Allochtonous Organic Matter Research Articles

URRENT STATE OF THE ECOSYSTEM OF LAKE UROZERO, KARELIA, ASSESSED THROUGH PRIMARY PRODUCTION AND DESTRUCTION INDICATORS

Lake Urozero has the status of a regional-level state hydrological nature monument in the Republic of Karelia. Up until the mid-2000’s, the lake have been noted for very high water transparency and the ultra-oligotrophic state of the ecosystem. In 2018, the prima-ry production and destruction characteristics of the Urozero ecosystem were studied as integral indicators of the current state and direction of its functioning. Such assessments are necessitated by the modified climatic conditions in Karelia, which affect catchments. These changes result in enlarged flow of allochtonous organic matter to water bodies. The values of photosynthesis (average 22 μg C/l per day), chlorophyll a(average 1.6 μg/l), daily assimilation number (on average 21 μg C/μg Chl), P/B factor (average 1.2 days-1) and water transparency (average 9.8 m) were measured in May, July and September. These measurements confirm that the lake ecosystem has retained its ultra-oligotrophic state. In spring and summer, when solar radiation is excessive and water transparency is high, the vertical distribution of chlorophyll ashowed a pattern unusual for Karelia, with maximum values found at the depth of one transparency. The change in the values of or-ganic matter destruction down the water column corresponds to the vertical dynamics of chlorophyll a. This vertical distribution of the values of destruction, as well as the con-sistently high transparency of the lake water, indicates that allochtonous organic mat-ter does not affect the water ecosystem. The natural ecological state of Lake Urozero in the current circumstances of climate change in the catchment area and human pres-sure is retained owing to the absence of surface inflows and nature conservation mea-sures to counteract pollution.

Importance of nitrate reduction in benthic carbon mineralization in two eutrophic estuaries: Modeling, observations and laboratory experiments

Estuaries are important nutrient filters between rivers and coastal zones. However, the quantification of the nutrient mitigation capacity related to benthic diagenesis is still poorly quantified. In this paper, we investigated carbon mineralization and the contribution of benthic nitrate reduction in two macrotidal eutrophic estuaries (Elorn and Aulne, Brittany, France) during winter and spring. These anthropized estuaries exhibited large variations of bottom water nitrate concentrations from very high values in upstream waters (up to 500 μM) to low values downstream (andlt; 10 μM). Bottom water oxygen concentrations presented small gradients compared to nitrate concentrations gradients resulting in large variation in nitrate to oxygen ratios NOx −/O2 between downstream and upstream (0.03–1.6). We combined the use of diagenesis modeling with field data (porosity, organic carbon and nitrogen, pore water profiles of dissolved oxygen, nitrogen, iron, manganese and sulfide concentrations, published in Khalil et al., 2013) and experimentally-determined nitrate reduction rates, in order to investigate the different organic carbon mineralization pathways in these estuarine sediments including denitrification and the contribution of benthic nitrate reduction to the estuarine N budget. Overall a good agreement between pore water data (organic carbon, oxygen, nitrate and ammonium) and model simulations was observed. The modeled organic matter mineralization rates were high in the upstream estuary and low in the saline estuary for the two estuaries Aulne and Elorn. This decrease may be related to the dilution and the trapping of allochtonous organic matter in estuarine sediments and its subsequent recycling in the upper estuary. Organic carbon mineralization rates were higher in the Elorn than in the Aulne estuary, which is most likely related to the labile character of the organic matter from urban origin exported from the Elorn watershed. The contribution of nitrate reduction to the total mineralization was generally high in upstream sediments (15–35%) of both Aulne and Elorn estuaries and decreased consistently downstream to 5–10%. The relative large contribution of nitrate reduction to organic matter degradation was to a large extent related to high bottom water nitrate concentrations that fueled 37–78% of total nitrate reduction in the upstream part of the estuaries. Overall, the reduction of bottom water nitrate by denitrification to N2 represented 3–13% of the river flux of nitrate in these estuaries in winter and spring, and could reach ~ 50% during summer. These results highlight that nitrate reduction in the sediment attenuate the high river nitrate flux, despite the huge quantities of anthropogenic nitrate discharged by the two rivers to the estuaries.

Sedimentary organic matter in two Spitsbergen fjords: Terrestrial and marine contributions based on carbon and nitrogen contents and stable isotopes composition

The aim of this study was to estimate the spatial variability of organic carbon (Corg) and total nitrogen (Ntot) concentrations, Corg/Ntot ratios, stable isotopes of carbon and nitrogen (δ13Corg, δ15Ntot) and the proportions of autochthonous and allochtonous organic matter within recently deposited sediments of two Spitsbergen fjords: the Hornsund and the Adventfjord, which are affected to a different degree by the West Spitsbergen Current. Corg concentrations ranged from 1.38% to 1.98% in the Hornsund and from 1.73% to 3.85% in the Adventfjord. In both fjords the highest Corg concentrations were measured at the innermost stations and they decreased towards the mouths of the fjords. This suggests fresh water runoff to be an important source of organic matter (OM) for surface sediments. The results showed that both fjords differ significantly in terms of sedimentary organic matter characteristics. The samples from the Hornsund, except those from the innermost station in the Brepollen, had relatively low Corg/Ntot ratios, all within a narrow range (from 9.7 to 11.3). On the other hand significantly higher Corg/Ntot ratios, varying within a broad range (from 14.6 to 33.0), were measured in the Adventfjord. The samples from the Hornsund were characterized by higher δ13Corg (from −24.90‰ to −23.87‰) and δ15Ntot (from 3.02‰ to 4.93‰) than those from the Adventfjord (−25.94‰ to −24.69‰ and from 0.71‰ to 4.00‰, respectively). This is attributed to a larger proportion of marine organic matter. Using the two end-member approach proportions of terrestrial organic matter were evaluated. Terrestrial OM contribution for the Adventfjord was in the range of 82-83%, while in case of the Hornsund the results were in the range of 69–75%, with the exception of the innermost part of the fjord, where terrestrial organic matter contribution ranged from 80 to 82%. The strong positive correlation between δ13Corg and δ15Ntot was revealed. This was taken as an indicator that fresh, labile organic matter is the base of the trophic pyramid. The conclusion regarding a more complex food web in the Horsund, based on larger δ15Ntot values, is further substantiated by the larger proportion of autochthonous, labile organic matter found in the Hornsund’s sediments.

Are Algae Relevant to the Detritus-Based Food Web in Tank-Bromeliads?

We assessed the occurrence of algae in five species of tank-bromeliads found in contrasting environmental sites in a Neotropical, primary rainforest around the Nouragues Research Station, French Guiana. The distributions of both algal abundance and biomass were examined based on physical parameters, the morphological characteristics of bromeliad species and with regard to the structure of other aquatic microbial communities held in the tanks. Algae were retrieved in all of the bromeliad species with mean densities ranging from ∼102 to 104 cells/mL. Their biomass was positively correlated to light exposure and bacterial biomass. Algae represented a tiny component of the detrital food web in shaded bromeliads but accounted for up to 30 percent of the living microbial carbon in the tanks of Catopsis berteroniana, located in a highly exposed area. Thus, while nutrient supplies are believed to originate from wind-borne particles and trapped insects (i.e., allochtonous organic matter), our results indicate that primary producers (i.e., autochtonous organic matter) are present in this insectivorous bromeliad. Using a 24-h incubation of size-fractionated and manipulated samples from this plant, we evaluated the impact of mosquito foraging on algae, other microorganisms and rotifers. The prey assemblages were greatly altered by the predation of mosquito larvae. Grazing losses indicated that the dominant algal taxon, Bumilleriopsis sp., like protozoa and rotifers, is a significant part of the diet of mosquito larvae. We conclude that algae are a relevant functional community of the aquatic food web in C. berteroniana and might form the basis of a complementary non-detrital food web.

Functional shifts in unvegetated, perhumid, recently-deglaciated soils do not correlate with shifts in soil bacterial community composition

Past work in recently deglaciated soils demonstrates that microbial communities undergo shifts prior to plant colonization. To date, most studies have focused on relatively 'long' chronosequences with the ability to sample plant-free sites over at least 50 years of development. However, some recently deglaciated soils feature rapid plant colonization and questions remain about the relative rate of change in the microbial community in the unvegetated soils of these chronosequences. Thus, we investigated the forelands of the Mendenhall Glacier near Juneau, AK, USA, where plants rapidly establish. We collected unvegetated samples representing soils that had been ice-free for 0, 1, 4, and 8 years. Total nitrogen (N) ranged from 0.00 approximately 0.14 mg/g soil, soil organic carbon pools ranged from 0.6 approximately 2.3 mg/g soil, and both decreased in concentration between the 0 and 4 yr soils. Biologically available phosphorus (P) and pH underwent similar dynamics. However, both pH and available P increased in the 8 yr soils. Nitrogen fixation was nearly undetectable in the most recently exposed soils, and increased in the 8 yr soils to approximately 5 ng N fixed/cm(2)/h, a trend that was matched by the activity of the soil N-cycling enzymes urease and beta-l,4-N-acetyl-glucosa-minidase. 16S rRNA gene clone libraries revealed no significant differences between the 0 and 8 yr soils; however, 8 yr soils featured the presence of cyanobacteria, a division wholly absent from the 0 yr soils. Taken together, our results suggest that microbes are consuming allochtonous organic matter sources in the most recently exposed soils. Once this carbon source is depleted, a competitive advantage may be ceded to microbes not reliant on in situ nutrient sources.

The structure of Dreissena polymorpha (Pallas) biocenosis and the role of mollusk in roach Rutilus rutilus (Linnaeus) feeding in Pleshcheevo Lake

As a result of studies on the macrozoobenthos composition of zebra mussel biocenosis in Lake Pleshcheevo carried out in 1996, a total of 44 species of bottom macroinvertebrates were found. The richest in terms of species composition were chironomids (17 species), oligochaetes (13 species), and mollusks and leeches (5 species each). After the introduction of zebra mussel Dreissena polymorpha (Pallas) into the lake, a natural biophilter was formed in the waterbody at depths of 4.5 to 9 m. This biophilter intercepts a substantial part of degrading macrophytes and allochtonous organic matter. Thus, the filter prevents the income of this organic matter in the lake’s profundal zone. Two roach Rutilus rutilus (Linnaeus) groups had inhabited Lake Pleshcheevo before dreissena introduction. Comparatively fast growing roach fed predominantly on mollusks of g. g. Valvata and Bithynia, while slowly growing roach fed mostly on zooplankton. After the introduction and mass development of D. polymorpha in the lake, roach started to consume these mollusks. This resulted in increases in the fish growth rate and maximum body size. Roach starts to feed on dreissena and other mollusks after reaching a body length of 15.0 cm. This relates to the third and the last change in the pharyngeal teeth shape, making possible for the fish to consume mollusks and to crush their shells.

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.

Relationship of bacterioplankton production with primary production and respiration in a shallow estuarine system (Ria de Aveiro, NW Portugal)

The response of bacterial growth to phytoplankton production and planktonic respiration (RESP) variation was examined over different stations and dates in the shallow estuarine system Ria de Aveiro. The temporal and spatial profiles of bacterial productivity (2.7-744.2mg Cm(-3)d(-1)) did not coincide with those of primary production (PP) (0.2-19.1 g Cm(-3)d(-1)) and RESP (0.1-8.2 g Cm(-3) d(-1)). The bacterioplankton production/PP ratio varied differently, depending on the season and location. The heterotrophic zones, with the lowest values of PP, exhibited the most intense bacterial secondary production. Moreover, the variation of PP in the system was rather small when compared with that of bacterial secondary production. These suggest that, in a large extension of the lagoon and throughout the year, bacterioplankton growth is largely dependent on non-phytoplanktonic carbon sources. Benthic PP and/or allochtonous organic matter from land have a fundamental role in the dynamics of the planktonic compartment of the estuarine system.

Sources of suspended organic matter and selective feeding by zooplankton in an estuarine mangrove ecosystem as traced by stable isotopes

Between January 1995 and August 1996, suspended matter and zooplankton were sam- pled at different locations in a mangrove ecosystem located in the Gautami Godavari estuary and adjacent Kakinada Bay (Andhra Pradesh, India). Suspended matter was sampled at 13 different sta- tions, and was found to have a highly variable carbon stable isotope composition, with δ 13 C values ranging overall between -30.94 and -19.18 ‰, and a highly variable elemental (C:N) composition. Our data suggest that the phytoplankton component has a seasonally and spatially variable δ 13 C sig- nature, which is surpressed by the terrestrial signal but may at times fall in the same range as the δ 13 C of the allochtonous matter. It is argued that the phytoplankton δ 13 C decreases after the onset of the monsoon rains, most likely due to the 13 C-depletion of the DIC pool caused by the microbial respira- tion of the allochtonous organic matter. At each of the 4 sites selected for concurrent zooplankton sampling, the zooplankton showed a much wider range of δ 13 C than did the suspended matter, with overall δ 13 C values between -30.14 and -16.45‰. In addition, spatial differences in average δ 13 C were much more pronounced for zooplankton than for total suspended matter. These data indicate that zooplankton feed on a component of the suspended matter pool, which has more pronounced seasonal and spatial δ 13 C variations than the total suspended matter. Thus, despite the large amounts of terrestrial and mangrove detritus present in the water column, the locally produced phytoplankton appears to be a more important carbon source for the zooplankton.

Influence of basin scale on structure of natural aquatic communities

The aim of the study was to analyze the influence of aquatic ecosystem size on community structure. Analysis is based on quantitative indices, describing integral communities and comparison of their biomass size spectra with standard patterns. Comparative analysis of widely differing aquatic communities shows that certain characteristics of the community structure withstand considerable changes of many important parameters of the abiotic environment and taxonomic composition of the community. At the same time, there are some changes in fine structure of the community size spectra, which can now be documented and measured with relatively high precision due to development of modern automated means of data acquisition. In this study, application of spectral descriptions is discussed as applied to communities of River Jordan-Lake Kinneret aquatic system. It follows from the theoretical scheme developed that, for analysis, the most important part of the community size spectrum is its right extreme, i.e. body size of the largest species of the ecosystem. In the case of Lake Kinneret, that is fish. The fish biomass size spectra were obtained using dual-beam hydro-acoustics techniques. The parameter comparison shows that for riverine systems (i.e. ecological systems with a high role of allochtonous organic matter in the total energy influx of the community), both the water area and the watershed basin (including its terrestrial part) deserve attention as the appropriate scaling parameter.

Benthic nutrient fluxes on a basin-wide scale in the Skagerrak (North-Eastern North Sea)

Benthic ammonium, nitrite, nitrate, phosphate and silicate fluxes were measured on a basin-wide scale (14 locations) in the open Skagerrak. Fluxes were measured in situ at two of the locations using a benthic chamber lander. The benthic flux measurements revealed patterns of geographic variation of nutrient fluxed in the Skagerrak. Nitrate fluxes generally reflected sediment deposition patterns and were mainly directed into the sediment in the high accumulation areas, and out of the sediment in areas with relatively little import of allochtonous organic matter. The nitrate fluxes were related to C/N-ratios of sediments. Low C/N-ratios were associated with high (in relative terms) nitrate effluxes and high C/N-ratios were associated with high nitrate fluxes into the sediment, suggesting that the fastest net regeneration (and nitrification) of nitrogen occurred in nitrogen-rich (low C/N) sediments. The nitrate flux into nitrogen-poor (high C/N) sediments appeared to be due to denitrification in the main sediment deposition areas, where mainly allochtonous organic matter is thought to accumulate. Areas of net benthic nitrification were thus on the Danish shelf and in the western part of the Norwegian Trench. Areas of net denitrification were in the eastern, northeastern and also central deep part of the Skagerrak. In these areas virtually all of the dissolved inorganic nitrogen fluxes were directed into the sediment and they are suggested to constitute considerable sinks for non-gaseous nitrogen. Phosphate fluxes were highest in the central deep part and lower on the margins of the Skagerrak. They appeared to be positively related to clay contents of sediments. Silicate fluxes varied little: almost all fluxes were between 1 and 2 mmol·m −2·d −1. Sediment oxygen uptake did not correlate any of the nutrient fluxes except with those of silicate. It is suggested that benthic silicate fluxes reflected the deposition of a large proportion of the fast-sinking, autochtonously produced diatoms on the sea-floor of the Skagerrak, whereas a great deal of other fresh in situ produced algal material may be flushed out of this sea. There was no relation between either organic carbon contents of sediments or water depths and benthic fluxes of any of the nutrients. The phosphate and silicate fluxes measured did not correlate with any of the other nutrient fluxes, nor with each other. The ammonium fluxes were, however, generally inversely related to the nitrate fluxes with high (in relative terms) influxes of ammonium correlating with high effluxes of nitrate. We suggest this was due to nitrification, and that the nitrifying bacteria could not meet their ammonium demand with what was regenerated in the sediment, so that additional ammonium had to be taken up from the overlying water. High nitrite influxes were associated with both high nitrate influxes and effluxes. Uptake of nitrate from the overlying water in association with nitrate effluxes is interpreted as a consumption of nitrate during nitrification, and uptake of nitrate in association with nitrate uptake was probably mainly due to nitrite consumption during denitrification. The observed relation between nitrite and nitrate fluxes indicates that the rate-limiting step in benthic nitrification was the oxidation of ammonium to nitrite, and in dentrification it probably was the reduction of nitrate to nitrite.

Plankton and hydrography in a moderately eastern Adratic bay (Gruž Bay)

Gruž Bay (south-eastern Adriatic) is moderately eutrophicated, mostly by discharge from the karst river Ombla. Input of inorganic nitrogen might be attributed to enrichment from the open sea during strong and continuous north winds in winter 1988/89. Annual succession of primary producers, herbivores and decomposers was defined by seven stages and induced by specific physical-chemical characteristics. In the period April–August, biological production was mostly due to small size fractions of phytoplankton and zooplankton. Recycling of planktonic biomass occurred in September, of allochtonous organic matter in February and March.

Variations morphologiques et adaptations morphofonctionnelles chez les ostracodes: Signification environnementale

Ostracodes present a diversity and a variability affecting their distribution as well as their morphology, which reflect with accuracy and reliability the characteristics and the fluctuations of marine and continental biotopes. An inventory of variable morphologies and their relationships with the adaptation of biological and physiological functions (morphofunctional aspect) is undertaken, using chosen examples in post-paleozoic times. The considered morphological elements are as follows: central muscle scars pattern, marginal zones and vestibule (internal characters), size, carapace geometry, ocular tubercles, external ornamentation, normal pore canals. In recent and past environments, each of the considered elements and/or the combination of several of them, is used to trace one of some parameters, generally interdepending on the environment: hydrological, physico-chemical, trophic, dynamic and climatic parameters. For example, there are relationships between the variation of the valve reticulation and carbonate equilibrium at the water-sediment interface; nodation is an indication of low salinity or of an enrichment in allochtonous organic matter; the presence and development of an ocular tubercle is characteristic of life in the photic zone; the size of the vestibule in some species is related to the oxygene concentration. In conclusion, the reliability limits for application of available informations are discussed and future prospects evolved.

On the quantitative characteristics of the pelagic ecosystem of Dalnee lake (Kamchatka)

The parameters of biomass and productivity of the main components of the pelagic ecosystem have been estimated in lake Dalnee (Kamchatka) during the first phase of the period of vegetation in July 1969. The water column in the lake during this period was stratified. The layer-character of vertical distribution of bacteria, phytoplankton, protozoa, rotifers and young stages of crustaceans was elucidated. The adult copepods migrate during the day. The nutrition of the mass species of zooplankton was studied using the C14-method. The data on the spectrum of feeding, on rations and on optimal food concentrations were ascertained. All these data, together with the observations in the lake, were used for the construction of a scheme of energy flow. The scheme shows that the ecosystem of the lake receives the third part of its energy from the land as allochtonous organic matter via microbial biosynthesis. The main part of energy accessible to the animals of the second trophical level is used by protozoa, and of a third part by the predatory rotiferAsplanchna.