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| Titel |
The capacity of peatland buffer areas to retain inorganic nitrogen |
| VerfasserIn |
Anu Vikman, Sakari Sarkkola, Hannu Nousiainen, Annu Kaila, Mika Nieminen |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250045159
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| Zusammenfassung |
| Natural and restored peatland buffer areas have proven to be effective constructions in
reducing element transport such as nitrogen (N), phosphorus (P) and suspended solids from
forested catchments (Nieminen et al. 2005, Väänänen et al. 2008) . In this study,
nitrogen retention capacities of six peatland buffer areas were studied by adding
ammonium nitrate (NH4NO3-N) solution into the inflow waters once (one area) or twice
(five areas). The first addition was made in 2003, 2004 or 2005 and the second
in 2008 and the duration of each addition event lasted for four days. The buffer
areas were either undrained mires or drained peatlands rewetted 4-7 years before
the present study and they covered an area of 0.1 - 4.9% of the catchment area
upstream.
Samples of the inflow and outflow waters were collected between 2002 and 2009, before
and after the two additions. Samples of soil water, vegetation, peat and N2O were collected
during 2007-2009. The emissions of N2O were measured using the closed chamber technique
six to seven times before the N addition in 2008 and eight to nine times after it. The sampling
was introduced from eight sampling plots at each buffer area. The biomass of above-ground
and below-ground parts of plants was harvested from each of the study sites at peak standing
crop in August of 2007 and 2008; before and after the second N addition. The samples were
collected from 17-20 plots that were placed systematically to cover each buffer
area as a grid. The below-ground parts of biomass were collected simultaneously
with the above-ground biomass from the same plots. Peat monoliths (3Ã4Ã15 cm)
down to a depth of 15 cm were sampled and divided into two layers of 7.5 cm
thickness.
Except for the first N addition in one area, the three largest buffer areas (relative size
higher than 1%) retained the added inorganic N almost completely; their retention efficiencies
during the year of addition were higher than 93% for both NO3-N and NH4-N.
Two of the three smallest buffers (relative size lower than 0.25%) were still able
to reduce inorganic N from the through-flow waters effectively, as their retention
capacities for inorganic nitrogen varied between 58 and 89%. However, one small buffer
area had a retention capacity of less than 20%. The factors contributing to efficient
N retention were hydrological load during N addition, relative size of the buffer
area, and the length of the buffer area, i.e. the distance between the inflow and
outflow points. The buffer areas appeared to be efficient and long-term sinks for
inorganic nitrogen, because the release of N during the 2-4 years after N addition was
minor.
The N2O emissions correlated significantly with the water table level and the
concentrations of NO3-N and NH4-N in the soil water. Thus, in buffer areas with a high water
table level the concentrations of NO3-N in the soil water and the emissions of N2O increased
soon after the N addition had started. The total N loss as N2O was also larger than in areas
where the water table level was lower and the concentrations of NO3-N in the soil water
remained low. Compared with the high amount of NÂ applied in the buffer areas, the loss of N
as N2O was low from all buffer areas.
The N content in the vegetation increased by about 6-43 kg (9-67 kg ha-1)
at four of the five buffer areas, while a decrease in N content of about -2 kg was
observed at one buffer area. The proportional retention in the vegetation was about
11-83% of the added N, except for the one buffer area. We suggest that a significant
proportion of the N added has also been retained in microbial biomass and in the peat
matrix.
References
Nieminen, M., E. Ahti, H. Nousiainen, S. Joensuu & M. Vuollekoski, 2005. Capacity of
riparian buffer zones to reduce sediment concentrations in discharge from peatlands drained
for forestry. Silva Fennica 39: 331-339.
Väänänen, R., M. Nieminen, M. Vuollekoski, H. Nousiainen, T. Sallantaus,
E-S. Tuittila & H. Ilvesniemi, 2008. Retention of phosphorus in peatland buffer
zones at six forested catchments in southern Finland. Silva Fennica 42: 211-231. |
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