Aeration‐Induced Changes in Temperature and Nitrogen Dynamics in a Dimictic Lake

Abstract

Low levels of oxygen (O) in the hypolimnion layer of lakes are harmful to benthic animals and fish; they may also adversely affect nutrient cycles. Artificial aeration is often used in lake management to counteract these problems, but the effects of aeration on nitrogen (N) cycling are not known. We studied the effects of hypolimnetic aeration on N dynamics and temperature in a eutrophic lake by comparing continuous and pulsed aeration with a nonaerated station. Aeration decreased the accumulation of NH-N deep in the lake (20-33 m) by supplying O for nitrification, which in turn provided substrate for denitrification and promoted N removal. Aeration also increased the temperature in the hypolimnion. Denitrification rate was highest in the nonaerated deep areas (average, 7.62 mg N m d) due to very high rates during spring turnover of the water column, demonstrating that natural turnover provides O for nitrification. During stratification, denitrification was highest at the continuously aerated station (4.06 mg N m d) and lowest at the nonaerated station (3.02 mg N m d). At the periodically aerated station, aeration pauses did not restrict the increase in temperature but resulted in accumulation of NH-N and decreased the contribution of denitrification as a nitrate reduction process. Our findings demonstrate that hypolimnetic aeration can substantially affect N cycling in lakes and that the effect depends on the aeration strategy. Because N is one of the main nutrients controlling eutrophication, the effects of aeration methods on N removal should be considered as part of strategies to manage water quality in lakes.

Long-Term Water Quality Changes as a Result of a Sustainable Restoration—A Case Study of Dimictic Lake Durowskie

“…The deep oxygen deficit occurred less and less during summer, and its range from the bottom included an increasingly smaller part of the water column. A similar shortening of the duration and range of oxygen deficits has been observed as an effect of hypolimnetic aeration in other lakes [31,32]. Initially, oxygen supplied by a pulverizing aerator to the sediment-water interphase caused the intensification of organic matter mineralization.…”

“…Ammonia N release in the anoxic hypolimnion of eutrophic and hypertrophic lakes exceeds 15 mgNm −2 d −1 , and its accumulation in deep water layers results from the lack of nitrification and decreased assimilation [25]. Low oxygen concentrations due to water aeration allow oxidizing ammonium N to nitrates, which in turn provide substrate for denitrification [31]. An intense denitrification process in the initial period of restoration was indicated by the total depletion of nitrates in the hypolimnion of the lake.…”

“…Respiratory denitrification is considered as an important nitrogen removal pathway [35], which can be accelerated by artificial aeration [31]. The process of fermentative dissimilatory nitrate reduction to ammonium (DNRA) might well be responsible for ammonium N content decrease, although it is believed that it is favored in nitrate-limited environments rich in labile carbon, reductive conditions and higher temperature [31,35,36], thus it might contribute to the diminishment of ammonium N only at the beginning of restoration process. Low concentration of oxygen in the water overlying the sediment, however, allowed the annamox process to take place, i.e., the reduction of ammonium nitrogen to N 2 [37].…”

“…Nitrogen transformations were accelerated, as the correlation between ammonium N/nitrates and temperature was noted (r = 0.347, p < 0.01 and r = −0.360, p < 0.01, respectively). Such changes are often observed during hypolimnetic aeration/oxygenation [29,31,38] and may stimulate the decomposition of organic matter, resulting in further increased oxygen demand. Long-term treatment, including water aeration and other measures aiming at the reduction of fresh organic matter deposition in the sediments are required to suppress the potential effects of elevated temperature.…”

Benthic fluxes of oxygen and inorganic nutrients in the archipelago of Gulf of Finland, Baltic Sea – Effects of sediment resuspension measured in situ

“…DSi may also be efficiently adsorbed by both iron (Fe) and aluminum (Al) oxides under oxygenated conditions (Anderson and Benjamin, 1985;Tallberg et al, 2008;Tuominen et al, 1998) and resuspension of Feand Al-oxides may affect the net benthic fluxes of both DIP and DSi by changing the concentration gradients. Since an oxygen deficit may also affect the reaction and transformation pathways of nitrogen and thereby alter the benthic fluxes of different nitrogen forms (Hannig et al, 2007;De Brabandere et al, 2015;Holmroos et al, 2016), resuspension-altered oxygen consumption may also influence nitrogen fluxes. This may in turn have implications for the mainly nitrogen-limited primary production of the Baltic Sea (Tamminen and Andersen, 2007).…”