Multivariate statistical analysis of the distribution patterns of carbohydrates and surface-active substances in the northern Adriatic Sea

Dissolved and particulate carbohydrates (DTCHO and PTCHO) as well as surface-active substances concentrations and relative acidities (SAST and Acr) were studied in the northern Adriatic Sea during the period between 1998 and 2005 with the aim to investigate their temporal and spatial dynamics in the basin and possible links with the mucilage events with help of comprehensive statistical data analysis. The investigated time period encompassed 3 years characterized by intensive appearance of mucilage aggregates (mucilage years) and 3 years without this phenomenon (non-mucilage years). In order to explore possible regularities in the distribution and covariation of investigated parameters, univariate and multivariate analyses of variance (MANOVA) were performed, considering effects of different parameters, including water column depth, geographic location, season, individual year, and mucilage appearance. The investigated organic matter parameters showed a significant complexity of their temporal (seasonal, interannual) and spatial (vertical and horizontal) distribution patterns. Although some characteristics of the distribution patterns, such as seasonality and differences between surface (0.5m) and deeper layers, were already described in the literature, this work provides the first rigorous statistical analysis performed on a larger data set, allowing quantitative assessment of the observed differences. It was shown that mucilage years in the northern Adriatic were characterized by different patterns of the investigated four organic matter parameters, compared to those of the non-mucilage years. Moreover, it was shown that carbohydrates substantially contribute to the overall surfactant activity of the present organic matter, especially in the surface layer of the most productive western part of the basin, indicating new production, triggered by river-born nutrients, as the predominant source. To the best of our knowledge, this is the first evidence for a possible coupling between CHO and surfactant-activity in environmentally relevant conditions.