Analyses and assessment of the spatial and temporal distribution of nitrogen compounds in surface waters Nedyalka Georgieva 1 , Zvezdelina Yaneva 1 & Gergana Kostadinova 2 1 Chemistry Unit, Department of Pharmacology, Animal Physiology and Physiological Chemistry, Faculty of Veterinary Medicine, Students Campus, Trakia University, Stara Zagora, Bulgaria and 2 Applied Ecology Unit, Department of Applied Ecology and Animal Hygiene, Faculty of Agriculture, Students Campus, Trakia University, Stara Zagora, Bulgaria Keywords ammonium; hierarchical cluster analysis; nitrates; nitrites; principal component analysis; Stara Zagora Region; surface waters. Correspondence Nedyalka Georgieva, Chemistry Unit, Department of Pharmacology, Animal Physiology and Physiological Chemistry, Faculty of Veterinary Medicine, Trakia University, Students Campus, 6000 Stara Zagora, Bulgaria. Email: nvgeorgieva@vmf.uni-sz.bg doi:10.1111/j.1747-6593.2012.00341.x Abstract The temporal concentration variations and spatial distribution of nitrogen com- pounds (nitrate, nitrite, ammonium) in the natural surface waters of Stara Zagora Region, Bulgaria, over a period of 1 year were assessed in the present study. Nitrate- nitrogen concentrations in all surface water samples, except for the December value – 21.8 mg/L in Zetyovo Reservoir, were within the permissible national quality standards. NO2 – -N could be classified as a priority pollutant of Chirpan and Zetyovo Reservoirs waters. The greatest extent of NH4 + -N pollution was registered in Chirpan Reservoir surface waters. The correlation study revealed appreciable mutual rela- tionship only between NH4 + -N and NO2 – -N in the surface waters. The hierarchical cluster analysis (HCA) exhibited divergent apportionment of nitrogen compounds in the surface water bodies. Introduction Over decades, increasing anthropogenic inputs of nutrients have led to deterioration of natural water quality (Mohlenberg et al. 2007). Nitrogen compounds constitute one of the major groups of contaminants of natural and drinking waters. They are applied in several different industries: ammonia synthesis; by-products of colouring and synthetic agent production; food freezing technologies; food additives; detergents (nitriloacetate); agents for superconductor and ceramic devel- opment; sprays and fire extinguishers, rocket fuel oxidator (N 2O4); constituents of explosives; decomposition products of sewage water treatment plants; landfill leachate, etc. (Mason 2002). The main sources of nitrogen compounds in water are commercial fertilizers: inorganic, predominantly – NaNO3 and NH4NO3, and organic, containing mainly ammonia, ammo- nium, urea and amines (Howart et al. 2002; Ribbe et al. 2008; Drolc & Koncan 2010). According to the investigations of two American groups of scientists (Randall & Mulla 2001; Chen et al. 2007), noncontrollable factors such as climate and soil organic matter have a profound influence on NO3 – -N concen- trations and loadings in subsurface drainage water. Nitrate concentration in natural water bodies is a complex phenomenon which involves both soil N cycle and the hydro- biology of the water resource (Garnier et al. 2010). Previous studies have shown that nitrate leaching is also strongly affected by management practices such rural land uses, especially agricultural practices. Fertilizer application, irriga- tion and planting patterns, can contribute nitrate to ground- water [Rodvang & Simpkins 2001; WHO (World Health Organization) 2004; Sankararamakrishnan et al. 2008]. Nitri- fication of naturally occurring ammonia in raw alluvial water can result in higher nitrate levels in the finished water. A recent study on the occurrence of ammonia, nitrite, nitrate and nitrifying bacteria in a number of Iowa alluvial supplies found that many supplies with elevated ammonia levels in their raw water had higher nitrite and nitrate levels in their distribution systems and that bacterial growth (even with chlorination) was sufficient to lead to the conversion of ammonia to nitrite and eventually to nitrate in the system (Weyer et al. 2006). Large amounts of nitrate in natural water bodies may cause eutrophication, which means an excess of nutrients resulting in oxygen deprivation and fish deaths (Mason 2002; Seitzinger et al. 2002). Nitrite is known to be a precursor of toxic and carcinogenic N-nitrosamines and induces cancer in experimental animals. Nitrate on the other hand can be reduced to nitrite in vivo, causing abdominal pain, blood in stool and urine, weakness and collapse (Okafor & Ogbonna 2003). The ammonia in natural waters results from the incomplete degradation of nitrogen-containing organic substances or from groundwa- ters. When the measured NH 3/NH4 + concentrations in the Water and Environment Journal. Print ISSN 1747-6585 187 Water and Environment Journal 27 (2013) 187–196 © 2012 CIWEM.