Rivers
Understanding annual river discharges is essential for diagnosing issues for implementing targeted solutions. The flows (Sankey) diagram above (Figure 3-4) shows the annual average discharges from the major rivers and their catchments that drain into and form the greater basin of the Black Sea. The line thicknesses are proportional to each other, showing inflows to the Black Sea itself in blue and outflows from the Black Sea to the Sea of Marmara in red (back flows to the Sea of Azov from the Black Sea are minimal). Information about water quality is available to some extent through localized water quality monitoring. Mass ‘loading’ is the concentration of a particular effluent multiplied by the discharge - see Figure 3‑5.
Figure 3‑5: Nitrogen and phosphorous loading from rivers flowing into the Black Sea
*Results are preliminary as the Pollution Diagnostics Report from the World Bank is not yet published
To better understand pollution streams, it is important to have a more detailed overview of basin dynamics and the status of wastewater treatment (WWT). During the stakeholder workshop, it was highlighted that several regions, like the Baltic states, are currently undertaking partial sewage treatment, leading to the discharge of untreated sewage into the Danube river basin. For specific information on the location, type, and size of wastewater treatment plants in the Danube river basin, please refer to Appendix A5. Changing hydrological and morphological dynamics have affected the regulation of water quality in the Black Sea. Over the decades, the Danube floodplain has undergone significant alterations to its original natural state, leading to significant impacts as outlined in Table 3-1 below (Cogălniceanu, 2021). This table also demonstrates how traditional engineering, while solving one problem, can give rise to several others.
Table 3‑1: Major human activities and impacts in the Danube River floodplain
Type of activity | Purpose | Impact | Ecological services lost or diminished | |
|---|---|---|---|---|
1 | Wetland drainage | Agriculture and urban development | Destruction of wetlands and fragmentation of floodplain connectivity | Sediment retention |
2 | Dikes | Protecting localities and economic activities from floods | Isolation and fragmentation of wetlands associated with the floodplain | Sediment retention |
3 | Channelization | Navigation, flood control, erosion prevention, infrastructure | Disrupts the floodplain structure and destroys the riparian habitats | Diffuse pollution control by riparian vegetation |
4 | Dam construction | Water supply and hydroelectric power | Creation of reservoir disrupts the connectivity of the river and limits dispersal of biota | Sediment transport |
5 | Water abstraction | Water for domestic, industrial or agricultural use | Decrease in water flow and floodplain water table, increased salinity at sea level | Biological productivity of aquatic habitats |
6 | Dredging | Gravel and sand extraction, facilitating navigation | Bank instability, increased erosion and water flow | Sediment retention |
7 | Fishing, forestry and reed harvesting | Food and animal feed, wood and timber, construction materials | Decrease in biodiversity, overexploitation | Maintaining high biodiversity |
8 | Introduction of alien species | Improve yields in fisheries and forestry | Decrease in biodiversity | Maintaining high biodiversity |
- 1 Adapted after Mant and Janes
- 2 Activities 1-3 cause deterioration, destruction and fragmentation of natural habitats, while activities 4-8 represent exploitation of natural renewable resources
Frequently, negative externalities emerge during efforts to enhance agricultural and urban development. Consider the drainage of wetlands, which occurred without full acknowledgment of their valuable ecosystem services. Notably, wetlands played a critical role in improving water quality by naturally recycling, absorbing, and retaining pollutants and excess nutrients. However, prevailing priorities, knowledge gaps, or policies may not have comprehensively recognized the inherent value of wetlands, prompting their drainage primarily for economic purposes associated with agriculture and urban development. NBS can provide alternatives to short-term development solutions.
- 1 Average annual discharges from various hydrological studies (produced with e-sankey) see reference section for details.