Water Quality Assessment Based on the Macroinvertebrate Fauna - the Pcinja River Case Study - page 04

 

Discussion

According to our investigation of the Pcinja River, considerably high macroinvertebrate taxa richness was recorded. A total of 40 families were identified. Trichoptera (10), Ephemeroptera (6) and Diptera (5) were the most diverse groups, taking into consideration the number of families, while the other taxa groups were less diverse. The structure of the community was found to be similar to the results reported by Simić and Simić (2003).

A decrease was recorded in the number of families along the watercourse in the downstream direction, which indicates environmental stress. The observed change in the community structure indicates the presence of pollution, but also a change of the type of watercourse. Namely, the upper and middle part of the river was characterised by a greater macroinvertebrate taxa richness, expressed as the number of recorded families (16-22) which is related to the stability of the environment (Wynes and Wissing, 1981). The decrease of taxa richness at sites T6 and T8 (11 and 13 families respectively), as well as the absence of Trichoptera at T8, clearly indicates water quality deterioration. The absence of caddis flies (Trichoptera) taxa is probably a consequence of organic load, since some of the representatives of this order typically inhabit the lower stretches of rivers.

The change of type is illustrated by a change in the community composition in the lower course of the Pcinja River. The site T8 is characterised by the presence of Mollusca, Odonata, Ephemeroptera, Oligochaeta, Chironomidae and Hemiptera, taxa groups which are typical for lowland rivers. In addition, among Baetidae and Caenidae families that were recorded within the stretch, there are representatives characteristic for the lower part of rivers (Vidinova et al., 2006). Heptageniidae species, with some exceptions (Vidinova and Rusev, 1997) inhabit mountainous and foothill streams. However, having in mind that few species are widely spread in the hypopotamal rivers (Vidinova and Rusev, 1997), their presence in the mouth region of the Pcinja River could be expected. These results concur with an observation by Ikonomov (1963) who found a presence of the Heptageniidae species in the mouth of the Bregalnica River, one of the left tributaries of the River Vardar. Several species of Heptageniidae were also found within the lower stretches of the rivers in Serbia (Paunović et al., 2006, 2007).

The composition and structure of benthic communities, as well as the values of selected macroinvertebrate based metrics (BMWP/ASPT) indicate a healthy, natural or near natural water ecosystem or good ecological status along the river course, from the source region to the sampling point T5. According to the classification given by Armitage et al., (1983) low BMWP and ASPT values show poor conditions at the sampling point T6 (the mouth of Kumanovska River). Consequently, the Kumanovska River causes a deterioration of the water quality downstream of the confluence. Therefore, sampling point T7 is characterised by a deterioration of water quality compared to upstream sites. Selected metrics indicate a moderate ecological status at the T7. The last sampling point (T8) shows a good to moderate status. Such a degree of category recorded in the confluence area of a river shows that the river Pcinja has a high capacity for self-purification.

 





To summarise, the results of this study show that the Kumanovska River has a strong negative influence on the Pcinja River ecosystem. Therefore, an adequate monitoring and management strategy should be implemented in the Pcinja River watershed. The matching of the established categories based on macroinvertebrates once again underscores the necessity for a parallel implementation of both biological components in the process of assessing the status of an aquatic ecosystem. According to the WFD requirements, five biological components are proposed, so a further more extensive investigation should be followed.

Our study has indicated that methods of ecological status assessment, based on selected macroinvertebrates, would be a good approach for effective monitoring and screening of aquatic ecosystem health in selected river types. The use of family level indication based on a macroinvertebrate community was found to be an effective indicator of environmental pollution. This made the process of biomonitoring more efficient, because family level identification of taxa requires less time for sample processing, and thus it is much more cost effective.

The EPT family index was effective for use only in rivers with hard bottom substrates. The index clearly reflects the quality of the aquatic environment (Bode et al., 1997). Nevertheless, the effectiveness of the index decreases along the river continuum and in the case of typical lowland rivers, the metric is not a good indicator of environmental stress, since the EPT taxa within those river habitats naturally occur with a lower number of species and lower population densities (Paunović, 2007). The situation of a decrease of EPT effectiveness for ecological status assessment in the downstream direction was demonstrated in our study as well. The decrease in the number of EPT families needed additional explanation in the case of sites situated in the lower stretch of the Pcinja River, due to the fact that part of the community changes are a consequence of natural changes, while part is a result of an increase of pollution.

Regarding the BMWP score, the index was found to be effective. Taking into consideration the original indicator table used for BMWP evaluation (Armitage et al., 1983), the resolution of the metric could be improved by preparing the modification for the territory of Macedonia. A possible improvement of the indicator table scores is mostly related to a change of resulting indicator values for selected taxa among taxa groups (e.g. among the Baetidae family) or splitting some taxa groups into two groups that better reflect the water status (e.g. among Oligochaeta, the Tubificidae family should be separated from the rest of the group

 

Acknowledgements

This research was supported by MED - Macedonian Ecological Society. We would also like to thank Aleksandar Sarov for his technical assistance in GIS analysis.