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2 2024

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The Lithological Composition of the Bed Sediments Collected Along the Sf. Gheorghe Branch (km 85 - km 15) (Streams, Artificial Canals, Rectified Meanders, Including Lateral Channels and Lakes), Danube Delta, Romania

Catianis Irina, Dutu Florin, Pavel Ana-Bianca, Borzan Ovidiu

Inżynieria Mineralna

2024

Vol. 1, no. 2

art. no. 32

The Sf. Gheorghe distributary (the oldest branch of the Danube River) is subject to different hydro-sedimentary impacts due to the anthropogenic meander cut-off plans undertaken in the last decades for navigational purposes. This study aimed to determine the contents of the main lithological levels (i.e., organic matter – TOM%, carbonates – CAR% and siliciclastics – SIL%) in the bed sediments, using the LOI (Loss in Ignition) method. In this sense, a field sediment investigation has been conducted in 58 sampling sites located on the Sf. Gheorghe Arm (km 85 – km 15) (rivers, artificial channels, rectified meanders, including side channels and lakes), during May 2024. The distribution of the organic matter, carbonates and siliciclastics showed a significant spatial variability. The implemented analyses made it possible to distinguish mineral-rich sediments (>15-30%SIL) found especially in river sections, while organic-rich sediments (>15-30%TOM) were mainly identified in lakes. From these outcomes, it seems reasonable to conclude that the sediment deposition and accumulation are strongly influenced by the local hydrodynamic conditions (fluvial and lacustrine environments) which allow the accumulation of a mixture of different sediments. This study enables quantitative evidence related to the main lithological components of the bed sediments within the Sf. Gheorghe Arm (km 85 – km 15), and present a database for future sustainable ecosystem restoration and management measures, to protect and maintain wildlife habitat and biodiversity on the Danube Delta edifice.

Hydrological connectivity, structural and ecological functionality of a meandering ecosystem of the Danube Delta

Dutu Laura, Dutu Florin, Pavel Ana-Bianca, Catianis Irina, Vasiliu Dan, Lupascu Naliana, Stanescu Ion

Inżynieria Mineralna

2024

Vol. 1, no. 1

323--328

The pressure control of the climate change and anthropogenic factors have consequences on the ecological systems, generating structural changes. The abiotic (i.e., water hydrology and hydraulics, sediment load, water physic-chemistry) and biotic (i.e., biodiversity, structure and functionality of food webs) characteristics of river-channels-lakes from deltas depend on several factors; however, the main driver of these characteristics is represented by the hydrologic connectivity with the main stem of the river. Floodplain lakes can be permanently, temporarily or disconnected with the main stem of the river producing interruptions in the transfer of fresh water and thus affecting benthic macroinvertebrates, by decrease in their population, diversity and even loss of sensitive taxa. Multidisciplinary investigations (hydrodynamics, sedimentological and ecological measurements and analyses) were made to investigate a river-channel-lake site type situated on the St. George branch formed by a cutoff meander (Mahmudia meander), a connective channel (Uzlina Canal) and a lake (Uzlina Lake) to observe how much the fresh water and sediment input to the delta depressions is affected by the structural changes of the meander physiography. The Mahmudia meander was rectified 40 years ago and the response of the channel consisted in a very fast silting of the former meander, currently receiving less than 5% of the upstream water and sediment discharge. The lateral connectivity with the deltaic depressions thought the lateral canals is compromised.