| Abstract |
Seagrass meadows rank among the most valuable Blue Carbon (BC) ecosystems. They
sequester and store organic carbon (Corg) permanently in their sediments and as such
they contribute to climate change mitigation and adaptation. Similarly, seagrass
meadows store nitrogen in their sediments through active uptake by the plant and
trapping of allochthonous material, acting as natural filters for coastal eutrophication.
The aim of the present study was to investigate the capacity of seagrass meadows of
the Amvrakikos Gulf (i.e., Zostera noltei and Cymodocea nodosa) to store carbon and
nitrogen and determine the potential change of stocks with seagrass degradation. The
vertical distribution of sediment properties (dry bulk density, grain size), the
concentration of elements (Corg, Cinorg, TN) and stable isotope ratios (d13C, d15N)
with sediment depth were measured in two stations and one station located inside the
Gulf and inhabited by C. nodosa. Principal Component Analysis (PCA) revealed a clear
clustering of stations, which explained the 86% of the variability in our samples. Stocks
of Corg in the top meter of sediment were similar among Z. noltei stations (15.8 ± 3.7
kg m-2 and 14.1 ± 2.5 kg m-2 at Mazoma and Logarou, respectively), and significantly
higher than that of C. nodosa (6.2 ± 1.3 kg m-2). Moreover, the stocks of TN were lower
in C.nodosa station (0.4 ± 0.1 kg m-2) than in Z. noltei stations (1.2 ± 0.4 kg m-2 at
Mazoma and 1.4 ± 0.2 kg m-2 at Logarou). Stocks of Cinorg seemed to differ a lot
between C.nodosa and Z.noltei stations. At C.nodosa station the average value of
Cinorg stock (47.8 ± 5.3 kg m-2) was significantly higher than these of Z.noltei stations
(15.4 ± 2.8 kg m-2 at Mazoma and 8.0 ± 2.4 kg m-2 at Logarou). Mixing models were
used to identify the origin of the organic matter present trapped in Z.noltei and C.nodosa
sediments. In Z.noltei sediments the Corg was mostly Chlorophyta (32%) at Mazoma
and seagrass leaves (52%) at Logarou but in C.nodosa sediments the Corg was more
allochtonous (62% seston). Therefore, our results showed the significance of Z.noltei
and C.nodosa meadows as blue carbon ecosystems.
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Blue carbon and nitrogen storage in seagrass meadows of Amvrakikos Gulf
