<p>The Philippines is one of the world’s leading producers of pineapples, wherein production is comprised mostly of small family farms that are less than 2 hectares in size. As by-product, they generate a large amount of plant residues (e.g., crowns and stems) that are commonly left at the edge of the field. This practice releases substantial amount of greenhouse gas (GHG) emissions and neglects the potential value of pineapple residue. Enabling a waste treatment by returning them to the field through incorporation or mulching holds the potential to maintain soil fertility, reduce climate impact, secure yield stability, and achieving a high resource efficiency by closing material cycles locally. It may also increase soil organic carbon stock (SOC) and reduce greenhouse gas (GHG) emissions. To date, however, the knowledge about this is still very sparse.</p><p>The rePRISING project aims to demonstrate that returning pineapple residue either through mulching or incorporation to the field may help promote the closing of nutrient-cycles (C/N/P/K) locally, thus helping to increase soil fertility and soil C sequestration, while reducing GHG emissions.<strong> </strong>Within the project, the recycling of pineapple residue together with various local organic and inorganic amendments will be studied during a two-year field experiment using the manual closed chamber method. The field study will be supplemented by pot-scale greenhouse and incubation experiments, used inter alia to determine baseline GHG emissions and carbon budgets of pineapple cultivation systems and residue treatments.</p><p>Here we present first results of a pot experiment performed during winter 2020-2021 used to develop a suitable procedure for the in-situ determination of dynamic net ecosystem C balances (NECB) for pineapple cultivation systems. This will be further utilized for upcoming field study. This is challenging in so far as pineapple plants use the Crassulacean acid metabolism (CAM photosynthesis) and the manual closed chamber method has not yet been applied to determine NECB from CAM plants.</p><p><strong>Keywords: </strong>nutrient-cycling, carbon sequestration, greenhouse gas (GHG) emissions, pineapple residue, climate change mitigation</p>

<div> <div> <div><strong>Barbara Vergara Niedermayr</strong><sup>1</sup>,Danica Antonijevic,Oscar Monzón,and Matthias Hoffmann</div> <div><span>Barbara Vergara Niedermayr et al. </span> <span><strong>Barbara Vergara Niedermayr</strong><sup>1</sup>, Danica Antonijevic, Oscar Monzón, and Matthias Hoffmann</span></div> </div> <div> <ul><li><sup>1</sup>Universität Potsdam, Potsdam, Germany (bvergaraniedermayr@gmail.com)</li> <li><sup>2</sup>Leibniz-Zentrum für Agrarlandschaftsforschung (ZALF) e.V.</li> </ul><div> <ul><li><sup>1</sup>Universität Potsdam, Potsdam, Germany (bvergaraniedermayr@gmail.com)</li> <li><sup>2</sup>Leibniz-Zentrum für Agrarlandschaftsforschung (ZALF) e.V.</li> </ul></div> </div> <div><!-- COMO-HTML-CONTENT-START --> <p>Due to the large number of small and strongly anthropogenic influenced ponds (area <1 ha; IPCC 2019) and ditches there is a substantial emission of GHG, originating globally from open water (e.g., Peacock et al. 2017, Holgerson & Raymond 2016). Within those systems, high nutrient loadings from surrounding agriculture as well as low oxygen levels yield in N<strong><sub>2</sub></strong>O and especially CH<sub>4</sub> emissions, sometimes exceeding those of small natural waterbodies many times over. The impact of land use and land use change on GHG emission regimes of these strongly anthropogenic influenced small systems is however still fairly unknown due to a lack of more broad data sets, exceeding single years and/or single case studies. The reason for this lies in the sheer variability of these systems (e.g., land use, underlying environmental conditions, hydrology, soil type, intensity of anthropogenic disturbances, etc.) as well as in the complexity to perform GHG emission measurements at a great number of locations with limited resources. The latter is even more of a problem, when considering the usually high cost-insensitivity of GHG emission measurements, as well as the persistence of an underrepresentation of data from developed or developing countries in e.g., Southeast Asia and or sub-Saharan Africa due to the long-term focus in GHG research on the northern hemisphere.</p> <h3>Here we present first results of an inexpensive, semi-automatic, do-it-yourself (DIY) floating chamber design, which can be used for in-situ measurements of CO<sub>2 </sub>and CH<sub>4</sub> emissions from ponds and ditches. The floating chamber design consists of a star-shaped floating body (“rose dich”) with a cantered PVC chamber (A: 0,194 m²; V: 0,63m³. Low-cost NDIR-Sensors were attached to the chamber, for measuring CO<sub>2</sub> (SCD30; 400-5,000 ppm, ± 50 ppm accuracy) and CH<sub>4</sub> concentrations (Figaro Gas-Sensor TGS-2611; …). Environmental conditions during chamber deployment were recorded using a DHT-22 (humidity and temperature) and a BMP280 (air pressure) sensor device. All sensors were connected to a Bluetooth enabled, battery powered, compact microcontroller-based logger unit for data visualization and storage. Measured CO<sub>2</sub> and CH<sub>4</sub> emissions from ditches and ponds obtained on three locations spread over NE Germany were validated against in parallel performed GHG flux measurements using evacuated glass bottles for air sampling and subsequent GC-14A and GC-14B analyses (Shimadzu Scientifec Instruments, Japan).</h3> <h3> </h3> <h3>First results indicate a generally good overall agreement of measured CO<sub>2</sub> and CH<sub>4</sub> emissions. Thus, the presented, semi-automatic floating chamber design might help to broaden the data basis/representativeness of GHG emission estimates of the globally relevant, small, strongly anthropogenic influenced ponds and ditches.</h3> <h3> </h3> <p>Keywords: Land use change, greenhouse gas emissions, low-cost floating chamber, semi-automatic measurements of CO<sub>2</sub> and CH<sub>4</sub>, anthropogenic pond and ditches</p></div></div>

<p>When drained for e.g. agricultural use, natural peatlands turn from a net C sink to a net C source. It is therefore suggested that restoration of peatlands, despite of increasing CH<sub>4</sub> emissions, holds the potential to mitigate climate change by reducing their overall global warming potential. The time span required for this transition, however, is fairly unknown. Moreover, greenhouse gas emission measurements from peatlands are often limited to a couple of years only. This is problematic in so far, as most peatland ecosystems are in transitional stage due to restoration related disturbances (e.g. enhanced water table) and global climate change. This might affect GHG emissions in one way or another which emphasizes the necessity of longer-term observations to avoid misinterpretations and premature conclusions.        <br>Exemplary for that, we present 14 consecutive years of CH<sub>4</sub> flux measurements following restoration at a formerly long-term drained fen grassland within the Peene river catchment (near the town of Zarnekow: 53.52⁰N, 12.52⁰E). Restoration of peatland was done by simply opening the dike. Thus, no water table management was established and water table was strongly fluctuating.  CH<sub>4</sub> flux measurements were conducted at two sites (restored vs. non-restored) using non-flow-through non-steady-state (NFT-NSS) opaque chambers.  <br>Throughout the 14 years study period, distinct stages of an ecosystems transition, differing in their impact on measured CH<sub>4</sub> emissions, were observed. During the first two years of the measurement period directly following restoration in autumn 2004, an eutrophic shallow lake was formed. This development was accompanied by a fast vegetation shift from dying off cultivated grasses to submerged hydrophytes and helophytes and evidenced substantially increased CH<sub>4</sub> emissions. Since 2008, helophytes have gradually spread from the shore line into the established shallow lake especially during drying years. This process was only periodically delayed by exceptional inundation, such as in 2011, 2012 and 2015, and finally resulted in coverage of the measurement site in 2016 and 2017. While, especially the period between 2009 and 2015 showed exceptionally high CH<sub>4</sub> emissions, these decreased significantly after helophytes were established at the measurement site. Hence, CH<sub>4</sub> emissions only decreased after ten years transition following restoration and potentially reaching a new steady state.</p>

<p>Agricultural used wetlands with high SOC stocks cover large parts of northeast (NE) Germany. Drainage and modification of groundwater levels by agricultural water management during the last century not only lead to a change in their hydrological processes but also reversed many biogeochemical processes like soil C dynamics and GHG emissions. In addition, climate projections indicate that climate change will substantially alter seasonal precipitation and temperature regimes in NE Germany with an increasing risk of severe summer droughts such as in 2018. Both might have the potential to significantly increase SOC stock losses and GHG emissions. Hence, there is an emergent importance to investigate the interconnectivity between water level, soil C dynamics, and GHG emissions.</p><p>To better understand this interconnectivity, we investigated the influence of a different GWL on dynamics of GHG emissions and the net ecosystem C balance (NECB) as a proxy for SOC stock changes. Therefore, GHG emission measurements and estimates of NECB were performed for four weighable lysimeters containing soil monoliths, which were established during 2009 in an agricultural used wetland area (Spreewald region, 51<sup>◦</sup>52’N, 14<sup>◦</sup>02’E). The study site represents an agricultural used (pasture) grassland typical for the Spreewald region. Weighable lysimeters were used to simulate two different GWL regimes: growing season dropdown of GWL due to e.g. summer drought vs. no growing season GWL dropdown. GHG emission measurements (CO<sub>2</sub> (R<sub>eco</sub> and NEE)<sub>, </sub>CH<sub>4 </sub>and N<sub>2</sub>O) were conducted campaign wise every 2 to 4 weeks from 2021 onwards, using a manual (N)FT-NSS closed chamber system (Livingston and Hutchinson 1995). In addition, environmental conditions, aboveground biomass development (e.g. plant height, RVI, NDVI) and in situ water parameters (e.g., oxygen, pH, hydrogen carbonate, el. conductivity, temperature, redox potential) were obtained.</p><p>Here we present GHG emission measurements and NECB estimates for the first study year of 2021. Higher GWL generally resulted in a lower biomass production. Consequently, clear differences between the two different GWL´s were also obtained in case of derived CO<sub>2</sub> flux components R<sub>eco</sub> and GPP as well as to a lower extend for overall NEE, with higher GWL showing an only slightly higher overall net CO<sub>2</sub> exchange. Thus, higher NECB values were detected for lower GWL. In contrast, overall GHG emissions (incl. CO<sub>2</sub>, CH<sub>4</sub> and N<sub>2</sub>O) were lower for lower compared to higher GWL.</p>