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Abstracts - S11 Stofomsætning i det marine miljø
78. Seasonal variations in plankton community production and respiration
for Roskilde Fjord and Great Belt
Mustafa Mantikci, Stiig Markager, Jørgen L. S. Hansen
Bioscience, Aarhus Universitet, Frederiksborgvej 399, 4000 Roskilde amm@dmu.dk
The seasonal patterns in plankton community production and respiration were investigated in the
surface waters of two stations, Roskilde Fjord (RF) and Great Belt (GB), between January 2012 and
July 2012. Generally, planktonic respiration has not been considered during several years of
primary production research and even when taken into account, respiration measurements have
done by dark bottle single start and end point oxygen measurements. In our study, community
respiration rates were determined by continuous measurement of oxygen consumption in darkness
for 48 hours. Preceding the respiration measurement, we determined photosynthetic rates as a
function of irradiance by the 14 C technique by 2 hours of light incubation in a linear incubator.
Oxygen concentrations were measured with optodes (fiber-optic oxygen meter) by using oxygen
sensor spots that was fixed to the inner wall of 60 ml BOD bottles. Respiration rates were calculated
by fitting a model to the raw data which assumes respiration decreases exponentially from an initial
value, R0, approaching a constant “Maintenance” respiration, Rm. Maximum photosynthesis (Pmax)
normalized to Chl-a values increased markedly over the 6-month sampling period, from 0.9 to 3.8
and 0.7 to 6.5 gC g -1 Chl-a h -1 at GB and RF respectively and was significantly correlated with
temperature. R0 varied between 0.1 and 1.9 µmolO2l -1 h -1 and Rm varied from 0.02 to 0.6 µmol O2 l -
1 h -1 Rm was significantly correlated with temperature, POC and Pmax. Q10 values for POC turnover
and Pmax of 2.5 and 2 respectively suggests community respiration was much more sensitive to
temperature than photosynthesis in the study areas. Future studies will focus on the role of light
history on dark respiration and the calculation of GPP and P:R ratios more accurately in order to
understand carbon cycle at the pelagic systems. This work increases our understanding of
planktonic respiration and its relationship with biotic and abiotic factors.
Program 17. danske havforskermøde, 102