Nitrogen elimination in two deep eutrophic lakes

Abstract

Nitrogen elimination was investigated in two eutrophic Swiss lakes with different hypolimnetic oxygen conditions. Nitrogen burial was estimated from sediment-trap and sediment-core studies. Denitrification and NO, --ammonification rates were quantified with IsNO,-and acetylene incubation experiment! and whole-lake mass balances. The study confirmed earlier reports that the acetylene-block technique yields denitrification rates that are systematically too low. Denitrification rates obtained from isotope tracer experiments were compatible with nitrogen consumption rates observed in flux chamber experiments and whole-lake mass balances. The NO,--ammonification contributed <5% to the NO,-consumption rate in Lake Baldegg. Coupled nitrification-denitrification seemed to be insignificant at the deepest station of Lake Baldegg. The comparison of in situ denitrification rates measured at the deepest site (4.3 mmol m-* d-l) with the denitrification rate obtained from whole-lake mass balances (6.1 mmol rnd2 d-l) indicates that enhanced denitrification may be present in shallower sediments with a better supply of 0,. Mass transfer coefficients for NO,-were similar in both lakes (21.7 and 21.4 m yr-). The NO,-concentration seems to be a key parameter in determining denitrification rates.

Cycling of calcite in hard water lakes of different trophic states

“…The nearby eutrophic Lakes Baldegg (maximum depth 66 m) and Hallwil (maximum depth 47 m) have been similarly oxygenated and aerated since 1982 and 1986, respectively (Mengis et al 1997;Moosmann et al 2006). Before these remediation activities, the water columns of the latter two, nearly meromictic lakes were anoxic at depths .10 m during most of the year.…”

How polluted is the Yangtze river? Water quality downstream from the Three Gorges Dam

“…A fraction of the dissolved NO 3 − may also be denitrified in the newly formed anaerobic sediments of the reservoir (e.g. Mengis et al, 1997;Friedl and Wüest, 2002). This may explain the lower concentrations of NO 3 − and DIP at…”

Seasonal variation of the δC and δN of particulate and dissolved carbon and nitrogen in Lake Lugano: Constraints on biogeochemical cycling in a eutrophic lake

“…Nitrogen mass balance calculations show that the total net elimination of nitrogen in the South Basin amounted to 336 ϫ 10 3 kg N in 1999 (Table 2), corresponding to approximately 22% of the total nitrogen inventory. Net organic nitrogen burial generally does not contribute much to the total N removal in eutrophic lakes (e.g., Mengis et al 1997). For example, Meile (1996) has shown that, in the northern basin of Lake Lugano, N burial accounts for less than 13% of total annual N loss from this basin.…”