scholarly journals Reviews and syntheses: Effects of permafrost thaw on Arctic aquatic ecosystems

2015 ◽  
Vol 12 (23) ◽  
pp. 7129-7167 ◽  
Author(s):  
J. E. Vonk ◽  
S. E. Tank ◽  
W. B. Bowden ◽  
I. Laurion ◽  
W. F. Vincent ◽  
...  
Keyword(s):  
Organic Matter ◽  
Aquatic Ecosystems ◽  
Freshwater Ecosystems ◽  
The Arctic ◽  
Food Web Structure ◽  
Thermokarst Lakes ◽  
Freshwater Systems ◽  
Permafrost Thaw ◽  
Modifying Factors ◽  
Lake Morphology

Abstract. The Arctic is a water-rich region, with freshwater systems covering about 16 % of the northern permafrost landscape. Permafrost thaw creates new freshwater ecosystems, while at the same time modifying the existing lakes, streams, and rivers that are impacted by thaw. Here, we describe the current state of knowledge regarding how permafrost thaw affects lentic (still) and lotic (moving) systems, exploring the effects of both thermokarst (thawing and collapse of ice-rich permafrost) and deepening of the active layer (the surface soil layer that thaws and refreezes each year). Within thermokarst, we further differentiate between the effects of thermokarst in lowland areas vs. that on hillslopes. For almost all of the processes that we explore, the effects of thaw vary regionally, and between lake and stream systems. Much of this regional variation is caused by differences in ground ice content, topography, soil type, and permafrost coverage. Together, these modifying factors determine (i) the degree to which permafrost thaw manifests as thermokarst, (ii) whether thermokarst leads to slumping or the formation of thermokarst lakes, and (iii) the manner in which constituent delivery to freshwater systems is altered by thaw. Differences in thaw-enabled constituent delivery can be considerable, with these modifying factors determining, for example, the balance between delivery of particulate vs. dissolved constituents, and inorganic vs. organic materials. Changes in the composition of thaw-impacted waters, coupled with changes in lake morphology, can strongly affect the physical and optical properties of thermokarst lakes. The ecology of thaw-impacted lakes and streams is also likely to change; these systems have unique microbiological communities, and show differences in respiration, primary production, and food web structure that are largely driven by differences in sediment, dissolved organic matter, and nutrient delivery. The degree to which thaw enables the delivery of dissolved vs. particulate organic matter, coupled with the composition of that organic matter and the morphology and stratification characteristics of recipient systems will play an important role in determining the balance between the release of organic matter as greenhouse gases (CO2 and CH4), its burial in sediments, and its loss downstream. The magnitude of thaw impacts on northern aquatic ecosystems is increasing, as is the prevalence of thaw-impacted lakes and streams. There is therefore an urgent need to quantify how permafrost thaw is affecting aquatic ecosystems across diverse Arctic landscapes, and the implications of this change for further climate warming.

scholarly journals Reviews and Syntheses: Effects of permafrost thaw on arctic aquatic ecosystems

2015 ◽  
Vol 12 (13) ◽  
pp. 10719-10815 ◽  
Author(s):  
J. E. Vonk ◽  
S. E. Tank ◽  
W. B. Bowden ◽  
I. Laurion ◽  
W. F. Vincent ◽  
...  
Keyword(s):  
Organic Matter ◽  
Aquatic Ecosystems ◽  
Soil Layer ◽  
Freshwater Ecosystems ◽  
The Arctic ◽  
Food Web Structure ◽  
Thermokarst Lakes ◽  
Freshwater Systems ◽  
Permafrost Thaw ◽  
Lake Morphology

Abstract. The Arctic is a water-rich region, with freshwater systems covering 16 % of the northern permafrost landscape. The thawing of this permafrost creates new freshwater ecosystems, while at the same time modifying the existing lakes, streams, and rivers that are impacted by thaw. Here, we describe the current state of knowledge regarding how permafrost thaw affects lentic and lotic systems, exploring the effects of both thermokarst (thawing and collapse of ice-rich permafrost) and deepening of the active layer (the surface soil layer that thaws and refreezes each year). Within thermokarst, we further differentiate between the effects of thermokarst in lowland areas, vs. that on hillslopes. For almost all of the processes that we explore, the effects of thaw vary regionally, and between lake and stream systems. Much of this regional variation is caused by differences in ground ice content, topography, soil type, and permafrost coverage. Together, these modifying variables determine the degree to which permafrost thaw manifests as thermokarst, whether thermokarst leads to slumping or the formation of thermokarst lakes, and the manner in which constituent delivery to freshwater systems is altered by thaw. Differences in thaw-enabled constituent delivery can be considerable, with these modifying variables determining, for example, the balance between delivery of particulate vs. dissolved constituents, and inorganic vs. organic materials. Changes in the composition of thaw-impacted waters, coupled with changes in lake morphology, can strongly affect the physical and optical properties of thermokarst lakes. The ecology of thaw-impacted systems is also likely to change, with thaw-impacted lakes and streams having unique microbiological communities, and showing differences in respiration, primary production, and food web structure that are largely driven by differences in sediment, dissolved organic matter and nutrient delivery. The degree to which thaw enables the delivery of dissolved vs. particulate organic matter, coupled with the composition of that organic matter and the morphology and stratification characteristics of recipient systems will play an important role in determining the balance between the release of organic matter as greenhouse gases (CO2 and CH4), its burial in sediments, and its loss downstream. The magnitude of thaw impacts on northern aquatic ecosystems is increasing, as is the prevalence of thaw-impacted lakes and streams. There is therefore an urgent need to address the key gaps in understanding in order to predict the full effects of permafrost thaw on aquatic ecosystems throughout the Arctic, and their consequential feedbacks to climate.

scholarly journals Fungi and viruses as important players in microbial mats

2020 ◽  
Vol 96 (11) ◽  
Author(s):  
Cátia Carreira ◽  
Christian Lønborg ◽  
Michael Kühl ◽  
Ana I Lillebø ◽  
Ruth-Anne Sandaa ◽  
...  
Keyword(s):  
Organic Matter ◽  
Aquatic Ecosystems ◽  
Microbial Mats ◽  
Freshwater Ecosystems ◽  
Food Web Structure ◽  
Element Cycling ◽  
Functional Roles ◽  
Web Structure ◽  
Experimental Approaches ◽  
And Function

ABSTRACT Microbial mats are compacted, surface-associated microbial ecosystems reminiscent of the first living communities on early Earth. While often considered predominantly prokaryotic, recent findings show that both fungi and viruses are ubiquitous in microbial mats, albeit their functional roles remain unknown. Fungal research has mostly focused on terrestrial and freshwater ecosystems where fungi are known as important recyclers of organic matter, whereas viruses are exceptionally abundant and important in aquatic ecosystems. Here, viruses have shown to affect organic matter cycling and the diversity of microbial communities by facilitating horizontal gene transfer and cell lysis. We hypothesise fungi and viruses to have similar roles in microbial mats. Based on the analysis of previous research in terrestrial and aquatic ecosystems, we outline novel hypotheses proposing strong impacts of fungi and viruses on element cycling, food web structure and function in microbial mats, and outline experimental approaches for studies needed to understand these interactions.

Facilitated Heterogeneous Photodegradation of Dissolved Organic Matter by Particulate Iron

2004 ◽  
Vol 1 (3) ◽  
pp. 197 ◽  
Author(s):  
Julia A. Howitt ◽  
Darren S. Baldwin ◽  
Gavin N. Rees ◽  
Barry T. Hart
Keyword(s):  
Organic Matter ◽  
Iron Oxide ◽  
Dissolved Organic Matter ◽  
Iron Oxides ◽  
Aquatic Ecosystems ◽  
Photochemical Reactions ◽  
Freshwater Systems ◽  
Particulate Iron ◽  
Presence And Absence ◽  
Australian Freshwater

Environmental Context. Iron oxides, as suspended minerals or as a colloidal phase, are common in Australian freshwater systems. Freshwater systems are also loaded with carbon-based substances, ‘dissolved organic matter’, but not all is biologically available as food to freshwater organisms. However, photochemical interactions between these iron oxides and dissolved organic matter provide a mechanism for biologically resistant carbon to re-enter the food web. Suspended iron oxides thus need to be considered in carbon cycles in aquatic ecosystems. Abstract. The photochemical degradation of dissolved organic matter (DOM) derived from the leaves of River Red Gum (Eucalyptus camaldulensis) was examined, with a particular focus on the photochemical generation of CO2, consumption of O2, and the effect of particulate iron minerals on these photochemical reactions. Solutions of leaf leachate were irradiated with ultraviolet and visible light in the presence and absence of amorphous iron oxides. Addition of fresh iron oxide was found to increase the rate of photodegradation of the organic matter by up to an order of magnitude compared to the reactions without added iron oxide. The ratio of CO2 produced to O2 consumed was ~1:1 in both the presence and absence of iron oxyhydroxide. The reactivity of the iron oxides was dependent on the preparation method and decreased with increased storage time. These results suggest that photochemical reactions on particle surfaces should be considered when examining carbon transformation in aquatic ecosystems, especially at sites with potential for the production of iron oxyhydroxides.

scholarly journals Organic matter across subsea permafrost thaw horizons on the East Siberian Arctic Shelf

2018 ◽  
Author(s):  
Birgit Wild ◽  
Natalia Shakhova ◽  
Oleg Dudarev ◽  
Alexey Ruban ◽  
Denis Kosmach ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Luminescence Dating ◽  
Arctic Shelf ◽  
The Arctic ◽  
Organic Carbon Content ◽  
Study Region ◽  
Permafrost Thaw ◽  
Siberian Arctic ◽  
Subsea Permafrost

Abstract. Thaw of subsea permafrost across the Arctic Ocean shelves might promote the degradation of organic matter to CO2 and CH4, but also create conduits for transfer of deeper CH4 pools to the atmosphere and thereby amplify global warming. In this study, we describe sedimentary characteristics of three subsea permafrost cores of 21–56 m length drilled near the current delta of the Lena River in the Buor–Khaya Bay on the East Siberian Arctic Shelf, including content, origin and degradation state of organic matter around the current thaw front. Grain size distribution and optically stimulated luminescence dating suggest the alternating deposition of aeolian silt and fluvial sand over the past 160 000 years. Organic matter in 3 m sections across the current permafrost table was characterized by low organic carbon contents (average 0.7 ± 0.2 %) as well as enriched δ13C values and low concentrations of the terrestrial plant biomarker lignin compared to other recent and Pleistocene deposits in the study region. The lignin phenol composition further suggests contribution of both tundra and boreal forest vegetation, at least the latter likely deposited by rivers. Our findings indicate high variability in organic matter composition of subsea permafrost even within a small study area, reflecting its development in a heterogeneous and dynamic landscape. Even with this relatively low organic carbon content, the high rates of observed subsea permafrost thaw in this area yield a thaw-out of 1.6 kg OC m−2 year−1, emphasizing the need to constrain the fate of the poorly described and thawing subsea permafrost organic carbon pool.

scholarly journals Three-Dimensional Stefan Equation for Thermokarst Lake and Talik Geometry Characterization

2021 ◽  
Author(s):  
Noriaki Ohara ◽  
Benjamin M. Jones ◽  
Andrew D. Parsekian ◽  
Kenneth M. Hinkel ◽  
Katsu Yamatani ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Ground Subsidence ◽  
The Arctic ◽  
Permafrost Region ◽  
Boundary Area ◽  
Near Surface ◽  
Thermokarst Lakes ◽  
Thermokarst Lake ◽  
Permafrost Thaw ◽  
Transient Electromagnetic

Abstract. Thermokarst lake dynamics, which plays an essential role in carbon release due to permafrost thaw, is affected by various geomorphological processes. In this study, we derive a three-dimensional (3D) Stefan equation to characterize talik geometry under a hypothetical thermokarst lake in the continuous permafrost region. Using the Euler equation in the calculus of variations, the lower bounds of the talik were determined as an extremum of the functional describing the phase boundary area with a fixed total talik volume. We demonstrate that the semi-ellipsoid geometry of the talik is optimal for minimizing the total permafrost thaw under the lake for a given annual heat supply. The model predicting ellipsoidal talik geometry was verified by talik thickness observations using transient electromagnetic (TEM) soundings in Peatball Lake on the Arctic Coastal Plain (ACP) of Alaska. The lake width-depth ratio of the elliptic talik can characterize the energy flux anisotropy in the permafrost although the lake bathymetry cross section may not be elliptic due to the presence of near-surface ice-rich permafrost. This theory suggests that talik development stabilizes thermokarst lakes by ground subsidence due to permafrost thaw while wind-induced waves and currents are likely responsible for the elongation and orientation of thermokarst lakes in certain regions such as the ACP of northern Alaska.

IMPROVEMENT OF THE METHOD FOR ASSESSMENT OF THE HETEROTROPHIC ACTIVITY OF FRESHWATER BACTERIA BY STUDYING HOW BACTERIAL COMMUNITY CONSUMES THE ORGANIC MATTER EXCRETED BY ALGAE: ISSUES OF WATER QUALITY

Fisheries ◽  
2020 ◽  
Vol 2020 (2) ◽  
pp. 61-66 ◽  
Author(s):  
Anatoly Sadchikov
Keyword(s):  
Water Quality ◽  
Organic Matter ◽  
Aquatic Ecosystems ◽  
Aquatic Organisms ◽  
Freshwater Ecosystems ◽  
Trophic Levels ◽  
Organic Substances ◽  
Heterotrophic Activity ◽  
Freshwater Bacteria ◽  
Methods And Techniques

The article describes an improved and approved methodology for assessing the heterotrophic activity of freshwater bacteria using a specific example. Namely, the example of studying the bacterial consumption of organic matter excreted by algae. Utilization of organic substances in water bodies by microorganisms and their oxidation are an important part of the functioning of aquatic ecosystems and water self-purification. This article details innovative modifications to the method based on the use of 14C-labeled organic matter by aquatic organisms. All these methods and techniques have been tested in the study of production and destruction processes in freshwater ecosystems of different trophic levels including mesotrophic, eutrophic and hypertrophic surface ecosystems.

Lability of dissolved organic carbon from boreal peatlands: interactions between permafrost thaw, wildfire, and season

2020 ◽  
Vol 100 (4) ◽  
pp. 503-515 ◽  
Author(s):  
Katheryn Burd ◽  
Cristian Estop-Aragonés ◽  
Suzanne E. Tank ◽  
David Olefeldt
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Carbon Cycling ◽  
Aquatic Ecosystems ◽  
Food Web Structure ◽  
Near Surface ◽  
Permafrost Thaw ◽  
Boreal Peatlands ◽  
Doc Production ◽  
Peat Plateaus

Boreal peatlands are major sources of dissolved organic carbon (DOC) to downstream aquatic ecosystems, where it influences carbon cycling and food web structure. Wildfire and permafrost thaw alter peatland vegetation and hydrology and may affect the quantity and chemical composition of exported DOC. We studied the influence of wildfire and thaw on microbial and photochemical lability of near-surface porewater DOC, assessed through 7 d incubations. We carried out these incubations in spring, summer, and fall but only found differences in spring when DOC biodegradability (% loss during dark incubations) increased with lower DOC aromaticity and C/N ratios. During spring, the most labile DOC was found in recently formed thermokarst bogs along collapsing peat plateau edges (25% loss), which was greater than in mature sections of thermokarst bogs (3%), and peat plateaus with intact permafrost (9%). Increased DOC lability following thaw was likely linked to high DOC production and turnover associated with productive hydrophilic Sphagnum mosses and sedges, rather than thawed permafrost peat. A wildfire (3 yr prior) reduced DOC biodegradability in both peat plateaus (4%) and rapidly collapsing peat plateau edges (14%). Biodegradability of DOC in summer and fall was low across all sites; 2% and 4%, respectively. Photodegradation was shown to potentially contribute significantly to downstream DOC degradation but did not vary across peatland sites. We show that disturbances such as permafrost thaw and wildfire have the potential to affect downstream carbon cycling, particularly as the largest influences were found in spring when peatlands are well connected to downstream aquatic ecosystems.

scholarly journals Coloured dissolved organic matter in aquatic ecosystems of three representative regions of the Arctic according to the data obtained in year 2019

2020 ◽  
Vol 163 ◽  
pp. 04006
Author(s):  
Anastasiia Pashovkina ◽  
Irina Fedorova
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Kola Peninsula ◽  
Aquatic Ecosystems ◽  
River Delta ◽  
The Arctic ◽  
Yamal Peninsula ◽  
Lena River ◽  
Lena River Delta ◽  
The Yamal Peninsula

In this study the laboratory analysis of water samples from three representative regions of the Arctic for content of coloured dissolved organic matter (CDOM) – the important component of natural waters, which has a direct impact on state of aquatic ecosystems, was made. Samples were collected from water objects from the Kola Peninsula, the Yamal Peninsula and the Lena River Delta. The results of the analysis made it possible to determine CDOM concentrations in water. According to the average values, the highest values were obtained for the Yamal Peninsula and lowest – for the Kola Peninsula. The predominance of allochthonous CDOM in the water objects from all three regions was revealed. Moreover, the complete absence of photodegradation processes was determined. For the lakes and rivers from the Kola Peninsula it was also possible to follow seasonal dynamic of CDOM concentration in water and to compare it with earlier obtained data concerning seasonal CDOM dynamic in the Lena River Delta. Results are actual due to the currently existing tendency of climate change which leads to intensification of thermal denudation and thermal erosion processes in the cryolithozone, which are consequently increasing income of allochthonous CDOM in water objects.

scholarly journals A global review of the spatial, taxonomic, and temporal scope of freshwater fisheries hydroacoustics research

2016 ◽  
Vol 24 (3) ◽  
pp. 333-347 ◽  
Author(s):  
Riley A. Pollom ◽  
George A. Rose
Keyword(s):  
Aquatic Ecosystems ◽  
Developed Countries ◽  
Freshwater Ecosystems ◽  
Target Strength ◽  
Taxonomic Identification ◽  
Freshwater Systems ◽  
Bony Fishes ◽  
Fish Morphology ◽  
The Status ◽  
Taxonomic Range

This review assessed the status and scope of freshwater hydroacoustic fisheries research in global aquatic ecosystems with emphasis on (i) geographical and spatial scope, (ii) taxonomic range at the species and family levels (restricted to bony fishes of the Actinopterygii and Sarcopterygii), and (iii) temporal scope. Hydroacoustic measures have been used by ecologists and managers of freshwater systems for several decades, with major progress in technology and methods in recent years. A literature review indicated 296 research contributions that employed hydroacoustics to study freshwater fisheries in 294 different aquatic ecosystems. Spatially, hydroacoustics research in freshwater systems have thus far been concentrated in developed countries, particularly in North America and Northern and Central Europe (83% of the studies reviewed here). Most studies were small in spatial scale and short-term, with 80% including only a single body of water and 63% conducted over a single year or season (75% spanning less than two years). In addition, effects of fish morphology and behavior on acoustic target strength (TS) and taxonomic identification are not well parameterized, with only 21 species receiving empirical study of TS. Despite progress, the present study reveals gaps in the knowledge needed for wider applications to management. These include larger biogeographical and temporal scales of study and further empirical research on TS and taxonomic identification. Recent advances in size rather than species-based methods and theory offer potential solutions to this issue but require further investigation. We conclude with recommendations for systematic hydroacoustic research to enable more effective monitoring, management, and conservation of fisheries and freshwater ecosystems.

scholarly journals DOM degradation by light and microbes along the Yukon River-coastal ocean continuum

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Brice K. Grunert ◽  
Maria Tzortziou ◽  
Patrick Neale ◽  
Alana Menendez ◽  
Peter Hernes
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Salinity Gradient ◽  
Coastal Ocean ◽  
Interactive Effects ◽  
The Arctic ◽  
Yukon River ◽  
Spring Freshet ◽  
Dom Composition

AbstractThe Arctic is experiencing rapid warming, resulting in fundamental shifts in hydrologic connectivity and carbon cycling. Dissolved organic matter (DOM) is a significant component of the Arctic and global carbon cycle, and significant perturbations to DOM cycling are expected with Arctic warming. The impact of photochemical and microbial degradation, and their interactive effects, on DOM composition and remineralization have been documented in Arctic soils and rivers. However, the role of microbes, sunlight and their interactions on Arctic DOM alteration and remineralization in the coastal ocean has not been considered, particularly during the spring freshet when DOM loads are high, photoexposure can be quite limited and residence time within river networks is low. Here, we collected DOM samples along a salinity gradient in the Yukon River delta, plume and coastal ocean during peak river discharge immediately after spring freshet and explored the role of UV exposure, microbial transformations and interactive effects on DOM quantity and composition. Our results show: (1) photochemical alteration of DOM significantly shifts processing pathways of terrestrial DOM, including increasing relative humification of DOM by microbes by > 10%; (2) microbes produce humic-like material that is not optically distinguishable from terrestrial humics; and (3) size-fractionation of the microbial community indicates a size-dependent role for DOM remineralization and humification of DOM observed through modeled PARAFAC components of fluorescent DOM, either through direct or community effects. Field observations indicate apparent conservative mixing along the salinity gradient; however, changing photochemical and microbial alteration of DOM with increasing salinity indicate changing DOM composition likely due to microbial activity. Finally, our findings show potential for rapid transformation of DOM in the coastal ocean from photochemical and microbial alteration, with microbes responsible for the majority of dissolved organic matter remineralization.

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