Olsen, Yngvar, Reinertsen, Helge, Sommer, Ulrich and Vadstein, Olav (2014) 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. Science of the Total Environment, 473-474 . pp. 262-274. DOI 10.1016/j.scitotenv.2013.12.028.

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Abstract

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 relevance of our suggestions, how results can be extrapolated to a broader geographical scale, and we propose a science-based concept for the management of nutrient emission to open coastal waters.

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