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Abstract
MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 616:37-49 (2019) - DOI: https://doi.org/10.3354/meps12927 Fertilizer-derived N in opportunistic macroalgae after flooding of agricultural land Sandra Walløe Thorsen*, Erik Kristensen, Thomas Valdemarsen, Mogens R. Flindt, Cintia Organo Quintana, Marianne Holmer Department of Biology, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark *Corresponding author: sandrawt@biology.sdu.dk ABSTRACT: Managed realignment by deliberate flooding of coastal areas is an adaptation to sea level rise but may risk enriching the coastal zone with nutrients when seawater floods agricultural soil. This study focuses on the early development of macroalgae and their sources of nitrogen (N) in Gyldensteen Coastal Lagoon, Denmark. The lagoon was claimed for agricultural purposes in 1871 and reflooded by managed realignment 143 yr later (2014). Our hypotheses were: (1) that nutrients of agricultural origin from the newly flooded soil initiate opportunistic macroalgal blooms; and (2) that the isotopic composition of green algae rapidly reflects the origin of nutrient sources. We monitored macroalgal cover and conducted stable isotope (δ15N) analyses to assess the origin of N sources. Intense green macroalgal blooms occurred during the first summer after flooding and diminished in the 2 following years as a result of rapid water exchange. Low δ15N in macroalgae in the first year (mean ± SE, 4.2 ± 0.3‰) increased significantly in the next year (8.0 ± 0.1‰). A laboratory experiment tested the δ15N response of opportunistic green macroalgae (Ulva spp.) exposed to organic manure and synthetic inorganic fertilizers. Higher δ15N (11.1 ± 0.1‰) characterized manure-treated algae compared to fertilizer-treated algae (2.7 ± 0.2‰). Based on these field and laboratory results, we accept both hypotheses and conclude that the major N source supporting macroalgal growth in 2014 was derived from synthetic fertilizers; however, rapid tidal flushing during the following years resulted in nutrient limitation and lower macroalgal growth. KEY WORDS: Nitrogen · Macroalgal bloom · Nutrient sources · Sea level rise · Coastal realignment · Gyldensteen Coastal Lagoon Full text in pdf format PreviousNextCite this article as: Thorsen SW, Kristensen E, Valdemarsen T, Flindt MR, Quintana CO, Holmer M (2019) Fertilizer-derived N in opportunistic macroalgae after flooding of agricultural land. Mar Ecol Prog Ser 616:37-49. https://doi.org/10.3354/meps12927 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 616. Online publication date: May 09, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.
Highlights
Sea level is expected to rise by up to 16 mm yr−1 as a result of climate change, increasing to a global average of 0.85 m within the 21st century (IPCC 2014), and low-lying coastal areas are at risk of flooding
Managed realignment by deliberate flooding of coastal areas is an adaptation to sea level rise but may risk enriching the coastal zone with nutrients when seawater floods agricultural soil
This study focuses on the early development of macroalgae and their sources of nitrogen (N) in Gyldensteen Coastal Lagoon, Denmark
Summary
Sea level is expected to rise by up to 16 mm yr−1 as a result of climate change, increasing to a global average of 0.85 m within the 21st century (IPCC 2014), and low-lying coastal areas are at risk of flooding. Many of these areas in Europe, including Denmark, were shallow marine areas claimed for agricultural purposes that are protected from the sea by dikes (Peirup 2006, Rupp-Armstrong & Nicholls 2007). Blooms of macroalgae may delay the development of realigned coastal areas into stable ecosystems
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