Reconstructing mid–late Holocene ecosystem dynamics in the Upper Brahmaputra Valley of Assam, Northeast India, using non-pollen palynomorphs (NPPs)

This study presents the first detailed investigation of non-pollen palynomorphs (NPPs) from a 1.5 m-deep sediment profile of an endangered wetland in the Upper Brahmaputra Valley, Assam. A total of 34 NPP types were identified, dominated by fungal spores with notable amount of algal, zoological and biostructured phytoclast remains. The assemblages delineate five distinct zones, reflecting past climatic shifts, vegetation dynamics and faunal interactions. NPP analysis emerges as a valuable proxy for reconstructing ecological and anthropogenic changes beyond the resolution of pollen data. The first NPP zone, spanning 4,040–2,260 cal yrs, BP indicates a relatively warm and humid climate that supported woody vegetation, as evidenced by marker fungal spores such as Gelasinospora , Cookeina , Geastrum and Tetraploa , as well as the presence of degraded brown phytoclasts. Subsequently, from 2,260 to 1,460 cal yrs BP, relatively warmer conditions and a rich diversity of NPPs, was recorded, indicating favourable ecological conditions. In contrast, Zone 3 (1,460–1,100 cal yrs BP) reflects a shift toward colder and drier conditions, marked by a notable decline in fungal spores and algal remains. However, taxa such as Diplodia , Alternaria and Telitia , known for their resilience in drier climates, showed relatively high abundance during this phase. During 1,100–500 cal yrs BP, the retrieval of warmer, moderately humid climatic conditions was observed, likely corresponding to the Medieval Climatic Anomaly, and saw a resurgence of vegetation and wood-associated fungi such as Nigrospora , Curvularia , Valsaria and Glomus , indicating increased soil erosion. Over the past 500 cal yrs BP onwards, warmer but less humid conditions have persisted, with a rise in coprophilous spores, such as Sordaria , Cercophora , Arnium and Delitschia , suggesting intensified human activity, grazing and nearby agriculture, as evidenced by the abundance of Helminthosporium . The overall study highlights the growing utility of NPPs as sensitive indicators of past environments, vegetation dynamics, grazing pressure and anthropogenic influence.