Water Quality Assessment Based on the Macroinvertebrate Fauna - the Pcinja River Case Study - page 03

 

Namely, the most sensitive stoneflies completely disappeared and the presence of pollution tolerant ET families (Baetidae and Hydropsychidae) was recorded. According to Simić (1998), stoneflies, as the most sensitive group, immediately disappear under disturbance, while mayflies and caddis flies vanish in conditions of higher pollution stress. The main representatives of the benthic community at T6 were generally the most pollution tolerant groups Hirudinea, Isopoda, Chironomidae and Oligochaeta (Armitage et al., 1983). This community type is characteristic for degraded stream zones influenced by organic loading. This statement was confirmed by the absolute dominance of Asellus sp. toward Gammarus (gamarids were absent) which is also associated with organically rich discharges (Whitehurst, 1991).

According to the macroinvertebrate community structure, the Kumanovska River has a negative influence on the Pcinja River, which is reflected in the lower EPT values (Figure 2) at the sampling site situated downstream from this tributary (T7), as well as the presence of few tolerant groups (Table 1).

The site T8 is characterised by the domination of Mollusca, Odonata, Ephemeroptera, Oligochaeta, Chironomidae and Hemiptera (Table 1). A low EPT value (3 families) was recorded (Figure 2), indicating a change of watercourse type in addition to moderate impact. Trichoptera and Plecoptera were absent in the collected material.

 





Regarding Plecoptera, their absence could be explained by a change of the watercourse type from a typical hilly-mountainous stream in the upper stretch, to a lowland river, since stoneflies assemblages consist mostly of cold stenothermic representatives that are typical for higher altitudes (Miserendino, 2006).

The absence of caddis flies (Trichoptera) taxa is probably a consequence of organic load, since some of the representatives of this order typically inhabit lowland rivers. Concerning mayflies, only Baetidae, Caenidae and Heptageniidae were recorded at the sampling site T8.

 

Water quality assessment based on BMWP and ASPT – family level approach

Table 2 presents a biological assessment of the status of the Pcinja River based on macroinvertebrates. The composition and structure of benthic communities, as well as the BMWP/ASPT values indicate a healthy, natural or near natural water ecosystem or a good ecological status along the river course, from the source region to the sampling point T5.  Low BMWP and ASPT values clearly show poor conditions at the sampling point T6 (the mouth of Kumanovska River). The sampling point T7 is characterised by a deterioration of water quality in comparison with upstream sites – a moderate ecological status at the T7. The last sampling point (T8) shows a good to moderate status.