| | | 9.4 Conclusions |
To decrease HABs and improve water quality in coastal marine waters a threshold based mainly on the loading of inorganic N and P has been discussed. In those values organic nitrogen or phosphorus are thus not included, and until recently there has been only scanty knowledge on the availability of organically bound nutrients for HAB growth. Even now we are far from understanding what nutrients in e. g. humic matter represents for HAB biomass production in the Baltic Sea, even less in other seas as attention have not been devoted yet to this subject. One thing we can be rather confident about is that if there has been an increase in the number and severity of HABs over, say, the last 50 years (which there are strong indications for), it is safe to assume that the increase has to do with human activity. This may be due to direct pollution, but also indirectly through e.g. the greenhouse effect causing increased leakage of humic matter. Disruption of the pelagic food chain due e. g. to selective fishing or overfishing, also a consequence of human activity, may also promote HABs. Thus not only loading of inorganic nutrients, but also organic matter loadings and fishing activities should be subjected to thresholds to manage algal blooms.
Ultimately decreasing or mitigating harmful algal blooms will have a positive impact on natural marine and inland waters by restoring them to near pristine conditions, with very large economic benefits with respect to biodiversity, aquaculture, harvesting of wild fish and recreational activities.
| | | 9.4 Conclusions |