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Determining dominating control mechanisms of inland water carbon cycling processes and associated gross primary productivity on regional and global scales
Abstract
Inland water carbon (C) sequestration rates play a potentially important role in the balance between C supplies from the atmosphere and associated watersheds and the net demand of primary producers. This study conducts a comprehensive analysis of influencing factors associated with inland water C cycling processes as well as their C sequestration potential and gross primary productivity (GPP). Additionally, we also analyze changes in the balance between C sequestration processes and GPP. Furthermore, this study describes applicable research methods used to quantify C cycling and GPP processes as well as providing corresponding estimates on regional and global scales. Finally, we offer a scientific basis to chronicle how inland water productivity controls exogenous C inputs as well as changes to biological, physical, and chemical factors. Investigations into inland water C sequestration processes under a background of climate warming will become more critical in the future, necessitating the inclusion of different aquatic system component classifications and plant species community types to determine the effects associated with GPP and C dynamic mechanisms within aquatic systems that constitute this diverse water system.
... Spring represents a return to semi-arid conditions in most of the Timgad basin by more than 88%, with semi-humid areas persisting only in the local northern areas. According to (Gao et al., 2021), the seasonal decrease in soil moisture during spring increases the need for irrigation to support agriculture, especially as temperatures begin to rise. ...
... This phase, influenced by winter precipitation, is essential for water retention and ecosystem vitality. Winter precipitation decreases reliance on irrigation by naturally satisfying agricultural water needs (Gao et al., 2021). ...
... By April, the majority of regions revert to semi-arid classifications, with only a few isolated locations maintaining elevated humidity levels. This transition highlights the transient effect of winter precipitation, as elevated temperatures necessitate enhanced irrigation to offset the swift decline in natural moisture (Gao et al., 2021). ...
Knowledge of drought conditions is necessary for the rational use of water resources, the prevention of the dangers resulting from them, and for explaining landscape and ecology characteristics. To analyze annual, seasonal and monthly aridity trends in the Timgad Basin, North-East Algeria, climate data from 07 meteorological stations within the 1975-2009 period were used. After computing the De Martonne aridity index at each station, a geographic information system (GIS) was utilized to maps this index throughout the region and specify drought trends, visualizing detected annual, seasonal and monthly tendencies. On an annual scale, the De Marton Drought Index shows a semi-arid climate in the entire Timgad Basin. On a seasonal scale, the winter season shows a dry semi-humid climate - from Mediterranean to semi-humid conditions, and the climate of the region in autumn and spring is semi-arid except for some eastern areas, which are characterized by a dry semi-humid climate - from Mediterranean conditions in spring. In contrast, summer shows from very dry to dry. The period extending from May to October is characterized by a semi-arid to dry climate; December and January reveal humid conditions, while November, February, March and April belong to a semi-arid to Mediterranean climate.
... Vegetation is a principal component of terrestrial ecosystems [12]. Drought intensification can seriously threaten vegetation growth and productivity by causing systematic and abrupt changes in the ecosystem structure and services [13,14]. Drought also has complex environmental and most of them did not document detailed spatial-temporal drought trends. ...
... Vegetation growth can be affected by drought conditions and can also be used as an indicator of drought conditions [13,14]. Given their strong correlation, numerous studies have investigated the relationship between SPEI and NDVI and found that drought is a major factor in vegetation growth [80]. ...
Understanding the spatiotemporal characteristics of drought and its impacts on vegetation is a timely prerequisite to ensuring agricultural, environmental, and socioeconomic sustainability in Sri Lanka. We investigated the drought characteristics (duration, severity, frequency, and intensity) from 1990 to 2020 by using the Standardized Precipitation Evapotranspiration Index (SPEI) at various timescales and the cumulative and lagged effects on vegetation between 2000 and 2020 across the climatic zones of Sri Lanka (Dry, Wet, and Intermediate). SPEI indexes at 1-, 3-, 6-, 12-, and 24-month scales were used to analyze the drought characteristics. Frequent droughts (~13%) were common in all zones, with a concentration in the Dry zone during the last decade. Drought occurrences mostly ranged from moderate to severe in all zones, with extreme events more common in the Dry zone. This research used SPEI and the Standardized Normalized Difference Vegetation Index (SNDVI) at 0 to 24-month scales to analyze the cumulative and lagged effects of drought on vegetation. Cumulated drought effects and vegetation had maximum correlation coefficient values concentrated in the −0.41–0.98 range in Sri Lanka. Cumulated drought effects affected 40% of Dry and 16% of Intermediate zone vegetation within 1–4 months. The maximum correlation between the lagged drought effect and vegetation SNDVI showed coefficient values from −0.31–0.94 across all zones, and the high correlation areas were primarily distributed in Dry and Intermediate zones. Over 60% of the Dry and Intermediate zones had a lagged drought impact within 0 to 1 month, while 52% of the Wet zone experienced it over 11 months. The resulting dominant shorter timescale responses indicate a higher sensitivity of vegetation to drought in Sri Lanka. The findings of this study provide important insights into possible spatiotemporal changes of droughts and their possible impact on vegetation across climate zones.
... Poulter et al., 2014;Grill et al., 2019). However, highly natural biogeochemical processes and enhanced anthropogenic perturbations (such as urban expansion and artificial storage) results in a large uncertainty in above estimates in inland rivers, and thus the studies on the controls of riverine carbonate system attract increasing attention in recent years to mitigate global climate change (Lauerwald et al., 2015;Marx et al., 2017;Gao et al., 2021;Ran et al., 2021). ...
... Globally, the impact of anthropogenic direct input on riverine DIC has received increasing attention (Raymond et al., 2008;Yang et al., 2018;Gao et al., 2021), especially sewage input from urban areas (Yoon et al., 2017;Park et al., 2018Park et al., , 2021Chanda et al., 2020). Taiyuan City between station F8 and F11 is the capital of Shanxi Province with a 5.3 million population and a 62 billion $ GDP in 2021. ...
Different from rivers in humid areas, the variability of riverine CO2 system in arid areas is heavily impacted by anthropogenic disturbance with the increasing urbanization and water withdrawals. In this study, the water chemistry and the controls of carbonate system in an urbanized river (the Fenhe River) on the semi-arid Loess Plateau were analyzed. The water chemistry of the river water showed that the high dissolved inorganic carbon (DIC) concentration (about 37 mg L−1) in the upstream with a karst land type was mainly sourced from carbonate weathering involved by H2CO3 and H2SO4, resulting in an oversaturated partial pressure of CO2 (pCO2) (about 800 µatm). In comparison, damming resulted in the widespread appearance of non-free flowing river segments, and aquatic photosynthesis dominated the DIC and pCO2 spatiality demonstrated by the enriched stable isotope of DIC (δ13CDIC). Especially in the mid-downstream flowing through major cities in warm and low-runoff August, some river segments even acted as an atmospheric CO2 sink. The noteworthy is wastewater input leading to a sudden increase in DIC (> 55 mg L−1) and pCO2 (> 4500 µatm) in the downstream of Taiyuan City, and in cold November the increased DIC even extended to the outlet of the river. Our results highlight the effects of aquatic production induced by damming and urban sewage input on riverine CO2 system in semi-arid areas, and reducing sewage discharge may mitigate CO2 emission from the rivers.
... 2,3 At the waterair interface, C exchange processes are mainly coupled with biological-physical-chemical processes, where biological production and metabolic mechanisms in water effectuate C cycling complexity. 4,5 At the water-sediment interface, C deposition predominates, namely, from particulate C that derives from biological detritus and OC decomposition to carbon dioxide (CO 2 ), which is released into inland waterbodies via microbial mineralization processes. 6 Through these multi-interfaces, C cycling processes drive inland waterbody C source-sink effects. ...
... Therefore, strengthening research on metabolic C processes and their C source-sink effects and associated driving mechanisms can provide a new means by which to discover these "missing C sinks", which would be highly significant for accurately quantifying ecosystem C budgets globally. 4,5 Accordingly, the intent of this review is to clarify inland water metabolic C processes and associated biological regulations. This will allow for the systematic analysis of C cycling processes and associated C source-sink effects specific to inland waterbodies while also revealing the driving mechanisms behind metabolic C processes and how they affect C source-sink stability. ...
Inland water carbon (C) cycling processes determine C source-sink stability status. ■ Metabolic C processes drive carbon source-sink instability in inland waterbodies. ■ Insights into metabolic C processes are key to quantifying C budgets globally. BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Citation: Jia J., Dungait J., Lu Y., et al., (2023). Inland water metabolic carbon processes and associated biological mechanisms that drive carbon source-sink instability. The Innovation Geoscience 1(3), 100035. Due to their complexity, inland water carbon (C) cycling processes significantly impact the C source-sink stability status of terrestrial ecosystems over short-term, long-term, and geological timescales. Stable C source-sink processes primarily include terrestrial biospheric production, litho-spheric organic carbon (OC) oxidization, rock weathering, and riverine C transport. Conversely, the effect of metabolic C processes on the C source-sink status of inland waterbodies is not stable. Therefore, inland water metabolic C processes may cause significant C sink underestimations, which relevant studies have largely ignored. A new way to account for this missing inland water C sink is an in-depth understanding of the metabolic C processes and associated driving effects of biological regulation mechanisms on the C source-sink status. This new approach can help to more accurately quantify the global ecosystem C budget. The purpose of this review is threefold: (i) to clarify metabolic C processes and associated biological regulation mechanisms of inland waterbodies; (ii) to systematically analyze C cycling processes and associated C source-sink statuses of inland waterbodies at different timescales; (iii) to reveal driving mechanisms of metabolic C processes on C source-sink stability in inland water-bodies. Doing so will help us better understand how to more accurately calibrate C source-sink functions globally while also garnering an in-depth understanding of the role that terrestrial ecosystems play in C neutraliza-tion under global climate change. INTRODUCTION Inorganic carbon (IC) and organic carbon (OC) exchanges take place at the water-air interface, the water-sediment interface, and the water-land interface of inland waterbodies, which collectively constitute their carbon (C) cycling processes. 1 At the water-land interface, C exchange processes are mainly driven by anthropogenic activities or riverine emissions. 2,3 At the water-air interface, C exchange processes are mainly coupled with biological-physical chemical processes, where biological production and metabolic mechanisms in water effectuate C cycling complexity. 4,5 At the water-sediment interface, C deposition predominates, namely, from particulate C that derives from biological detritus and OC decomposition to carbon dioxide (CO 2), which is released into inland waterbodies via microbial mineralization processes. 6 Through these multi-interfaces, C cycling processes drive inland waterbody C source-sink effects. Inland waterbodies are characterized by rapid water cycling and strong C cycling intensity. This is especially the case for shallow lakes, highly eutrophic lakes, and highly productive lakes, which are more complex and heterogenic in nature. 7 Additionally, the complexity and intensity of inland water C cycling processes significantly impact the C source and sink statuses of terrestrial ecosystems that are closely connected to rivers, lakes, and reservoirs. Accordingly, it would be highly beneficial to increase our overall understanding of the roles that inland water plays in current and prospective global C cycling. For instance, this will allow us to accurately quantify ecosystem C budgets globally, which will ultimately help us attain our C neutrality goals. The C source-sink effect is driven by Earth's various C cycling processes. This effect can either exist in one of two statuses (i.e., stable or unstable) over short-term (seconds, minutes, hours, and days), long-term (months, years,
... 2,3 At the waterair interface, C exchange processes are mainly coupled with biological-physical-chemical processes, where biological production and metabolic mechanisms in water effectuate C cycling complexity. 4,5 At the water-sediment interface, C deposition predominates, namely, from particulate C that derives from biological detritus and OC decomposition to carbon dioxide (CO 2 ), which is released into inland waterbodies via microbial mineralization processes. 6 Through these multi-interfaces, C cycling processes drive inland waterbody C source-sink effects. ...
... Therefore, strengthening research on metabolic C processes and their C source-sink effects and associated driving mechanisms can provide a new means by which to discover these "missing C sinks", which would be highly significant for accurately quantifying ecosystem C budgets globally. 4,5 Accordingly, the intent of this review is to clarify inland water metabolic C processes and associated biological regulations. This will allow for the systematic analysis of C cycling processes and associated C source-sink effects specific to inland waterbodies while also revealing the driving mechanisms behind metabolic C processes and how they affect C source-sink stability. ...
Due to their complexity, inland water carbon (C) cycling processes significantly impact the C source-sink stability status of terrestrial ecosystems over short-term, long-term, and geological timescales. Stable C source-sink processes primarily include terrestrial biospheric production, lithospheric organic carbon (OC) oxidization, rock weathering, and riverine C transport. Conversely, the effect of metabolic C processes on the C source-sink status of inland waterbodies is not stable. Therefore, inland water metabolic C processes may cause significant C sink underestimations, which relevant studies have largely ignored. A new way to account for this missing inland water C sink is an in-depth understanding of the metabolic C processes and associated driving effects of biological regulation mechanisms on the C source-sink status. This new approach can help to more accurately quantify the global ecosystem C budget. The purpose of this review is threefold: (i) to clarify metabolic C processes and associated biological regulation mechanisms of inland waterbodies; (ii) to systematically analyze C cycling processes and associated C source-sink statuses of inland waterbodies at different timescales; (iii) to reveal driving mechanisms of metabolic C processes on C source-sink stability in inland waterbodies. Doing so will help us better understand how to more accurately calibrate C source-sink functions globally while also garnering an in-depth understanding of the role that terrestrial ecosystems play in C neutralization under global climate change.
... reduced continuous and cumulative stratification duration) (Château et al., 2019;Haas et al., 2020;Exley et al., 2021). However, while severe shading could inhibit the growth of submerged macrophytes (e.g., Gao et al., 2021), some macrophytes may exhibit phenotypic responses to adapt to low light. For example, macrophyte species with erect stems may compensate for light limitation by increasing internodal growth towards the water surface not covered by leaves (Middelboe and Markager, 1997). ...
Floating photovoltaic (FPV) systems are a rapidly expanding renewable energy technology, yet their potential ecological impacts, particularly cross-ecosystem effects, remain poorly understood. This review synthesises current knowledge on organic matter (OM) dynamics and carbon (C) fluxes in lake ecosystems, examining how FPV installations may influence lake C cycling, insect emergence, and greenhouse gas (GHG) emissions. FPV can alter OM availability, shifting the balance between autochthonous and allochthonous inputs. In the short term, installation may increase OM deposition due to the rapid decline of primary producers and riparian vegetation removal. Long-term effects remain uncertain but could drive metabolic regime shifts toward autotrophy or heterotrophy, depending on initial lake conditions. These changes, combined with reduced oxygen and temperature, could significantly alter aquatic food webs, modify GHG fluxes, and alter C dynamics. Increased OM sedimentation could enhance GHG production, while reduced and delayed insect emergence may weaken C transfer to terrestrial ecosystems. Declines in emergent insect biomass could impact terrestrial predators, such as bats and birds, triggering cascading ecological effects. Overall, FPV may reshape carbon fluxes across aquatic–terrestrial boundaries, with impacts varying by FPV coverage and lake-specific factors. There is an urgent need for ecosystem-scale studies and long-term data to assess FPV-induced changes in C fluxes and mitigate its potential impacts on biodiversity and the global C cycle.
... These biological carbon compounds are often recalcitrant compounds (e.g., cellulose and lignin), thus they easily form refractory carbon pools and thereby increasing carbon stock capacity [26,54]. However, the increase in submerged macrophyte biomass also implies a rise in CO 2 and CH 4 produced through their respiration and decomposition after decay [12]. Additionally, the increase in submerged macrophyte biomass may directly or indirectly promote CH 4 formation via aerobic methanogenesis or co-metabolic effects [1,42]. ...
Background
With the increase in the inorganic carbon input from watersheds, elevated dissolved inorganic carbon (DIC) concentrations will significantly impact the carbon cycle in freshwater ecosystems. Moreover, the limited diffusion rate of CO2 in water, coupled with the lack of functional stomata, greatly restricts the ability of submerged macrophytes to absorb CO2 from their aquatic environment. The importance of bicarbonate (HCO3⁻) for submerged macrophytes becomes more pronounced. Current research focuses on the effects of DIC (notably HCO3⁻) on the phenotypic plasticity of submerged macrophytes, while its impact on their carbon stock capabilities has rarely been reported.
Results
In this study, Myriophyllum spicatum served as the model macrophyte within a mesocosm experimental system to assess the impact of HCO3⁻ enrichment (0.5 to 2.5 mmol L⁻¹) on carbon stocks and emissions across a one-year period. Our findings indicated that the addition of HCO3⁻ had a non-significant inhibitory effect on the diffusive fluxes of methane (CH4) emissions. Concurrently, it significantly reduced CO2 fluxes within the systems. The annual average CO2 fluxes across the four HCO3⁻ addition levels were -3.48 ± 7.60, -6.78 ± 5.87, -7.15 ± 8.68, and -14.04 ± 14.39 mol m⁻² yr⁻¹, respectively, showing significant differences between low /medium- and high- HCO3⁻ addition levels.
Conclusion
The addition of HCO3⁻ enhanced carbon stocks in water, macrophytes and the entire system, with minimal effects on carbon sedimentation stocks. Our study provides valuable insights into understanding the carbon sink capacity of aquatic ecosystems and elucidates the underlying mechanisms driving these processes on a system scale.
... As will be described in a separate paper, areal nutrient supply (N area ) has typically the strongest effect by far on whole-lake algal biomass and primary production in the Lake2D model, followed by lake mean depth (through its effects on sinking losses in very shallow lakes and the underwater light climate in deep lakes). Yet, current global estimates of lake GPP neglect both benthic producers and any morphometric information beyond lake area and mean depth (Gao et al., 2021;Jia et al., 2024;Lewis Jr, 2011). Given that our analysis suggests that 1D-approaches underestimate GPP in shallow lakes on the order of 20% and that shallow lakes, because of their shear abundance (Cael et al., 2017) and high productivity (Qin et al., 2020), account for more than half of the estimated global rate of GPP from all freshwater lentic and lotic ecosystems (Rabaey et al., 2024), we believe that global estimates of lake GPP may have to be corrected for the systematic errors inflicted by the prevailing 1D-approaches. ...
Basin morphometry can strongly affect lake-internal processes relevant for productivity, such as turbulent mixing, photosynthetic energy acquisition, sedimentation, and nutrient recycling. Yet, in both empirical and theoretical studies of whole-lake primary production, lake morphometry is often simplified to a single 1-dimensional measure - lake mean depth. Using the conceptual, process-based model ′Lake2D′, we addressed the question: To what extent can pelagic and benthic producer dynamics, integrated over a lake basin, be captured by approaches that use mean depth as the only morphometrical variable? We created two models of algal biomass dynamics in a radially symmetric, cone-shaped lake - one preserving the lake′s vertical and radial dimensions and one preserving only the lake′s mean depth - and compared model predictions of algal biomass dynamics across a wide range of lake sizes, mixing conditions, water transparency, and nutrient content. Our analyses reveal that model predictions differ substantially but predictably in much of the investigated parameter space, and identifies the light environment set by lake depth, water clarity and pelagic nutrients, but also lake area, as main drivers of the differences. Most commonly, the model based on mean depth underestimates benthic algal biomass and overestimates pelagic algal biomass, the net effect on total biomass being a 5-50% underestimate in shallow lakes and a 5-20% overestimate in many deeper lakes. Since gross primary production (GPP) in our model scales with algal biomass, we believe that global estimates of lake GPP should be corrected for the systematic errors inflicted by the prevailing 1-dimensional approaches.
... External factors such as climate change also influence the carbon cycle, both directly and indirectly. Changes in temperature, rainfall, and weather patterns affect the ecosystem's ability to absorb and store carbon, ultimately impacting the existing carbon reserves [23]. Ecological techniques used in forest restoration and management can have a positive impact on carbon reserves, such as through the improvement of vegetation and soil quality, which can increase carbon storage capacity [19,24]. ...
... Despite covering only about 2% of the global land surface, lakes exhibit significantly higher carbon turnover rates than soils and oceans. [9][10][11][12][13] Over long timescales, sedimentary carbon burial represents the primary mechanism of lacustrine carbon sequestration, influenced by climatic conditions, watershed characteristics, lake properties, and anthropogenic activities. While the importance of lakes as terrestrial carbon sinks has gained increasing recognition, the role of inorganic carbon in lake carbon burial remains understudied. ...
Lake inorganic carbon burial in global closed basins has been recognized as a significant component of the terrestrial carbon cycle. However, the controlling factors governing its long-term dynamics and its future trajectory remain insufficiently understood. Here, we present a comprehensive dataset encompassing lake inorganic and organic carbon burial records from global closed basins since the Last Glacial Maximum (LGM), along with associated lake-level reconstructions, modern observations and climate model outputs. Through integrated analysis of lake carbon burial records and lake area simulation, our results indicate that inorganic carbon burial in closed-basin lakes since the LGM has been approximately twice that of organic carbon burial. The total carbon burial is estimated to be around 174 Pg, which accounts for roughly one-tenth of the soil carbon pool in global drylands, underscoring its significance in the global carbon cycle. Lake carbon burial rate has shown a continuous increase since the LGM, with interannual variations of lake carbon burial amount closely linked to fluctuations in lake area, which are primarily modulated by westerly winds and monsoon circulation in different closed basins. Under future global warming scenarios, with projected drying trend in global closed basins, the lake carbon burial potential by 2100 is estimated to be approximately 1 Pg, which is about 5% lower compared to scenarios with stable lake area, highlighting the substantial role of lake carbon burial in shaping the future global carbon budget.
... Furthermore, this study confirms a negative correlation between carbon emissions and green area and stream/river length, while a positive correlation exists with carbon storage. Conservation of green areas (including forests) and streams/rivers can decrease carbon emissions and increase carbon storage (Gao et al., 2021;Ge et al., 2023;Li et al., 2015;Xu et al., 2023). The spatial heterogeneity of each indicator's influence on carbon emissions and storage serves as a valuable reference for incorporating carbon dynamics into urban planning. ...
Urban areas in coastal regions are increasingly vulnerable to climate change but can serve as a pivotal starting point for climate mitigation. Understanding carbon dynamics in coastal urban areas is essential for sustainable development. This study investigates the influence of urban spatial structure (USS) elements on carbon emissions and storage in the Samarinda Metropolitan Area during 2021, prior to Indonesia’s capital relocation. Using Ordinary Least Squares and Geographically Weighted Regression, the study examines the impacts of USS elements (functional mix, built-up environment, and natural environment) on carbon dynamics across three different models (combined, coastline, and no coastline), emphasizing the spatial heterogeneity of these interactions. The findings reveal a higher concentration of carbon emissions on the eastern coast, while carbon storage across the region remained favorable due to the presence of extensive natural land covers. In the combined model, the cumulative impact of USS elements on carbon emissions was found to be stronger than their effect on carbon storage. Notably, USS elements’ influence on carbon emissions was more pronounced in inland areas (no coastline model), whereas their impact on carbon storage was stronger along the coast (coastline model). These results also underscore the spatial heterogeneity of the impacts, serving as the foundation for zone classifications. Finally, integrating carbon dynamics into urban planning can lead to more sustainable development in coastal region. This study highlights the need for targeted strategies that focus on specific spatial zones and USS indicators to effectively reduce emissions and enhance carbon storage.
... Water residence time (WRT) is defined as the time required for a water parcel to leave the region of interest for the first time [1][2][3] and serves as a pivotal timescale parameter for understanding ocean hydrodynamics and marine biogeochemistry cycling [4,5]. In coastal regions, nutrient cycling, primary production, pollutant dispersion, and ecosystem resilience are highly related to the WRT [5][6][7]. A short WRT promotes water renewal, which limits pollutant accumulation but may restrict nutrient retention, potentially inhibiting primary production. ...
Water residence time (WRT) is a crucial parameter for evaluating the rate of water exchange and it serves as a timescale for elucidating hydrodynamic processes, pollutant dispersion, and biogeochemical cycling in coastal waters. This study investigates the tidal-driven WRT patterns in the Bohai and Yellow Seas (collectively known as BYS) by employing a tidal model in conjunction with an adjoint WRT diagnostic model and explores the influence of tidal constituents on WRT. The findings indicate that the tidal-driven WRT in the BYS is approximately 2.11 years, exhibiting a significant spatially heterogeneous distribution. The WRT pattern shows a strong correlation with the pattern of tidal-driven Lagrangian residual currents (LRCs). Semidiurnal tides have a more pronounced effect on WRT than diurnal tides. Semidiurnal tides significantly reduce WRT across the entire BYS, while diurnal tides predominantly influence WRT in the Bohai Sea (BS). The M2 tidal constituent is the most influential in decreasing WRT and enhancing water exchange, owing to its dominant energy contribution within the tidal system. In contrast, the S2 tidal constituent has a minimal effect; however, its interaction with the M2 tidal constituent plays a significant role in reducing the WRT. The K1 and O1 constituents exert more localized effects on WRT, particularly in the central BS, where their energy ratios relative to M2 are relatively high. Although the amplitude of the S2 constituent exceeds that of K1 and O1, its contribution to LRC—and consequently to WRT—is limited due to the overlapping tidal wave with M2. This research contributes to a deeper understanding of the influence of tidal dynamics on long-term water transport and associated timescales, which are vital for enhancing predictions of material transport and ecosystem dynamics in tidal-dominated environments.
... Net Primary Production (NPP), Gross Primary Production (GPP), and respiration are all essential concepts in understanding the functioning of aquatic ecosystems, including pond water productivity (Gao et al., 2021). Net Primary Production (NPP) refers to the amount of organic matter produced by photosynthetic organisms, such as algae and aquatic plants, in a given period. ...
Studying the seasonal variations of the physicochemical and biological components of water bodies is essential to understand the confounding factors of the abiotic factors and the relationship among them. This study aimed to assess the impact of seasonal variations on the water quality and zooplankton diversity of ponds in Haryana, India. For the present investigation, water samples were collected from ponds in the four different villages of district Sonipat, i.e., Rohat, Baiyanpur, Lehrara, and Jatwara. Water samples were collected monthly from January to December, and the physicochemical parameters were measured. The physicochemical characterization and minerals profiling of pond water in different seasons (summer, monsoon, and winter) were investigated to determine the seasonal variation in water quality parameters and mineral composition of ponds in the study area. Water samples were collected from four different ponds during the summer, monsoon, and winter seasons and analyzed for various physicochemical parameters such as pH, electrical conductivity (EC), total dissolved solids (TDS), dissolved oxygen (DO), and minerals composition such as calcium, magnesium, potassium, and sodium. The seasonal variation of minerals level in available zooplankton in ponds was investigated to determine the relationship between mineral levels and the abundance and diversity of zooplankton during different seasons (summer, monsoon, and winter). Water samples and zooplankton were collected from four different ponds during the three seasons, and the mineral level in the zooplankton samples were measured using standard techniques. The results showed significant seasonal variations in the physicochemical and mineral parameters of the pond water. The pH of the pond water was found to be alkaline in all seasons, with the highest value recorded in the summer. The EC, TDS, and DO levels were higher in the monsoon season, indicating increased mineral and organic matter content in the pond water during this season. The mineral composition analysis showed that calcium and magnesium were the most abundant minerals in all seasons, with the highest concentration in winter. Potassium and sodium levels were found to be relatively low in all seasons. The findings of this study suggest that seasonal variations in water quality parameters and mineral composition should be considered when managing ponds for different purposes. The results showed significant seasonal variations in the physicochemical and mineral parameters of the pond water. The pH of the pond water was found to be alkaline in all seasons, with the highest value recorded in the summer. The study found that the composition and abundance of zooplankton communities varied significantly among seasons. The highest diversity of zooplanktons was observed in the monsoon season, with the highest number of taxa identified. In contrast, the lowest diversity was observed in the winter season, with the least number of taxa identified. The most common zooplankton groups identified across all seasons were rotifers, copepods, and cladocera, with rotifers dominating the communities in the summer and winter seasons and copepods and cladocera dominating in the monsoon season. The study found significant seasonal variations in pond productivity, with the highest rates of Net Primary Productivity and Gross Primary Productivity observed during the monsoon season and the lowest rates observed during the winter. The respiration rates were also highest during the monsoon season, indicating higher metabolic activity in the pond ecosystem during this season. The diversity of zooplankton communities was positively correlated with pond productivity, with the highest diversity observed during the monsoon season when pond productivity was highest. The study found significant seasonal variations in the mineral levels in available zooplankton, with higher levels observed during the monsoon season and lower levels observed during the summer and winter seasons. The minerals most commonly found in the zooplankton samples were calcium, magnesium, and potassium, with calcium being the most abundant mineral in all seasons. The diversity and abundance of zooplankton communities were positively correlated with the mineral levels in the samples, with higher mineral levels supporting higher zooplankton diversity and abundance. Zooplankton diversity was also recorded. The results showed that the water quality parameters such as temperature, pH, dissolved oxygen, and total dissolved solids varied significantly among the seasons. The highest temperature and total dissolved solids values were recorded during the summer, while the lowest values were recorded during the winter. The pH and dissolved oxygen values were highest during the monsoon season and lowest during summer. Zooplankton diversity also showed significant variations among the seasons, with the highest diversity recorded during winter and the lowest during summer. The dominant species were Rotifera and Cladocera, followed by Copepoda and Ostracoda. The study also revealed a positive correlation between zooplankton diversity and some water quality parameters, including pH and dissolved oxygen.
Seasonal variations in water quality parameters and mineral composition should be considered when managing ponds for different purposes. Nutrient management strategies and habitat management practices should be developed to support optimal water quality and mineral uptake by aquatic organisms in different seasons. Further research is needed to understand the effect of other environmental factors, such as temperature, light, and nutrients, on pond water quality and mineral composition. Seasonal variations in environmental conditions, such as temperature, dissolved oxygen, and nutrient availability, can significantly impact the composition and diversity of zooplankton communities in ponds. Management strategies should be developed to support optimal water quality conditions for zooplankton communities, particularly during the monsoon season when the diversity of these communities are highest.
Further research is needed to understand the effects of other environmental factors, such as pH and mineral composition, on zooplankton communities in ponds. Seasonal variations in pond productivity significantly impact zooplankton diversity, with higher productivity supporting higher zooplankton diversity. Management strategies should be developed to support optimal pond productivity conditions during the monsoon season to support the diversity and abundance of zooplankton communities. Further research is needed to understand the effects of other environmental factors, such as nutrient availability, on pond productivity and its relationship with zooplankton diversity. However, the findings of this study suggest that seasonal variations in mineral levels in available zooplankton significantly impact zooplankton communities in ponds. Management strategies should be developed to maintain optimal mineral levels in pond water during the monsoon season to support the diversity and abundance of zooplankton communities.
Further research is needed to understand the effects of other environmental factors, such as temperature and nutrient availability, on mineral levels in available zooplankton and their relationship with zooplankton diversity and abundance. In conclusion, seasonal variations significantly impacted the water quality and zooplankton diversity of the pond in Haryana, India. This study highlights the need for regular monitoring of water quality and zooplankton diversity in the region to understand the dynamics of pond ecosystems and to develop effective management strategies to conserve the area's aquatic biodiversity.
... Carbon cycling processes in lakes are crucial components of the global carbon cycle, as well as associated carbon sources and sinks [3,4]. Lakes participate in the carbon cycle primarily through carbon dioxide (CO 2 ), methane (CH 4 ), total organic carbon (TOC), and total inorganic carbon (TIC) [5,6]. Lake sediments serve as a significant carbon pool. ...
Carbon burial patterns in lakes and their dynamic changes significantly impact terrestrial carbon sink fluxes and global carbon budgets. In this study, multi-indicator analysis of sediment core samples (P1, P2, and P3) from Pipahai Lake was conducted. Integrating the chronological sequences of ²¹⁰Pb and ¹³⁷Cs, we identified the historical changes and spatial characteristics of total organic carbon (TOC) and inorganic carbon (TIC) burial in Pipahai Lake since 1884. The results show that the TOC content was higher than that of the TIC. They exhibited an increasing trend with decreasing depth. Linear regression results indicated that the variation of TOC is less directly affected by precipitation (R = 0.39) and temperature (R = 0.58), while temperature may have a greater impact on TOC. From 1884 to 1995, nutrients were not the primary factor influencing changes in TOC. The synchronous variation in TIC and TOC contents reflects a higher contribution of external inputs to carbon burial in the Pipahai Lake basin. After 1996, nutrients may have begun to affect variations in TOC. The TOC primarily originates from distal aeolian transport or autochthonous sources, though human activity has played a role in its evolution. The TIC content is controlled by the TOC content and autochthonous sources. This study will contribute to the understanding of the carbon cycling dynamics and their influencing mechanisms in a high-altitude lake ecosystem.
... Los humedales constituyen un elemento clave en la dinámica biogeoquímica global del carbono. Una vez que el carbono procedente de los ecosistemas terrestres adyacentes es incorporado a las masas de agua, éste puede sufrir diversas transformaciones biogeoquímicas, ser incorporado al sedimento donde permanecerá secuestrado por largos periodos de tiempo, o ser emitido a la atmósfera en forma de flujos de gases de efecto invernadero como CO2 (Gao et al. 2021). ...
En esta nota presentamos una cámara diseñada por el Grupo de Ecología Marina y Limnología de la Universidad de Málaga, que permite la determinación fiable de flujos de CO2 en humedales muy someros, con profundidades de entre 0.5 y 5.5 cm. La ventaja de este diseño es que garantiza la renovación del agua en el interior de la cámara durante el tiempo de medida, a la vez que evita cualquier riesgo de varamiento en el sedimento que pueda favorecer la entrada o salida de gas de la misma. Esta cámara permite determinar flujos de CO2 resultantes del intercambio entre el sistema sedimento-lámina de agua y la atmósfera. Además, nuestro diseño es de reducido coste (~250 euros) en comparación con sistemas comerciales, que suelen tener precios un orden de magnitud superior.
... The wetland area ranges from 1623 to 3850 km 2 Figure 4 Carbon stock, carbon sink rate and carbon sink pathway of wetland ecosystems in China. Data from (Bauer et al., 2013;Gao et al., 2021;Jia et al., 2020;Xiao et al., 2019). Blue arrows represent the carbon balance at the water-gas interface. ...
Wetland ecosystems have become one of the long-term solutions for mitigating global climate change due to their strong carbon sequestration potential. However, the key carbon cycle processes in wetland ecosystems still lack a systematic summary. In the context of wetland protection and restoration, there is still a lack of consensus on the technical pathways to realize carbon sink multiplication in wetland ecosystems. In this paper, the key processes of carbon cycle, such as photosynthetic carbon uptake, microbial carbon decomposition and carbon deposition and burial, are sorted out and summarized in four major wetland types, namely, swamp and peat wetlands, river and riparian wetlands, lake and lakeshore wetlands, and estuarine and coastal wetlands. Based on the key processes of carbon cycle, three technological pathways for carbon sink multiplication are proposed, including, vegetation carbon sequestration and sink enhancement technology, soil carbon emission reduction technology and carbon deposition and burial technology. The key technologies under each pathway are further refined. And the carbon sink effects of the carbon sink technologies in different wetland types are qualitatively described. Also, wetland protection and restoration methods in corresponding regions are given in the light of the regional characteristics of wetlands in China. This will provide a scientific basis for the strategy of doubling the carbon sinks of China’s wetland ecosystems.
... They proposed the direction of better land use structure development. Therefore, quantifying the relationship between LUCC and CS as well as enhancing CS through the rational management of LUCC contributes to mitigating environmental issues, being crucial for the carbon sequestration capacity of ecosystems [18][19][20]. ...
The most extensive carbon reservoir system on Earth is found in the vegetation and soil in terrestrial ecosystems, which are essential to preserving the stability of ecosystems. Land use/cover change (LUCC) patterns in terrestrial ecosystems significantly impact carbon storage (CS). Therefore, it is imperative to investigate the relationship between LUCC and CS to coordinate regional ecological conservation and industrial development. In this study, the characteristics of spatial and temporal changes in land use and CS in the Yanqi Basin from 2000 to 2020 were revealed using the PLUS (patch-generating land use simulation) model and the CS module of the InVEST (Integrated Valuation of Ecosystem Services and Tradeoffs) model. This study also predicted the spatial and temporal evolution of CS and the response mechanism of the Yanqi Basin from four scenarios—natural development scenario (NDS), ecological protection scenario (EPS), cropland protection scenario (CPS), and urban development scenario (UDS) for the years 2030, 2040, and 2050. This study shows the following: (1) Between 2000 and 2020, the Yanqi Basin witnessed an expansion in cropland and construction land, the order of the land use dynamic degree which is as follows: construction land > cropland > woodland > unused land > water > grassland. At the same time, the CS exhibited a trend of growth that was followed by a decline, a cumulative decrease of 3.61 Tg. (2) Between 2020 and 2050, woodland, grassland, and unused land decreased under the NDS and UDS. Meanwhile, grassland and woodland showed an expanding trend, and there was a decrease in cropland and construction land under the EPS; the CPS projected an increase in cropland to 3258.06 km² by 2050. (3) CS under the UDS is always the lowest, and CS under the EPS is the highest; moreover, by 2050, CS under the EPS is projected to increase by 1.18 Tg compared with that under the UDS. The spatial distribution of CS shows a high value in the western part of the region and a low value in the eastern part of the region, which is more in line with the historical spatial distribution. (4) The development of land by human activities is one of the major factors leading to the change of CS. The direct cause of the decrease in CS is the transformation of large areas of cropland and woodland into construction land. Therefore, woodlands must be protected to improve CS and prevent ecological degradation. At the same time, future land use planning in the Yanqi Basin needs to limit the conversion rate of various types of land, control the construction land, optimize the urban pattern, improve the regional CS level, adhere to the concept of striving to achieve carbon neutrality, and realize the sustainable development of the region to provide scientific suggestions for carrying out macro-decision making regarding land use planning in arid areas.
... GPP, a measure of the total carbon fixed by plants through photosynthesis, serves as the primary energy source driving terrestrial ecosystems and is crucial for understanding carbon cycling within these systems [56]. PsnNet quantifies the net carbon gain in plants after accounting for respiration losses, providing insights into the actual carbon accumulation in plant biomass, which directly affects crop yield [57]. Fpar indicates the proportion of incoming solar radiation in photosynthetically active wavelengths absorbed by the plant canopy, essential for estimating photosynthetic efficiency and potential growth rates [58]. ...
The accurate prediction of crop yields is crucial for enhancing agricultural efficiency and ensuring food security. This study assesses the performance of the CNN-LSTM-Attention model in predicting the yields of maize, rice, and soybeans in Northeast China and compares its effectiveness with traditional models such as RF, XGBoost, and CNN. Utilizing multi-source data from 2014 to 2020, which include vegetation indices, environmental variables, and photosynthetically active parameters, our research examines the model’s capacity to capture essential spatial and temporal variations. The CNN-LSTM-Attention model integrates Convolutional Neural Networks, Long Short-Term Memory, and an attention mechanism to effectively process complex datasets and manage non-linear relationships within agricultural data. Notably, the study explores the potential of using kNDVI for predicting yields of multiple crops, highlighting its effectiveness. Our findings demonstrate that advanced deep-learning models significantly enhance yield prediction accuracy over traditional methods. We advocate for the incorporation of sophisticated deep-learning technologies in agricultural practices, which can substantially improve yield prediction accuracy and food production strategies.
... 13 It should be noted that phytoplankton widely distributed in lakes and reservoirs could absorb a large amount of CO 2 via photosynthesis. 48,49 The total C sequestration capacity by phytoplankton (indicated by gross primary productivity [GPP]) respective to China's inland lakes and reservoirs was estimated at 19.41 Tg C yr −1 . 50 If transported and buried C are ignored in the estimates (allowing for the fact that no accurate estimations currently exist), China's inland lakes and reservoirs over recent years could be regarded as a large C sink, with a C sequestration capacity of 12.63 Tg C yr −1 . ...
Lakes and reservoirs act as active carbon (C) reactors and regulators. Both play a crucial terrestrial ecosystem C balance role via carbon dioxide (CO2) exchange processes across the water-air interface. It has previously been confirmed that CO2 flux from lakes and reservoirs generally exhibits significant spatiotemporal heterogeneity. Nevertheless, spatiotemporal CO2 flux variation has seldom been considered in global and regional CO2 emission estimates from lakes and reservoirs. By accounting for spatiotemporal CO2 flux and water surface area variability, we evaluated spatial and temporal CO2 emission dynamics from China��s inland lakes and reservoirs using national real-time water quality monitoring data and machine learning (ML) models. Between 2021�C2022, we estimated total C emission flux at 6.78 (��2.5) Tg C yr?1, where seasonal and regional distribution both exhibited significant heterogeneity. Our state-of-the-art estimate is significantly lower than previous estimates of 7.9~25 Tg C yr?1 from the 1980s to the 2010s. Water quality parameters (pH and dissolved oxygen [DO]) and climate factors (air temperature) were identified as the general environmental CO2 flux controls. For the first time, this study clarifies the spatiotemporal patterns and drivers of CO2 flux from China��s inland lakes and reservoirs, providing a more complete C budget picture of China��s aquatic ecosystems.
Bacteria and phytoplankton play an essential role in processing organic and inorganic waste nutrients, making the nutrients reutilized by higher trophic levels in an aquatic food web. Understanding the complex interaction between the microbial food web, nutrients, and cultured animals is crucial to achieving optimum production while minimizing the negative impact of aquaculture production on the environment. Mathematical models have been known as a research tool to conceptualize real systems, beneficial as management and decision‐support tools, and addressing predictive, exploratory, or normative questions. This study is a narrative review of 29 models published from 1984 to 2024 focusing on aquaculture production, particularly the dynamics of microorganisms in fish ponds and their influence on nutrient dynamics and fish growth performance. This study is structured to address several questions: What are the different nutrient inputs considered in farm scale models (FSMs)? What microorganisms are often included in FSMs? How to determine food web dynamics? How are the food web dynamics related to nutrient dynamics and fish growth dynamics? The application of food web dynamics in determining carrying capacity and feed formulation is discussed. Finally, this review discusses the importance of stoichiometry, the limitations of current knowledge, and important considerations for developing or selecting models that are suitable for intended users.
Inland waters (lakes, reservoirs, and rivers) serve as important regulators of global climate change and carbon (C) cycling. China's inland water systems significantly regulate regional C budgets. However, our understanding of the long-term spatiotemporal patterns and underlying mechanisms of dissolved carbon (DC) storages and fluxes in inland waters remains limited. This study examined lake and reservoir DC storage and river DC flux, quantifying their changes in China over the past three decades. We found that inland water DC stocks in China increased from 96 Tg C in the 1990s to 142 Tg C in the 2010s while DC river flux did not significantly change (13.2 ± 0.4 Tg C/yr). Findings also showed that a combination of climate change, anthropogenic disturbance, and water chemistry collectively drove inland water DC dynamics. River DC was more directly driven by climate and anthropogenic factors (>50%) while lakes and reservoirs were more directly influenced by water chemistry (>70%). Additionally, climate factors can explain changes in dissolved inorganic carbon (DIC) concentrations via water chemistry factors (i.e., electrical conductivity (EC) and pH), while, collectively, climate and the nutrient status can typically explain changes in DOC concentrations. This study emphasizes the important role that inland water plays in the global C balance and underscores the necessity of considering it in future C budgets.
This study introduces a novel dynamical climate change hotspot index standard Euclidean distance, capturing variations in temperature and precipitation through average, variability, and extreme values, and utilizes ensemble empirical mode decomposition to analyze nonlinear long-term trends globally. Results highlight pronounced regional disparities, with regions like the Tibetan Plateau, Mongolia, and the Arabian Peninsula emerging as persistent hotspots due to rapid warming responses. In contrast, the southeastern United States exhibits early-stage declines, though vulnerability to extreme weather is growing. A latitude-time analysis reveals asymmetric hemispheric trajectories, driven by distinct climate dynamics and anthropogenic influences. The transition from systemic temperature-influenced hotspots to localized, extreme event-influenced phenomena underscores the intensifying impact of extreme climate events. These findings provide critical insights into the spatial and temporal evolution of climate change impacts and highlight the necessity of region-specific adaptation strategies.
Depending on various indicators, climate change may affect each region globally at varying risk levels. Therefore, identifying the ‘hotspots’ most likely to be affected by climate change in the future is a crucial step in ensuring those areas rapidly adapt to it. The study estimated the Standard Euclidean Distance (SED) for identifying hotspots of Türkiye using high‐resolution climate projection data (10 × 10 km) and examined regional vulnerability in the long‐term future over a 75‐year period (2024–2099). The projections were made using RegCM4.4 driven by MPI‐ESM‐MR under the optimistic (RCP4.5) and pessimistic (RCP8.5) scenarios. The findings indicate that the hotspot regions in Türkiye are Southeastern Anatolia, Eastern Anatolia and the Mediterranean for RCP4.5, and Southeastern Anatolia, Eastern Anatolia, the Mediterranean and Central Anatolia for RCP8.5. The most critical indicators, however, are temperature‐related indicators (i.e., Mean Air Temperature, Hot Seasons and Temperature Variability). Based on the findings, it is necessary to take preventive measures, particularly in highly vulnerable regions, to minimise potential damage. Additionally, multi‐model ensemble studies should be applied to reduce the uncertainties and model‐related variability, as well as to provide robust evidence of climate change.
Soil microbes play a significant role in the carbon cycle. However, our understanding of how soil microbes respond to different carbon substrates is still limited. Here, we investigated the ecological mechanisms behind the overall carbon metabolism differences under different fertilizations in a paddy ecosystem. Four fertilization treatments, no fertilizers (CK), mineral nitrogen, phosphorus and potassium fertilizers (NPK), mineral fertilizers plus organic manures (NPKM) and mineral fertilizers plus straw return (NPKS) were set up. Our results indicated that fertilization drove shifts in microbial community structure, with a reduction in the abundance of Actinobacteriota and an increase in the abundance of Chloroflexi . NPKS and CK exhibited higher carbon utilization capacity across various carbon sources, with particularly higher metabolic activity for carbohydrates than NPK and NPKM treatments. The weighted gene co‐expression network analysis (WGCNA) was used to evaluate the correlation between the modules of WGCNA and carbon metabolism. We found that microbes in the modules are important contributors to the variations of carbon metabolism. It was found that a key species in the module affecting carbohydrate utilization is C0119 , which belongs to Ktedonobacteria in the Chloroflexi . Our results suggest that fertilization could mediate core bacterial species to affect microbial utilization of different carbon substrates and finally mediate the soil carbon metabolism function.
Aquaculture contributes to global CO2 emission, but the intensity varies across different aquaculture systems. In this study, we compared the CO2 emission between earthen aquaculture ponds (EAP), plastic-lined ponds (PLAP), and mangrove wetland eco-aquaculture systems (MWEAS) in the coastal region of the Guangxi Province, South China. Results showed that CO2 emissions varied between -27.28 and 12.39 mg m-2 h-1 from PLAP and between -17.78 and 14.18 mg m-2 h-1 from MWEAS, both significantly lower than those from EAP (2.76 to 19.30 mg m-2 h-1). The largest emission fluxes were observed during the growth stage of the farming period. On average, PLAP and MWEAS acted as CO2 sinks, whereas EAP acted as a source, and Chlorophyll-a, phosphorus and carbon substrates were the main environmental factors influencing the variation in CO2 emissions. The overall average CO2 emission flux from our aquaculture ponds was 2.54 ± 1.11 mg m-2 h-1, which was much lower than those observed in freshwater and brackish coastal aquaculture ponds, but higher than certain high-salinity aquaculture environments. In summary, enhancing water salinity levels and encouraging the adoption of plastic liners alongside ecological aquaculture systems could serve as effective strategies for mitigating CO2 emissions in coastal aquaculture.
Large datasets of carbon dioxide, energy, and water fluxes were measured with the eddy-covariance (EC) technique, such as FLUXNET2015. These datasets are widely used to validate remote-sensing products and benchmark models. One of the major challenges in utilizing EC-flux data is determining the spatial extent to which measurements taken at individual EC towers reflect model-grid or remote sensing pixels. To minimize the potential biases caused by the footprint-to-target area mismatch, it is important to use flux datasets with awareness of the footprint. This study analyze the spatial representativeness of global EC measurements based on the open-source FLUXNET2015 data, using the published flux footprint model (SAFE-f). The calculated annual cumulative footprint climatology (ACFC) was overlaid on land cover and vegetation index maps to create a spatial representativeness dataset of global flux towers. The dataset includes the following components: (1) the ACFC contour (ACFCC) data and areas representing 50%, 60%, 70%, and 80% ACFCC of each site, (2) the proportion of each land cover type weighted by the 80% ACFC (ACFCW), (3) the semivariogram calculated using Normalized Difference Vegetation Index (NDVI) considering the 80% ACFCW, and (4) the sensor location bias (SLB) between the 80% ACFCW and designated areas (e.g. 80% ACFCC and window sizes) proxied by NDVI. Finally, we conducted a comprehensive evaluation of the representativeness of each site from three aspects: (1) the underlying surface cover, (2) the semivariogram, and (3) the SLB between 80% ACFCW and 80% ACFCC, and categorized them into 3 levels. The goal of creating this dataset is to provide data quality guidance for international researchers to effectively utilize the FLUXNET2015 dataset in the future.
Evaluating the extent of CO 2 emissions from lakes exhibiting diverse trophic levels is essential for advancing our current understanding of the influence of ecological and climatic processes on these ecosystems.
Plain Language Summary
The damming of rivers is one of the most impactful modifications of the flows of water and associated materials from land to sea. Included in these materials are nutrient elements like nitrogen and phosphorus, which are elements required by all life on Earth, and silicon, which is required by diatoms, the algae that account for the largest fraction of biological productivity of the oceans. Past studies have shown that if you alter the ratios in which these nutrient elements enter the coastal oceans, plankton communities can change, even causing harmful algal blooms or “red tides” to occur. Here, we use models of nitrogen, phosphorus, and silicon cycling in dam reservoirs to determine how dams change the ratios delivered to coastal zones worldwide. We predict that by midcentury, more than half of the rivers flowing to the sea will experience greater removal of silicon over nitrogen and phosphorus, in response to ongoing construction of many new hydroelectric dams. This will impact the role of diatoms in nearshore marine production, as they are increasingly outcompeted by other, potentially harmful, algae that do not need silicon to grow.
The management of river-lake systems is hindered by limitations in the applicability of existing models that describe the relationship between environmental factors and phytoplankton community characteristics but rarely include common and indirect effects on algae dynamics. In this study, we assumed that the interaction of light, water, temperature, pH, and nutrients, including direct and indirect effects, are the potential factors affecting phytoplankton dynamics. We determined which of these are the main drivers of phytoplankton community structure and production in a river-lake system by using three different models based on the partial least squares structural equation modeling method. Our results indicated that the models achieved more than 60% of the overall explanatory power of various environmental factors on phytoplankton characteristics, including indirect and direct effects. In particular, light, pH, and nutrient content and ratios commonly control phytoplankton dynamic characteristics rather than a single nutrient, but light is the main driving force of phytoplankton community characteristics. Controlling the underwater light conditions, and nitrogen and phosphorus pollution load could effectively regulate algal blooms, increase productivity, promote ecological balance, and reduce water pollution. Our findings provide a scientific and theoretical basis for water resource management and pollution control.
The phytoplankton (internal driving forces) and environmental variables that affect complex biochemical reactions (external driving forces) play an important role in regulating photosynthetic carbon fixation. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) exists in various phytoplankton species and is an important enzyme in the photosynthetic process. To investigate the phytoplankton composition (internal driving forces), we selected the functional gene of the Rubisco large subunit (rbcL) as the target gene for this study. Phytoplankton gross primary productivity was measured using light and dark biological oxygen demand bottles to assess the carbon sequestration potential. The fundamental environmental indicators were determined to analyze the mechanisms that drive the carbon fixation process. The correlation results indicated that green algae were only controlled by nitrate, and that diatoms were positively correlated with phosphate. The cluster analysis results demonstrated that nitrite was the major driver controlling phytoplankton primary productivity. During the wet seasons (spring and summer), the contribution of the planktonic community respiration to the carbon sequestration potential was higher than net primary productivity (NPP), followed by dissolved organic carbon and nitrate. During the dry season (autumn), NPP, total nitrogen, and nitrite ranked highest in terms of carbon sequestration potential. The contributions of green algae and diatoms to the carbon sequestration potential were temporally higher than those of cyanobacteria. The maximum carbon sequestration potential occurred during autumn because of diatom production and the function of phosphate, whereas the minimum carbon sequestration potential occurred in summer. Spatially, the upstream carbon sequestration potential was higher compared with downstream because of the effect (contribution) of cyanobacteria (Phormidium), diatoms (Surirella solea and Thalassiosira pseudonana), and environmental variable (nitrite). These findings provide a better understanding of the underlying mechanisms of phytoplankton productivity and the influences of environmental variables on carbon sequestration in urban river ecosystems.
In the past three decades, China has built more than 87 000 dams with a storage capacity of ≈6560 km 3 and the total surface area of inland water has increased by 6672 km 2. Leaching of N from fertilized soils to rivers is the main source of N pollution in China, but the exposure of a growing inland water area to direct atmospheric N deposition and N leaching caused by N deposition on the terrestrial ecosystem, together with increased N deposition and decreased N flow, also tends to raise N concentrations in most inland waters. The contribution of this previously ignored source of N deposition to freshwaters is estimated in this study, as well as mitigation strategies. The results show that the annual amounts of N depositions ranged from 4.9 to 16.6 kg · ha −1 · yr −1 in the 1990s to exceeding 20 kg · ha −1 · yr −1 in the 2010s over most of regions in China, so the total mass of N (the net contribution of N deposition to the increase in N concentration) for lakes, rivers and reservoirs change from 122.26 Gg N · yr −1 in the 1990s to 237.75 Gg N · yr −1 in the 2010s. It is suggested that reducing the N deposition from various sources, shortening the water-retention time in dams and decreasing the degree of regulation for rivers are three main measures for preventing a continuous increase in the N-deposition pollution to inland water in China.
The China Seas include the South China Sea, East China Sea, Yellow Sea, and Bohai Sea. Located off the Northwestern Pacific margin, covering 4700000 km² from tropical to northern temperate zones, and including a variety of continental margins/basins and depths, the China Seas provide typical cases for carbon budget studies. The South China Sea being a deep basin and part of the Western Pacific Warm Pool is characterized by oceanic features; the East China Sea with a wide continental shelf, enormous terrestrial discharges and open margins to the West Pacific, is featured by strong cross-shelf materials transport; the Yellow Sea is featured by the confluence of cold and warm waters; and the Bohai Sea is a shallow semi-closed gulf with strong impacts of human activities. Three large rivers, the Yangtze River, Yellow River, and Pearl River, flow into the East China Sea, the Bohai Sea, and the South China Sea, respectively. The Kuroshio Current at the outer margin of the Chinese continental shelf is one of the two major western boundary currents of the world oceans and its strength and position directly affect the regional climate of China. These characteristics make the China Seas a typical case of marginal seas to study carbon storage and fluxes. This paper systematically analyzes the literature data on the carbon pools and fluxes of the Bohai Sea, Yellow Sea, East China Sea, and South China Sea, including different interfaces (land-sea, sea-air, sediment-water, and marginal sea-open ocean) and different ecosystems (mangroves, wetland, seagrass beds, macroalgae mariculture, coral reefs, euphotic zones, and water column). Among the four seas, the Bohai Sea and South China Sea are acting as CO2 sources, releasing about 0.22 and 13.86–33.60 Tg C yr⁻¹ into the atmosphere, respectively, whereas the Yellow Sea and East China Sea are acting as carbon sinks, absorbing about 1.15 and 6.92–23.30 Tg C yr⁻¹ of atmospheric CO2, respectively. Overall, if only the CO2 exchange at the sea-air interface is considered, the Chinese marginal seas appear to be a source of atmospheric CO2, with a net release of 6.01–9.33 Tg C yr⁻¹, mainly from the inputs of rivers and adjacent oceans. The riverine dissolved inorganic carbon (DIC) input into the Bohai Sea and Yellow Sea, East China Sea, and South China Sea are 5.04, 14.60, and 40.14 Tg C yr⁻¹, respectively. The DIC input from adjacent oceans is as high as 144.81 Tg C yr⁻¹, significantly exceeding the carbon released from the seas to the atmosphere. In terms of output, the depositional fluxes of organic carbon in the Bohai Sea, Yellow Sea, East China Sea, and South China Sea are 2.00, 3.60, 7.40, and 5.92 Tg C yr⁻¹, respectively. The fluxes of organic carbon from the East China Sea and South China Sea to the adjacent oceans are 15.25–36.70 and 43.93 Tg C yr⁻¹, respectively. The annual carbon storage of mangroves, wetlands, and seagrass in Chinese coastal waters is 0.36–1.75 Tg C yr⁻¹, with a dissolved organic carbon (DOC) output from seagrass beds of up to 0.59 Tg C yr⁻¹. Removable organic carbon flux by Chinese macroalgae mariculture account for 0.68 Tg C yr⁻¹ and the associated POC depositional and DOC releasing fluxes are 0.14 and 0.82 Tg C yr⁻¹, respectively. Thus, in total, the annual output of organic carbon, which is mainly DOC, in the China Seas is 81.72–104.56 Tg C yr⁻¹. The DOC efflux from the East China Sea to the adjacent oceans is 15.00–35.00 Tg C yr-1. The DOC efflux from the South China Sea is 31.39 Tg C yr⁻¹. Although the marginal China Seas seem to be a source of atmospheric CO2 based on the CO2 flux at the sea-air interface, the combined effects of the riverine input in the area, oceanic input, depositional export, and microbial carbon pump (DOC conversion and output) indicate that the China Seas represent an important carbon storage area.
Streams play a key role in the global carbon cycle. The balance between carbon intake through photosynthesis and carbon release via respiration influences carbon emissions from streams and depends on temperature. However, the lack of a comprehensive analysis of the temperature sensitivity of the metabolic balance in inland waters across latitudes and local climate conditions hinders an accurate projection of carbon emissions in a warmer future. Here, we use a model of diel dissolved oxygen dynamics, combined with high-frequency measurements of dissolved oxygen, light and temperature, to estimate the temperature sensitivities of gross primary production and ecosystem respiration in streams across six biomes, from the tropics to the arctic tundra. We find that the change in metabolic balance, that is, the ratio of gross primary production to ecosystem respiration, is a function of stream temperature and current metabolic balance. Applying this relationship to the global compilation of stream metabolism data, we find that a 1 °C increase in stream temperature leads to a convergence of metabolic balance and to a 23.6% overall decline in net ecosystem productivity across the streams studied. We suggest that if the relationship holds for similarly sized streams around the globe, the warming-induced shifts in metabolic balance will result in an increase of 0.0194 Pg carbon emitted from such streams every year.
Burial in sediments removes organic carbon (OC) from the short-term biosphere-atmosphere carbon (C) cycle, and therefore prevents greenhouse gas production in natural systems. Although OC burial in lakes and reservoirs is faster than in the ocean, the magnitude of inland water OC burial is not well constrained. Here we generate the first global-scale and regionally resolved estimate of modern OC burial in lakes and reservoirs, deriving from a comprehensive compilation of literature data. We coupled statistical models to inland water area inventories to estimate a yearly OC burial of 0.15 (range, 0.06–0.25) Pg C, of which ~40% is stored in reservoirs. Relatively higher OC burial rates are predicted for warm and dry regions. While we report lower burial than previously estimated, lake and reservoir OC burial corresponded to ~20% of their C emissions, making them an important C sink that is likely to increase with eutrophication and river damming.
Using stable isotopes to assess surface water source dynamics and hydrological connectivity in a high-latitude wetland and permafrost influenced landscape, Journal of Hydrology (2017), doi: https://doi. Abstract Climate change is expected to alter hydrological and biogeochemical processes in high-latitude inland waters. A critical question for understanding contemporary and future responses to environmental change is how the spatio-temporal dynamics of runoff generation processes will be affected. We sampled stable water isotopes in soils, lakes and rivers on an unprecedented spatio-temporal scale along a 1700 km transect over three years in the Western Siberia Lowlands. Our findings suggest that snowmelt mixes with, and displaces, large volumes of water stored in the organic soils and lakes to generate runoff during the thaw season. Furthermore, we saw a persistent hydrological connection between water bodies and the landscape across permafrost regions. Our findings help to bridge the understanding between small and large scale hydrological studies in high-latitude systems. These isotope data provide a means to conceptualise hydrological connectivity in permafrost and wetland influenced regions, which is needed for an improved understanding of future biogeochemical changes.
Nutrient limitation of oceanic primary production exerts a fundamental control on marine food webs and the flux of carbon into the deep ocean. The extensive boundaries of the oligotrophic sub-tropical gyres collectively define the most extreme transition in ocean productivity, but little is known about nutrient limitation in these zones. Here we present the results of full-factorial nutrient amendment experiments conducted at the eastern boundary of the South Atlantic gyre. We find extensive regions in which the addition of nitrogen or iron individually resulted in no significant phytoplankton growth over 48 hours. However, the addition of both nitrogen and iron increased concentrations of chlorophyll a by up to approximately 40-fold, led to diatom proliferation, and reduced community diversity. Once nitrogen-iron co-limitation had been alleviated, the addition of cobalt or cobalt-containing vitamin B12 could further enhance chlorophyll a yields by up to threefold. Our results suggest that nitrogen-iron co-limitation is pervasive in the ocean, with other micronutrients also approaching co-deficiency. Such multi-nutrient limitations potentially increase phytoplankton community diversity.
Picophytoplankton are acknowledged to contribute significantly to primary production (PP) in the ocean while now the method to measure PP of picophytoplankton (PPPico) at large scales is not yet well established. Although the traditional ¹⁴C method and new technologies based on the use of stable isotopes (e.g., ¹³C) can be employed to accurately measure in situ PPPico, the time-consuming and labor-intensive shortage of these methods constrain their application in a survey on large spatiotemporal scales. To overcome this shortage, a modified carbon-based ocean productivity model (CbPM) is proposed for estimating the PPPico whose principle is based on the group-specific abundance, cellular carbon conversion factor (CCF), and temperature-derived growth rate of picophytoplankton. Comparative analysis showed that the estimated PPPico using CbPM method is significantly and positively related (r² = 0.53, P < 0.001, n = 171) to the measured ¹⁴C uptake. This significant relationship suggests that CbPM has the potential to estimate the PPPico over large spatial and temporal scales. Currently this model application may be limited by the use of invariant cellular CCF and the relatively small data sets to validate the model which may introduce some uncertainties and biases. Model performance will be improved by the use of variable conversion factors and the larger data sets representing diverse growth conditions. Finally, we apply the CbPM-based model on the collected data during four cruises in the Bohai Sea in 2005. Model-estimated PPPico ranged from 0.1 to 11.9, 29.9 to 432.8, 5.5 to 214.9, and 2.4 to 65.8 mg C m⁻² d⁻¹ during March, June, September, and December, respectively. This study shed light on the estimation of global PPPico using carbon-based production model.
Kettle holes are often abundant within agriculturally used moraine landscapes. They are highly enriched with nutrients and considered hotspots of carbon turnover. However, data on their primary productivity remain rare. We analysed two kettle holes typical to Germany with common aquatic plant communities during one year. We hypothesised that gross primary production (GPP) rates would be high compared to other temperate freshwater ecosystems, leading to high sediment deposition. Summer GPP rates (4.5–5.1 g C m−2 day−1) were higher than those of most temperate freshwater systems, but GPP rates were reduced by 90% in winter. Macrophytes dominated GPP from May to September with emergent macrophytes accounting for half of the GPP. Periphyton contributed to most of the system GPP throughout the rest of the year. Sediment deposition rates were high and correlated with GPP in one kettle hole. In contrast, due to prolonged periods of anoxia, aerobic sediment mineralisation was low while sediment phosp
The biological carbon pump (BCP) transports organic carbon from the surface to the ocean's interior via sinking particles, vertically migrating organisms, and passive transport of organic matter by advection and diffusion. While many studies have quantified sinking particles, the magnitude of passive transport remains poorly constrained. In the Southern Ocean weak thermal stratification, strong vertical gradients in particulate organic matter, and weak vertical nitrate gradients suggest that passive transport from the euphotic zone may be particularly important. We compile data from seasonal time series at a coastal site near Palmer Station, annual regional cruises in the Western Antarctic Peninsula (WAP), cruises throughout the broader Southern Ocean, and SOCCOM (Southern Ocean Carbon and Climate Observations and Modeling) autonomous profiling floats to estimate spatial and temporal patterns in vertical gradients of nitrate, particulate nitrogen (PN), and dissolved organic carbon. Under a steady state approximation, the ratio of ∂PN/∂z to ∂NO3⁻/∂z suggests that passive transport of PN may be responsible for removing 46% (37%–58%) of the nitrate introduced into the surface ocean of the WAP (with dissolved organic matter contributing an additional 3–6%) and for 23% (19%–28%) of the BCP in the broader Southern Ocean. A simple model parameterized with in situ nitrate, PN, and primary production data suggested that passive transport was responsible for 54% of the magnitude of the BCP in the WAP. Our results highlight the potential importance of passive transport (by advection and diffusion) of organic matter in the Southern Ocean but should only be considered indicative of high passive transport (rather than conclusive evidence) due to our steady state assumptions.
Microphytoplankton species composition, diversity, abundance and biomass (chlorophyll-a) was studied for the first time in the shallow continental shelf (< 20 m bathymetry) of the northern Bay of Bengal during winter (December, 2011 to February, 2012). Species specific chlorophyll and carbon stock has been computed from biovolume calculation using standard formulae. Nutrient stoichiometry along with related biogeochemical variables has also been studied. Forty five phytoplankton species were recorded in total, out of which 38 were diatoms and the rest were dinoflagellates. Thalassionema frauenfeldii was the most abundant species, followed by Thalassionema nitzschioides and Coscinodiscus radiatus. Highest cell chlorophyll and carbon content was found in Coscinodiscus gigas. Dinoflagellate species were found to comprise 15.55% of the total taxa. Amongst the dinoflagellates, Ceratium furca had the highest abundance, whereas Ceratium symmetricum had the maximum species-specific chlorophyll and carbon stock. The nutrient stoichiometry was highly deviated from the standard Redfield ratio of Si: N: P (16:16:1). [
Environmental context
Extracellular polymeric substances provide a nucleation site for calcium carbonate and hence are important for bio-calcification processes, with implications for sediment formation and the global carbon cycle. We investigate the calcification potential of polymeric substances produced by five species of cyanobacteria. The results indicate that the protein content and alkaline functional groups of the extracellular polymeric substances may have a significant effect on cyanobacterial calcification.
Abstract
Cyanobacterial calcification plays a crucial role in the formation of freshwater calcium carbonate precipitates, with cyanobacterial extracellular polymeric substances (EPSs) contributing significantly, partly by providing a nucleation site for calcium carbonate. Despite this, cyanobacterial EPS and their effect on calcification processes have not been completely characterised. In the present study, five cyanobacterial species were selected. First, EPS characteristics of these cyanobacterial species were examined, showing that proteins dominated both EPSs released in to solution (REPSs) and cell-surface bound (LEPSs). The major EPS functional groups included acidic groups, such as carboxyl groups, and highly alkaline groups, such as hydroxyl and amino groups. The calcification ability of different cyanobacterial species was found to vary dramatically. Solution pH increased during the calcification process, which was beneficial to the supersaturation of CaCO3, and could affect the calcification potential. Precipitation, however, was positively correlated with EPS protein content and the concentration of basic functional groups, such as amino or hydroxyl groups. These results suggest EPS protein content and alkaline functional groups may have a significant effect on cyanobacterial calcification. The results also provide a potential application in that EPS proteins of cyanobacteria may have beneficial positive applications in the removal of multivalent cations from wastewater.
In remote regions of the world, whole lake metabolic estimates are scarce, largely because long incubations, intensive sampling and deployment of monitoring equipment are impractical. The oxygen isotope (δ18O) mass balance approach represents a simple and efficient alternative to measure whole-lake gross primary production (GPP) and respiration (R) from a single point sample, yet this option has not been extensively explored in habitats such as remote northern lakes. Here, we explored the applicability of the method using a sensitivity analysis on simulated data, showing that in large, heterotrophic (i.e., R > GPP) lakes, model outputs are sensitive to input terms for isotopic fractionation and air–water gas exchange. Despite these sensitivities, field applications of the δ18O method generated promising results that were generally consistent with parallel, free-water diel DO metabolic modelling, but greater than in vitro incubation measurements. The isotopic approach captured both wide-ranging metabolic conditions in in situ experimental mesocosms, and the seasonal trends in GPP and R in a shallow, dystrophic lake. In a clearer, deeper heterotrophic lake, the isotope approach integrated a fraction of metalimnetic metabolism missed by diel DO metabolic estimates. Overall, metalimnetic contributions to surface δ18O–DO dynamics had the greatest impact on model outputs, but with accurate information on air–water gas exchange, mixing depth, and the vertical DO and light regime of a given system, these effects can be accounted for and the isotopic approach can yield well constrained, spatio-temporally integrated rates of GPP and R. The approach is clearly suitable for use in oligo- and mesotrophic lakes, especially in remote regions where sampling is logistically difficult.
The damming of rivers represents one of the most far-reaching human modifications of the flows of water and associated matter from land to sea. Dam reservoirs are hotspots of sediment accumulation, primary productivity (P) and carbon mineralization (R) along the river continuum. Here we show that for the period 1970–2030, global carbon mineralization in reservoirs exceeds carbon fixation (P<R); the global P/R ratio, however, varies significantly, from 0.20 to 0.58 because of the changing age distribution of dams. We further estimate that at the start of the twenty-first century, in-reservoir burial plus mineralization eliminated 4.0±0.9 Tmol per year (48±11 Tg C per year) or 13% of total organic carbon (OC) carried by rivers to the oceans. Because of the ongoing boom in dam building, in particular in emerging economies, this value could rise to 6.9±1.5 Tmol per year (83±18 Tg C per year) or 19% by 2030.
Rivers play an important role in carbon (C) exchange between terrestrial and oceanic water bodies and the atmosphere. The aim of this study was to systematically quantify fluxes in riverine C export and C exchange in the air–sea interface of marine ecosystems in China. Results show that annual C transport from rivers to coastal ecosystems in China can reach up to 64.35 TgC, which accounts for approximately 4.8%–8.1% of global C transport from river systems. In the Bohai Sea, particulate inorganic carbon is the main form of C influx, and it can reach up to 20.79 TgC/yr. Conversely, dissolved inorganic carbon is the main form of C influx into the East China Sea, and it can reach up to 10.52 TgC/yr, which is 42.6% of the total annual C imported into the East China Sea. China's marine ecosystems including the Yellow Sea, the Bohai Sea, the East China Sea, and the South China Sea can absorb 65.06 TgC/yr from the atmosphere.
In many northern temperate regions, the water color of lakes has increased over the past decades (“lake browning”), probably caused by an increased export of dissolved organic matter from soils. We investigated if the increase in water color in two lakes in Norway has resulted in increased burial of organic carbon (OC) and mercury (Hg) in the sediments, and if the Hg was prone to methylation. Lake Solbergvann experienced a 3-fold water color increase, and OC burial increased ~2-fold concomitant to the water color increase. This lake had prolonged periods of anoxic bottom water, and anoxic OC mineralization rates were only about half of the oxic OC mineralization rates (7.7 and 17.5 g C m-2 yr-1, respectively), contributing to an efficient OC burial. In Lake Elvåga, where water color increase was only ~2-fold and bottom water was oxygenated, no recent increase in OC burial could be observed. Hg burial increased strongly in both lakes (3-fold and 1.6-fold in Lake Solbergvann and Lake Elvåga, respectively), again concomitant to the recent water color increase. The proportion of methylated Hg (MeHg) in surficial sediment was one order of magnitude higher in Lake Elvåga (up to 6% MeHg) than in Lake Solbergvann (0.2-0.6% MeHg), probably related to the different oxygenation regimes. We conclude that lake browning can result in increased OC and Hg burial in lake sediments, but the extent of browning and the dominating mode of sediment respiration (aerobic or anaerobic) strongly affect burial and fate of OC and Hg in sediments.
Lakes and ponds cover only about 4% of the Earth's non-glaciated surface, yet they represent disproportionately large sources of methane and carbon dioxide. Indeed, very small ponds (for example, <0.001 km 2) may account for approximately 40% of all CH 4 emissions from inland waters. Understanding how greenhouse gas emissions from aquatic ecosystems will respond to global warming is therefore vital for forecasting biosphere-carbon cycle feedbacks. Here, we present findings on the long-term effects of warming on the fluxes of GHGs and rates of ecosystem metabolism in experimental ponds. We show that shifts in CH 4 and CO2 fluxes, and rates of gross primary production and ecosystem respiration, observed in the first year became amplified over seven years of warming. The capacity to absorb CO2 was nearly halved after seven years of warmer conditions. The phenology of greenhouse gas fluxes was also altered, with CO2 drawdown and CH 4 emissions peaking one month earlier in the warmed treatments. These findings show that warming can fundamentally alter the carbon balance of small ponds over a number of years, reducing their capacity to sequester CO2 and increasing emissions of CH 4; such positive feedbacks could ultimately accelerate climate change. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
Many freshwater systems receive substantial inputs of terrestrial organic matter. Terrestrially derived dissolved organic carbon (t‐DOC) inputs can modify light availability, the spatial distribution of primary production, heat, and oxygen in aquatic systems, as well as inorganic nutrient bioavailability. It is also well‐established that some terrestrial inputs (such as invertebrates and fruits) provide high‐quality food resources for consumers in some systems.
In small to moderate‐sized streams, leaf litter inputs average approximately three times greater than the autochthonous production. Conversely, in oligo/mesotrophic lakes algal production is typically five times greater than the available flux of allochthonous basal resources.
Terrestrial particulate organic carbon (t‐POC) inputs to lakes and rivers are comprised of 80%–90% biochemically recalcitrant lignocellulose, which is highly resistant to enzymatic breakdown by animal consumers. Further, t‐POC and heterotrophic bacteria lack essential biochemical compounds that are critical for rapid growth and reproduction in aquatic invertebrates and fishes. Several studies have directly shown that these resources have very low food quality for herbivorous zooplankton and benthic invertebrates.
Much of the nitrogen assimilated by stream consumers is probably of algal origin, even in systems where there appears to be a significant terrestrial carbon contribution. Amino acid stable isotope analyses for large river food webs indicate that most upper trophic level essential amino acids are derived from algae. Similarly, profiles of essential fatty acids in consumers show a strong dependence on the algal food resources.
Primary production to respiration ratios are not a meaningful index to assess consumer allochthony because respiration represents an oxidised carbon flux that cannot be utilised by animal consumers. Rather, the relative importance of allochthonous subsidies for upper trophic level production should be addressed by considering the rates at which terrestrial and autochthonous resources are consumed and the growth efficiency supported by this food.
Ultimately, the biochemical composition of a particular basal resource, and not just its quantity or origin, determines how readily this material is incorporated into upper trophic level consumers. Because of its highly favourable biochemical composition and greater availability, we conclude that microalgal production supports most animal production in freshwater ecosystems.
We investigated the long-term variations in primary production in Lake Taihu using Moderate Resolution Imaging Spectroradiometer (MODIS) data, based on the Vertically Generalized Production Model (VGPM).We firstly test the applicability of VGPM in Lake Taihu by comparing the results between the model-derived and the in situ results, and the results showed that a strong significant correlation (R² = 0.753, p < 0.001, n = 63). Then, VGPM was used to map temporal-spatial distributions of primary production in Lake Taihu. The annual mean daily primary production of Lake Taihu from 2003 to 2013 was 1094.06 ± 720.74 mg·C·m⁻²·d⁻¹. Long-term primary production maps estimated from the MODIS data demonstrated marked temporal and spatial variations. Spatially, the primary production in bays, especially in Zhushan Bay and Meiliang Bay, was consistently higher than that in the open area of Lake Taihu, which was caused by chlorophyll-a concentrations resulting from high nutrient concentrations. Temporally, the seasonal variation of primary production from 2003 to 2013 was: summer > autumn > spring > winter, with significantly higher primary production found in summer and autumn than in winter (p < 0.005, t-test), primarily caused by seasonal variations in water temperature. On a monthly scale, the primary production exerts a clear character of bimodality, increasing from January to May, decreasing in June or July, and finally reaching its highest value during August or September. Wind is another important factor that could affect the spatial variations of primary production in the large, eutrophic and shallow Lake Taihu.
The input of dissolved organic and inorganic carbon (DOC and DIC) via direct groundwater seepage to boreal lakes is often assumed to be small in non-carbonaceous areas. However, measurements are rare. We estimated the terrestrial load of DOC, DIC and methane (CH4) to a small boreal lake for the open-water period, on the basis of measured concentrations of carbon species in near-shore groundwater wells and inlet streams, and measured area-specific discharge. The sub-catchment directly draining into the lake via groundwater seepage contributed 18 % to the total water input during the open-water season. Compared to stream and lake water, near-shore groundwater concentrations of DOC were slightly elevated, and groundwater DIC and CH4 concentrations were highly elevated. Consequently, direct groundwater seepage contributed 27% to the total DOC load, 64% to the total DIC load, and 96% to the total CH4 load from the catchment to the lake. Groundwater DIC import corresponded only to 5-8% of lake carbon dioxide (CO2) emission. In incubation experiments, we observed higher photochemical DOC loss rates in stream and groundwater samples (18-55% DOC loss upon 72 hours UV-A exposure) than in lake water (15% DOC loss), and detected significant DOC flocculation in groundwater samples in both light and dark incubations (2-24% DOC loss). We conclude that even in regions where lake hydrology is dominated by surface water inflow via inlet streams, direct groundwater seepage can represent an important carbon source to boreal lakes, and groundwater DOC may be susceptible to in-lake removal via degradation and flocculation.
The frequency and magnitude of extreme events are expected to increase in the future, yet little is known about effects of such events on ecosystem structure and function. We examined how extreme precipitation events affect exports of terrestrial dissolved organic carbon (t-DOC) from watersheds to lakes as well as in-lake heterotrophy in three north-temperate lakes. Extreme precipitation events induced large influxes of t-DOC to our lakes, accounting for 45–58% of the seasonal t-DOC load. These large influxes of t-DOC influenced lake metabolism, resulting in lake net heterotrophy following 67% of the extreme precipitation events across all lakes. Hydrologic residence time (HRT) was negatively related to t-DOC load and heterotrophy; lakes with short HRT had higher t-DOC loads and greater net heterotrophy. The fraction of t-DOC mineralized within each lake following extreme precipitation events generally exhibited a positive relationship with lake HRT, similar to the previous studies of fractions mineralized at annual and supra-annual time scales. Event-associated turnover rate of t-DOC was higher than what is typically reported from laboratory studies and modeling exercises and was also negatively related to lake HRT. This study demonstrates that extreme precipitation events are ‘hot moments’ of carbon load, export, and turnover in lakes and that lake-specific characteristics (for example, HRT) interact with climatic patterns to set rates of important lake carbon fluxes.
Estuaries are biogeochemical hot spots because they receive large inputs of
nutrients and organic carbon from land and oceans to support high rates of
metabolism and primary production. We synthesize published rates of annual
phytoplankton primary production (APPP) in marine ecosystems influenced by
connectivity to land – estuaries, bays, lagoons, fjords and inland seas.
Review of the scientific literature produced a compilation of 1148 values of
APPP derived from monthly incubation assays to measure carbon assimilation or
oxygen production. The median value of median APPP measurements in 131
ecosystems is 185 and the mean is 252 g C m−2 yr−1, but the
range is large: from −105 (net pelagic production in the Scheldt Estuary)
to 1890 g C m−2 yr−1 (net phytoplankton production in Tamagawa
Estuary). APPP varies up to 10-fold within ecosystems and 5-fold from year to
year (but we only found eight APPP series longer than a decade so our
knowledge of decadal-scale variability is limited). We use studies of
individual places to build a conceptual model that integrates the mechanisms
generating this large variability: nutrient supply, light limitation by
turbidity, grazing by consumers, and physical processes (river inflow, ocean
exchange, and inputs of heat, light and wind energy). We consider method as
another source of variability because the compilation includes values derived
from widely differing protocols. A simulation model shows that different
methods reported in the literature can yield up to 3-fold variability
depending on incubation protocols and methods for integrating measured rates
over time and depth.
Although attempts have been made to upscale measures of estuarine-coastal
APPP, the empirical record is inadequate for yielding reliable global
estimates. The record is deficient in three ways. First, it is highly biased
by the large number of measurements made in northern Europe (particularly the
Baltic region) and North America. Of the 1148 reported values of APPP, 958
come from sites between 30 and 60° N; we found only 36
for sites south of 20° N. Second, of the 131 ecosystems where APPP
has been reported, 37% are based on measurements at only one location
during 1 year. The accuracy of these values is unknown but probably low,
given the large interannual and spatial variability within ecosystems.
Finally, global assessments are confounded by measurements that are not
intercomparable because they were made with different methods.
Phytoplankton primary production along the continental margins is tightly
linked to variability of water quality, biogeochemical processes including
ocean–atmosphere CO2 exchange, and production at higher trophic levels
including species we harvest as food. The empirical record has deficiencies
that preclude reliable global assessment of this key Earth system process. We
face two grand challenges to resolve these deficiencies: (1) organize and
fund an international effort to use a common method and measure APPP
regularly across a network of coastal sites that are globally representative
and sustained over time, and (2) integrate data into a unifying model to
explain the wide range of variability across ecosystems and to project
responses of APPP to regional manifestations of global change as it continues
to unfold.
Kettle holes as a specific group of isolated, small lentic
freshwater
systems (LFS) often are (i) hot spots of biogeochemical cycling and (ii) exposed to frequent sediment desiccation and rewetting. Their ecological functioning is greatly determined by immanent carbon and nutrient transformations. The objective of this review is to elucidate effects of a changing hydrological regime (i.e., dry–wet cycles) on carbon and nutrient cycling in kettle hole sediments. Generally, dry–wet cycles have the potential to increase C and N losses as well as P availability. However, their duration and frequency are important controlling factors regarding direction and intensity of biogeochemical and microbiological responses. To evaluate drought impacts on sediment carbon and nutrient cycling in detail requires the context of the LFS hydrological history. For example, frequent drought events induce physiological adaptation of exposed microbial communities and thus flatten metabolic responses, whereas rare events provoke unbalanced, strong microbial responses. Different potential of microbial resilience to drought stress can irretrievably change microbial communities and functional guilds, gearing cascades of functional responses. Hence, dry–wet events can shift the biogeochemical cycling of organic matter and nutrients to a new equilibrium, thus affecting the dynamic balance between carbon burial and mineralization in kettle holes.
The relationship between carbon biomass and cell abundance in net phytoplankton was determined to improve standing stock research in marine ecology. Based on samples from six cruises in the Yellow Sea and the East China Sea, significant regression equations for all net phytoplankton cells, diatoms, dinoflagellates and each dominant genus were obtained. The relationships could be described by the equation log10 y = k × log10 x + b, where x represents cell abundance based on cell counts (cells m–3), y represents carbon biomass (μg C m–3), and k and b are constants. The values of k and b were 0.48 and 0.49 respectively for total net phytoplankton, 0.75 and –1.46 respectively for diatoms in summer, 0.54 and –0.11 respectively for diatoms in spring and autumn, and 0.92 and –0.90 respectively for dinoflagellates. Regression equations for Chaetoceros, Coscinodiscus, Pseudo-nitzschia, Skeletonema, Ceratium, Protoperidinium and Pyrophacus were also obtained. We suggest using these carbon biomass : cell abundance relationships established for net phytoplankton to assess phytoplankton standing stocks and for reanalysing historical data.
Water clarity controls a wide range of physical, chemical, and biological processes and thus is an important environmental variable for assessing both the climatic and human activity factors that affect lake ecosystems. Here, we use 30-year Landsat series data to investigate the patterns and trends of water clarity in the Xin’anjiang Reservoir, the largest freshwater, man-made reservoir in the Yangtze River Delta region of China. Three empirical models based on Landsat 5, 7 and 8 data were developed and validated to remotely estimate the water clarity. The validation results show that the three models performed well in deriving water clarity, with the mean absolute percent differences (MAPDs) less than 30%. The long-term trends and spatial distribution patterns of water clarity from 1986 to 2016 were constructed using the three developed models. A significant decreasing trend in water clarity was observed, with a reduction of approximately 0.2 m, indicating a gradual water quality decrease. Eleven explanatory variables, including air temperature, rainfall, gross domestic product (GDP), population, chemical fertilizer usage, industrial sewage, and land-use change, were used to explore the driving force of the long-term trend of water clarity with the multiple regression and variation partitioning model. Air temperature, rainfall, cropland, and industrial sewage were the four potential driving forces and explained 63% of the long-term variation in water clarity. Increasing built-up land, air temperature and rainfall, and decreasing forest and grassland jointly caused the decreasing water clarity. Therefore, several reservoir management measurements should be implemented to stop water clarity decreasing.
From a molecular level to an ecosystem scale, different coupling mechanisms take place during coupled carbon-nitrogen-water (C-N-H2O) cycles, of which essential are water flux and related biogeochemical processes through physicochemical reactions associated with terrestrial and aquatic ecosystems. Meanwhile, regional coupled C-N-H2O cycle will subsequently impact regional gross primary productivity (GPP) and C and N exchanges during air-water interactions that occur downstream of watersheds. This study aimed to first synthetically analyze the regional dynamics of C, N and H2O cycles in ecosystems and determine their interactional relationships; second, to specify regional C-N-H2O coupled relationships of ecosystems and their theoretical ecological principles; third, to classify coupled regional response and adaptation of the C-N-H2O cycle to climatic and environmental changes under anthropogenic activities, providing a theoretical basis to fully understand and make adjustments to interactional C, N and H2O cycling relationships at different ecosystem scales and under associated coupling processes.
Eutrophication mitigation is an ongoing priority for aquatic ecosystems. However, the current eutrophication control strategies (phosphorus (P) and/or nitrogen (N)) are guided mainly by nutrient addition experiments in small waters without encompassing all in-lake biogeochemical processes that are associated largely with lake morphological characteristics. Here we use a global lake data set (573 lakes) to show that the relative roles of N vs. P in affecting eutrophication are underpinned by water depth. Mean depth and maximum depth relative to mixing depth were used to distinguish shallow (mixing depth > maximum depth), deep (mixing depth < mean depth), and transitional (mean depth ≤ mixing depth ≤ maximum depth) lakes in this study. TN:TP ratio (by mass) was used as an indicator of potential lake nutrient limitation, i.e. N only limitation if N:P < 9, N+P co-limitation if 9 ≤ N:P < 22.6 and P only limitation if N:P ≥ 22.6. The results show that eutrophication is favored in shallow lakes, frequently (66.2%) with N limitation while P limitation predominated (94.4%) in most lakes but especially in deep ones. The importance of N limitation increases but P limitation decreases with lake trophic status while N and P co-limitation occurs primarily (59.4%) in eutrophic lakes. These results demonstrate that phosphorus reduction can mitigate eutrophication in most large lakes but a dual N and P reduction may be needed in eutrophic lakes, especially in shallow ones (or bays). Our analysis helps clarify the long debate over whether N, P, or both control primary production. While these results imply that more resources be invested in nitrogen management, given the high costs of nitrogen pollution reduction, more comprehensive results from carefully designed experiments at different scales are needed to further verify this modification of the existing eutrophication mitigation paradigm.
The increased use of hydropower is currently driving the greatest surge in global dam construction since the mid-20th century, meaning that most major rivers on Earth are now dammed. Dams impede the flow of essential nutrients, including carbon, phosphorus, nitrogen and silicon, along river networks, leading to enhanced nutrient transformation and elimination. Increased nutrient retention via sedimentation or gaseous elimination in dammed reservoirs influences downstream terrestrial and coastal environments. Reservoirs can also become hotspots for greenhouse gas emission, potentially impacting how ‘green’ hydropower is compared with fossil-fuel burning. In this Review, we discuss how damming changes nutrient biogeochemistry along river networks, as well as its broader environmental consequences. The influences of construction and management practices on nutrient elimination, the emission of greenhouse gases and potential remobilization of legacy nutrients are also examined. We further consider how regulating hydraulic residence time and environmental flows (or e-flows) can be used in planning and operation from dam conception to deconstruction.
The transport of trace metals in river-lake systems can potentially increase or decrease primary productivity in some basins and subsequently affect the carbon cycle of watersheds. In this study, we investigated a variety of trace metal concentrations and transport flux in the Poyang Lake basin during four seasons. Results show that the Gan River transports 78% of selenium (Se) and 42% of lead (Pb) into Poyang Lake each year, resulting in heavy metal pollution dominated by Pb and Se in 30%-75% of its water. Although toxic heavy metals, such as Pb, chromium (Cr), and copper (Cu), inhibit phytoplankton growth and decrease its gross primary productivity (GPP), excessive Se could effectually promote productivity. However, the negative effect of Pb on GPP is more significant than the positive effect of Se on GPP; hence, their interaction effectuates a decrease in total primary productivity. Additionally, under high nutrients level, the synergistic effect of heavy metals and nutrients will reduce GPP. Agricultural fertilizer is likely the source of both Pb, Cu, Se and N. Gan River contributes 35%-80% of the heavy metal inputs to Poyang Lake. It is therefore necessary to improve the ecological environment of phytoplankton and promote productivity in the Poyang Lake basin by reducing the application of agricultural chemical fertilizers to control pollution. Our results indicate that the role of certain, less studied trace elements (e.g., Pb, Cr, Cu, and Se) in regulating primary productivity of watershed ecosystems is more important than previously thought. This study also discusses potential impacting mechanisms associated with these metals on phytoplankton, whose biological functions need to be verified in future experiments.
The interpretation of environmental effect on phytoplankton growth is not straightforward, especially in ecosystems with high variation in hydrological conditions due to confounding variables. Lake Poyang is characterized by high fluctuation of water level (WL) due to its free connection to the Yangtze River. High frequency (weekly) and long-term (2009–2018) samplings were conducted in Lake Poyang resulting in 170 samples. Our study aimed to illustrate that whether the key factors determining phytoplankton growth change with WL. Furthermore, the impact of WL on phytoplankton was also detected. Six periods were classified in our study, i.e., dry season, raising period (I and II), wet season, and falling period (I and II) based on WL variation. Environmental characteristics were significantly (P < 0.01) different among these periods with the exception of orthophosphate. Based on the whole data set, water temperature (WT) was the critical parameter affecting phytoplankton growth. However, according to time series analysis, the key factors varied in different periods. Underwater light condition, which was represented by Secchi depth (SD), was the most critical factor controlling phytoplankton growth, especially in the periods with relatively high WL and WT (i.e., raising period II, wet season, and falling period I). The role of water temperature on phytoplankton was more evident in falling periods. In dry season with the lowest WL, total phosphorus limited phytoplankton growth. Regarding WL, its impact on phytoplankton was mainly through change in environmental parameters, such as water flow velocity, water transparency, and nutrients. Furthermore, time series analysis well simulated phytoplankton chlorophyll a in Lake Poyang, with larger R²adj (except raising period II and falling period II) and lower model error in all 6 periods. Our results revealed that the critical factors controlling phytoplankton growth were various with WL. Additionally, time series analysis will benefit local water resource management.
Inland lakes receive growing attentions on eutrophication and their roles in global carbon cycle. However, understanding how inland lakes contribute to global carbon cycle is seriously hampered due to a shortage of long-term records. This study investigated the carbon dioxide (CO2) flux from the Lake Taihu, a large (2400 km2) and shallow (mean depth 1.9 m) eutrophic lake in subtropical region, based on a long-term (2000-2015) measurement of the partial pressure of carbon dioxide (pCO2) at high spatiotemporal resolution. We found that the Lake Taihu was a significant source of atmospheric CO2 with an average CO2 emission flux at 18.2 ± 8.4 mmol m-2 d-1 (mean±1standard deviation) and a mean annual pCO2 value of 778 ± 169 μatm. The highest pCO2 and CO2 flux were observed in eutrophic zone with a high external input of carbon and nutrient, and the lowest in non-eutrophic zones with no direct external input of nutrient and carbon. A substantial seasonal pattern in pCO2 was observed, particularly in eutrophic pelagic area, and was significantly negatively correlated with chlorophyll a. Long-term measurement showed the interannual variation in annual lake CO2 dynamics, which was highly sensitive to human-induced nutrient input. Watershed input of carbon and nutrient leads to the high CO2 level, counterbalancing the in-lake primary production. All lines of evidence suggest that human activities may have predominate contribution to CO2 source in the Lake Taihu, and this mechanism might be widespread in global freshwater lakes.
The effects of heat stress are spatially heterogeneous owing to local variations in climate response, population density, and social conditions. Using global climate and impact models from the Inter-Sectoral Impact Model Intercomparison Project, our analysis shows that the frequency and intensity of heat events increase, especially in tropical regions (geographic perspective) and developing countries (national perspective), even with global warming held to the 1.5 °C target. An additional 0.5 °C increase to the 2 °C warming target leads to >15% of global land area becoming exposed to levels of heat stress that affect human health; almost all countries in Europe will be subject to increased fire danger, with the duration of the fire season lasting 3.3 days longer; 106 countries are projected to experience an increase in the wheat production-damage index. Globally, about 38%, 50%, 46%, 36%, and 48% of the increases in exposure to health threats, wildfire, crop heat stress for soybeans, wheat, and maize could be avoided by constraining global warming to 1.5 °C rather than 2 °C. With high emissions, these impacts will continue to intensify over time, extending to almost all countries by the end of the 21st century: >95% of countries will face exposure to health-related heat stress, with India and Brazil ranked highest for integrated heat-stress exposure. The magnitude of the changes in fire season length and wildfire frequency are projected to increase substantially over 74% global land, with particularly strong effects in the United States, Canada, Brazil, China, Australia, and Russia. Our study should help facilitate climate policies that account for international variations in the heat-related threats posed by climate change. Keywords: Global warming, Exposure, Heat-related extremes, 1.5 °C warming target
Anthropogenic activities strengthen atmospheric reactive nitrogen (Nr) emission and deposition, which led to aggravate nitrogen (N) pollution and change gross primary productivity (GPP) in waterbodies. Over the past three decades, the annual Nr deposition over China increased by approximately 25% and the rate of Nr deposition nationwide increased from 11.1 to 15.3 kg ha⁻¹∙yr⁻¹, which has led to 2.0–2.5 × 10⁸ kg N∙yr⁻¹ from Nr deposition to inland water, with an estimated increase in N concentration of 76.6–93.9 μg L⁻¹∙yr⁻¹ in inland water. The Nr deposition was significantly higher in the humid zone than in the arid zone, and Nr deposition in the subtropical zone was higher than in the temperate zone. The large increases in total Nr input via deposition to reservoirs can be found annually in various hydroclimatic zones. In addition, the coupled cycling of C, N and P exhibit limitation on GPP by varying availability in aquatic ecosystem. Therefore, the spatial patterns of the GPP caused by Nr deposition showed a decreasing trend from southern China to western and northern China. However, P would be an important external macronutrient source and limiting factor for the GPP in many lake ecosystems rather than N.
Rivers and lakes have been traditionally studied as separate entities for carbon transport. However, there is a gap in our knowledge of the connectivity of dissolved carbon in a river-lake continuum. In this study, we analyzed dissolved carbon along the Little River-Catahoula Lake in subtropical Louisiana, United States to assess carbon biogeochemistry in such a river-lake continuum. Monthly in-situ measurements and water sample collections were made at four locations during April 2015 to February 2016 to determine riverine carbon transport into and out of the lake. Results show that much of the dissolved inorganic carbon (DIC) in the river-lake continuum originated from 13 C depleted sources with an average δ 13 C DIC of −18.5‰. Significant decreases in DIC were found after the river passed through the lake (from 482 to 399 μmol L −1), which was most prevalent when the lake was not affected by backwater flow from the downstream river. CO 2 outgassing could be mainly responsible for the sink behavior of the lake for DIC. Dissolved organic carbon (DOC) in the studied watershed were mostly terrigenous with low δ 13 C DOC averaged at −29.2‰. Significant, consistent decreases in DOC concentrations were found from the river to the lake inflow and then to the lake outflow. During the majority of the year, the lake reduced DOC concentrations from the river inflow water, but switched to functioning as a source of DOC during warmer, dryer conditions in September and October due to increased water residence time. Therefore, the lake functioned both as a sink and as a source for DOC. [Read full text at https://authors.elsevier.com/a/1XHggB8ccgbSW]
Diatoms sustain the marine food web and contribute to the export of carbon from the surface ocean to depth. They account for about 40% of marine primary productivity and particulate carbon exported to depth as part of the biological pump. Diatoms have long been known to be abundant in turbulent, nutrient-rich waters, but observations and simulations indicate that they are dominant also in meso- and submesoscale structures such as fronts and filaments, and in the deep chlorophyll maximum. Diatoms vary widely in size, morphology and elemental composition, all of which control the quality, quantity and sinking speed of biogenic matter to depth. In particular, their silica shells provide ballast to marine snow and faecal pellets, and can help transport carbon to both the mesopelagic layer and deep ocean. Herein we show that the extent to which diatoms contribute to the export of carbon varies by diatom type, with carbon transfer modulated by the Si/C ratio of diatom cells, the thickness of the shells and their life strategies; for instance, the tendency to form aggregates or resting spores. Model simulations project a decline in the contribution of diatoms to primary production everywhere outside of the Southern Ocean. We argue that we need to understand changes in diatom diversity, life cycle and plankton interactions in a warmer and more acidic ocean in much more detail to fully assess any changes in their contribution to the biological pump.
Seasonal responses in estuarine metabolism (primary production, respiration, and net metabolism) were examined using two complementary approaches. Total ecosystem metabolism rates were calculated from dissolved oxygen time series using Odum’s open water method. Water column rates were calculated from oxygen-based bottle experiments. The study was conducted over a spring-summer season in the Pensacola Bay estuary at a shallow seagrass-dominated site and a deeper bare-bottomed site. Water column integrated gross production rates more than doubled (58.7 to 130.9 mmol O2 m⁻² day⁻¹) from spring to summer, coinciding with a sharp increase in water column chlorophyll-a, and a decrease in surface salinity. As expected, ecosystem gross production rates were consistently higher than water column rates but showed a different spring-summer pattern, decreasing at the shoal site from 197 to 168 mmol O2 m⁻² day⁻¹ and sharply increasing at the channel site from 93.4 to 197.4 mmol O2 m⁻² day⁻¹. The consistency among approaches was evaluated by calculating residual metabolism rates (ecosystem − water column). At the shoal site, residual gross production rates decreased from spring to summer from 176.8 to 99.1 mmol O2 m⁻² day⁻¹ but were generally consistent with expectations for seagrass environments, indicating that the open water method captured both water column and benthic processes. However, at the channel site, where benthic production was strongly light-limited, residual gross production varied from 15.7 mmol O2 m⁻² day⁻¹ in spring to 86.7 mmol O2 m⁻² day⁻¹ in summer. The summer rates were much higher than could be realistically attributed to benthic processes and likely reflected a violation of the open water method due to water column stratification. While the use of sensors for estimating complex ecosystem processes holds promise for coastal monitoring programs, careful attention to the sampling design, and to the underlying assumptions of the methods, is critical for correctly interpreting the results. This study demonstrated how using a combination of approaches yielded a fuller understanding of the ecosystem response to hydrologic and seasonal variability. © 2017 Coastal and Estuarine Research Federation (outside the USA)
Recent research showed inland water including rivers, lakes, and groundwater may play some role in carbon cycling, although its contribution has remained uncertain due to limited amount of reliable data available. In this study, the author developed an advanced model coupling eco-hydrology and biogeochemical cycle (NICE-BGC). This new model incorporates complex coupling of hydrologic-carbon cycle in terrestrial-aquatic linkages and interplay between inorganic and organic carbon during whole process of carbon cycling. The model could simulate both horizontal transports (export from land to inland water 2.01 ± 1.98 PgC/yr, and transported to ocean 1.13 ± 0.50 PgC/yr) and vertical fluxes (degassing 0.79 ± 0.38 PgC/yr, and sediment storage 0.20 ± 0.09 PgC/yr) in major rivers in good agreement with previous researches, which was an improved estimate of carbon flux from previous studies. The model results also showed global net land flux simulated by NICE-BGC (-1.05 ± 0.62 PgC/yr) decreased carbon sink a little in comparison with revised LPJWHyMe (-1.79 ± 0.64 PgC/yr) and previous materials (-2.8 – -1.4 PgC/yr). This is attributable to CO2 evasion and lateral carbon transport explicitly included in the model, and the result suggests most previous researches have generally overestimated the accumulation of terrestrial carbon and underestimated the potential for lateral transport. The results further implied difference between inverse techniques and budget estimates suggested can be explained to some extent by a net source from inland water. NICE-BGC would play an important role in re-evaluation of greenhouse gas budget of the biosphere, quantification of hot spots, and bridging the gap between top-down and bottom-up approaches to global carbon budget.
The diel (24-h) oxygen (O2) curves approach has become a popular method for analyzing gross primary production (GPP) and ecosystem respiration (ER) rates in aquatic systems. Despite the simplicity of this approach, there remain aspects of the calculation and interpretation of diel O2 curves which may skew results, with potentially large implications for estimates of metabolic rates. One common problem in lakes is the occurrence of unexpected changes in O2 concentrations (for instance, increasing overnight O2 concentrations). Such changes have typically been ascribed to the random mixing of pockets of O2. It has thus been suggested that negative GPP or positive ER values should be included in calculations, on the assumption that under- and overestimates should occur with equal frequency, and thus cancel each other out. Our data from a shallow, eutrophic lake provided a high share of negative GPP values. We argue that these may have been the result of elevated littoral productivity coupled with convective currents produced by consistent differences in the heating or cooling of littoral and offshore waters. Such phenomena might be common in small, sheltered lakes where the role of mixing by wind is diminished. We conclude that a failure to account for consistent metabolic gradients and periodic convective mixing may lead to a chronic underestimation of metabolic rates in lakes when using the diel O2 curves method.
Once fixed by photosynthesis carbon becomes part of the marine food web. The fate of this carbon has two possible outcomes, it may be respired and released back to the ocean and potentially to the atmosphere as CO 2 or retained in the ocean interior and/or marine sediments for extended time scales. The most important biologically mediated processes responsible for long-term carbon storage in the ocean are the biological carbon pump (BCP) and the microbial carbon pump (MCP). While acting simultaneously in the ocean, the balance between these two mechanisms is thought to vary depending on the trophic state of the environment. Using previously published formulations, we propose a modelling framework to simulate variability in the MCP:BCP ratio as a function of external nutrients. Our results suggest that the role of the MCP might become more significant under future climate change conditions where increased stratification enhances the oligotrophic nature of the surface ocean. Based on these model results, we propose a conceptual framework in which the internal stoichiometry of phytoplankton, modulating both grazing pressure and dissolved organic matter production (via phytoplankton exudation), plays a crucial role in regulating the MCP:BCP ratio. KEYWORDS: microbial carbon pump; biological carbon pump; plankton stoichiometry; recalcitrant DOM; marine ecosystem models available online at www.plankt.oxfordjournals.org
We investigated the influence of light, nutrients, and organic matter on gross primary production (GPP), ecosystem respiration (R), and net ecosystem production (NEP = GPP - R) in a dystrophic forest lake and an open eutrophic lake. Forest vegetation reduced incoming irradiance (20%) and wind speed (34%) in dystrophic Gribsø, having thermal stratification 1 month longer than in eutrophic Slotssø. While Gribsø had nutrient-limited phytoplankton during most of the year, Slotssø only experienced nutrient depletion during algal blooms. Colored dissolved organic matter (CDOM) absorbed most light (average 82%) in dystrophic Gribsø, while phytoplankton and other particles absorbed most light (45%) in eutrophic Slotssø. GPP and NEP were positively related to irradiance in both lakes. However, because of higher CDOM absorbance, three times more light was needed to attain autotrophy in Gribsø, being net heterotrophic (NEP < 0) for 79% of all days, compared to 59% in Slotssø. This difference vanished when NEP was scaled to light absorption by pigments, although the eutrophic lake maintained a higher photon yield. Metabolic rates varied much more in Slotssø, where higher light and nutrient availability facilitated occasional phytoplankton blooms, while low light and nutrient availability in Gribsø dampened temporal variability. Both lakes were annually net heterotrophic with similar annual areal rates (NEP, -14 mol C m⁻²). Net heterotrophy in dystrophic Gribsø derives from high import of organic carbon-rich water, while heterotrophy in eutrophic Slotssø is fueled by degradation of sediment pools of organic matter accumulated under previous hypereutrophic conditions, emphasizing the importance of lake history on the contemporary metabolic state.
Seagrass meadows are among the most efficient and long-term carbon sinks on earth, but disturbances could threaten this capacity, so understanding the impacts of disturbance on carbon stored within seagrass meadows—‘blue carbon’—is of prime importance. To date, there have been no published studies on the impacts of seagrass loss on ‘blue carbon’ stocks. We experimentally created several kinds of small-scale disturbances, representative of common grazer and boating impacts, within seagrass (Zostera nigracaulis) meadows in Port Phillip Bay (Australia) and measured the impacts on sediment organic carbon stocks (‘Corg’, and other geochemical variables—%N, δ13C, δ15N). Disturbance had no detectable effect on Corg levels within seagrass sediments, even for high-intensity disturbance treatments, which remained bare (i.e. no seagrass recovery) for 2 years after the disturbance. These findings challenge the widely held assumption that disturbance and concomitant loss of seagrass habitat cause release of carbon, at least for small-scale disturbances. We suggest that larger (e.g. meadow scale) disturbances may be required to trigger losses of ‘blue carbon’ from seagrass meadows.
The C sequestration in coastal blue carbon (Cb) ecosystems, including mangroves, seagrasses and saltmarshes, was discovered to be useful in mitigating the increasing trend of carbon dioxide (CO2) emission due to climate change. In this study, we systematically estimate traditional Cb ecosystem distribution and the associated Cb sequestration rate, and then further quantify the Cb sinks fishery contribution to Cb ecosystem due to human activity in coastal ecosystem. The results show that the global Cb ecosystem is able to store 10.8 PgC, wherein biomass and soil are able to store 2.13 and 8.68 PgC, respectively. In China, the Cb pools are 162 TgC in mangroves, 67 TgC in saltmarshes and 75 TgC in seagrass. The human activity induced global Cb sink fishery on Cb ecosystem is about 26.58–37.6 TgC yr− 1, accounting for 30.7%–43.4% of the world's traditional Cb sequestration ecosystem.The global Cb sequestration potential reaches up to 86.59 Tg yr− 1, while China can explain 1.70% of the world's total Cb sequestration. However, in China, the Cb sequestration due to human activity reaches up to 6.32–7.89 TgC yr− 1, accounting for 20.9%–23.7% of global Cb sink fishery. Therefore, it is very important to build the Cb sink fisheries measure and monitor system to scientifically valuate Cb sink fisheries and associated development potential.
Using the radioisotope 51Cr, we investigated the controls of cellular Cr accumulation in an array of marine phytoplankton grown in environmentally relevant Cr concentrations (1-10 nM). Given the affinity of Cr(III) for amorphous Fe-hydroxide mineral surfaces, and the formation of these mineral phases on the outside of phytoplankton cells, extracellular Cr was monitored in a model diatom species (Thalassiosira weissflogii) as extracellular Fe concentrations varied. Extracellular Cr in T. weissflogii increased with increasing extracellular Fe, demonstrating that Cr may be removed from seawater via extracellular adsorption to phytoplankton. Short-term Cr(VI) and Cr(III) uptake experiments performed with T. weissflogii demonstrated that Cr(III) was the primary oxidation state adsorbing to cells and being internalized by them. Cellular Cr:C ratios (<0.5 μmol Cr mol C-1) of the eight phytoplankton species surveyed were significantly lower than previously reported Cr:C ratios in marine particles with a high biogenic component (10-300 μmol Cr mol C-1). This indicates that Cr(III) likely accumulates in marine particles due to uptake and/or adsorption. Mass balance calculations demonstrate that surface water Cr deficits can be explained via loss of Cr(III) to exported particles, thereby providing a mechanism to account for the nutrient depth profile for Cr in modern seawater. Given the large fractionation of stable Cr isotopes during Cr(VI) reduction, Cr(III) associated with exported organic carbon is likely enriched in lighter isotopes. Most sedimentary Cr isotope studies have thus far neglected internal fractionating processes in the marine Cr cycle, but our data indicate that loss of Cr to exported particles may be traced in the sedimentary δ53Cr record.
The water samples from Lake Poyang were collected in January(dry season) and July(wet season) of 2014 in order to measure the corresponding physical factors, chlorophyll-a concentration and photosynthetically active radiation. Vertically Generalized Production Model was used to estimate the primary productivity of phytoplankton, characteristics and relationship with the lake environmental factors. Results show that the range of phytoplankton's primary productivity in Lake Poyang is fluctuated between 83.50 and 355.43 mg C/(m³·d), and the average is 193.33 mg C/(m³·d) during the dry season. The spatial distribution of primary productivity is mainly affected by different types of water quality in dry season. The primary productivity is negatively correlated with nutrients, of which NH4⁺-N was highly significant due to the absences of nutrient limitation. In wet season the range of primary productivity of phytoplankton is between 113.80 and 1134.06 mg C/(m³·d), and the average is 412.12 mg C/(m³·d), which was affected by the river flow inputs. Primary productivity was significantly positively correlated with the total phosphorus and suspended solids concentrations. Because the positive effect caused by suspended solids was greater than the negative effect on phytoplankton, these effects caused that the restricted phosphorus nutrients occur frequently. The overall average velocity is about 0.28 m/s in the Lake Poyang which is beneficial to the growth of phytoplankton. However, the average speed in the south is approximately 0.21 m/s, while it is approximately 0.35 m/s in the north. Therefore, eutrophication, or even algal bloom are more often occurred in the southern Lake Poyang.