Harvesting beach wrack biomass (stranded seaweed) from coastal zones to use in agriculture could mitigate eutrophication while contributing to resource substitution of fossil-based inputs in food production. As such, beach wrack holds great resource potential in a bio-based circular economy, but its chemical properties prove challenging, and more research is required to develop treatment techniques that will allow the realization of such a system. We compiled results from chemical analyses of fresh beach wrack conducted 2012–2023 from a database within the marine policy scheme LOVA in Gotland, Sweden, to study spatial and seasonal variations in macronutrients and cadmium (Cd) content since cadmium is a highlighted risk metal for beach wrack use. This data was complemented by sampling composted beach wrack from compost sites (passive pile treatment), including analysis of ammonium and nitrate. There was considerable variation in the chemical composition of the beach wrack depending on location and season. Fresh beach wrack from the LOVA-sampling exhibited an average C content of 17.32 %, N content of 1.24 %, P content of 0.17 %, and K content of 1.3 %, which is in line with earlier studies. Composted material also showed significant differences between locations in C, N, C/N, ammonium-N, nitrate-N, P, K and Cd. The C/N and ammonium-N/nitrate-N ratios in composted beach wrack differed significantly between different composts, indicating differences in mineralization processes and maturity. Average cadmium levels were below the EU cd-limit for biofertilisers 1,5 mg/kg DW, cd-level in fresh beach wrack (LOVA − 1,24 mg/kg), and in composted beach wrack (1,09 mg/kg DW). However, single values exceed the EU limit, and long-term effects of cadmium soil accumulation could not be ruled out. The results confirm that regional variations in beach wrack quality require investments in treatment techniques and strategies to make beach wrack usable.

Harvesting beach-cast can help mitigate marine eutrophication by closing land-marine nutrient loops and provide a blue biomass raw material for the bioeconomy. Cost–benefit analysis was applied to harvest activities during 2009–2018 on the island of Gotland in the Baltic Sea, highlighting benefits such as nutrient removal from the marine system and improved recreational opportunities as well as costs of using inputs necessary for harvest. The results indicate that the activities entailed a net gain to society, lending substance to continued funding for harvests on Gotland and assessments of upscaling of harvest activities to other areas in Sweden and elsewhere. The lessons learnt from the considerable harvest experience on Gotland should be utilized for developing concrete guidelines for carrying out sustainable harvest practice, paying due attention to local conditions but also to what can be generalized to a wider national and international context.

The blooming of beach-cast seaweed has caused environmental degradation in some coastal regions. Therefore, a proper treating and utilizing method of beach-cast seaweed is demanded. This study investigated the potential of producing power or biofuel from pyrolysis of beach-cast seaweed and the effect of the ash-washing process. First, the raw and washed beach-cast seaweeds (RS and WS) were prepared. Thereafter, thermogravimetric analysis (TG), bench-scale pyrolysis experiment, process simulation, and life cycle assessment (LCA) were conducted. The TG results showed that the activation energies of thermal decomposition of the main organic contents of RS and WS were 44.23 and 58.45 kJ/mol, respectively. Three peak temperatures of 400, 500, and 600 degrees C were used in the bench-scale pyrolysis experiments of WS. The 600 degrees C case yielded the most desirable gas and liquid products. The bench-scale pyrolysis experiment of RS was conducted at 600 degrees C as well. Also, an LCA was conducted based on the simulation result of 600 degrees C pyrolysis of WS. The further process simulation and LCA results show that compare to producing liquid biofuel and syngas, a process designed for electricity production is most favored. It was estimated that treating 1 ton of dry WS can result in a negative cumulative energy demand of -2.98 GJ and carbon emissions of -790.89 kg CO2 equivalence.

In this study we evaluate a project-based learning course called Applied Ecology, within the master program Sustainable Technology at the Division of Industrial Ecology, at KTH—Royal Institute of Technology in Stockholm, Sweden. The case study in the course is focused on the effects of a relatively large Bay, “Burgsviken”, situated on the island Gotland in the middle of the Baltic Sea, that has changed due to the eutrophication in the area. The eutrophication of the Bay has initiated bottom up processes of discussion and engagement among the stakeholders in the area, for the enhancement of the water quality and biological services of the bay, that would in turn improve fishing, swimming, biological diversity and tourism. There are several stakeholders involved in the project: a local non-profit organisation, farmers, entrepreneurs, authorities, permanent and seasonal inhabitants, researchers and others. The course is evaluated according to the methodology of Brundiers and Wiek (2013). Student evaluations have been conducted and analysed in relation to four phases: (1) Orienting phase, formulation of research question. (2) Framing phase, methodology and study planning. (3) Research phase, field study and other examinations. (4) Implementation phase, communication of the results with different stakeholders. The Applied Ecology course shares many of the positive features of other PPBL courses in the sustainability field—namely that it focuses on a real sustainability problem and that the student-centred learning approach and interactions between students and stakeholders make the student partnership in the project feel real, thus providing a practical insight of complex societal challenges. There are potential ways of improving all four phases of the course that were studied, but especially in the research phase and the implementation phase more efforts are needed. Feedback and reflections in the research phase could be improved by a clearer communication and to some extent changed pedagogical process through the course. All phases will be improved by increased communication before, during and after fieldwork between student, teachers and stakeholders.

Today, concerns prevail about the unsustainable use of phosphorus and worldwide eutrophication, thus requiring efficient management of phosphorus flows. With increasing population and associated urban growth, urban management of phosphorus flows in the perspectives of recycling, eutrophication and total budget becomes increasingly important. This study mapped phosphorus flows for a reference year (2013) and a future year (2030) using different scenarios for the city of Stockholm, Sweden. The results indicated that the Swedish goal of recycling phosphorus from wastewater would cover the majority of the total phosphorus budget for Stockholm. However, in 2013, only 10% of phosphorus was recycled for agricultural use, around half of which was from sewage sludge and the other half from food waste. Almost 50% of total phosphorus was sent to landfill/mining waste capping with sewage sludge, for economic reasons and lack of market. Among the scenarios of upstream and downstream urban management options studied in combination with population growth, recovery of phosphorus from sewage sludge had the greatest potential to increase the fraction recycled to agriculture. However, only upstream measures, e.g. changed diet, were able to reduce the total phosphorus budget. Urban management of phosphorus flows based on the different perspectives of recycling, eutrophication or total budget was shown to potentially result in different preferred management actions and both upstream and downstream measures need to be considered. Moreover, management needs to pay attention to small but environmentally sensitive flows, particularly when setting city goals on phosphorus recycling by percentage in a large budget.

Managing nutrient flows to urban lakes is one of the main challenges to environmental sustainability in cities. Considering that future urban and climate changes may increase the challenge of handling future eutrophication, prediction of future nutrient loadings to aquatic environments in urban catchments has become increasingly important. Based on a new, innovative, structured Substance Flow Analysis (SFA) approach, where a source model was coupled to a Generalised Watershed Loading Functions (GWLF) model, this study investigated nutrient (nitrogen and phosphorus) delivery from sources to a water recipient for an urban catchment, using the case of Racksta Trask in Stockholm, Sweden, as an example. Potential effects from future changes in atmospheric deposition, vehicle volume and land use and from climate change (temperature and precipitation) were examined by comparing model scenarios in two periods (2000-2009 and 2050-2059). Model results suggested that climate change may have a greater impact on nitrogen loading to Racksta Trask lake than increasing vehicle volume and land use change. In addition, the results suggested that nitrogen loading to the lake may increase taking into account all changes examined, despite the expected decrease in background atmospheric deposition of nitrogen. In contrast, a marginal impact was found for phosphorus loading to the lake under all scenarios examined, resulting in only a slight increase in the combined scenario. From a nutrient pathways perspective, the results suggested that major pathways of nutrient loadings to the lake may not be much affected under most future scenarios examined, although groundwater was found to be a potentially sensitive pathway of nitrogen transport in the climate scenario. The model results provided important information for managers who need to plan for future nutrient handling in urban catchments, and the coupled SFA-GWLF model was suggested to be worthy of further testing at other sites and conditions.

The ecological consequences of using beachcast compost as an agricultural resource input merit study. Using beachcast compost as a biofertiliser has multiple positive effects on agroecosystems, while also serving to remedy the negative effects on marine ecosystems caused by excessive beachcast production due to eutrophication. This process thus presents an opportunity to contribute to circular nutrient management and the development of sustainable agricultural, but it may also result in accumulation Cd (Cd) in the soil. In Gotland, Sweden, an example of cross-scale interaction between marine and agricultural domains has emerged from a national policy subsidising beachcast harvesting, which may help reintroduce the historical tradition of using beachcast in agriculture. To estimate potential risks, a field experiment and Cd mass balance were conducted to predict the rate of Cd accumulation, changes in soil Cd fractions, and potential beachcast application methods that avoid Cd soil accumulation. In the scenario where the maximum Cd input from beachcast compost is set to the same threshold as the level established for sewage sludge—0.75 g ha–1 year–1—beachcast compost with a Cd content of 1.5 mg kg–1 dw (the EU threshold for biofertilisers) could be applied in an amount of approximately 2000 kg ha–1 per year (one-tenth of the amount applied in this study). Therefore, the long-term effects of Cd soil accumulation resulting from continuous application of beachcast as fertiliser on agroecosystems cannot be disregarded and are of global relevance. 

Harvesting beachcast from coastal zones to use the biomass in agriculture or horticulture could mitigate eutrophication while contributing to resource substitution of fossil-based inputs in food production. As such, beachcast holds great resource potential in a bio-based circular economy, but its chemical properties prove challenging, and more research is required to develop treatment techniques that will allow the realisation of such a system. We compiled results from chemical analyses of fresh beachcast from a database within the marine policy scheme, LOVA, in Gotland, Sweden, to study local and seasonal variations in macronutrients, C:N ratio, and Cd content. This data complemented with analyses of fresh and composted beachcast (passive pile treatment), for which the contents of macronutrient, ammonium, nitrate, and Cd, were measured, calculating C:N ratios and maturity indices (NH4+-N/NO3—N). The results confirm that regional variations in the above-mentioned properties require investments in treatment techniques and strategies to make beachcast usable.