Field Quantification of Ammonia Emission following Fertilization of Golf Course Turfgrass in Sub/Urban Areas

Low cost and favorable handling characteristics make urea (46-0-0) a leading nitrogen source for frequent, foliar N fertilization of golf course putting greens in season. Yet few field investigations of resulting NH3 volatilization from putting greens have been directed. Meanwhile, NH3 emissions degrade air and surface water quality. Our objective was to quantify NH3 volatilization following practical, low-N rate, and foliar application of commercial urea-N fertilizers. Over the 2019 and 2020 growing seasons in University Park, PA, USA, an industrial vacuum pump, H3BO3 scrubbing flasks, and sixteen dynamic flux chambers were employed in four unique experiments to measure NH3 volatilization from creeping bentgrass putting greens (Agrostis stolonifera L. ‘Penn G2’) in the 24 h period ensuing foliar application of urea based-N at a 7.32 or 9.76 kg/ha rate. Simultaneous and replicated flux chamber trapping efficiency trials showing 35% mean NH3 recovery were used to adjust NH3 volatilization rates from treated plots. Under the duration and conditions described, 3.1 to 8.0% of conventional urea N volatilized from the putting greens as NH3. Conversely, 0.7 to 1.1% of methylol urea liquid fertilizer (60% short-chain methylene urea) or 0.7 to 2.2% of urea complimented with dicyandiamide (DCD) and N-(n-butyl) thiophosphoric triamide (NBPT) volatilized as NH3.

Gaseous Elemental Mercury Exchange Fluxes over Air-Soil Interfaces in the Degraded Grasslands of Northeastern China

Mercury (Hg) is a global pollutant that may potentially have serious impacts on human health and ecologies. The gaseous elemental mercury (GEM) exchanges between terrestrial surfaces and the atmosphere play important roles in the global Hg cycle. This study investigated GEM exchange fluxes over two land cover types (including Artemisia anethifolia coverage and removal and bare soil) using a dynamic flux chamber attached to the LumexR RA915+ Hg analyzer during the growing season from May to September of 2018, in which the interactive effects of plant coverage and meteorological conditions were highlighted. The daily mean ambient levels of GEM and the total mercury concentrations of the soil (TSM) were determined to be 12.4 ± 3.6 to 16.4 ± 5.6 ng·m−3 and 32.8 to 36.2 ng·g−1, respectively, for all the measurements from May to September. The GEM exchange fluxes (ng·m−2·h−1) during the five-month period for the three treatments included the net emissions from the soil to the atmosphere (mean 5.4 to 7.1; range of −27.0 to 47.3), which varied diurnally, with releases occurring during the daytime hours and depositions occurring during the nighttime hours. Significant differences were observed in the fluxes between the vegetation coverage and removal during the growing months (p < 0.05). In addition, it was determined that the Hg fluxes were positively correlated with the solar radiation and air/soil temperature levels and negatively correlated with the air relative humidity and soil moisture under all the conditions (p < 0.05). Overall, the results obtained in this study demonstrated that the grassland soil served as both a source and a sink for atmospheric Hg, depending on the season and meteorological factors. Furthermore, the plants played an important inhibiting role in the Hg exchanges between the soil and the atmosphere.

Assessing the spatial and temporal variability of GHG emissions from different configurations of on-site wastewater treatment system using discrete and continuous gas flux measurement

Global emissions linked to wastewater treatment are estimated to account for up to 1.5 % of total greenhouse gas (GHG) emissions globally. However, few studies have measured GHG emissions from domestic on-site treatment systems (DWWTSs) directly. In this study, two DWWTSs were monitored for 446 days and > 42,000 gas flux measurements were conducted using both discrete spot measurements and continuous flux chamber deployments. The observed GHG fluxes from biological activity in the soil and water phase were found to be highly spatially and temporally variable and correlated to environmental factors, water usage patterns and system design. In total, the results show that a septic tank discharging effluent into a well-designed soil treatment unit is estimated to emit a net 9.99 kg-CO2eq cap−1 yr−1, with approximately 63 %, 27 % and 10 % of the total CO2-equivalent net emissions in the form of CO2, CH4 and N2O, respectively. Emissions from the septic tank surface contributed over 50 % of total emissions and tended to be strongly underestimated by one-off discrete measurements, especially when episodic ebullitive events are to be considered. Fluxes from the soil treatment unit (STU) stemmed from both the soil surface and the vent system, but were also found to be periodically negative, i.e. net uptakes. Soil fluxes were mostly influenced by temperature but peaked regularly under conditions of rapidly changing soil water content. Vent fluxes were mostly governed by effluent quality and a low number of high emission events was responsible for the majority of total observed vent emissions. Owing to the strong overall spatial and temporal heterogeneity of observed fluxes from DWWTSs across all modules, future studies should focus on continuous deployments of a number of flux chambers over discrete measurements to accurately assess GHG emissions from on-site systems. This study also provided insights into managing GHG emissions from DWWTSs by different system configuration design, as well as indicating that the current IPCC emission factors for CH4 and N2O are significantly overestimating emissions for on-site wastewater treatment systems.

High-Resolution Spatio-Temporal Estimation of Net Ecosystem Exchange in Ice-Wedge Polygon Tundra Using In Situ Sensors and Remote Sensing Data

Land-atmosphere carbon exchange is known to be extremely heterogeneous in arctic ice-wedge polygonal tundra regions. In this study, a Kalman filter-based method was developed to estimate the spatio-temporal dynamics of daytime average net ecosystem exchange (NEEday) at 0.5-m resolution over a 550 m by 700 m study site. We integrated multi-scale, multi-type datasets, including normalized difference vegetation indices (NDVIs) obtained from a novel automated mobile sensor system (or tram system) and a greenness index map obtained from airborne imagery. We took advantage of the significant correlations between NDVI and NEEday identified based on flux chamber measurements. The weighted average of the estimated NEEday within the flux-tower footprint agreed with the flux tower data in term of its seasonal dynamics. We then evaluated the spatial variability of the growing season average NEEday, as a function of polygon geomorphic classes; i.e., the combination of polygon types—which are known to present different degradation stages associated with permafrost thaw—and microtopographic features (i.e., troughs, centers and rims). Our study suggests the importance of considering microtopographic features and their spatial coverage in computing spatially aggregated carbon exchange.

The role of termite CH₄ emissions on the ecosystem scale: a case study in the Amazon rainforest

The magnitude of termite methane (CH4) emissions is still an uncertain part of the global CH4 budget and current emission estimates are based on limited field studies. We present in situ CH4 emission measurements of termite mounds and termite mound subsamples performed in the Amazon rainforest. Emissions from five termite mounds of the species Neocapritermes brasiliensis were measured by use of a large flux chamber connected to a portable gas analyser measuring CH4 and CO2. In addition, the emissions of mound subsamples were measured, after which the termites were counted so that a termite CH4 and CO2 emission factor could be determined. Mound emissions were found to range between 17.0 and 34.8 nmol mound−1 s−1 for CH4 and between 1.1 and 13.0 µmol mound−1 s−1 for CO2. A termite emission factor of 0.35 µmol CH4 gtermite-1 h−1 was found, which is almost twice as high as the only other reported value for the Amazon. By combining mound emission measurements with the termite emission factor, colony sizes could be estimated, which were found to range between 55–125 thousand individuals. Estimates were similar to literature values, and we therefore propose that this method can be used as a quick non-intrusive method to estimate termite colony size in the field. The role of termites in the ecosystem's CH4 budget was evaluated by use of two approaches. Termite mound emission values were combined with local mound density numbers, leading to an estimate of 0.15–0.71 nmol CH4 m−2 s−1, on average, emitted by termite mounds. In addition, the termite CH4 emission factor from this study was combined with termite biomass numbers, resulting in an estimate of termite-emitted CH4 of ∼1.0 nmol m−2 s−1. Considering the relatively low net CH4 emissions previously measured at this ecosystem, we expect that termites play an important role in the CH4 budget of this terra firme ecosystem.

Innovative approach for new estimation of NOx snow-source on the Antarctic Plateau

&lt;p&gt;Previous Antarctic summer campaigns have shown unexpectedly high levels of oxidants in the continental interior as well as at coastal regions, with atmospheric hydroxyl radical (OH) concentrations up to 4 x 10&lt;sup&gt;6&lt;/sup&gt; cm&lt;sup&gt;-3&lt;/sup&gt;. It is now well established that such high reactivity of the summer Antarctic boundary layer results in part from the emissions of nitrogen oxides (NO&lt;sub&gt;x&lt;/sub&gt; &amp;#8801; NO + NO&lt;sub&gt;2&lt;/sub&gt;) produced during the photo-denitrification of the snowpack. Despite the numerous observations collected at various sites during previous campaigns such as ISCAT 1998, 2000, ANTCI, NITE-DC and OPALE, a robust quantification of the NO&lt;sub&gt;x&lt;/sub&gt; emissions on a continental scale over Antarctica is still lacking. Only NO emissions were measured during ISCAT and the ratio NO&lt;sub&gt;2&lt;/sub&gt;:NO was measured during NITE-DC and OPALE using indirect NO&lt;sub&gt;2&lt;/sub&gt; measurements. This leaves significant uncertainties on the snow-air-radiation interaction. To overcome this crucial lack of information, direct NO&lt;sub&gt;2&lt;/sub&gt; measurements are needed to estimate the NO&lt;sub&gt;x&lt;/sub&gt; flux emissions with reduced uncertainties.&lt;/p&gt;&lt;p&gt;For the first time, new developed optical instruments based on the IBB-CEAS technique and allowing direct measurement of NO&lt;sub&gt;2&lt;/sub&gt; with detection limit of 10 x 10&lt;sup&gt;-12&lt;/sup&gt; mol mol&lt;sup&gt;-1&lt;/sup&gt;, (1&amp;#963;), (Barbero et al., 2020) were deployed on the field during the 2019&amp;#8211;2020 summer campaign at Dome C (75&amp;#176;06'S, 123&amp;#176;20'E, 3233m a.s.l). They were coupled with new designed dynamic flux chamber experiments. Snows of different ages ranging from newly formed drift snow to 16-20 year-old firn were sampled. Unexpectedly, the same daily average photolysis constant rate of (2.18 &amp;#177; 0.38) x 10&lt;sup&gt;-8&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt; (1&amp;#963;) was estimated for the different type of snow samples, suggesting that the photolabile nitrate behaves as a single-family source with common photochemical properties. Daily summer NO&lt;sub&gt;x&lt;/sub&gt; fluxes were estimated to be (4.4 &amp;#177; 2.3) x 10&lt;sup&gt;7&lt;/sup&gt; molec cm&lt;sup&gt;-2&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt;, 10 to 70 times less than what has been estimated in previous studies at Dome C and with uncertainties reduced by a factor up to 30. Using these results, we extrapolated an annual continental snow source NO&lt;sub&gt;x&lt;/sub&gt; budget of 0.025 &amp;#177; 0.013 Tg.N y&lt;sup&gt;-1&lt;/sup&gt;, more than three times the N-budget of the stratospheric denitrification estimated to be 0.008 &amp;#177; 0.003 Tg.N y&lt;sup&gt;-1&lt;/sup&gt; for Antarctica (Savarino et al., 2007), making the snowpack source a rather significant source in Antarctica. This innovative approach for the parameterization of nitrate photolysis using flux chamber experiments could &amp;#160;significantly improve future global atmospheric models.&lt;/p&gt;

Complete Enclosure of Stunted Trees to Study Greenhouse Gas Fluxes in Birch-Invaded Peatland

&lt;p&gt;Ombrotrophic, naturally open peatlands are increasingly susceptible to invasion by scrub and trees due to human disturbance, N deposition and climate change. There is limited research on the effect these trees have on ecosystem functions and their removal can be costly, making decisions over best management practice challenging. The adverse growing conditions associated with many of these peatlands can result in stunted tree growth meaning that complete enclosure of a tree remains a practical possibility. In this study we aim to quantify the CH&lt;sub&gt;4&lt;/sub&gt; and CO&lt;sub&gt;2&lt;/sub&gt; fluxes from whole trees growing on a disturbed peatland and assess their significance relative to the fluxes between the vegetated peat surface and atmosphere. We also aim to identify if the establishment of trees impacts CH&lt;sub&gt;4&lt;/sub&gt; and CO&lt;sub&gt;2&lt;/sub&gt; fluxes from the vegetated peat surface, as compared to adjacent uninvaded peatland.&lt;/p&gt;&lt;p&gt;We have developed a removable chamber capable of enclosing whole trees of up to 3 metres high, making it suitable for use on juvenile or stunted trees. Being able to enclose an entire tree removes potential errors caused by estimating whole tree fluxes by upscaling measurements from a subsample of tree surfaces. The chamber is constructed with a transparent membrane and removable cover so that light and dark measurements can be taken. We use the chamber to take CH&lt;sub&gt;4&lt;/sub&gt; and CO&lt;sub&gt;2&lt;/sub&gt; flux measurements on a site with approximately 20-year-old silver birch trees (Betula pendula) of an average height of 2-3 metres. Flux measurements have been taken from the trees and ground collars at different times of year. We have also studied diurnal variation.&lt;/p&gt;&lt;p&gt;Our initial results have shown that the trees on our site are emitters of CH&lt;sub&gt;4&lt;/sub&gt;, although this emission is small in comparison to that produced by the rest of the habitat. The vegetated peat surface in the wooded area had lower CH&lt;sub&gt;4&lt;/sub&gt; emission but reduced CO&lt;sub&gt;2&lt;/sub&gt; uptake as compared to the open area. The diurnal study on one tree indicates that methane emissions increase at night. A further diurnal study is planned to explore this further. This study extends the limit on the size of vegetation that can be sampled by a manually operated flux chamber.&lt;/p&gt;

Tropical forest CH4: from termite mounds to tower measurements

&lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;p&gt;Methane (CH&lt;sub&gt;4&lt;/sub&gt;) is one of the most important anthropogenic greenhouse gases.&amp;#160; Despite its importance, natural sources of methane, such as tropical wetlands and termites, are still not well understood and a large source of uncertainty in the tropical CH&lt;sub&gt;4&lt;/sub&gt; budget. The Amazon rainforest is a key region for the (global) CH&lt;sub&gt;4&lt;/sub&gt; budget but, due to its remote location, continous CH&lt;sub&gt;4&lt;/sub&gt; concentration and flux measurements are still rare.&lt;/p&gt; &lt;p&gt;The 50 m high K34 tower (field site ZF2) is located in a pristine &amp;#8216;Terra Firme&amp;#8217; tropical forest region 60 km northwest of Manaus (Brazil), and is located next to a waterlogged valley, a possible location for anaerobic CH&lt;sub&gt;4&lt;/sub&gt; production. In October 2018, in addition to the existing EC CO&lt;sub&gt;2&lt;/sub&gt; system, an in-situ FTIR-analyzer (measuring CO&lt;sub&gt;2&lt;/sub&gt;, CO, CH&lt;sub&gt;4&lt;/sub&gt;, N&lt;sub&gt;2&lt;/sub&gt;O and &amp;#948;&lt;sup&gt;13&lt;/sup&gt;CO&lt;sub&gt;2&lt;/sub&gt;) was set up to measure tower profile concentrations, above and below the canopy, continuously. By analyses of vertical and temporal nighttime concentrations patterns, an emission estimate for all gases could be made, and an ecosystem emission of ~1 nmol CH&lt;sub&gt;4&lt;/sub&gt; m&lt;sup&gt;-2&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt;&amp;#160; was estimated. In addition, by use of different types of flux chambers, possible&amp;#160; CH&lt;sub&gt;4&lt;/sub&gt; sinks and sources such as soils, trees, water and termite mounds were measured.&lt;/p&gt; &lt;p&gt;By combining tower and flux chamber measurements, the role and magnitude of different ecosystem sources could be assessed. In this presentation, an overview of the measured CH&lt;sub&gt;4&lt;/sub&gt; forest concentrations and fluxes will be given.&lt;/p&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt;