Abteilung Aquatische Ökologie

Material fluxes are ubiquitous in nature within and across ecosystems, connecting habitats with vastly different characteristics, like forests to rivers and lakes.^1,2,3 Although individual fluxes and their cascading effects are well known,^4,5,6 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.^9,10,11

The late Smithian and Smithian-Spathian boundary (SSB) witnessed significant conodont extinction approximately 2.7 million years after the major Permian-Triassic boundary extinction. This study offers a detailed examination of the Smithian-Spathian transition at the Guryul Ravine section in the Srinagar district, Kashmir, focusing on conodonts and δ¹³C_carb values. The section features an unprecedented conodont taxonomic richness, with 53 species from 17 genera, including three newly formalized species: Neospathodus aristatus n. sp., Neospathodus guryulensis n. sp. and Borinella? prima n. sp. Additionally, Borinella ex gr. buurensis and Scythogondolella ex gr. milleri are subdivided into multiple morphotypes, facilitating a refined biochronological scheme.
A high-resolution δ¹³C_carb record spanning the Early Triassic captures global carbon isotope excursions. The integration of δ¹³C_carb with conodont biostratigraphy enhances global correlation of the Smithian-Spathian transition. The late Smithian conodont extinction aligns with a globally observed positive δ¹³C_carb excursion, reaching an exceptional value of + 12 ‰, likely of diagenetic origin.
This study proposes a new conodont biochronological framework based on the Unitary Association Method (UAM). Placing the SSB between the extinction climax and re-diversification onset, the framework relies on a rich conodont collection from Guryul Ravine, Kashmir, and a comprehensive reassessment of conodont data from 19 other sections along the northern Gondwana margin. The resulting 16 Unitary Association Zones (UAZs) are cross-referenced with lithological, chemostratigraphical (δ¹³C_carb), and ammonoid markers, establishing an unprecedentedly robust basis for defining the SSB. The proposed boundary is within UAZ₈ but allows for future refinements.

Aquatic and terrestrial ecosystems are linked through the reciprocal exchange of materials and organisms. Aquatic-to-terrestrial subsidies are relatively small in most terrestrial ecosystems, but they can provide high contents of limiting resources that increase consumer fitness and ecosystem production. However, they also may carry significant contaminant loads, particularly in anthropogenically impacted watersheds. Global change processes, including land use change, climate change and biodiversity declines, are altering the quantity and quality of aquatic subsidies, potentially shifting the balance of costs and benefits of aquatic subsidies for terrestrial consumers. Many global change processes interact and impact both the bright and dark sides of aquatic subsidies simultaneously, highlighting the need for future integrative research that bridges ecosystem as well as disciplinary boundaries. We identify key research priorities, including increased quantification of the spatiotemporal variability in aquatic subsidies across a range of ecosystems, greater understanding of the landscape-scale extent of aquatic subsidy impacts and deeper exploration of the relative costs and benefits of aquatic subsidies for consumers.