Typha latifolia paludiculture effectively improves water quality and reduces greenhouse gas emissions in rewetted peatlands

Paludiculture, the cultivation of crops on wet or rewetted agricultural peatlands, sustainably integrates productive land use with the provision of multiple ecosystem services. Paludiculture crops thrive under waterlogged conditions that stimulate nitrogen (N) and phosphorus (P) removal from soil and water and convert serious drainage-induced carbon (C) losses to C sequestration. Nutrient uptake by paludicrops can prevent mobilisation after rewetting and provide opportunities for purification of nutrient-rich water. Uncertainty remains, however, if and to what extent N loading and a subsequent increase in biomass productivity affect nutrient cycling as well as emissions of the potent greenhouse gases methane (CH4) and nitrous oxide (N2O). In this study, we use mesocosms with rewetted peat to investigate the effect of different N sources in surface water on biomass production of Typha latifolia, a typical paludiculture crop, and the emissions of CH4 and N2O. Organic (Azolla filiculoides; urea) or mineral (KNO3 ; NH4NO) N was supplied either a single time (steady state) or repeatedly (pulse) to simulate a total surface water load of 150 kg N ha(-1) . We found that N stimulated aboveground and belowground biomass production and nutrient uptake by T. latifolia. These effects were absent in Azolla treatments. Whereas after two months CH4 emissions arose to substantial amounts (> 10 mg CH4 m(-2) day(-1)) in unvegetated mesocosms loaded with organic N, they remained very low (<1 mg CH4 m(-2) day(-1)) in vegetated mesocosms, despite the labile C pool in the extensive belowground biomass and organic N loading. Overall, N2O emissions were close to zero and were only detected episodically after NO(3)(- )loading, irrespective of plant presence. Our findings support that T. latifolia as a paludicrop effectively removes various forms of N and P when harvested, and strongly mitigates CH4 emission after the rewetting of agricultural peat soils compared to unvegetated conditions

Methane dynamics in vegetated habitats in inland waters: quantification, regulation, and global significance

Freshwater ecosystems, including lakes, wetlands, and running waters, are estimated to contribute over half the natural emissions of methane (CH4) globally, yet large uncertainties remain in the inland water CH4 budget. These are related to the highly heterogeneous nature and the complex regulation of the CH4 emission pathways, which involve diffusion, ebullition, and plant-associated transport. The latter, in particular, represents a major source of uncertainty in our understanding of inland water CH4 dynamics. Many freshwater ecosystems harbor habitats colonized by submerged and emergent plants, which transport highly variable amounts of CH4 to the atmosphere but whose presence may also profoundly influence local CH4 dynamics. Yet, CH4 dynamics of vegetated habitats and their potential contribution to emission budgets of inland waters remain understudied and poorly quantified. Here we present a synthesis of literature pertaining CH4 dynamics in vegetated habitats, and we (i) provide an overview of the different ways the presence of aquatic vegetation can influence CH4 dynamics (i.e., production, oxidation, and transport) in freshwater ecosystems, (ii) summarize the methods applied to study CH4 fluxes from vegetated habitats, and (iii) summarize the existing data on CH4 fluxes associated to different types of aquatic vegetation and vegetated habitats in inland waters. Finally, we discuss the implications of CH4 fluxes associated with aquatic vegetated habitats for current estimates of aquatic CH4 emissions at the global scale. The fluxes associated to different plant types and from vegetated areas varied widely, ranging from−8.6 to over 2835.8 mg CH4 m−2 d−1, but were on average high relative to fluxes in non-vegetated habitats. We conclude that, based on average vegetation coverage and average flux intensities of plant-associated fluxes, the exclusion of these habitats in lake CH4 balances may lead to a major underestimation of global lake CH4 emissions. This synthesis highlights the need to incorporate vegetated habitats into CH4 emission budgets from natural freshwater ecosystems and further identifies understudied research aspects and relevant future research directions

Water level and vegetation type control carbon fluxes in a newly-constructed soft-sediment wetland

Wetlands support unique biodiversity and play a key role in carbon cycles, but have dramatically declined in extent worldwide. Restoration is imperative yet often challenging to counteract loss of functions. Nature-based solutions such as the creation of novel ecosystems may be an alternative restoration approach. Targeted restoration strategies that account for the effects of vegetation on greenhouse gas (GHG) fluxes can accelerate the carbon sink function of such systems. We studied the relationships between vegetation, bare soil, and GHG dynamics on Marker Wadden in the Netherlands, a newly-created 700-ha freshwater wetland archipelago created for nature and recreation. We measured CO2 and CH4 fluxes, and soil microbial activity, in three-year-old soils on vegetated, with distinct species, and adjacent bare plots. Our results show that CH4 fluxes positively related to organic matter and interacted between organic matter and water table in bare soils, while CH4 fluxes positively related to plant cover in vegetated plots. Similarly, Reco in bare plots negatively related to water table, but only related positively to plant cover in vegetated plots, without differences between vegetation types. Soil microbial activity was higher in vegetated soils than bare ones, but was unaffected by substrate type. We conclude that GHG exchange of this newly-created wetland is controlled by water table and organic matter on bare soils, but the effect of vegetation is more important yet not species-specific. Our results highlight that the soil and its microbial community are still young and no functional differentiation has taken place yet and warrants longer-term monitoring

Better assessments of greenhouse gas emissions from global fish ponds needed to adequately evaluate aquaculture footprint

While providing protein for a fast-growing human population, the ongoing boom in global aquaculture comes with environmental costs. Particularly, the intense greenhouse gas (GHG) emissions reported for several aquaculture systems are a source of concern. Still, we argue that actual emissions could be multiple times higher than currently thought. Most studies supporting existing estimates solely rely on measurements of water-atmosphere diffusive fluxes of GHG, whereas methane (CH4) and nitrous oxide (N2O) emissions during drainage and refilling and CH4 bubbles emerging from sediments are largely ignored. Yet, abundant evidence for similar aquatic ecosystems suggests that these largely unaccounted emission pathways may be responsible for a large share of annual GHG emissions. Uncertainties from overlooking important emission pathways may have serious consequences, including incorrect advice on mitigation strategies and overly optimistic assessments of the GHG footprint of cultured freshwater fish. To ensure a low-carbon future for global aquaculture, we contend that GHG assessments in fish-farming ponds must extend beyond the focus on diffusive water-atmosphere fluxes and include all emission pathways and possible carbon burial in the sediment. In parallel, we call for a better understanding of the biological, microbiological and physical drivers of aquaculture emissions to effectively support mitigation strategies to minimize the footprint of this nutritionally valuable protein source. (C) 2020 Elsevier B.V. All rights reserved

Removing 10 cm of degraded peat mitigates unwanted effects of peatland rewetting: a mesocosm study

Topsoil removal (TSR) is a management option performed before rewetting drained agricultural peatlands to reduce greenhouse gas (GHG) emissions and remove nutrients. Currently, its common practice to remove 30 to 60 cm of topsoil, which is labor-intensive, costly, and highly disruptive. However, optimal TSR depth for mitigating carbon emissions from rewetted peat soils has neither been determined nor linked to soil biogeochemical factors driving carbon emissions. We performed two mesocosm experiments to address this. In experiment 1, we removed the topsoil of two contrasting drained peat soils before rewetting (i.e., extensively managed, acid peat and intensively managed, near-neutral peat) with a 5 cm interval up to 25 cm TSR. In experiment 2, we combined TSR with the presence and absence of Typha latifolia on intensively managed, near-neutral peat soil. The experiments ran for 22 and three months, respectively, in which we measured carbon dioxide (CO2) and methane (CH4) emissions and porewater chemistry. Our experiments reveal that (i) 5 cm TSR greatly reduced CH4 and CO2 emissions irrespective of peat nutrient status during the 22-month experiment, and (ii) the presence of T. latifolia further reduced CH4 emissions during the 3-month experiment. Specifically, CH4 emissions were six to 10-times lower with 5 cm TSR compared to 0 cm TSR. Peak CH4 emissions occurred after three months with 0 cm TSR and strongly decreased thereafter. Random forest analyses highlighted that variation in CH4 emissions could mainly be explained by cumulative root biomass and porewater alkalinity. Furthermore, 5 cm TSR reduced porewater values of pH, alkalinity, CH4, and ammonium. The effectiveness of TSR in preventing the build-up of phosphorus, iron, and sulfur in porewater was site-specific. Our results show that only 5 to 10 cm TSR may already effectively prevent the adverse effects of rewetting former agriculturally peatlands by reducing undesirable CH4 emissions and avoiding nutrient release. Further, we argue that target setting and site-specific assessments are crucial to optimize the amount of TSR to reduce carbon emissions while minimizing disturbance and costs

Data_Sheet_1_Widespread dominance of methane ebullition over diffusion in freshwater aquaculture ponds.docx

An ever-increasing demand for protein-rich food sources combined with dwindling wild fish stocks has caused the aquaculture sector to boom in the last two decades. Although fishponds are potentially strong emitters of the greenhouse gas methane (CH4), little is known about the magnitude, pathways, and drivers of these emissions. We measured diffusive CH4 emissions at the margin and in the center of 52 freshwater fishponds in Brazil. In a subset of ponds (n = 31) we additionally quantified ebullitive CH4 fluxes and sampled water and sediment for biogeochemical analyses. Sediments (n = 20) were incubated to quantify potential CH4 production. Ebullitive CH4 emissions ranged between 0 and 477 mg m−2 d−1 and contributed substantially (median 85%) to total CH4 emissions, surpassing diffusive emissions in 81% of ponds. Diffusive CH4 emissions were higher in the center (median 11.4 mg CH4 m−2 d−1) than at the margin (median 6.1 mg CH4 m−2 d−1) in 90% of ponds. Sediment CH4 production ranged between 0 and 3.17 mg CH4 g C−1 d−1. We found no relation between sediment CH4 production and in situ emissions. Our findings suggest that dominance of CH4 ebullition over diffusion is widespread across aquaculture ponds. Management practices to minimize the carbon footprint of aquaculture production should focus on reducing sediment accumulation and CH4 ebullition.</p

Removing 10 cm of degraded peat mitigates unwanted effects of peatland rewetting: a mesocosm study

This data file is part of the scientific article that demonstrates that 5 to 10 cm of topsoil removal (TSR) may already reduce undesirable methane emissions and nutrient release of rewetting former agricultural peatlands. The two experiments ran at Radboud University facilities using peat soil cores from two sites in the Netherlands. This file includes (see codebook below for details) data obtained during the two experiments