The trapping of organic matter within plant patches in the channels of the Okavango Delta: a matter of quality

Schoelynck, Jonas; Schaller, Jörg; Murray-Hudson, Mike; Frings, Patrick J.; Conley, Daniel J.; Pelt, Dimitri van; Mosimane, Keotshephile; Gondwe, Mangaliso J.; Wolski, Piotr; Meire, Patrick; Struyf, Eric

doi:10.1007/s00027-017-0527-2

Cited by 8 publications

(10 citation statements)

References 61 publications

(53 reference statements)

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“…BSi accumulation in vegetation varied per lagoon and was dependent on plant species dominance [see Prychid et al (2003) and Hodson et al (2005) for BSi contents in plants related to their phylogenetic position]. The BSi stock in macrophytes ranged from 0.054 to 0.288 t BSi ha −1 , which is situated between values reported for submerged macrophytes in the Okavango Delta channels (0.008 t BSi ha −1 ; Schoelynck et al, 2017) and values reported for emergent wetland vegetation in the Okavango Delta (ranging from 0.010 to 1.600 t BSi ha −1 ; Struyf et al, 2015). The highest BSi concentrations were found in macrophytes collected from Kodjoboue lagoon and were related to the dominance of emergent species (A. zizanioides, B.…”

Section: The Role Of Macrophytes and Diatoms In Lagoon Bsi Storagementioning

confidence: 98%

“…The carbon occluded in the phytoliths of wetland plant species potentially even forms an important sink to consider in the carbon cycle (Li et al, 2013). Exemplary to this is the strong (permanent) silica sink in the Okavango Delta sediments (Botswana) that can be associated with a dominance of silica-rich tropical giant-grasses such as Cyperus papyrus L. (Struyf et al, 2015;Mosimane et al, 2017;Schoelynck et al, 2017). BSi accumulation in macrophytes, and thus potentially in sediments, varies strongly between species.…”

Section: Introductionmentioning

confidence: 99%

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The Role of Macrophytes in Biogenic Silica Storage in Ivory Coast Lagoons

2019

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Lagoons are shallow aquatic environments that typically show a broad variety in colonization by macrophytes. We present the biogenic silica (BSi) data obtained from 11 macrophyte species randomly collected in three small lagoons (Ono, Kodjoboue, and Hebe) of Ivory Coast during 12 consecutive months. BSi concentrations were different between species and between lagoons with average values ranging from 2 to 36 mg g −1 .The highest values were found in Hebe and Kodjoboue lagoons due to the dominance of emergent plant species belonging to Poaceae and Cyperaceae families. However, because total plant coverage was low (5% of the lagoon surface), the total BSi stock in vegetation was low (0.2 and 6.1 t, respectively). Oppositely, lower BSi concentrations were found in plants from Ono lagoon, yet the abundance of macrophytes covered 66% of its surface area which resulted in a larger vegetation BSi stock (17.4 t). Dissolved silica in surface water varied seasonally between 1.7 and 10.8 mg L −1 , and variation is assumed to be linked to diatom blooms rather than to macrophyte uptake. Sediment data showed that the three lagoons store a large quantity of BSi in their sediments with values ranging from 2 to 8 t BSi ha −1 . Because of macrophyte influence in these lagoons, macrophyte phytoliths were expected to contribute significantly to this sediment BSi stock. However, microscopic analysis revealed that this stock is absolutely dominated by diatom frustules and sponge spicules rather than plant phytoliths. We conclude that macrophytes in these lagoons contribute only marginally to BSi storage in sediments but that fragile phytogenic silica structures may affect local silica cycling.

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Section: The Role Of Macrophytes and Diatoms In Lagoon Bsi Storagementioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

The Role of Macrophytes in Biogenic Silica Storage in Ivory Coast Lagoons

2019

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“…Tussocks of wetland sedges efficiently retain biogenic silica, giving them a competitive advantage (Opdekamp et al, 2012). In the Okavango delta, aquatic macrophytes accumulate and concentrate organic matter in sediments below patches, allowing high productivity in an otherwise oligotrophic environment (Schoelynck et al, 2017). Liu et al (2017) also found this 'soil island' effect around isolated and clustered tamarisk (Tamarix chinensis Lour.)…”

Section: Solutesmentioning

confidence: 99%

Biophysical Interactions in Fragmented Marine Canopies: Fundamental Processes, Consequences, and Upscaling

Folkard

2019

Front. Mar. Sci.

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Spatial fragmentation is a near-ubiquitous characteristic of marine canopies. Biophysical interactions with fragmented canopies are multi-faceted and have many significant implications at multiple scales. The aims of this paper are to review research on biophysical interactions in fragmented marine canopies, identify current gaps in knowledge and understanding, and propose ways forward. The review starts at the patch/gap scale and focuses initially on hydrodynamic interactions. It then considers the consequences of these interactions for particulate and dissolved material, and distributions of canopy-associated organisms. Finally, it addresses issues of upscaling to landscape-scale and ways in which this research can be applied to marine landscape management. Work on a broad range of canopy types is considered, including micro-algal biofilms and turf algae; macro-algae, seagrasses and coral reefs; saltmarsh vegetation and mangroves. Although the focus is on marine canopies, insights from studies of fragmented canopies in other contexts are drawn on where relevant. These include freshwater environments and terrestrial forests, grasslands, crop canopies, and urban areas. Specific areas requiring greater attention are highlighted. As a result of this meta-analysis, the following recommendations are made for further research. A lack of basic data is identified across all canopy types regarding the formation, fate and spatial and temporal characteristics of canopy patches, gaps, and spatial structure. Studies of hydrodynamics with fragmented canopies would benefit from shifting focus toward more non-uniform, realistic configurations, while ecological research in this area would benefit from a move toward configurations that are more controlled and tractable for quantitative modeling. More comparative studies across canopy types would enable understanding of their biophysical interactions and their consequences to be more fully tested and developed. A greater incorporation of chemical aspects of canopy systems into work that has hitherto focused on biophysical interactions would also be pertinent. Upscaling of patch and gap-scale phenomena to landscape-scale is identified as a crucial topic, since it is at the latter scale that management efforts are most readily carried out. Overall, an approach that balances hydrodynamics, marine canopy ecology, spatial analysis of landscapes, biogeochemistry, and socio-environmental interactions is recommended.

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“…Rooted macrophytes act as "ecosystem engineers" for N removal (Jones, Lawton, & Shachak, 1994;Vila-Costa et al, 2016) by influencing denitrification in several ways: for example, by (i) increasing organic matter accumulation (i.e. root exudates, decaying plant biomass, trapped suspended material), thus providing labile organic carbon whose mineralization promotes anoxic conditions (Hang et al, 2016;Schoelynck et al, 2017;Taylor, Moore, & Scott, 2015); (ii) releasing oxygen in the rhizosphere and establishing oxic−anoxic interfaces where the coupling of aerobic and anaerobic processes (such as organic N mineralization, nitrification, and denitrification) occurs (Rehman, Pervez, Khattak, & Ahmad, 2017;Soana et al, 2015); and (iii) promoting microbial population growth and diversity through the provision of submerged surfaces (e.g., stems and leaves) available for colonization (Soana, Gavioli, et al, 2018;Toet, Huibers, Van Logtestijn, & Verhoeven, 2003). Denitrification results in permanent removal of bioavailable N. Thus, assessing this process is a pivotal scientific and management task for decreasing eutrophication of aquatic ecosystems in human-impacted watersheds.…”

Section: Introductionmentioning

confidence: 99%

Nitrate availability affects denitrification in Phragmites australis sediments

et al. 2020

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Understanding relationships between an increase in nitrate (NO3−) loading and the corresponding effects of wetland vegetation on denitrification is essential to designing, restoring, and managing wetlands and canals to maximize their effectiveness as buffers against eutrophication. Although Phragmites australis (Cav.) Trin. ex Steud. is frequently used to remediate nitrogen (N) pollution, no information is available on how NO3− concentration may affect plant‐mediated denitrification. In the present study, denitrification was measured in outdoor vegetated and unvegetated mesocosms incubated in both summer and winter. After spiking the mesocosms with NO3− concentrations typical of agricultural drainage water (0.7−11.2 mg N L−1), denitrification was quantified by the simultaneous measurement of NO3− consumption and dinitrogen gas (N2) production. Although denitrification rates varied with vegetation presence and season, NO3− availability exerted a significant positive effect on the process. Vegetated sediments were more efficient than bare sediments in adapting their mitigation potential to an increase in NO3−, by yielding a one‐order‐of‐magnitude increase in NO3− removal rates, under both summer (743−6007 mg N m−2 d−1) and winter (43−302 mg N m−2 d−1) conditions along the NO3− gradient. Denitrification was the dominant sink for water NO3− in winter and only for vegetated sediments in summer. Nitrification likely contributed to fuel denitrification in summer unvegetated sediments. Since denitrification rates followed Michaelis–Menten kinetics, P. australis‐mediated depuration may be considered optimal up to 5.0 mg N L−1. The present outcomes provide experimentally supported evidence that restoration with P. australis can work as a cost‐effective means of improving water quality in agricultural watersheds.

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The trapping of organic matter within plant patches in the channels of the Okavango Delta: a matter of quality

Cited by 8 publications

References 61 publications

The Role of Macrophytes in Biogenic Silica Storage in Ivory Coast Lagoons

The Role of Macrophytes in Biogenic Silica Storage in Ivory Coast Lagoons

Biophysical Interactions in Fragmented Marine Canopies: Fundamental Processes, Consequences, and Upscaling

Nitrate availability affects denitrification in Phragmites australis sediments

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