35
4.1.6 Ammonium production
In the overlying water of the Neckar River, NH4 + concentrations ranged from 0.01 to
0.04 mM, and increased rapidly with depth in the porewater. The maximum values of
NH4 § in the sediments were 15 mM at Lauffen, 3.6 mM at Kochendorf, and 8.4 mM
at Wieblingen (Fig. 4. I la).
Only a slight increase ofNH4 + was found in the sediments of the Elsenz River. The
.4.
maximum value was 0.44 mM. In the Enz River sediments, a rapid increase of NH4
was measured below 20 cm depth. NH4 § concentrations in the sediments of the
Schwarzbach River show a different tendency: they increased to 50 cm depth, and
subsequently decreased with depth (Fig. 4.11b). No distinct seasonal changes were
§
,
,
.
apparent from the porewater NH 4 profiles obtained m the sediments at Lauffen (Fig.
4.1 lc).
In anoxic sediments, SO42" reduction and CH 4 fermentation are the predominant
processes in the mineralization of organic matter (Aller 1980a; Billen 1982; Klump
and Martens 1987; Barbanti et al. 1992a):
(CH20)113(NH3)15H3PO4 + 56.5 SO42"
--~113 HCO 3" + 15 NH 3 + H3PO 4 + 56.5 HS" + 56.5 H +
(CH20)113(NH3)IsH3PO4 ~ 56.5 CH4 + 56.5 CO2 +15 NH 3 + H3PO 4
The NH4 + profiles from different sites vary considerably. In most cases, particularly
m the sedunents at Wlebhngen, the NH4 profiles can be separated into two zones: m
2.
2the SO4 reductton zone and m the zone below the SO4 reduction zone (Fig. 4.1 I).
9 .
.
.
.
.
2The SO4- reducuon zone is clearly defined by exponenual decrease m SO4
.
.
.
.
.
2concentrations. Below this zone, there is no further contnbutmn from SO4
reduction, yet NH4 § concentrations continued to increase more or less rapidly,
suggesting contribution from CH4 fermentation. In the sediments of Lake
Washington, Kuivila at al. (1989) found that CH4 production rate was low until SO42"
concentrations decreased below 0.03 mM. Only then did CH4 production start to
increase. The spatial separation of SO42- reduction and CH,t fermentation indicates
competition of both processes in anoxic freshwater sediments. In a laboratory
experiment, Winfrey and Zeikus (1977) reported that when SO42" was added to lake
sediment samples, CH4 fermentation was suppressed until SO~ 2" was consumed. In
another experiment, when molybdate - a specific inhibitor of SO42"reduction - was
added to the sediments, methane fermentation increased under the presence of SO42(Capone et al. 1983). This can be interpreted as a result of competition between
9
2 o
,
.
methane producing- and SO4 -reducing bacteria for acetate and hydrogen. Kuivila et
al. (1989) reported, for the first time, the separation of methane production and SO42reduction in low-SO42" (0.1 raM) freshwater sediments of Lake Washington.
Likewise, the separate NH4 + profiles in the porewater suggest that SO42" reduction
and CH4 fermentation are spatially separated in the sediments of the study area,
which have high SO42" concentrations. This situation is observed only in highly
eutrophic and polluted sediments where organicmatter input to the sediments
4.1.6 Ammonium production
In the overlying water of the Neckar River, NH4 + concentrations ranged from 0.01 to
0.04 mM, and increased rapidly with depth in the porewater. The maximum values of
NH4 § in the sediments were 15 mM at Lauffen, 3.6 mM at Kochendorf, and 8.4 mM
at Wieblingen (Fig. 4. I la).
Only a slight increase ofNH4 + was found in the sediments of the Elsenz River. The
.4.
maximum value was 0.44 mM. In the Enz River sediments, a rapid increase of NH4
was measured below 20 cm depth. NH4 § concentrations in the sediments of the
Schwarzbach River show a different tendency: they increased to 50 cm depth, and
subsequently decreased with depth (Fig. 4.11b). No distinct seasonal changes were
§
,
,
.
apparent from the porewater NH 4 profiles obtained m the sediments at Lauffen (Fig.
4.1 lc).
In anoxic sediments, SO42" reduction and CH 4 fermentation are the predominant
processes in the mineralization of organic matter (Aller 1980a; Billen 1982; Klump
and Martens 1987; Barbanti et al. 1992a):
(CH20)113(NH3)15H3PO4 + 56.5 SO42"
--~113 HCO 3" + 15 NH 3 + H3PO 4 + 56.5 HS" + 56.5 H +
(CH20)113(NH3)IsH3PO4 ~ 56.5 CH4 + 56.5 CO2 +15 NH 3 + H3PO 4
The NH4 + profiles from different sites vary considerably. In most cases, particularly
m the sedunents at Wlebhngen, the NH4 profiles can be separated into two zones: m
2.
2the SO4 reductton zone and m the zone below the SO4 reduction zone (Fig. 4.1 I).
9 .
.
.
.
.
2The SO4- reducuon zone is clearly defined by exponenual decrease m SO4
.
.
.
.
.
2concentrations. Below this zone, there is no further contnbutmn from SO4
reduction, yet NH4 § concentrations continued to increase more or less rapidly,
suggesting contribution from CH4 fermentation. In the sediments of Lake
Washington, Kuivila at al. (1989) found that CH4 production rate was low until SO42"
concentrations decreased below 0.03 mM. Only then did CH4 production start to
increase. The spatial separation of SO42- reduction and CH,t fermentation indicates
competition of both processes in anoxic freshwater sediments. In a laboratory
experiment, Winfrey and Zeikus (1977) reported that when SO42" was added to lake
sediment samples, CH4 fermentation was suppressed until SO~ 2" was consumed. In
another experiment, when molybdate - a specific inhibitor of SO42"reduction - was
added to the sediments, methane fermentation increased under the presence of SO42(Capone et al. 1983). This can be interpreted as a result of competition between
9
2 o
,
.
methane producing- and SO4 -reducing bacteria for acetate and hydrogen. Kuivila et
al. (1989) reported, for the first time, the separation of methane production and SO42reduction in low-SO42" (0.1 raM) freshwater sediments of Lake Washington.
Likewise, the separate NH4 + profiles in the porewater suggest that SO42" reduction
and CH4 fermentation are spatially separated in the sediments of the study area,
which have high SO42" concentrations. This situation is observed only in highly
eutrophic and polluted sediments where organicmatter input to the sediments