Location

Lake Palic and Lake Ludas are typical shallow Pannonian lakes located in the North of Serbia, in Subotica municipality. The lakes are situated on either side and close to the motorway M22. They can be conveniently reached by a 1½-hour drive from Novi Sad and in 2½-hours from Belgrade. The Hungarian border is just 20 min away.

Hydrology

Lake Palic has the shape of a mirrored “L”, is approx. 8 km long and up to 1 km wide and a surface area of 556 ha.

It is on average 2.5-3 meters deep, with a maximum depthof 3.5 meters. Lake Ludas has the shape of a “T” with a length of about 4.5 km, a width of up to 2 km and a surface area of 380 ha.

It is on average 1m deep, with amaximum depth of 2 meters.

Time Schedule

Project start: 10.09.2018
Project duration: 33 months, thereof 24 months investment period
Project end: End of November 2021.

There is a small delay due to the global pandemic of Covid-19, but there is a contract extension due to increase of the investment budget made available.

The Situation at project start

Lake water quality and fish population: Regular lake monitoring is performed by the Subotica Public Health Institute. Data show that after commissioning of the modern Subotica wastewater treatment plant (WWTP) pollution values in the lakes have dropped. The WWTP is designed for nutrient removal which means that not only carbon substances (COD and BOD5) are removed, but also nitrogen (N) and phosphorus (P). Both elements must be available at high concentrations in water, that eutrophication can happen. High N and P enable excessive growth of algae which leads to algae bloom (blue or red color of the lake).

The high biological activity uses up the free oxygen in water, causes high turbidity (reduced transparency) which in turn eventually leads to massive fish kills. Only certain types of fish are able to survive in such an environment leading to a reduction of biodiversity and domination of one fish species. As a result of this, the Prussian carp (colloquially “babushka”) which is not a native (autochthon) species in these lakes, has massively developed in population.

Experts estimate that the fish biomass in Lake Palic is about 150 tons, whereby a healthy population would be less than half of this. A pilot fishing campaign performed in 2016 revealed that more than 90% of it is babushka.

The treated wastewater discharged from the Subotica wastewater treatment plant (WWTP) constitutes approx. 2/3 of the inflow to Lake Ludas, the rest is surface and groundwater inflow from the nearby area. The lake volume is about 10 Million m³ and water exchange takes about 7-8 months. Therefore, the quality of the WWTP effluent is of utmost importance for the water conditions in Lake Ludas. The Tisa-Palic Channel was completed in 1995 with the purpose of pumping water from the Tisa River to Lake Palic – which turned out to be uneconomic and is therefore not in use.

The Palic-Ludas Channel constitutes the outflow of Lake Palic and the main inflow to Lake Ludas. Obviously, the water quality of Palic influences that of Ludas. Lake Ludas discharges into the Kereš River which is a tributary to the Tisza River which in turn discharges into the Danube.

Both lakes are extremely important stop-over locations for birds migrating north-south. The lakes are home to 238 bird species including a large number of white eye ducks (ferruginous duck) and white-headed ducks (Oxyuraleucocephala). In recognition of its ecological importance, Lake Ludaš was classified as a RAMSAR site in 1977. https://www.ramsar.org/

1996, Lake Palić and its shores were declared the Lake Palic Nature Park with a park area of 712 ha and a total protection zone of 1698 ha.

In 2003, the Kamaraš Landscape Protection Area of 5,370 ha was established which includes Lake Palić Lake Ludas and the Subotica Sands (Subotica Pescara).

In 2006, Lake Ludas Nature Reserve was established with an area of 846 ha.

Before the Second World War, Lake Palic was a highly appreciated recreational and tourist area. The luxurious historic buildings at the lakeshore in Palic are signs of the prosperous times. However, since then, heavy soil and water pollution and industrial activities have negatively affected the ecology and tourism around the lakes which has led to several fish kills and repeated algae blooms.

With the recognition of the specific ecological value of this site, the Local, Provincial and National Governments have embarked on a program for ecological rehabilitation and economic development based on moderate tourism. The company Park Palic was founded for the purpose of economic and touristic development of the region. The recently developed master plan foresees promotion of sports and activity tourism on Lake Palic and eco-tourism on Lake Ludas: http://www.serbia.com/visit-serbia/natural-beauties/rivers-lakes/palic-a-lake-made-of-tears/

Biomanipulation is the appropriate solution to this problem. Biomanipulation means that through targeted measures, the ecosystem is brought back into balance. Biomanipulation is based on the following 3 actions:

  1. Ensure that either N or P, or both values in the water are very low. Usually, the phosphorus concentration is targeted and should be maintained at below 0.1 mg/L.
  2. Reduction of biomass by Selective Fishing i.e. landing big amounts of babushka only;
  3. Introduction/stimulation of predator fish population e.g. Zander and Pike

The Subotica WWTP was upgraded in 2009 to produce an effluent standard which complies with EU standards for “sensitive areas” (EU Urban Waste Water Directive 91/271/EEC). It produces on average a total phosphorus (TP) outflow concentration of less than 1.0 mg/l, whereby the effluent quality was clearly better in the initial years of operation. This effluent is usually good enough to avoid eutrophication in the receiving water body – which in most cases is a river. In the particular case of Subotica, where the effluent is the main inflow to the lake, this value is still not good enough. An average effluent value of 0.5 mg/l must be achieved to make sure that biomanipulation is successful and that algae bloom is avoided.

Lack of maintenance, which was caused by insufficient available funds has gradually deteriorated the performance quality of the WWTP in the 10-years of operation. Repair and rehabilitation measures are needed at the WWTP to achieve again the very high effluent quality needed. Furthermore, maintenance and emergency plans must be developed and sufficient budget must be provided to the PUC Waterworks to make sure preventive maintenance can be completed.

Much of the area of the sewerage network of Palic does not cover all built-up areas. Many households are using septic tanks which are unlined and therefore leaking, polluting the groundwater and finally the lakes. Even if a sewer line exists next to houses, no legal obligation exists in Subotica municipality to connect to the sewerage system, which is unusual. The project foresees the extension of the sewerage network in Palic residential and tourist areas and the connection to it must be made obligatory.

The project foresees the construction of a new wastewater pump station (WWPS) in Palic and a pumping line to Subotica which will bring all collected wastewater to the Subotica WWTP.

Until recently, agricultural land pots extended directly up to the lake shore. This caused air pollution by dust and groundwater pollution from fertilizers.

The project foresees the establishment of a buffer zone around the lake. This will be on average a 20 meter wide stretch of grass, bushland with trees, also accommodating a service road for buffer zone maintenance and a bicycle track.

Current Situation and Project Progress

WWTP upgrading: Construction of the phosphorus polishing station comprising of the pumping station, phosphorus precipitation plant and state-of-the-art rotating disc filters has been completed. The test operation has started on 15 September 2021. Bulk flow meters were installed which allow establishing a precise water balance and phosphorus balance of the WWTP. The sludge dewatering facilities were generally overhauled and a canopy was built over the sludge loading area to avoid rain diluting the dewatered sludge. A hook loader truck and containers were procured so that PUC can transport the dewatered sludge to the regional landfill, where it is used for producing compost. An emergency response plan has been developed to enable PUC to react quickly in case of an emergency at the WWTP in order to minimise potential phosphorus spills to Lake Palic. Through all these measures the phosphorus discharge to Lake Palic will be significantly reduced.

Palic WWPS: construction of the wastewater pumping station was completed. Since the beginning of August, the WW of Palic is pumped to the Subotica WWTP and treated there. Special water hammer equipment was installed to protect the 5 km long pumping main from hydraulic damages. The pumping station was taken over by PUC on 15 September 2021. Optimization of the plant and finalising outstanding activities continues.

Palic sewerage: the construction of an 18.6 km sewer network was originally planned; 21.9 km were actually constructed and works were completed in October 2020.

Construction of buffer zones: Construction works for the buffer zones (green belt) around Lake Palic and Lake Ludas are completed to approx. 85% and works are scheduled to be completed in November 2021. A long period is required, since planting trees and bushes is only possible in spring and autumn. Watering of the trees and bushes and cutting of grass and invasive plant species is ongoing. Machines and equipment (tractor, multi-purpose machine, trailer, mowing machines etc.) has been procured for maintaining the buffer zone, and PE Palic-Ludas is intensively using it. Construction of bird watchtowers and rest areas was completed in September 2021 and the facilities are well accepted by visitors. The construction of foot paths and bicycle lanes has been completed in June 2021. 2214 meters were originally planned and 2690 meters have actually been constructed. Right from the date of completion, the facilities have been intensively used by the local population and by visitors.

Biomanipulation: A specialised fishery boat, 8 trap nets and other fishery equipment were procured and are now used by PE Palic-Ludas for selective fishing. Selective fishing campaigns were performed in 2019, 2020, 2021 and will continue in future, as it is necessary to control the population of the Prussian Carp (Babuska). The 2021 campaign was re-started on 2 September and the amount of landed is very satisfactory. This fish species is not native in the region and reproduces massively if not continuously controlled by selective fishing; an overpopulation of the fish would negatively affect the water quality. As part of the project, scientific research was done by the Scientific Institute of Veterinary Medicine of Serbia, led by Dr Vladimir Radosavljevic. It was possible to clearly prove that the seasonal fish kill of the Prussian carp is caused by an outbreak of the herpesvirus hematopoietic necrosis (HVHN) and is not related to the water quality. The virus affects only the Prussian carp, not the other fish species in the lake and is not harmful to human beings.

Due to the long turn-over period of the lake body, the positive effects of all the above measures on the water quality of Lake Palic will be fully visible and measurable only about 8 months after the facilities are in operation. Therefore, the lake monitoring will be continued till the end of 2022.

The investment period of the project has been extended till November 2021 due to COVID restriction measures.

Project Activities / Scope of Works

The project activities are split into A – Investment measures and B – Accompanying measures.

Services A – Investment Measures:

A1 – Upgrade of the Subotica wastewater treatment plant (WWTP)

A2 – New wastewater pumping station in Palic and pumping main to Subotica

A3 – Extension of the sewerage system in Palic

A4 – Construct buffer zone around Lake Palic and Lake Ludas with bicycle lanes, visitor viewpoints

A5 – Perform biomanipulation on Lake Palic.

Services B – Accompanying Measures

B1 – Technical Assistance to PUC “Water and Sewerage” Subotica, including monitoring industrial discharges, strategy for emptying septic tanks, tariffs, PR activities

B2 – Technical Assistance to PE “Palic-Ludas”, including buffer zone operation & maintenance, sources of income to finance buffer zone maintenance, PR activities

B3 – City of Subotica, including groundwater monitoring, establish project website, environmental education, cooperation with tourism associations, the involvement of NGOs, PR activities

Budget and Financing

6.5 Million EUR (approx. 780 Million RSD) grant financing from the Government of Germany, administered by the KfWEntwicklungs bank

1.0 Million EUR (approx. 120 Million RSD) by Local Government (City of Subotica) for land acquisition and compensation payments and contributions in kind.

Financing