Accumulations of seagrass, macroalgae and other matter, collectively known as wrack, commonly occur on many sandy beaches, and can play an important role in coastal and nearshore ecosystems. Despite this, wrack removal from sandy beaches is a widespread and increasingly common practice globally, and there is little information regarding the ecological effects of such wrack removal on sandy beaches. The aim of this thesis was to establish the ecological importance of wrack in South Australian (SA) sandy-beach ecosystems. As a first step in furthering our understanding of the effects of wrack removal, I aimed to assess the importance of wrack, independent of the effects of wrack removal. The second over-riding aim of this thesis was to assess the ecological effects of wrack removal on aspects of these systems. To date, the methods used for quantifying the size of wrack deposits on sandy beaches have had limited use due to the time and expertise required to conduct thorough sampling. In Chapter 2, I thus tested the accuracy of a rapid “photopoint” method to visually estimate percentage wrack cover as well as provide an archived record. Comparisons of results obtained from conventional transects with those from photopoints indicated that the photopoint technique can be used to rapidly and accurately estimate % wrack cover on sandy beaches. The photopoint method has a wide range of potential applications and represents a valuable advance in the field. Currently our knowledge of the amounts and types of wrack on SA shores is limited, despite these accumulations being a feature of some SA beaches. Wrack deposits in three biogeographical regions of SA were thus repeatedly surveyed to assess spatial (between and within regions) and temporal (seasonal and inter-annual) variation (Chapter 2). Both wrack cover and the composition of wrack deposits varied spatially and temporally. Wrack deposits contained a diverse array of seagrass, algal, other biotic materials and anthropogenic debris. The South East region of SA had distinctly-different wrack deposits compared to the Metropolitan and Fleurieu Peninsula regions; in general, the cover of wrack was higher, and the diversity and biomass of kelps, red algae and green algae was higher in this region compared to the other two regions. South Australian wrack deposits are thus dynamic and complex. The amount of wrack deposited and retained on a beach may be affected by the beach morphology but, to date, few studies have investigated this link. I assessed wrack cover on beaches with a range of morphodynamic types and found that beaches that were more dissipative in nature had a greater cover of wrack than beaches of the reflective type. I also examined whether wrack deposits affected the sediment characteristics of underlying and nearby sediments. Wrack deposits had little measurable effect on underlying sediments and did not affect particle-size distribution or organic-matter content. There was, however, a trend for beaches in the South East region of SA to have higher organic matter content in their sediments, and these beaches also have higher wrack cover and higher proportions of algae in their deposits. There was also a trend for beaches with higher wrack cover to have less compacted sediments, although this trend was not consistent. Overnight pit-fall trapping surveys of the macrofauna on four SA sandy beaches indicated that local macrofaunal communities were diverse (representing 72 species from 19 Orders in total), abundant, and variable in both time and space. The macrofauna encountered were mostly terrestrial taxa with only 2 truly marine species, and spanned multiple trophic levels, concurring with the results of previous studies. Macrofaunal abundances were higher where associated with wrack than in bare sand, and macrofaunal communities differed between the driftline of wrack and wrack patches away from the driftline. Within the driftline itself, there were few differences between bare sand and wrack-covered areas, suggesting that the entire driftline area is important as a habitat and food resource. Thus, wrack deposits provide an important habitat and food source for macrofauna, and the driftline provides an area of beach with concentrated resources, which in turn concentrates a distinct macrofaunal community. Wrack deposition on sandy beaches varies spatially and is affected by morphological features on the beach-face such as cusps. In Chapter 5, I thus tested a series of hypotheses regarding the differences in wrack deposits, sediments and macrofaunal communities between cusp bays and horns. Bays had greater cover and larger pieces of wrack than horns. Sediment organic-matter content was greater on horns than in bays but mean particle size did not differ consistently between bays and horns. Macrofaunal diversity was higher in bays and this pattern was probably driven by differences in the cover of wrack between bays and horns. Cusp morphology thus influences the distribution of wrack on the beach-face, which in turn influences the distribution of macrofauna. Studies of sandy beaches with cusps should therefore be explicitly designed to sample cusp features and their associated wrack deposits. Chapter 6 assesses the incorporation of wrack into beach and nearshore ecosystems via two pathways: decomposition and incorporation into trophic webs. I assessed the decomposition of algal and seagrass wrack using litterbag experiments and found that after a very rapid initial loss of mass, likely due to cell lysis and leaching, the rate of decomposition of wrack was much slower. Most release of nutrients from organic matter decay thus appears to occur in the first few days after deposition and the processes affecting the rate and nature of wrack decomposition vary among taxa (i.e. algal versus seagrass and among species). Stable isotopes of C and N were used to assess whether beach macrofauna or nearshore macro-invertebrates and fish might rely on wrack as a source of nutrition. I found that seagrasses did not provide a food source for any consumers but algae, particularly brown algae including kelps, appeared to be potential sources of nutrition for beach and nearshore consumers. The incorporation of wrack into beach and nearshore ecosystems may thus occur primarily through consumption of algal wrack by herbivores such as amphipods and dipterans, with predation on them being important pathways for the transfer of nutrients and energy into higher trophic levels. The amount of wrack in the surf zone did not affect the abundance and species richness of fish and invertebrates netted there. The aim of Chapter 7 was to determine the effects of wrack removal on sandy beach macrofaunal communities. In the first study the effects of large-scale commercial harvest of wrack on the macrofaunal communities at Kingston were assessed. The macrofaunal communities present in the ‘Natural’ area of Kingston beach were far more diverse and abundant, and included different species, compared to the ‘Cleared’ area at Kingston. In the second part of Chapter 7, I experimentally removed wrack from the driftline of beaches to assess short-term effects on macrofaunal communities. The experimental treatment did not appear to have any measurable effects on the macrofaunal communities. I also analysed material that was removed from the beach in the raking experiments and found that a large proportion of the material (e.g. 81% of the DW) was sand. I recommend that future studies into the effects of wrack removal use large cleared areas of beach, attempt to use the same wrack removal methods and/or machinery used locally, and assess the macrofaunal communities repeatedly and over longer times following wrack removal activities. In Chapter 8, I attempt to assess the effects of removal of wrack for beach ‘cleaning’ or commercial ‘harvest’ of wrack by comparing key indicators from Chapters 2 to 7. Implications and recommendations for the management of wrack are discussed, including with regard to the techniques used in this thesis and their applicability in managing wrack deposits. I attempt to identify the shortcomings of this research as well as directions for further research. Thus I have demonstrated that wrack in SA provides an important link between offshore habitat and nearshore, beach and terrestrial habitats via the transfer of organic matter and nutrients. Wrack interacts with beach morphology and sediments, provides habitat for macrofauna, remineralises nutrients through its decomposition, and provides the basis of a complex trophic web. I conclude that wrack is a key component in beach ecosystems.

Östersjön har flertalet regionala miljöproblem, exempelvis övergödning samt höga halter av tungmetaller vilka beror på mänsklig påverkan. På Gotland spolas det årligen upp stora mängder släke, alger och vattenlevande växter på stränderna, som idag inte nyttjas i större utsträckning. Denna rapport syftar att bedöma lämpligheten att använda det gotländska släket för produktion av biokol. Under denna studie har ett studiebesök till Gotland, flertalet intervjuer samt en litteraturstudie genomförts vilka lagt grund för beräkningar av energi- och materialbalanser kopplat till släkesbaserad biokolsproduktion. Släket har ett kadmiuminnehåll på cirka 0,9 mg/kg och består till 80 % av vatten, där vanligt förekommande arter är bland annat bandtång och kräkel. För beräkningar av energi- och materialbalanser nyttjades två olika förbehandlingsalternativ av släket, där alternativ A var en värmebehandling och alternativ B innefattar en kompostering samt avlsutande värmebehandling. Alternativ B är mer energieffektiv sett till energiförbrukning per kilo producerat biokol vilket var 14,5 MJ/kg jämfört med 29,8 MJ/kg. Det finns både för- och nackdelar med användning av släke för biokolsproduktion. Släke är en outnyttjad resurs som kan ingå i biokolsframställning, dock är processen energikrävande på grund av det höga vatteninnehållet i biomassan. Användningen av ett kadmiumrikt biokol är även problematiskt i och med risken för utlakning av denna tungmetall. Utifrån resultatet är det därmed svårt att bedöma lämpligheten av ett släkesbaserat biokol. / The Baltic sea has multiple environmental problems, such as over-fertilization and high concentration of certain heavy metals, caused by human activity. Yearly, beach-cast is washed up on the shores of Gotland and this biomass is today not utilised to a considerable extent. This report aims to assess the suitability of producing biochar from the left over beach-cast. During this study a visit to Gotland, interviews and a literature study has been completed, which has laid the groundwork for calculations of energy and material balances regarding algae-based biochar production. The beach-cast contains approximately 0.9 mg cadmium per kg and consists of 80 % water, in which common species found are eelgrass and furcellaria, among others. For the calculations of energy- and material balances, two different pretreatment alternatives were used before the pyrolysis. Alternative A simply uses preheating and alternative B consist of a composting step before a finishing preheating session. The most energy efficient was alternative B as the power consumption per kilo produced biochar was 14,5 MJ/kg compared to 29,8 MJ/kg. The use of beach-cast for manufacturing biochar has benefits as well as disadvantages. Beach-cast is an unexploited resource that could be used for biochar production, but on the other hand the process is demanding energy-wise due to the high amount of water in the biomass. The utilisation of cadmium rich biochar is also problematic due to the risk of the heavy metal leaching. Based on the results it is therefore complicated to estimate the suitability of a beach-cast based biochar.

Accumulation of beach cast biomass on coastal zones around Gotland is an increasing problem that reduce the recreational value of beaches and cause environmental degradation of coastal environments. Beach cast was once regularly harvested on Gotland, as it was considered a valued biofertilizer, but as it seized to be used in combination with the eutrophication of the Baltic sea, beach cast accumulation has increased in scale. The use of beach cast as a resource for bioenergy and agriculture does not only provide important services that can replace the use of greenhouse gases and finite resources but can also mitigate eutrophication and increase the quality of coastal zones as nutrients are retrieved from the water. Macroalgae and seaweeds are hyperaccumulators of heavy metals which pose a challenge for the utilization of beach cast as a fertilizer. Especially cadmium, a heavy metal that is harmful for human consumption, is strictly regulated and limits the amount of beach cast that can be used for agriculture. This thesis has analysed the potential benefit of beach cast harvesting and three potential utilization strategies of beach cast; fertilizer to food crops, fertilizer to fast growing energy forest (Salix) and biogas production with digestate utilization. The result indicate that all strategies are possible and viable utilization strategies under certain conditions. Because of the complex and site specific factors that affect beach cast utilization, adapting strategies depending on the conditions and needs of the local coastal zones is required. Cadmium uptake is affected by a range of factors that can be controlled so that beach cast can provide nutrients and improve soil structure without contaminating the soil. Especially promising is the prospect of fertilizing Salix with beach cast as the cadmium absorption and growth rate of Salix enables large amounts of beach cast to be spread without risk for it accumulating in the soil. The cadmium contained within the Salix can later be removed from the environment entirely as it is collected from the ash when Salix is converted to bioenergy. Recent studies also indicate that food crops can be safely fertilized with beach cast without cadmium being transferred if specific crops are chosen. Cadmium uptake to crops can also be limited if specific beach cast with low cadmium content are used and if the beach cast is pre-composted with other substrates. Both for Salix and food crops its instead legal restraints on cadmium spreading that limits the use of beach cast. When abiding by the set cadmium restrictions, beach cast can only marginally supply the macronutrient requirement of the average food crop on Gotland. Biogas production and digestate utilization from beach cast provides many environmental benefits as clean renewable energy is generated that can replace fossil fuels and the nutrients contained in the digestate can be spread on arable land. From the conducted energy balance of the system on Gotland it was found that beach cast has theoretically good conditions to ferment beach cast. However, beach cast isn’t practically viable on Gotland because the substrate can’t compete financially with other available substrates and it requires costly pre-treatments. Regardless of which beach cast utilization strategy chosen, harvesting is concluded to have a positive effect on mitigating coastal eutrophication and beach and water quality. Although it cannot on its own mitigate a net nutrient loading to coastal zones in Gotland, harvesting easily available beach cast can reduce the nutrient loading to coastal zones on Gotland with up to 27 % and 4,5 % phosphorus and nitrogen respectively.

En av de största utmaningarna för Östersjöregionen gäller bekämpningen av övergödning orsakad av människors utsläpp av näringsämnen till havet. Övergödningen har flera allvarliga konsekvenser för miljön, inte minst enorma algblomningar samt stora mängder alger och tång som så småningom spolas upp längs Östersjöns stränder och börjar förmultna. På gotländska kallas dessa organiska massor på stränderna för “släke” och ses oftast som ett problem då de kan försämra kustmiljön och störa turister och lokalbor som vill bada eller vistas på stranden. Släken är dock rik på näring, och att skörda släken för att använda den som en resurs skulle kunna bidra till att skapa cirkulära flöden då näring återtas från havet, samtidigt som stranden rensas och släken kan bli en potentiellt värdefull resurs som exempelvis jordförbättringsmedel eller biobränsle. Det finns dock flera hinder i vägen för att få till en hållbar skörd och användning av släke.  Projektets syfte är att undersöka vilka möjligheter som finns för att på ett hållbart sätt skörda och använda släke som en bioresurs på Gotland. Detta gjordes dels genom att identifiera hinder och incitament för släkeskörd med hjälp av en litteraturstudie över släkeskörd i Östersjöområdet samt genom en intervju med en person som arbetar med släkehanteringsfrågan i Gotlands länsstyrelse. Det undersöktes även genom en fallstudie där hinder identifierades och utvärderades för att uppskatta möjligheterna för släkeskörd inom ett valt studieområde på Gotlands östkust.  Ett flertal hinder för skörd och användning av släke kunde identifieras i litteraturstudien, som sedan delades in i de följande huvudsakliga kategorierna: skräp, erosion, biologisk mångfald, maskiner, kostnader, juridiska hinder, tidspress, kvalitet, logistik samt tungmetaller. Resultat från intervjun styrker att flera av dessa hinder är aktuella på Gotland, däribland biologisk mångfald som kan riskera att ta skada vid skörd och avlägsnande av släke, olika juridiska hinder för att få bidrag för att skörda släke, och det potentiella innehållet av tungmetaller i släke som kan begränsa dess användning, bland annat. I fallstudien framkom det att några av de viktigaste hindrena är juridiska hinder i form av olika naturskydd, som exempelvis naturreservat, som begränsar eller på andra sätt påverkar möjligheten att skörda släke. Risk för erosion genom bortförande av sand samt kostnader i samband med skörd med maskiner är ytterligare faktorer som påverkar lämpligheten för släkeskörd. Även inblandning av antropogent skräp i släken togs upp.  En slutsats som kan dras är att det finns många fördelar men även många hinder kring skörd och användning av släke. För att kunna avgöra huruvida det är möjligt att skörda och använda släke på ett hållbart sätt behöver skördeområdet först analyseras utifrån dessa hinder och sedan vägas mot fördelarna. Fallstudien visade att stränderna i studieområdet hade olika förutsättningar för hållbar släkeskörd utifrån de studerade hindrena. Flera hinder kunde dock inte appliceras på studieområdet på grund av bristande data, och det går därför inte att dra någon fullvärdig slutsats om hållbar släkeskörd i studieområdet. / One of the biggest challenges for the Baltic Sea region concerns the mitigation of eutrophication induced by nutrient emissions caused by humans. Eutrophication has numerous severe impacts on the environment, such as massive macroalgal blooms that contribute to the presence of large amounts of algae and seaweed that are eventually washed ashore on the Baltic Sea coast where they begin decomposing. On Gotland, these organic masses are called “släke”, beach wrack or beach cast in English, and are usually considered a nuisance as they can bother beach tourists. Beach cast is however very rich in nutrients, and harvesting beach cast to use it as a resource could contribute to creating circular flows as nutrients are removed from the sea while simultaneously the beach is cleaned and the beach cast could pose a potentially valuable resource useful for soil improvement or biofuel, for example. There are, however, several obstacles in the way of sustainably harvesting and using beach cast. The purpose of this project is to investigate the available possibilities to sustainably harvest and use beach cast as a bioresource on Gotland. This was done partly by identifying obstacles and incentives for beach cast harvesting in the Baltic region using a literature study as well as an interview with a government figure on Gotland. It was also explored through a case study where these obstacles were used to estimate the possibility of harvesting beach cast in a chosen study area on the east coast of Gotland. Several obstacles for harvest and use of beach cast could be identified in the literature study and were then divided into the following main categories: trash, erosion, biodiversity, machines, costs, juridical obstacles, time constraint, quality, logistics and heavy metals. Results from the interview corroborate that many of these obstacles are present on Gotland, among others, biodiversity that is susceptible to damage caused by harvesting or the removal of beach cast, various juridical obstacles to attain funding, and the potential contents of heavy metals in beach cast that can limit its possible uses. The case study also showed that some of the most important obstacles are juridical obstacles such as different forms of environmental protection such as nature reserves, that limit the possibility to harvest beach cast. The risk of erosion through removal of sand and costs due to harvesting with machines are other factors that affect the suitability of harvesting beach cast. Also, anthropogenic trash mixed in with the beach cast was mentioned. A conclusion that can be drawn is that there are many advantages as well as obstacles when it comes to harvest and use of beach cast. To be able to harvest and use beach cast in a sustainable manner the harvest site needs to be analyzed using these obstacles and be weighed against the advantages in order to determine whether harvesting is suitable. The case study also showed that different beaches have different qualifications for sustainable beach cast harvesting based on the obstacles. Several of the obstacles found in literature or from the interview couldn’t be applied to the study area, however, due to limited data, and therefore it is not possible to draw any exclusive conclusions concerning sustainable beach cast harvesting in the area.

In the eutrophicated Baltic, algal blooms with toxin-producing algae and plant overgrowth is a large threat to the marine environment, humans and animals. The use of external nutrient inputs into agriculture, such as mineral fertilizers (NPK), is reaching the Baltic through runoff which causes a constant, linear nutrient flow from land to the sea, which is one of the main contributors to accelerated eutrophication. Beach-cast is rich in nutrients and plant promoting substances and was widely used as fertilizer on Gotland before the introduction of NPK. Nowadays large amounts of beach-cast are washed up on the shores of Gotland and most of it is not used. Using beach-cast as fertilizer could contribute to a decrease in external nutrient input into the Baltic and increase a circular flow of nutrients. This study was a part of a broader project operated by KTH with the purpose of evaluating beach-cast as a potential bioresource. The aim of this study was to examine the effects on nutritional content and crop size from the usage of composted beach-cast as fertilizer in comparison with the NPK fertilizer in outdoor cultivation of radish and carrots on Gotland. After the crops were cultivated and harvested, the mass of the root and haulm of the carrot and radishes was determined along with quantification of the content of carbohydrates, pigments, main vitamins and fatty acids. The result revealed a significant increase in 1) mass for three out of four (for all but the carrot root which borderlines the limit of 95% significance), 2) mass ratio between root/blast for the radish, 3) concentration of beta-carotene, vitamin A and fatty acids for the carrot root and 4) concentration of chlorophyll for both haulm. Other observed differences, although not statistically significant, was an increased carrot root mass, increased in concentration of anthocyanin for radish, unchanged mass ratio between carrot root/blast, increase B3 vitamin concentration for all crops, increased concentration of carbohydrates for carrots and decreased concentration for radish, decrease in fatty acids for carrot haulm and radish root and haulm and finally a decrease in vitamin C for all crops. The use of beach-cast as fertilizer has shown to induce growth of the crops, and the majority of the quality parameters were in the same range or exceeded in comparison with the crops cultivated with NPK. A complementary use of beach-cast fertilizer could thus prove beneficial for farmers and at the same time decrease the external nutrient input to the Baltic. / Algblomning och giftalger i övergödda Östersjön är ett stort hot för den marina miljön, människor och djur. Extern input av näringsämnen till lantbruket, i form av exempelvis mineralgödsel (NPK), når Östersjön via avrinning och orsakar en konstant, linjär näringstillförsel från land till hav, vilket är en av de huvudsakliga orsakerna till ökad övergödning. Det näringsrika släket innehåller växtbefrämjande ämnen och spelade en viktig roll i jordbruket på Gotland innan mineralgödsel introducerades. Idag spolas stora mängder släke upp på stränderna och det mesta läggs på hög utan att användas. Användning av släke som gödsel kan bidra till en minskning i extern input av näringsämnen till Östersjön och istället öka det cirkulära näringsflödet. Denna studie var en del av ett större projekt, drivet av KTH, vars syfte var att utvärdera släke som en potentiell bioresurs. Syftet med denna studie var att undersöka den effekt släkegödsling hade på rädisor och morötter för dess storlek och näringshalt, i jämförelse med NPK, i frilandsodling på Gotland. Efter att grödorna odlats och skördats bestämdes massan och mängden kolhydrater, pigment, huvudsakliga vitaminer och fettsyror för rot och blast för båda grödor. Resultatet visade en signifikant ökning i 1) massa i tre av fyra fall (alla utom för morötterna som låg precis under gränsen för 95% statistisk signifikans), 2) förhållandet i massa mellan rot/blast för rädisorna, 3) betakarotenkoncentration vitamin A och fettsyror för morötterna och 4) klorofyllkoncentration i blasterna för båda grödorna. Övriga observerade skillnader, utan statistiskt signifikans, var en ökning i massa för morötterna, ökad koncentration av anthocyanin i rädisorna, ökad koncentration av kolhydrater för morötter inklusive blast, minskad koncentration av kolhydrater för rädisor inklusive blast och slutligen en minskning i vitamin C koncentration för samtliga fyra fall. Användning av släke i form av gödsel gav grödorna en ökad massa och majoriteten av kvalitetsparametrarna överskreds eller var inom samma spann i jämförelse med grödor odlade med NPK. Användning av släke som komplement till mineralgödsel kan därför vara förmånligt för odlare, och bidrar samtidigt till en minskad extern input av näringsämnen till Östersjön.