berlin.de)