One of the signs of eutrophication is the excessive growth of opportunistic macroalgae, a worldwide phenomenon
also observed in the Baltic Sea. Mats of macroalgae may drift long distances and accumulate at the seashore,
considerably decreasing the recreational value of beaches. The matter accumulating at the shore is treated usually
as waste. However, it could be used, for example, as a resource for biogas production. The aim of this work was to
verify the hypothesis that collecting of macrophyta accumulating on the beach and potential usage of this material
for biogas production will decrease nutrient reserves in the sea to counteract eutrophication and the increase
in greenhouse effects. Samples of macrophyta were collected in 2011 and 2012 and analysed for their C, N, and P
contents, and degree of degradation (% Chl-a in the sum of chloropigments-a); the results were analysed statistically.
The nutrient content was studied in macrophyta accumulating on the beach (Sopot, Gulf of Gdańsk,
Poland) and for comparison, macrophyta collected from their habitats in less nutrient polluted area (off the
Skåre coast, Trelleborg, Sweden). The nutrient content (N, P) in macrophyta depends primarily on their morphology
and only secondarily on environmental nutrient pollution. Collecting the macrophyta biomass accumulating
on beaches will not significantly change the eutrophication of the Baltic as a whole; any improvements in this respect
are likely to be on a local scale only. Collecting macrophyta removes more nitrogen than phosphorous, so
this would decrease the N/P ratio in seawater. This macrophyta biomass is a substantial reserve of renewable energy,
which could be utilized with the appropriate technology for biomass collection/preservation and biofuel
production as an additive to other carbon-rich biomasses. And the biofuel production should be evaluated not
only from the standpoint of economic efficiency but also from the environmental point of view