Controlling the nitrogen environment for optimal Rhodomonas salina production

The microalga Rhodomonas salina is a widely used species for rearing live feed organisms in the aquaculture feed market. A species-specific medium is an essential step towards enhancing productivity and decreasing production costs for microalgae cultivation. However, relevant aspects of medium composition such as nitrogen source and elemental ratio have not yet been characterized for this alga. This study aimed to optimize the following three aspects of culture media: 1) optimal ratio between nitrogen and phosphorus (N:P ratio); 2) preferred source of nitrogen; and 3) tolerance of R. salina towards free ammonia. To investigate this, we conducted a series of controlled laboratory experiments in shake flasks. Our experiments revealed a 45% increase in growth rate when an N:P ratio of 15:1 was used compared to the standard ratio of 25:1. Ammonium and nitrate were equally well accepted as a nitrogen source, however, a mix of ammonium and nitrate resulted in significant growth reduction. Free ammonia did not affect growth of the alga at the tested concentrations of up to 5 mg ammonia–nitrogen L−1. We conclude that for optimal R. salina cultivation, an N:P ratio of 15:1 is strongly preferred, as it leads to a significant increase in growth rate. Further, media with a single source of nitrogen promote faster growth over media with mixed sources, and ammonium may safely be used as a nitrogen source, since R. salina tolerates certain levels of free ammonia. Overall, this work provides insights into the optimal cultivation conditions for R. salina, allowing for more efficient and reliable production of this relevant species

Elevated micro-topography boosts growth rates in <i>Salicornia procumbens</i> by amplifying a tidally driven oxygen pump:Implications for natural recruitment and restoration

• Background and Aims: The growth rate of pioneer species is known to be a critical component determining recruitment success of marsh seedlings on tidal flats. By accelerating growth, recruits can reach a larger size at an earlier date, which reduces the length of the disturbance-free window required for successful establishment. Therefore, the pursuit of natural mechanisms that accelerate growth rates at a local scale may lead to a better understanding of the circumstances under which new establishment occurs, and may suggest new insights with which to perform restoration. This study explores how and why changes in local sediment elevation modify the growth rate of recruiting salt marsh pioneers. • Methods: A mesocosm experiment was designed in which the annual salt marsh pioneer Salicornia procumbens was grown over a series of raised, flat and lowered sediment surfaces, under a variety of tidal inundation regimes and in vertically draining or un-draining sediment. Additional physical tests quantified the effects of these treatments on sediment water-logging and oxygen dynamics, including the use of a planar optode experiment. • Key Results: In this study, the elevation of sediment micro-topography by 2 cm was the overwhelming driver of plant growth rates. Seedlings grew on average 25 % faster on raised surfaces, which represented a significant increase when compared to other groups. Changes in growth aligned well with the amplifying effect of raised sediment beds on a tidally episodic oxygenation process wherein sediment pore spaces were refreshed by oxygen-rich water at the onset of high tide. • Conclusions: Overall, the present study suggests this tidally driven oxygen pump as an explanation for commonly observed natural patterns in salt marsh recruitment near drainage channels and atop raised sediment mounds and reveals a promising way forward to promote the establishment of pioneers in the field

Post-fire peatland recovery by peat moss inoculation depends on water table depth

Peatland restoration is essential to preserve biodiversity and carbon stored in peat soils. Common restoration techniques such as rewetting do not always result in the full recovery of peatland taxonomic and functional properties, threatening the resilience of restored peatlands and their carbon stores. Here, we study the use of peat moss inoculation in stimulating the short-term taxonomic and functional recovery of a wildfire-impacted peatland using mesocosms at high and low water table depth, representing ideal and adverse hydrological conditions respectively. Inoculation in conjunction with high water tables accelerated the recovery of the vascular plant and prokaryote communities. Importantly, Sphagnum—the keystone genus in these peatlands—only established in inoculated mesocosms. Together, this resulted in an increased CO2 uptake by approximately 17 g m−2 day−1 and reduced overall nutrient content in the peat pore water. Synthesis and applications. Our results indicate that inoculation can be used to accelerate the establishment of peatland-specific species. In addition, they suggest the potential to combine peat moss inoculation and hydrological restoration to accelerate the uptake of carbon back into the system post-fire. This offers a basis for future work exploring the long-term use of inoculation to return disturbed peatlands to their pre-degraded state, and a wider application of soil inoculation as a mechanism for functional recovery

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

Recovering wetland biogeomorphic feedbacks to restore the world's biotic carbon hotspots

Biogeomorphic wetlands cover 1% of Earth's surface but store 20% of ecosystem organic carbon. This disproportional share is fueled by high carbon sequestration rates and effective storage in peatlands, mangroves, salt marshes, and seagrass meadows, which greatly exceed those of oceanic and forest ecosystems. Here, we review how feedbacks between geomorphology and landscape-building vegetation underlie these qualities and how feedback disruption can switch wetlands from carbon sinks into sources. Currently, human activities are driving rapid declines in the area of major carbon-storing wetlands (1% annually). Our findings highlight the urgency to stop through conservation ongoing losses and to reestablish landscape-forming feedbacks through restoration innovations that recover the role of biogeomorphic wetlands as the world's biotic carbon hotspots

Self-facilitation and negative species interactions could drive microscale vegetation mosaic in a floating fen

Aim: The formation of a local vegetation mosaic may be attributed to local variation in abiotic environmental conditions. Recent research, however, indicates that self-facilitating organisms and negative species interactions may be a driving factor. In this study, we explore whether heterogeneous geohydrological conditions or vegetation feedbacks and interactions could be responsible for a vegetation mosaic of rich and poor fen species. Location: Lake Aturtaun, Roundstone Bog, Ireland. Methods: In a floating fen, transects were set out to analyze the relation between vegetation type and rock–peat distance and porewater electrical conductivity. Furthermore, three distinct vegetation types were studied: rich fen, poor fen and patches of poor fen within rich fen vegetation. Biogeochemical measurements were conducted in a vertical profile to distinguish abiotic conditions of distinct vegetation types. Results: Geohydrological conditions may drive the distribution of poor and rich fen species at a larger scale in the floating fen, due to the supply of minerotrophic groundwater. Interestingly, both rich and poor fen vegetation occurred in a mosaic, when electrical conductivity values at 50 cm depth were between 300 µS/cm and 450 µS/cm. Although environmental conditions were homogeneous at 50 cm, they differed markedly between rich and poor fen vegetation at 10 cm depth. Specifically, our measurements indicate that poor fen vegetation lowered porewater alkalinity, bicarbonate concentrations and pH. No effects of rich fen vegetation at 10 cm depth on biogeochemistry was measured. However, rich fen litter had a higher mineralization rate than poor fen litter, which increases the influence of minerotrophic water in rich fen habitat. Conclusions: These results strengthen our hypothesis that species can drive formation of vegetation mosaics under environmentally homogeneous conditions in a floating fen. Positive intraspecific self-facilitating mechanisms and negative species interactions could be responsible for a stable coexistence of species, even leading to local ecosystem engineering by the species, explaining the local vegetation mosaic at the microscale level in a floating fen

Wetscapes : Restoring and maintaining peatland landscapes for sustainable futures

Peatlands are among the world's most carbon-dense ecosystems and hotspots of carbon storage. Although peatland drainage causes strong carbon emissions, land subsidence, fires and biodiversity loss, drainage-based agriculture and forestry on peatland is still expanding on a global scale. To maintain and restore their vital carbon sequestration and storage function and to reach the goals of the Paris Agreement, rewetting and restoration of all drained and degraded peatlands is urgently required. However, socio-economic conditions and hydrological constraints hitherto prevent rewetting and restoration on large scale, which calls for rethinking landscape use. We here argue that creating integrated wetscapes (wet peatland landscapes), including nature preserve cores, buffer zones and paludiculture areas (for wet productive land use), will enable sustainable and complementary land-use functions on the landscape level. As such, transforming landscapes into wetscapes presents an inevitable, novel, ecologically and socio-economically sound alternative for drainage-based peatland use

Mimicry of emergent traits amplifies coastal restoration success

Contains fulltext : 221224.pdf (publisher's version ) (Open Access

Impacts of shelter on the relative dominance of primary producers and trophic transfer efficiency in aquatic food webs: Implications for shallow lake restoration

Wind-induced turbulence can strongly impact ecological processes in shallow lake ecosystems. The creation of shelter against wind can be expected to affect both primary producers and herbivores in aquatic food webs. Shelter may benefit particular primary producers more than others by changing relative resource availabilities for different primary producers. Herbivore community compositions may be affected either directly or indirectly as a consequence of changes in their food quantity and quality that, in turn, may affect the transfer efficiency between primary producers and herbivores. A reduction in trophic transfer efficiency resulting from wind-induced turbulence potentially can lead to declines of higher trophic levels, but is generally understudied. Here, we focus on the impact of wind on aquatic primary producers and trophic transfer efficiency. We hypothesised that reducing wind-induced turbulence will stimulate higher trophic production in shallow lakes. However, the multitude of impacts of wind-induced turbulence on aquatic food webs make it challenging to predict the direction of change when creating sheltered conditions. We tested our hypothesis in the shallow waters of a newly constructed archipelago named Marker Wadden in lake Markermeer in the Netherlands. Lake Markermeer has experienced declining numbers of birds and fish. These declines have been related to wind-induced sediment resuspension that potentially limits primary production and trophic transfer efficiency. Marker Wadden is a large-scale restoration project that aims to add sheltered and heterogeneous habitat to the otherwise mostly homogeneous lake, thus targeting the potential problems associated with wind-induced turbulence. We executed a 2-month manipulative field mesocosm experiment in the shallow waters of Marker Wadden to study the effect of reduced wind-induced turbulence (i.e., shelter) on aquatic food webs. Specifically, we studied the effects on primary producers, trophic transfer efficiency between phytoplankton and zooplankton (using zooplankton biomass divided by phytoplankton Chl a as a proxy), and benthic fauna. The experiment consisted of three treatments: no shelter, shelter without macrophytes and shelter with submerged macrophytes (Myriophyllum spicatum) present at the start of the experiment. Our results clearly showed that under unsheltered conditions phytoplankton was the dominant primary producer, whereas in sheltered conditions submerged macrophytes became dominant. Interestingly, submerged macrophytes appeared rapidly in the sheltered treatment where first no macrophytes were visibly present; hence, at the end of the experiment, there was little difference among the sheltered treatments with and without initial presence of submerged macrophytes. Despite that phytoplankton concentrations were 23-fold higher under the unsheltered conditions, this did not result in higher zooplankton biomass. This can be explained by a five-fold greater trophic transfer efficiency between phytoplankton and zooplankton under the sheltered conditions. Furthermore, under the sheltered conditions the Gastropoda density reached 746 individuals m−2, whereas no Gastropoda were found under the no shelter treatment. These findings indicate that for shallow lakes that are negatively affected by wind-induced turbulence, measures aimed at ameliorating this stressor can be effective in facilitating submerged macrophyte recovery, increasing Gastropoda densities and restoring trophic transfer efficiency between phytoplankton and zooplankton. Ultimately, this may support higher trophic levels such as fish and water birds by increasing their food availability in shallow lake ecosystems

Sphagnum farming in a eutrophic world: The importance of optimal nutrient stoichiometry

Large areas of peatlands have worldwide been drained to facilitate agriculture, which has adverse effects on the environment and the global climate. Agriculture on rewetted peatlands (paludiculture) provides a sustainable alternative to drainage-based agriculture. One form of paludiculture is the cultivation of Sphagnum moss, which can be used as a raw material for horticultural growing media. Under natural conditions, most Sphagnum mosses eligible for paludiculture typically predominate only in nutrient-poor wetland habitats. It is unknown, however, how the prevailing high nutrient levels in rewetted agricultural peatlands interfere with optimal Sphagnum production. We therefore studied the effect of enriched nutrient conditions remaining even after top soil removal and further caused by external supply of nutrient-rich irrigation water and (generally) high inputs of atmospheric nitrogen (N) to habitat biogeochemistry, biomass production and nutrient stoichiometry of introduced Sphagnum palustre and S. papillosum in a rewetted peatland, which was formerly in intensive agricultural use. Airborne N was responsible for the major supply of N. Phosphorus (P) and potassium (K) were mainly supplied by irrigation water. The prevailing high nutrient levels (P and K) are a result of nutrient-rich irrigation water from the surroundings. Peat porewater (10 cm below peatmoss surface) CO2 concentrations were high, bicarbonate concentrations low, and the pH was around 4.2. Provided that moisture supply is sufficient and dominance of fast-growing, larger graminoids suppressed (in order to avoid outshading of Sphagnum mosses), strikingly very high biomass yields of 6.7 and 6.5 t DW ha(-1) yr(-1) (S, palustre and S. papillosum [including S. fallax biomass], respectively) were obtained despite high N supply and biomass N concentrations. Despite high P and K supply and uptake, N:P and N:K ratios in the Sphagnum capitula were still low. Sphagnum mosses achieved high nutrient sequestration rates of 34 kg N, 17 kg K and 4 kg P ha(-1) yr(-1) from May 2013 to May 2014, which shows that the site acted as an active nutrient sink. Nutrient management still needs further improvement to reduce the competitive advantage of fast growing peatmoss species (cf. S. fallax) at the expense of slower growing but preferred peatmosses as horticultural substrate (S. palustre and S. papillosum) to optimize the quality of biomass yields. In conclusion, Sphagnum farming is well able to thrive under high N input provided that there is a simultaneous high input of P and K from irrigation water, which facilitates high production rates. Due to the lack of suitable, nutrient poor sites, it seems to be useful to remove the topsoil (mainly P removal) prior to start growing Sphagnum mosses. In addition, bicarbonate concentrations have to stay sufficientlylow to ensure a low pH, CO2 supply from the peat soil should be sufficiently high to prevent C limitation, and graminoids should be mown regularly. (C) 2016 Elsevier B.V. All rights reserved