The Case Study addresses small urban streams (average flow < 1 m³ s^-1) in the City of Lodz (Poland) integrated with the city sewerage. Their channelisation reduces self-purification capacity and deteriorates water quality. Highly impermeable catchments reduce water retention in landscape and increase stormwater peak flows. This periodically impacts purification capacity of the wastewater treatment plant. The Case Study objectives include application of ecohydrology to address the above issues. Their harmonisation with technological measures aims to improve residents' health, quality of life and economic benefits.

Restoration concept towards sustainable sewage system management: phytoremediation for sewage sludge utilization and bioenergy production (Zalewski and Wagner, 2006).

Background

The City of Lodz with 776,000 inhabitants (2004) is the second biggest city in Poland. Recent development of education, scientific and high-technology centres changes the city's profile and expectations of the society and rises the need for high quality of life, including e.g., development of infrastructure, revitalisation of industrial architecture and environment rehabilitation.

The city area is divided into 18 catchments drained by streams with average flows < 1 m³ s^-1. Rapid expansion of the city in the first quarter of the 19th century contributed to severe degradation of natural resources - the streams were channelised and covered. They were adapted as sewerage channels and play this role thus far. The slope of the rivers and channels amounting up to 5-7 ‰  contributes to accelerated runoff and high flows during wet weather.

Lodz is serviced by a mix of two sewer systems - combined sewers in the centre and separate sewers in the suburbs (Zawilski, 2001). The industrial and domestic sewage (from about 80% of population) as well as stormwater (in combined sewers) are conveyed to the central city Wastewater Treatment Plant (WWTP). After physical and biological treatment, treated sewage (average flow 2,5 m³/s) is discharged into the Ner river, with a natural discharge of less than 0,8 m³/s. The flow of sewage increases more than tens times during storms, exceeds the treatment capacity of the WWTP and impacts on the quality and ecological stability of the river.

Key aquatic habitat issues in urban water management

Adaptation of small city rivers for interception of stormwater loads

The city location, catchments morphology and development reduce water retentiveness in the landscape. The effects of these activities are especially pronounced in small urban catchments, where streams and rivers are channelised for stormwater detention according to traditional engineering rules. As listed by Bocian & Zawilski (2005), disturbances of the water cycle in Lodz include: (i) acceleration of surface flow and increase of flood peaks, (ii) decrease of groundwater recharge, (iii) decrease of groundwater runoff, and (iv) decrease and extent of low flows.

Degradation of rivers habitats and of their self-purification potential

Degradation of freshwater habitats by their channelisation seriously handicaps ecosystems functioning, by impacting their biotic structure, biological diversity and destroying functional links within the ecosystem. Those impacts, superimposed by the disturbances listed in the previous section, reduce ecosystems resilience, impacting its self-regulatory processes. Reduced self-purification together with high pollutant loads lower the assimilative capacity of streams and deteriorates water quality. As a result, toxic cyanobacterial blooms were observed in some reservoirs (Izydorczyk, unpublished data), and the concentrations of the produced toxins reached in 2006 extremely high values of up to 60 ug/l (Jurczak, unpublished data).

Decreased ability of the WWTP for combined sewage purification and sewage sludge utilisation

Increased inflows into the WWTP during flood peaks reduce the plant ability to purify sewage and lower the water quality in the receiving water - the Ner river. Years of sewage disposal contaminated river and floodplain sediments with heavy metals and organic compounds. The total heavy metal concentrations in the floodplain soils range from: 11 to 598 mg/kg for Zn, 7 to 390 mg/kg for Cr, 7 to 121 mg/kg for Cu and 11 to 93 mg/kg for Pb (Bocian, unpublished data) and positively correlate with the organic matter content. Decrease in water use and sewage disposal within the last 15 years lowered groundwater level and accelerated sediments mineralisation. It resulted in leaching of heavy metals and their accumulation in food chains in floodplains used for agriculture. The process is enhanced by high combined sewerage flows through the WWTP in wet weather. Utilisation of sewage sludge produced by the WWTP constitutes another economic and ecological issue.

Objectives of the Case Study

i) Environmental goals

• rehabilitation of selected sections of the city rivers based on harmonisation of hydrotechnical and ecological measures, for increasing hydrological and ecological capacity of urban aquatic ecosystems in coping with human impacts;
• reclamation of degraded urban river floodplains and wetlands and natural measures for stormwater retention;
• increased number of green areas and open waters in the city for improvement of microclimate, human health and quality of life;
• providing ecological solutions complementary to operating technologies in the Wastewater Treatment Plant in Lodz, increasing the ecological and economic efficiency, according to the EU directives requirements (utilisation of sewage sludge, bioenergy production, protective green zone around the WWTP, and capital savings).

ii) Societal goals

• providing solutions for secure water resources for social safety (preventing toxic algae blooms, heavy metals contamination) and increasing quality of life;
• providing ecological solutions complementary to operating technologies in the WWTP for increasing ecological and economic efficiency and meeting the EU directives requirements (e.g., utilisation of sewage sludge, bioenergy production, protective green zone around the WWTP);
• ensuring strategy for development of high quality recreation areas in a good state environment;
• increasing awareness of good quality water and environmental resources value and their role for the quality of life;
• attraction of new investments and people of action, contributing to increasing city attractiveness, creating strong city image and local patriotism;
• improving internal (within the city stakeholders) and external (national, international) cooperation, enhancing knowledge sharing, experience flow and broad city promotion;
• building a basis for participatory approach to environmental and city problems, promotion/strengthening of bottom up initiatives;

ii) Policy and Administration goals

• defining clear priorities in water management and related sectors, and accelerating investments in the related infrastructure;
• incorporating IUWM know-how and ecohydrological innovations into local (city level) legislation and policy, and its up-scaling to the national level;
• adopting water management and related issues to the EU standards and requirements of the EU directives;
• improvement of efficient cooperation and information sharing between stakeholders, governmental and self-governmental authorities and services, on the city water resources management strategy;
• development of strategy for fundraising;

Stakeholders

• Department of Applied Ecology, University of Lodz
• European Regional Centre for Ecohydrology, Polish Academy of Sciences
• Municipal Office of Lodz
• Technical University of Lodz
• Recently, the activities have been enriched by the European Integrated Project of the 6^th Framework Programme SWITCH.
• The Learning Alliance (LA) established within this project assembles the self-government, local national authorities, the city's liaisons, scientific institutions, NGOs, schools, media and society representatives.

See References