Annette Bruhn

Bioenergy potential of Ulva lactuca: Biomass yield, methane production and combustion

The biomass production potential at temperate latitudes (56°N), and the quality of the biomass for energy production (anaerobic digestion to methane and direct combustion) were investigated for the green macroalgae, Ulva lactuca. The algae were cultivated in a land based facility demonstrating a production potential of 45T (TS) ha(-1) y(-1). Biogas production from fresh and macerated U. lactuca yielded up to 271 ml CH(4) g(-1) VS, which is in the range of the methane production from cattle manure and land based energy crops, such as grass-clover. Drying of the biomass resulted in a 5-9-fold increase in weight specific methane production compared to wet biomass. Ash and alkali contents are the main challenges in the use of U. lactuca for direct combustion. Application of a bio-refinery concept could increase the economical value of the U. lactuca biomass as well as improve its suitability for production of bioenergy.

Bioremediation of reject water from anaerobically digested waste water sludge with macroalgae (Ulva lactuca, Chlorophyta)☆

Phosphorus and biologically active nitrogen are valuable nutrient resources. Bioremediation with macroalgae is a potential means for recovering nutrients from waste streams. In this study, reject water from anaerobically digested sewage sludge was successfully tested as nutrient source for cultivation of the green macroalgae Ulva lactuca. Maximal growth rates of 54.57±2.16% FW d(-1) were achieved at reject water concentrations equivalent to 50 μM NH4(+). Based on the results, the growth and nutrient removal was parameterised as function of NH4(+) concentration a tool for optimisation of any similar phycoremediation system. Maximal nutrient removal rates of 22.7 mg N g DW(-1) d(-1) and 2.7 mg P g DW(-1) d(-1) were achieved at reject water concentrations equivalent to 80 and 89 μM NH4(+), respectively. A combined and integrated use of the produced biomass in a biorefinery is thought to improve the feasibility of using Ulva for bioremediation of reject water.

Can Seaweed Farming Play a Role in Climate Change Mitigation and Adaptation

Seaweed aquaculture, the fastest-growing component of global food production, offers a slate of opportunities to mitigate and adapt to climate change. Seaweed farms release carbon that maybe buried in sediments or exported to the deep sea, therefore acting as a CO2 sink. The crop can also be used, in total or in part, for biofuel production, with a potential CO2 mitigation capacity, in terms of avoided emissions from fossil fuels, of about 1500 tons CO2 km-2 year-1. Seaweed aquaculture can also help reduce the emissions from agriculture, by improving soil quality substituting synthetic fertilizer and, when included in cattle fed, lowering methane emissions from cattle. Seaweed aquaculture contributes to climate change adaptation by damping wave energy and protecting shorelines, and by elevating pH and supplying oxygen to the waters, thereby locally reducing the effects of ocean acidification and de-oxygenation. The scope to expand seaweed aquaculture is, however, limited by the availability of suitable areas and competition for suitable areas with other uses, engineering systems capable of coping with rough conditions offshore and an increasing market demand for seaweed products, among other factors. Despite these limitations, seaweed farming practices can be optimized to maximize climate benefits, which may, if economically compensated, improve the income of seaweed farmers.

An Objective Framework to Test the Quality of Candidate Indicators of Good Environmental Status

Large efforts are on-going within the EU to prepare the Marine Strategy Framework Directive’s (MSFD) assessment of the environmental status of the European seas. This assessment will only be as good as the indicators chosen to monitor the eleven descriptors of good environmental status (GEnS). An objective and transparent framework to determine whether chosen indicators actually support the aims of this policy is, however, not yet in place. Such frameworks are needed to ensure that the limited resources available to this assessment optimize the likelihood of achieving GEnS within collaborating states. Here, we developed a hypothesis-based protocol to evaluate whether candidate indicators meet quality criteria explicit to the MSFD, which the assessment community aspires to. Eight quality criteria are distilled from existing initiatives, and a testing and scoring protocol for each of them is presented. We exemplify its application in three worked examples, covering indicators for three GEnS descriptors (1, 5 and 6), various habitat components (seaweeds, seagrasses, benthic macrofauna and plankton), and assessment regions (Danish, Lithuanian and UK waters). We argue that this framework provides a necessary, transparent and standardized structure to support the comparison of candidate indicators, and the decision-making process leading to indicator selection. Its application could help identify potential limitations in currently available candidate metrics and, in such cases, help focus the development of more adequate indicators. Use of such standardized approaches will facilitate the sharing of knowledge gained across the MSFD parties despite context-specificity across assessment regions, and support the evidence-based management of European seas.

Emiliania huxleyi (Prymnesiophyceae): nitrogen-metabolism genes and their expression in response to external nitrogen sources.

The availability and composition of dissolved nitrogen in ocean waters are factors that influence species composition in natural phytoplankton communities. The same factors affect the ratio of organic to inorganic carbon incorporation in calcifying species, such as the coccolithophore Emiliania huxleyi (Lohman) W. W. Hay et H. Mohler. E. huxleyi has been shown to thrive on various nitrogen sources, including dissolved organic nitrogen. Nevertheless, assimilation of dissolved nitrogen under nitrogen‐replete and ‐limited conditions is not well understood in this ecologically important species. In this study, the complete amino acid sequences for three functional genes involved in nitrogen metabolism in E. huxleyi were identified: a putative formamidase, a glutamine synthetase (GSII family), and assimilatory nitrate reductase. Expression patterns of the three enzymes in cells grown on inorganic as well as organic nitrogen sources indicated reduced expression levels of nitrate reductase when cells were grown on NH4+ and a reduced expression level of the putative formamidase when growth was on NO3−. The data reported here suggest the presence of a nitrogen preference hierarchy in E. huxleyi. In addition, the gene encoding for a phosphate repressible phosphate permease was more highly expressed in cells growing on formamide than in cells growing on inorganic nitrogen sources. This finding suggests a coupling between phosphate and nitrogen metabolism, which might give this species a competitive advantage in nutrient‐depleted environments. The potential of using expression of genes investigated here as indicators of specific nitrogen‐metabolism strategies of E. huxleyi in natural populations of phytoplankton is discussed.

Bioextraction potential of seaweed in Denmark — An instrument for circular nutrient management

The aim of the study is to assess the efficacy of seaweed for circular nutrient management to reduce eutrophication levels in the aquatic environment. We performed a comparative Life Cycle Assessment (LCA) of two reference waste management systems treating seaweed as biowaste, i.e. landfill disposal and combustion, and an alternative scenario using the seaweed Saccharina latissima as a resource for biobased fertilizer production. Life Cycle Impact Assessment (LCIA) methods were improved by using a cradle-to-cradle approach, quantifying fate factors for nitrogen and phosphorus loss from fertilized agriculture to the aquatic environment. We also differentiated between nitrogen- and phosphorus-limited marine water to improve the traditional freshwater impact category, making this indicator suitable for decision support in relation to coastal water management schemes. Offshore cultivation of Saccharina latissima with an average productivity of 150Mg/km(2) in Danish waters in 2014 was applied to a cultivation scenario of 208km(2). The bioresource scenario performs better than conventional biowaste management systems, delivering a net reduction in aquatic eutrophication levels of 32.29kgNeq. and 16.58kgPO4(3-)eq. per Mg (dry weight) of seaweed, quantified by the ReCiPe and CML impact assessment methods, respectively. Seaweed cultivation, harvest and reuse of excess nutrients from the aquatic environment is a promising approach for sustainable resource cycling in a future regenerative economy that exploits manmade emissions as a resource for closed loop biobased production while significantly reducing eutrophication levels in 3 out of 7 Danish river basin districts. We obtained at least 10% bioextraction of phosphorus manmade emissions (10%, 89% and >100%) and contributed significantly to local nitrogen reduction goals according to the Water Framework Directive (23%, 78% and >100% of the target).

The effect of light and nutrient availability on growth, nitrogen, and pigment contents of Saccharina latissima (Phaeophyceae) grown in outdoor tanks, under natural variation of sunlight and temperature, during autumn and early winter in Denmark

Late summer harvest of cultivated Saccharina latissima, prior to seasonally determined negative length growth, is considered advantageous in North Atlantic waters to optimize biomass yields. We hypothesized that seasonal increase in tissue protein and pigments over autumn and early winter would counterbalance the loss of biomass, and increase the absolute harvestable amount of protein and pigments. The hypothesis was tested in a land-based, factorial-designed, pilot-scale experiment using whole algae individuals exposed to naturally relevant high or low availability of nutrients and light. The experiment was conducted during fall/early winter in Grenaa, Denmark, in outdoor tanks, exposed to ambient light and temperature variations. With high nutrient availability, the absolute harvestable amounts of nitrogen, fucoxanthin, and chlorophyll a increased by 50.1–60.1, 21.7–53.7, and 47.0–73.5 %, respectively, despite a loss of biomass of 16.2–18.7 %. Under low nutrient availability, there was a net loss of biomass (8.1–9.5 %), tissue nitrogen (10.7–44.1 %), and fucoxanthin (7.1–17.2 %), and a minor increase in chlorophyll a (2.5–22.8 %). Nutrient availability had a significant negative impact on the biomass growth, but a positive control on the tissue concentration of nitrogen, chlorophyll a, and fucoxanthin. Our results, from a land-based experiment, indicate that early winter harvest of S. latissima biomass grown under high nutrient availability in Denmark, fulfills a higher degree of nutrient bioremediation, and has an improved biomass quality in regards of increased concentrations of pigments and nitrogen rich compounds.

Genetic diversity of Saccharina latissima (Phaeophyceae) along a salinity gradient in the North Sea–Baltic Sea transition zone

The North Sea–Baltic Sea transition zone constitutes a boundary area for the kelp species Saccharina latissima due to a strong salinity gradient operating in the area. Furthermore, the existence of S. latissima there, along Danish waters, is fairly patchy as hard bottom is scarce. In this study, patterns of genetic diversity of S. latissima populations were evaluated along the salinity gradient area of Danish waters (here designated brackish) and were compared to reference sites (here designated marine) outside the gradient area, using microsatellite markers. The results showed that the S. latissima populations were structured into two clusters corresponding to brackish versus marine sites, and that gene flow was reduced both between clusters and between populations within clusters. In addition, results provided empirical evidence that marginal populations of S. latissima in the salinity gradient area exhibited a distinct genetic structure when compared to marine ones. Brackish populations were less diverse, more related, and showed increased differentiation over distance compared to marine populations. The isolation of the brackish S. latissima populations within the salinity gradient area of Danish waters in conjunction with their general low genetic diversity makes these populations vulnerable to ongoing environmental and climate change, predicted to result in declining salinity in the Baltic Sea area that may alter the future distribution and performance of S. latissima in the area.

Biodiversity in Marine Ecosystems—European Developments toward Robust Assessments

Sustainability of marine ecosystems and their services are dependent on marine biodiversity, which is threatened worldwide. Biodiversity protection is a major target of the EU Marine Strategy Framework Directive, requiring assessment of the status of biodiversity on the level of species, habitats, and ecosystems including genetic diversity and the role of biodiversity in food web functioning and structure. This paper provides a summary of the development of new indicators and refinement of existing ones in order to address some of the observed gaps in indicator availability for marine biodiversity assessments considering genetic, species, habitat, and ecosystem levels. Promising new indicators are available addressing genetic diversity of microbial and benthic communities. Novel indicators to assess biodiversity and food webs associated with habitats formed by keystone species (such as macroalgae) as well as to map benthic habitats (such as biogenic reefs) using high resolution habitat characterization were developed. We also discuss the advances made on indicators for detecting impacts of non-native invasive species and assessing the structure and functioning of marine food-webs. The latter are based on indicators showing the effects of fishing on trophic level and size distribution of fish and elasmobranch communities well as phytoplankton and zooplankton community structure as food web indicators. New and refined indicators are ranked based on quality criteria). Their applicability for various EU and global biodiversity assessments and the need for further development of new indicators and refinement of the existing ones is discussed.

Glacial vicariance drives phylogeographic diversification in the amphi-boreal kelp Saccharina latissima

Glacial vicariance is regarded as one of the most prevalent drivers of phylogeographic structure and speciation among high-latitude organisms, but direct links between ice advances and range fragmentation have been more difficult to establish in marine than in terrestrial systems. Here we investigate the evolution of largely disjunct (and potentially reproductively isolated) phylogeographic lineages within the amphi-boreal kelp Saccharina latissima s. l. Using molecular data (COI, microsatellites) we confirm that S. latissima comprises also the NE Pacific S. cichorioides complex and is composed of divergent lineages with limited range overlap and genetic admixture. Only a few genetic hybrids were detected throughout a Canadian Arctic/NW Greenland contact zone. The degree of genetic differentiation and sympatric isolation of phylogroups suggest that S. latissima s. l. represents a complex of incipient species. Phylogroup distributions compared with paleo-environmental reconstructions of the cryosphere further suggest that diversification within S. latissima results from chronic glacial isolation in disjunct persistence areas intercalated with ephemeral interglacial poleward expansions and admixture at high-latitude (Arctic) contact zones. This study thus supports a role for glaciations not just in redistributing pre-existing marine lineages but also as a speciation pump across multi-glacial cycles for marine organisms otherwise exhibiting cosmopolite amphi-boreal distributions.