B11F-01 INVITED
The Effect of Sulfate Deposition on Wetland Methane Emissions: Historical, Experimental and Emissions Monitoring Evidence
Methane emitting wetlands are subject to pollutant sulfur deposition from both anthropogenic and
volcanogenic sources. Results from a range of studies demonstrate that methane emissions are suppressed
by sulfate deposition within the range commonly experienced in regions affected by both anthropogenic and
volcanogenic pollution. We report findings from experimental studies and a historical assessment of the
effects of a large Icelandic eruption that together with an ongoing literature based data synthesis study
(RICHES – Regional Integration of CH4 Emissions Studies), suggest the likely magnitude of the effect of
sulfate pollution on CH4 emission while shedding light on the processes responsible for the
suppression. While microbial interactions play a key role in the suppression, the effect of sulfur on plants
may also be an important variable in determining the extent of suppression.
http://cepsar.open.ac.uk/pers/v.gauci/
B11F-02
Responses of Bog Vegetation and CO2 Exchange to Experimental N and PK Addition
Atmospheric nitrogen (N) deposition has the potential to alter the structure and functioning of nutrient poor wetland ecosystems. It is important to quantify the effect of N input on ecosystem carbon (C) sequestration in these globally important C storages. We address this issue at the temperate Mer Bleue bog, ON, Canada. After 6 years of experimental fertilization, we saw that high N deposition can change mixed Sphagnum and dwarf shrub dominated communities to taller and denser dwarf shrub communities that are losing moss cover, and which might have even lower net C uptake. Now, after 8 years of fertilization and with new treatments we quantify the relationship between the plant community structure and ecosystem CO2 exchange. Three levels of N fertilization were applied with or without phosphorus and potassium (PK) into triplicate plots. We measured light saturated net ecosystem CO2 exchange (NEE), and its components ecosystem respiration and gross photosynthesis using clear and dark chambers (May-August). Vegetation characteristics were quantified by measuring foliage cover (LAI), amount of woody and foliar biomass, and abundance of moss species (point interception technique), moss growth (cranked wires) and green area of vascular leaves and moss. Addition of PK fertilizer did not alter NEE or its components relative to the control. The 8-year low N addition alone and with PK, and the 4-year fertilization with high N levels resulted in the highest net ecosystem CO2 uptake relative to the control. The ecosystem respiration increased with increasing N input rate. All levels of N fertilization resulted in higher gross photosynthesis than the control, but there was no increasing trend with increasing N input. Vascular foliage increased, while moss cover drastically decreased with increasing levels of N fertilization. At the highest level of N (and PK) addition woody biomass increased at the expense of leaf increment. Dependencies of ecosystem CO2 exchange on the vegetation structure will be inspected.
B11F-03
Impact of Long-term N Deposition on N Mobility and Transformations in A Northern Peatland
Nitrogen (N) saturation in peatland ecosystem be expected at the total inorganic N deposition rates of 1.5 -
2.0 g m-2 yr-1, but whether the threshold value can be modified by the availability of phosphorus
(P) and potassium (K) and changes in vegetation community structure is unknown. To address this question,
a field experiment and 15N tracer study were conducted on 18 research plots in the Sphagnum-
dominated, ombrotrophic bog Mer Bleue, Canada. Significant increases in N concentration and a reduced C:
N ratio (32.1) were observed in the exclusively N fertilized plots (1.6 g N m-2 yr-1 loading) rather
than plots with even higher N loading but additional P and K fertilization. Except in the highest N loading plots
(6.4 g N m-2 yr-1) with P and K input, there were no significant differences in NH4+ and
NO3- concentration in soil solution among most of plots. NH4+ and NO3-
concentrations ranged from 2.2 to 4.2 μmol L-1 and 4.6 to 7.7 μmol L-1, respectively,
while in the highest N loading plots, average NH4+ and NO3- concentration were 9.2 and
15.5 μmol L-1, respectively, indicating some potential for nitrate leaching. Application of P and K
significantly increased the available P and K by a factor of 100 compared to controls and exclusive N fertilized
plots. P was depleted in exclusively N fertilized plots (1.9 μmol L-1 PO43-); whereas K
still remained high, indicating that N deposition resulted in P limitation of the vegetation. This result is
consistent with previous studies, but the inorganic N concentrations were still low and no N saturation
occurred. An efficient transformation into organic nitrogen can be possible explanation. Enhanced P and K
availability slowed the translocation of mineral N, but when N loading was higher than 3.2 g N m-2 yr-
1, even the application of P and K can not prevent some nitrate leaching. The isotope study showed that
mosses had a higher mass based N retention capacity than vascular plant, but with the nutrient loading, the
N retention power of vascular plant increased. Considering the decline in moss biomass and shift to vascular
plant in high nutrient loading plots, the N filter function of ombrotrophic bogs will be highly influenced by
interactions with shifts in plant community structure and other nutrients.
http://www.agu.org
B11F-04
Silicon-carbon interactions in high latitude watersheds
Changes in climate and hydrology in high latitude regions could liberate large amounts of previously inactive organic carbon (OC) during a prolonging thawing period, and new studies have shown that a great deal of this organic C is remineralized as CO2 during its transport to the sea. However, OC (with its origin in atmospheric carbon) and dissolved silicate (DSi) concentrations in taiga and tundra rivers are intimately linked, and higher concentrations of weathering products are found in taiga and tundra rivers with a higher percentage of peat in their watersheds. It appears that the weathering regime of taiga and tundra watersheds is tightly linked to carbon-silicon interactions, in which carbon acts both as a weathering agent (soil CO2 from degradation of OC) and as a weathering product (DSi and bicarbonate). Whereas respiration of OC can be regarded as a positive feedback to global warming, weathering can be regarded as a negative feedback to global warming since atmospheric CO2 is converted to bicarbonate and thereby locked into the aquatic phase for geological time scales. Thus, bicarbonate export may compensate for significant amounts of exported OC thereby reducing the positive feedback to atmospheric CO2. However, the silicon-carbon interactions are not straight forward as suggested by classical inverse modelling,using the stochiometry of rock forming minerals as base, since high latitude wetlands contain a massive stock of amorphous silica (diatoms and phytoliths) buffering the actual DSi export, suggesting that the Si cycle is to a large extent biologically controlled.
B11F-05
Wetland Methane Emission Response to Last Glacial Maximum Atmospheric Carbon Dioxide Concentration
Ice core records show that the atmospheric concentration of methane (CH4) during the Last Glacial Maximum (LGM) (~21,000 years ago) was 40% lower than the preindustrial Holocene. The contribution of natural wetlands to the global CH4 budget during the LGM is determined by modelling their spatial extent and productivity. Although models provide an estimated flux of ~75-180 Tg yr-1, they adopt present day physiological relationships to reconstruct past wetland emissions. Here we show that the LGM (180 ppm) carbon dioxide (CO2) concentration lowers CH4 emissions from peat cores incubated in controlled environments compared to cores maintained under a modern atmospheric CO2 concentration (380 ppm). Peat cores (110 x 400 mm) collected from a UK minerotrophic fen and upland ombrotrophic bog were maintained either in a [CO2] of 180 ppm or 380 ppm over 21 months. CH4 fluxes were measured on a monthly/weekly basis using static chambers with [CH4] measured via an LGR Fast CH4 Analyser and GC-FID. Results show that total CH4 flux from the minerotrophic fen was suppressed by 17 and 31% in season 1 and 2 respectively under LGM CO2 starvation. The ombrotrophic bog cores were suppressed by 20% in year 1 and 10% in year 2. Both peat types exhibited a rapid initial response to the sub-ambient [CO2] treatment with a change in CH4 flux recorded 5 days into the experiment. We also measured the influence of an LGM [CO2] atmosphere on CH4 flux temperature response during years 1 and 2. These results suggest that both wetland plants, and the underlying biogeochemistry of the rhizosphere, are sensitive to a reduction in [CO2] in the atmosphere and this has yet to be incorporated into global wetland CH4 models.
B11F-06
Impact of experimental drought and rewetting on redox transformations and methanogenesis in mesocosms of a northern fen
The impact of climate change on the greenhouse gas balance of peatlands is debated as they function both
as sinks of carbon and significant sources of methane. To study redox transformations influencing methane
production, we incubated two intact soil monoliths from a northern temperate fen and compared a
permanently wet treatment to a treatment undergoing an experimentally induced drought for 50 days. Net
turnover of dissolved inorganic carbon (DIC), methane (CH4) and electron acceptors in the saturated zone
was calculated using a mass balance approach, and sulfate gross reduction rates were determined using a
35S radiotracer. Thermodynamic energy yield of different electron accepting processes was calculated and
related to the observed respiration patterns.
Permanently wet conditions lead to a depletion of electron acceptors within 50 days and onset of
methanogenic conditions. During drought, electron acceptors were renewed and methanogenesis was
temporarily suppressed in most of the peat for another 20-50 days after rewetting. Methanogenesis began,
however, apparently locally before electron acceptors were fully depleted in the remainder of the peat, and
iron and sulfate reduction occurred simultaneously. Anaerobic production of DIC could mostly but not fully be
explained by reduction of nitrate, sulfate and ferric iron. Sulfate gross reduction rates of up to ~450 nmol cm-
3 d-1 determined with 35S-SO4 and potentially explained the surplus of 50-60 mmol m-2 of DIC production in
one treatment; however, the sulfate pools were too small to sustain such rates beyond some hours to days.
Furthermore, anaerobic DIC production proceeded at constant rates after depletion of dissolved inorganic
electron acceptors, although not being balanced by methane production. An unknown electron acceptor was
thus consumed, and sulfate and potentially other electron acceptors recycled, either by humic substances or
by oxygen in the rhizosphere and capillary fringe at low levels of air filled porosity.
http://www.bayceer.uni-bayreuth.de/fg_bp/index.php?lang=en
B11F-07
Bryophyte Evapotranspiration in a Boreal Forest Chronosequence
Forest water fluxes, in particular evapotranspiration (ET), are less well constrained than are carbon fluxes, and the effect of changing stand age on forest ET is not well understood. We combined field and lab measurements to estimate the bryophyte contribution to ET in a black spruce-dominated boreal chronosequence in Manitoba, Canada. Site ages were 17, 42, 76 and 156 years, and each site contained separate well- and poorly-drained stands (bogs). Field plots (N=4) were surveyed for moss diversity and microtopography; meteorological variables were recorded continuously. Field measurements were made 3-4 times during the growing season using a custom chamber attached to a LI-COR 6400. In addition, large tubs of moss were incubated in a controlled-environment chamber and water loss rates measured via weighing; these tubs were also measured using the same protocol as performed in the field. In the lab, fully-saturated feathermoss and Sphagnum lost water at rates as high as 1.5 and 4.5 mm day-1, respectively, at 25 °C. Over the entire year, modeled bryophyte ET ranged from 0.2-0.3 and 0.2-0.5 mm day-1 in the well- and poorly-drained stands, respectively. During the growing season, these rates were 0.7-0.8 and 0.6- 1.4 mm day-1. Ignoring bog microtopography would have resulted in underestimation of fluxes by ~10%. There was no clear trend of moss ET flux with stand age, except at the very youngest stands, where bryophyte spatial coverage was low. Our results emphasize the important contribution that bryophytes make to the ET flux of boreal forests.