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Abstract
There is a lack of understanding of the main drivers that form the picture of biological communities of transitional waters in deltaic ecosystems under the influence of terrestrial sources. Analysis of hydrochemical parameters in relation to phytoplankton communities in the Ukrainian part of the Danube coastal zone (in August 2018) is the focus of current work. The goal was to identify patterns in the distribution of environmental parameters (salinity and nutrients) in the area of the shipping channel through the Bystry arm, as well as to assess the state of water quality. The ecological bioindicators approach using modern statistical methods, and ecological mapping shows sufficient achievements in interpreting the results. The indicators of salinity (mesohalobes) had better describe the character of the transportation of fresh riverine waters than salinity gradient. The composition of 35 indicator phytoplankton species corresponds to 3 and 4 water quality classes in the coastal zone. High N:P ratios showed an imbalance in the ecosystem as an indicator of production and destruction processes. Statistical maps of the indicator species distribution revealed the river current’s influence on the nearshore water mass. Ecological maps of surface and bottom variables show various environmental impacts resulting from dredging in the shipping channel and excavated soil dumping. Canonical correspondence analysis (CCA) and statistical maps revealed two pools of factors with oppositely directed effects on phytoplankton: salinity, on one hand, and nutrients, on the other. Miozoa and Chlorophyta have an opposite interaction with salinity and oxygen and can be ecosystem change indicators in further analysis
Highlights
The Danube River plays a great role for the Black Sea by forming the hydrochemical regime in the northwestern shelf, which is the biggest shallow area in the sea with the high stocks of biological production
The distribution of hydrochemical parameters at the Danube nearshore area in August 2018 was characterized by significant spatial variability, which is associated with both the two-layer structure of the waters and the development of production-destruction processes (Tables 2 and A1; Figures 2–6)
As a result of the analysis in August 2018, the 66 species of microalgae from six divisions were revealed in the Ukrainian part of the Danube nearshore area
Summary
The Danube River plays a great role for the Black Sea by forming the hydrochemical regime in the northwestern shelf, which is the biggest shallow area in the sea with the high stocks of biological production. Modern statistical programs and mapping have already been tested for many freshwater objects in different climatic zones [13,14,15,29,30,31] Applying these approaches to assessing the state of marine ecosystems has not yet received widespread use due to the limited number of indicator species [20,21,32]. The combined approach of studying the species composition of algae and statistics in the coastal area has good examples of its application [28] We believe it rational to apply this complex of methods for the Danube nearshore area—a dynamically changing ecosystem, using phytoplankton’s structural indicators and the content of nutrients. The sites that were included in the analysis are distinguished according to the tasks of ecological monitoring: dredging operations on the offshore approach channel to the mouth of the Bystryi Arm with depths of 0–10 m (sites DR0, 1, 2, 3); dumping area of dredging soil with depths of 23–25 m (sites DUM 1, 2, 3, 4); background areas to the north and south of the mouth of the Bystryi Arm and dumping area (sites B1, 2, 3, 4) with depths of 17–23 m
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