Autochthonous Organic Matter Production Research Articles

Reconstructing eutrophication trends of a shallow lake environment using biomarker dynamics and sedimentary sterols

Major extractable lipid biomarkers (hydrocarbons, sterols and fatty acids) were assessed in Lake Seeburg, a shallow eutrophic lake that has increasingly been suffering from cyanobacterial blooms due to continued anthropogenic nutrient inputs over the last decades. Over the course of one year (2018/19), the distributions of these compounds were analyzed in the inflow, the lake water, and the topmost sediments (0–2 cm) to assess their origin and transfer into the lake deposits. Principal component analysis (PCA) was used to cluster the studied biomarkers into 5 groups with similar characteristics. These groups were comprised of (i) compounds delivered from external sources via the inflow, (ii) autochthonous compounds formed in the lake by eukaryotes or (iii) bacteria, (iv) compounds accumulating in the surface sediment, and (v) C27 to C29 stenols together with their degradation products, C27 to C29 5α(H)-stanols. Their seasonal partition clearly revealed that C27 stenols mainly derived from autochthonous sources within the lake, whereas C29 stenols largely reflect allochthonous material reaching the lake via the inflow. Analysis of stenol plus stanol concentrations with depth in two lake sediment cores (≈30 and 50 cm) found highest C27 to C29 ratios in surface sediments with lowest ratios at depth. These signals are interpreted to reflect the increasing trend of eutrophication of Lake Seeburg and, thus, enhanced autochthonous organic matter production in the lake over the last decades. The abundances of C27 vs. C29 stenols, summed with their respective degradation products, 5α(H)-stanols, are considered as suitable molecular indicators to qualitatively reconstruct historical eutrophication trends.

Temperature is a better predictor of stable carbon isotopic compositions in marine particulates than dissolved CO2 concentration

The stable carbon isotopic composition of marine particulate organic matter (δ13CPOM) varies with source and environmental conditions. Dissolved carbon dioxide (CO2) concentration is thought to influence δ13CPOM more than temperature, but this relationship is poorly constrained in marginal seas. Here we present δ13CPOM, hydrographic and carbonate system variables at the deep chlorophyll maxima of the southern Yellow Sea in late summer 2017. We find δ13CPOM values varied between stable and cyclonic gyre regions, but indicated autochthonous organic matter production and were more strongly correlated with temperature than dissolved CO2 concentration throughout. We find that the relationship between temperature and δ13CPOM was independent of CO2 concentration, whereas the relationship between δ13CPOM and CO2 concentration was dependent on temperature also being correlated with CO2 concentration. We suggest that temperature is the primary determinant of marine δ13CPOM due to temperature-dependent metabolism in phytoplankton, irrespective of inorganic carbon acquisition mode.

Cyanobacteria and cyanophage contributions to carbon and nitrogen cycling in an oligotrophic oxygen-deficient zone

Up to half of marine N losses occur in oxygen-deficient zones (ODZs). Organic matter flux from productive surface waters is considered a primary control on N2 production. Here we investigate the offshore Eastern Tropical North Pacific (ETNP) where a secondary chlorophyll a maximum resides within the ODZ. Rates of primary production and carbon export from the mixed layer and productivity in the primary chlorophyll a maximum were consistent with oligotrophic waters. However, sediment trap carbon and nitrogen fluxes increased between 105 and 150 m, indicating organic matter production within the ODZ. Metagenomic and metaproteomic characterization indicated that the secondary chlorophyll a maximum was attributable to the cyanobacterium Prochlorococcus, and numerous photosynthesis and carbon fixation proteins were detected. The presence of chemoautotrophic ammonia-oxidizing archaea and the nitrite oxidizer Nitrospina and detection of nitrate oxidoreductase was consistent with cyanobacterial oxygen production within the ODZ. Cyanobacteria and cyanophage were also present on large (>30 μm) particles and in sediment trap material. Particle cyanophage-to-host ratio exceeded 50, suggesting that viruses help convert cyanobacteria into sinking organic matter. Nitrate reduction and anammox proteins were detected, congruent with previously reported N2 production. We suggest that autochthonous organic matter production within the ODZ contributes to N2 production in the offshore ETNP.

Biogeochemical markers across a pollution gradient in a Patagonian estuary: A multidimensional approach of fatty acids and stable isotopes

A combined approach merging stable isotopes and fatty acids was applied to study anthropogenic pollution in the Río Negro estuary. Fatty acid markers of vegetal detritus indicated considerable allochthonous inputs at freshwater sites. Correlative evidence of diatom fatty acids, δ13C, chlorophyll and particulate organic matter suggested the importance of diatoms for the autochthonous organic matter production at the river mouth. Low δ15N values (~0‰) and high fatty acid 18:1(n-7) concentrations in the suspended particulate matter, in combination with the peaks of coliforms and ammonium, indicated a strong impact of untreated sewage discharge. The 15N depletion was related to oxygen-limited ammonification processes and incorporation of 15N depleted ammonium to microorganisms. This work demonstrates that the combined use of lipid and isotopic markers can greatly increase our understanding of biogeochemical factors and pollutants influencing estuaries, and our findings highlight the urgent need for water management actions to reduce eutrophication.

Catchment land use-dependent effects of barrage fishponds on the functioning of headwater streams.

Extensive fish production systems in continental areas are often created by damming headwater streams. However, these lentic systems favour autochthonous organic matter production. As headwater stream functioning is essentially based on allochthonous organic matter (OM) supply, the presence of barrage fishponds on headwater streams might change the main food source for benthic communities. The goal of this study was thus to identify the effects of barrage fishponds on the functioning of headwater streams. To this end, we compared leaf litter breakdown (a key ecosystem function in headwater streams), their associated invertebrate communities and fungal biomass at sites upstream and downstream of five barrage fishponds in two dominant land use systems (three in forested catchments and two in agricultural catchments). We observed significant structural and functional differences between headwater stream ecosystems in agricultural catchments and those in forested catchments. Leaf litter decay was more rapid in forest streams, with a moderate, but not significant, increase in breakdown rate downstream from the barrage fishponds. In agricultural catchments, the trend was opposite with a 2-fold lower leaf litter breakdown rate at downstream sites compared to upstream sites. Breakdown rates observed at all sites were closely correlated with fungal biomass and shredder biomass. No effect of barrage fishponds were observed in this study concerning invertebrate community structure or functional feeding groups especially in agricultural landscapes. In forest streams, we observed a decrease in organic pollution (OP)-intolerant taxa at downstream sites that was correlated with an increase in OP-tolerant taxa. These results highlighted that the influence of barrage fishponds on headwater stream functioning is complex and land use dependent. It is therefore necessary to clearly understand the various mechanisms (competition for food resources, complementarities between autochthonous and allochthonous OM) that control ecosystem functioning in different contexts in order to optimize barrage fishpond management.

Autochthonous Versus Allochthonous Organic Matter in Recent Soil C Accumulation Along a Floodplain Biogeomorphic Gradient: An Exploratory Study

Abstract The mechanisms controlling soil succession in floodplains remain much less studied than in uplands due to the complexity that flooddriven erosion and sedimentation bring into soil development processes. The amount of organic matter and C generally grows with soil ageing and is controlled by multiple and interacting allogenic and autogenic factors, but to what extent the production of organic matter by in situ vegetation contributes to soil formation in floodplains remains unknown. The objective of this work was to explore the importance of autochthonous organic matter versus allochthonous organic matter in organic C accumulation of floodplain forest soils along a vegetation succession and hydrogeomorphic connectivity gradient. Physicochemical analyses of sediment collected after one single flood event in a large Mediterranean floodplain (Middle Ebro, a 9th order regulated river reach in NE Spain) were used to estimate the proportion of organic C found in the topsoil (first 10 cm) samples of young (<25 yr), mature (25-50 yr) and old (>50 yr) floodplain forests that had an allochthonous (i.e., % of organic C deposited by floods) or autochthonous (i.e., % of organic C produced in situ by vegetation) source. Results of this exploratory study showed that the accumulation of autochthonous organic C in the floodplain topsoil only occurred in floodplain forests older than 50 year-old, but even then, it was more than six-fold less abundant than that with an allochthonous origin. Moreover, a linear mixed effect model showed that, although autochthonous organic C accumulation was mainly explained by the forest structure, a small proportion of it was also controlled by an allogenic factor, the groundwater table depth. Then, groundwater table depth variations could be partly controlling autochthonous organic matter production and decomposition in this Mediterranean floodplain. Although flow regulation and embankment has dramatically limited the hydrogeomorphic dynamics of the river, allogenic overbank sedimentation during flood events still controls floodplain soil succession and organic C accumulation in the floodplain.

Sediment accumulation rates in European lakes since AD 1850: trends, reference conditions and exceedence

Sediment accumulation rate (SAR) is an important physical parameter in all lakes and increases have been observed in many over the last c.100 years. This has been ascribed to changes in land-use and land-management causing accelerated catchment soil erosion and an increase in autochthonous organic matter production. The EU Water Framework Directive requires that assessment of biological, hydromorphological and chemical elements of water quality should be based on the degree to which present day conditions deviate from those expected in the absence of significant anthropogenic influence, termed reference conditions. Currently however, the reference condition for sediment accumulation rate for lakes of different types is undefined. To improve our understanding of the controls on SARs we compiled SAR and lake typology data for 207 European lakes derived from 210Pb dated cores to assess how rates have changed through time (in 25 year classes) both overall and for lakes of different types. Seventy-one percent of these sediment cores showed surface SARs higher than “basal” (mainly nineteenth century) rates, 11% showed no change while 18% showed a decline. Lakes were then classified into lake-types using four variables: alkalinity (3 classes), altitude (3 classes), maximum depth (2 classes) and lake area (2 classes). This generated a possible 36 lake classes of which 25 were represented in the dataset. Nine lake-types contained >10 lakes. Little change in SAR occurred prior to 1900 and most increases occurred in more recent periods, in particular 1950–1975 and post-1975. This indicates a general acceleration in SAR in European lakes during the second half of the twentieth century. Reference SARs were estimated for six lake-types with the highest number of sites. European mountain lakes had the lowest reference SAR (0.005 ± 0.003 g cm−2 yr−1) while lowland, high alkalinity sites had the highest (0.03–0.04 g cm−2 yr−1). SARs for other lake-types ranged between 0.012 and 0.024 g cm−2 yr−1. Using the mountain lake-type as an example, the 1850 reference SAR appears to show good agreement with available data for lakes beyond Europe indicating these values may be more broadly applicable. Contemporary SARs in lakes of all classes showed exceedence over their defined reference SAR. This may be partly due to diagenetic processes. Greatest exceedences were found in shallow, low altitude lakes and these are considered to be the ones under the greatest threat from continued elevation of SAR. It is considered that climate change may play a progressively more important role in driving SAR in the future.

Analysis of the hydrophysical structure of the Sea of Azov in the period of the bottom anoxia development

The hydrophysical and hydrochemical structure of the Sea of Azov, with developed bottom anoxia, was studied during the RV “Akvanavt” cruise from July 31 to August 03, 2001. The anoxic zone with a thickness from 0.5 to 4 m above the bottom was found in all deep regions of the Sea. Concentrations of hydrochemical parameters were similar to the pronounced anoxic conditions (about 90 mmol m − 3 of hydrogen sulfide, 17 mmol m − 3 of ammonia, 6 mmol m − 3 of phosphate, 7 mmol m − 3 of total manganese). The hydrophysical structure was characterized by the uniform distribution of temperature in the upper 6–7 m mixed layer (UML). Below this a thin (0.4–0.8 m) thermocline layer was observed, just above the anoxic waters. Formation of this phenomenon was connected with that summer weather conditions. Intensive rains led to increased influx of river waters in June. That resulted in large input of allochtonous organic matter (OM) and inorganic nutrients; the latter were consumed on the additional autochthonous organic matter production. In July the weather was characterized by a significant rise in the daily averaged air temperature and large oscillations of temperature during the day. In this period a wind of constant direction was absent, but wind bursts were observed. The completed analyses showed that the formation of such a structure could be connected with the following factors: (i) positive growth trends of the daily averaged temperature and the daily oscillations of temperature, (ii) presence of wind bursts. The joint action of these factors resulted in the formation of the UML. The amplitude of wind bursts determined the depth of UML, and the value of trend determined the value of the temperature change in the thermocline. An initial presence of bottom halocline (caused by the Black Sea water influx to the bottom of the Sea of Azov) prevented the heating of the bottom layer and therefore led to an increase of vertical gradient of temperature in the thermocline. The spatial distribution of the turbulent exchange coefficient confirmed the existence of a “stagnation” area located above the anoxia zone, which is also, apparently, the reason for its occurrence.

Biomarkers and geochemical indicators of Holocene environmental changes in coastal Lake Sarbsko (Poland)

Organic-rich samples from the Holocene sedimentary sequence of Lake Sarbsko were investigated to reconstruct variations in the aquatic system in response to environmental change. The aims were to (i) identify organic matter (OM) sources, (ii) examine changes in soluble OM composition in relation to fluctuations in limnological conditions and (iii) validate the sensitivity of organic geochemical indicators in tracing environmental changes. Diatom frustules are abundant in all samples. Alginite macerals and terrigenous organic matter further contribute to the sedimentary OM. Organic petrography, total organic carbon (TOC)/N ratio values and high content of biogenic silica (SiO 2 biogenic ) argue for a predominant algal source of OM. In contrast, the n-alkane distributions, high relative abundance of C 29 steroid hydrocarbons and high content of detrital quartz in the sediments provide evidence for the input of terrigenous material as a major OM source within the basin. The terpenoid biomarker composition indicates a contribution from conifers and angiosperms. From the diterpenoids in the samples a contribution from species of the coniferales family Pinaceae is concluded. TOC/S and Mg/Ca values, as well as steroid/hopanoid concentration ratios, reflect enhanced water salinity in this coastal lake due to ingression of brackish water from the Baltic Sea during the Atlantic and Sub-Atlantic periods. As indicated by the positive relationship between δ 13C of TOC and Mg/Ca, δ 13C values are influenced by changing contribution of marine vs. freshwater phytoplankton. Additional isotopic heterogeneity in δ 13C may result from differences in terrigenous OM supply vs. autochthonous OM production in the lake. The isotopic composition of calcites supports the establishment of freshwater conditions in the lake during the Sub-Boreal period. Pristane/phytane and Fe/Mn ratios are interpreted to reflect differences in the redox conditions. Oxygenation of bottom waters was temporarily variable, with highest levels of oxygen availability during the Sub-Boreal (freshwater lake). High contents of hopanoid hydrocarbons argue for enhanced microbial activity in the water column and sediment. The occurrence of 2β-methyl-hopanes is related to the presence of cyanobacteria or methylotrophic bacteria. The results demonstrate that in coastal basins of the Baltic Sea sedimentary OM content and composition are a function of the degree of isolation from the sea water. Therefore, organic geochemical data of coastal lake and lagoonal sediments are sensitive indicators for tracing environmental changes during the Holocene.

Palaeoenvironment of the Eocene Eckfeld Maar lake (Germany): implications from geochemical analysis of the oil shale sequence

Drill core samples from the depth interval between 19.4 and 32.0 m of the laminated central lake facies of the Eocene Eckfeld Maar were investigated for biomarker and stable isotope composition. Bulk organic geochemical parameters (C/N, HI) and the molecular composition of the soluble organic matter indicate a dominance of particulate organic matter from land plants and microbially derived lipids in the lower part of the sedimentary succession. An angiosperm-dominated vegetation is indicated from the terpenoid biomarker composition. Abundant 4-methylsteroids in the 25.6–30.8 m section of the oil shale sequence reflect a contribution of algal-derived biomass. Samples with high concentrations of methylsteroids are characterized by low amounts of triterpenoids related to the arborane skeleton, and vice versa. This pattern is interpreted as reflecting differences in autochthonous organic matter production vs. microbial activity. In the lowermost section (32.0–30.6 m), a trend towards heavier δ 18O and δ 13C values indicates the evolution of permanently meromictic conditions in the lake and an increase in methanogenesis. High δ 13C values of siderites (>10‰) throughout most of the sequence are consistent with permanently anoxic conditions at the sediment–water interface. The lighter δ 18O values of siderites from turbidites, relative to siderites from biogenic laminites, are postulated to have been caused by temporary phases of increased precipitation, followed by landslides and improved circulation within the lake. Depletion of the organic matter in 13C (average δ 13C = −29.4‰), in comparison with the fossil wood (ranging from −23.1‰ to −26.6‰), is explained by the dominance of waxy, lipid-rich land plant material (e.g., leaf waxes, resins, bark) over wood supplied to the lake. Carbon cycling during anoxic decomposition of organic matter is assumed to further affect the δ 13C values through the activity of anaerobic (e.g., methanogenic) bacteria, resulting in a depletion of the biomass in 13C. The overall trend in the isotopic composition of organic carbon towards heavier values in the depth interval between 26.0 and 3.2 m is accompanied by decreasing C/N ratios, indicating an increase in aquatic organic matter production. The geochemistry of the oil shale succession points towards a highly productive, eutrophic ecosystem with intense microbial activity under meromictic conditions in the Maar lake. Beside the high input of land plants to the biomass, major contributions from bacteria and phytoplankton are indicated by the biomarker composition.

Seasonal dynamics of bacterial growth efficiencies in relation to phytoplankton in the southern North Sea

ABSTRACT: The main function of heterotrophic bacterioplankton in marine carbon cycling is theconversion of dissolved organic carbon (DOC) into biomass and CO 2 . The relative importance of bac-terial biomass production (BP) versus respiration (BR) is expressed by the bacterial growth efficiency(BGE = BP/(BP + BR) ×100). Studies on the dynamics of the BGE of bacterioplankton growing on nat-ural DOC covering entire seasonal cycles are scarce. We measured BP and BR over a seasonal cyclein the southern North Sea at a total of 150 stations to determine seasonal variability in BGE. While BPvaried over 1 order of magnitude over the seasonal cycle, BR varied only 2-fold. Cell-specific BP wasrelated to primary production while BR was not. Mean BGE increased from 6 ± 3% in the winter to25 ± 9% in the spring and summer. Depth-integrated BR was fairly stable over the seasonal cycle,averaging 57% of the particulate primary production. Based on the bacterioplankton respiration andthe mean annual BGE of 20%, bacterioplankton organic carbon demand amounts to ∼70% of theparticulate primary production in the southern North Sea, suggesting that autochthonous organicmatter production is sufficient to fuel bacterioplankton carbon demand.KEY WORDS: Bacterioplankton · Bacterial production · Bacterial respiration · Bacterial growthefficiency · Primary production · North Sea

An organic matter and nitrogen dynamics model for the ecological analysis of integrated aquaculture/agriculture systems: I. model development and calibration

A dynamic and mechanistic mass balance model (Integrated Aquaculture/Agriculture System model, or IAAS) for predicting nitrogen and organic matter outputs from aquaculture ponds and their subsequent recycling in conventional agriculture practices has been developed and calibrated using data from Honduras, Thailand and Malawi. The model, developed using Stella™ modeling software (High Performance Systems, Inc. Hanover, New Hampshire), simulates individual fish growth, organic matter, nitrogen (organic, total ammonia and nitrate), dissolved oxygen and phytoplankton, crop growth, soil nitrogen concentrations and soil water balance. Processes included in the model are fish growth, crop biomass growth, allochthonous and autochthonous organic matter production, organic matter decomposition, nitrogen input, nitrogen mineralization, nitrification, denitrification, diffusion, uptake and leaching. The model has been calibrated using literature and observed parameter values from experiments. The calibration procedure involves running the model using inputs from observed data, comparing the model output to observed data, and making appropriate adjustments to parameter values until a general fit between the model and observed values is observed. The structure of the model allows users to modify parameter values to suit different simulation scenarios via a user interface display that also includes graphs and tables for model output.

A detailed ecosystem model of phosphorus dynamics in created riparian wetlands

A generalized yet detailed wetland ecosystem model was calibrated and validated with 3 years’s data from four similarly constructed wetlands in northeastern Illinois, USA. The model was used to explore the role of different wetland structure and function in relation to phosphorus retention, to integrate collected data and provide a better understanding at the ecosystem level about constructed wetlands, and to predict the sediment and phosphorus retentions under different hydrologic conditions. Four submodels — hydrology, primary productivity, sediments, and phosphorus — were included in the model. Phosphorus cycling was reasonably simulated with one set of parameters for a total of 10 wetland-years. The model showed that autochthonous organic matter production varies from 300 to 1036 g dw m −2 year −1, with 12 to 103 g dw m −2 year −1 accumulating as bottom detritus. This compares to inflows of sediments from the river (allochthonous) of 192–934 g dw m −2 year −1. Simulated sediment accumulation ranged from 6 to 29 mm year −1 with high inflow wetlands having higher sediment accumulation rates than low flow wetlands. Model estimates are well below the 50–100 mm year −1 rates predicted by sedimentation trap data in previous studies. Total phosphorus retained with sedimentation is simulated at a rate of 1.08–2.47 g P m −2 year −1, in the range of values reported for other wetlands. Simulations showed that macrophytes pumped about 0.31–1.66 g P m −2 year −1 out of deep sediments, and increased total phosphorus in the water column mostly during the non-growing season. Simulated phosphorus retention increased by 5.1% when macrophytes were removed from the wetland. Simulated phosphorus retention decreased from 90 to 50% when inflow increases from 8 cm week −1 to 200 cm week −1. Manipulating the hydrologic regime to increase phosphorus removal efficiency may be a desirable strategy for constructed wetlands. Constructed wetlands are dynamic ecosystems for which we generally have poor predictive capabilities; ecological modelling provides us with a useful tool for understanding wetland function and structure, testing hypothesis, and making predictions.