| Popis: |
The dynamics of the physicochemical and biological parameters were followed during the decline of a Cymodocea nodosa meadow in the northern Adriatic Sea from July 2017 to October 2018. During the regular growth of C. nodosa from July 2017 to March 2018, C. nodosa successfully adapted to the changes of environmental conditions and prevented H2S accumulation by its re-oxidation, supplying the sediment with O2 from the water column and/or leaf photosynthesis. The C. nodosa decline was most likely triggered in April 2018 by a reduction of light availability which affected photosynthesis of C. nodosa and the oxidation capability of below-ground tissue. Simultaneously, a depletion of oxygen due to intense oxidation of H2S occurred in the sediment, thus creating anoxic conditions in most of the rooted areas. These linked negative effects on the plant performance caused an accumulation of H2S in the sediments of the C. nodosa meadow. During the decay of above- and below-ground tissues, culminating in August 2018, high concentrations of H2S were reached and accumulated in the sediment as well as in bottom waters. The influx of oxygenated waters in September 2018 led to the re-establishment of H2S oxidation and recovery of the below-ground tissue. Our results indicate that if disturbance of environmental conditions, particularly those compromising the light availability, take place during the recruitment phase of plant growth when metabolic needs are at maximum and stored reserves minimal, a sudden and drastic decline of the seagrass meadow occurs. |
