The effects of a small low-head dam on benthic invertebrate communities and particulate organic matter storage in the Ilm stream (Thuringia / Germany) Dissertation zur Erlangung des akademischen Grades doctor rerum naturalium (Dr. rer. nat.) vorgelegt dem Rat der Biologisch-Pharmazeutischen-Fakultät der Friedrich-Schiller-Universität Jena von Jens Arle geboren am 19. Februar 1975 in Gera Jena, im Januar 2005 Contents i Table of contents Chapter 1 General introduction 1. Introduction...................................................................................................... 1 Chapter 2 The effects of a small dam on invertebrate communities and the distribution of particulate organic matter storage (POM) 2.1 Introduction...................................................................................................... 7 2.2 Methods........................................................................................................... 10 2.3 Results ............................................................................................................ 21 2.3.1 Abiotic parameters .......................................................................................... 21 2.3.2 Spatial and seasonal variability of invertebrate communities.......................... 23 2.3.3 Functional feeding group structure and community composition .................... 25 2.3.4 Pool-Riffle comparison for invertebrate community variables ......................... 26 2.3.5 Spatial and seasonal variability of particulate organic matter (POM).............. 27 2.3.6 Relationship between invertebrate community variables and POM ................ 29 2.3.7 Influence of environmental factors on invertebrate community composition... 29 2.4 Discussion....................................................................................................... 32 Chapter 3 The dam as a barrier – effects on invertebrate assemblages and downstream drift. 3.1 Introduction...................................................................................................... 41 3.2 Methods........................................................................................................... 43 3.2.1 Study part I - Invertebrate assemblages on stones......................................... 43 3.2.2 Study part II - Invertebrate downstream drift and seston transport ................. 48 3.3 Results ............................................................................................................ 51 3.3.1 Invertebrate assemblages on stones .............................................................. 51 3.3.2 Invertebrate downstream drift and seston transport........................................ 54 3.4 Discussion....................................................................................................... 57 3.4.1 Invertebrate assemblages on stones .............................................................. 57 3.4.2 Invertebrate downstream drift and seston transport........................................ 61 ii Contents Chapter 4 The effects of multiple impoundments on the longitudinal zonation of benthic invertebrates 4.1 Introduction ...................................................................................................... 65 4.2 Methods ........................................................................................................... 66 4.3 Results ............................................................................................................. 72 4.4 Discussion........................................................................................................ 76 Chapter 5 Experiments on invertebrate feeding and detritus processing 5.1 Introduction ...................................................................................................... 81 5.2 Methods ........................................................................................................... 85 5.3 Results ............................................................................................................. 94 5.3.1 Abiotic changes during the experiments .......................................................... 94 5.3.2 Survival and growth ......................................................................................... 94 5.3.3 Leaf mass loss ................................................................................................. 96 5.3.4 Amount and composition of particles generated during leaf breakdown.......... 97 5.3.5 Chemical and isotopical changes during the experiments............................... 99 5.4 Discussion........................................................................................................ 106 6. General discussion........................................................................................ 117 7. Summary / Zusammenfassung..................................................................... 127 7.1 Summary.......................................................................................................... 127 7.2 Zusammenfassung .......................................................................................... 130 8. References...................................................................................................... 135 8.1 Literature cited ................................................................................................. 135 8.2 Invertebrate identification keys ........................................................................ 154 Appendix......................................................................................................... 157 Appendix A – Chapter 2................................................................................... 158 Appendix B – Chapter 3................................................................................... 164 Appendix C – Chapter 4................................................................................... 169 Appendix D – Chapter 5................................................................................... 171 Danksagung ................................................................................................... 181 Curriculum vitae / Lebenslauf....................................................................... 183 Selbstständigkeitserklärung......................................................................... 187 Contents iii List of Tables Chapter 2 Table 2.1 Environmental characteristics of the study sites ...................................... 22 Chapter 3 Table 3.1 Major biotic variables (Minimum, Maximum, Mean ± 1 S.D.) for invertebrate assemblages and the organic content of the stones sampled ................................................................................................... 51 Table 3.2 Physical and chemical conditions measured during drift sampling.......... 54 Table 3.3 Biotic and abiotic drift variables (Mean ± 1 S.D.) measured at the sample sites............................................................................................. 56 Chapter 4 Table 4.1 Physical, chemical, geographical and geomorphological characteristics at the sampling stations along the Ilm profile........................................... 67 Table 4.2 The four categories used to rank the invertebrates by their abundance.. 68 Table 4.3 The eight categories, their codes and rank scores used for analysis ...... 69 Table 4.4 The seven flow preference categories, their codes and a description of the categories used for analysis ................................................................ 71 Table 4.5 The eight habitat-preference categories used in this study ..................... 71 Table 4.6 Invertebrate taxon richness at seven sampling stations along the longitudinal profile of the Ilm during 1992-93 ........................................... 72 Chapter 5 Table 5.1 The leaf material fractions analyzed in this study .................................... 91 Table 5.2 Survival (%) of G.pulex and B. rhodani in the experiments ..................... 94 Table 5.3 The amount of particles generated during breakdown experiments relative to leaf mass initially added and relative to leaf mass loss........... 98 Table 5.4 Chemical and isotopical composition of the leaf materials and the changes observed during leaching experiments...................................... 99 iv Contents List of Figures Chapter 2 Figure 2.1 Maps of Germany, Thuringia and a schematic view to the study sites (SS1 to SS4), the dam is located within the town Stadtilm (11°05´ E, 50°46´ N, 360 m a.s.l.)........................................................................... 10 Figure 2.2 Map of the Ilm section, containing the four study sites .......................... 11 Figure 2.3 A picture of the dam investigated in this study. (View from the site immediately downstream)...................................................................... 12 Figure 2.4 Discharge at the permanent gauge Gräfinau-Angstedt 10 km up- stream from the study area from 1. January 2000 to 30. October 2002....................................................................................................... 13 Figure 2.5 Schematic view of the Hess-Sampler used in this study ....................... 16 Figure 2.6 Means (± 1 S.D.) for invertebrate density (A), biomass (B), Simpson`s index of diversity (C), expected taxon richness (D), number of taxa (E) and number of invertebrate eggs (F) during four seasons at the four sampling sites .......................................................