Koop-Jakobsen Ketil

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Koop-Jakobsen
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Ketil
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  • Article
    Biomechanical traits of salt marsh vegetation are insensitive to future climate scenarios
    (Nature Research, 2022-12-08) Paul, Maike ; Bischoff, Christina ; Koop-Jakobsen, Ketil
    Salt marshes provide wave and flow attenuation, making them attractive for coastal protection. It is necessary to predict their coastal protection capacity in the future, when climate change will increase hydrodynamic forcing and environmental parameters such as water temperature and COcontent. We exposed the European salt marsh species Spartina anglica and Elymus athericus to enhanced water temperature (+ 3°) and CO(800 ppm) levels in a mesocosm experiment for 13 weeks in a full factorial design. Afterwards, the effect on biomechanic vegetation traits was assessed. These traits affect the interaction of vegetation with hydrodynamic forcing, forming the basis for wave and flow attenuation. Elymus athericus did not respond to any of the treatments suggesting that it is insensitive to such future climate changes. Spartina anglica showed an increase in diameter and flexural rigidity, while Young's bending modulus and breaking force did not differ between treatments. Despite some differences between the future climate scenario and present conditions, all values lie within the natural trait ranges for the two species. Consequently, this mesocosm study suggests that the capacity of salt marshes to provide coastal protection is likely to remain constantly high and will only be affected by future changes in hydrodynamic forcing.
  • Article
    Salt marsh ecosystem biogeochemical responses to nutrient enrichment : a paired 15N tracer study
    (Ecological Society of America, 2009-09) Drake, Deanne C. ; Peterson, Bruce J. ; Galvan, Kari A. ; Deegan, Linda A. ; Hopkinson, Charles S. ; Johnson, J. Michael ; Koop-Jakobsen, Ketil ; LeMay, Lynsey E. ; Picard, Christian
    We compared processing and fate of dissolved NO3− in two New England salt marsh ecosystems, one receiving natural flood tide concentrations of 1–4 μmol NO3−/L and the other receiving experimentally fertilized flood tides containing 70–100 μmol NO3−/L. We conducted simultaneous 15NO3− (isotope) tracer additions from 23 to 28 July 2005 in the reference (8.4 ha) and fertilized (12.4 ha) systems to compare N dynamics and fate. Two full tidal cycles were intensively studied during the paired tracer additions. Resulting mass balances showed that essentially 100% (0.48–0.61 mol NO3-N·ha−1·h−1) of incoming NO3− was assimilated, dissimilated, sorbed, or sedimented (processed) within a few hours in the reference system when NO3− concentrations were 1.3–1.8 μmol/L. In contrast, only 50–60% of incoming NO3− was processed in the fertilized system when NO3− concentrations were 84–96 μmol/L; the remainder was exported in ebb tidewater. Gross NO3− processing was 40 times higher in the fertilized system at 19.34–24.67 mol NO3-N·ha−1·h−1. Dissimilatory nitrate reduction to ammonium was evident in both systems during the first 48 h of the tracer additions but <1% of incoming 15NO3− was exported as 15NH4+. Nitrification rates calculated by 15NO3− dilution were 6.05 and 4.46 mol·ha−1·h−1 in the fertilized system but could not be accurately calculated in the reference system due to rapid (<4 h) NO3− turnover. Over the five-day paired tracer addition, sediments sequestered a small fraction of incoming NO3−, although the efficiency of sequestration was 3.8% in the reference system and 0.7% in the fertilized system. Gross sediment N sequestration rates were similar at 13.5 and 12.6 mol·ha−1·d−1, respectively. Macrophyte NO3− uptake efficiency, based on tracer incorporation in aboveground tissues, was considerably higher in the reference system (16.8%) than the fertilized system (2.6%), although bulk uptake of NO3− by plants was lower in the reference system (1.75 mol NO3−·ha−1·d−1) than the fertilized system (10 mol NO3−·ha−1·d−1). Nitrogen processing efficiency decreased with NO3− load in all pools, suggesting that the nutrient processing capacity of the marsh ecosystem was exceeded in the fertilized marsh.