engleski

Dynamics of environmental conditions during the decline of a Cymodocea nodosa meadow

The dynamics of the physicochemical and biolog- ical parameters were followed during the decline of a Cy- modocea 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, the species suc- cessfully adapted to the changes in environmental conditions and prevented H2S accumulation by its reoxidation, supply- ing the sediment with O2 from the water column and/or leaf photosynthesis. The C. nodosa decline was most likely trig- gered in April 2018 when light availability to the plant was drastically reduced due to increased seawater turbidity that resulted from increased terrigenous input, indicated by a de- crease in salinity accompanied with a substantial increase in particulate matter concentration, combined with resuspen- sion of sediment and elevated autotrophic biomass. Light re- duction impaired photosynthesis of C. nodosa and the oxida- tion capability of belowground tissue. Simultaneously, a de- pletion 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 per- formance caused an accumulation of H2S in the sediments of the C. nodosa meadow. During the decay of aboveground and belowground tissues, culminating in August 2018, high con- centrations of H2S were reached and accumulated in the sed- iment as well as in bottom waters. The influx of oxygenated waters in September 2018 led to the re- establishment of H2S oxidation in the sediment and remainder of the belowground tissue. Our results indicate that if disturbances of environ- mental conditions, particularly those compromising the light availability, take place during the recruitment phase of plant growth when metabolic needs are at a maximum and stored reserves minimal, a sudden and drastic decline of the sea- grass meadow occurs.

Cymodocea nodosa ; decline ; sediment ; H2S accumulation

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