Largest Freshwater Ecosystem Research Articles

Food web structure across basins in Lake Erie, a large freshwater ecosystem

Understanding spatial variation of aquatic food web structure and how ecosystem boundaries should be delineated is important. Here, we investigated the spatial variation in food web structure within Lake Erie across its three basins using δ13C and δ15N. Fish and lower trophic level composition were similar but differences in food web structure were observed between basins. The food web in the central basin had the smallest δ13C and δ15N range and total area based on stable isotope values by the aquatic community, likely due to chronic epibenthic hypoxia in the summer that affects fish habitat and resources. The largest δ15N range was in the east, driven by the high trophic position of lake trout present in this deepest basin. The western basin had the largest mean distance to the centroid (CD) of all three basins, indicating a large trophic diversity, probably due to high nutrient loadings and productivity. This research revealed spatial variability of food web structure in large lake ecosystems and the importance of considering smaller sub-units, such as basin, in large lakes.

Polyphosphate phosphorus in the Great Lakes

AbstractPolyphosphate (polyP) is important to phytoplankton ecology, but a unified view of its variability and roles in ecosystem‐scale phosphorus (P) cycling is lacking. We study polyP in the world's largest freshwater ecosystem, the Laurentian Great Lakes, covering pelagic to nearshore areas across a wide nutrient gradient. We show that polyP (average 10.99 ± 3.90 nmol L−1) constitutes 3.8–30.2% (average 18.1 ± 7.2%) of total particulate P (TPP). PolyP accumulation is higher in low‐P pelagic waters compared with more productive nearshore areas. PolyP is preferentially degraded in the water column of the Great Lakes, enhancing P recycling and relieving the nitrogen (N) : P imbalance. Our data enables a coherent large‐scale freshwater‐to‐oceanic comparison. We show that while different plankton groups accumulate different levels of polyP with smaller plankton accumulating more, P availability is the key driver of polyP variability within and across systems.

Revisiting the influence of top-down and bottom-up pressures on Wa hia hé:ta (yellow perch Perca flavescens Mitchill, 1814) population dynamics in Kaniatarowanenneh (the Upper St. Lawrence River): implications for collaborative research

Kaniatarowanenneh (the St. Lawrence River) is the outflow of one of the world’s largest freshwater ecosystems and its ecological health has implications for resource management. The population dynamics of an ecologically and economically important fish, the Wa hia hé:ta, Mohawk for yellow perch ( Perca flavescens), are considered by including data that extend to the past century to redress temporal gaps in comparative literature. We found both a significant top-down effect from piscivorous fish as well as a significant bottom-up effect related to total phosphorus on yellow perch relative abundance in the Lake Ontario–Upper St. Lawrence system. Regarding the bottom-up effect, the current state of yellow perch reflects the population size prior to cultural eutrophication (pre-1940s/50s) likely responding to the re-oligotrophication of the system. These findings emphasize the importance of considering historical records in fish population dynamics research to incorporate shifting population baselines into fisheries management. The study also demonstrates the need for collaborative approaches that bring critical new insights and multivocality.

Interkingdom network analyses reveal microalgae and protostomes as keystone taxa involved in nutrient cycling in large freshwater lake sediment.

Few studies have explored the role of interkingdom interactions between bacteria and microeukaryotes in nutrient cycling in lake ecosystems. We conducted sediment sampling from 40 locations covering Hongze Lake and analyzed their chemical properties. Intra- and interkingdom networks were constructed using 16S and 18S rRNA gene amplicon sequencing. Microeukaryotic intranetworks were more complex in spring than in autumn, while no clear variation in the complexity of bacterial intranetworks was found between autumn and spring. Larger and more complex bacterial-microeukaryotic bipartite networks emerged in spring than in autumn, correlated with lower carbon, nitrogen, and phosphorus levels in spring, likely resulting in intense microbial competition. Bacteria and microeukaryotes played different topological roles in interkingdom networks, with microeukaryotes contributing to the networks' greater complexity. Seven keystone modules were identified in spring and autumn nutrient cycling. Importantly, keystone taxa in these modules belonged to photoautotrophic microalgae or predatory protostomes, indicating that these organisms are key drivers in lake sediment nutrient cycling. Our results suggested that nutrient content variation in autumn and spring changes interkingdom networks' topological structure between bacteria and microeukaryotes. Microalgae and protostomes are essential in freshwater lake nutrient cycling and may be targeted to modulate nutrient cycling in large freshwater ecosystems.

Quantifying oxythermal fish habitat quality in a large freshwater ecosystem

The global occurrence and severity of aquatic hypoxia has been exacerbated by anthropogenic activities such as excess nutrient loading and climate change. There are various mechanisms by which hypoxia may affect aquatic organisms and impacts of hypoxia may occur synergistically with other environmental conditions (e.g., temperature). Nonetheless, aquatic resource managers often lack appropriate indicators for measuring the strength and severity of hypoxic conditions. Without standard methods to index hypoxic conditions, it is difficult to evaluate whether management practices are resulting in water quality and habitat improvements. We developed a novel framework for the application of fish habitat quality modeling to assess the severity of hypoxia in a large lake ecosystem. The framework produces three-dimensional measures of fish bioenergetic growth-rate potential in response to spatially-explicit oxythermal conditions and can be applied to other aquatic systems where vertical profile data are collected. We applied this framework to the seasonally hypoxic central basin of Lake Erie using a long-term water quality dataset, then compared our biological indicator to recognized drivers and indices of hypoxic conditions in Lake Erie. Our model application summarized spatiotemporally complex habitat quality conditions for six different fish species and life stages. Annual summary indices of habitat quality varied among years and species. Furthermore, our annual indicator was not strongly correlated with annual nutrient loading and an existing index of hypoxia severity. We suggest that quantification of this habitat quality index is a useful approach for studying the annual impact of hypoxia on biota in aquatic systems.

Erratum: Stakeholders and Invasive Asian Carp in the Great Lakes

Correction| May 24 2023 Erratum: Stakeholders and Invasive Asian Carp in the Great Lakes Shannon Orr Shannon Orr 1Political Science, Bowling Green State University, OH, USA Email: skorr@bgsu.edu Search for other works by this author on: This Site PubMed Google Scholar Email: skorr@bgsu.edu Case Studies in the Environment (2023) 7 (1): 1422170c. https://doi.org/10.1525/cse.2023.1422170c Connected Content This is a correction to: Stakeholders and Invasive Asian Carp in the Great Lakes Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation Shannon Orr; Erratum: Stakeholders and Invasive Asian Carp in the Great Lakes. Case Studies in the Environment 23 January 2023; 7 (1): 1422170c. doi: https://doi.org/10.1525/cse.2023.1422170c Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentCase Studies in the Environment Search Keywords: Asian carp, stakeholders, environmental policy The manuscript contains the statement, “Since that time, they have been slowly swimming their way north and can now be found in 46 states, and most worrisome, just a few miles away from the Great Lakes—the largest freshwater ecosystem in the world with a commercial fishing industry worth more than US$7 billion” (p. 1). There have been recorded captures of grass carp in all of the Great Lakes except for Lake Superior [1]. However, there has only been three captures of any other type of carp (Bighead) and thus doesn’t fit the description. Not all have swum there; some were introduced [2]. The sentence should state, “Grass carp can now be found in 46 states, and most worrisome, in the Great Lakes—the largest freshwater ecosystem in the world with a fishing industry worth more than US$7 billion.” The manuscript contains the statement, “Such hopes however proved... View Original Article You do not currently have access to this content.

Application of a deep learning image classifier for identification of Amazonian fishes.

Given the sharp increase in agricultural and infrastructure development and the paucity of widespread data available to support conservation management decisions, a more rapid and accurate tool for identifying fish fauna in the world's largest freshwater ecosystem, the Amazon, is needed. Current strategies for identification of freshwater fishes require high levels of training and taxonomic expertise for morphological identification or genetic testing for species recognition at a molecular level. To overcome these challenges, we built an image masking model (U-Net) and a convolutional neural net (CNN) to classify Amazonian fish in photographs. Fish used to generate training data were collected and photographed in tributaries in seasonally flooded forests of the upper Morona River valley in Loreto, Peru in 2018 and 2019. Species identifications in the training images (n = 3068) were verified by expert ichthyologists. These images were supplemented with photographs taken of additional Amazonian fish specimens housed in the ichthyological collection of the Smithsonian's National Museum of Natural History. We generated a CNN model that identified 33 genera of fishes with a mean accuracy of 97.9%. Wider availability of accurate freshwater fish image recognition tools, such as the one described here, will enable fishermen, local communities, and citizen scientists to more effectively participate in collecting and sharing data from their territories to inform policy and management decisions that impact them directly.

Cyanotoxins accumulate in Lake St. Clair fish yet their fillets are safe to eat

Consuming fish exposed to cyanobacterial harmful algal blooms (HABs) may be a major route of microcystin toxin exposure to humans. However, it remains unknown whether fish can accumulate and retain microcystins temporally in waterbodies with recurring seasonal HABs, particularly before and after a HAB event when fishing is active. We conducted a field study on Largemouth Bass, Northern Pike, Smallmouth Bass, Rock Bass, Walleye, White Bass, and Yellow Perch to assess the human health risks to microcystin toxicity via fish consumption. We collected 124 fish in 2016 and 2018 from Lake St. Clair, a large freshwater ecosystem in the North American Great Lakes that is actively fished pre- and post-HAB periods. Muscles were analyzed using the 2-methyl-3-methoxy-4-phenylbutyric acid (MMPB) Lemieux Oxidation method for total microcystins, which was used to perform a human health risk assessment for comparison against fish consumption advisory benchmarks available for Lake St. Clair. From this collection 35 fish livers were additionally extracted to confirm the presence of microcystins. Microcystins were detected in all livers at widely varying concentrations (1–1500 ng g−1 ww), suggesting HABs are an underappreciated and pervasive stressor to fish populations. Conversely, microcystin levels were consistently low in muscles (0–15 ng g−1 ww) and presented negligible risk, empirically supporting that fillets may be safely consumed before and after HAB events following fish consumption advisories.

Analysis of spatiotemporal variation in dissolved organic carbon concentrations for streams with cropland-dominated watersheds

It remains a challenge to understand how dissolved organic carbon (DOC) is cycled from farmlands to rivers due to the complex interaction between farming practices, the baseflow hydrology of predominantly flat lowlands, and seasonal environmental influences such as snowpack. To address this, field DOC concentrations were measured monthly throughout the year at sub-basin scales across the Chippewa River Watershed, which falls within the Corn Belt of the Midwestern United States. These DOC dynamics in stream water from croplands were benchmarked against the data sampled from hilly forested areas in the Connecticut River Watershed. The Soil Water Assessment Tool (SWAT) simulation was applied to provide potential predictive variables associated with daily baseflow. Our study outlines a framework using the combination of primary field data, hydrological modeling, and knowledge-based reclassification of Land Use/Land Cover (LULC) data to analyze the viability of modeling the spatial and temporal variations of cropland stream DOC concentrations. Calibration of the SWAT model resulted in the overall daily Nash–Sutcliffe model efficiency coefficient (NSE) of 0.67 and the corresponding R2 = 0.89. Our main results show: 1) baseflow DOC concentrations from croplands were substantially higher throughout the year relative to other landcover areas, especially for spring runoff/snowmelt scenarios, 2) an empirical analysis explained ~82 % of the spatial gradient of annual mean observed DOC concentrations, and 3) with the addition of hydrological simulated variables, a linear model explained ~81 % of monthly and 54 % of daily variations of observed DOC concentrations for cropland sub-basins. Our study identified key factors regulating the spatiotemporal DOC concentrations in cropland streamflow; the contribution here promotes to strengthen future analytical models that link watershed characteristics to carbon cycling processes in a large freshwater ecosystem.

Lake Erie fish safe to eat yet afflicted by algal hepatotoxins

Toxic harmful algal blooms (HABs) pose serious threats to human health and instances of wildlife death have been documented across taxa. However, the extent of toxicological impacts on wildlife species is largely unresolved, raising uncertainty about the repercussions of increasingly severe HABs on the biodiversity and functioning of aquatic ecosystems. Here, we conducted a field study to assess human health risks from consuming fish caught across all stages of a HAB and to determine the pervasiveness of potentially harmful levels of the cosmopolitan toxin microcystin on fish populations. We collected 190 fish in 2015 and 2017 from Lake Erie, a large freshwater ecosystem that is highly productive for fisheries and is an epicenter of HABs and microcystin toxicity events. Fish muscles and livers were analyzed for total microcystins, which was used to conduct a human health risk assessment for comparison against fish consumption advisory benchmarks available for Lake Erie. We found microcystins pose low risks to human health from fillet consumption (mean 1.80 ng g−1 ww) but substantial risks to fish health and recruitment from liver concentrations measured well before and after seasonal bloom events (mean 460.13 ng g−1 ww). Our findings indicate HABs are a previously underappreciated but pervasive threat to fish populations.

The ecological role of permanent ponds in Europe: a review of dietary linkages to terrestrial ecosystems via emerging insects

ABSTRACT Permanent ponds are valuable freshwater systems and biodiversity hotspots. They provide diverse ecosystem services (ESs), including water quality improvement and supply, food provisioning, and biodiversity support, despite significant pressure from multiple anthropogenic stressors and the impacts of ongoing global change. However, ponds are largely overlooked in management plans and legislation, and ecological research has focused on large freshwater ecosystems, such as rivers or lakes. Protection of ponds is often insufficient or indirectly provided via associated habitats such as wetlands. This situation is likely exacerbated by the lack of a full-scale understanding of the importance of ponds. In this review, we provide a detailed overview of permanent ponds across Europe, including their usages and the biodiversity they support. By discussing the concepts of pondscape and metacommunity theory, we highlight the importance of connectivity among and between ponds and identified fluxes of emerging insects as another ES of ponds. Those insects are rich in essential nutrients such as polyunsaturated fatty acids (PUFAs), delivered through them to the terrestrial environment; however, the extent and impact of this ES remains largely unexplored. Several potential stressors, especially related to ongoing global change, that influence pond diversity and integrity are discussed. We provide our insights on future pond management. Adaptive measures, taking into account the pond system per se within the pondscape, are the most promising to mitigate the loss of natural ponds and restore and conserve natural small waterbodies as refuges and diversity hotspots in increasingly urbanized landscapes.

A Plea for Considering Processes That Take Place on the Micrometer Scale in Modelling the Groundwater Ecosystems’ Functions

The largest freshwater ecosystem on earth is in the subsurface: the groundwater. It is populated by animals of almost all phyla and by bacteria, archaea, and fungi. Processes on the macro-, meso-, and micro-scale shape this ecosystem. Bioremediation, i.e., the degradation of contaminants, is steered on the scale of micrometers. However, processes that take place on the micrometer scale are still poorly understood and have not been studied extensively. They are usually lacking from models. In this communication, the plea for studying and making models for the processes that take place on the micrometer scale is based on the conceptual model of bottom-up effects of the pore scale environment. Such conceptual models may influence how quantitative models are built by structuring them.

Vector control reduces the rate of species invasion in the world's largest freshwater ecosystem

AbstractThe Great Lakes‐St Lawrence River basin is the world's most invaded freshwater system. Ballast water release from transoceanic shipping is deemed responsible for 65% of invasions in the basin since the modern St. Lawrence Seaway opened in 1959. Regulations requiring mid‐ocean exchange of ballast water applied in 1993 failed to stem ship‐mediated invasions because the procedure was not mandated for all ships. In 2006 and 2008, Canada and the United States, respectively, mandated that all transoceanic ships should conduct open ocean flushing to ensure that partially filled ballast tanks intended for discharge into the Great Lakes contained water of salinity ≥30 ppt before entering the Seaway. These regulations have been strictly enforced through record inspections and tests of ballast tank salinities of inbound ships. Before‐and‐after comparisons of total organismal abundance and species richness in ballast tanks revealed a substantial reduction in invasion risk from ships that conducted saltwater flushing. Since 2006, the rate of discovery of newly established non‐native species in the Great Lakes declined by 85% to its lowest level in two centuries. While multiple factors could plausibly contribute to this decline, empirical evidence supports the 2006/2008 ballast water regulation as the primary cause, highlighting the benefit of internationally coordinated vector control.

Review on the Change Trend, Attribution Analysis, Retrieval, Simulation, and Prediction of Lake Surface Water Temperature

Lake surface water temperature (LSWT) is indicative of changes in climate and geomorphology. It has been found that LSWT has shown faster warming than air temperature in recent decades, which has greatly affected the aquatic ecosystem of lakes and even led to ecological collapse. It was mainly caused by climate warming and geomorphological changes caused by human activities. However, lakes with different properties respond differently to these changes, resulting in temporal and spatial heterogeneity in the changes of LSWT. After an extensive literature review, it was found that the research on LSWT is mainly focused on the following aspects: (1) qualitative or quantitative analysis of natural and anthropogenic factors affecting LSWT changes; (2) impacts of LSWT changes on lake ecology; (3) acquisition of LSWT data, such as retrieval based on remote sensing (RS) imagery, model-based simulation prediction; (4) study of temporal and spatial variation characteristics of LSWT long time series. Dynamically monitoring LSWT changes, predicting and quantifying the response of lakes with different properties to abrupt or gradual climate changes and changes in human activity intensity, can inform modeling of ecosystem response processes and long-term management planning of large freshwater ecosystems. Therefore, this paper provides a systematic review of LSWT from the above four aspects to provide empirical insight and methodological reference for conducting LSWT research.

A statistical framework for testing impacts of multiple drivers of surface water quality in nearshore regions of large lakes

In nearshore regions of large freshwater ecosystems, complex biophysical processes across large geographic regions, combined with the common logistical challenges of data collection by multiple research agencies and shifting monitoring survey designs over time, present challenges for detecting and managing the influence of multiple sources of nutrients and pollution. We present a statistical framework using linear mixed models (LMMs) to test impact of multiple drivers on nearshore water quality of large lakes. Under this framework, we analyzed a 12-year dataset of water quality variables that were measured from a nearshore region along the Canadian shoreline of Lake Ontario (~86 km2), near Pickering and Ajax. Spatial interpolation showed that almost all water quality parameters decreased in magnitude from the shoreline to the offshore. Two exceptions to this nearshore-offshore gradient occurred in a region that extended ~8 km southwest from the outfall of the Duffin Creek Water Pollution Control Plant (DCWPCP) where ammonia + ammonium (NH3+4) increased and pH decreased slightly. Other LMMs combined explanatory factors into major groups (geographic proximities to shoreline tributary mouths and stormwater drains [inflows], tributary discharges, discharge or loading from the DCWPCP, and climate factors). These models showed that geographic proximity to shoreline inflows and/or tributary discharges were the most important drivers for most water quality parameters including concentrations of phosphorus, a key variable for regulating proliferation of harmful algae blooms and nuisance benthic algae in the Great Lakes. Air temperature was correlated with decreased phosphorus concentrations and nitrate + nitrite, whereas total precipitation and snow were correlated with increased concentrations of most nutrients except NH3+4, which was negatively correlated with duration of lake ice cover in winter. Our framework highlights how influence of individual nutrient sources can be distinguished from climate factors within a dominant nearshore-offshore gradient in water quality within nearshore regions of large lakes.

Teasing Apart Impacts of Human Activity and Regional Drought on Madagascar’s Large Vertebrate Fauna: Insights From New Excavations at Tsimanampesotse and Antsirafaly

Madagascar experienced a major faunal turnover near the end of the first millenium CE that particularly affected terrestrial, large-bodied vertebrate species. Teasing apart the relative impacts of people and climate on this event requires a focus on regional records with good chronological control. These records may document coeval changes in rainfall, faunal composition, and human activities. Here we present new paleontological and paleoclimatological data from southwestern Madagascar, the driest part of the island today. We collected over 1500 subfossil bones from deposits at a coastal site called Antsirafaly and from both flooded and dry cave deposits at Tsimanampesotse National Park. We built a chronology of Late Holocene changes in faunal assemblages based on 65 radiocarbon-dated specimens and subfossil associations. We collected stalagmites primarily within Tsimanampesotse but also at two additional locations in southern Madagascar. These provided information regarding hydroclimate variability over the past 120,000 years. Prior research has supported a primary role for drought (rather than humans) in triggering faunal turnover at Tsimanampesotse. This is based on evidence of: (1) a large freshwater ecosystem west of what is now the hypersaline Lake Tsimanampesotse, which supported freshwater mollusks and waterfowl (including animals that could not survive on resources offered by the hypersaline lake today); (2) abundant now-extinct terrestrial vertebrates; (3) regional decline or disappearance of certain tree species; and (4) scant local human presence. Our new data allow us to document the hydroclimate of the subarid southwest during the Holocene, as well as shifts in faunal composition (including local extirpations, large-vertebrate population collapse, and the appearance of introduced species). These records affirm that climate alone cannot have produced the observed vertebrate turnover in the southwest. Human activity, including the introduction of cattle, as well as associated changes in habitat exploitation, also played an important role.

Spatio-temporal dynamics of bacterial communities in the shoreline of Laurentian great Lake Erie and Lake St. Clair\u2019s large freshwater ecosystems

BackgroundLong-term trends in freshwater bacterial community composition (BCC) and dynamics are not yet well characterized, particularly in large lake ecosystems. We addressed this gap by temporally (15 months) and spatially (6 sampling locations) characterizing BCC variation in lakes Erie and St. Clair; two connected ecosystems in the Laurentian Great Lakes.ResultsWe found a spatial variation of the BCC between the two lakes and among the sampling locations (significant changes in the relative abundance of 16% of the identified OTUs at the sampling location level). We observed five distinct temporal clusters (UPGMA broad-scale temporal variation) corresponding to seasonal variation over the 15 months of sampling. Temporal variation among months was high, with significant variation in the relative abundance of 69% of the OTUs. We identified significant differences in taxonomic composition between summer months of 2016 and 2017, with a corresponding significant reduction in the diversity of BCC in summer 2017.ConclusionsAs bacteria play a key role in biogeochemical cycling, and hence in healthy ecosystem function our study defines the scope for temporal and spatial variation in large lake ecosystems. Our data also show that freshwater BCC could serve as an effective proxy and monitoring tool to access large lake health.

Temporal variation of crude and refined oil biodegradation rates and microbial community composition in freshwater systems

Freshwater systems are vulnerable to contamination by oil extraction and transportation. Thus, it is critical to understand how large freshwater ecosystems such as the Great Lakes will respond to released oil. In this study, we investigated differences in the microbial response to oil in the Straits of Mackinac at different times throughout the year and if crude (Bakken) and refined (non-highway diesel) oil exposure differentially altered the microbial community composition and hydrocarbon biodegradation rates. We also investigated the impact of temperature on the microbial response to oil by incubating samples collected in October of 2018 at 23 °C and at 4 °C. Ambient microbial communities differed between sample collection times, with significantly enriched microbial groups present between most sample types. We found significantly different microbial communities between control and oil-amended samples, but no significant differences between either oil type. We found that the bacterial family Solimonadaceae were significantly enriched in all oil-amended microcosms compared to the control microcosms across sampling times. We assessed oil biodegradation using CO2 production as a proxy for hydrocarbon metabolism. We observed a general trend of increased respiration rates with oil amendment compared to the control. No statistically significant differences in daily CO2 production rates existed between the two oil types. These findings suggest that microbial community in the Straits of Mackinac shifts over time even without oil amendment, and that the microbial communities in the Straits of Mackinac are compositionally and metabolically responsive to the presence of varying oil types throughout the year.

Biogeographic Pattern of Methanogenic Community in Surface Water along the Yangtze River

Methanogenesis from oxic water has been proven to be a significant component of methane source in large and deep freshwater ecosystems. However, the biogeography of methanogenic community in surface water of large rivers remains uncertain. Here, the community ecology and biogeographic pattern of methanogenic community along the Yangtze River (one of the largest rivers in the world) were studied by using high-throughput sequencing, and the relative importance of environmental and spatial variables on the assemblage of methanogenic community was assessed. The results showed a distinct spatial distribution that the Shannon diversity and Shannon evenness of methanogenic community in downstream of the Yangtze River were significantly higher than those in upstream and midstream sections. The most abundant three genera of methanogenic community were Methanobacterium, Methanosarcina and Methanosaeta, which did not exhibit significant difference between different sections. Besides, the composition of methanogenic community also showed a clear spatial variation along the river. Significant distance effects appeared on both methanogenic community and environmental variables. However, no significant relationship was found between methanogenic community and environmental variables. Compared to the limited contributions of spatial and environmental variables, interactions among taxa could be an important driver in structuring the assembly of methanogenic community. In addition, Methanobacteriales, Methanomassiliicoccales and Methanocellales were the key species of methanogenic community in upstream, midstream and downstream sections, respectively. Overall, the methanogenic community exhibited obvious biogeographic pattern along the Yangtze River, which was attributed to a joint effect of abiotic and biotic factors.

Prioritizing coastal wetlands for marsh bird conservation in the U.S. Great Lakes

Human activity surrounding the Laurentian Great Lakes basin has significantly degraded coastal wetland habitats, resulting in severe marsh bird population declines and reduced coastal resilience to changing environmental conditions. Given the need to conserve remaining coastal wetlands for wildlife and people, we developed a spatial prioritization to identify the most important U.S. Great Lakes coastal wetlands for 14 marsh bird species. We modeled occurrence and relative abundance of each species using boosted regression trees, a machine learning algorithm, to relate standardized monitoring data to ten remotely-sensed environmental covariates. We then used Zonation conservation planning software to rank every wetland cell based on its importance for the suite of marsh bird species. Evaluation of the drivers of marsh bird occurrence and abundance revealed that open water, herbaceous wetland, latitude, longitude, and impervious surface were the most important predictors across focal species. The high-priority wetlands for marsh birds (defined as grid cells ranked in the top 20%) occurred along the shores of eastern Lake Ontario, western Lake Erie/St. Clair, Saginaw Bay, Green Bay, northern lakes Michigan and Huron, and western Lake Superior. Overall, less than half (42%) of high-priority coastal wetlands across the Great Lakes basin are currently under some level of protection, with Lake Ontario priority wetlands being the least protected (25%). Our findings represent an opportunity to improve coastal wetland conservation in a region where wetland loss and degradation continue to threaten marsh bird populations and the integrity of one of the world's largest freshwater ecosystems.