DIATOM SPECIES COMPOSITION OF THE NIŠAVA RIVER AND ITS TRIBUTARIES JERMA AND TEMSKA RIVERS (SOUTHERN SERBIA)

The main objective of this paper is to report the diatom taxa identified from the Nišava River and its tributaries, the Jerma and Temska rivers. The study area included 11 sampling sites along the Nišava River, with one site on the Jerma River and one on the Temska River. Monthly samples (from stones, sediments and macrophytes) were collected from May 2008 to May 2009. Diatom frustules were cleaned with chemical agents, and mounted on permanent slides. In total, 194 diatom taxa were identified. The most species rich genera are Navicula (25), Nitzschia (17) and Gomphonema (13), while other genera are presented with one or more species. Detailed floristic analysis of the benthic diatom flora has not been conducted before on these rivers. Therefore, this paper provides a baseline for future research.


INTRODUCTION
Benthic algae are primary producers in streams and are the main source of energy in a food chain for aquatic organisms (Biggs, 1996).Diatoms are often the dominant group of algae in streams (Dodds, 2002).In this regard, their taxonomic diversity is an important aspect of an aquatic community because it reflects the biodiversity and stability of a river ecosystem.
The Nišava River is the biggest tributary of the South Morava River.It belongs to the Black Sea drainage basin, originates in the Stara Planina Mountains, arising from the Ginska and Vrbnica rivers at an elevation of 640 m, near the village Toden in Bulgaria.It enters Serbia 6 km from the city of Dimitrovgrad, flows generally westward, until it empties into the South Morava River, about 10 km from the city of Niš.Along with Ginska River, it is 202 km long, with a catchment area of 4068 km 2 (the Serbian part is 151 km long, the catchment area is 2971.5 km 2 ).Major tributaries of the Nišava River are the Temska, Visočica and Jerma rivers (Gavrilović and Dukić, 2002).The Nišava River is an important water resource for Niš (Branković et al., 2007), though the negative impact of Niš's wastewater has been reported by Branković et al. (2009).Pirot's communal waste is also a major pollution point (Miljojković et al., 2010).Martinović-Vitanović (1985) has reported a few plankton diatom species from the Nišava River, as part of the South Morava drainage basin, while Branković et al. (2007) and Trajković el at. (2008) have reported 17 benthic diatom species from Sićevo and Prosek localities.
The main objective of the manuscript is to present 194 diatom taxa identified from 13 sampling sites in order to create baseline date for future research.The diatom flora is described and the physico-chemical properties of the water are presented.

MATERIALS AND METHODS
The study area included 11 sampling sites along the Nišava River, with one site on the Jerma River and one on the Temska River (see Fig. 1).The sampling sites were located before and after the cities of Dimitrovgrad, Pirot, Bela Palanka and Niš, and before and after the Jerma River estuary.

Diatom species composition
A total of 194 diatom taxa were identified in this investigation (Table 1): 177 in the Nišava River, 116 in the Jerma River and 92 in the Temska River.Of the 194 taxa, 69 occurred in all three rivers.Several diatom taxa occurred in only one river: 57 in the Nišava River, 9 in Jerma River and 6 in the Temska River.
The dominant species were: Achnanthidium minutissimum, A. pyrenaicum, Amphora copulata, Cocconeis placentula, Gomphonema minutum, G. pumilum, Navicula cryptotenella, N. reichardtiana, N. tripunctata, Nitzschia dissipata and N. fonticola.These species were abundantly-developing in mass and strongly predominating over the other diatom species in the community, and frequently-appearing in the majority of samples.Several diatom species were also abundant, but only at individual sites: Diatoma moniliformis and D. vulgaris at site no. 1, Nitzschia palea at site no.2, Navicula tripunctata at site no.7, Cocconeis pediculus at sites no.6 and 8, Eolimna subminuscula, Navicula capitoradiata and Ulnaria ulna at site no.11.The presence of plankton species such as Asterionella formosa and Cyclotella meneghiniana in the benthos was probably a result of drift from dams situated on the Nišava River.The highest species diversity was recorded at site no. 1, and lowest at site no. 5.
The recorded composition of the benthic diatom community is typical of running water and is similar to the diatom communities from other rivers in Serbia (Ržaničanin, 2004;Simić, 1996;Laušević, 1993;Nikitović, 1998;Tomašević, 2000;Jurišić, 2004).Similar to our study, Navicula was the most species rich genus in the West Morava River (Jurišić, 2004), Trgoviški Timok River (Simić, 1996) and in the Samokovska River (Laušević, 1993).Species belonging to the genera Navicula and Nitzschia are highly motile and capable of moving through sediments (Round, 1990).The high number of samples from epipelon might explain the high number of species of the Navicula and Nitzchia genera in our study.The availability of these microhabitats might play an important role in determining the spatial distribution of the species, though the distinct niche preferences of the diatoms in the samples collected from the rivers may not be so obvious (Round, 1991(Round, ,1993)).Ecological data about Achnanthidium minutissimum are controversial in the literature.The species is ubiquitous (van Dam, 1994), reported to be both tolerant to pollution (Stevenson and Bahl, 1999) and found in nutrient-poor waters (Kelly and Whitton, 1995;Potapova and Charles, 2007).In our study, the species was dominant at site no. 1, the Jerma and Temska rivers, where nutrient concentrations were lower in comparison to the other sites.Navicula cryptotenella, N. reichardtiana, N. tripunctata, Nitzschia dissipata and N. fonticola are tolerant to moderately tolerant to heavy organic pollution (Rott, 1999), and were dominant at sites nos.2, 6 and 11.Physico-chemical analysis indicated elevated concentrations of nitrates and ammonium ions at these sites, which can be linked to the industrial and communal wastewaters from Dimitrovgrad, Pirot and Niš.An increase in nutrient concentration after Pirot and Niš has also been reported by Branković et al. (2009) and Miljojković et al. (2010).Species such as Achnanthidium minutissimum, Amphora pediculus, Cocconeis placentula, Gomphonema parvulum and Ulnaria ulna appear to be widely distributed inhabitants in three diatom communities on riverbeds and cosmopolitans (Ivanov et al., 2006;Voicino et al., 2004;Komulaynen, 2009;Potapova and Charles, 2003;Wunsam et al., 2002;Bere and Tundsi, 2011).The structure of the diatom assemblages from the Nišava, Jerma and Temska rivers agrees with findings in the literature, which indicate that diatom communities are dominated by a few species that occur frequently and a large number of rare species that occur occasionally, or sometimes only once (Round, 1993;Kelly and Whitton, 1995) (Fig. 3).
A previous study of the biota from the Nišava River (Branković et al., 2007;Trajković et al., 2008) reported 17 diatom species.The number of samples studied (326 samples in total), collected monthly from diverse microhabitats, was probably the factor contributing to the much greater number of taxa identified (194 taxa).

Fig. 2 .
Fig. 2. Minimal, maximal and mean values of measured environmental variables in the Nišava, Jerma and Temska Rivers

Table 1 .
List of the benthic diatoms, found in the Nišava, Jerma and Temska Rivers.Species names are listed in alphabetical order.Abbreviations: N-Nišava River, J-Jerma River, T-Temska River.The symbol +͵ represents the presence of a species, and -͵ represents the absence of a species.

Table 2 .
List of diatom genera with the number of species from the Nišava, Jerma and Temska Rivers