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At least 91 records · Page 5Linked to original sources
USGS2008

Advances and limitations of individual-based models to analyze and predict dynamics of mangrove forests: A review

Mangrove ecosystems are considered vulnerable to climate change as coastal development limits the ecosystem services and adaptations important to their survival. Although they appear rather simple in terms of species diversity, their ecology is complex due to interacting geophysical forces of tides, surface runoff, river and groundwater discharge, waves, and constituents of sediment, nutrients and saltwater. These interactions limit developing a comprehensive framework for science-based sustainable management practices. A suite of models have been developed independently by various academic and government institutions worldwide to understand the dynamics of mangrove ecosystems and to provide ecological forecasting capabilities under different management scenarios and natural disturbance regimes. The models have progressed from statistical tables representing growth and yield to more sophisticated models describing various system components and processes. Among these models are three individual-based models (IBMs) (FORMAN, KIWI, and MANGRO). A comparison of models’ designs reveal differences in the details of process description, particularly, regarding neighbor competition among trees. Each model has thus its specific range of applications. Whereas FORMAN and KIWI are most suitable to address mangrove forest dynamics of stands, MANGRO focuses on landscape dynamics on larger spatial scale. A comparison of the models and a comparison of the models with empirical knowledge further reveal the general needs for further field and validation studies to advance our ecological understanding and management of mangrove wetlands.

Aquatic Botany↗
USGS2024

Habitat use of anadromous and amphidromous sturgeons in North America: A systematic review

Sturgeons are among the most endangered fishes in the world. Identifying habitat use characteristics to inform restoration projects is crucial for recovery. However, small sample sizes, inadequate replication of studies, and limited spatial extents complicate our ability to effectively apply the findings of single studies to endangered species conservation across the larger riverscape. We synthesized information from amphidromous and anadromous sturgeons in North America to identify species-specific knowledge gaps and conduct a quantitative comparison of species–habitat relationships. We provided a qualitative summary of substrate use and synthesized estimates of depth and velocity during spawning and non-spawning activity. Generalized patterns among species were identified, such as spawning in fast water on hard substrate and then using slow water with soft substrate areas when not spawning. We noted species-specific variability during spawning that may be attributed to historical maximum length, egg characteristics, and watershed features. This study provides some of the first estimates of habitat use that can be adapted for many populations. Results can contribute to empirically grounded decision-support tools used to prioritize information needs for recovery.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS1984

Distribution and abundance of manatees along the northern coast of the Gulf of Mexico

A review of historical and recent records of manatee ( Trichechus manatus ) sightings along the coast of the northern Gulf of Mexico indicates that their numbers have declined in Texas, but increased in Louisiana and Mississippi. This is due to their extirpation in Mexico and dramatic increase along the southern Big Bend coast of northwestern peninsular Florida. The distribution of manatees along the southern Big Bend coast is related to their need for warm water and the distribution of fresh water and submerged aquatic and marine food plants. The spring-fed headwaters of Crystal and Homosassa rivers are important warm water winter refuges; nearly 90% of the same individuals return each winter. The estuaries and grass beds associated with these two rivers and the Suwannee, Withlacoochee, and Chasshowitzka rivers are the principal summer habitats. The Suwannee and Crystal rivers are "high-use" rivers, whereas the other three are "low-use" rivers. Low human-caused mortality, high fecundity, some immigration, and high site fidelity are responsible for the increasing numbers of manatees using the southern Big Bend coast. Since this region of Florida has experienced relatively little development compared with the rest of the state, the best long-term future for this endangered marine mammal in the United States lies along the southern Big Bend coast.

Alabama, Florida, Louisiana, Mississippi, Texas↗
USGS1991

Distribution and dispersal of the zebra mussel ( Dreissena polymorpha ) in the Great Lakes region

Dreissena polymorpha (Pallas), a small mussel common throughout most of Europe, was discovered in June of 1988 in the southern part of Lake St. Clair. Length–frequency analyses of populations from the Great Lakes and review of historical benthic studies suggest that the mussel was introduced into Lake St. Clair in late 1986, probably as a result of the discharge of ballast water from an ocean-crossing vessel. Following the 1990 reproductive season, Dreissena populations ranged from the head of the St. Clair River, through Lake St. Clair, the Detroit River, Lake Erie, the Welland Canal, and the Niagara River to the western basin and southern shoreline of Lake Ontario. Isolated populations were found in the St. Lawrence River and in harbours in Lakes Huron, Michigan, and Superior. The rapid dispersal of this organism has resulted from its high fecundity, pelagic larval stage, bysso-pelagic drifting ability of juveniles, and human activities associated with commercial shipping, fishing, and boating (research and pleasure). Virtually any waterbody that can be reached by boaters and fisherman within a few days travel of the lower Great Lakes, particularly Lake Erie, seems to be at risk of being invaded by this nuisance species.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2016

Food webs of the Delta, Suisun Bay and Suisun Marsh: an update on current understanding and possibilities for management

This paper reviews and highlights recent research findings on foodweb processes since an earlier review by Kimmerer et al. (2008). We conduct this review within a conceptual framework of the Delta-Suisun food web, which includes both temporal and spatial components. The temporal component is based on knowledge that the landscape has changed markedly from historical conditions. The spatial component of our framework acknowledges that the food web is not spatially static; it varies regionally and across habitat types within regions. The review highlights the idea of a changing baseline with respect to foodweb function. New research also indicates that interactions between habitat-specific food webs vary across the current landscape. For example, based on early work in the South Delta, the food web associated with submerged aquatic vegetation was thought to provide little support to species of concern; however, data from other regions of the estuary suggest that this conceptual model may not apply across the entire region. Habitat restoration has been proposed as a method of re-establishing historic foodweb processes to support species of concern. Benefits are likely for species that directly access such restored habitats, but are less clear for pelagic species. Several topics require attention to further improve the knowledge of food webs needed to support effective management, including: 1) synthesis of factors responsible for low pelagic biomass; 2) monitoring and research on effects of harmful algal blooms; 3) broadening the scope of long-term monitoring; 4) determining benefits of tidal wetland restoration to species of concern, including evaluations of interactions of habitat-specific food webs; and 5) interdisciplinary analysis and synthesis. The only certainty is that food webs will continue to change in response to the changes in the physical environment and new species invasions.

Californina↗
USGS2014

Predictive Management of Asian Carps in the Upper Mississippi River System

Prolific non-native organisms pose serious threats to ecosystems and economies worldwide. Nonnative bighead carp ( Hypophthalmichthys nobilis ) and silver carp ( H. molitrix ), collectively referred to as Asian carps, continue to colonize aquatic ecosystems throughout the central United States. These species are r-selected, exhibiting iteroparous spawning, rapid growth, broad environmental tolerance, high density, and long-distance movement. Hydrological, thermal, and physicochemical conditions are favorable for establishment beyond the current range, rendering containment and control imperative. Ecological approaches to confine Asian carp populations and prevent colonization characterize contemporary management in the United States. Foraging and reproduction of Asian carps govern habitat selection and movement, providing valuable insight for predictive control. Current management approaches are progressive and often anticipatory but deficient in human dimensions. We define predictive management of Asian carps as synthesis of ecology and human dimensions at regional and local scales to develop strategies for containment and control. We illustrate predictive management in the Upper Mississippi River System and suggest resource managers integrate predictive models, containment paradigms, and human dimensions to design effective, socially acceptable management strategies. Through continued research, university-agency collaboration, and public engagement, predictive management of Asian carps is an auspicious paradigm for preventing and alleviating consequences of colonization in the United States.

Reviews in Fisheries Science & Aquaculture↗
USGS2021

Critical review of mercury methylation and methylmercury demethylation rate constants in aquatic sediments for biogeochemical modeling

Mercury is a toxin that causes neurological impairments in adults, is particularly harmful for fetuses and children, and is deadly in severe cases, making it a worldwide health concern. Methylmercury (MeHg) is the environmentally relevant form of mercury (Hg) because it biomagnifies along the food chain. Methylmercury is mainly produced in aquatic sediments via methylation of inorganic Hg (Hg(II)) and transformed back via demethylation. Because transformation rates determine MeHg concentrations, quantification of methylation and demethylation rates is needed to inform management of MeHg. Published rate constants for Hg(II) methylation ( 𝑘 𝑚 ) and MeHg demethylation ( 𝑘 𝑑 ) vary greatly, stemming partly from differences in experimental methods. We conducted a comprehensive review of rate laws, evaluated published rate constants, and performed biogeochemical simulations to assess variability in reported 𝑘 𝑚 and 𝑘 𝑑 . Based on selected studies employing the same pseudo-first-order rate law and similar experimental methods, we found that 𝑘 𝑚 = 0.04 ± 0.03 d −1 is a reasonable range for wetland sediments. Over a number of environments, maximum 𝑘 𝑑 was smaller at sites without Hg source ( 𝑘 𝑑 = 0.5 d −1 ) than at sites with identified Hg source ( 𝑘 𝑑 = 1.8 d −1 ). Larger variability and higher uncertainty in 𝑘 𝑑 compared to 𝑘 𝑚 highlight the need for more research on MeHg demethylation rates. This critical review: (a) aids the design of future experimental studies of 𝑘 𝑚 and 𝑘 𝑑 ; (b) provides guidance for comparing rate constants from different studies; (c) presents a biogeochemical reaction model to assess rate constants; and (d) informs selection of 𝑘 𝑚 and 𝑘 𝑑 values from the literature for use in model simulations.

Critical Reviews in Environmental Science and Tech↗
USGS2017

Ecological impacts of winter water level drawdowns on lake littoral zones: A review

Freshwater littoral zones harbor diverse ecological communities and serve numerous ecosystem functions that are controlled, in part, by natural water level fluctuations. However, human alteration of lake hydrologic regimes beyond natural fluctuations threaten littoral zone ecological integrity. One type of hydrologic alteration in lakes is winter water level drawdowns, which are frequently employed for hydropower, flood control, and macrophyte control, among other purposes. Here, we synthesize the abiotic and biotic responses to annual and novel winter water level drawdowns in littoral zones of lakes and reservoirs. The dewatering, freezing, and increased erosion of exposed lakebeds drive changes in the littoral zone. Shoreline-specific physicochemical conditions such as littoral slope and shoreline exposure further induce modifications. Loss of fine sediment decreases nutrient availability over time, but desiccation may promote a temporary nutrient pulse upon re-inundation. Annual winter drawdowns can decrease taxonomic richness of macrophytes and benthic invertebrates and shift assemblage composition to favor taxa with r-selected life history strategies and with functional traits resistant to direct and indirect drawdown effects. Fish assemblages, though less directly affected by winter drawdowns (except where there is critically low dissolved oxygen), experience negative effects via indirect pathways like decreased food resources and spawning habitat. We identify eight general research gaps to guide future research that could improve our understanding about the complex effects of winter drawdowns on littoral zone ecology.

Aquatic Sciences↗
USGS2023

Future-proofing the Emergency Recovery Plan for freshwater biodiversity

Freshwater biodiversity loss is accelerating globally, but humanity can change this trajectory through actions that enable recovery. To be successful, these actions require coordination and planning at a global scale. The Emergency Recovery Plan for global freshwater biodiversity aims to reduce the risk for freshwater biodiversity loss through six priority actions: (1) accelerate implementation of environmental flows; (2) improve water quality to sustain aquatic life; (3) protect and restore critical habitats; (4) manage exploitation of freshwater species and riverine aggregates; (5) prevent and control nonnative species invasions in freshwater habitats; and (6) safeguard and restore freshwater connectivity. These actions can be implemented using future-proofing approaches that anticipate future risks (e.g., emerging pollutants, new invaders, and synergistic effects) and minimize likely stressors to make conservation of freshwater biodiversity more resilient to climate change and other global environmental challenges. While uncertainty with respect to past observations is not a new concern for freshwater biodiversity, future-proofing has the distinction of accounting for the uncertainty of future conditions that have no historical baseline. The level of uncertainty with respect to future conditions is unprecedented. Future-proofing of the Emergency Recovery Plan for freshwater biodiversity will require anticipating future changes and developing and implementing actions to address those future changes. Here, we showcase future-proofing approaches likely to be successful using local case studies and examples. Ensuring that response options within the Emergency Recovery Plan are future-proofed will provide decision makers with science-informed choices, even in the face of uncertain and potentially new future conditions. We are at an inflection point for global freshwater biodiversity loss; learning from defeats and successes can support improved actions toward a sustainable future.

Environmental Reviews↗
USGS2020

Ecological effects of climate-driven salinity variation in the San Francisco Estuary: Can we anticipate and manage the coming changes?

Climate change-driven sea level rise and altered precipitation regimes are predicted to alter patterns of salt intrusion within the San Francisco Estuary. A central question is: Can we use existing knowledge and future projections to predict and manage the anticipated ecological impacts? This was the subject of a 2018 symposium entitled “Ecological and Physiological Impacts of Salinization of Aquatic Systems from Human Activities.” The symposium brought together an inter-disciplinary group of scientists and researchers, resource managers, and policy-makers. Here, we summarize and review the presentations and discussions that arose during the symposium. From a historical perspective, salt intrusion has changed substantially over the past 10,000 years as a result of changing climate patterns, with additional shifts from recent anthropogenic effects. Current salinity patterns in the San Francisco Estuary are driven by a suite of hydrodynamic processes within the given contexts of water management and geography. Based on climate projections for the coming century, significant changes are expected in the processes that determine the spatial and temporal patterns of salinity. Given that native species—including fishes such as the Delta Smelt and Sacramento Splittail—track favorable habitats, exhibit physiological acclimation, and can adaptively evolve, we present a framework for assessing their vulnerability to altered salinity in the San Francisco Estuary. We then present a range of regulatory and structural management tools that are available to control patterns of salinity within the San Francisco Estuary. Finally, we identify major research priorities that can help fill critical gaps in our knowledge about future salinity patterns and the consequences of climate change and sea level rise. These research projects will be most effective with strong linkages and communication between scientists and researchers, resource managers, and policy-makers.

California↗
USGS2021

Riverscape approaches in practice: Perspectives and applications

Landscape perspectives in riverine ecology have been undertaken increasingly in the last 30 years, leading aquatic ecologists to develop a diverse set of approaches for conceptualizing, mapping and understanding ‘riverscapes’. Spatiotemporally explicit perspectives of rivers and their biota nested within the socio-ecological landscape now provide guiding principles and approaches in inland fisheries and watershed management. During the last two decades, scientific literature on riverscapes has increased rapidly, indicating that the term and associated approaches are serving an important purpose in freshwater science and management. We trace the origins and theoretical foundations of riverscape perspectives and approaches and examine trends in the published literature to assess the state of the science and demonstrate how they are being applied to address recent challenges in the management of riverine ecosystems. We focus on approaches for studying and visualizing rivers and streams with remote sensing, modelling and sampling designs that enable pattern detection as seen from above (e.g. river channel, floodplain, and riparian areas) but also into the water itself (e.g. aquatic organisms and the aqueous environment). Key concepts from landscape ecology that are central to riverscape approaches are heterogeneity, scale (resolution, extent and scope) and connectivity (structural and functional), which underpin spatial and temporal aspects of study design, data collection and analysis. Mapping of physical and biological characteristics of rivers and floodplains with high-resolution, spatially intensive techniques improves understanding of the causes and ecological consequences of spatial patterns at multiple scales. This information is crucial for managing river ecosystems, especially for the successful implementation of conservation, restoration and monitoring programs. Recent advances in remote sensing, field-sampling approaches and geospatial technology are making it increasingly feasible to collect high-resolution data over larger scales in space and time. We highlight challenges and opportunities and discuss future avenues of research with emerging tools that can potentially help to overcome obstacles to collecting, analysing and displaying these data. This synthesis is intended to help researchers and resource managers understand and apply these concepts and approaches to address real-world problems in freshwater management.

Biological Reviews↗
USGS2003

Fish community change in Lake Superior, 1970-2000

Changes in Lake Superior's fish community are reviewed from 1970 to 2000. Lake trout ( Salvelinus namaycush ) and lake whitefish ( Coregonus clupeaformis ) stocks have increased substantially and may be approaching ancestral states. Lake herring ( Coregonus artedi ) have also recovered, but under sporadic recruitment. Contaminant levels have declined and are in equilibrium with inputs, but toxaphene levels are higher than in all other Great Lakes. Sea lamprey ( Petromyzon marinus ) control, harvest limits, and stocking fostered recoveries of lake trout and allowed establishment of small nonnative salmonine populations. Natural reproduction supports most salmonine populations, therefore further stocking is not required. Nonnative salmonines will likely remain minor components of the fish community. Forage biomass has shifted from exotic rainbow smelt ( Osmerus mordax ) to native species, and high predation may prevent their recovery. Introductions of exotics have increased and threaten the recovering fish community. Agencies have little influence on the abundance of forage fish or the major predator, siscowet lake trout, and must now focus on habitat protection and enhancement in nearshore areas and prevent additional species introductions to further restoration. Persistence of Lake Superior's native deepwater species is in contrast to other Great Lakes where restoration will be difficult in the absence of these ecologically important fishes.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2022

Contaminants of emerging concern in the Great Lakes: Science to inform management practices for protecting the health and integrity of wildlife populations from adverse effects: GLRI action plan I, focus area 1, goal 5

Executive Summary: Under Action Plan I (2010-2014) of the Great Lakes Restoration Initiative (GLRI), Federal and Academic partners began an investigation of the presence and distribution of contaminants of emerging concern (CECs) in the Great Lakes and potential impacts on fish and wildlife. The term CECs is applied to a broad range of chemicals that are currently in use but for which we currently lack good understanding of whether fish, wildlife, or humans are being exposed and/or whether negative health or environmental effects are expected if exposure occurs. Pharmaceuticals, personal care products, flame retardants, many current use pesticides, and poly- and perfluorinated chemicals are some well-known groups of CECs, but there is no definitive or comprehensive list that can be used to support the management of CECs to reduce impacts on the Great Lakes ecosystem. Four overarching goals were identified for this collaborative investigation: 1. Evaluate the sources, occurrence, and distribution of CECs across the Great Lakes Basin. 2. Examine associations between the distribution of CECs and land-use patterns. 3. Review both scientific literature and field-generated data to determine the potential for CECs to cause adverse effects on Great Lakes fish and wildlife populations. 4. Develop efficient strategies to survey and/or monitor for threats that CECs may pose in order to take effective management actions before those threats evolve into large scale impacts on Great Lakes ecosystems or the services they provide. Achievement of these goals ensures progress towards Focus Area 1: Toxic Substances and Areas of Concern from GLRI Action Plan I, Goal 5: “ The health and integrity of wildlife populations and habitat are protected from adverse chemical and biological effects associated with the presence of toxic substances in the Great Lakes Basin ”. This large-scale research effort was comprised of individual and collaborative projects from multiple federal agencies and academic institutions, involving over 85 investigators, and overseen by the U.S. Environmental Protection Agency (EPA) Region 5, Great Lakes National Program Office. Partners include the United States Geological Survey, the National Oceanic and Atmospheric Administration, U.S. Fish and Wildlife Service, Saint Cloud State University, the U.S. EPA Office of Research and Development, and the U.S. Army Corps of Engineers. Key findings: 1. Contaminants of emerging concern were found throughout the monitored Great Lakes tributaries, but types and concentrations vary in association with regional land use. CECs were detected in nearly all samples collected. The type and concentration of the specific contaminants detected varied considerably among field sites and in association with land use type, such as urban, agricultural, wetland, 2 or forest. Contaminants were detected in the water column, sediment, and tissues of all species surveyed in the current work (mussels, aquatic insects, fish, and insect-eating birds). 2. There were over 20 contaminants for which CEC concentrations approached or exceeded those reported to cause toxicity in laboratory experiments. This was based on detection in water, sediments and or biota at one or more field sites. These contaminants represent compounds that warrant further investigation and monitoring with respect to potential impacts in certain areas of the Great Lakes basin. Based on the present investigation, compounds of greatest concern include: polycyclic aromatic hydrocarbons, associated with oil-based products and combustion of organic matter; atrazine, an herbicide; dichlorvos, an insecticide; and ibuprofen and venlafaxine, both pharmaceuticals. 3. Results suggest that mixtures of CECs presently found in most Great Lakes tributary locations surveyed may elicit subtle biological effects, but likely are not, alone, causing obvious detriment to current communities of fish and wildlife. CECs detected in the Great Lakes were associated with subtle biological effects like changes in gene expression, altered circulating glucose, etc. in both wild-caught and laboratory-reared organisms. These effects were generally not indicative of reproductive failure or mortality. However, the effects may have more serious implications when combined with other sources of stress like habitat degradation, changing climate conditions, and competition with invasive species. Due to limited historical data, it is unknown whether severe CEC-related impacts have already affected aquatic communities in waterbodies that have received long-term inputs of these contaminants. Likewise, under Action Plan I, biological effects were not necessarily evaluated at the sites where CEC concentrations exceeding laboratory toxicity thresholds were detected. As a result, strategic, ongoing surveillance and monitoring of CECs is warranted. This collaborative investigation resulted in new tools, approaches, and data that can be used to inform and support the management of CECs to reduce their impacts on Great Lakes natural resources. The following products of this research effort are available through https://communities.geoplatform.gov/glri/ or by contacting the investigators (see technical chapters found in Appendices A-F): 1. Database of CEC occurrence and concentrations in US tributary streams. The database includes CEC detections in water, sediment, and fish and wildlife tissues, and represents the most comprehensive survey of CECs in the Great Lakes Region. 2. Synopses of results and key findings. Integrated summaries of results, conclusions, and management implications of the CEC research are available through reports, topical fact sheets, and presentations. 3. Technical publications: This collaborative research effort has resulted in over 50 peer-reviewed publications, agency reports, and data releases that can be of use to resource managers, the scientific community, and members of the public. 4. Innovative tools. Innovative monitoring devices, sampling equipment, conceptual frameworks, and software applications were developed over the course of this 3 research. These tools are transferable to stakeholders via internet accessibility or via specifications, instructions, and demonstration detailed in technical publications. Hypotheses to guide CECs research under Action Plan II. Findings from 2010-2014 were used to guide further research in 2015-2018 for basin-wide surveillance of CECs and for sites warranting further study of potential biological impacts of CECs. Additional surveillance included both evaluation of additional classes of contaminants and expanded lists for chemical classes shown to be of greatest concern. Mixtures of some of the most frequently detected contaminants were also tested in laboratory studies to understand whether long term exposures to multiple contaminants may result in effects not evident from uncontrolled, short-term field experiments.

Great Lakes↗
USGS2025

Principles of riverscape health

Riverscapes are the integration of terrestrial and aquatic systems from headwaters to estuaries that provide habitat and ecosystem benefits when in good health. However, current riverscape degradation is pervasive, impairing the function and resulting benefits of these systems. Healthy riverscapes are adaptive and some can ‘heal’ after disturbance with minimal to no human assistance. As riverscape health is threatened, a need exists to address current degradation and understand the potential for riverscape restoration—concisely communicating what comprises healthy riverscapes is essential to direct limited resources and increase efficacy of restoration and conservation efforts. Healthy riverscapes have (i) space to interact within their valley bottom; (ii) natural flow, sediment, and vegetation regimes appropriate to the biophysical setting and river type; and (iii) structural forcing to support diversity and that creates varied residence times for water, sediment, and vegetation. These three principles are grounded in interdisciplinary science and lessons from riverscape scientists and restoration practitioners across the world. Understanding the context, anthropogenic influences, boundary conditions, and legacy effects influencing riverscapes is essential for the appropriate application of these principles in pursuit of achieving riverscape health. Emphasizing a holistic, biogeomorphic view of riverscapes through these principles can guide policies, restoration actions, and monitoring frameworks that ensure that riverscapes remain capable of accommodating and adjusting to disturbances while continuing to support biodiversity and human benefits.

WIREsWATER (Wiley Interdisciplinary Reviews Primer↗
USGS2023

Roles of climatic and anthropogenic factors in shaping Holocene vegetation and fire regimes in Great Dismal Swamp, eastern USA

The Great Dismal Swamp wetland, spanning >400 km 2 along the Virginia and North Carolina border, was shaped by a complex combination of geomorphic, climatic, and anthropogenic forcings during the last 14,000 years. Pollen, macrofossils, charcoal, and physical properties from sediment cores at seven sites provide a detailed record of the spatial heterogeneity of the wetland and the roles played by natural hydrologic variability, wildfire, and human modification of drainage in shaping vegetation and habitats. Cold-temperate forests occupied regional uplands from at least 13.5–10.3 cal ka BP. Marshes dominated by grasses and other herbaceous taxa began developing along low-elevation streams as early as 10.3 cal ka BP, resulting in accumulation of organic silts. Long-hydroperiod, peat accumulating marshes, with abundant floating aquatic plants, developed as early as 9.6 cal ka BP, as rapid rates of sea-level rise elevated the water table and facilitated wetland development and peat accumulation along stream courses. By the mid-Holocene (c. 7–6.5 cal ka BP), when local sea-level rise began slowing and reached about 12–15 m below present, shorter hydroperiod, peat-accumulating marshes dominated the landscape, with increased wildfire activity. Great Dismal Swamp vegetation shifted from marshes to peat-accumulating forested wetlands by c. 3.7 cal ka BP; these were dominated by varying combinations of Nyssa (tupelo), Taxodium (cypress), and Chamaecyparis thyoides (Atlantic white cedar). Wildfires were infrequent during this time, and the forested wetlands persisted, with minor compositional changes related to climate-driven fluctuations in stream flow, until colonial ditching and logging began in the swamp during the late 18th century. These activities decreased cypress and cedar populations, and, by the mid-20th century, expanded ditching resulted in even drier conditions and expansion of maple-gum (dominated by Acer and Liquidambar ) , and pine-pocosin (dominated by Pinus ) forests. The distribution of these forests differs from that of the late Holocene and represents a fundamental shift in hydrology, peat structure, vegetation, and fire regime due to landscape alterations of the last few centuries.

North Carolina, Virginia↗
USGS2005

Ecology of the Lake Huron fish community, 1970-1999

We review the status of the Lake Huron fish community between 1970 and 1999 and explore the effects of key stressors. Offshore waters changed little in terms of nutrient enrichment, while phosphorus levels declined in inner Saginaw Bay. Introduced mussels ( Dreissena spp.) proliferated and may have caused a decline in Diporeia spp. This introduction could have caused a decline in lake whitefish ( Coregonus clupeaformis ) growth and condition, with serious repercussions for commercial fisheries. Bythotrephes , an exotic predatory cladoceran, and other new exotics may be influencing the fish community. Sea lampreys ( Petromyzon marinus ) remained prevalent, but intensive control efforts on the St. Mary's River may reduce their predation on salmonines. Overfishing was less of a problem than in the past, although fishing continued to reduce the amount of lake trout ( Salvelinus namaycush ) spawning biomass resulting from hatchery-reared fish planted to rehabilitate this species. Massive stocking programs have increased the abundance of top predators, but lake trout were rehabilitated in only one area. Successful lake trout rehabilitation may require lower densities of introduced pelagic prey fish than were seen in the 1990s, along with continued stocking of hatchery-reared lake trout and control of sea lamprey. Such reductions in prey fish could limit Pacific salmon ( Oncorhynchus spp.) fisheries.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2026

Guidelines for producing integrated 210Pb and 14C age-models

Accurate reconstructions of past environmental changes are crucial in paleoecological research and require reliable chronologies of sedimentary archives. Establishing robust age-models and obtaining the most appropriate proxies for analysis is a complex scientific endeavor, requiring extensive resources and collaboration among specialists, including radiochronologists. Radiometric dating methods, such as 210 Pb and radiocarbon ( 14 C), are frequently employed to establish chronologies in aquatic sedimentary deposits and peat bogs. In this study, we review key aspects of sampling, analysis, and the principles underlying 210 Pb and 14 C age-models, focusing on methods for developing robust joint chronologies for paleoenvironmental research. Drawing largely from the authors' experiences and group discussions during and after a scientific workshop in 2022, we discuss important considerations for site selection, sampling strategies, and radiometric dating to construct integrated 210 Pb and 14 C age-models. Using expert consensus, this group – called Paleostats – aims to provide a set of best practices for other geochronologists with this methods paper. Among our conclusions, we emphasize the importance of accounting for site-specific factors such as prior information on sedimentation rates to establish appropriate sampling and analytical strategies. The use of appropriate coring devices can minimize disturbance to sediments and ensure the core surface remains intact and preserved until sectioning. Where excess 210 Pb is expected, sectioning at intervals of ≤1 cm provides an adequate sampling resolution for 210 Pb dating. Exceptions are possible, allowing for ~2–3 cm sections in areas with confirmed high sedimentation rates (e.g., > 1 cm yr −1 ). Recovering deeper core sections for 14 C dating with sufficient overlap allows for accounting errors in depth estimates made in the field. Special attention is advised during time intervals where validation proxies, such as the human-made radionuclides 137 Cs or post-bomb 14 C, are expected, and to determine the depth of secular equilibrium between 210 Pb and 226 Ra. Radiocarbon analyses are commonly performed by accelerator mass spectrometry, and age models are constructed mainly using Bayesian statistics with Markov Chain Monte Carlo techniques (e.g., Bacon ). A Bayesian approach ( Plum ) is now available for producing 210 Pb age-models, which infers the 210 Pb ex flux, eliminates the need for selecting an equilibrium depth, and allows dating cores with incomplete 210 Pb ex inventory. Plum offers improved chronologies by integrating raw 210 Pb and 14 C data, and these age-models can be enriched with other dating methodologies, such as identifying tephras and other well-recorded historical events. Harmonized reporting would contribute to making radiometric age-models reproducible, which would benefit from an international effort. Using 210 Pb and 14 C to produce integrated age-models may yield better insights into the interplay between natural and recent anthropogenic forcings on ecosystems. This can enhance our understanding of environmental processes and their impacts on climate change, ultimately supporting science-based assessments and decisions.

Earth-Science Reviews↗
USGS2013

Lateglacial and Holocene climate, disturbance and permafrost peatland dynamics on the Seward Peninsula, western Alaska

Northern peatlands have accumulated large carbon (C) stocks, acting as a long-term atmospheric C sink since the last deglaciation. How these C-rich ecosystems will respond to future climate change, however, is still poorly understood. Furthermore, many northern peatlands exist in regions underlain by permafrost, adding to the challenge of projecting C balance under changing climate and permafrost dynamics. In this study, we used a paleoecological approach to examine the effect of past climates and local disturbances on vegetation and C accumulation at a peatland complex on the southern Seward Peninsula, Alaska over the past ∼15 ka (1 ka = 1000 cal yr BP). We analyzed two cores about 30 m apart, NL10-1 (from a permafrost peat plateau) and NL10-2 (from an adjacent thermokarst collapse-scar bog), for peat organic matter (OM), C accumulation rates, macrofossil, pollen and grain size analysis. A wet rich fen occurred during the initial stages of peatland development at the thermokarst site (NL10-2). The presence of tree pollen from Picea spp. and Larix laricinia at 13.5–12.1 ka indicates a warm regional climate, corresponding with the well-documented Bølling–Allerød warm period. A cold and dry climate interval at 12.1–11.1 ka is indicated by the disappearance of tree pollen and increase in Poaceae pollen and an increase in woody material, likely representing a local expression of the Younger Dryas (YD) event. Following the YD, the warm Holocene Thermal Maximum (HTM) is characterized by the presence of Populus pollen, while the presence of Sphagnum spp. and increased C accumulation rates suggest high peatland productivity under a warm climate. Toward the end of the HTM and throughout the mid-Holocene a wet climate-induced several major flooding disturbance events at 10 ka, 8.1 ka, 6 ka, 5.4 ka and 4.7 ka, as evidenced by decreases in OM, and increases in coarse sand abundance and aquatic fossils (algae Chara and water fleas Daphnia ). The initial peatland at permafrost site (NL10-1) is characterized by rapid C accumulation (66 g C m −2 yr −1 ), high OM content and a peak in Sphagnum spp. at 5.8–4.6 ka, suggesting the lack of permafrost. A transition to extremely low C accumulation rates of 6.3 g C m −2 yr −1 after 4.5 ka at this site suggests the onset of permafrost aggradation, likely in response to Neoglacial climate cooling as documented across the circum-Arctic region. A similar decrease in C accumulation rates also occurred at non-permafrost site NL10-2. Time-weighted C accumulation rates are 21.8 g C m −2 yr −1 for core NL10-1 during the last ∼6.5 ka and 14.8 g C m −2 yr −1 for core NL10-2 during the last ∼15 ka. Evidence from peat-core analysis and historical aerial photographs shows an abrupt increase in Sphagnum spp. and decrease in area of thermokarst lakes over the last century, suggesting major changes in hydrology and ecosystem structure, likely due to recent climate warming. Our results show that the thermokarst–permafrost complex was much more dynamic with high C accumulation rates under warmer climates in the past, while permafrost was stabilized and C accumulation slowed down following the Neoglacial cooling in the late Holocene. Furthermore, permafrost presence at local scales is controlled by both regional climate and site-specific factors, highlighting the challenge in projecting responses of permafrost peatlands and their C dynamics to future climate change.

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