The yield of microphytobenthic chlorophyll from nutrients: Enriched experiments in microcosms Ana C. Brito a,b, ⁎, Alice Newton b , Paul Tett a , John Icely c , Teresa F. Fernandes a a School of Life Sciences, Edinburgh Napier University, Edinburgh EH10 5DT, UK b IMAR-FCT-Gambelas, University of Algarve, 8000-117 Faro, Portugal c Sagremarisco L da – Apartado 21, 8650-999 Vila do Bispo, Portugal abstract article info Article history: Received 28 July 2009 Received in revised form 12 November 2009 Accepted 16 November 2009 Keywords: Chlorophyll Eutrophication Microcosm Microphytobenthos Nitrogen Ria Formosa The yield of phytoplankton chlorophyll from nitrogen is a useful parameter in the study of eutrophication of coastal waters, providing the link between chlorophyll formation and nutrient consumption. This parameter has been estimated for microphytobenthos from Ria Formosa lagoon on the south coast of Portugal with a series of three experiments conducted in May and September 2007. Six sediment cores were collected from Ria Formosa in acrylic cylinders and cork stoppers were placed in the bottom. Water samples were collected in large containers and prepared (filtered and enriched) to be pumped to the top of the sediment inside the acrylic cylinders, which are the microcosms of the experiments. Microcosms were isolated to avoid water exchanges and placed in large tanks full of water to maintain temperature stability. Experiments were run for 5 to 9 days in a continuous diluted nutrient enriched system. One of the experiments was carried out with half the microcosms in the dark to evaluate the nutrient fluxes between the sediment and the water column, when no algal growth is expected. Nutrient fluxes of muddy sediments, during the two last days of the experiment in the dark were estimated to be 0.1015 μmol cm -2 d -1 for nitrogen, -0.0015 μmol cm -2 d -1 for phosphorus, and 0.1395 μmol cm -2 d -1 for silicon. The yield of chlorophyll was determined to be between 3.65 and 4.11 μg chl (μmol N) -1 from nitrogen and between 4.03 and 4.77 μg chl (μmol Si) -1 for silicon in muddy sediments. It was not possible to determine the yield from phosphorus. These values are higher than for phytoplankton which may be due to physiological reasons, or due to the presence of a smaller fraction of microheterotrophs, which would divert nutrients. For sand, smaller yields were obtained but it is likely that this was mainly due to the fact that the values of the sediment fluxes used were the ones obtained for mud, which are higher than they should be for sand. This extra input of nutrients is considered to be taken up by algae, thereby decreasing the value of the yield. Therefore, reliable chlorophyll yield estimates for sand could not be obtained. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Eutrophication in marine coastal waters has been identified in recent years as a potentially serious environmental problem (Howarth and Marino, 2006; Nixon, 1995), especially in enclosed areas with restricted exchange, such as coastal lagoons (Tett et al., 2003). The problem arises from the increased use of nitrogen and phosphorus-rich compounds, such as detergents, fertilizers and wastewaters (Bricker et al., 1999; Jensen et al., 2006; Howarth and Marino, 2006; Schindler, 2006). Chlorophyll concentration is current- ly an important indicator of eutrophication (Tett et al., 2003; Nobre et al., 2005; Yoshiyama and Sharp, 2006). In this context the assess- ment of the relationship between nutrient consumption and chlo- rophyll production is of utmost importance. This relationship has been investigated by several authors due to its importance in predicting and avoiding eutrophication events (e.g. Gowen et al., 1992; Edwards et al., 2003, 2005). The quantification of this relationship can be addressed by the assessment of the yield of algal chlorophyll from nitrogen (q), which is considered to be the limiting nutrient in temperature coastal waters of the North Atlantic (e.g. Taylor et al., 1995a; Edwards et al., 2003; Tett et al., 2003; Mills et al., 2004; Loureiro et al., 2005, 2008). This parameter is essential for the development of models such as CSTT model that simulates the nutrient and chlorophyll conditions and predicts eutrophication (CSTT, 1994, 1997; Tett et al., 2003). Gowen et al. (1992) have estimated a median yield of about 1.1 μg chl (μmol N) -1 from regression analyses using data sets for some natural sites in Scotland. Gowen et al. (1992) have had to rely on the assumption that there are no differences in the uptake and use of the different forms of nitrogen and that the results in terms of phytoplankton growth would be the same. Another assumption is that the yield is not dependent on the physiological state of cells and the Journal of Experimental Marine Biology and Ecology 384 (2010) 30–43 ⁎ Corresponding author. School of Life Sciences, Edinburgh Napier University, Edinburgh EH10 5DT, UK. Tel.: +44 1314552350; fax: +44 1314552291. E-mail addresses: a.brito@napier.ac.uk, ana_brito@hotmail.com (A.C. Brito). 0022-0981/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jembe.2009.11.010 Contents lists available at ScienceDirect Journal of Experimental Marine Biology and Ecology journal homepage: www.elsevier.com/locate/jembe