Methodology of Macroinvertebrate Survey on Large Rivers: A Case Study on the Romanian Lower Danube

 Béla Csányi1, József Szekeres1, Ágnes Irma György1, Zoltán Szalóky1 and István Falka2

 

 

1 VITUKI – Hydrobiological Laboratory, Budapest, June 2012

2 National Institute for Research and Development in Enviromental Protection, Bucharest, Romania

 

Abstract

The aim of this study was to assess the indicative ecological status of the investigated section within the Lower Danube (rkm 198-347) based on aquatic macroinvertebrates, before the river regulation works,. Sampling on representative river stretches was performed by using different sampling procedures: both littoral and deep water samples were taken from the entire cross section of the river in order to effectively determine the macroinvertebrate assemblages. This paper provides the analysis of completed cross section dredging and littoral K&S sampling in order to complete the detailed taxon list of the investigated localities. One of the most important outcomes of our investigations was the necessity for use of different sampling methods for effective large river survey design programs. The investigated Danube section is situated in the Eastern Wallachian ecoregion and belongs to the Very Large Lowland River typological category. Habitat availability and habitat types both principally influence community structure and species richness. Generally it can be concluded that more abundant macroinvertebrate communities exists in the littoral zone than in the deeper river bed. The individual numbers are usually very low in the deep water zone which is dominated by continually shifting sand.

Keywords: Lower Danube, macroinvertebrate sampling, large river, community structure, species richness

 

Introduction


The application of the EU Water Framework Directive (WFD) requirements for biological data collection on large rivers, in order to fulfill the ecological status assessment, is still under development. Standardized sampling methods for the Danube River are generally lacking in important biological quality elements such as aquatic macroinvertebrates and fish stock.

There are manifold causes of this sampling difficulty:

  • Principally, the dimensions of a large lowland river have to be considered. The accessibility of different regions existing along the water body is always limited;
  • The dynamic changes of hydrological and hydraulic conditions result in spatial (and temporal) heterogeneity that should be taken into account during sampling;

The size of large lowland rivers implies a difficult question in regards to sampling design: what is the meaning of representativeness in case of a given – theoretically homogeneous but in reality heterogeneous - water body? Different depths existing across a cross section and this having important consequences for appropriate sampling.

The properties of different physical habitats in the water body are determined by very different hydrological and hydraulic conditions. Besides discharge and water level variations, usually the dynamically changing shear stress from water flow are principally important in determining the actual grain size distribution and parallel, habitat texture along the river bed. The texture of bottom material can vary from place to place providing various colonization possibilities for different invertebrate taxonomic groups.

The physical environment is provided by the river as a result of complex constraints. The community of aquatic macroinvertebrates consists of very different taxonomic groups that differ in their life strategy, colonization capacity and generally, moving ability. In order to describe this very complex system, detailed information is necessary both on biota and the abiotic environment. Only a spatially extended sampling design can offer a better understanding of how large river communities can coexist.

 

 

Two international longitudinal survey programs were recently executed along the Danube River: the Joint Danube Survey 1 (JDS1) in 2001 (Literáthy et al. 2002) and JDS2 in 2007 (Graf et al. 2008). The sampling methodology of these two programs was different. During JDS1 a polyp grab was used for the macroinvertebrate sampling on, specifically, the rip-rap embankments. Additional Kick and Sweep (K&S) samples were collected on the Hungarian Danube section at the same time, using the multi-habitat approach. During JDS2 macroinvertebrates were collected by an Air-lift in the deep river zone, while the K&S and dredging method were applied simultaneously at the same locations. The detailed comparison of these different methods in terms of efficiency and taxonomic resolution is still not evaluated. Therefore, in conclusion, it was determined necessary to include marginal, shallow and deeper river zones including the deepest regions and the whole cross section, because important information can be collected in that way.

In the framework of the "Monitoring the Environmental impact of the works regarding the improvement of the navigation conditions on the Danube River Calarasi and Braila, km 375 and km 175, Code CPV 71313450-4." a longitudinal sampling program of a benthic macroinvertebrate community survey was completed. All of those 10 localities were included in the sampling program where the interventions were planned in terms of river regulations of specific arms and islands on the Danube. The field sampling was carried out during the early summer period, from May 31 to June 4, 2011.

Several data sets - many of them available only in Romanian - about the macroinvertebrate communities of the Romanian Danube section, deal mainly with the group of Malacostraca of the Iron Gate section (Popescu-Marinescu and Elian 1974, Popescu-Marinescu and Diaconu 1989, Popescu-Marinescu et al. 2001, Popescu-Marinescu 2003, 2004, 2005a, 2005b, Popescu-Marinescu and Oaie 1996). Some data indicate the faunal composition of the upper Romanian section between Bazias and Calafat/Vidin (Slobodník et al. 2005, Csányi and Paunovic 2006). Other results of international surveys JDS1 (Literáthy et al. 2002) and JDS2 (Graf et al. 2008) are referring only to a few localities on the Lower Romanian Danube.

Our aim was to describe the basic ecological status of the selected section of the Danube before starting any of the river regulation activities (preconstruction phase). For this reason the macroinvertebrate sampling on representative river stretches was executed with different approaches: both the littoral and the deep water samples were taken from the entire cross section of the river in order to characterize/determine the real structure and possible differences of macroinvertebrate assemblages between the examined sites. This paper provides the analysis of completed cross section dredging and littoral K&S sampling in order to complete the detailed taxonomic list of the investigated localities.

 

Material and Method

Benthic macroinvertebrates were sampled at 11 localities (indicated by river km values) along the Danube River. Altogether 36 sub-samples were taken along different cross sections by hand net and dredge, respectively (Table 1). A hand net was used in the littoral, shallow zone with a 1 mm mesh size using the Kick and Sweep sampling method (K&S). Multi-habitat sampling (MHS) was carries out at each littoral sampling site using the same effort in all cases. A bottom dredge was applied in the deep water zones in the given cross section using a motor boat for pulling the sampler along the bottom surface (Dredging). At all sites, approximately 10 liters of bottom sediment was collected by dredging from a 5 cm thick river bed top layer. Localities, dates and coordinates are given in Table 1 and Figures 1-7.

 

Table 1: Sampling localities, coordinates, sample types and date of sampling along the Lower Romanian Danube

Tab1