Summary

The river Vjosa, located in the south of Albania, is considered to be the last free flowing river in Europe. Its entire catchment area, from the upper reaches to the confluence with the Adriatic Sea, still represents a dynamic fluvial ecosystem with unchanged hydromorphology, while in some of its tributaries some small WKU systems are already in operation. Recently he has been threatened by several new hydroelectric projects.

This study examines the longitudinal distribution of macroinvertebrates along the Vjosa and its main tributaries. It is a first attempt to investigate the predictions of two international scientific concepts - River Continuum Concept (RCC) and Serial Discontinuity Concept (SDC) - in a free flowing river in Europe. Sampling covered various geomorphological habitats along the catchment area as much as possible, including canyon, braided and meandering areas.

However, this is a preliminary study, more samples will be needed to better examine the longitudinal distribution and the influence of serial discontinuities along the river. The results of this study will serve as a guide for an upcoming study that will include more measurements and be more complementary.

Goal of the project

The aim of this project is to study the longitudinal distribution of macroinvertebrates along the Vjosa River and to determine the factors that determine their composition. The data are compared with the prediction from the flow continuum concept and the concept of serial discontinuity in order to investigate the influence of discontinuities in the free flowing Vjosa river system.

The research question is to show whether this is the most important factor

• the position within the river system, e.g. that the flow continuum principle generally prevails,
• the local channel gradient or the tributaries of the tributaries, which means that such discontinuities dominate the composition of the invertebrate community at least locally,
• or, alternatively, when neither RCC nor SDC but some small-scale mesohabitat variables (perhaps covariables of the gradient), such as sediment particle size or periphyton abundance, determine the composition of the invertebrate community.

Methods and field of study

For this study, sampling was carried out in the Vjosa River in Albania and its main tributaries Sarantaporos, Langarica and Bënça. The samples were collected in a total of eight locations in two seasons - April and September 2017. Five of them are in the Vjosa, and three in each tributary.

The sampling covered, as much as possible, different geomorphological habitats along the catchment area, including two tributaries with the presence of gorges (Langarica, Bënça) and a tributary with great influence on the sediment regime (Sarantaporos), as well as branched and meandering areas along the main course.

The samples are taken with the standard sampling method of the Kick-net with the dimensions 23 cm x 25 cm and a mesh size of 0.5 mm (ISO: EN 27828: 1994) and stored in 75% ethanol.

During the stay at the Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB) Berlin, the samples from the sediment are sorted and determined at the lowest possible taxonomic level. Once identified, the macroinvertebrates are grouped into the most important functional diet types (pasture / scraper, chopper, gatherer, filter feeder and predator) and compared with the classification of the river continuum concept. The number of taxa, their abundance and species richness were calculated for each location and for each sampling period.

Discussion

The composition of the macroinvertebrate community was found to be very different in the four rivers studied. The greatest differences are between the tributaries due to their large differences in geomorphological and chemical parameters. More similarities are seen between Vjosa and Bënça because they have better water quality and less influence from external factors. Such as HPP-s, thermal springs, changes in the water regime or turbidity. Due to the large differences between the three tributaries, we expect that they will heavily influence the Vjosa River and most likely create a local canal gradient and an at least locally dominant community composition.

Macroinvertebrate diversity was greatest in the middle section of the river and is dominated by grazers and foragers. The longitudinal composition of the macroinvertebrate functional groups along the river is generally consistent with the RCC predictions, but some small-scale mesohabitat variables such as sediment type, peryphyton occurrence, temperature, chemical parameters, etc., are also very important factors influencing the composition determine the macroinvertebrate community.

However, this is a preliminary study, more samples will be needed to better examine the longitudinal distribution and the influence of serial discontinuities along the river. The results of this study will form the basis for a future study that will include more measurements and be more complementary.