Total Primary Production Research Articles

Dynamics of transparent exopolymer particles (TEP) during the VAHINE mesocosm experiment in the New Caledonian lagoon

Abstract. In the marine environment, transparent exopolymeric particles (TEP) produced from abiotic and biotic sources link the particulate and dissolved carbon pools and are essential vectors enhancing vertical carbon flux. We characterized spatial and temporal dynamics of TEP during the VAHINE experiment that investigated the fate of diazotroph-derived nitrogen and carbon in three replicate dissolved inorganic phosphorus (DIP)-fertilized 50 m3 enclosures in the oligotrophic New Caledonian lagoon. During the 23 days of the experiment, we did not observe any depth-dependent changes in TEP concentrations in the three sampled depths (1, 6, 12 m). TEP carbon (TEP-C) content averaged 28.9 ± 9.3 and 27.0 ± 7.2 % of total organic carbon (TOC) in the mesocosms and surrounding lagoon respectively and was strongly and positively coupled with TOC during P2 (i.e., days 15–23). TEP concentrations in the mesocosms declined for the first 9 days after DIP fertilization (P1 = days 5–14) and then gradually increased during the second phase. Temporal changes in TEP concentrations paralleled the growth and mortality rates of the diatom–diazotroph association of Rhizosolenia and Richelia that predominated the diazotroph community during P1. By P2, increasing total primary and heterotrophic bacterial production consumed the supplemented P and reduced availability of DIP. For this period, TEP concentrations were negatively correlated with DIP availability and turnover time of DIP (TDIP), while positively associated with enhanced alkaline phosphatase activity (APA) that occurs when the microbial populations are P stressed. During P2, increasing bacterial production (BP) was positively correlated with higher TEP concentrations, which were also coupled with the increased growth rates and aggregation of the unicellular cyanobacterial Group C (UCYN-C) diazotrophs that bloomed during this period. We conclude that the composite processes responsible for the formation and breakdown of TEP yielded a relatively stable TEP pool available as both a carbon source and facilitating aggregation and flux throughout the experiment. TEP were probably mostly influenced by abiotic physical processes during P1, while biological activity (BP, diazotrophic growth and aggregation, export production) mainly impacted TEP concentrations during P2 when DIP availability was limited.

The fascinating diatom frustule—can it play a role for attenuation of UV radiation?

Diatoms are ubiquitous organisms in aquatic environments and are estimated to be responsible for 20–25 % of the total global primary production. A unique feature of diatoms is the silica wall, called the frustule. The frustule is characterized by species-specific intricate nanopatterning in the same size range as wavelengths of visible and ultraviolet (UV) light. This has prompted research into the possible role of the frustule in mediating light for the diatoms’ photosynthesis as well as into possible photonic applications of the diatom frustule. One of the possible biological roles, as well as area of potential application, is UV protection. In this review, we explore the possible adaptive value of the silica frustule with focus on research on the effect of UV radiation on diatoms. We also explore the possible effect of the frustules on UV radiation, from a theoretical, biological, and applied perspective, including recent experimental data on UV transmission of diatom frustules.

Empirical links between trace metal cycling and marine microbial ecology during a large perturbation to Earth's carbon cycle

Understanding the global redox state of the oceans and its cause-and-effect relationship with periods of widespread organic-carbon deposition is vital to interpretations of Earth's climatic and biotic feedbacks during periods of expanded oceanic oxygen deficiency. Here, we present a compilation of new and published data from an organic-rich locality within the proto-North Atlantic Ocean during the Cenomanian–Turonian boundary event that shows a dramatic drawdown of redox-sensitive trace elements. Iron geochemistry independently suggests euxinic deposition (i.e., anoxic and sulfidic bottom waters) for the entire section, thus confirming its potential as an archive of global marine metal inventories. In particular, depleted molybdenum (Mo) and vanadium (V) concentrations effectively record the global expansion of euxinic and oxygen-deficient but non-sulfidic waters, respectively. The V drawdown precedes the OAE, fingerprinting an expansion of oxygen deficiency prior to an expansion of euxinia. Molybdenum drawdown, in contrast, is delayed with respect to V and coincides with the onset of OAE2. Parallel lipid biomarker analyses provide evidence for significant and progressive reorganization of marine microbial ecology during the OAE in this region of the proto-North Atlantic, with the smallest relative eukaryotic contributions to total primary production occurring during metal-depleted intervals. This relationship may be related to decreasing supplies of enzymatically important trace elements. Similarly, box modeling suggests that oceanic drawdown of Mo may have approached levels capable of affecting marine nitrogen fixation. Predictions of possible nitrogen stress on eukaryotic production, locally and globally, are consistent with the low observed levels of Mo and a rise in 2-methylhopane index values during the peak of the OAE. At the same time, the environmental challenge presented by low dissolved oxygen and euxinia coincides with increased turnover rates of radiolarian clades, calcareous nanofossils, and foraminifera, suggesting that the temporal patterns of anoxia/euxinia and associated nutrient limitation may have contributed to the fabric of OAE2-related turnover.

Size-selective microzooplankton grazing on the phytoplankton in the Curonian Lagoon (SE Baltic Sea)

Summary Dilution experiments were performed to estimate phytoplankton growth and microzooplankton grazing rates at two sites: freshwater (Nida) and brackish water (Smiltyne) in the Curonian Lagoon (SE Baltic Sea). Using the size-fractionation approach and dilution experiments, we found that the microzooplankton community was able to remove up to 78% of nanophytoplankton (2–20 μm) standing stock and 130% of the total daily primary production in the brackish waters of the lagoon, and up to 83% of standing stock and 76% of the primary production of picophytoplankton (0.2–2 μm) in the freshwater part. The observed differences were attributed to the changes in ciliate community size and trophic structure, with larger nano-filterers (30–60 μm) dominating the brackish water assemblages and pico-nano filterers (

The contribution of trees and grasses to productivity of an Australian tropical savanna

Abstract. Savanna ecosystems cover 20 % of the global land surface and account for 25 % of global terrestrial carbon uptake. They support one fifth of the world's human population and are one of the most important ecosystems on our planet. Savanna productivity is a product of the interplay between trees and grass that co-dominate savanna landscapes and are maintained through interactions with climate and disturbance (fire, land use change, herbivory). In this study, we evaluate the temporally dynamic partitioning of overstory and understory carbon dioxide fluxes in Australian tropical savanna using overstory and understory eddy covariance measurements. Over a 2-year period (September 2012 to October 2014) the overall net ecosystem productivity (NEP) of the savanna was 506.2 (±22 SE) g C m−2 yr−1. The total gross primary productivity (GPP) was 2267.1 (±80 SE) g C m−2 yr−1, of which the understory contributed 32 %. The understory contribution was strongly seasonal, with most GPP occurring in the wet season (40 % of total ecosystem in the wet season and 18 % in the dry). This study is the first to elucidate the temporal dynamics of savanna understory and overstory carbon flux components explicitly using observational information. Understanding grass productivity is crucial for evaluating fuel loads, as is tree productivity for quantifying the tree carbon sink. This information will contribute to a significant refinement of the representation of savannas in models, as well as improved understanding of relative tree-grass productivity and competition for resources.

Estimating the production and mortality of fine roots using minirhizotrons in a Pinus densiflora forest in Gwangneung, Korea

The aim of this study was to estimate fine root production (FP) and fine root mortality (FM) at 0–10, 10–20, and 20–30 cm soil depths using minirhizotrons in a 75-year-old Pinus densiflora Sieb. et Zucc. forest located in Gwangneung, Korea. We developed the conversion factors (frame cm−2) of three soil depths (0.158 for 0–10 cm, 0.120 for 10–20 cm, and 0.131 for 20–30 cm) based on soil coring and minirhizotron data. FP and FM were estimated using conversion factors from March 26, 2013 to March 2, 2014. The annual FP and FM values at the 0–30 cm soil depth were 3200.2 and 2271.5 kg ha−1 yr −1, respectively. The FP estimate accounted for approximately 17 % of the total net primary production at the study site. FP was highest in summer (July 31–September 26), and FM was highest in autumn (September 27–November 29). FP was positively correlated with seasonal change in soil temperature, while FM was not related to that change. The seasonality of FP and FM might be linked to above-ground photosynthetic activity. Both FP and FM at the 0–10 cm depth were significantly higher than at 10–20 and 20–30 cm depths, and this resulted from the decrease in nutrient availability with increasing soil depth. The minirhizotron approach and conversion factors developed in this study will enable fast and accurate estimation of the fine root dynamics in P. densiflora forest ecosystems.

Importance of coastal primary production in the northern Baltic Sea.

In this study, we measured depth-dependent benthic microalgal primary production in a Bothnian Bay estuary to estimate the benthic contribution to total primary production. In addition, we compiled data on benthic microalgal primary production in the entire Baltic Sea. In the estuary, the benthic habitat contributed 17 % to the total annual primary production, and when upscaling our data to the entire Bothnian Bay, the corresponding value was 31 %. This estimated benthic share (31 %) is three times higher compared to past estimates of 10 %. The main reason for this discrepancy is the lack of data regarding benthic primary production in the northern Baltic Sea, but also that past studies overestimated the importance of pelagic primary production by not correcting for system-specific bathymetric variation. Our study thus highlights the importance of benthic communities for the northern Baltic Sea ecosystem in general and for future management strategies and ecosystem studies in particular.Electronic supplementary materialThe online version of this article (doi:10.1007/s13280-016-0778-5) contains supplementary material, which is available to authorized users.

Changing temperature response of respiration turns boreal forest from carbon sink into carbon source

Seventeen years (1997–2013) of carbon dioxide (CO2) fluxes were measured in a boreal forest stand in northern Sweden using the eddy covariance technique. During the measurement period the forest turned from a net carbon sink into a net carbon source. The net ecosystem exchange (NEE) was separated using values from periods of darkness into the gross components of total ecosystem respiration (TER) and gross primary productivity (GPP), which was calculated as GPP=−NEE+TER. From the gross components we could determine that an increase in TER during the autumn (September to end of November) and spring (March to end of May) periods resulted in the forest becoming a net source of CO2. We observed no increase in the GPP from the eddy covariance measurements. This was further supported by measurements of tree growth rings. The increased TER was attributed to a change in the forest’s temperature response at lower temperatures (−5 to 10°C) rather than to a temperature increase. This study shows that changes in ecosystem functioning can have a larger impact on the carbon balance than climate warming per se.

Canopy cover and anurans: nutrients are the most important predictor of growth and development

Bottom-up effects such as the availability of light and nutrients can have large impacts on primary producer quantity and quality, which is then translated into the growth and development of consumers. The use of “canopy cover” as a bottom-up predictive factor is a broad categorization, as canopy cover controls both the amount of light allowed into a pond and the nutrient load through leaf litter. To test how light and nutrients influence pond ecosystems, we manipulated inorganic nutrients and light in a 2 × 3 full-factorial, large-scale mesocosm experiment. Larval American Bullfrogs (Lithobates catesbeianus (Shaw, 1802)) were reared for 6 weeks at low densities and then assessed for development, growth, and survival at the end of the experiment. We also collected weekly samples of potential food resources (phytoplankton and periphyton) for the estimation of algal production and stoichiometric quality (carbon:nitrogen:phosphorus). Light had strong effects on food resource quality; however, resource quality did not significantly predict tadpole growth or development. Instead, nutrients seemed to be the most important factor as a stimulator of total algal primary production and some unknown pathway, which in turn affected tadpole development. Ours is the first study to investigate canopy cover using a comprehensive causal model, and our results suggest in regards to tadpole growth and development, canopy cover is important mainly as a source of nutrients to ponds.

Cacao Cultivation under Diverse Shade Tree Cover Allows High Carbon Storage and Sequestration without Yield Losses.

One of the main drivers of tropical forest loss is their conversion to oil palm, soy or cacao plantations with low biodiversity and greatly reduced carbon storage. Southeast Asian cacao plantations are often established under shade tree cover, but are later converted to non-shaded monocultures to avoid resource competition. We compared three co-occurring cacao cultivation systems (3 replicate stands each) with different shade intensity (non-shaded monoculture, cacao with the legume Gliricidia sepium shade trees, and cacao with several shade tree species) in Sulawesi (Indonesia) with respect to above- and belowground biomass and productivity, and cacao bean yield. Total biomass C stocks (above- and belowground) increased fivefold from the monoculture to the multi-shade tree system (from 11 to 57 Mg ha-1), total net primary production rose twofold (from 9 to 18 Mg C ha-1 yr-1). This increase was associated with a 6fold increase in aboveground biomass, but only a 3.5fold increase in root biomass, indicating a clear shift in C allocation to aboveground tree organs with increasing shade for both cacao and shade trees. Despite a canopy cover increase from 50 to 93%, cacao bean yield remained invariant across the systems (variation: 1.1–1.2 Mg C ha-1 yr-1). The monocultures had a twice as rapid leaf turnover suggesting that shading reduces the exposure of cacao to atmospheric drought, probably resulting in greater leaf longevity. Thus, contrary to general belief, cacao bean yield does not necessarily decrease under shading which seems to reduce physical stress. If planned properly, cacao plantations under a shade tree cover allow combining high yield with benefits for carbon sequestration and storage, production system stability under stress, and higher levels of animal and plant diversity.

Root-knot nematodes (Meloidogyne hapla) can modify the positive plant intraspecific diversity-productivity effect on red clover in clover-grass communities

Plant diversity and soil organisms are both widely studied for their contributions to ecosystem functions. It has been recently shown that soil biota may drive the plant species diversity-function relationship in grasslands, while so far studies on plant intraspecific diversity are lacking. To improve the understanding of how ecosystem functions may be influenced by plant intraspecific diversity, soil organisms, and their interactions, we used a field setting to examine the effects of plant intraspecific diversity and functionally dissimilar soil organisms (manipulated by the addition of northern root-knot nematodes, earthworms, and arbuscular mycorrhizal fungi) on aboveground primary production, pollination and shoot herbivory. Plant intraspecific diversity was manipulated by sowing different seed mixtures of Trifolium pratense L. and Lolium perenne L. cultivars. We found a positive effect of plant intraspecific diversity on total aboveground primary production, contributed mostly by T. pratense. The plant intraspecific diversity-productivity effect on T. pratense was mediated by the nematodes, i.e. aboveground biomass was increased by intraspecific diversity only in the nematode treatment. Further, the average floral visitation length was decreased by earthworm addition, while the abundance of pollinators tended to be increased by high plant intraspecific diversity. Leaf damage of T. pratense were not influenced by the treatments. We conclude that plant intraspecific diversity and soil organisms can interactively or independently modify functions such as aboveground primary production and pollination of T. pratense in the field. Specifically, the positive plant intraspecific diversity effect appears to only emerge under conditions of stress (high nematode abundance). This result indicates that plant intraspecific diversity may be important for the maintenance of ecosystem functions, especially in an agricultural context, where pest pressure can be high and can have large detrimental consequences.

The influence of seasonality on benthic primary production in a Red Sea coral reef

Northern Red Sea coral reefs experience pronounced seasonal variations in environmental factors such as water temperature, light intensity, and nutrient availability. This allows studying related effects on primary production by different functional groups. The present study therefore quantified primary production of all dominant benthic primary producers from a Jordanian fringing reef (29° 27′ 31″ N, 34° 58′ 26″ E) by measuring net photosynthesis (P n) and dark respiration (R) using stirred respirometry chamber incubations during all four seasons of 2013. Annual mean P n was highest for the macroalga Caulerpa (901 nmol O2 cm−2 h−1) and lowest for both the soft coral Sarcophyton and sedimentary microphytobenthos (212 and 223 nmol O2 cm−2 h−1, respectively). Sedimentary microphytobenthos exhibited the strongest response to seasonality with 5.7 times higher P n in spring than in winter. R was highest in hard corals among all groups in every season, likely due to nighttime calcification and heterotrophic activity. Gross photosynthesis-to-respiration ratios (P g:R) were highest for turf algae and macroalgae as well as cyanobacterial mats. While R was primarily positively related to PAR and temperature and P g:R to inorganic nutrients, few groups revealed significant relations between P n and environmental parameters. Seasonal budgets found daily gross primary production and respiration to be dominated by hard and soft corals. Total reef gross primary production was comparable between less oligotrophic spring and more oligotrophic summer. This indicates that processes such as heterotrophic feeding and microbial dinitrogen fixation may help the functional groups overcome potential nutrient limitation of primary production in summer.

A comprehensive framework for functional diversity patterns of marine chromophytic phytoplankton using rbcL phylogeny.

Marine chromophytes are taxonomically diverse group of algae and contribute approximately half of the total oceanic primary production. To understand the global patterns of functional diversity of chromophytic phytoplankton, robust bioinformatics and statistical analyses including deep phylogeny based on 2476 form ID rbcL gene sequences representing seven ecologically significant oceanographic ecoregions were undertaken. In addition, 12 form ID rbcL clone libraries were generated and analyzed (148 sequences) from Sundarbans Biosphere Reserve representing the world’s largest mangrove ecosystem as part of this study. Global phylogenetic analyses recovered 11 major clades of chromophytic phytoplankton in varying proportions with several novel rbcL sequences in each of the seven targeted ecoregions. Majority of OTUs was found to be exclusive to each ecoregion, whereas some were shared by two or more ecoregions based on beta-diversity analysis. Present phylogenetic and bioinformatics analyses provide a strong statistical support for the hypothesis that different oceanographic regimes harbor distinct and coherent groups of chromophytic phytoplankton. It has been also shown as part of this study that varying natural selection pressure on form ID rbcL gene under different environmental conditions could lead to functional differences and overall fitness of chromophytic phytoplankton populations.

Primary productivity at the time-series stations in the northwestern Pacific Ocean: is the subtropical station unproductive?

A comparative study of primary productivity in the northwestern Pacific Ocean was conducted at time-series stations K2 and S1 in the nutrient-rich subarctic gyre and oligotrophic subtropical gyre, respectively. The estimated annual means of net primary production (NPP) at the two stations were virtually identical: 292 mg C m−2 day−1 at K2 and 303 mg C m−2 day−1 at S1, whereas the annual mean of gross primary production (GPP) at S1 was 1.5 times that at K2. NPP was very much limited by the supply of nutrients, typified by nitrate at S1, although it was enhanced during winter due to mitigation of nutrient limitation. The NPP/GPP ratios were remarkably lower at S1 during the spring-to-autumn time interval than in winter. The reduced NPP/GPP ratio means that photosynthetically assimilated carbon was lost at a higher rate via respiration and extracellular release of dissolved organic carbon (DOC). The carbon loss (difference between GPP and NPP) was higher at S1 than at K2, probably because of the enhanced respiration due to the relatively high temperature throughout the year, as well as the enhanced DOC release by nutrient limitation. The released DOC should be accounted for as primary production, because it contributes to oceanic biogeochemistry in a manner similar to the photosynthesized compounds. Consequently, total primary production, the sum of NPP and DOC release, was higher at S1 than at K2.

Spring plankton dynamics in the Eastern Bering Sea, 1971–2050: Mechanisms of interannual variability diagnosed with a numerical model

AbstractA new planktonic ecosystem model was constructed for the Eastern Bering Sea based on observations from the 2007–2010 BEST/BSIERP (Bering Ecosystem Study/Bering Sea Integrated Ecosystem Research Program) field program. When run with forcing from a data‐assimilative ice‐ocean hindcast of 1971–2012, the model performs well against observations of spring bloom time evolution (phytoplankton and microzooplankton biomass, growth and grazing rates, and ratios among new, regenerated, and export production). On the southern middle shelf (57°N, station M2), the model replicates the generally inverse relationship between ice‐retreat timing and spring bloom timing known from observations, and the simpler direct relationship between the two that has been observed on the northern middle shelf (62°N, station M8). The relationship between simulated mean primary production and mean temperature in spring (15 February to 15 July) is generally positive, although this was found to be an indirect relationship which does not continue to apply across a future projection of temperature and ice cover in the 2040s. At M2, the leading direct controls on total spring primary production are found to be advective and turbulent nutrient supply, suggesting that mesoscale, wind‐driven processes—advective transport and storminess—may be crucial to long‐term trends in spring primary production in the southeastern Bering Sea, with temperature and ice cover playing only indirect roles. Sensitivity experiments suggest that direct dependence of planktonic growth and metabolic rates on temperature is less significant overall than the other drivers correlated with temperature described above.

An Ecosystem Approach for understanding status and changes of Nador lagoon (Morocco): application of food web models and ecosystem indices

The work applies food web models to the Lagoon of Nador (Morocco) and subsequently estimates ecosystem indices. This effort supports the evaluation of the ecosystem status and the implementation of the Ecosystem Approach (EcAp), endorsed by the contracting parties of the Barcelona Convention for the Mediterranean Sea. The Lagoon of Nador, on the Mediterranean coast of Morocco, suffered from eutrophication during recent decades. We used indices derived from Ecological Network Analysis for investigating the most relevant features of ecosystem functioning in the decade 2000−2010 (present scenario), and comparing them with those of the 1980s (past scenario). As the Lagoon includes different habitats, the methodology was applied to each of them, in order to assess their contribution to the functioning of the whole ecosystem. Results highlighted an increase in Total System Throughput (TST) in the present scenario when compared with the past one, also associated to an increase of Total Respiration (TR) and of the ratio between Total Primary Production and Total Respiration (TPP/TR). Under the present scenario Nador lagoon shows a decreased cycling efficiency. The sensitivity analysis highlighted the capability of TST and Comprehensive Cycling Index (CCI) in detecting changes, in agreement with other recent studies on responses of food web functioning to eutrophication. The results are discussed in respect to three specific aspects, related with the application of food Web Models and Ecological Network Analysis in the EcAp context: i) data availability; ii) spatialization of indicators; iii) selected set of indicators. The results also highlight the important role of sensitivity/uncertainty analysis when implementing food web models in data-scarce systems.

Accounting for littoral primary production by periphyton shifts a highly humic boreal lake towards net autotrophy

Abstract The prevailing view that many humic lakes are net heterotrophic is commonly based on pelagic measurements alone. Poor light conditions in humic lakes are assumed to constrain littoral primary production (PP), such that the littoral zone has been considered an insignificant contributor to whole‐lake PP. However, that assumption is based on models and inferences from pelagic processes which do not take littoral zone structure into account. Many lakes have an extensive ring of aquatic vegetation lying near the water surface, which provides substratum for epiphytic algae under well‐illuminated conditions. We measured both pelagic and littoral PP and community respiration (CR) in Mekkojärvi, a small, highly humic headwater lake, in southern Finland throughout the open water season in 2012. We used a 14C incorporation technique to measure pelagic PP, while littoral PP was determined using changes in dissolved inorganic carbon concentrations during in situ incubations. We then estimated whole‐lake PP and CR for both the littoral and pelagic zones. We found that littoral PP usually dominated whole‐lake PP, contributing >90% to total PP in summer. A mean pelagic production to respiration ratio (GPP : CR) of 0.4 clearly indicated strong net heterotrophy, but a value of 2.2 for the littoral zone indicated strong autotrophy. For both habitats combined, the mean whole lake GPP : CR was 1.6, indicating net autotrophy. We suggest that littoral PP can contribute significantly to whole‐lake PP even in highly humic lakes, and that the littoral contribution can shift some lakes which have been considered net heterotrophic to metabolic balance or even net autotrophy during the ice‐free period. Small humic lakes like Mekkojärvi with rings of littoral vegetation are widespread, especially in the boreal zone, and at least for similar lakes, evaluating lake metabolism from pelagic measurements alone is likely to be misleading.

Toward an ecological understanding of a flood-pulse system lake in a tropical ecosystem: Food web structure and ecosystem health

Tonle Sap Great Lake (TSL) is the largest freshwater lake ecosystem in Southeast Asia and receptacle of impressive biodiversity. However, there is surprisingly little knowledge of its ecosystem structure and functioning. The main objective of the current work was to quantify the food web structure and assess the ecosystem health status of the TSL system by constructing the first holistic food web model using Ecopath with Ecosim (EwE). The results indicate that the ecotrophic efficiency (EE) values were very high for most of functional groups (EE>0.5) except molluscs (0.146) and macrophytes (0.102). The high EE values together with the MTI (Mixed Trophic Impact) analysis indicated the overexploitation and degradation of fishery resources in the TSL system. The discrete trophic levels varied from 1 (phytoplankton, macrophytes and detritus) to 3.17 (snakehead). The energy transfer in the TSL food web was based mostly on the detrital food chain (77.9%) rather than the grazing food chain (22.1%), with an average transfer efficiency of 8.27%. The ratios of total primary production to respiration (TPP/TR) and to biomass (TPP/TB) were 1.23 and 2.04, respectively, while the Ascendency and Finn cycling index (FCI) of the system were estimated at 27.4% and 23.62%. Nevertheless, the connectance index (CI: 0.253) and system omnivory index (SOI: 0.075) were in-between compared to other lake ecosystems, which indicated that the food web structure was characterized by linear, rather than web-like features. Systematic analysis and indicators suggested that the ecosystem was a relatively healthy ecosystem achieving a certain stage of maturity, albeit with a vulnerable food web structure. Accordingly, some ecosystem-based strategies are presented for the improvement of fishery management and ecosystem conservation in TSL.

Ecosystem model intercomparison of under‐ice and total primary production in the Arctic Ocean

AbstractPrevious observational studies have found increasing primary production (PP) in response to declining sea ice cover in the Arctic Ocean. In this study, under‐ice PP was assessed based on three coupled ice‐ocean‐ecosystem models participating in the Forum for Arctic Modeling and Observational Synthesis (FAMOS) project. All models showed good agreement with under‐ice measurements of surface chlorophyll‐a concentration and vertically integrated PP rates during the main under‐ice production period, from mid‐May to September. Further, modeled 30‐year (1980–2009) mean values and spatial patterns of sea ice concentration compared well with remote sensing data. Under‐ice PP was higher in the Arctic shelf seas than in the Arctic Basin, but ratios of under‐ice PP over total PP were spatially correlated with annual mean sea ice concentration, with higher ratios in higher ice concentration regions. Decreases in sea ice from 1980 to 2009 were correlated significantly with increases in total PP and decreases in the under‐ice PP/total PP ratio for most of the Arctic, but nonsignificantly related to under‐ice PP, especially in marginal ice zones. Total PP within the Arctic Circle increased at an annual rate of between 3.2 and 8.0 Tg C/yr from 1980 to 2009. This increase in total PP was due mainly to a PP increase in open water, including increases in both open water area and PP rate per unit area, and therefore much stronger than the changes in under‐ice PP. All models suggested that, on a pan‐Arctic scale, the fraction of under‐ice PP declined with declining sea ice cover over the last three decades.

基于生态通道模型的长江口水域生态系统结构与能量流动分析

PDF HTML阅读 XML下载 导出引用 引用提醒 基于生态通道模型的长江口水域生态系统结构与能量流动分析 DOI: 10.5846/stxb201501150129 作者: 作者单位: 中国科学院生态环境研究中心,南京水利科学研究院,中国水产科学研究院东海水产研究所,南京水利科学研究院,三峡大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目（51425902，51409242）；国家重点基础研究发展计划973项目（2010CB429000） Analysis of the ecosystem structure and energy flow of the Yangtze River estuary and adjacent seas, based on the Ecopath model Author: Affiliation: RCEES,NHRI,,, 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:利用Ecopath with Ecosim在前期研究的基础上构建了3个时期（2000年秋、2006年秋、2012年秋）长江口水域生态系统的生态通道模型，分析对比了三峡工程蓄水前中后期，长江口水域生态系统结构与能量流动特征。模型将长江口水域生态系统划分为鱼类、虾类、蟹类、头足类、底栖动物、浮游动物、浮游植物、碎屑等17个功能组，基本覆盖了长江口生态系统能量流动的主要途径。模型结果分析表明：蓄水前中后期，长江口水域生态系统各功能组营养级组成和分布相近，但由于长江口渔业过度捕捞，蓄水中后期多数功能组的生态营养转换率被动提高。长江口渔获物的组成未发生明显变化，但渔获物的平均营养级降低，渔获量减少。蓄水中后期，生态系统中牧食食物链的重要性增加，碎屑食物链的重要性降低，这与蓄水之后长江入海径流改变、泥沙量减少、陆源污染增加关系密切。结果表明，蓄水前中后期，生态系统均处于不成熟阶段，蓄水后生态系统总生物量、初级生产量及流向碎屑的能量呈降低趋势，但系统的净效率和再循环率升高。 Abstract:The cumulative impacts of water conservancy projects in the Yangtze River basin, especially the Three Gorges Reservoir, have had a significant effect on the biological and ecological integrity of the Yangtze River estuarine ecosystem. This research establishes three ecopath models of the Yangtze River estuary and adjacent seas before (the autumn of 2000), during (the autumn of 2006), and after (the autumn of 2012) the impoundments of the Three Gorges Reservoir, using Ecopath and Ecosim software to characterize and compare the estuarine ecosystem's food web structure and energy flow. Sensitivity analyses were carried out to evaluate the uncertainty levels of the models. The three models consisted of 17 functional groups covering the main paths of the ecosystem food web, including piscivorous fishes, generalist predators, shrimp predators, zooplanktivores, crab predators, other pelagic fishes, other demersal fishes, other benthic fishes, shrimp, crabs, jellyfish, cephalopods, macrobenthos, meiobenthos, zooplankton, phytoplankton, and detritus. The simulated results showed that the values of trophic levels (TL) ranged from 1.000 to 3.802 in 2000 (before the impoundments), from 1.000 to 4.058 in 2006 (during the impoundments), and from 1.000 to 4.019 in 2012 (after the impoundments). This indicates that the TLs distributions of the functional groups were similar under all three conditions. However, the ecotrophic efficiencies of commercial species, such as Pseudosciaena polyactis, were elevated because of the increased fishing intensity in the Yangtze River estuary. The structure of catches did not change noticeably during this period, but the mean trophic level of the catch decreased from 3.406 to 3.369, as did the number of catches (from 1.026 t km-2 a-1 to 0.719 t km-2 a-1). Meanwhile, after the impoundments the role of the detritus food chain became less important to the energy transfer process than that of the grazing food chain, and over 90% of the energy flows were assembled in TL I and II, most of which flow into detritus and could be a source of internal pollution. The total transfer efficiency of the Yangtze River estuary ecosystem was 10.2% in 2000, 10.0% in 2006 and 9.4% in 2012. All of these negative effects are likely to be closely related to reductions in freshwater and sediment discharges, as well as the increase of land-based pollution in the Yangtze River Basin. Furthermore, the result also showed that the parameters of total biomass, total primary production, and the sum of all flows into detritus gradually decreased; however, the gross efficiency, Finn cycling index, Finn's mean path length, and system omnivory index increased. The ecosystems (before, during, and after impoundments) were found to remain in the immature stage. 参考文献 相似文献 引证文献