Kaido Soosaar

Reed canary grass cultivation mitigates greenhouse gas emissions from abandoned peat extraction areas

We studied the impact of reed canary grass (RCG) cultivation on greenhouse gas emission in the following sites of an abandoned peat extraction area in Estonia: a bare soil (BS) site, a nonfertilized Phalaris (nfP) plot, a fertilized Phalaris (fP) plot, and a natural bog (NB) and a fen meadow (FM) as reference areas. The C balance and global warming potential (GWP) were estimated by measuring CO2, CH4, and N2O emissions and aboveground and belowground biomass variations. The high CO2 flux from the nfP and fP sites and the low CO2 emission from the BS are due to the enhancement of mineralization by plant growth on planted sites and inhibited mineralization by the recalcitrant C of BS. The NB site emitted 24 kg CH4 ha−1 yr−1, whereas the almost zero CH4 emission from the Phalaris plots and the BS site was due to the high S concentration in peat, which probably inhibited methanogenesis. The N2O flux varied from <0.1 kg on the Phalaris plots and the NB to 2.64 kg N2O ha−1 yr−1 on the FM. The highest yield of RCG was obtained in autumn (13.9 t and 8.0 t dw ha−1 on the fP and nfP, respectively). By spring, the biomass yield on the fP and nfP plot was 12.7 and 7.9 t dw ha−1, respectively. The C balance of nfP and fP plots was negative in comparison to the BS (−3322, −5983, and 2504 kg CO2 ha−1 yr−1, respectively). This indicates that the cultivation of RCG transformed them from a net source of C into a net sink of C. The GWP for the fP and nfP sites was −5981 and −3885 kg CO2 eq ha−1 yr−1, respectively. The BS site had a total GWP of 2544 kg CO2 eq ha−1 yr−1.

Cattail population in wastewater treatment wetlands in Estonia: biomass production, retention of nutrients, and heavy metals in phytomass.

Abstract The aim of this article is to evaluate and compare common cattail (Typha latifolia) biomass production and annual accumulation of nitrogen, phosphorus, carbon, and heavy metals (Cd, Cu, Pb, Zn) in phytomass in 3 treatment wetland systems in Estonia. The biomass samples (roots/rhizomes, shoots with leaves, and spadixes) and litter were collected from 1 × 1 m plots—15 plots in Tänassilma seminatural wetland, 15 plots in Põltsamaa constructed wetland, and 10 plots in Häädemeeste constructed wetland.The highest average total cattail phytomass was 2.54 kg DW m−2 in Häädemeeste. In Tänassilma and Põltsamaa this value was 2.3 and 2.11 kg DW m−2, respectively. The average total aboveground biomass production and roots/rhizomes phytomass was not significantly different in three studied wetland systems. We have found significantly less spadixes and litter in Tänassilma than in Põltsamaa and Häädemeeste. In Põltsamaa, the N and P content in all plant fractions were higher than in other test areas.The Cd concentration in all samples (shoots, spadixes, litter) varied from < 0.01 to < 0.02 mg/kg. The average concentration of Zn in litter varied from 12.2 mg kg−1 in Häädemeeste to 12.6 mg kg−1 in Tänassilma and 13.3 mg kg−1 in Põltsamaa. There has been found a significantly higher average contents of Cu (39.3 mg kg−1), Pb (30.4 mg kg−1), and Zn (412.3 mg kg−1) in Tänassilma than those in Häädemeeste or Põltsamaa: Cu—11.6 and 15.9, Pb—2.3 and 3.3, and Zn—57.5 and 73.2 mg kg−1, respectively. The highest heavy metal retention (303.2 mg Pb m−2, 29.4 mg Zn m−2, 22.9 mg Cu m−2, and 0.35 mg Cd m−2) was observed in root and rhizome samples from the Tänassilma wetland.

Isotopologue ratios of N2O and N2 measurements underpin the importance of denitrification in differently N-loaded riparian alder forests.

Known as biogeochemical hotspots in landscapes, riparian buffer zones exhibit considerable potential concerning mitigation of groundwater contaminants such as nitrate, but may in return enhance the risk for indirect N2O emission. Here we aim to assess and to compare two riparian gray alder forests in terms of gaseous N2O and N2 fluxes and dissolved N2O, N2, and NO3(-) in the near-surface groundwater. We further determine for the first time isotopologue ratios of N2O dissolved in the riparian groundwater in order to support our assumption that it mainly originated from denitrification. The study sites, both situated in Estonia, northeastern Europe, receive contrasting N loads from adjacent uphill arable land. Whereas N2O emissions were rather small at both sites, average gaseous N2-to-N2O ratios inferred from closed-chamber measurements and He-O laboratory incubations were almost four times smaller for the heavily loaded site. In contrast, groundwater parameters were less variable among sites and between landscape positions. Campaign-based average (15)N site preferences of N2O (SP) in riparian groundwater ranged between 11 and 44 ‰. Besides the strong prevalence of N2 emission over N2O fluxes and the correlation pattern between isotopologue and water quality data, this comparatively large range highlights the importance of denitrification and N2O reduction in both riparian gray alder stands.

Global Boundary Lines of N2O and CH4 Emission in Peatlands

Predicting N2O (nitrous oxide) and CH4 (methane) emissions from peatlands is challenging because of the complex coaction of biogeochemical factors. This study uses data from a global soil and gas sampling campaign. The objective is to analyse N2O and CH4 emissions in terms of peat physical and chemical conditions. Our study areas were evenly distributed across the A, C and D climates of the Koppen classification. Gas measurements using static chambers, groundwater analysis and gas and peat sampling for further laboratory analysis have been conducted in 13 regions evenly distributed across the globe. In each study area at least two study sites were established. Each site featured at least three sampling plots, three replicate chambers and corresponding soil pits and one observation well per plot. Gas emissions were measured during 2–3 days in at least three sessions. A log-log linear function limits N2O emissions in relation to soil TIN (total inorganic nitrogen). The boundary line of N2O in terms of soil temperature is semilog linear. The closest representation of the relationship between N2O and soil moisture is a local regression curve with its optimum at 60–70 %. Semilog linear upper boundaries describe the effects of soil moisture and soil temperature to CH4 best.

Nitrogen-rich organic soils under warm well-drained conditions are global nitrous oxide emission hotspots

Nitrous oxide (N2O) is a powerful greenhouse gas and the main driver of stratospheric ozone depletion. Since soils are the largest source of N2O, predicting soil response to changes in climate or land use is central to understanding and managing N2O. Here we find that N2O flux can be predicted by models incorporating soil nitrate concentration (NO3−), water content and temperature using a global field survey of N2O emissions and potential driving factors across a wide range of organic soils. N2O emissions increase with NO3− and follow a bell-shaped distribution with water content. Combining the two functions explains 72% of N2O emission from all organic soils. Above 5 mg NO3−-N kg−1, either draining wet soils or irrigating well-drained soils increases N2O emission by orders of magnitude. As soil temperature together with NO3− explains 69% of N2O emission, tropical wetlands should be a priority for N2O management.In a global field survey across a wide range of organic soils, the authors find that N2O flux can be predicted by models incorporating soil nitrate concentration (NO3–), water content and temperature. N2O emission increases with NO3– and temperature and follows a bell-shaped distribution with water content.