Rapid Communications Sediment Biotests

The Multispecies Freshwater Biomonitor A P o t e n t i a l N e w T o o l f o r S e d i m e n t B i o t e s t s a n d B i o m o n i t o r i n g

Almut Gerhardt':" and Stefanie Schmidt

LimCo International, An der Aa 5, D-49477 IbbenbLiren, Germany

* Corresponding author (limco.int@t-online.de)

In t roduct ion

Sediments are an ecologically important component of the aquatic habitat, concentrate toxic substances and act as sinks for toxins. Therefore, toxicity in the water column, often monitored with planktonic or pelagic organisms does not give sufficient indication of toxicity in the sediment. Many benthic invertebrates perform parts or their whole life-cycle in the sedi- ment. Therefore, sediment toxicity has to be assessed and monitored at the same time as toxicity of the water. This is also necessary for pollution pulses, which first exert toxic re- sponses/effects in the water cotunm; however, later and at a greater distance, these substances enter the sediment, where they can cause short and even long-term effects on the benthic fauna. In the TRIAD approach (Chapman 1986), an integra- tion of chemical, ecotoxicological and biological data is re- quired for evaluation of sediment quality. Sediment toxicity tests are often performed with pore water, extracts or sedi- ment eluates, seldom the real sediment are used, partly due to the tack of methods to directly observe the test organisms and to quantitatively measure parameters such as mortality, physi- ology and behaviour. However, every treatment of the sedi- ment involves a change in quality and quantity of the compo- sition, and concentration and bioavailability of the toxins (Burton 1991). In situ sediment tests are best performed with sediment chambers, originally proposed two decades ago, al- though no studies had been published until 1991 (Burton 1991). Until now, no automated and cost-effective, easy-use method is available for application in sediment (eco)toxicology.

In standard sediment toxicity testing, only two insect taxa are used (USA: Chironomus tentans (Diptera) and Hexagenia lim- bata (Ephemeroptera), Europe: Chironomus gr. thummi). However, chironomids are difficult in taxonomy and often very tolerant, the burrowing mayfly is difficult to culture and there is no pendant in Europe (Burton 1991). Hydropsyche angustipennis (Curtis 1834) was chosen as a wide-spread univoltine benthic insect species common in European streams. As the species builds nets, feeds on particles (algae and detri- tus) and older larvae live 'hemisessil' in cases made of sedi- ment material, it has close contact to the sediment and can be considered an appropriate insect species for sediment biotests (Gerhardt 1996). Hydropsyche angustipennis has not been used for toxicity tests, however, since responses to metals were seen to induce changes in competition behaviour (Vuori 1994), changes in ventilation and inactivity (van der Geest et al. 1999), growth and mortality (Vuori 1995), colour and structure of the tracheal gills and anal papillae (Vuori and Parkko 1995), anomalies in the net structure (Petersen and Petersen 1984) and changes in guild structure (Petersen 1986). The responses indicate a battery of potentially sensitive toxicity parameters. Hydropsyche angustipennis has been used in the Multispecies Freshwater Biomonitor (MFB) in experiments with polluted surface water, resulting in clearly defined types of behaviour, locomotion and pumping (regular abdomen undulations for creation of water flow, i.e. ventilation) (Gerhardt 1996).

The aim of this study was to use the MFB for the first time ever in automated recording of behavioural patterns of organisms in the sediment. Hydropsyche angustipennis was chosen due to 1) previous experiences in the MFB in water, 2) close sediment contact of the species, 3) taxonomic group of insects and 4) species with an appropriate size (larvae were I cm long) for the test chambers to generate clear behavioural signals.

1 Materials and Methods

The Multispecies Freshwater Biomonitor (MFB) is based on quadropole impedance conversion technology (Gerhardt et al. 1994, Gerhardt et al. 1998). The organisms are placed in a cylindrical flow through an acryl glass chamber with screw- rings covered with nylon netting (500 lira) on both sides. At the inner chamber walls, two pairs of stainless steel elec- trode plates are arranged, so that one pair generates a high frequency alternating current over the chamber and the other, non-current carrying pair senses impedance changes due to

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Sediment Biotest Rapid Communications

an organism's movements in the chamber. Typical behav- iours generate typical signals, such as locomotion and venti- lation (Gerhardt et al. 1994, Gerhardt 1999 2000).

Test chambers (3 cm long, 2 cm in diameter) were filled with either stream water ('water only' treatment) or 10 g wet sandy sediment ('sediment only' treatment). The sedi- ment was taken from the stream at the site where the organ- isms were collected. In the 'choice' experiments, two cham- bers were glued together to a 'double' chamber and exposed in vertical position in the aquarium filled with stream water. The bottom test chamber contained 10 g of wet sediment and the top chamber contained only water. There was free passage between both chambers. Sixteen 1 cm long larvae of Hydropsyche angustipennis (Trichoptera) were placed individually in the respective chambers and behaviour was recorded every 10 min for a recording time of 4 min for a duration of about 24 hours. In the 'choice' experiment, one larva was placed in the sediment compartment of each 'dou- ble-chamber'. Data processing consisted of a Fast Fourier Transformation (FFT), which generated a histogram of sig- nal frequencies, which occurred during the whole recording time of 4 min The FFTs were the basis for the following non-parametrical statistical comparisons of the two groups, 'water only' and 'sediment only', as well as for the 'water' and 'sediment' compartment in the 'double' chambers.

2 Results and Discussion

Typical behavioural patterns of Hydropsyche angustipennis consisted of locomotion at 0.5-2.0 Hz (swimming, walk-

ing), pumping at 0.5-1.5 Hz ('ventilation') and inactivity (Fig. 1) in conformity with earlier results (Gerhardt 1996). These types of behaviour have also been recorded and proven sensitive to Cu with an impedance technique by van der Geest et al. (1999). The behaviours were shown in the 'water only' and 'sediment only' chamber, although significantly less time was spent in the latter on behaviour in favour of inactivity (p <0.05, Mann-Whitney U test on two groups). Similar re- suits have been found for Corophium vohttator in a similar experimental design (Kirkpatrick et al. in prep). In a sedi- ment-filled chamber, an organism might be less active due to either lack of space for an usually highly active species, or presence of shelter for an usually non-active, hemisessil species such as H. angustipennis, or increasing morbidity due to oxygen depletion stress. However, the maximal sig- nal amplitudes were the same in 'water only' and 'sediment only' chambers, indicating that the sediment did not affect the behavioural measurements of the larvae in case it moved around (Fig. 2). Over a long-term observation the activity of the larvae in sediment was on average half (p < 0.05) and consisted of significantly more variations and inactivity phases (p <0.05) compared to larvae exposed in 'water only' (Fig. 3). There was 100% survival of the larvae in the 'wa- ter only' and 'choice' experiments, but only 69% survived 24 h in the 'sediment only' treatments.

The MFB is the first online biomonitor to measure activity patterns of benthic invertebrates in the sediment. Meanwhile, other species have also been tested in the MFB with sedi- ment-filled chambers, such as Nematoda (Gerhardt et al., in press) and Corophmm volutator (Kirkpatrick et al., in prep.),

Fig. 1 : Typical types of behaviour of larvae of Hydropsyche angustipennis (Trichoptera). Left: Original behavioural signal amplitudes in Volt over 45 s. Right: Fast Fourier Fransformation (FFT), i.e. histogram of percentage occurrence of signal frequencies in 0.5 Hz intervals. Top: Locomotion with high signal amplitudes of up to 2.5 V. Middle: Ventilation behaviour consisting of abdomen undulations of low signal amplitudes (<1.3 V). Bottom: Phase of inactivity followed by locomotion

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Rapid Communications Sediment Biotests

Fig. 2: Behavioural signals of H. angustipennis in test chambers filled with stream water only (top) and with wet sandy sediment only (bottom) over a recording period of 250 s. Left: Original signals. Right: FFTs

Fig. 3: Selected behavioural frequencies of t4. angustipennis over a recording time of ca. 12 h. Left: In water-filled chamber. Right: In sediment-filled chamber

showing that the MFB can measure behaviour in the sedi- ment with the same accuracy as in water. This is very impor- tant, as behaviour should be measured under realistic and 'natural' exposure conditions in order to get reliable results. Moreover, sediment toxicity can only be realistically evaln-

ated if natural sediment is provided, as pore-water, eluates and artificial sediment all alter the composition and bio- availability of toxins to the organism. Thus, the MFB offers enormous possibilities in the application in sediment (eco)- toxicology and biomonitoring, by providing an ecologically

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Sediment Biotest Rapid Communications

Fig. 4: Choice experiment with H. angustipennis in a 'double' chamber with a water-filled compartment (top) and a sediment compartment (bottom), and free passage of the organism

r e l e v a n t a p p r o a c h for l a b o r a t o r y a n d in situ t ox ic i ty t es t ing a n d on l ine b i o m o n i t o r i n g of sens i t ive b e h a v i o u r a I c h a n g e s in b e n t h i c aqua t i c species.

In the ' cho ice ' - e x p e r i m e n t , it b e c a m e c lear t h a t y o u n g lar- vae of Hydropsyche angustipennis def in i t ive ly p r e f e r r ed the ' w a t e r ' to a ' s e d i m e n t ' c o m p a r t m e n t of a ' d o u b l e ' c h a m b e r (Fig. 4). Th i s was su rp r i s ing , as they h a d been co l lec ted in s a n d y s ed imen t , w h i c h was used for the e x p e r i m e n t s also. Howeve r , the p a c k i n g dens i ty of the s e d i m e n t par t ic les migh t h a v e been d i f fe ren t f r o m t h a t in the field. M o r e o v e r , t he re was n o c u r r e n t in the e x p e r i m e n t s . T h e s e f ac to r s m i g h t have c a u s e d the la rvae to leave the s e d i m e n t . M o r e s tud ies are n e e d e d to c lar i fy the p re f e r ence of s e d i m e n t or w a t e r for d i f fe ren t l a rva l s tages of Hydropsyche angustipennis w i t h d i f f e ren t s e d i m e n t cha r ac t e r i s t i c s a n d f l ow c o n d i t i o n s , in o r d e r to der ive a c o n c l u s i o n a b o u t the a p p r o p r i a t e n e s s of th is t r i c h o p t e r a n for s e d i m e n t b ioassays .

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Received: November 27th, 2001 Accepted: May 8th, 2002

OnlineFirst: May 13th, 2002

7 0 JSS J Soils & Sediments 2 (2) 2002