Model for remediation of urban ecosystem water bodies under climate change.

Water bodies as elements of urbanised ecological systems are of particular scientific and practical interest. Typical sources of pollution, physical, chemical and microbiological characteristics, the feasibility of establishing a dedicated monitoring network, and the development of specific water remediation measures tailored to local conditions are unique challenges for communities and regional authorities.

The authors' experience in solving practical problems of neutralising eutrophication in reservoirs can serve as an important example for application in other areas or for scaling up instrumental approaches to solving hydroecological problems.

Of course, against the backdrop of climate change, a general decrease in water availability, changes in precipitation intensity and deterioration of the composition of effluents, the most important issues are the modernisation of storm water drainage systems, the audit and repair of water supply networks, the clear monitoring of unsewered neighbouring villages, the control of fertiliser use on adjacent agricultural land, and environmental cooperation with neighbouring communities.

Thanks to cooperation with the Regional Office of the State Water Agency, the authors were able to conduct a complete diagnosis of the reservoir, create a bathymetric map, conduct a series of studies of silt deposits and water samples, design and install aeration shore fountains and a rainwater collector in the Taras Shevchenko Coastal Park, cleaned the bottom in the two most problematic areas, and applied biological treatment. Plans include the installation of a bottom outlet next to the Nadstavna Church (following the example of Olsztyn) and the modernisation of the sluices.

The team of authors developed their own algorithm, which was applied in the city of Ternopil. In particular, the following work and research were carried out in the following areas:

1. Assessment of the processes of stability and self-cleaning capacity of the reservoir ecosystem, including: toxicological assessment of sources of pollution of the pond's hydroecosystem; establishment of patterns of migration and transformation of toxicants in ecosystem components; establishment of patterns of the impact of toxic substances on the structure, functioning and productivity of pond communities at the organism and supra-organism levels; research and establishment of the impact of pollution, especially excess biogenic substances, the degree of formation of adaptive-protective processes aimed at neutralising toxicants through their accumulation (deposition) and metabolic oxidation in order to reduce their active concentration and biological effect, as well as metabolism towards the conversion of substances into forms with reduced or absent biological reactivity; establishing the level of ecological transformations of the water body ecosystem – ecological and metabolic regression (disappearance of species and general reduction of biological activity of the biocenosis, suppression of production and destruction processes).
   
2. Priority engineering and hydraulic measures: cleaning of bottom sediments (silt) along the dam at a distance of 25-30 m from the embankment; aeration as a process of removing harmful impurities (gases, iron ions, colloids, etc.) from water and supplying aerobic bacteria with oxygen by mixing: a system of fountains (the optimal layout would be a series of aeration points, about 5-7) of small capacity (1.0-2.0 thousand dm3/hour), located along the dam at a distance of 25-30 m from each other and about 35-50 m from the embankment, where silting is most severe, stagnation in water and silt, high activity of anaerobic decomposition of organic residues and toxicants, eutrophication (‘blooming’ of the reservoir), etc.; reduction of organic pollution as a way to reduce the development of algae that cause eutrophication (‘blooming’) of the reservoir by: engineering and technical improvement of collector and drainage systems; improvement (restoration) of phytosanitary protection zones; recultivation of sandy shores – cleaning or replacement of sand (beach areas); introduction (planting) of biogenic-accumulative plant species in the coastal zone; creation of a bioplat system for the treatment and post-treatment of domestic, industrial wastewater and contaminated surface runoff, which requires no (or almost no) electricity consumption and the use of chemical reagents with minimal operational maintenance.

Promising measures:

- creation of a system for bottom discharge of water from the pond into the Seret River with a system for purification from solid pollutants and introduction of an automatic system for regulating the water level in the reservoir depending on hydrochemical and hydrobiological indicators in accordance with standards of saprobity and water quality;

- creation of an additional water filling system for the Ternopil Reservoir by constructing an accompanying (satellite) hydroaccumulating reservoir (floodplain of the Seret River) above the Ternopil Reservoir;

Hydrobiological measures: introduction of aerobic organisms (green algae, higher plants), organisms that accumulate biogenic substances in the reservoir and bioplat (primarily nitrogen and phosphorus) and filter organisms (remediating plants, certain species of invertebrates and molluscs); stocking the reservoir with omnivorous and herbivorous fish species.

Use of biofilters - a series of solid-substrate (attached to the bottom or partially floating) island-type biofilters (diameter 4-6 m), combined with aeration points (about 5-7), placed like fountains along the dam at a distance of 25-30 m from each other and 35 to 50 m from the dam and/or at the confluence of sewage collectors; optimisation (reduction) of water storage reservoirs in Topilche Park (according to the western, central and eastern lines – acceleration of water discharge from the Ternopil Reservoir and water storage reservoirs) in order to accelerate water exchange in the recreational part of the park and prevent eutrophication (blooming) of reservoirs; deepening of the fairway (1.5–2.5 m wide and 1.3–1.8 m deep) of the Seret River and part of the water channels in the Topilche Park and strengthening the banks with rocky and sandy riverbed sediments while preserving the vegetation of the coastline. [40]

Prospective measures include:

- introduction of green algae biopoint biotechnology for water purification and biomass production (raw material for biofuel, feed, raw material for the cosmetics industry).

Indicators of the effectiveness of the measures taken:

- reduction of the negative impact of wastewater by 60%;

- reduction of pollution levels by 55%; overall improvement of the sanitary and epidemiological situation of the reservoir by 50%;

- reduction of the level of pathogenicity and degradation of biotic components of the reservoir;

- prevention of a decrease in water quality standards;

- improvement of the ecological stability and development of the reservoir ecosystem by 60%;

- improvement of the quality of the natural reserve fund of the water body and adjacent territories by 60%;

- improvement of the ecological, aesthetic and recreational properties of the water body and adjacent territories by 60%;

- creation of conditions for the economic use of the water body's biological resources.