Total Primary Production Research Articles

Exploring effects of dredging and organic waste on the functioning and the quantitative biomass structure of the Ems estuary food web by applying Input Method balancing in Ecological Network Analysis

Detailed food webs of the three main Ems estuary reaches (Lower Reaches/LR, Middle Reaches/MR and Dollard/DO) representing the 1975–1980 period, were used for explorations. The effects of turbidity and organic waste were explored for ∼1955 (waste loads and low suspended matter) and ∼2005 (no waste loads and high suspended matter) by applying the Input Method-based balancing as part of the Ecological Network Analysis (ENA) package to analyse food web carbon flows. The total phytoplankton primary production (sum of true phytoplankton and resuspended microphytobenthos) of the LR in 2005 is reduced by 56% compared to 1955. For MR and DO the primary production reduction over the same period is ∼70%. Expressed in tons carbon the 2005 total primary production (including microphytobenthos) of the entire estuary is 59% of that in 1955. In 2005 the total (all living compartments) estuarine biomass is 63% of that in 1955. The data suggest a further fast future biomass decline. Compared to 1955 the relative biomass changes of the living compartments are in 2005 −71.1% for LR, −66.7% for MR and −70% for the Dollard. Results are in line with independent monitoring. The biomass changes per species range for LR from −1.3% (microzooplankton) and −1.5% (intertidal bivalves) to −71.7% (pelagic bacteria), for MR from −15.3% (mesozooplankton, Sprattus sprattus, Clupea harengus) to −90.5% (pelagic bacteria) and for DO from −6.6% (Chelon labrosus) to −97.4% (pelagic bacteria). The relative mean total biomass changes caused by the sanitation of the organic waste loads are −1.5% for LR, −5.0% for MR and −12.5% for DO. The IM-based balancing results in an increasing ratio between detritivory and herbivory and increase of the carbon cycling. The effects are strongest for the LR. The described changes are driven by i) the combination of changed system boundary conditions and the species specific diets and ii) the absence of international political collaboration because of a disputed border that results in the absence of an internationally agreed integral solution via one master plan Ems estuary. The varying changes at the species level and the strong connection of pelagic and benthic systems in intertidal flat estuaries demand an integral approach for assessments and management.

Ecosystem attributes of trophic models before and after construction of artificial oyster reefs using Ecopath

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 11:111-127 (2019) - DOI: https://doi.org/10.3354/aei00284 Ecosystem attributes of trophic models before and after construction of artificial oyster reefs using Ecopath Min Xu1,2,3,6,7, Lu Qi4, Li-bing Zhang1,2,3, Tao Zhang1,2,3,*, Hong-sheng Yang1,2,3, Yun-ling Zhang5 1CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, PR China 2Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, PR China 3Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, PR China 4Ocean University of China, Qingdao 266100, PR China 5Hebei Provincial Research Institute for Engineering Technology of Coastal Ecology Rehabilitation, Tangshan 063610, PR China 6Present address: Key Laboratory of East China Sea and Oceanic Fishery Resources Exploitation, Ministry of Agriculture, Shanghai 200090, PR China 7Present address: East China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Shanghai 200090, PR China *Corresponding author: tzhang@qdio.ac.cn ABSTRACT: The deployment of artificial reefs (ARs) is currently an essential component of sea ranching practices in China due to extensive financial support from the government and private organizations. Blue Ocean Ltd. created a 30.65 km2 AR area covered by oysters in the eastern part of Laizhou Bay, Bohai Sea. It is important for the government and investors to understand and assess the current status of the AR ecosystem compared to the system status before AR deployment. We provide that assessment, including trophic interactions, energy flows, keystone species, ecosystem properties and fishing impacts, through a steady-state trophic flow model (Ecopath with Ecosim). The model estimated values of 4721.2 and 4697.276 t km-2 yr-1 for total system throughput and 534.74 and -519.9 t km-2 yr-1 for net system production before and after AR deployment, respectively. After AR deployment, sea cucumber and oyster showed the same trophic level (TL = 2.0) while veined whelk Rapana venosa had TL = 3.0. The mean TL of catches was 2.484 after AR deployment and the primary production required to support fisheries (PPR) was 1104 t km-2. Detritus production dominated over primary production and represented 73.82% (2530.82 t km-2) of total primary production required. The sea cucumber showed the lowest PPR/catch value (5.6) among functional groups, indicating that fishing catch biomasses were close to primary production values. The total primary production to total respiration and total primary production to total biomass ratios showed higher system maturity after AR deployment. The trophic flow diagram showed 1 grazing and 2 detritus food chains. Pelagic and bottom fish and different benthic organisms, including large crustaceans and zoobenthos, were the dominant community before AR deployment. Zoobenthos was the key functional group, followed by large crustaceans and Gobiidae, which were the most important prey for top predators after AR deployment. We draw the following conclusions for the management of this area: (1) AR deployment contributes to the maturity of the improved ecosystem; (2) the artificial oyster system is similar to a natural reef system; (3) the enhancement and release of benthic animals in the AR area benefit the ecosystem; and (4) low TL catches do not cause the system to collapse. KEY WORDS: Ecopath model · Artificial oyster reef · Apostichopus japonicus · Rapana venosa · Ecosystem properties · Sea ranching Full text in pdf format Supplementary material PreviousNextCite this article as: Xu M, Qi L, Zhang Lb, Zhang T, Yang Hs, Zhang Yl (2019) Ecosystem attributes of trophic models before and after construction of artificial oyster reefs using Ecopath. Aquacult Environ Interact 11:111-127. https://doi.org/10.3354/aei00284 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 11. Online publication date: March 14, 2019 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2019 Inter-Research.

Constructing the Microbial Association Network from Large-Scale Time Series Data Using Granger Causality.

The increasing availability of large-scale time series data allows the inference of microbial community dynamics by association network analysis. However, correlation-based association network analyses are noninformative of causal, mediating and time-dependent relationships between microbial community functional factors. To address this insufficiency, we introduced the Granger causality model to the analysis of a recent marine microbial time series dataset. We systematically constructed a directed acyclic network, representing both internal and external causal relationships among the microbial and environmental factors. We further optimized the network by removing false causal associations using the conditional Granger causality. The final network was visualized as a Granger graph, which was analyzed to identify causal relationships driven by key functional operators in the environment, such as Gammaproteobacteria, which was Granger caused by total organic nitrogen and primary production (p < 0.05 and Q < 0.05).

Pelagic contribution to gross primary production dynamics in shallow areas of York River, VA, U.S.A.

AbstractThe pelagic contribution to total gross primary production (GPP) is often used to evaluate the assemblages of primary producers in shallow estuarine and coastal ecosystems that shift between benthic‐dominated and pelagic‐dominated status as a response to nutrient loading change. This study investigated the spatial and temporal variability of the pelagic contribution to ecosystem GPP for the years 2003–2015 in shallow areas of the York River. The monthly average values of ecosystem GPP and pelagic GPP were estimated by using 15‐min observational data of dissolved oxygen and chlorophyll a, respectively. A larger pelagic contribution, generally, corresponded to a higher pelagic GPP, while pelagic GPP showed significant positive correlations to riverine discharge and total nitrogen loading at mesohaline and polyhaline stations. The interannual variability in benthic GPP (ecosystem GPP – pelagic GPP), however, exhibited a non‐monotonic relationship to the increase in pelagic GPP. A conceptual model with four ecosystem stages in response to nutrient loading changes is proposed based on changes in the relationship between benthic GPP and pelagic GPP, and that between pelagic contribution and pelagic GPP. The model can explain the different responses of an ecosystem to nutrient loading observed in various estuaries and can be used to evaluate the status of an ecosystem undergoing the eutrophication/oligotrophication process. The stages of York River ecosystems during the study period were quantitatively examined. Results suggest that benthic GPP shows negative correlations to pelagic GPP in the downstream York River over most months of the year, indicating a gradual degradation of the benthic community.

Impact of spatial variations in water quality and hydrological factors on the food-web structure in urban aquatic environments

Global aquatic ecosystems are essential to human existence and have deteriorated seriously in recent years. Understanding the influence mechanism of habitat variation on the structure of the food-web allows the effective recovery of the health of degraded ecosystems. Whereas most previous studies focused on the selection of driving habitat factors, the impact of habitat variation on the food-web structure was rarely studied, resulting in the low success rate of ecosystem restoration projects globally. This paper presents a framework for exploring the effects of spatial variations in water quality and hydrological habitat factors on the food-web structure in city waters. Indices for the evaluation of the food-web structure are first determined by integrating model-parameter extraction via literature refinement. The key water quality and hydrological factors are then determined by coupling canonical correspondence analysis with partial least squares regression. Their spatial variation is investigated using spatial autocorrelation. Finally, fuzzy clustering is applied to analyze the influence of the spatial variations in water quality and hydrological factors on the food-web structure. The results obtained in Ji'nan, the pilot city of water ecological civilization in China, show that the Shannon diversity index, connectance index, omnivory index, and the ratio of total primary production to the total respiration are important indicators of food-web structural change. They show that the driving factors affecting the aquatic food-web structure in Ji'nan are hydrological factors (e.g., river width, water depth, and stream flow), physical aspects of water quality (e.g., air temperature, water temperature, electrical conductivity, and transparency), and chemical aspects (e.g., potassium, dissolved oxygen, calcium, and total hardness). They also show that the stability of the food-web is more prone to spatial variations in water quality than in hydrological factors. Higher electrical conductivity, potassium, total hardness, and air temperature lead to deteriorated food-web structures, whereas better transparency improves structure and stability. We found that water and air temperature are the most important factors in the spatial variation of the food-web structure in the study area, followed by total hardness. Transparency is the least important factor. Large disparities and varied spatial distributions exist in the driving effects of water quality and hydrological factors across regions attributable to differences in geographical environments, water salinity (fresh vs. sea water), and environmental factors (e.g., water pollution). The above methods and results serve as a theoretical and scientific basis for a high success rate of aquatic ecosystem restoration projects in the study area and other cities worldwide.

青藏高原两种植被类型净初级生产力与气候因素的关系及周转值分析

PDF HTML阅读 XML下载 导出引用 引用提醒 青藏高原两种植被类型净初级生产力与气候因素的关系及周转值分析 DOI: 10.5846/stxb201808301852 作者: 作者单位: 中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所,中国科学院西北高原生物研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41730752，31700395，31770532，31400483）；海南州小流域的综合治理及示范（2019-ST-152） The response of net primary productivity of two different vegetation types to climatic factors and root turnover analysis on the Qinghai-Tibet Plateau Author: Affiliation: Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology,Northwest Plateau Institute of Biology Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:基于2008-2016年青海海北站9年净初级生产力及气候因子监测数据，分析了青藏高原高寒小嵩草草甸和高寒金露梅灌丛两种植被净初级生产力年际动态，并探讨了气候因子对其影响及其不同土层深度根系周转值特征。结果表明：（1）年际尺度上，小嵩草草甸地上净初级生产力表现为显著增加趋势，增幅为7.02 g m-2 a-1，而金露梅灌丛地上净初级生产力相对较为稳定；对于其地下净初级生产力和总生产力，小嵩草草甸和金露梅灌丛均表现为增加趋势（P > 0.05），9年间小嵩草草甸地上、地下和总净初级生产力平均值分别为（217.55±9.95）、（1882.75±161.33）g m-2 a-1和（2100.30±163.38）g m-2 a-1，金露梅灌丛地上、地下和总净初级生产力9年间平均值分别为（256.27±11.4）、（1614.31±173.03）g m-2 a-1和（1870.58±177.93）g m-2 a-1。（2）不同植被类型地上净初级生产力对气候因素响应不同，金露梅灌丛地上净初级生产力主要受温度影响，而温度对小嵩草草甸地上净初级生产力无显著影响。此外，降水不是限制高寒生态系统草地地上净初级生产力主要因子，相比于降水影响，高寒生态系统地上净初级生产力更受温度调控。（3）年均温和年降水对金露梅灌丛和小嵩草草甸地下净初级生产力均无显著影响（P > 0.05），表明高寒生态系统，其地下生产力受外界气候条件变化影响微弱，是一个稳定的碳库。（4）两种植被类型其根系周转值均随着土壤深度的增加呈逐渐增加趋势，且高寒灌丛根系周转值明显高于高寒草甸根系周转值。研究表明，在全球气候变暖背景下将会增加金露梅灌丛地上净初级生产力，而对小嵩草草甸地上净初级生产力无显著影响。 Abstract:Based on nine years (from 2008 to 2016) of monitoring data of net primary productivity (NPP) and climatic factors at Haibei Station, the interannual NPP dynamics of alpine Kobresia pygmaea meadow and alpine Potentilla fruticosa shrubs were analyzed. In addition, the effects of climatic factors on NPP and the characteristics of root turnover across different soil layers were also assessed. The results showed that (1) on an interannual scale, the aboveground net primary productivity (ANPP) of Kobresia pygmaea meadow showed a significant increasing trend (7.02 g m-2 a-1), but the ANPP of Potentilla fruticosa shrubs remained relatively stable. Both belowground net primary productivity (BNPP) and total net primary productivity (NPP) of the two vegetation types showed a slight increase (P>0.05). The average ANPP, BNPP, and NPP for the Kobresia pygmaea meadow were (217.55±9.95) g/m2, (1882.75±161.33) g/m2 and (2100.30±163.38) g/m2, respectively. The average ANPP, BNPP, and NPP for Potentilla fruticosa shrubs were (256.27 ±11.4) g/m2, (1614.31 ±173.03) g/m2, and (1870.58±177.93) g/m2, respectively. (2) The ANPP of the vegetation types responded differently to climatic factors. The mean annual air temperature had a significant effect on ANPP for Potentilla fruticosa shrubs, but no significant impact on the ANPP of Kobresia pygmaea meadow. Furthermore, precipitation was not a key factor limiting the NPP of grassland in alpine ecosystems; temperature exerted a stronger effect on the ANPP of alpine ecosystems compared with precipitation. (3) The mean annual air temperature and mean annual precipitation showed no notable effect on the BNPP, indicating that the BNPP was less affected by external climatic factors than the ANPP. (4) Root turnover increased with soil depth and the root turnover of Potentilla fruticosa shrubs was higher than that of Kobresia pygmaea meadow. Our study implies that the ANPP of Potentilla fruticosa shrubs will increase with climate change, but no significant change is expected for the ANPP of Kobresia pygmaea meadow. 参考文献 相似文献 引证文献

Influence of precipitation on CO2 soil emission in pine forests of the Central Siberia boreal zone

Boreal forests in Siberia cover more than 70% of the area of this region. Due to climate change these ecosystems represent a very sensitive and significant source of carbon. In the forests, the total ecosystem respiration tends to be dominated by the soil respiration, which accounts for approximately 70% of this large flux. Global models predict that the soil respiration will increase more than the total net primary productivity in response to climate warming and increasing precipitation. In consequence, the terrestrial carbon sink is expected to decline. However, for the Siberian boreal forest there is still a gap in understanding of the future response of soil emission to drought or overprecipitation conditions. In our study we estimate how various moisture conditions could change soil emission in the boreal zone. From field observation data we find optimal soil moisture conditions. The highest dependence between the soil temperature and soil emission rates has been obtained under the optimal soil moisture conditions.

Grazing intensity determines pasture spatial heterogeneity and productivity in an integrated crop‐livestock system

AbstractSpatial heterogeneity is a property of natural ecosystems. Integrated crop‐livestock systems (ICLS) aim to mimic natural ecosystem functions as pillars of sustainable intensification, and grazing is a process that potentially affects spatial heterogeneity. Then, we investigated the effect of different grazing intensities, defined according to a range of sward heights (intensive grazing, 10 cm; moderate grazing, 20 cm; moderate‐light grazing, 30 cm; light grazing, 40 cm; and ungrazed), on the spatial heterogeneity and biomass productivity of mixed Italian ryegrass (Lolium multiflorum Lam.) and black oat (Avena strigosa Schreb.) pastures. The mixture was grazed by steers under continuous variable stocking, using put‐and‐take animals to maintain targeted sward heights. The pasture was in rotation with soybean in an integrated crop‐livestock system for 15 years. Data concerns pasture phase on the 15th rotation cycle. Cattle grazing at moderate to light intensities increased pasture spatial heterogeneity and total aboveground primary productivity, while intensive grazing led to homogeneous overgrazed canopies with frequent bare soil patches. Pre‐grazing sward structure suggests that the summer crop rotation buffers the contrasts created by grazing at different intensities. This study suggests that moderate to light grazing intensities increase pasture productive efficiency and create more heterogeneous canopies in ICLS, while intensive grazing should be avoided.

An approach towards quantification of ecosystem trophic status and health through ecological network analysis applied in Hooghly-Matla estuarine system, India

The structure and function of food web of Hooghly-Matla estuarine system (HMES) including Sundarban mangroves is studied to assess the health of the system. HMES, provides shelter and make a home to many economically important shell and fin fishes. This estuary is exposed to various threats such as increasing salinity, deterioration of soil fertility and productivity, pollution and loss of biodiversity. Ecological network analysis (ENA) is applied for the HMES to model the trophic flows in 22 ecological compartments using Ecopath (a software for network analysis), integrating ecological data for the 2013–2015. ENA is performed, including a set of indices, keystoneness and trophic spectrum analysis to describe the contribution of the 22 groups to the HMES functioning. Results show that 22 compartments of the HMES including primary producers (trophic level TL 1) to the top consumers (elasmobranch, TL 3.5), the ecotrophic efficiency ranges from 0.016 to 0.989. Small demersal fishes, prawns, shrimps and crabs are the most exploited groups of this ecosystem. Herbivory and detritivory ratio is 1:1 indicating relative absence of top predators and low maturation level. Maturity of the system, organization, relative order and disorder within the system, diversity of flow of material among compartments and overhead of the system has been assessed. Biomass over Total system throughput ratio (TB/TST), Total primary production over total respiration ratio (TPP/TR), Total primary production over biomass (TPP/TB) and system omnivory index (SOI) indicate the moderate maturity level of the system. The HMES trophic network has a moderate recycling level (FCI = 12.99%), a high total system throughput (TST = 22976.03 tonnes km−2 yr−1) and a low ascendency (A = 25799 tonnes km−2 yr−1), but a relatively low connectance (CI = 0.27), high internal relative ascendency (A = 29.6%) and a high omnivory index (OI = 0.203), indicating that this estuary is immature but relatively organized and complex, with strong production. HMES has some unique features in comparison to similar functioning geographically close estuaries or estuaries with similar environmental characteristics. System robustness and exergy are also estimated to assess ecosystem health and compared with other tropical systems. From a holistic point of view, present study conveys fundamental information and categorizes the status of the system.

Mapping and comparing ecosystem service indicators of global climate regulation in Schleswig-Holstein, Northern Germany

Estimating and mapping Ecosystem Services (ESS) is a primary basis for reasonable ecosystem managing policies. Assessing ESS and optimising the accuracy of ESS assessment is relevant to identify suitable indicators. This study aims to gain a better understanding of global climate regulation service assessments resulting from the application of several indicators that have been derived based on Co-Ordination of INformation on the Environment (CORINE) land cover classes. Therefore, 17 CORINE land cover classes were used to evaluate their effects on the distributions of the annual total Gross Primary Production (GPP), the annual total Net Primary Production (NPP), Soil Organic Carbon (SOC) and Carbon Stocks (CS) in the German federal state Schleswig-Holstein. In addition to the spatial distributions, correlations of distinct quantitative indicators (annual total GPP, annual total NPP, SOC and CS) and a qualitative indicator of Global Climate Regulation (GCR) derived from the ecosystem service matrix method were analysed. We found that qualitative and quantitative indicators of the global climate regulation service had significant correlations based on the comparison analysis of all indicators. The differences in mapping the service with the five indicators resulted from different strategies of the reclassified land covers. In addition, the distinct areas among the land cover classes contributed to the differences in global climate regulation mapping. The interrelations among the annual total GPP, the annual total NPP and statistical data on total harvest of different agricultural products also correlated significantly. Based on the results, GPP, NPP, SOC, CS and GCR are available indicators of global climate regulation service in Schleswig-Holstein. Nevertheless, we especially recommend CS as the indicator owning to its high accuracy in assessments. The indicators and methodology in our study can also be applied to other researches targeted with evaluating global climate regulation service.

Structural and functional analyses of Rubisco from arctic diatom species reveal unusual posttranslational modifications

The catalytic performance of the major CO2-assimilating enzyme, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), restricts photosynthetic productivity. Natural diversity in the catalytic properties of Rubisco indicates possibilities for improvement. Oceanic phytoplankton contain some of the most efficient Rubisco enzymes, and diatoms in particular are responsible for a significant proportion of total marine primary production as well as being a major source of CO2 sequestration in polar cold waters. Until now, the biochemical properties and three-dimensional structures of Rubisco from diatoms were unknown. Here, diatoms from arctic waters were collected, cultivated, and analyzed for their CO2-fixing capability. We characterized the kinetic properties of five and determined the crystal structures of four Rubiscos selected for their high CO2-fixing efficiency. The DNA sequences of the rbcL and rbcS genes of the selected diatoms were similar, reflecting their close phylogenetic relationship. The Vmax and Km for the oxygenase and carboxylase activities at 25 °C and the specificity factors (Sc/o) at 15, 25, and 35 °C were determined. The Sc/o values were high, approaching those of mono- and dicot plants, thus exhibiting good selectivity for CO2 relative to O2 Structurally, diatom Rubiscos belong to form I C/D, containing small subunits characterized by a short βA-βB loop and a C-terminal extension that forms a β-hairpin structure (βE-βF loop). Of note, the diatom Rubiscos featured a number of posttranslational modifications of the large subunit, including 4-hydroxyproline, β-hydroxyleucine, hydroxylated and nitrosylated cysteine, mono- and dihydroxylated lysine, and trimethylated lysine. Our studies suggest adaptation toward achieving efficient CO2 fixation in arctic diatom Rubiscos.

Modelling N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fixation related to &amp;lt;i&amp;gt;Trichodesmium&amp;lt;/i&amp;gt; sp.: driving processes and impacts on primary production in the tropical Pacific Ocean

Abstract. Dinitrogen fixation is now recognized as one of the major sources of bio-available nitrogen in the ocean. Thus, N2 fixation sustains a significant part of the global primary production by supplying the most common limiting nutrient for phytoplankton growth. The “Oligotrophy to UlTra-oligotrophy PACific Experiment” (OUTPACE) improved the data coverage of the western tropical South Pacific, an area recently recognized as a hotspot of N2 fixation. This new development leads us to develop and test an explicit N2 fixation formulation based on the Trichodesmium physiology (the most studied nitrogen fixer) within a 3-D coupled dynamical–biogeochemical model (ROMS-PISCES). We performed a climatological numerical simulation that is able to reproduce the main physical (e.g. sea surface temperature) and biogeochemical patterns (nutrient and chlorophyll concentrations, as well as N2 fixation) in the tropical Pacific. This simulation displayed a Trichodesmium regional distribution that extends from 150∘ E to 120∘ W in the south tropical Pacific, and from 120∘ E to 140∘ W in the north tropical Pacific. The local simulated maximuma were found around islands (Hawaii, Fiji, Samoa, New Caledonia, Vanuatu). We assessed that 15 % of the total primary production may be due to Trichodesmium in the low-nutrient low-chlorophyll regions (LNLC) of the tropical Pacific. Comparison between our explicit and the often used (in biogeochemical models) implicit parameterization of N2 fixation showed that the latter leads to an underestimation of N2 fixation rates by about 25 % in LNLC regions. Finally, we established that iron fluxes from island sediments control the spatial distribution of Trichodesmium biomasses in the western tropical South Pacific. Note, this last result does not take into account the iron supply from rivers and hydrothermal sources, which may well be of importance in a region known for its strong precipitation rates and volcanic activity.

Do microplastics affect marine ecosystem productivity?

Marine and coastal ecosystems are among the largest contributors to the Earth's productivity. Experimental studies have shown negative impacts of microplastics on individual algae or zooplankton organisms. Consequently, primary and secondary productivity may be negatively affected as well. In this study we attempted to estimate the impacts on productivity at ecosystem level based on reported laboratory findings with a modelling approach, using our biogeochemical model for the North Sea (Delft3D-GEM). Although the model predicted that microplastics do not affect the total primary or secondary production of the North Sea as a whole, the spatial patterns of secondary production were altered, showing local changes of ±10%. However, relevant field data on microplastics are scarce, and strong assumptions were required to include the plastic concentrations and their impacts under field conditions into the model. These assumptions reveal the main knowledge gaps that have to be resolved to improve the first estimate above.

Net primary production in plantations of Pinus taeda and Eucalyptus cloeziana compared with a mountain miombo woodland in Mozambique

Planting monocultures of fast-growing non-native (exotic) species is one way to slow or reverse deforestation and forest degradation in tropical zones. This study compared the effects on total net primary production (NPP) of first-rotation monoculture (34-year-old) plantations of Pinus taeda and Eucalyptus cloeziana and adjacent mountain miombo woodland in Mozambique. Total NPP was defined as the sum of annual carbon (C) sequestration in total aboveground tree biomass, belowground coarse root biomass, fine roots (≤2 mm) and fine litterfall.Field measurements were conducted over one year in three 30 m × 30 m permanent sampling plots for each forest type and involved monitoring litterfall and fine root production using in-growth cores and stem diameter growth. Carbon increment in aboveground tree biomass and belowground coarse root biomass was determined using allometric equations, for P. taeda, E. cloeziana, and root-to-shoot ratio, for miombo woodland.Major findings were that total NPP in P. taeda (14.1 Mg C ha−1 yr−1) and E. cloeziana (19.7 Mg C ha−1 yr−1) stands was significantly higher than in miombo woodland stands (5.9 Mg C ha−1 yr−1). These differences were largely attributable to lower basal area and presumably lower leaf biomass in miombo stands. There were several indications that the miombo stands studied had been degraded by selective cutting and other forms of use of forest resources. The difference in total NPP was also reflected in differences in patterns of C sequestration. Carbon in litterfall was the largest component of total NPP in miombo stands (41%), whereas C increment in aboveground tree biomass was the largest component of total NPP in plantation stands (44% in P. taeda and 51% in E. cloeziana).If the aim of forest management is to increase NPP and C sequestration in biomass of degraded miombo stands, our results indicate that replacement with plantations of P. taeda or E. cloeziana can be a useful management option, provided that the plantations are protected from anthropogenic disturbances, particularly fire. However, this aim needs to be balanced against other environmental aims and the socio-economic needs of local communities, since miombo woodland provides a wide range of unique economic, social and ecological benefits.

Structure of the Biotic Component in the Rybinsk Reservoir Ecosystem: Importance of Heterotrophic Bacteria (Review)

The total biomass of the biotic component of the ecosystem has been determined and the contribution of the main ecological groups—autotrophic and heterotrophic organisms from different habitats—to its formation has been estimated in a large plain meso-eutrophic reservoir (Rybinsk Reservoir, Upper Volga). Particular attention is paid to the role of heterotrophic bacteria in the structure and functioning of the biota in the reservoir. The total biomass of the biotic component of the ecosystem is 71536 t C, which is 5.2% of the total organic carbon in the reservoir. Higher aquatic plants make the largest contribution to the formation of the biomass in the reservoir. Their biomass, including epiphyton, was 6.0 and 1.9 times larger than the biomass of plankton and benthos, respectively. Heterotrophic bacteria, most of which inhabit bottom sediments, rank second in respect to their contribution to the total biomass. The comparison of the total primary production of all phototrophic organisms and the carbon demand of heterotrophic bacteria indicates the importance of allochthonous organic matter in the functioning of the reservoir ecosystem.

Linkage Between Dinitrogen Fixation and Primary Production in the Oligotrophic South Pacific Ocean

AbstractThe import of nitrogen via dinitrogen fixation supports primary production, particularly in the oligotrophic ocean; however, to what extent dinitrogen fixation influences primary production, and the role of specific types of diazotrophs, remains poorly understood. We examined the relationship between primary production and dinitrogen fixation together with diazotroph community structure in the oligotrophic western and eastern South Pacific Ocean and found that dinitrogen fixation was higher than nitrate‐based new production. Primary production increased in the middle of the western subtropical region, where the cyanobacterium Trichodesmium dominated the diazotroph community and accounted for up to 7.8% of the phytoplankton community, and the abundance of other phytoplankton taxa (especially Prochlorococcus) was high. These results suggest that regenerated production was enhanced by nitrogen released from Trichodesmium and that carbon fixation by Trichodesmium also contributed significantly to total primary production. Although volumetric dinitrogen fixation was comparable between the western and eastern subtropical regions, primary production in the western waters was more than twice as high as that in the eastern waters, where UCYN‐A1 (photoheterotroph) and heterotrophic bacteria were the dominant diazotrophs. This suggests that dinitrogen fixed by these diazotrophs contributed relatively little to primary production of the wider community, and there was limited carbon fixation by these diazotrophs. Hence, we document how the community composition of diazotrophs in the field can be reflected in how much nitrogen becomes available to the wider phytoplankton community and in how much autotrophic diazotrophs themselves fix carbon and thereby influences the magnitude of local primary production.

New to total primary production ratio (f-ratio) in the Bay of Bengal using isotopic composition of suspended particulate organic carbon and nitrogen

Variations in the content and isotopic compositions of carbon and nitrogen in the suspended particulate matter were analysed to identify sources of nutrients and compute f-ratios (ratio of new production to primary production) in the Bay of Bengal (BoB) during the post-monsoon period (November-December 2013). Remote sensing data during our observation period indicated that the study region encompassed meso-scale cyclonic (CE) and anticyclonic eddies (ACE) and was influenced by tropical cyclone Madi between 6 and 12 December 2013. Relatively higher concentrations of nitrate were observed in the CE and in the cyclone-influenced region compared to that in the ACE. Variable concentrations of nutrients controlled the size distributions of phytoplankton. Overall, the picoplankton population dominated, but the contributions of micro- and nano-plankton populations were significantly higher in the CE region because of higher concentration of nutrients. The δ13Csus, C:N molar ratios and C: Chl-a ratios suggested that suspended matter is mainly contributed by in situ processes during the study period. The δ15Nsus of suspended matter suggested that vertical supply of nutrients brought from subsurface water supported new production in the CE and cyclone-influenced regions, whereas regenerated nutrients supported phytoplankton production in the ACE. The f-ratios computed using δ15Nsus and depth of nitracline were high in the CE (0.41 ± 0.14) and cyclone-influenced region (0.54 ± 0.12) and lower in the ACE (0.27 ± 0.06). This study revealed that the meso-scale CEs are more important in enhancing exportable production in the BoB. As more than 30 CEs form annually in the BoB, their impact on basin-wide new production and export flux to the deeper ocean must be evaluated using both observations and high-resolution models.

Strusture, biomass and production of the biotic component of the ecosystem of an growing eutrophic reservoir

Using our own data and data from the literature, we assessed the total biomass of the biotic component of the ecosystem of the Ivankovo Reservoir (Upper Volga, Russia), a eutrophic reservoir which is becoming overgrown with macrophytes. The biotic component of freshwater ecosystems is formed by communities of multicellular and unicellular organisms and viruses in the water layer (plankton) and bottom sediments (benthos) and also macrophytes and autotrophic and heterotrophic organisms growing on their surface (epiphyton). The biomass of the biotic component of the Ivankovo Reservoir equaled 39,853 tons С. Plankton, benthos and macrophytes with epiphyton equaled 3.6%, 41.6% and 54.8% of the total biomass respectively. We determined the contribution of higher aquatic plants, algae, cyanobacteria, heterotrophic bacteria, viruses, protozoans, multicellular invertebrates and fish to the formation of total biomass. The largest share was taken up by higher aquatic plants (54.5%). The second largest share was taken by heterotrophic bacteria (37.4%), most of which live in the bottom sediments. The high concentration of bacteria and invertebrates in the bottom sediments indicate significant provision of the organic substrates from the water column. The biomass of fish, the highest trophic link in the reservoir, equaled 15.0% of the biomass of their potential food substrates, invertebrate animals, and 0.7% of the total biomass of the biotic component. The greater part of the autochthonous organic compound in the reservoir is formed as a result of activity of phytoplankton, which provides 69.4% of total primary production of macrophytes, phytoepiphyton, phytoplankton and phytobenthos. The total primary production during the vegetation period was approximately forty times higher than the annual production of the fish. Currently, the share in the phytoplankton of large colonial cyanobacteria not consumed by zooplankton, the share of non-heterocystic species of cyanobacteria capable of heterotrophic feeding and the share of mixotrophic flagellates is increasing. Eutrophication of the reservoir is significantly stimulated by the development of macrophytes, and, presumably, the contribution of macrophytes to the total primary production of the reservoir will continue to increase.

Fire in sub‐Saharan Africa: The fuel, cure and connectivity hypothesis

AbstractAimPast analyses of satellite‐based fire activity in tropical savannas support the intermediate fire–productivity hypothesis (IFP), which posits a close correlation with estimates of total net primary productivity in drier savannas and declines towards the extremes. However, these analyses ignore the distinct roles played by herbaceous and woody vegetation in fire ignition and spread. We hypothesize that, as herbaceous vegetation provides the primary fuel, fire activity in African savannas is asymptotically correlated with herbaceous production. Conversely, woody production affects fires indirectly through effects on herbaceous production and its connectivity. In contrast to the IFP, we propose the fuel, cure and connectivity (FCC) conceptual model for tropical fire activity. The FCC model makes explicit the distinct role of herbaceous and woody fuels, avoiding the confounding interpretation of the role of total production, while providing opportunities to quantify fuel curability, effects of trees on herbaceous fuel growth and connectivity, and human management.LocationSub‐Saharan Africa (SSA).Time period2003–2015.Major taxa studiedWoody and herbaceous vegetation.MethodsWe used boosted regression tree analysis to test competing models explaining fire activity: (a) aggregate fuel loads; and (b) partitioned woody and herbaceous fuel loads; both derived from MODIS leaf area index.ResultsHerbaceous fuel load was consistently most influential, providing more explanatory power than overall biomass in fire activity. Fuel curability rated second, then human population density (HPD), and woody biomass was least important. We observed an asymptotic relationship between herbaceous fuel load and fire activity consistent with the FCC model; trees promote fires at low densites but suppress fires at higher densities; fires were rare in wetter regions, emphasizing the need for fuel to cure; and fires were concentrated in areas of low human population, underscoring the crucial role of land management.ConclusionsThe proposed FCC framework provides a more nuanced understanding of fire activity in tropical ecosystems, where herbaceous biomass is the key determinant of fire activity.

Characteristics of CO2 Flux in a Mature Apple (Malus demestica) Orchard Ecosystem on the Loess Plateau

Apples (Malus demestica) in the Loess Plateau region are grown in the largest apple orchards in the world and China, playing an important role in the improvement of the ecological environment. However, there is little research on the scale of the ecological system of the apple orchard in the Loess Plateau region. In this study, the CO2 flux of a mature apple orchard in the Loess Plateau region was observed using an eddy covariance technique in the Shannxi Province. Based on the observation data sets observed from January 2016 to December 2016, a quantitative analysis of the apple orchard net ecosystem exchange (NEE), ecosystem respiration (Reco), total ecosystem primary productivity (GPP) changes at different time scales, changes in main meteorological factors, the effects of soil temperature (Ts) and air temperature (Ta) at different levels, and PAR on NEE were discussed. The results showed that during the study period, the apple orchard ecosystem NEE monthly totals were positive (as a carbon source) in the non-growing season in December, January, February and March, were negative (a carbon sink) in the growing season from April to November, and functioned as a strong carbon sink year round. The maximum peak NEE (absolute value) monthly average daily change appeared in August[-17.08 μmol ·(m2 ·s)-1], and the smallest peak appeared in November[-4.47 μmol ·(m2 ·s)-1] during the growing season. The NEE monthly average daily change value during the non-growing season is very weak, though the change is not obvious. GPP, Reco, and NEE maximum daily total values were 11.12, 5.04, and -7.34 g ·(m2 ·d)-1, respectively. GPP, Reco, and NEE maximum monthly total values were 238.97, 105.38, and -144.44 g ·(m2 ·month)-1, respectively, as GPP and NEE maintained high cumulative values that were relatively stable from May through August. The annual GPP, Reco, and NEE were 1223.2, 525.2, and -698.0 g ·(m2 ·a)-1. The observations show that the mature apple orchard ecosystem in the Chinese Loess Plateau has a relatively high carbon sequestration capacity. Nighttime ecosystem respiration Reco.n was positively correlated with the soil temperature and air temperature at different levels, and the correlation coefficients were Ts-5 cm > Ts-10 cm > Ta-4 m > Ta-8 m, The photosynthetic active radiation (PAR) can explain more than 80% of the daytime NEE changes.