Anthropogenic nutrient enrichment of stream and river waters can lead to the eutrophication of coastal ecosystems. While eutrophication in coastal waters is often a consequence of riverine loads of inorganic nitrogen (N) and phosphorus (P), these may also occur alongside increasing transports of coloured dissolved organic carbon (DOC) (i.e., brownification). Browning may, in turn, lead to increased inputs of potentially bioavailable fractions of organic N and P. Yet, while inorganic nutrient dynamics have been extensively researched, it is unclear how the pool of bioavailable dissolved organic P (BDOP) responds to the individual and interactive effects of reduced light, increased DOC and inorganic nutrients. To address this issue, we conducted a fully factorial mesocosm experiment manipulating inorganic nutrient supply, labile carbon (C) concentration and water colour, and we carried out bioassays to estimate BDOP. Whereas we found no link between C and BDOP, we found that inorganic nutrient enrichment corresponded to increases in BDOP. There was an interaction effect of BDOP concentration with colour, indicating that inorganic nutrients only triggered BDOP accumulation in clear waters, whereas in dark waters, BDOP remained relatively constant. We argue that, in clear and nutrient-rich waters, the increased turnover and degradation of phytoplankton biomass may contribute to increasing BDOP concentrations. Therefore, continued brownification and eutrophication of coastal waters, is likely to decrease DOP concentrations that are bioavailable for the plankton communities.

Primary Presenter: Mayra Rulli, Lund University (mayra.rulli@nateko.lu.se)

Authors:

Aurélie Garnier, Swedish University of Agricultural Sciences, Department of Aquatic Resources  (aurelie.garnier.research@gmail.com)

Magnus Huss, Swedish University of Agricultural Sciences, Department of Aquatic Resources  (magnus.huss@slu.se)

Ryan Sponseller, Umeå University, Department of Ecology and Environmental Science  (ryan.sponseller@umu.se)

Ann-Kristin Bergström, Umeå University, Department of Ecology and Environmental Science  (ann-kristin.bergstrom@umu.se)

Olivia Bell, Swedish University of Agricultural Sciences, Department of Aquatic Resources  (olivia.bell@slu.se)

Jenny Ask, Umeå Marine Sciences Center, Umeå University  (jenny.ask@umu.se)

Martin Berggren, Lund University, Physical Geography and Ecosystem Science  (martin.berggren@nateko.lu.se)