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The conversion processes of macroalgae for biofuels can be divided into thermochemical (dry) and microbiological (wet) processes. The chemical composition of macroalgae together with the pre-treatment method, conversion conditions, and the characteristics of the microbes involved (wet processes) determine the yield and the properties of the biofuel produced. Macroalgae are often rich in carbohydrates, and therefore well suited for biogas, biobutanol and bioethanol productions. The content of triacylglycerols (TAGs) is the best indicator for the suitability of the alga for biodiesel production. TAGs have a high conversion rate to biodiesel, high percentage of fatty acids, and they lack phosphorus, sulfur and nitrogen. Macroalgae can have high metal concentrations, which can have an impact on conversion processes: metals may inhibit or catalyse the processes. High sulfur (especially in green algae) and nitrogen contents are also characteristic to macroalgae, and may be problematic in the production of biogas (NH3-toxicity) and the use of the oil and biodiesel (high concentrations of H2S and NOx-compounds). Macroalgae have proven to be suitable material for conversion processes, but further optimization of the processes is needed. At present, macroalgae are not economically, or in many cases not even environmentally, sustainable material when the whole production chain is considered. In this review we summarize information on the chemical composition of macroalgae in a prospect of biofuel production, and the current situation in the field of macroalgal-based biofuel production.

Steep redoxclines form between oxic surface water and the stagnant, sulfidic hypolimnion in the eutrophied, brackish water Baltic Sea. Nitrification, denitrification, and anammox were measured at and below the redoxcline to quantify the role of water-column nitrogen processes in the overall magnitude of nitrogen removal in the Baltic Sea. Rates of nitrification were very high (up to 85 nmol N L21 d21) at the oxic–anoxic interface, but, surprisingly, nitrification was separated from the processes reducing nitrate to N2 (up to 810 nmol N L21 d21 )b y tens of meters in depth. N2 production was dominated by chemolithotrophic denitrification, with anammox playing only a negligible role, and limited to the water layers in which nitrite or nitrate coexisted with sulfide. The alternating oxygen concentrations in the basin induce irregular bursts of nitrogen removal. Nitrification takes place after mixing of ammonium-rich deep water with oxic water, and denitrification uses the formed nitrite and nitrate once anoxic conditions re-establish. Although removal rates can be high, conditions allowing such rates are likely short-lived. While the sedimentary denitrification rates at the shallower, oxic areas are lower, they are more constant in time, highlighting the need to avoid hypoxia, which would prevent sedimentary denitrification. The Baltic Sea is a large and shallow brackish inland sea in northern Europe (415,266 km 2 , average depth 52 m) that suffers from heavy anthropogenic nutrient loading, and large cyanobacterial blooms are a regular phenomenon. It has been suggested that internal feedbacks sustain the eutrophication (Vahtera et al. 2007). One of the key factors in this feedback mechanism is the effect that increased hypoxia has on the biogeochemical cycles of nutrients. The mechanisms that lead to phosphorus release from the sediments during anoxia are well known, but the effects of hypoxia on nitrogen cycling are still uncertain (Conley et al. 2009), despite the critical role nitrogen has as one of the main nutrients regulating not only the extent but also the species composition of phytoplankton blooms (Smith 1983). Two naturally occurring microbial processes, denitrification and anammox, have the potential to remove nitrogen from the water via the production of N2 gas (Codispoti et al. 2001; Kuypers et al. 2005). These anaerobic processes reduce oxidized substrates (nitrate and nitrite), originating from an aerobic nitrification process, to harmless dinitrogen gas. Therefore, nitrification and the processes that mediate the production of N2 are

A 2-week multidisciplinary study of the physical, chemical, and biological mechanisms controlling the initiation of the late summer blooms of the diazotrophic cyanobacteria, Aphanizomenon jlos-aqua2 Ralfs and Nodularia spumigena Mertens, in the Baltic Sea was carried out in a frontal region at the entrance to the Gulf of Finland in July 1993. The front is formed by inflowing sa‘itier waters of the northern Baltic proper and outflowing fresher waters from the gulf, and its position and shape are largely controlled by wind conditions. In general, the waters of the northern Baltic proper are less stratified than the outflowing lesssaline waters. At the time of the study, the two major water masses differed in terms of phytoplankton community structure, both at species level and at the level of functional groups. Wind-induced vertical mixing was instrumental in bringing nutrient pulses to the upper mixed layer in the less-stratified, high-saline water mass. Nutrient pulses were followed by enhancement of primary productivity and assimilation number (primary productivity/Chl a) in cyanobacterial (> 20 pm) and flagellate (< 20 vrn) size fractions. It is proposed that mesoscale blooms of A. flos-aquae benefit from the nutrient-pulsing events. Calm weather and solar heating, as reflected by rising temperatures in the upper mixed layer and overriding of water masses in the frontal region, resulted in substantial shallowing of the upper mixed layer, which initiated the bloom of N. spumifena.

Nutrient limitation and grazing control of the planktonic community were studied in the northern Baltic Sea off the SW coast of Finland during the phytoplankton growth season of 1985. In situ experiments based on a 23 factorial design were performed in mesocosm enclosures on 10 occasions. The manipulations used included phosphorus (PO,? ) and nitrogen (NH,+ ) additions and the removal of metazooplankton by 1 OO+m prefiltration. In each experiment, the responses of phytoplankton, bacterioplankton, heterotrophic nanoflagellates, and protozooplankton were followed for 2 d. Orthogonal multiple regression analysis was used to reveal which manipulations had statistically significant effects. Nitrogen was found to be the basic limiting nutrient for phytoplankton throughout the productive season. During early summer, only the combined addition of P and N evoked a clear increase in the growth of phytoplankton. In general, bacterial productivity was not highly affected by the manipulations. In summer the removal of metazooplankton caused a rapid increase in the amount of protozooplankton in the units with loo-pm prefiltration or prefiltration combined with N addition. In the absence of metazooplankton, the nutrient-induced increase in primary productivity was channeled to protozooplankton, whose growth in the units where metazooplankton was present was severely limited by food competition or by direct metazooplankton grazing.