27 Oct 2020

27 Oct 2020

Review status: a revised version of this preprint was accepted for the journal BG and is expected to appear here in due course.

Rain-fed streams dilute inorganic nutrients but subsidise organic matter-associated nutrients in coastal waters of the northeast Pacific Ocean

Kyra A. St. Pierre1,2, Brian P. V. Hunt1,2,3, Suzanne E. Tank1,4, Ian Giesbrecht1,5, Maartje C. Korver1,a, William C. Floyd6,7, Allison A. Oliver1,4,b, and Ken P. Lertzman1,5 Kyra A. St. Pierre et al.
  • 1Hakai Institute, Tula Foundation, Heriot Bay BC, V0P 1H0, Canada
  • 2Institute for the Oceans and Fisheries, University of British Columbia, Vancouver BC, V6T 1Z4, Canada
  • 3Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver BC, V6T 1Z4, Canada
  • 4Department of Biological Sciences, University of Alberta, Edmonton AB, T6G 2E9, Canada
  • 5School of Resource and Environmental Management, Simon Fraser University, Burnaby BC, V5A 1S6, Canada
  • 6Ministry of Forests, Lands and Natural Resource Operations, Nanaimo BC, V9T 6E9, Canada
  • 7Vancouver Island University, Nanaimo BC, V9R 5S5, Can
  • acurrent address: McGill University, Department of Geography, Montréal QC, H3A 0B9, Canada
  • bcurrent address: Skeena Fisheries Commission, Kispiox BC, V0J 1Y4 Canada

Abstract. In coastal regions, rivers and streams may be important sources of nutrients limiting to primary production in marine waters; however, sampling is still only rarely conducted across the land-to-ocean aquatic continuum, precluding conclusions from being drawn about connectivity between freshwater and marine systems. Here we use a more than four year dataset (2014–2018) of nutrients (nitrogen, phosphorus, silica, iron) and dissolved organic carbon spanning streams draining coastal watersheds and nearshore marine surface waters along the Central Coast of British Columbia Canada, at the heart of the North Pacific coastal temperate rainforest region. Mean freshwater and surface marine N : Si : P ratios were 4 : 18 : 1 (P : Fe = 1 : 58) and 6 : 11 : 1, respectively, showing relative consistency across the land-ocean interface but deviation from the extended Redfield ratio. Inorganic nutrient concentrations (NO3+NO2, PO43−, Si(OH)4) in freshwaters were less than in the receiving marine environment, indicating that freshwater nutrient inputs in this region were of little importance to – or even diluted – the pool of readily available inorganic nutrients in nearshore waters. Conversely, freshwaters increased the pool of organic matter-associated nutrients, namely dissolved organic nitrogen and iron. The organic matter-rich landscapes of the region yielded globally significant quantities of dissolved organic nitrogen (304–381 kg km−2 y−1) and iron (463–596 kg km−2 y−1); thus acting as important sources of potentially limiting nutrients to both nearshore and offshore waters. These exports may subsidise heterotrophic microbial communities capable of directly consuming and remineralising these nutrients, potentially compensating for the dilution of inorganic nutrients by freshwater inputs. We highlight the need to better understand nutrient limitation in coastal waters and for concerted research efforts to study the spatial and temporal dynamism at the land-ocean interface along the northeast Pacific coast.

Kyra A. St. Pierre et al.

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Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Kyra A. St. Pierre et al.

Data sets

Freshwater and marine water quality (nutrients and carbon) - Calvert Island - 2014 to 2018 St. Pierre, K. A., Hunt, B .P. V., Tank, S. E., Giesbrecht, I., Floyd, W. C., Korver, M. C., Oliver, A. A., and Lertzman, K.

Kyra A. St. Pierre et al.


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Short summary
Using a four year dataset of paired fresh and marine water quality from British Columbia (Canada), we show that coastal temperate rainforest streams bordering the northeast Pacific Ocean are sources of organic nitrogen, iron and carbon, but not the nutrients that are easily used by marine phytoplankton. This distinction has possibly critical implications for coastal food webs, and highlights the need to sample both fresh and marine waters year-round to fully understand coastal dynamics.