Heather L. Moorhouse

Water bodies located in floodplains and tropical forests are known to be important carbon stores, but many are subjected to intensive pressures from damming, land use and climate changes. Sedimentary records preserve long‐term archives for understanding how such changes affect the quantity and quality of carbon stores. We analysed sediment cores from seven sites across a flood‐pulse multi‐basin wetland, Tasik Chini in Peninsular Malaysia (for percentage LOI₅₅₀, sediment density and spheroidal carbonaceous particles), and conducted more analyses on three ²¹⁰Pb‐dated cores (X‐ray fluorescence of elements, grain size analysis, carbon isotopes, C/N ratios, carotenoid pigments) to gain an understanding of the drivers of organic carbon accumulation rates (OCARs) since 1860 ce. The median OCAR of 85 g m⁻² a⁻¹ for the basin since 1945 ce was higher than in other floodplain and temperate lakes and in line with other tropical forest lakes. However, we found evidence for different mechanisms of OC deposition across the basin. In ‘autochthonous mode’, the site with minimal local land disturbance had lowest OCARs and OC was derived mainly from autochthonous production, which rose slightly around 1940 ce when regional land disturbance increased nutrient influx to the basin. The site with the most long‐term and intensive land disturbance through forest removal (1940s) and then conversion to rubber and oil palm farming (1980s) functioned mainly in ‘allochthonous mode’; that is, increases in OCARs after 1940 ce were driven by deposition of soil‐derived OC. The highest OCARs were in the basin that was converted to oil palm after the 1980s and had increased iron mining activity in the 2000s; because this site was located distal from the flood pulse and became increasingly hydrologically disconnected after a low rainfall period in the 1970s, the lake responded strongly in ‘autochthonous mode’, through encroachment of fringing swamp, the spread of benthic algae and macrophytes, and efficient sediment retention. Weir installation in 1995 ce raised water levels and increased lentic conditions, promoting autochthonous OC production and sedimentation across all basins. The long‐term fate of this more recently deposited OC remains uncertain because it is more labile. Overall Tasik Chini has responded strongly to land use changes since at least the 1940s, earlier than anticipated in this region of Southeast Asia, and the sedimentary proxies indicate large changes in the ecosystem function and capacity for C storage over the past ca. 80 years. Most of these shifts have increased OC accumulation by strengthening autochthonous production or allochthonous OC fluxes, but the implications for other aspects of the C cycle, including catchment soil C loss and greenhouse gas production, need to be accounted for when evaluating the overall impacts of land and hydrological disruption.

This paper uses multimedia to showcase the narratives and lived experiences of those who live and work in tropical Asian mega‐deltas, and as such is the first journal article of its kind in the field of Regional Geography. Using videos, photography and audio this paper describes the characteristics of ponds and their place in the intrinsically connected human‐environmental fabric of these delta regions. The aim is to bring to life descriptive inventories and provide greater weight in support of our conclusion that tropical Asian mega‐delta ponds are important and threatened systems. River deltas comprise just 1% of land cover worldwide but support the livelihoods of more than 500 million people. Delta research has historically focused on the major river channels and the socio‐ecological role of ponds has been overlooked despite their large number and surface area. Ponds are intrinsically linked to daily life (potable water, sanitation, bathing, washing), industry (aquaculture, agriculture) and the natural‐cultural heritage (religion, folklore) of deltas. In contrast to the larger river channels, ponds are likely to be significant stores and processors of nutrients, including carbon, and pollutants at annual to decadal scales, on account of their heavy anthropogenic use and smaller individual sizes. Consequently, they are severely polluted water sources and pose significant public health risks. In this review, we use case studies from three Asian mega‐deltas (the Red River Delta and the Mekong River Delta, Vietnam, and the Ganges‐Brahmaputra‐Meghna Delta, India and Bangladesh) to highlight the importance of Asian mega‐delta ponds as important socio‐ecological systems in their own right. We discuss future environmental challenges, knowledge gaps on the ecological function and biodiversity of these habitats, management and policy practices, and the capacity of ponds to achieve the UN Sustainable Development Goals.

The Living Deltas Hub is a UKRI GCRF-funded community investigating the environmental, societal, and natural-cultural heritage of three South and Southeast Asian mega-deltas; the Ganges-Brahmaputra-Meghna delta spanning India and Bangladesh, and the Mekong Delta and Red River Delta of Vietnam. Globally, deltas occupy only 1% of the total land area, but support the livelihoods of ~500 million citizens. As a consequence of growing human populations and intensified anthropogenic activity these deltas face multiple challenges, such as eustatic sea level rise, land subsidence, saline intrusion, unsustainable extraction of natural resources, habitat loss, pollution, and are currently on a trajectory towards collapse. The waterscape of the deltas place SDG 6 (clean water and sanitation) at the heart of sustainable development. Thus, the Hub aims to quantify and assess human impacts on the water quality of major river channels, canals, and ponds by establishing catchment-wide water quality monitoring supplemented by historical data, biomonitoring networks, community science projects (including water quality and participatory GIS) and local knowledge of water quality. This will result in improved understanding of the impacts of the multi-functionality of water sources in Asian mega-deltas from basic domestic use (bathing and drinking water) up to industrial scale aquaculture, and can lead to the success of SDG 6 (clean water), SDG 3 (good health and wellbeing), SDG 2 (zero hunger – here, through sustainable aquaculture), and SDG 14 (life below water). In addition, the combined methodology of water quality monitoring and understanding lived experiences can be used to identify the concerns of local communities, identify inequalities in the access to safe water (working towards SDG 10 reduced inequalities) and understand the female experience (working towards SDG 5 gender inequality). Using a literature review of pond water quality and use in the delta regions and data from household surveys conducted in three regions of the Mekong Delta (Ben Tre, An Giang and Can Tho), we will use ponds as a case study to demonstrate how this approach can be used to improve understanding of community access to safe water.  

Freshwater ecosystems are threatened by multiple anthropogenic stressors acting over different spatial and temporal scales, resulting in toxic algal blooms, reduced water quality and hypoxia. However, while catchment characteristics act as a ‘filter’ modifying lake response to disturbance, little is known of the relative importance of different drivers and possible differentiation in the response of upland remote lakes in comparison to lowland, impacted lakes. Moreover, many studies have focussed on single lakes rather than looking at responses across a set of individual, yet connected lake basins. Here we used sedimentary algal pigments as an index of changes in primary producer assemblages over the last ~200 years in a northern temperate watershed consisting of 11 upland and lowland lakes within the Lake District, United Kingdom, to test our hypotheses about landscape drivers. Specifically, we expected that the magnitude of change in phototrophic assemblages would be greatest in lowland rather than upland lakes due to more intensive human activities in the watersheds of the former (agriculture, urbanization). Regional parameters, such as climate dynamics, would be the predominant factors regulating lake primary producers in remote upland lakes and thus, synchronize the dynamic of primary producer assemblages in these basins. We found broad support for the hypotheses pertaining to lowland sites as wastewater treatment was the main predictor of changes to primary producer assemblages in lowland lakes. In contrast, upland headwaters responded weakly to variation in atmospheric temperature, and dynamics in primary producers across upland lakes were asynchronous. Collectively, these findings show that nutrient inputs from point sources overwhelm climatic controls of algae and nuisance cyanobacteria, but highlights that large‐scale stressors do not always initiate coherent regional lake response. Furthermore, a lake's position in its landscape, its connectivity and proximity to point nutrients are important determinants of changes in production and composition of phototrophic assemblages.