POSTER Session 4

HISTORICAL MEASUREMENTS OF SECCHI DEPTH IN THE NORTHWESTERN BLACK SEA – QUESTIONING THE CONCLUSIONS OFFERED BY A HETEROGENEOUS DATASET

Significant changes have been identified in most of the coastal ecosystems in the northwestern Black Sea following 1960. Eutrophication phenomena have gradually evolved, leading to significant changes in phytoplankton structure and primary production. This mainly came as a result of intensifying agricultural practices (fertilizers containing high levels of phosphorus and nitrogen) in riparian countries – particularly in Danube, Dniester and Dnieper basins. Water transparency represents a first-order indicator of aquatic ecosystem health. Although a subjective measure, Secchi Depth (ZSD) is one of the “oldest” and most widely used optical parameters to assess the clarity of surface waters, with probably millions of observations in the last one and a half centuries. As more recent satellite observations do not cover such extended periods from the past, a comprehensive understanding of the spatiotemporal dynamics of water transparency requires historical data. To achieve this goal, this study integrates long-term archives of in situ ZSD measurements available for the northwestern Black Sea (1960-2015). A key and innovative consideration, neglected in prior studies, is a proper understanding of the dataset at hand. The degree of heterogeneity is a key element that needs to be addressed. This study proposes a methodology that investigates the spatial, statistical and temporal consistency of the historical dataset, with the aim of ascertaining the reliability of results. The outcomes indicate that long-time archives of in situ data should be used with precaution, as may offer questionable conclusions.

*Ioan Daniel Serban, University of Bucharest, Romania, [email protected], https://orcid.org/0000-0003-0117-3109

Sorin Constantin, Terrasigna, Romania, [email protected]

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