Seasonal dynamics of detritus flows and decomposition across ecosystem boundaries

Material fluxes are ubiquitous in nature within and across ecosystems, connecting habitats with vastly different characteristics, like forests to rivers and lakes.1–3 Although individual fluxes and their cascading effects are well known,4–6 very few studies address the intra-annual phenology of ecosystem processes, despite the pronounced seasonality of fluxes. Here, we empirically quantified and resolved fluxes of recalcitrant and labile types of leaf litter in temperate riparian forests and streams across a year, representing one of the most emblematic examples of seasonal systems. We quantified intra-annual variation in litter inputs from terrestrial plants to forest floors and streams and estimated aquatic and terrestrial decomposition rates across the year at 6-week intervals. Our data show that the autumn pulse of leaf litter is complemented by smaller magnitude but more constant-through-the-year lateral flows to the stream ecosystems. Decomposition of labile litter fluctuated seasonally, on a different phenology, with generally higher rates in summer, but rates of recalcitrant litter decomposition remained largely constant. Microorganisms were the main contributors to the decomposition process in both forests and streams. Overall, our work highlights the asynchronous and seasonally variable changes in decomposition rates between recalcitrant and labile detritus despite their initial synchronized availability and suggests that the dominating presence of recalcitrant litter buffers ecosystem responses to the concentrated temporal distribution of litter resources.7,8 Investigating such ecological processes both across ecosystem borders and at fine intra-annual resolutions is imperative to understand complex system responses in the context of species’ shifts in phenologies and resource quality.9–1

Blue and green food webs respond differently to elevation and land use

While aquatic (blue) and terrestrial (green) food webs are parts of the same landscape, it remains unclear whether they respond similarly to shared environmental gradients. We use empirical community data from hundreds of sites across Switzerland and a synthesis of interaction information in the form of a metaweb to show that inferred blue and green food webs have different structural and ecological properties along elevation and among various land-use types. Specifically, in green food webs, their modular structure increases with elevation and the overlap of consumers’ diet niche decreases, while the opposite pattern is observed in blue food webs. Such differences between blue and green food webs are particularly pronounced in farmland-dominated habitats, indicating that anthropogenic habitat modification modulates the climatic effects on food webs but differently in blue versus green systems. These findings indicate general structural differences between blue and green food webs and suggest their potential divergent future alterations through land-use or climatic changes

Blue and green food webs respond differently to elevation and land use.

While aquatic (blue) and terrestrial (green) food webs are parts of the same landscape, it remains unclear whether they respond similarly to shared environmental gradients. We use empirical community data from hundreds of sites across Switzerland and a synthesis of interaction information in the form of a metaweb to show that inferred blue and green food webs have different structural and ecological properties along elevation and among various land-use types. Specifically, in green food webs, their modular structure increases with elevation and the overlap of consumers' diet niche decreases, while the opposite pattern is observed in blue food webs. Such differences between blue and green food webs are particularly pronounced in farmland-dominated habitats, indicating that anthropogenic habitat modification modulates the climatic effects on food webs but differently in blue versus green systems. These findings indicate general structural differences between blue and green food webs and suggest their potential divergent future alterations through land-use or climatic changes

Biodiversität der Makrozoobenthos – Lebensgemeinschaft in zwei kleinen Oberläufen des Untersees (Bodenseegebietes) : Fokus Trichoptera

Zertifikatsarbeit CAS Makrozoobenthos Gewässerbeurteilung und Artenkenntni (MZB)Die Vielfalt von aquatischen wirbellosen Kleinlebewesen wird in unterschiedlichen Monitoring Programmen im Rhein oder am Bodensee untersucht, während Daten von kleinen Fliessgewässern weniger oft über längere Zeit erhoben werden. Aus diesem Grund plant die Eawag ein intensives Monitoring mit wiederholenden Amphipodenbestandesaufnahmen und einem langzeit Laubabbau Experiment in zwei Oberläufen des Bodenseegebietes durchzuführen. Im Rahmen dieser Arbeit wurde die Zusammensetzung der wirbellosen Kleinlebewesen am Gewässergrund dieser zwei Oberläufen des Untersees im Bodenseegebiet (Kanton Thurgau) untersucht mit einem Fokus auf die vorkommenden Köcherfliegenarten. Dabei wurden in beiden Oberläufen (Eschlibach, Mannebach) an je drei Standorten nach dem Modul Makrozoobenthos (Stufe F) des Modulstufenkonzeptes acht Proben genommen und die aquatischen Invertebraten bestimmt. Die Abundanz des Makrozoobenthos ist im Eschlibach um 60% höher als im Mannebach. Beide Oberläufe wiesen nach IBCH_2019 auf einen guten ökologischen Zustand hin, wobei nach IBCH_2019_R der oberste Abschnitt im Mannebach in die mässige Kategorie wechselt. Nach dem SPEAR_2018 Index zeigen die bewaldeten drei Abschnitte einen guten Zustand, nicht aber die unteren Abschnitte beider Bäche und der oberste am Mannebach. Bei den unteren Abschnitten könnte dies an den Einflüssen des umliegenden Siedlungsgebiets liegen. Am oberen Abschnitt des Mannebachs könnte der mässige ökologische Zustand mit reduzierter Anzahl von Steinfliegenlarven und Gammariden auf einen Schadstoffeinfluss hindeuten. Die Lebensgemeinschaften beider Oberläufe weisst mit 36% im Eschlibach und 43% im Mannebach eine grosse Individuenanzahl von Ephemeroptera-Plecoptera-Trichoptera (EPT) Arten auf, wobei die Köcherfliegenlarven die kleinste Individuenanzahl stellen. Von den vorkommenden 12 Köcherfliegenarten ist nur eine als verletzlich und zwei als potenziell gefährdet nach den Roten-Liste-Arten eingestuft. Die vorkommenden Taxa weisen auf eine natürliche Lebensgemeinschaft hin. Um den Rückgang der Bachflohkrebse und Steinfliegenlarven zu untersuchen sollten weitere Probenahmen der Benthosorganismen gekoppelt mit Wasseranalysen oder In-Situ Versuche mit Bachflohkrebsen durchgeführt werden. Der Überblick über den ökologischen Zustand der Bäche hilft die Gewässer zu überwachen und mögliche Schutzkonzepte für den Erhalt der Artenvielfalt zu entwickeln

Veliger density and environmental conditions control quagga mussel colonization rates in two perialpine lakes

Quagga and zebra mussels (Dreissena bugensis and D. polymorpha) are spreading across lakes in Europe and North America. In particular, quagga mussels colonize lakes to great depths (>200 m). To better understand the colonization pattern of quagga mussels in deep lakes, we studied the settlement of quagga mussels along a depth gradient on colonization plates at multiple depths (1–140 m) in the pelagic zone of two recently invaded perialpine lakes, Lake Constance and Lake Geneva. We measured colonization rates every three months over one year on colonization plates deployed in both lakes at defined depths. We also assessed long-term population dynamics from abundance and size distribution using repeated photogrammetry of colonization plates. Highest colonization rates and largest mussel sizes occurred above 8 m depth, and almost no zebra mussels were found. Colonization rates decreased to almost zero below 30 m. Colonization rates on plates were associated with variation in environmental conditions as well as veliger densities in the plankton across season and depth. Temperature was the most important environmental parameter that influenced colonization. Our results will help to better understand the seasonal colonization patterns of invasive quagga mussels in deep lakes.ISSN:0380-133

Blue and green food webs respond differently to elevation and land use

AbstractWhile aquatic (blue) and terrestrial (green) food webs are parts of the same landscape, it remains unclear whether they respond similarly to shared environmental gradients. We use empirical community data from hundreds of sites across Switzerland, and show that blue and green food webs have different structural and ecological properties along elevation as a temperature proxy, and among various land-use types. Specifically, in green food webs, their modular structure increases with elevation and the overlap of consumers’ diet niche decreases, while the opposite pattern is observed in blue food webs. Such differences between blue and green food webs are particularly pronounced in farmland-dominated habitats, indicating that anthropogenic habitat modification moderates the climatic effects on food webs but differently in blue versus green systems. These findings indicate general structural differences between blue and green food webs and suggest their potential divergent future alterations through land use or climatic changes.</jats:p