A new evaluation technique of potamo-plankton for the assessment of the ecological status of rivers
Borics, Gábor; Várbíró, Gábor; Grigorszky, István; Krasznai, Enikö; Szabó, Sándor; Kiss, Keve Tihámer
Large Rivers Vol. 17, No. 3 -4 Arch. Hydrobiol. Suppl. 161/3-4, p. 465-486, Oktober 2007 A new evaluation technique of potamo-plankton for the assessment of the ecological status of rivers Gabor Borics1, Gabor Varbiro1, Istvan Grigorszky2, Eniko Krasznai3, Sandor Szabo4 and Keve Tihamer Kiss5 With 5 figures and 5 tables in the text A bstract: Based on the phytoplankton associations described for lakes (R e y n o l d s, 2002), an assessment method has been elaborated for rivers. All phytoplankton associations were evaluated and scored by a number between 0-5. As many rivers can be defined as shallow, turbid, mesotrophic ecosystems of short residence time, those associations that prefer this type of environment were given high factor numbers, and those that are typical of stable hypertrophic lakes have got the lowest values. Highest values were given to those assemblages that contain mainly periphytic diatoms. To achieve an index, each species in the sample must be assigned to the appropriate functional group. Then the relative share of each functional groups are calculated. Relative shares are then multiplied by the factor number. The sum of these scores is the index. The reference values of the upper river sections are close to 5, while those of the lower river stretches are approximately 4. The method has been tested with hundreds of phytoplankton samples, it is simple, and after applying to a phytoplankton database can be computerised easily. Another advantage of the method that it is not restricted to a specific geographic region. Introduction The increasing demand for developing new assessment methods for evaluating the ecological status of lakes and rivers has mainly been fuelled by the WFD (2000) in the recent years. The Directive does not deem necessary to investigate the phyto- A uthors’ addresses: 1 Environmental Protection, Nature Conservation and Water Authority, Trans-Tiszanian Region, Hatvan u. 16, H-4025 Debrecen, Hungary; E-mails: boricsg@gmail. com; varbirog@gmail. com 2 Debrecen University, Department of Hydrobiology, Egyetem ter 1, H-4010 Debrecen, Hungary; E-mail: gege@tigris. klte. hu Debrecen University, Department of Ecology, Egyetem ter 1; H-4010 Debrecen, Hungary; E-mail: ekrasznai@gmail. com 4 College of Nyiregyhaza, Department of Botany, P. O. Box 166, H-4401 Nyiregyhaza, Hungary; E-mail: szabos@zeus. nyf. hu 5 Institute of Ecology and Botany, Hungarian Danube Research Station of the Hungarian Academy of Sciences, Javorka S. u. 14, H-2131God, Hungary; E-mail: kis7972@ella. hu 0945-3784/07/0161-0465 $5. 50 © 2007 E. Schweizerbart’sche Verlagsbuchhandlung, D-70176 Stuttgart 466 G. Borics et al. plankton in rivers which is not surprising, because the streams owing to the predominance of allochthonous organic material over the autochthonous primary production are naturally heterotrophic systems (R e y n o l d s 2000). Nevertheless several investigations proved (U h e r k o v ic h 1971; D esc y et al. 1988; K iss 1994; D o k u l il 1996; S k id m o r e et al. 1998) that the lower sections of the large, sluggish rivers (especially in lowland areas) can be characterized by highly eutrophic phytoplankton. Analysis of the Hungarian water quality database that contains more than 60, 000 chlorophyll-a data for the Hungarian rivers (V i'g h 2002) has also demonstrated the development of eutrophic, and even worse, hypertrophic situations in most of the lowland rivers in Hungary (Fig. 1). Undesirable increment of the phytoplankton biomass is at least as problematic in riverine ecosystems as it is in lakes, because it may have deleterious effect on the other assemblages of the river, and it impairs water uses. The basic characteristics of the rivers are, that during their course they change their trophic state from heterotrophy to autotrophy. In line with this, the philosophy of the river monitoring approaches also have to change. Although the water quality monitoring of the streams is usually based on the composition of the macroinvertebrate fauna and the benthic diatoms, because of the above mentioned reasons, the investigation of the riverine phytoplankton for monitoring purposes is unavoidable. Methodology of the rheoplankton investigations (including the sampling, counting etc. ) has been worked out in details for decades (U h e r k o v ic h 1971; K iss et al. 1995, 1996). These are being applied as routine techniques by those organizations which are responsible for the water quality monitoring. Nevertheless phytoplankton-based quality assessment of the rivers has not been elaborated yet, therefore in several countries the old saprobic systems (P a n t l e & B u c k 1955) are in current use. The aim of this study is to present a new phytoplankton-based method, by which the ecological state of the rivers can be assessed. In compliance with the expectations of the WFD, we make an attempt to give the characteristic phytoplankton assemblages of the rivers. Elaboration of the new assessment method Earlier assessment methods tried to characterize the water quality on an absolute scale, and gave some kind of “water-goodness” instead of the real water quality. The new procedures have to be based on the degree of deviation from a pristine ecological state. This approach needs a detailed description of the type specific reference conditions for those biological elements which the assessment methods are based on. The main problem with this philosophy is to find enough aquatic ecosystems of pristine state to the “reference conditions” with the required statistical certainty. The probability of finding untouched aquatic ecosystems among the large lakes and rivers of higher order is virtually zero (R e v e n g a et al. 2000).