Flow Parameters and Trophic Structuring of River Mesta Invertebrate Communities

1. COMPLICITY OF FLOW PARAMETERS IN TROPHIC STRUCTURING THE BOTTOM INVERTEBRATE COMMUNITIESOF THE RIVER MESTA (SW BULGARIA) Yordan UZUNOV*, Snejana DAKOVA**, Emilia VARADINOVA* *Central Laboratory of General Ecology **National Institute of Meteorology & Hydrology Bulgarian Academy of Sciences, Sofia 

2. A backbone principle of the River Continuum Concept(Vannote et al. 1980) is: changing hydrological conditions generate series of biotic responses in stream communities along rivers creating a continuum of the lotic environment. The community trophic structure should be considered as a reflection of dominating ecological situation with respect to both hydrological features of a given stretch and the amount and availability of the organic matter. Instead of common recognition of stream hydrology in structuring and functioning of the invertebrate communities, there is a few number of papers on the specific role that flow parameters play in establishing and dynamics of the functional feeding groups (FFGs) within the community trophic structure.

3. The aims of the report: to represent the behavior of the FFGs in a model river system as connected with some flow parameters, water thermal regime and degree of loading with biodegradable organic matter (saprobity). The River Mesta was selected as a model as far as its ecological status has been well studied for the last 25 years in terms of its hydrology, benthic invertebrate fauna, community trophic structure and water quality.

4. vmountain river with mean basin altitude of 1318 m River Mesta (Nestos): YAKO Bulgaria IZTK v126-km length v2770 km2 of catchment area • average annual discharge from 4.63 m3.s-1 at YAKO to about 25 m3.s-1 at the KUPN site KUPN

5. mean maximal flow ranged from 8 m3.s-1 at YAKO-site to 73 m3.s-1 at the KUPN-site • in summer, especially in August-October, the flow falls down to about 0.7-0.8 m3.s-1 • since 1975 the streamflow has been influenced by water intakes and transferring derivations to the high-mountain reservoir “Belmeken”.

6. 3 sites at gauging stations selected: site of YAKO - high/good ecological status (slightly disturbed, non-polluted), site of IZTK - poor ecological status (heavily polluted by organic matter), site of KUPN – moderate/good ecological status (recovered, due to the selfpurification,) Flow parameters selected at each of the gauging stations: stream flow discharge (Q, m3.s-1), cross-section area (F, m2), mean current velocity (V, m.s-1), water depth (H, m) Biological samples gathered using a quantitative net (Surber’s type) covering 0.1 m2 of bottom surface Saprobic status determined by using the Pantle & Buck’s saprobic index S in its latest modification

7. 6 basic FFGs identified: shredders (SH), collectors-gatherers (CL), filterers (FL), grazers/scrapers (SC), predators (PR), deposit feeders (DF) Pearson’s correlation coefficient, multi-regression analyses and linear multi-regression models investigated further the relationships among the hydrographic and biological parameters RDA (CANOCO 3.1) performed to determine which environmental variables were significant in explaining the variations of the community trophic structure as represented by the percentage share of the basic FFGs

11. One-dimensional models (Pearson’s correlation) showed poor and usually negative correlation between flow discharge (Q) and most of the functional feeding groups (FFGs) in terms of their percentage share. There were only few cases of relatively higher correlation, for instance between Q and SH (R = 0.409) and CL (R = -0.356) at the site of KUPN.

12. 3- and 5-parameter regression models with participation of the flow parameters (Q or V, F, and H), water temperature (T) and saprobic index (S) described of the FFGs dynamics at the selected sites: The percentage share of each FFG was regulated by the dynamics of at least three stream parameters: the flow (Q), the heath (T) and the organic matter (S) which values created unique combination along the river continuum at every given moment/site

13. S +1.0 DF Q CL PR SH SC FL T -1.0 -1.0 +1.0 Biplot for RDA for the site of YAKO

14. +1.0 S Q DF PR SC FL SH CL T -1.0 -1.0 +1.0 Biplot of RDA for the site of KUPN

15. Biplot of RDA for the site of IZTK

17. CONCLUSIONS Hydrological factor appeared to be of great importance for structuring the bottom invertebrate communities of the studied River Mesta Flow parameters as hydrological factors have no single effect in setting up the species content, time-space organization and trophic structure of the invertebrate communities

18. Effects of the stream hydrology were associated with the action of other important factors like water temperature (T) and available organic matter (estimated by S). Their joint action could explain up to 95% of the dynamics of FFGs like SH, CL, SC and DF Trophic structure as represented by relative share of FFGs might be accepted as a dynamic biotic response to the dominating combination of factors at given site and/or time

19. Thank you for your kind attention