Biogeochemical Cycling Of Nutrients Research Articles

Alkalinity, inorganic carbon and CO2 flux variability during extreme rainfall years (2010-2011) in two polluted tropical estuaries NE Brazil

Abstract The susceptibility of coastal environments to shifts in the biogeochemical cycles of carbon and nutrients driven by anthropogenic pressure and climate change is a real challenge for the scientific community. This paper evaluated the effects of an extreme rainfall event over the nutrients and carbonate parameters in two polluted tropical estuaries. Surface water samples were taken seasonally along a salinity gradient in the Capibaribe and Barra de Jangadas estuaries in order to investigate the spatial and seasonal variability of dissolved nutrients, chlorophyll-a, dissolved oxygen, total alkalinity, inorganic carbon, partial pressure of CO2 (pCO2) and CO2 fluxes. The increased riverine influence caused by the fluvial flooding during the extremely rainy season augmented the nitrogen concentrations in the plumes, which also presented reduced salinity, alkalinity and dissolved oxygen values. In the Capibaribe plume it has also shifted the mean CO2 flux value of - 4.01 mmolC m-2 d-1 during the dry season, to a positive mean flux of + 5.7 mmolC m-2 d-1 during the rainy season. Within the estuaries the BOD5,20 and dissolved phosphorus values were higher during the dry season (p<0.0001), they showed positive correlation with the phytoplanktonic blooms that reached a chl-a value of 85 mg m-3 in the Capibaribe. The high alkalinity found in both estuaries, with mean values between dry and wet seasons respectively from 1808 to 1373 µmol kg-1 in the Capibaribe estuary and 1616 to 1058 µmol kg-1 in Barra de Jangadas estuary, may act as a buffer to the process of coastal acidification due to eutrophication. The increased rivers discharge lead to a greater transport of organic matter and nutrients to the coast, decreasing the oxygen availability and shifting the metabolic status of the estuarine plume to heterotrophic, whereas increased the water quality within the estuaries due the flushing promoted by the extreme rainfall event.

Competition between Silicifiers and Non-silicifiers in the Past and Present Ocean and Its Evolutionary Impacts

Competition is a central part of the evolutionary process, and silicification is no exception: between biomineralized and non-biomineralized organisms, between siliceous and non-siliceous biomineralizing organisms, and between different silicifying groups. Here we discuss evolutionary competition at various scales, and how this has affected biogeochemical cycles of silicon, carbon, and other nutrients. Across geological time we examine how fossils, sediments, and isotopic geochemistry can provide evidence for the emergence and expansion of silica biomineralization in the ocean, and competition between silicifying organisms for silicic acid. Metagenomic data from marine environments can be used to illustrate evolutionary competition between groups of silicifying and non-silicifying marine organisms. Modern ecosystems also provide examples of arms races between silicifiers as predators and prey, and how silicification can be used to provide a competitive advantage for obtaining resources. Through studying the molecular biology of silicifying and non-silicifying species we can relate how they have responded to the competitive interactions that are observed, and how solutions have evolved through convergent evolutionary dynamics.

Single-cell genomics of multiple uncultured stramenopiles reveals underestimated functional diversity across oceans

Single-celled eukaryotes (protists) are critical players in global biogeochemical cycling of nutrients and energy in the oceans. While their roles as primary producers and grazers are well appreciated, other aspects of their life histories remain obscure due to challenges in culturing and sequencing their natural diversity. Here, we exploit single-cell genomics and metagenomics data from the circumglobal Tara Oceans expedition to analyze the genome content and apparent oceanic distribution of seven prevalent lineages of uncultured heterotrophic stramenopiles. Based on the available data, each sequenced genome or genotype appears to have a specific oceanic distribution, principally correlated with water temperature and depth. The genome content provides hypotheses for specialization in terms of cell motility, food spectra, and trophic stages, including the potential impact on their lifestyles of horizontal gene transfer from prokaryotes. Our results support the idea that prominent heterotrophic marine protists perform diverse functions in ocean ecology.

鄱阳湖湿地灰化苔草生长季氮磷含量与储量的变化

PDF HTML阅读 XML下载 导出引用 引用提醒 鄱阳湖湿地灰化苔草生长季氮磷含量与储量的变化 DOI: 10.5846/stxb201707131273 作者: 作者单位: 河南大学环境与规划学院,河南大学环境与规划学院,河南大学环境与规划学院,河南大学环境与规划学院 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（41371450，41101089）；河南省高等学校青年骨干教师项目（2014GGJS-025） Nitrogen and phosphorus concentration, and storage dynamics of Carex cinerascens during the spring growing season in Poyang Lake wetland Author: Affiliation: College of Environment and Planning, Henan University,College of Environment and Planning, Henan University,College of Environment and Planning, Henan University,College of Environment and Planning, Henan University 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:湿地植物在营养元素生物地球化学循环过程中起着重要作用，研究植物氮磷元素的吸收、分配和积累特征对于正确理解氮磷循环关键过程及其生态作用具有重要意义。基于野外实地观测和室内实验分析，研究了鄱阳湖淡水湿地灰化苔草春草生长季内不同部位生物量、氮磷含量及氮磷储量的动态变化。结果表明：在生长季内，灰化苔草各部位生物量随时间推移而增加，地上部分生物量在各生长期均高于地下部分，地下部分生物量积累速率相对稳定，而地上部分和总体平均积累速率表现为生长前期高于生长后期；各部位氮磷含量经历了先减少再增加的变化过程，其中地上部分氮元素在灰化苔草生长的中后期显著高于地下部分，而磷元素在中前期两者差异更为显著；生物量与氮磷储量均呈显著正相关，是灰化苔草氮磷储量动态变化的主导因子，氮磷元素主要储存在灰化苔草的地上部分；研究期间灰化苔草平均氮磷比介于3.32-3.83之间，按营养限制理论进行判断，氮元素可能是灰化苔草生长的限制性营养因子。 Abstract:Wetland plants play an important role in the biogeochemical cycling of nutrients. Studying the absorption, distribution, and accumulation of nitrogen (N) and phosphorus (P) in plants is of great significance in understanding the key processes of nutrient cycling and their ecological functions. Therefore, field observations and laboratory measurements were used to study the dynamic changes in biomass as well as the N and P contents and their storages in Carex cinerascens in the spring growing season in Poyang Lake wetland. The results showed that there was a time-dependent increase in the biomasses of different components of C. cinerascens during the spring growing season whereas the aboveground biomass was higher than that of the belowground in each growing period. Furthermore, the accumulation rate of the belowground biomass was relatively constant whereas that of the aboveground and total biomasses was higher in the early growing stage than it was in the late growing stage. The N and P contents in the different parts of C. cinerascens decreased from March to April and then increased from April to May. The N content of the aboveground part was higher than that of the belowground part in each growing period, and the difference was significant in April and May (P < 0.01). The P content had similar distribution characteristics to those of the N content, but the difference was more significant in March and April (P < 0.01) than it was in other months. The N and P storages in C. cinerascens showed a significantly positive correlation with the biomass (P < 0.01), and their dynamics were determined based on the biomass variation of C. cinerascens. Further, the aboveground part of C. cinerascens contained the main N and P pools. The N/P ratio is an important ecological indicator that can be used to detect the nutrient limitation. Based on the theory of nutrient limitation, N may be a key nutrient factor that limits the primary productivity of C. cinerascens. 参考文献 相似文献 引证文献

互花米草入侵影响下闽江河口湿地土壤有效硅的时空变化特征

PDF HTML阅读 XML下载 导出引用 引用提醒 互花米草入侵影响下闽江河口湿地土壤有效硅的时空变化特征 DOI: 10.5846/stxb201709041593 作者: 作者单位: 福建师范大学地理科学学院,福建师范大学地理科学学院,福建师范大学地理科学学院,福建师范大学地理科学学院,福建师范大学地理科学学院,福建师范大学地理科学学院 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（41401114）；福建省基金面上项目（2016J01184）；福建省公益类科研院所专项（2016R1032-1）；福建师范大学地理科学学院研究生科研创新基金 Spatial and temporal variations of available silica content in marsh soils under the Spartina alterniflora invasion in the Min River estuary Author: Affiliation: College of Geographical Sciences, Fujian Normal University,College of Geographical Sciences, Fujian Normal University,,,, 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:2016年1-12月，选择闽江河口鳝鱼滩的短叶茳芏湿地、互花米草湿地以及二者的交错带湿地为研究对象，采用定位研究方法探讨了互花米草入侵影响下湿地土壤有效硅含量的时空变化特征。结果表明：互花米草入侵影响下3块湿地土壤有效硅含量随时间推移整体呈波动上升趋势；互花米草入侵显著提高了鳝鱼滩湿地30-60 cm土层土壤有效硅含量（P < 0.01），与短叶茳芏湿地相比，交错带湿地和互花米草湿地30-60 cm土层土壤有效硅含量分别增加了8.56%和19.97%，逐步线性回归分析表明土温和电导是影响其变化的重要因素（P < 0.01）。研究互花米草入侵影响下湿地土壤有效硅含量的变化特征，对于揭示湿地生态系统生源要素硅生物地球化学循环过程以及互花米草入侵及其扩张机制具有重要意义。 Abstract:Silica (Si) is the second most abundant element after oxygen in the soil and plays an important role in many biogeochemical processes, such as controlling the functions of terrestrial, marine, coastal, and inland water ecosystems. Wetland ecosystems are considered very important for Si transport in nutrient biogeochemical cycles. In recent years, Spartina alterniflora has become one of the most important invasive plants in coastal wetland ecosystems in China, which has caused considerable effects on the invaded regions. The Shanyutan marsh is the largest tidal wetland in the Min River estuary in the subtropical zone of southeast China. S. alterniflora started to invade Shanyutan marsh in 2002, and since then has gradually expanded its cover across the intertidal zone. The invasion of S. alterniflora has an important impact on the cycling of carbon, nitrogen, phosphorus, and sulfur, but the effect on available silica (ASi) in the soil is not yet clear. To explore the spatial and temporal variations of ASi contents in marsh soils under the S. alterniflora invasion in Shanyutan of the Min River estuary, the Cyperus malaccensis marsh, S. alterniflora marsh, and their ecotonal marsh were studied from January to December 2016. Results showed that temporal variations of ASi contents of three different marshes generally increased with time. Compared to C. malaccensis marsh, S. alterniflora invasion significantly increased ASi contents in 30-60 cm soil layers, and values in the ecotonal and S. alterniflora marshes increased by 8.56% and 19.97%, respectively. The stepwise linear regression analyses showed that soil temperature and electrical conductivity were the crucial factors affecting the variations of ASi contents. The spatial and temporal variations of ASi contents in marsh soils are important to reveal the biogeochemical cycling of silica to better understand the invasion and expansion mechanisms of S. alterniflora in a marsh ecosystem. 参考文献 相似文献 引证文献

Моделирование растворенного органического вещества в Финском заливе (на англ.яз.), "Фундаментальная и прикладная гидрофизика"

Цель работы - усовершенствование Санкт-Петербургской модели эвтрофикции Балтийского моря (SPBEM) за счет включения уравнений неконсервативной примеси для растворенного органического азота и фосфора в двух формах - легкоокисляемой и стойкой. Численные эксперименты по тестированию усовершенствованной версии модели было выполнено для Финского залива для периода 2009-2014 гг. Начальные и граничные условия для численных экспериментов были получены на основе данных натурных наблюдений. Сравнение результатов моделирования с данными наблюдений показало хорошее совпадение пространственно-временной изменчивости гидрофизических и биогеохимических характеристик, в том числе почти идеальное соответствие между моделируемой и наблюдаемой динамикой органических форм азота и фосфора. Важнейшим отличием между рассчитанными и наблюдаемыми характеристиками является завышенное содержание неорганического азота и фосфора, что может быть вызвано неточностями в задании начальных и граничных условий, а также в используемых параметризациях потоков минерализации. Более тонкая настройка SPBEM-2 требует более тщательного анализа чувствительности.

Long-term effects of forest liming on mineral soil, organic layer and foliage chemistry: Insights from multiple beech experimental sites in Northern France

Abstract Most forest ecosystems grow on acid and nutrient poor soils. In many cases, a slow degradation of forest soil chemical fertility due to increasing external pressures (decreasing atmospheric inputs, intensification of biomass harvesting and silvicultural practices) has been observed and is a growing concern in the international forest community. When the pressure endured by low fertility forest ecosystems is too intense, nutrient losses and ecosystem function losses may occur, forest decline being the ultimate stage of this process. In such cases, forest liming with a carbonate product is a solution to restore soil fertility and reduce soil acidity, globally improve the ecosystem functioning and compensate for nutrient losses caused by biomass harvest and exportation. However, the effects of liming on ecosystem processes and the biogeochemical cycling of nutrients in forest ecosystems are still unclear. We studied the dynamics of magnesium and calcium originating from the dissolution of liming products in the different compartments (organic and mineral soil layers and, aboveground biomass) of five long-term (20 to 40 years) monitoring beech (Fagus sylvatica L.) plots located in Northern France from ecosystem magnesium and calcium budgets. Compared to the control plots, soil exchangeable pools of Mg and Ca in the 0–15 cm mineral soil layer increased during the first decade after liming but these differences rapidly decreased after 20–30 years. The effect of liming on foliar concentrations and tree growth was still observed after 40 years, most probably because the biological cycling of these elements was more dynamic in the limed plots. Liming increased the decomposition rate of the soil organic layer but the pools of Mg and Ca in this layer remained relatively stable over time, probably because Mg and Ca concentrations in foliage and litterfall increased after the liming. Liming effects varied between sites depending on the liming product and amount, and the initial chemical fertility level of the soil. Although liming operations may help improve forest soil fertility, they may also generate nutrient deficiencies and/or imbalances for nutrients that are poorly available in the soil. The planning of liming operations therefore necessitates a thorough soil chemical fertility diagnosis.

Extending the applications of sediment profile imaging to geochemical interpretations using colour

Whilst Sediment Profile Imaging (SPI) is a very widely used technique in the regulatory assessment of seabed environmental health, and in the study of seafloor sediment-biology interactions, the potential for SPI images to be used in a geochemical context has not been rigorously assessed. Here we have examined relationships between colour and geochemistry in a sediment core collected from the Celtic Sea, North West European Shelf, that was digitally imaged and on which detailed geochemical analyses were also performed. Average oxygen penetration depth was 4.08 ± 0.72 mm, (n = 5), whilst the apparent redox potential discontinuity (aRPD) as determined by sediment colour change was at 78 mm. As iron (oxyhydr)oxides decreased with depth, black sulfide phases increased, and the aRPD most closely correlated with this geochemical change rather than the oxygen penetration depth. Colour analysis of the image showed a clear correlation of brightness with black FeS (acid volatile sulfide). There was a general correlation of iron oxide phases with orange colour in the upper part of the sediment profile, whilst.in the lower part of the core the orange oxide phases appeared to be obscured by the black FeS present. The sulfide-brightness relationship indicates colour analysis can provide an estimate of FeS, and potentially the carrying capacity for toxic metals such as cadmium, zinc and copper as sulfides in this type of sediment. Additionally, detailed geochemical analyses of SPI cores may provide new insights into the activity and impacts of infauna and the link with sediment biogeochemical cycles of carbon and nutrients.

The sensitivity and stability of bacterioplankton community structure to wind-wave turbulence in a large, shallow, eutrophic lake

Lakes are strongly influenced by wind-driven wave turbulence. The direct physical effects of turbulence on bacterioplankton community structure however, have not yet been addressed and remains poorly understood. To examine the stability of bacterioplankton communities under turbulent conditions, we simulated conditions in the field to evaluate the responses of the bacterioplankton community to physical forcing in Lake Taihu, using high-throughput sequencing and flow cytometry. A total of 4,520,231 high quality sequence reads and 74,842 OTUs were obtained in all samples with α-proteobacteria, γ-proteobacteria and Actinobacteria being the most dominant taxa. The diversity and structure of bacterioplankton communities varied during the experiment, but were highly similar based on the same time of sampling, suggesting that bacterioplankton communities are insensitive to wind wave turbulence in the lake. This stability could be associated with the traits associated with bacteria. In particular, turbulence favored the growth of bacterioplankton, which enhanced biogeochemical cycling of nutrients in the lake. This study provides a better understanding of bacterioplankton communities in lake ecosystems exposed to natural mixing/disturbances.

Nutrients and Heavy Metals Contamination in an Urban Estuary of Northern New Jersey

The Newark Bay Estuary in northern New Jersey contains one of the largest urban wetland complexes in the United States, but the majority of the wetlands and habitats have been lost due to urbanization and industrialization. Field and laboratory research was conducted to understand the impacts of human activities on the biogeochemistry of nutrients and heavy metals in the urban estuary. Concentrations of dissolved nutrients such as nitrate, ammonia, and phosphate were higher in the Hackensack River than in the Passaic River or the Newark Bay, while the Hackensack River was more deficient in dissolved oxygen. Sediment oxygen demand and mobilization of nutrients were higher in sediments with higher organic matter content as a result of microbial decomposition of organic matter. Heavy metals (Cr, Cu, Pb, and Zn) and organic matter were more enriched in finer sediment grains such as silt and clay. There were positive correlations among heavy metals as well as organic matter in sediments. The results suggest that fine grained sediments, which can be readily suspended and transported during tidal cycles, may play a significant role in biogeochemical cycling of nutrients and heavy metals in the urban estuary. It appears that the current sources of nutrients and heavy metals in the water and sediment of the Newark Bay Estuary are mainly domestic effluents from sewage treatment plants during non-storm periods as well as combined sewer overflows during storm events, but further research including more frequent and pervasive water and sediment quality monitoring during dry and wet periods is needed.

Biogeochemical processes and turnover rates in the Northern Benguela Upwelling System

Abstract Biogeochemical cycles of carbon, nutrients, and oxygen transmit mean states, trends and variations of the physical realm in coastal upwelling systems to their food webs and determine their role in regional budgets of greenhouse gases. This contribution focuses on biogeochemical processes in the northern Benguela Upwelling System (NBUS), where low oxygen levels in upwelling source water are a major influence on carbon and nutrient cycles. Based on measurements during numerous expeditions and results of 3-D regional ecosystem modeling (project GENUS; Geochemistry and Ecology of the Namibian Upwelling System) we here examine source water character, effects of low oxygen conditions on nutrient masses and ratios, and of diazotrophic N2-fixation on productivity of the system and its transition to the adjacent eastern South Atlantic. In available observations, the effects of denitrification in water and sediment and phosphate release from sediments are minor influences on nitrate:phosphate ratios of the system, and excess phosphate in aged upwelling water is inherited from upwelling source water. Contrary to expectation and model results, the low N:P ratios do not trigger diazotrophic N2-fixation in the fringes of the upwelling system, possibly due to a lack of seeding populations of Trichodesmium. We also examine the flux of carbon from the sea surface to either sediment, the adjacent sub-thermocline ocean, or to regenerated nutrients and CO2. Observed fluxes out of the surface mixed layer are significantly below modeled fluxes, and suggest that regeneration of nutrients and CO2 is unusually intense in the mixed layer. This contributes to very high fluxes of CO2 from the ocean to the regional atmosphere, which is not compensated for by N2-fixation. Based on observations, the NBUS thus is a significant net CO2 source (estimated at 14.8 Tg C a− 1), whereas the CO2 balance is closed by N2-fixation in the model. Methane concentrations were low in surface waters in on-line measurements during 1 expedition, and based on these our estimate for the emission of methane for the entire Benguela system is below 0.2 Tg CH4 a− 1.

Land use not litter quality is a stronger driver of decomposition in hyperdiverse tropical forest.

In hyperdiverse tropical forests, the key drivers of litter decomposition are poorly understood despite its crucial role in facilitating nutrient availability for plants and microbes. Selective logging is a pressing land use with potential for considerable impacts on plant–soil interactions, litter decomposition, and nutrient cycling. Here, in Borneo's tropical rainforests, we test the hypothesis that decomposition is driven by litter quality and that there is a significant “home‐field advantage,” that is positive interaction between local litter quality and land use. We determined mass loss of leaf litter, collected from selectively logged and old‐growth forest, in a fully factorial experimental design, using meshes that either allowed or precluded access by mesofauna. We measured leaf litter chemical composition before and after the experiment. Key soil chemical and biological properties and microclimatic conditions were measured as land‐use descriptors. We found that despite substantial differences in litter quality, the main driver of decomposition was land‐use type. Whilst inclusion of mesofauna accelerated decomposition, their effect was independent of land use and litter quality. Decomposition of all litters was slower in selectively logged forest than in old‐growth forest. However, there was significantly greater loss of nutrients from litter, especially phosphorus, in selectively logged forest. The analyses of several covariates detected minor microclimatic differences between land‐use types but no alterations in soil chemical properties or free‐living microbial composition. These results demonstrate that selective logging can significantly reduce litter decomposition in tropical rainforest with no evidence of a home‐field advantage. We show that loss of key limiting nutrients from litter (P & N) is greater in selectively logged forest. Overall, the findings hint at subtle differences in microclimate overriding litter quality that result in reduced decomposition rates in selectively logged forests and potentially affect biogeochemical nutrient cycling in the long term.

The in situ spectral methods for examining redox status of c-type cytochromes in metal-reducing/oxidizing bacteria

The membrane-associated c-type cytochromes (c-Cyts) have been well known as the key enzymes mediating extracellular electron transfer to terminal electron acceptors, resulting in biogeochemical elemental transformation, contaminant degradation, and nutrient cycling. Although c-Cyts-mediated metal reduction or oxidation have been mainly investigated with the purified proteins of metal reducing/oxidizing bacteria, the in vivo behavior of c-Cyts is still unclear, given the difficulty in measuring the proteins of intact cells. Fortunately, the in situ spectroscopy would be ideal for measuring the reaction kinetics of c-Cyts in intact cells under noninvasive physiological conditions. It can also help the establishment of kinetic/thermodynamic models of extracellular electron transfer processes, which are essential to understand the electron transfer mechanisms at the molecular scale. This review briefly summarizes the current advances in spectral methods for examining the c-Cyts in intact cells of dissimilatory metal reducing bacteria and Fe(II)-oxidizing bacteria.

Consumer Aggregations Drive Nutrient Dynamics and Ecosystem Metabolism in Nutrient-Limited Systems

Differences in animal distributions and metabolic demands can influence energy and nutrient flow in an ecosystem. Through taxa-specific nutrient consumption, storage, and remineralization, animals may influence energy and nutrient pathways in an ecosystem. Here we show these taxa-specific traits can drive biogeochemical cycles of nutrients and alter ecosystem primary production and metabolism, using riverine systems that support heterogeneous freshwater mussel aggregations. Freshwater unionid mussels occur as distinct, spatially heterogeneous, dense aggregations in rivers. They may influence rates of production and respiration because their activities are spatially concentrated within given stream reaches. Previous work indicates that mussels influence nutrient limitation patterns, algal species composition, and producer and primary consumer biomass. Here, we integrate measures of organismal rates, stoichiometry, community-scaled rates, and ecosystem rates, to determine the relative source-sink nutrient dynamics of mussel aggregations and their influence on net ecosystem processes. We studied areas with and without mussel aggregations in three nitrogen-limited rivers in southeastern Oklahoma, USA. We measured respiration and excretion rates of mussels and collected a subset of samples for tissue chemistry and for thin sectioning of the shell to determine growth rates at each site. This allowed us to assess nutrient remineralization and nutrient sequestration by mussels. These rates were scaled to the community. We also measured stream metabolism at three sites with and without mussels. We demonstrated that mussel species have distinct stoichiometric traits, vary in their respiration rates, and that mussel aggregations influence nutrient cycling and productivity. Across all mussel aggregations, we found that mussels excreted more nitrogen than they sequestered into tissue and excreted more phosphorus than they sequestered except at one site. Furthermore, gross primary productivity was significantly greater at reaches with mussels. Collectively, our results indicate that mussels have ecosystem-level impacts on nutrient availability and production in nutrient-limited rivers. Within these streams, mussels are affecting the movement of nutrients and altering nutrient spiralling.

Predominant terminal electron accepting processes during organic matter degradation: Spatio-temporal changes in Ashtamudi estuary, Kerala, India

Anaerobic microbial communities in the anoxic zones degrade organic matter in estuarine sediments. Thermodynamic energy yield for the oxidation reactions with various electron acceptors decreases in the order of O2> NO3- > Mn4+> Fe3+> SO42- > CO2. The predominant terminal electron accepting (TEA) process has an influence on the biogeochemical cycles of nutrients as well as the production of important greenhouse gases such as nitrous oxide and methane from estuarine sediments. The research questions of this study were (1) what are the environmental factors (pH, salinity, organic carbon, sulphate, redox potential) explaining variability in TEA activities such as nitrate reduction rate (NRR), iron reduction rate (IRR), sulphate reduction rate (SRR) and methane production rate (MPR) and (2) which is the predominant TEA process during degradation of organic matter. To determine the TEA activities, sediment samples collected from 13 sampling stations of Ashtamudi estuary during monsoon 2014 and summer 2015 were incubated with sulphate depleted artificial seawater, under anaerobic conditions for 72 h, in microcosms. Spatial variations dominated temporal variations for environmental variables. Nevertheless, biogeochemical processes showed a distinct seasonal variation. Total TEA activity was higher during summer than monsoon, indicating the higher heterotrophic microbial activity favored by high temperature. Individually, SRR was the maximum during summer, while NRR, IRR and MPR were the maximum during monsoon. Sulphate reduction was observed to be the predominant electron accepting process in all sampling stations with cumulative values of 3125.79 and 4046.07 nmol cm-3 day-1 during monsoon and summer respectively. This was followed by NRR, IRR and MPR. Although thermodynamically more favorable, NRR could not predominate due to scarcity of nitrate in sediments. Nevertheless, two-fold and five-fold increase in methanogenesis and denitrification were observed respectively during monsoon in sampling stations, which cannot be ignored, owing to the importance of methane and nitrous oxide as a potent greenhouse gas.

Effects of river damming on biogenic silica turnover: implications for biogeochemical carbon and nutrient cycles

Rivers link terrestrial ecosystems and marine ecosystems, and they transport large amounts of substances into oceans each year, including several forms of silicon (Si), carbon (C), and other nutrients. However, river damming affects the water flow and biogeochemical cycles of Si, C, and other nutrients through biogeochemical interacting processes. In this review, we first summarize the current understanding of the effects of river damming on the processes of biogeochemical Si cycle, especially the source, composition, and recycling process of biogenic silica (BSi). Then, we introduce dam impacts on the cycles of C and some other nutrients. Dissolved silicon in rivers is mainly released from phytolith dissolution and silicate weathering. BSi in suspended matter or sediments in most rivers mainly consists of phytoliths and mainly originates from soil erosion. However, diatom growth and deposition in many reservoirs formed by river interception may significantly increase the contribution of diatom Si to total BSi, and thus significantly influence the biogeochemical Si, C, and nutrient cycles. Yet the turnover of phytoliths and diatoms in different rivers formed by river damming is still poorly quantified. Thus, they should be further investigated to enhance our understanding about the effects of river damming on global biogeochemical Si, C and nutrient cycles.

Spatial and Temporal Dynamics of Suspended Particle Characteristics and Composition in Navigation Pool 19 of the Upper Mississippi River

AbstractSuspended particles are an essential component of large rivers influencing channel geomorphology, biogeochemical cycling of nutrients, and food web resources. The Upper Mississippi River is a large floodplain river that exhibits pronounced spatiotemporal variation in environmental conditions and biota, providing an ideal environment for investigating dynamics of suspended particles in large river ecosystems. Here we investigated two questions: (i) How do suspended particle characteristics (e.g. size and morphology) vary temporally and spatially? and (ii) What environmental variables have the strongest association with particle characteristics? Water sampling was conducted in June, August, and September of 2013 and 2014 in Navigation Pool 19 of the Upper Mississippi River. A FlowCAM® (Flow Cytometer and Microscope) particle imaging system was used to enumerate and measure particles 53–300 μm in diameter for size and shape characteristics (e.g. volume, elongation, and symmetry). Suspended particle characteristics varied considerably over space and time and were strongly associated with discharge and concentrations of nitrate + nitrite (NO3−) and soluble reactive phosphorus. Particle characteristics in backwaters were distinct from those in other habitats for most of the study period, likely due to reduced hydrologic connectivity and higher biotic production in backwaters. During low discharge, phytoplankton and zooplankton made up relatively greater proportions of the observed particles. Concurrently during low discharge, concentrations of chlorophyll, volatile suspended solids, and total phosphorus were higher. Our results suggest that there are complex interactions among space, time, discharge, and other environmental variables (e.g. water nutrients), which drive suspended particle dynamics in large rivers. Copyright © 2017 John Wiley &amp; Sons, Ltd.

大阪湾における溶存有機物の起源推定および栄養塩の形態変化

大阪湾における溶存有機物の起源推定および栄養塩の形態変化

Agents of change and temporal nutrient dynamics in the Altamaha River Watershed

AbstractNutrient and carbon dynamics in river ecosystems are shifting, and climate change is likely a driving factor; however, some previous studies indicate anthropogenic modification of natural resources may supersede the effects of climate. To understand temporal changes in river ecosystems, consideration of how these agents act independently and collectively to affect watershed biogeochemistry is necessary. Through the Georgia Coastal Ecosystems Long‐Term Ecological Research Project, we assessed nutrient (phosphorus, nitrogen, silicate) and carbon dynamics, with specific regard to import and export, in the Altamaha River Basin from 2000 to 2012. This is the first study in the region to document the biogeochemical patterns in the Altamaha's four main tributaries, the Little Ocmulgee, Ocmulgee, Oconee, and Ohoopee rivers, and the relationships between biogeochemistry and historical precipitation and discharge patterns as well as agricultural and population census data. As discharge patterns are a primary driver of nutrient loads, we determined that water use was a dominant factor in the shifting ecosystem dynamics. Dissolved inorganic nitrogen loads were primarily driven by population density and dissolved inorganic phosphorus loads were strongly influenced by livestock biomass. Taken together, we conclude that both the transportation and biogeochemical cycling of nutrients within the Altamaha River Watershed were highly impacted by anthropogenic influences, which were then further exacerbated by continued climate change. Furthermore, the N‐ and P‐loads in the Altamaha River and tributaries were dominated by dissolved organic nitrogen and dissolved organic phosphorus, emphasizing a need to further study the bioavailability of these species and the mechanisms driving their potential ecological impacts.

Microbial Carbon, Mineral-N and Soil Nutrients in Indigenous Agroforestry Systems and Other Land Use in the upper Solim&amp;#245;es Region, Western Amazonas State, Brazil

Slash and burn cultivation systems carried out by many farmers in the Amazon region lead to changes in biogeochemical cycles of nutrients. To assess the extent of the impact of shifting cultivation on the soil in a floodplain portion of this region, samples of an Inceptisol surface layer (0 - 5 cm) under primary forest (FP), secondary forest at an advanced stage of recovery (FS), secondary forest at an initial stage of recovery (CAP), agroforestry (SAF), plantations (R?) in indigenous communities and small farmers, and pasture (PAS) in the Upper Solim?es region, Amazonas, were subjected to analysis of chemical composition during the wet (May) and dry (October) seasons, 2007. Soils were fertile with levels of P, K, Ca and Mg above those generally found in Amazon soils. Microbial content did not vary significantly in the systems studied in the wet season, but there was a reduction of around 60% with the change of season, except for soils with SAF. Ammonium nitrogen was predominant in all systems and seasons studied. Nitrate content was higher in R? soil, in two seasons, and lower in PAS. The type of management adopted by farmers in the region’s indigenous agroforestry systems resulted in small changes in P, K, Mg, MBC and mineral-N levels, independent of soil moisture.