Biochemical oxygen demand and concentration of ammonium in rivers

Thematic area — Water Name of Indicator — BOD and concentration of ammonium in rivers DPSIR — State Indicator type — A = descriptive indicator Definition of the indicator: Indicator shows the level of oxygen concentration in water bodies, expressed as biochemical oxygen demand (BOD), which is the amount of dissolved oxygen required for the aerobic decomposition of organic matter present in water, and the level of concentrations of ammonium in rivers. The indicator illustrates the current situation and trends regarding BOD and concentrations of ammonium (NH4) in rivers. Units: Annual average BOD after 5 days Incubation (BOD5) is expressed in mg O2/l and annual average total ammonium concentrations in micrograms N/l. Policy relevance of the indicator Legal framework includes: — Water Law # 727 from 23.12.2011 (cam into force on 26th of October) — Regulation on systematic monitoring evidence of the surface waters and groundwater’s status (Government Decision #932 from 20.11.2013) — Regulation on surface water environmental quality requirements (Government Decision # 890 from 12.11.2013) Strategic framework includes: Environmental Strategy (Government Decision #301 from 24th April 2014). International framework includes: — Convention on the Protection and Use of Transboundary Watercourses and International Lakes (Water Convention, Helsinki, 1992); — Convention on Wetlands of International Importance especially as Waterfowl Habitat (Ramsar, 1971) — Convention on Cooperation for the Protection and Sustainable Use of the River Danube (Convention for the Protection of the Danube River, Sofia); Targets — The National Environmental Strategy states that it should be implemented a management system of hydrographical basins in order to improve the surface water quality by 50 % (a. 2023) Agreement to the Regulation on surface water environmental quality requirements Republic of Moldova should improve the quality of surface water with one class. Key question — Has pollution of rivers by biochemical oxygen demand (BOD5) and ammonium noted decrease? Assessment During the assessed period from 1990 to 2014, a stable decreasing trend in BOD 5 and concentrations of ammonium in rivers was tracked up to 2011, followed by slow increase of the mean BOD5 (see Figure #1 and #2). Assessment done by monitoring stations shows that almost in all years concentration of BOD5 at Dubasari monitoring station (349.74 km downstream frontier) is higher with data from Soroca (569.118 km downstream frontier) and Olanesti (51.91 km downstream frontier) monitoring stations (see Figure #3). These results reflect the status of inefficient treatment of urban and industrial wastewaters in Soroca city, where wastewater treatment stations is absent. The same situation is characteristic for the NH4 concentration by monitoring stations (see Figure #4). Key messages: For the period 1990 to 2014 a stable decreasing trend in BOD 5 and concentrations of ammonium in rivers was tracked up to 2011, followed by slow increase of the mean BOD5. Water pollution in rivers is result of inefficient treatment of urban and industrial wastewaters in the country. Methodology: Determination of BOD5 (biochemical oxygen demand in 5 days) is carried out by iodometric method, based on an assessment of the amount of oxygen dissolved in water keeping the sample for 5 days in an incubator, where it is maintained a temperature of 200 C, mgO2/l. Reporting obligations: Convention on the Protection and Use of Transboundary Watercourses and International Lakes (Helsinki, 17 March, 1992), Danube River Protection Convention (Sofia, 29 June, 1994).