)pe Historical Change of Large Alluvial Rivers: Wesrern Europe Edited by G. E. Petrs Ian O1989 John Wiley & Sons Lrd ren, 11 ?rs, The Lower Rhine: Pølaeoecological tnd Analysis )ó. AIpxaNoER KLINK KIink Hydrobiological consurtants, Hydrobiologisch Adviesburo, Boterstrast 28, 6701 CW Wageningen, The Netherlands INTRODUCTION This chapter reviews the first few years of palaeoecological river research, by means of insect remains, in the Netherlands. In 1983 the first floodplain samples from the River Rhine were analysed and since then, progressively, we have been building up biological evidence concerning the history of the river. As is symptomatic of any new development in science, numerous questions arise from the analysed material and very few answeis can be given. Nevertheless' it has become clear that palaeoecological river research has considerable scope. HISTORICAL DATA ON THE INSECT FAUNA OF THE RHINE Data on the insects inhabiting the Rhine in the past are very scarce. From the most comprehensive record of riverine insects (Albarda, 1 889) it is apparent that the characteristic riverine Ephemeroptera, Plecoptera, Odonata and Trichopterà were still present in the lgth century. The best example of the Ephemeroptera is Palingenia longicøuda, which burrowed into the clay banks in large numbers: it was last recorded in 1907 (M;1, l9g5). The plecoptera in the Rhine included the genera oemopteryx, Isoperla and Chloroperla. These ston;flies became extinct in the early decades of this century (Geijskes, 1940). Gomphus fløvipes, a mud-dwelling dragonfly, was lasr collected in 1902 (Geijskes and van rà1, rsg:1. rlré Trichoptera included, among others, cheumatopsyche lepida, Lepidostoma hirtum, Psychomyia pusilla and many Hydropsyche species. The first two species have not been collected during the 20th century. The last record of Psychomyiø pusiiladates back to 1933 (Fischer, 1934). very little is known about the Diprera. van Der Wulp (1g77) notes that adult Simuliidae (only four species described) were very common on places near the rivers Rhine and Meuse. The chironomids mentioned in his work cannot be assigned to the typical river fauna. From the early records it can be concluded that in the second half of the lgth century and the first few decades of the 20th century a dramatic decline was observed in the largei insects' The river Rhine today is deprived of Ephemeroptera (except Caenis species), Plecoptera, Anisoptera and Simuliidae. Apparently Trichoptera have been absent from 183 lg4 Historical change of torge qlluvial rivers: western Europe The l the Rhine for a long period of time, too. From 1978 on, however, a remarkable return statisl (Van of Hydropsyche contubernalis and some other caddisflies has been observed the or Urk, 1984). Sin chara indusr CHEMICAL CHANGES IN THE RHINE been ; Evidence that early pollution of the Dutch rivers did not go unnoticed can be found in used i the following quotation from Velsen (1768): le80) were I 'Our people have always been utterly indifferent to a vital part of this country, the rivers. We used them and abused them as we pleased, without any supervision whatsoever. If the rivers were to die tomorrow not a soul would care or be grieved. Instead of worshipping her as gods or saints, we treat them as sewers' in which anyone may freely dispose of his wastes. This is what has caused their abominable state.' Most probably the pollution referred to above was predominantly organic. Large-scale mining àctivities did not start until the middle of the lgth century, and it was not until the 20th century that steel production became a major industry and pesticides based on pollution mercury and arsenic were commonly used. In Figure I the history of heavy metal is inferred from analyses of old river sediments and soil samples from a branch of the Lower Rhine. Organic pollution in former times has been deduced from the population Tentative development of the pollution in the R Rhine 1 983 1 981 1 979 1977 1975 1973 197 1 1 960 1940 1 920 1900 1750 000 050 100 150 2OO 25O 300 350 Maximum scoreicomPound = 1 00 direct and FIGURE FIGURE I Tentative compilation of the pollution history of the Rhine derived from indirect evidence The Lower 'pe Rhine: palaeoecological analysis lg5 Lrn statistics the Netherlands. of The first decades of the 20th century were characterized by an the onset of a steep rise in organic and heavy metal pollution in the Rhine. Since the Second World War an entirely new branch of industry has added its own characteristic compounds to the environment. with the development of the petrochemical industry the family of chlorinated hydrocarbons (DDT, pCBs, drins and dioxins) have been released into the river. In the 1960s and 1970s acetylcholinesterase inhibitors were used as insecticides, resulting in concentrations in the Rhine of up to 50 pgl-r (Greve, 1980). The initial rise in chlorinated hydrocarbons (as Eocl) is not known as ,ro analyses were made until 1973. In the mid nineteen seventies, however, concentrations as high as a Lle ril )n )n :ìe )n a' o(' ú m f' C) t -.{ KROMME RIJN NEOERRIJN úr a(, O 50 IOO km FIcun¡ 2. The Rhine-Meuse river system in the Netherlands. The sampling sites are numbered as in Table I sltuvial rivers: western Europe 186 Historicat chønge of lorge TABLE l. SamPling sites bY tYPe and date of sedimentation/sampling Date Number River Type -l'745 I Rhine Floodplain deposit dePosit -1880 2 Nederrijn Floodplain samPling 198 I J Nederrijn Exuviae ? 4 IJssel Sediment core samPling 1986 5 IJssel Exuviae ? 6 IJssel Sediment core samPling 1985 7 Waal Exuviae solids (> 100¡rm) - 1984 8 Waal Suspended dePosit 19l4 9 Boven Merwede Floodplain ßP core 2srrro l0 Nieuwe Merwede 9 Sediment ,| Nieuwe Merwede 12 Sediment core ll r 750- I 984 l2 Schoonrewoerdse Wiel Sediment core the pollution of the Rhine reached 30 ¡tgl-r were measured (Greve, 1980). concurrently, and a decline in micropollutants its maximum. Subsequently, improvements in oxygen content notably H' contubernalls could have been observed. tne ieturn of caddisflies in the Rhine, be the result of this improvement (Becker, 1987)' Localities and methods shown in Figure 2 and The sampling sites used in this survey of the Lower Rhine are listed in Table l. First, sediment cores from The sediment samples were collected in three different ways' research vessel' The core the river-bed were taken by means of a mudcorer installed on a gear. Secondly, floodplain from Schoonrewoerdse wiet (nr. 12) was taken by means of scuba research' The augers were drilled àeposits were collected with hand auger equipment for soil the former river-bed' Since into the soil until a layer of coarse sand was met, indicating the samples were taken from the these layers contain hárdly any remains of invertebrates, from the silt layer directly on top lf tú. sand. Thirdly, suspended solids were collected data with the present river itself by means of a driftnet (mesh 100 ¡rm). To compare these sampling stations from situation, monthly exuviae collections were carried out at three May to October by means of a driftnet (mesh 500¡rm)' were The dep mesh of 100 ¡rm n of 40-80 and OnlY handpicke ution five insect ufficient numbe while no of aquatic coleoptera remains was too local to take them into consideration, appeared to be absent odonata remains were found. of the non-insect groups, mollusc shells remains were not in all but a few samples, while Tricladida, oligochaeta and Hirudinea parts that stay intact in found at all. The Tricladida and Hirudinea contain no chitinous (chaetae and cuticular penis sheaths the sediment. The chitinous parts of the Oligochaeta during sorting with this in some Tubificidae) must háve been lost in sieving or overlooked were recognized' magnification. curiously no remains of Isopoda or Amphipoda the selected parts: The following group, are considered and identified according to (tergites); Trichoptera Ephemeroptera (manáibles); Plecoptera (maxilla); Heteroptera (frontoclypeus); and Diptera (headcapsule)' 'n Europe The Lower Rhine: paløeoecologicøl ønalysis lg7 The remains of the insects were identified by means of the available literature on the Date various groups. As single references rarely provided complete identification by means of the selected parts a wide variety of special articles was consulted. The remains that could -1745 not be identified -1880 in this way were compared to the material in reference collections. If 1981 this was not successful, the taxa were drawn and given a tentative name (for example ? Chironomini gen. no. l). r986 Abandoned main channels were selected for the dating of the floodplain deposits. As ? old river maps show, the filling of these channels process l 985 is a that may take no more than a few decades. -1984 The layer directly above the coarse sand (assumed to represent the former t9t4 channel bed) was taken for analyses of the remains as described and áated according to lo ßP lsr the period that the river abandoned that particular course. The estimated age of the ? sediment remains is the youngest possible age because the sediment contains an unknown i0- 1984 fraction of older resuspended deposits. The inferred age of the sediment, therefore, is an underestimation of the average age of the sediment. The sediment cores from e reached the present river-bed have not been dated, because no old river maps could be applied to ,pollutants the coring sites, and no sequential isotope decay series has been found or is Lxpectea røl¡s could to be found in the fluctuating sedimentation and resuspension environment that take place in rivers. The identified remains were treated as units. This means that a mandible of a mayfly was counted as one mayfly. Mathematically this is not correct, since one mandible stands for only one half of one of the 25 instars that mayflies usually have.