Productivity In Aquatic Systems Research Articles

Photosynthetic microorganisms effectively contribute to bryophyte CO2 fixation in boreal and tropical regions

Photosynthetic microbes are omnipresent in land and water. While they critically influence primary productivity in aquatic systems, their importance in terrestrial ecosystems remains largely overlooked. In terrestrial systems, photoautotrophs occur in a variety of habitats, such as sub-surface soils, exposed rocks, and bryophytes. Here, we study photosynthetic microbial communities associated with bryophytes from a boreal peatland and a tropical rainforest. We interrogate their contribution to bryophyte C uptake and identify the main drivers of that contribution. We found that photosynthetic microbes take up twice more C in the boreal peatland (~4.4 mg CO2.h−1.m−2) than in the tropical rainforest (~2.4 mg CO2.h−1.m−2), which corresponded to an average contribution of 4% and 2% of the bryophyte C uptake, respectively. Our findings revealed that such patterns were driven by the proportion of photosynthetic protists in the moss microbiomes. Low moss water content and light conditions were not favourable to the development of photosynthetic protists in the tropical rainforest, which indirectly reduced the overall photosynthetic microbial C uptake. Our investigations clearly show that photosynthetic microbes associated with bryophyte effectively contribute to moss C uptake despite species turnover. Terrestrial photosynthetic microbes clearly have the capacity to take up atmospheric C in bryophytes living under various environmental conditions, and therefore potentially support rates of ecosystem-level net C exchanges with the atmosphere.

Assessment of Nutrient Contents in River Waters Introduced to Beni Haroun Dam, North East Algeria

The main objective of this study was to assess the hydrochemical water quality of the rivers that flowed into the Beni Haroun dam by integrating the use of biogeochemical and multivariate statistical investigation methods. Water samples were collected from the four principal rivers (Oued Rhumel, Oued Radjas, Oued Kebir and Oued El-Kotone rivers) flowing into the Beni Haroun dam in February 2020. Essential physical parameters (pH, Electric Conductivity (EC), Total Dissolved Solids (TDS) and Dissolved Oxygen (O2)) and nutrient contents (dissolved inorganic nitrogen (DIN: NH4, NO3 and NO2), phosphate (PO4) and silicates (SiO4) were analysed. The results of our study showed important variations in physical parameters according to the characteristics of each river; additionally, SiO2, NO3 and NO2 were found to be highly abundant in Oued Rhumel, Oued Radjas and Oued El-Kotone rivers. This abundance could be explained by the fact that these three rivers were more exposed to anthropogenic pollution principally due to agricultural activities compared to the Oued Kebir river. In contrast, NH4, as well as phosphate (PO4), was present at high concentrations in both Oued Rhumel and Oued Radjas rivers. These biogeochemical conditions would have severe impacts on the functioning and productivity of aquatic systems.

Did the COVID-19 Lockdown-Induced Hydrological Residence Time Intensify the Primary Productivity in Lakes? Observational Results Based on Satellite Remote Sensing

The novel coronavirus pandemic (COVID-19) has brought countries around the world to a standstill in the early part of 2020. Several nations and territories around the world insisted their population stay indoors for practicing social distance in order to avoid infecting the disease. Consequently, industrial activities, businesses, and all modes of traveling have halted. On the other hand, the pollution level decreased ‘temporarily’ in our living environment. As fewer pollutants are supplied in to the hydrosphere, and human recreational activities are stopped completely during the lockdown period, we hypothesize that the hydrological residence time (HRT) has increased in the semi-enclosed or closed lake bodies, which can in turn increase the primary productivity. To validate our hypothesis, and to understand the effect of lockdown on primary productivity in aquatic systems, we quantitatively estimated the chlorophyll-a (Chl-a) concentrations in different lake bodies using established Chl-a retrieval algorithm. The Chl-a monitored using Landsat-8 and Sentinel-2 sensor in the lake bodies of Wuhan, China, showed an elevated concentration of Chl-a. In contrast, no significant changes in Chl-a are observed for Vembanad Lake in India. Further analysis of different geo-environments is necessary to validate the hypothesis.

Variability of particulate bioavailable phosphorus, particulate organic carbon and nitrogen in agricultural and urban rivers

Suspended sediments (SS) play a key role as carriers of particulate nutrients which support primary productivity in aquatic systems. In this study, we assessed the relationship between particulate bioavailable phosphorus (PBAP), particulate organic carbon (POC) and particulate organic nitrogen (PON) in rivers flowing through contrasting land use at high and low flow. PBAP as a percentage of particulate phosphorus varied from 5 to 54%, and at low flow, there was a significant increase in PBAP fraction in the urban river as compared to the agricultural river. In addition, elevated POC and PON concentrations in both rivers were associated with low flow. POC and PON concentrations in both rivers declined at high flow presumably due to the mixing effects of water from different sources in the watershed which could have altered the particulate organic matter composition. A significant correlation existed between POC and SS in both rivers, and POC to PON ratios of SS from the rivers point to the change in the nature of particulate organic matter at varying flow conditions. PBAP exhibited a positive relationship with POC and PON concentration in both rivers possibly an indication that particulate organic matter contributes to bioavailable phosphorus in the rivers.

Application of the Beer–Lambert Model to Attenuation of Photosynthetically Active Radiation in a Shallow, Eutrophic Lake

AbstractModels of primary production in aquatic systems must include a means to estimate subsurface light. Such models often use the Beer–Lambert law, assuming exponential attenuation of light with depth. It is further assumed that the diffuse attenuation coefficient may be estimated as a summation of scattering/absorbing constituent concentrations multiplied by their respective specific attenuation coefficients. While theoretical deviations from these assumptions have been documented, it is useful to consider the empirical performance of this common approach. Photosynthetically active radiation (PAR) levels and water quality conditions were recorded weekly from six to eight monitoring stations in western Lake Erie between 2012 and 2016. Exponential PAR extinction models yielded a mean attenuation coefficient of 1.55 m (interquartile range = 0.74–1.90 m). While more complex light attenuation models are available, analysis of residuals indicated that the simple Beer–Lambert model is adequate for shallow, eutrophic waters similar to western Lake Erie (R2 > 0.9 for 96% of samples). Three groups of water quality variables were predictive of PAR attenuation: total and nonvolatile suspended particles, dissolved organic substances (dissolved organic carbon and chromophoric dissolved organic matter), and organic solids (volatile suspended solids and chlorophyll). Multiple regression models using these variables predicted 3–90% of the variability in PAR attenuation, with a median adjusted R2 = 0.86. Explanatory variables within these groups may substitute for each other while maintaining similar model performance, indicating that various combinations of water quality variables may be useful to predict PAR attenuation, depending on availability within a model framework or monitoring program.

Nitrogen fixation and carbon uptake in a tropical estuarine system of Goa, western India

Biological production in aquatic systems is often nitrogen limited. Nitrogen (N2) fixation is an important contributor to nitrogen requirement of phytoplankton not only in oligotrophic but also in nutrient-replete waters. However, the importance of N2 fixation in meso-polyhaline estuaries is not well known. Here we report significant N2 fixation rates, ranging between 0.1 and 34 μmol N m−3 d−1 from the Mandovi and Zuari estuaries, two typical tropical monsoon-affected estuaries located along the Indian west coast. The estuarine waters were moderately rich in nutrients with nitrate concentration up to 5 μM in the Mandovi and 6 μM in the Zuari and PO4− up to 1 μM. Chlorophyll a concentration varied between 0.1 and 8 mg m−3 with moderate primary production (up to 262 mg C m−3 d−1). The organisms responsible for the observed diazotrophic activity in the estuaries still remain to be identified.

Different physiological responses of cyanobacteria to ultraviolet‐B radiation under iron‐replete and iron‐deficient conditions: Implications for underestimating the negative effects of UV‐B radiation

Iron deficiency has been considered one of the main limiting factors of phytoplankton productivity in some aquatic systems including oceans and lakes. Concomitantly, solar ultraviolet-B radiation has been shown to have both deleterious and positive impacts on phytoplankton productivity. However, how iron-deficient cyanobacteria respond to UV-B radiation has been largely overlooked in aquatic systems. In this study, physiological responses of four cyanobacterial strains (Microcystis and Synechococcus), which are widely distributed in freshwater or marine systems, were investigated under different UV-B irradiances and iron conditions. The growth, photosynthetic pigment composition, photosynthetic activity, and nonphotochemical quenching of the different cyanobacterial strains were drastically altered by enhanced UV-B radiation under iron-deficient conditions, but were less affected under iron-replete conditions. Intracellular reactive oxygen species (ROS) and iron content increased and decreased, respectively, with increased UV-B radiation under iron-deficient conditions for both Microcystis aeruginosa FACHB 912 and Synechococcus sp. WH8102. On the contrary, intracellular ROS and iron content of these two strains remained constant and increased, respectively, with increased UV-B radiation under iron-replete conditions. These results indicate that iron-deficient cyanobacteria are more susceptible to enhanced UV-B radiation. Therefore, UV-B radiation probably plays an important role in influencing primary productivity in iron-deficient aquatic systems, suggesting that its effects on the phytoplankton productivity may be underestimated in iron-deficient regions around the world.

Carbon, Nitrogen, and Phosphorus Stoichiometry and Eutrophication in River Thames Tributaries, UK

Core Ideas A novel graphical method for displaying C/N/P stoichiometry is presented. Five River Thames tributaries were used to assess the utility of stoichiometric plots. <13% total dissolved P limited chlorophyll a to <30 μg L−1. Primary productivity in aquatic systems relies on carbon (C), nitrogen (N), and phosphorus (P) availability, with a reference stoichiometric ratio of 106 C/16 N/1 P, known as the Redfield ratio. This paper presents a methodology to visualize river water C/N/P stoichiometry and examine phytoplankton response. Redfield total dissolved C/N/P concentration ratios (TDC/TDNR/TDPR) from five River Thames tributaries were plotted in a ternary diagram, allowing relationships between nutrient stoichiometry, total P concentrations, and chlorophyll a, as a surrogate for phytoplankton biomass, to be explored. Chlorophyll a concentrations above 100 μg L−1 were not observed below 14% TDPR, and concentrations above 30 μg L−1 were not observed below 13% TDPR. This indicates a potentially lower TDPR limit for highly eutrophic waters. These rivers are C and N rich, and this methodology should be applied to a wider range of rivers to explore C, N and P thresholds across different river typologies.

Body size drives allochthony in food webs of tropical rivers.

Food web subsidies from external sources ("allochthony") can support rich biological diversity and high secondary and tertiary production in aquatic systems, even those with low rates of primary production. However, animals vary in their degree of dependence on these subsidies. We examined dietary sources for aquatic animals restricted to refugial habitats (waterholes) during the dry season in Australia's wet-dry tropics, and show that allochthony is strongly size dependent. While small-bodied fishes and invertebrates derived a large proportion of their diet from autochthonous sources within the waterhole (phytoplankton, periphyton, or macrophytes), larger animals, including predatory fishes and crocodiles, demonstrated allochthony from seasonally inundated floodplains, coastal zones or the surrounding savanna. Autochthony declined roughly 10% for each order of magnitude increase in body size. The largest animals in the food web, estuarine crocodiles (Crocodylus porosus), derived ~80% of their diet from allochthonous sources. Allochthony enables crocodiles and large predatory fish to achieve high biomass, countering empirically derived expectations for negative density vs. body size relationships. These results highlight the strong degree of connectivity that exists between rivers and their floodplains in systems largely unaffected by river regulation or dams and levees, and how large iconic predators could be disproportionately affected by these human activities.

Wood mitigates the effect of hydropeaking scour on periphyton biomass and nutritional quality in semi-natural flume simulations

The daily fluctuating discharge from hydroelectric power plants, known as hydropeaking, has been shown to cause catastrophic drift in aquatic insect communities and limit secondary production, but relatively little attention has been given to its effects on periphyton, an important food resource for consumers. We simulated daily 5-h hydropeaking events over the course of 5 days in spring and summer in an open air, experimental flume system fed by a pristine 2nd order stream in the Italian Alps. We hypothesized that hydropeaking would suppress periphyton biomass and especially nutritional quality (i.e., fatty acid content). Hydropeaking resulted in decreased periphyton Chl-a and AFDM on tiles, but there was no corresponding loss on wood. Hydropeaking did not alter periphyton elemental nutrient stoichiometry but led to a disproportionate loss of periphyton fatty acid content on both substrates. Ordination of overall fatty acid profiles indicated different periphyton fatty acid profiles by substrate and a shift from physiologically important highly-unsaturated fatty acids to non-essential saturated fatty acids after hydropeaking. These results suggest that hydropeaking may have the potential to depress primary biomass and nutritional quality in downstream ecosystems, and that availability of wood substrate may mitigate part, but not all, of this effect. Since food nutritional quality, especially fatty acid content, has been suggested to be a limiting resource on production in aquatic systems, this may generate an indirect and potentially overlooked limiting effect on aquatic consumers in hydropeaking-impacted alpine rivers.

Erratum to: Dissolved nitrogen release from coarse and amphipod-produced fine particulate organic matter in freshwater column

Dissolved nitrogen (DN) is essential for primary production in aquatic systems. We investigated total DN (TDN) and nitrate and nitrite (NO3 − + NO2 −) releases from particulate organic matter (POM) by incubating POM of various sizes and chemical characteristics in stream water over a 2-week period. Large- and medium-sized fine POM (L-FPOM, 250–500 μm, and M-FPOM, 100–250 μm) were prepared by feeding five types of coarse POM (CPOM) to shredding amphipods in laboratory aquaria. For CPOM, the TDN release rate was greatest during the first day of the experiment while L-FPOM continued to release TDN during the experimental period, and the TDN release rate from L-FPOM in the second week was higher than those from the other size fractions. In addition, TDN release on the first day from FPOM was significantly affected by FPOM chemical qualities, with a negative correlation to lignin content and lignocellulose index. The present study indicates the importance of source and chemical quality of POM in the instream TDN release and the significance of amphipod-produced FPOM as a nitrogen source in streams despite being recalcitrant to microbial decomposition.

Dreissenid mussels enhance nutrient efflux, periphyton quantity and production in the shallow littoral zone of a large lake

Dreissenid mussels are notorious invasive organisms whose establishment is associated with large, ecosystem-scale changes to patterns of productivity in aquatic systems. We investigated how localized impacts of dreissenids affect the potential of littoral substrates to support primary and secondary production using in situ incubations and comparisons of natural mussel-colonized and mussel-free substrates in the littoral zone of a large, shallow lake. We compared dreissenid-colonized and dreissenid-free substrates in terms of nutrient balance, surface area, periphyton loads as well as benthic primary production and respiration rates. Dreissenid-colonized substrates acted as sources of dissolved nutrients to the water column, with mussel mass-specific rates of dissolved phosphorus and ammonia excretion averaging 7.2 ± 5.6 (mean ± SD), and 92.6 ± 64.7 μg/g mussel shell free dry mass/h, respectively. Mussel-colonized substrates also had higher surface area, and supported approximately double the amount of periphyton and organic matter loads compared to mussel-free substrates, as well as having higher rates of primary production and community respiration. We suggest that the localized effects of dreissenids can play an important role in changing whole-ecosystem production patterns, with the extent of dreissenid impacts strongly dependent on lake size and morphometry.

Nutrient recycling by coastal macrofauna: intra- versus interspecific differences

In the context of global change, improving our understanding of how species communities shape ecosystem functioning and stability is a key issue. Therefore, we have to adopt a functional approach by considering the role of organisms in ecosystem processes. Nutrient recycling is important for sustaining primary productivity in aquatic systems but has been largely overlooked for macro-organisms. In a Mediterranean coastal ecosystem we found that per capita ammonium and phosphate excretion rates for the 9 dominant nektonic macrofauna species exceeded those of 3 benthic bivalves by factor 100. Body mass and species identity together significantly explained these interspecific differences in excretion rates. Significant differences in the effect of body mass on nutrient excretion rates were also found among the 7 fish species. More studies are needed to further explore the biological determinants of the intra-and interspecific variability of excretion rates as well as their consequences on marine ecosystem functioning.

Phylotype-specific growth rates of marine bacteria measured by bromodeoxyuridine immunocytochemistry and fluorescence in situ hybridization

To explore the possibility of calculating phylotype-specific growth rates of marine bac- teria, we optimized a protocol that combines bromodeoxyuridine (BrdU) immunocytochemistry with fluorescence in situ hybridization (FISH). The protocol worked well with 8 isolates tested, showing a significant positive correlation between average cellular fluorescence intensity and cell-specific BrdU contents. The BrdU immunocytochemistry-FISH (BIC-FISH) was then applied to neritic sea- water in Hiroshima Bay, western Japan. Rhodobacter/Roseobacter and Bacteroidetes groups were dominant in BrdU-positive cells (22 ± 8 and 26 ± 8%), suggesting a significant contribution to bacte- rial community productivity in the water. Analysis of single-cell immunofluorescence showed higher BrdU incorporation rates in the Gammaproteobacteria, SAR86, and Vibrio groups, suggesting that these less abundant groups were growing more rapidly than other phylotypes. Our study suggests that BIC-FISH has the potential to estimate phylotype-specific variability of bacterial productivity in aquatic systems.

Direct and indirect coupling of primary production and diel nitrate dynamics in a subtropical spring‐fed river

We used high‐frequency in situ measurements of nitrate (NO3−) and dissolved oxygen (DO) from the springfed Ichetucknee River, Florida, to derive multiple independent estimates of assimilatory nitrogen (N) demand, and to evaluate the short‐term dependence of heterotrophic assimilation and dissimilation (e.g., denitrification) on gross primary productivity (GPP). Autotrophic N assimilation estimates derived from diel DO variability and GPP stoichiometry agreed closely with estimates based on integration of diel variation in NO3− concentration, although the correspondence of these metrics depended on the method used to estimate NO3− baselines. In addition, day‐to‐day changes in nocturnal NO3− concentration maxima were strongly negatively correlated with day‐to‐day changes in GPP. Diel temperature variation in the Ichetucknee River indicated that this pattern could not be explained by hydrologic dispersion, while relationships between N assimilation and O2 production at hourly intervals indicated minimal physiological lags. The estimated magnitude of heterotrophic assimilation was small, indicating that the relationship between changes in GPP and changes in nocturnal NO3− maxima reflects sensitivity of denitrification to variation in exudation of labile organic matter by primary producers. We estimate that ~ 35% of denitrification may be fueled by the previous day’s photosynthesis; this result is consistent with the broader hypothesis that the magnitude of autochthonous production in aquatic systems influences the fate of N via both direct and indirect mechanisms.

Is ambient chitobiase activity a monitoring tool for impacts on secondary production in lotic systems?

Chitobiase is one of two enzymes responsible for cleaving the chitin polymers that form arthropod exoskeletons and has been found to be predictive of secondary production for marine and freshwater zooplankton. Since chitobiase is released into water during molting by aquatic arthropods, it is possible that ambient chitobiase activity may be a useful proxy of secondary production in aquatic systems. In the present study, surface water samples from the upper Tennessee River basin, USA, were collected and analyzed for chitobiase to determine how enzyme levels vary with season, water depth, and proximity to sewage treatment outfalls. Additionally, chitobiase activity was correlated with three pharmaceutical compounds to assess if changes in chitobiase activity were associated with contaminants derived from sewage treatment plants. Chitobiase activity was significantly (p < 0.05) elevated in the fall relative to other seasons. Further, chitobiase activity displayed significant positive correlation (p < 0.05) between surface and subsurface samples and was negatively correlated (p < 0.05) with pharmaceutical concentrations in summer samples. These results indicate the potential for chitobiase as an assessment tool in estimating secondary production and as an ecotoxicological indictor.

Predation pressure on bacteria increases along aquatic productivity gradients

To elucidate how predation pressure on bacteria is affected by increasing productivity in aquatic systems, we ran model simulations of a microbial food web. In addition, we conducted a meta-analysi ...

Terrestrial Subsidies of Organic Carbon Support Net Ecosystem Production in Temporary Forest Ponds: Evidence from an Ecosystem Experiment

Recent research suggests that secondary production in aquatic systems can be driven by inputs of energy from terrestrial sources. Temporary forest ponds appear to be unproductive ecosystems that are reliant upon allochthonous inputs of energy to support secondary production, but the functioning of these systems has not been well quantified. To assess the metabolic state of this type of ecosystem as well as to quantify the importance of terrestrial subsidies of carbon to ecosystem function, we conducted an experiment in which we manipulated the amount of leaf litter in ponds. Litter was either removed or removed and replaced (that is, control) from the dry basins of ponds immediately after leaf abscission. Once the ponds filled, we monitored net ecosystem production (NEP) on a biweekly basis from 9 April to 27 May 2002. All ponds were consistently net heterotrophic; however, NEP was significantly less negative in removal ponds. Furthermore, removal ponds also had lower levels of respiration (R) and higher dissolved oxygen levels than control ponds. The removal of litter had no effect on gross primary production, indicating that the difference in NEP between treatments was driven by the change in R. Therefore, it appears that terrestrial inputs of organic carbon support heterotrophic respiration in these ponds, and that the endogenous production of carbon is insufficient to support secondary production.

Self-organization of dissolved organic matter to micelle-like microparticles in river water.

In aquatic systems, the concept of the 'microbial loop' is invoked to describe the conversion of dissolved organic matter to particulate organic matter by bacteria. This process mediates the transfer of energy and matter from dissolved organic matter to higher trophic levels, and therefore controls (together with primary production) the productivity of aquatic systems. Here we report experiments on laboratory incubations of sterile filtered river water in which we find that up to 25% of the dissolved organic carbon (DOC) aggregates abiotically to particles of diameter 0.4-0.8 micrometres, at rates similar to bacterial growth. Diffusion drives aggregation of low- to high-molecular-mass DOC and further to larger micelle-like microparticles. The chemical composition of these microparticles suggests their potential use as food by planktonic bacterivores. This pathway is apparent from differences in the stable carbon isotope compositions of picoplankton and the microparticles. A large fraction of dissolved organic matter might therefore be channelled through microparticles directly to higher trophic levels--bypassing the microbial loop--suggesting that current concepts of carbon conversion in aquatic systems require revision.

Contribution of major bacterial groups to bacterial biomass production (thymidine and leucine incorporation) in the Delaware estuary

Assimilation of 3HH‐thymidine and 3HH‐leucine was examined at the single‐cell level using a combination of microautoradiography and fluorescent in situ hybridization (Micro‐FISH) to determine the contribution of various bacterial groups to bacterial production in aquatic systems. All of the major phylogenetic groups of bacteria examined along the salinity gradient of the Delaware estuary, including alpha‐, beta‐, and gamma‐proteobacteria and Cytophaga‐like bacteria, assimilated 3H‐thymidine and 3H‐leucine. However, groups differed substantially in their contribution to the assimilation of these compounds. Alpha‐proteobacteria were the dominant substrate‐active bacteria at salinities of .9 PSU, whereas beta‐proteobacteria were more important in freshwater. At all salinities, Cytophaga‐like bacteria comprised the second most important group, and gamma‐proteobacteria were overall the least important. Bacterial abundance explained about half of the variation in 3H‐thymidine and 3H‐leucine assimilation by the major bacterial groups. The sizes of silver grains of active bacteria indicate no difference in singlecell activity for the bacterial groups, suggesting that the average growth rates of the groups we examined were similar. However, activity per cell was distributed differently in the phylogenetic groups. Our study suggests that estimates of bacterial production measured using 3H‐thymidine and 3H‐leucine include bacteria in all of the major phylogenetic groups found in aquatic systems and that growth rates within bacterial groups vary substantially.