Responses of biological and chemical components in North East Atlantic coastal water to experimental nitrogen and phosphorus addition – A full scale ecosystem study and its relevance for management

• Published in: Science of The Total Environment
• Main Authors: Olsen, Yngvar, Reinertsen, Helge, Sommer, Ulrich, Vadstein, Olav
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2014
• Subjects: Norway; North East Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/23206/; https://oceanrep.geomar.de/id/eprint/23206/1/Olsen%20et%20al%20STOTEN%202014.pdf; https://doi.org/10.1016/j.scitotenv.2013.12.028

Highlights: • A full-scale 5 year experimental study of ecosystem responses to increased nutrients. • Concentrations of DIN and DIP did not respond positively to increased nutrient input. • Concentrations of PON and POP and phytoplankton biomass responded positively. • PON is suggested as credible indicator for chemical and ecological state. • A general scientific concept for managing nutrient input to coastal waters is presented. Abstract: The objective of this study was to quantify chemical and biological responses to an experimentally increased nutrient input to an open coastal planktonic ecosystem and to contribute to a scientific concept and credible indicators for managing nutrient supply to coastal waters. Data were derived in a 5 year fertilisation experiment of a tidal driven coastal lagoon at the outer coast off Central Norway (63°36’ N, 9°33’ E), with a surface area of 275.000 m2, volume of 5.5 mill m3, mean depth of 22 m and a water exchange rate of 0.19 day- 1. The lagoon was fertilised in the summer season 1998 and 1999, while summer seasons 1996-97 and 2000 and inflowing water were used as unfertilised references. Most measured chemical and biological variables showed linear responses with an increasing loading rate of inorganic N and P (LN and LP, respectively). PON, POP and POC (< 200 μm) responded significantly (P < 0.05) as did chlorophyll a and phytoplankton C. DIN and DIP remained, however, constant and independent of LN and LP, respectively (P > 0.05) as did heterotrophic biomass (P > 0.05). We evaluate the response variables assuming a stepwise incorporation process of nutrients in the planktonic ecosystem and how that will interact with biological response times and water dilution rates. We suggest that PON is a credible indicator of both chemical and ecological states of the planktonic ecosystem and that natural background and upper critical concentrations are 46 and 88 mg PON m- 3, respectively. The study was supported by data from mesocosms. We discuss the scientific ...