Distribution and Biochemical Composition of Suspended and Sedimentary Organic Matter in the Northern Adriatic
In order to study the benthic-pelagic coupling in the northern Adriatic Sea, sediment and water samples were collected between July 1996 and March 1997 in two zones of the northern Adriatic, differently influenced by river outflow. In the northern area the concentrations of organic matter decreased from coast to open sea [particulate organic carbon concentrations in the coastal stations were on average 327.0 (from 1244 to 963.0) μgCl−1 during summer and 374.0 (from 88.6 to 1196.9) μgCl−1 in early spring], thus increasing the local sedimentary organic carbon concentrations [in the coastal area on average 2860.2 (from 2734.1 to 2986.2) μgC g−1 during summer, with a decrease in early spring to 868.4 (from 550.2 to 1186.5) μgC g−1]. By contrast, the open-sea area showed generally much lower organic matter concentrations (2 to 6 times lower than at coastal stations in water and sediments, respectively). In the southern area the absence of almost continuous and strong allochthonous inputs brought from the river, coupled with the presence of well defined frontal areas, resulted in increased sedimentary organic matter concentrations in the intermediate stations,that also displayed clear seasonal changes [2314.5 (2102.8–2526.2) μgC g−1 during summer, only 991.5 (856.4–1126.5) μgC g−1 during early spring]. In the water column, high values of suspended organic matter in the coastal stations were generally observed [on average 93.5 (31.2–252.5) μgC g−1 in summer and 242.3 (from 56.1 to 1358.0) μgCl−1 in early spring]. In both areas, proteins were the main biochemical class of organic compounds. The higher values of PRT:CHO ratios in the sediment as compared to the water column (7.8±1.7 vs 2.2±0.6, respectively) suggest the presence of a protein accumulation in the sediments. At the same time, the lower values of the RNA:DNA ratios observed in the water column of the northern area [summer values of 1.87 (0.01 –12.79) and early spring values of 1.04 (0.01 –4.62)] as compared to the southern area [summer values of 1.93 (0.05–18.10) and early spring values of 2.69 (0.07–34.91)] suggest the presence of a larger fraction of detrital DNA likely to be provided by the river discharge.
Although the relations between organic matter distribution and characterisation pointed out a clear pelagic-benthic coupling, in the northern Adriatic energy and materials transfer might be affected by spatially and temporally confined functional uncoupling, changing the balance between supply and exploitation of organic matter, thus forcing the systems to different trophic patterns.
KeywordsEarly Spring Particulate Organic Matter Southern Area Sedimentary Organic Matter Organic Matter Concentration
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