The influence of groundwater and pore-water exchange on dissolved organic matter (DOM) dynamics in coastal surface waters remains poorly understood. Here, we combine bottom up (i.e., ...groundwater-derived flux estimates) and top down (i.e., water column response) evidence to assess whether groundwater exchange drives DOM dynamics in shallow coastal waters. We rely on automated chromophoric DOM (CDOM, a proxy for DOM) and radon (222Rn, groundwater proxy) measurements over tidal time scales in 12 shallow systems, including tidal freshwater wetlands, estuaries, mangroves, coral reefs, coastal lakes, a saltmarsh, and a residential canal estate. Groundwater-derived dissolved organic carbon (DOC) fluxes ranged from 2 ± 2 mmol m−2 d−1 in a coral reef to 1941 ± 1325 mmol m−2 d−1 in a mangrove tidal creek. These groundwater fluxes replaced surface water DOC inventories on time scales ranging from ∼ 0.5 d to several weeks. Systems with short replacement times displayed positive correlations between radon and CDOM in surface waters. Groundwater exchange diluted surface water DOC in four systems. Using multiple lines of evidence, we interpreted groundwater to be an important source of DOM to surface waters in 4 out of the 12 systems, including an offshore coral reef lagoon with low surface water DOC concentrations. Groundwater discharge was a negligible source of DOM in systems with high surface water DOC and CDOM concentrations such as tidal freshwater wetlands and coastal lakes. This investigation highlights the high variability in groundwater-derived DOC fluxes and responses in the water column, and demonstrates that submarine groundwater discharge and advective pore-water exchange should be considered in coastal carbon budgets.
This open access book provides a cross-sectoral, multi-scale assessment of marine litter in Africa with a focus on plastics. From distribution, to impacts on environmental and human health, this book ...looks at what is known scientifically. It includes a policy analysis of the instruments that currently exist, and what is needed to help Africa tackle marine litter—including local and transboundary sources. Across 5 chapters, experts from Africa and beyond have put together a summary of the scientific knowledge currently known about marine litter in Africa. The context of the African continent and future projections form a backdrop on which the scientific knowledge is built. This scientific knowledge incorporates quantities, distributions, and pathways of litter into the marine environment, highlighting where the impacts of marine litter are most felt in Africa. These impacts have widespread effects, with ecological, social, economic, and human health repercussions. While containing detailed scientific information, this book provides a sound knowledge base for policymakers, NGOs and the broader public.
Iron (Fe) plays a key role in sedimentary diagenetic processes in coastal systems, participating in various redox reactions and influencing the burial of organic carbon. Large amounts of Fe enter the ...marine environment from boreal river catchments associated with dissolved organic matter (DOM) and as colloidal Fe oxyhydroxides, principally ferrihydrite. However, the fate of this Fe pool in estuarine sediments has not been extensively studied. Here we show that flocculation processes along a salinity gradient in an estuary of the northern Baltic Sea efficiently transfer Fe and OM from the dissolved phase into particulate material that accumulates in the sediments. Flocculation of Fe and OM is partially decoupled. This is likely due to the presence of discrete colloidal ferrihydrite in the freshwater Fe pool, which responds differently from DOM to estuarine mixing. Further decoupling of Fe from OM occurs during sedimentation. While we observe a clear decline with distance offshore in the proportion of terrestrial material in the sedimentary particulate organic matter (POM) pool, the distribution of flocculated Fe in sediments is modulated by focusing effects. Labile Fe phases are most abundant at a deep site in the inner basin of the estuary, consistent with input from flocculation and subsequent focusing. The majority of the labile Fe pool is present as Fe (II), including both acid-volatile sulfur (AVS)-bound Fe and unsulfidized phases. The ubiquitous presence of unsulfidized Fe (II) throughout the sediment column suggests Fe (II)-OM complexes derived from reduction of flocculated Fe (III)-OM, while other Fe (II) phases are likely derived from the reduction of flocculated ferrihydrite. Depth-integrated rates of Fe (II) accumulation (AVS-Fe + unsulfidized Fe (II) + pyrite) for the period 1970–2015 are greater in the inner basin of the estuary with respect to a site further offshore, confirming higher rates of Fe reduction in near-shore areas. Mössbauer 57Fe spectroscopy shows that refractory Fe is composed largely of superparamagnetic Fe (III), high-spin Fe (II) in silicates, and, at one station, also oxide minerals derived from past industrial activities. Our results highlight that the cycling of Fe in boreal estuarine environments is complex, and that the partial decoupling of Fe from OM during flocculation and sedimentation is key to understanding the role of Fe in sedimentary diagenetic processes in coastal areas.
Ancestral vertebrate habitats are subject to controversy and obscured by limited, often contradictory paleontological data. We assembled fossil vertebrate occurrence and habitat datasets spanning the ...middle Paleozoic (480 million to 360 million years ago) and found that early vertebrate clades, both jawed and jawless, originated in restricted, shallow intertidal-subtidal environments. Nearshore divergences gave rise to body plans with different dispersal abilities: Robust fishes shifted shoreward, whereas gracile groups moved seaward. Fresh waters were invaded repeatedly, but movement to deeper waters was contingent upon form and short-lived until the later Devonian. Our results contrast with the onshore-offshore trends, reef-centered diversification, and mid-shelf clustering observed for benthic invertebrates. Nearshore origins for vertebrates may be linked to the demands of their mobility and may have influenced the structure of their early fossil record and diversification.
Focused on forest management and governance, this book examines two decades of experience with Adaptive Collaborative Management (ACM), assessing both its uses and improvements needed to address ...global environmental issues. The volume argues that the activation and the empowerment of local peoples are critical to addressing current environmental challenges and that this must be enhanced by linking and extending such stewardship to global and national policymakers and actors on a broader scale. This can be achieved by employing ACM’s participatory approach, characterized by conscious efforts among stakeholders to communicate, collaborate, negotiate and seek out opportunities to learn collectively about the impacts of their action. The case studies presented here reflect decades of experience working with forest communities in three Indonesian Islands and four African countries. Researchers and practitioners who participated in CIFOR’s early ACM work had the rare opportunity to return to their research sites decades later to see what has happened. These authors reflect critically on their own experience and local site conditions to glean insights that guide us in more effectively addressing climate change and other forest-related challenges. They showcase how global and regional actors will have to work more closely with smallholders, Indigenous Peoples and local communities, recognizing the key local roles in forest stewardship. This book will be of great interest to students, scholars and practitioners working in the fields of conservation, forest management, community development, natural resource management and development studies more broadly.
Significance Paleontologists have long argued about what the fossil record call tell us about how species evolve over long periods. Simple models such as stasis and random walks have been used to ...explore evolutionary patterns, but these have not always adequately captured the ways in which traits change over time in fossil species. Here we find that models with complex evolutionary dynamics are often favored, especially for fossil series that sample many populations, suggesting that the underlying evolutionary reality is likely more complex than represented by simplified—though still useful—models of trait change.
Previous analyses of evolutionary patterns, or modes, in fossil lineages have focused overwhelmingly on three simple models: stasis, random walks, and directional evolution. Here we use likelihood methods to fit an expanded set of evolutionary models to a large compilation of ancestor–descendant series of populations from the fossil record. In addition to the standard three models, we assess more complex models with punctuations and shifts from one evolutionary mode to another. As in previous studies, we find that stasis is common in the fossil record, as is a strict version of stasis that entails no real evolutionary changes. Incidence of directional evolution is relatively low (13%), but higher than in previous studies because our analytical approach can more sensitively detect noisy trends. Complex evolutionary models are often favored, overwhelmingly so for sequences comprising many samples. This finding is consistent with evolutionary dynamics that are, in reality, more complex than any of the models we consider. Furthermore, the timing of shifts in evolutionary dynamics varies among traits measured from the same series. Finally, we use our empirical collection of evolutionary sequences and a long and highly resolved proxy for global climate to inform simulations in which traits adaptively track temperature changes over time. When realistically calibrated, we find that this simple model can reproduce important aspects of our paleontological results. We conclude that observed paleontological patterns, including the prevalence of stasis, need not be inconsistent with adaptive evolution, even in the face of unstable physical environments.
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