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1. The exploration of biodiversity has predominantly been based on taxonomicmeasures, whereas functional diversity, a key component of biodiversity, is compar-atively understudied. Therefore, studies simultaneously investigating patterns oftaxonomic and functional diversity change in biological communities are of increas-ing interest. 2. We collated high-resolution macroinvertebrate and environmental data from 70 boreal headwater stream sites across three European countries (Germany,Finland, Sweden) to (1) investigate seasonal variation in taxonomic diversity, func-tional diversity, and redundancy, and (2) identify their potential drivers of spatialand seasonal variation. 3. Seasonal changes in boreal macroinvertebrate taxonomic diversity were decoupledfrom changes in functional diversity. Seasonal shifts in environmental conditions,including acidity and nutrient variability, drove fluctuations in taxonomic diversitywhich were far more pronounced than those of functional diversity. 4. Seasonal shifts in environmental conditions including variation in the quantity, quality, and state of organic carbon (dissolved vs particulate) facilitate an exchange of taxa, leading to taxonomically unique communities that exploit the pool of available seasonal resources. Thus, similar levels of functional diversity across seasons—evenas taxonomic diversity changes—suggest limited differences in interspecific changesin community function, potentially indicating functional resistance rooted inredundancy. 5. We highlight the spatial and seasonal discrepancies of freshwater communities,emphasising the need for both taxonomic and functional diversity patterns to beassessed in future biodiversity monitoring programmes. biological traits, community ecology, environmental drivers, freshwater ecosystems, functionalredundancy, inter-regional analysis, multivariate statistics, organic carbon Seasonal and spatial variation of stream macroinvertebrate taxonomic and functional diversity across three boreal regions

Johnsen, S. I., Edsman, L., Singsaas, F. T. & Pilotto, F. 2022. Edelkreps og vannstandsendringer - En sammenstilling av eksisterende kunnskap og forslag til tiltak. NINA Rapport 2135. Norsk institutt for naturforskning For å øke kunnskapen om effekter av vannstandsfluktuasjoner på edelkreps er det gjennomført en litteraturstudie av tilgjengelig nasjonal og internasjonal litteratur innenfor temaet edelkreps og vannstandsendringer. Prosjektet skal frembringe kunnskap, som forvaltningen kan bruke til å sette gode vilkår for å ivareta edelkreps i reguleringsmagasiner. Nedtappingshastighet og heldige/uheldige tidspunkt på året er eksempler på sentrale tema. Rapporten har også skissert kunnskapshull og foreslått ulike undersøkelser eller prosjekter som er nødvendige, for å frembringe den kunnskapen som eventuelt mangler. Rapporten har hovedfokus på effekter av vannstandsendringer i reguleringsmagasiner og regulerte dammer. Det ble gjennomført et systematisk litteratursøk på «Web of Science», som ga 944 treff. Av disse ble 51 artikler vurdert som helt eller delvis relevante. Kun seks artikler ble vurdert som helt relevante, og tilsier at det er gjort svært få undersøkelser på vannstandsendringer og ferskvannskreps. I tillegg ble det gjort søk i andre databaser, og det ble sendt ut spørsmål til et utvalg forskere/relevante fagpersoner for å besvare særskilte spørsmål som oppdragsgiver ønsket svar på. Til sammen kom det tilbakemeldinger fra fem respondenter. Kapittelet om utfordringene rundt vannstandstandsendringer og kreps gir en beskrivelse av edelkrepsens livssyklus og i hvilke stadier av edelkrepsens liv hvor den er mest sårbar for vannstansendringer (da særlig vannstandssenkning). Videre gis det en beskrivelse av krepsens habitatkrav, da vannstandsendringer vil føre til at habitatomfanget og habitatkvaliteten som er tilgjengelig for krepsen endrer seg. Avslutningsvis gjøres det en gjennomgang av mulige effekter av vassdragsreguleringer på edelkreps (og andre krepsearter), og det gjøres en gjennomgang av spørsmålene som oppdragsgiver ønsket svar på. Det er stor variasjon mellom regulerte vann med tanke på reguleringshøyde og kjøremønster, og innsjøene kan være regulert til ulike formål som f. eks vannkraft og drikkevann. Felles for edelkreps (og andre arter av ferskvannskreps) i slike lokaliteter, er at de må takle endringer i vannstand, da med nedtappingsfasen som hovedutfordring. Tilgang på skjul er svært viktig for ferskvannskreps, og områdene med størst forekomst av grovt substrat/stein/skjul er størst i strandsonen (littoralsonen). Ved vannstandssenkning, f. eks i forbindelse med vannstandsregulering/nedtapping, vil disse områdene tørrlegges. Krepsen må da forlate sine skjulesteder og blir dermed mer utsatt for predasjon da de nye områdene under vannlinjen oftest har mindre skjul. Dette gjelder særlig yngre årsklasser. Generelt kan man konkludere med at redusert forekomst av skjul, som følge av vannstandsenkning, vil gi reduserte forekomster av edelkreps da graden av predasjon og kannibalisme øker. Ved vannstandssenkninger i innsjøer (og elver) kan kreps også bli innestengt på tørre områder eller områder med svært lav vannstand. I tillegg til at kreps som «strander» i disse områdene kan dø direkte av uttørking eller bli utsatt for stort predasjonstrykk, vil vannet i svært grunne områder kunne nå høye temperaturer og lave oksygennivåer. Ugunstige oksygen- og temperaturnivåer er vist i noen tilfeller gi økt dødelighet direkte, eller indirekte ved at kreps endrer atferd og blir mer utsatt for predasjon. Hovedfunnet fra litteraturgjennomgangen, det biologiske rasjonale og tilbakemeldingene fra ekspertvurderingene peker på at det er et godt tiltak å sikre gode biotoper for edelkreps i hele dybdeprofilen og å unngå en rask nedtapping. Dette sikrer tilgang på skjul i dypere områder når grunnere områder blir tørrlagt. August og september utpeker seg som de to månedene hvor edelkreps trolig blir minst negativt påvirket av vannstandsendringer. I denne perioden er yngelen mer mobil, og de større skallskifteperiodene er over. Det må imidlertid understrekes at det foregår skallskifter i denne perioden også, og at mot slutten på september så nærmer man seg tiden for parring.

Supplementary Figures 1 – 6. Supplementary Table 1.

The ongoing biodiversity crisis becomes evident in the widely observed decline in abundance and diversity of species, profound changes in community structure, and shifts in species’ phenology. Insects are among the most affected groups, with documented decreases in abundance up to 76% in the last 25–30 years in some terrestrial ecosystems. Identifying the underlying drivers is a major obstacle as most ecosystems are affected by multiple stressors simultaneously and in situ measurements of environmental variables are often missing. In our study, we investigated a headwater stream belonging to the most common stream type in Germany located in a nature reserve with no major anthropogenic impacts except climate change. We used the most comprehensive quantitative long‐term data set on aquatic insects available, which includes weekly measurements of species‐level insect abundance, daily water temperature and stream discharge as well as measurements of additional physicochemical variables for a 42‐year period (1969–2010). Overall, water temperature increased by 1.88 °C and discharge patterns changed significantly. These changes were accompanied by an 81.6% decline in insect abundance, but an increase in richness (+8.5%), Shannon diversity (+22.7%), evenness (+22.4%), and interannual turnover (+34%). Moreover, the community's trophic structure and phenology changed: the duration of emergence increased by 15.2 days, whereas the peak of emergence moved 13.4 days earlier. Additionally, we observed short‐term fluctuations (

Additional file 2. Mean annual precipitation in the study area from 1999 to 2014 in [mm]. The dotted line indicates the trend for the investigated period (data from https://www.dwd.de/DE/leistungen/zeitreihen/zeitreihen.html ).

Additional file 1. Mean annual temperature in the study area from 1970 to 2018 in [°C]. The red line indicates the increasing temperature trend previous to our studied period and the orange line the trend when considering the last 30 years prior to the last year of our studied period. The blue line indicated the temperature trend from the investigated period (data from https://www.dwd.de/DE/leistungen/zeitreihen/zeitreihen.html ).

Additional file 4. Study area. Sampling sites are marked as red circles. AT: Austria, DE: Germany, LU: Luxemburg, CZ: Czech Republic, F: France, B: Belgium, NL: Netherlands, and AT: Austria.

Additional file 3. Land use types in 2000 compared to land use types in 2012. Values are displayed in percent.

Large wood (LW) forms a key element in the morphology of river channels. Its presence can significantly influence the hydromorphological processes shaping the river channel by increasing hydraulic roughness, and thus modify prevailing flow patterns and sediment transport. The surface of LW has often been described as a hotspot of macroinvertebrate diversity and abundance, since it represents a hard and stable substrate suitable for animal attachment and oviposition, and it may additionally offer more diverse food resources. Such effects of LW are expected to be especially conspicuous in lowland sandy rivers, where LW logs represent the main roughness elements within the river channel, and also the unique stable substratum for colonization within the otherwise homogeneous and loose sandy or muddy river bottom. Despite this, previous studies on LW have focused on mountain streams with coarser sediments, and did thereby also hardly consider the effects of LW on the benthic macroinvertebrates colonizing the surrounding riverbed sediments. This thesis thus analysed the effects of the presence of in-channel pieces of LW on the physical habitat conditions and macroinvertebrate benthic assemblages of lowland sandy rivers. The study was based on field observations in river channels that were subjected to little human disturbances only, and were hence naturally rich in LW. The field records of hydraulic, morphological and biotic variables allowed for the identification of the mechanistic linkages between the changes in the physical and biotic components of the river ecosystems that were induced by the presence of LW. The effects of LW on macroinvertebrate communities were analysed in terms of taxonomic and functional composition, and of alpha and beta diversity. Results show that in the studied lowland rivers LW induced consistent patterns of habitat variability within the otherwise homogeneous sandy river channel, as e.g. a 57%-126% increased coefficient of variation of key abiotic variables such as mean flow velocity, turbulence, median grain size and organic content of the sediments. In particular, the presence of LW was associated with the appearance of both erosion and sedimentation areas, which resulted in the formation of habitat patches with distinct combinations of sediment composition, organic matter content and flow patterns. E.g., median sediment grain size decreased by up to 53% in the sedimentation patches whereas it increased by up to 243% in scouring patches, compared to adjacent river sections without LW. The changes in abiotic conditions and the persistence of the LW logs as stable substrata also increased the diversity of the trophic resources available for macroinvertebrate assemblages by enhancing both autochthonous primary production and the retention of allochthonous organic matter. This resulted in a 1.9-5.5 fold increased contributions of autochthonous primary production and a 1.3 fold increased contribution of allochthonous organic matter to the diet of local macro¬invertebrate assemblages. The elevated diversity of trophic resources and abiotic conditions in the river bed areas surrounding the LW pieces was paralleled by elevated values of alpha diversity (on average 45% higher in sites with LW) and beta diversity of the communities (on average 31% higher in sites with LW). Hence, it may be concluded that in sandy lowland rivers even single wood logs that affect a substantial part of the channel width will trigger the formation of much more heterogeneous habitat conditions in the surrounding channel areas extending at least 60 cm upstream and 160 cm downstream of the LW. Higher habitat and resource diversity will subsequently enable a diversification of benthic invertebrate communities colonizing streambed sediments. This elevated physical and biological diversity is likely to lead to increased temporal stability of the aquatic communities, especially to higher ecosystem resilience during disturbance events. River management practices should thus avoid to remove LW from river channels. On the other hand, the addition of even simple LW structures into degraded river sections represents an effective measure to significantly enhance ecosystem functions and health., Totholz stellt ein Schlüsselelement der Morphologie von Flussläufen dar. Seine Anwesenheit kann die hydromorphologischen Prozesse, die die Flussbetten gestalten, durch Erhöhung der Gerinnerauheit und damit auch durch die Veränderung der bestehenden Strömungsmuster und des Sedimenttransports wesentlich beeinflussen. Die Totholz-Oberfläche ist bereits oft als Hotspot der Makrozoobenthos-Diversität und -Abundanz beschrieben worden, da sie ein hartes und stabiles Substrat für das Festhalten und die Eiablage der Tiere darstellt, und sie kann zusätzlich vielfältige Nahrungsressourcen bieten. Solche Wirkungen von Totholz sollten in Tieflandsflüssen besonders deutlich werden, weil Totholzstämme dort die hauptsächlichen Rauheitselemente innerhalb des Flussgerinnes darstellen, und außerdem das einzige stabile Siedlungssubstrat auf der dort sonst homogenen und unbeständigen sandigen oder schlammigen Flusssohle bilden. Trotz dieser möglichen großen Bedeutung haben bisherige Arbeiten zu Totholz sich auf Bergbäche mit Grobsedimenten konzentriert, und haben dabei auch kaum die Wirkungen des Totholzes auf die benthischen Wirbellosen der umliegenden Flussbettsedimente betrachtet. Diese Doktorarbeit soll somit die Auswirkungen der Anwesenheit von großen Totholzstücken auf die abiotischen Lebensbedingungen in Flussgerinnen sowie auf die Lebensgemeinschaften des Makrozoobenthos in sandigen Flachlandflüssen aufzeigen. Die Studie basiert auf Feldunter¬suchungen in vom Menschen wenig gestörten Flussgerinnen, die daher von Natur aus reich an Totholz sind. Die Feldmessungen der hydraulischen, morphologischen und biotischen Variablen erlauben die Darstellung der durch Totholzvorkommen induzierten mechanistischen Zusammen¬hänge zwischen den Veränderungen der physikalischen und biotischen Komponenten der Fluss¬ökosysteme. Die Wirkungen des Totholzes auf die Makrozoobenthosgemeinschaften wurden im Hinblick auf ihre taxonomische und funktionelle Zusammensetzung analysiert sowie hinsichtlich ihrer Alpha- und Beta-Diversität. Die Ergebnisse zeigen, dass in den untersuchten Tieflandflüssen die Anwesenheit von Totholz konsistente Muster der Habitatheterogenität in dem sonst homogenen Sandflussgerinne induzierte wie z.B. ein um 57%-126% erhöhter Variationskoeffizient bei abiotischen Schlüsselvariablen wie mittlere Fließgeschwindigkeit, Turbulenz, mittlere Sedimentkorngröße und organischer Sediment¬anteil. Insbesondere war das Vorhandensein von Totholz mit dem Auftreten von Flächen sowohl der Erosion und Sedimentation verbunden, was zur Bildung von Kleinlebensräumen mit bestim¬mten Kombinationen von Ausprägungen der Sedimentzusammensetzung, organischem Gehalt und Strömungsmustern führte. Beispielsweise verringerte sich die mediane Sedimentkorngröße um bis zu 53% in den Sedimentationszonen, während sie in Auskolkungszonen um bis zu 243% anstieg im Vergleich zu benachbarten Flussabschnitten ohne Totholz. Die Änderungen der abiotischen Bedingungen und die Persistenz der Totholzstämme als stabile Substrate erhöhten außerdem die Vielfalt der trophischen Ressourcen, die für die Makrozoobenthosgemeinschaften zur Verfügung stehen, indem sowohl die autochthone Primärproduktion als auch die Retention allochthoner organischen Stoffe erhöht wurde. Dies führte zu einer 1.9-5.5 fach erhöhten Zunahme der autochthonen Primärproduktion sowie einer 1.3 fach erhöhten Zunahme des allochthonen organischen Materials in der Nahrung der dort vorhandenen Makrozoobenthosgemeinschaften. Die erhöhte Vielfalt der trophischen Ressourcen und der abiotischen Bedingungen im Gewässerbett in der Umgebung der Totholzstücke wurde begleitet von erhöhten Werten der Alpha-Diversität (an den Holz-Probestellen um im Durchschnitt 45% erhöht) und Beta-Diversität der Lebensgemeinschaften (an den Holz-Probestellen um im Durchschnitt 31% erhöht). Es kann somit geschlussfolgert werden, dass in sandige Tieflandflüssen bereits einzelne Baum¬stämme, die einen wesentlichen Teil der Gerinnebreite einnehmen, die Ausbildung von wesentlich heterogeneren Lebensbedingungen in einem Umfeld von mindestens 60 cm flussaufwärts und 160 cm flussabwärts auslösen. Diese erhöhte Habitat- und Ressourcenvielfalt ermöglicht anschließend eine Diversifizierung der benthischen Wirbellosengemeinschaften. Diese erhöhte physische und biologische Vielfalt führt dann wahrscheinlich auch zu größerer zeitlicher Stabilität der aquatischen Lebensgemeinschaften, insbesondere zu höherer Resilienz der Ökosysteme während Störungs¬ereignissen. In der Praxis der Flussbewirtschaftung sollte daher vermieden werden, Totholz aus Flussgerinnen zu entfernen. Auf der anderen Seite stellt die Zugabe selbst einfacher Totholzstruk¬turen in degradierte Flussabschnitte eine wirksame Maßnahme dar, um dort Ökosystem-Funktio¬nen und -Zustand erheblich zu verbessern.