Factors controlling primary productivity in a wet–dry tropical river

2013 ◽  
Vol 64 (7) ◽  
pp. 585 ◽  
Author(s):  
S. J. Faggotter ◽  
I. T. Webster ◽  
M. A. Burford
Keyword(s):  
Algal Blooms ◽  
Algal Biomass ◽  
Arid Zone ◽  
River System ◽  
Dry Season ◽  
Trophic Levels ◽  
Nutrient Inputs ◽  
Tropical River ◽  
Algal Production ◽  
The Impact

Algal production in rivers fuels foodwebs, and factors controlling this production ultimately affect food availability. Conversely, excessive algal production can have negative effects on higher trophic levels. The present study examined permanent waterholes in a disconnected wet–dry tropical river to determine the controls on algal production. Primary production in this river system was high compared with arid-zone and perennially flowing tropical rivers. Phytoplankton biomass increased over the dry season but this appeared to be because waterhole volume decreased, due to evaporation. Nitrogen (N) was the key limiting nutrient for phytoplankton, with rapid N turnover times, depletion of particulate 15N-nitrogen reflecting increasing N fixationover the dry season, and N stimulation in phytoplankton bioassays. The waterholes were shallow, providing sufficient light for accumulation of benthic algal biomass. Exclosure experiments were also conducted to determine the impact of top–down control on benthic algal biomass, with no evidence that exclusion of fish and crustaceans increased benthic algal biomass. The shallow off-channel waterhole in our study had substantially higher concentrations of nutrients and chlorophyll a than did the on-channel waterholes. This suggests that future anthropogenic changes, such as increased water extraction and increased nutrient inputs, could make the waterholes more vulnerable to deteriorating water quality, such as e.g. algal blooms, low concentrations of dissolved oxygen.

Nutrient-related selection mechanisms in marine phytoplankton communities and the impact of eutrophication on the planktonic food web

1995 ◽  
Vol 32 (4) ◽  
pp. 63-75 ◽  
Author(s):  
R. Riegman
Keyword(s):  
Algal Blooms ◽  
Algal Biomass ◽  
Resource Competition ◽  
Water Quality Management ◽  
Algal Species ◽  
Marine Phytoplankton ◽  
Commercial Fish ◽  
N Limitation ◽  
Phytoplankton Communities ◽  
The Impact

A general increase in nutrient discharges during the last few decades has caused various changes in the algal community structure along the European continental coast. Coincidentally and maybe consequently, the foodweb structure and functioning has altered in local areas causing various phenomena like oxygen depletion, mortality of groups of organisms, foam on beaches, and an increase in the productivity of benthic communities and some commercial fish species. The observed increases in algal biomass and shifts in species composition are discussed in relation to the involved key mechanisms: resource competition and selective grazing. Along the Dutch coastal zone of the North Sea eutrophication has caused a doubling of the yearly averaged algal biomass during the past three decades. The sudden appearance of Phaeocystis summer blooms coincided with a shift from P-limitation towards N-limitation in the Dutch coastal area due to a stronger increase in P-discharge relative to the increase in N-discharge. Competition experiments in continuous cultures showed Phaeocystis to become dominant under N-limitation. Additionally, the large Phaeocystis colonies, which can reach a diameter up to one centimetre, escape from microzooplankton grazing. A computer model is presented which demonstrates a shift from bottom-up towards top-down control if the pelagic environment becomes eutrophicated. Implementation of this concept in a size-differential phytoplankton control model generates the prediction that algal blooms are dominated by species that escape from grazing by those zooplankton species which have a high potential numerical response. In marine environments these are microzooplankton species. These organisms mainly feed on cyanobacteria, prochlorophytes and some nano-algal species. One of the consequences for foodweb structure and the carbon fluxes in marine foodwebs is that eutrophication will lead to the dominance of poorly edible algal species. Eutrophication favours the downward transport of carbon and nutrients towards the sediments not only due to higher algal biomasses but also as a consequence of a shift towards larger algal species with higher sedimentation characteristics. An example is given how these new insights can be used for water quality management purposes.

scholarly journals Tourists increase the contribution of autochthonous carbon to littoral zone food webs in oligotrophic dune lakes

2004 ◽  
Vol 55 (7) ◽  
pp. 701 ◽  
Author(s):  
Wade L. Hadwen ◽  
Stuart E. Bunn
Keyword(s):  
Food Webs ◽  
Littoral Zone ◽  
Algal Biomass ◽  
Carbon Sources ◽  
Nutrient Concentrations ◽  
Relative Importance ◽  
Nutrient Inputs ◽  
Oligotrophic Lakes ◽  
Dune Lakes ◽  
The Impact

Tourists can adversely influence the ecology of oligotrophic lakes by increasing algal production via direct nutrient inputs and/or re-suspension of sediments. To assess the influence of tourists on food web dynamics, we used the natural abundance of stable isotopes of carbon and nitrogen to calculate the relative importance of autochthonous and allochthonous carbon sources to littoral zone food webs across five variously visited perched dune lakes on Fraser Island, Australia. The relative importance of autochthonous (phytoplankton and periphyton) carbon to littoral zone consumers was highly variable across taxa and lakes. Despite the potential influence of algal biomass, ambient nutrient concentrations and tannin concentrations on the contribution of autochthonous carbon to littoral zone food webs, none of these variables correlated to the per cent contribution of autochthonous carbon to consumer diets. Instead, autochthonous sources of carbon contributed more to the diets of aquatic consumers in heavily visited lakes than in less visited lakes, suggesting that tourist activities might drive these systems towards an increased reliance on autochthonous carbon. The assessment of the contribution of autochthonous carbon to littoral zone food webs may represent a more robust indicator of the impact of tourists in oligotrophic lakes than standard measures of nutrient concentrations and/or algal biomass.

scholarly journals Seasonal Variation of Phthalate Esters in Urban River Sediments: A Case Study of Fengshan River System in Taiwan

2021 ◽  
Vol 14 (1) ◽  
pp. 347
Author(s):  
Kuan-Nan Lin ◽  
Chiu-Wen Chen ◽  
Chih-Feng Chen ◽  
Yee Cheng Lim ◽  
Chih-Ming Kao ◽  
...  
Keyword(s):  
Phthalate Esters ◽  
River Sediments ◽  
Aquatic Organisms ◽  
River System ◽  
Dry Season ◽  
Ecological Risks ◽  
Total Risk ◽  
Wet Season ◽  
Potential Risks ◽  
The Impact

The Fengshan River system is one of the major rivers in Kaohsiung City, Taiwan. This study investigated the concentration of eight phthalate esters (PAEs) in sediments of the river and the impact of potential ecological risks during the dry and wet seasons. The potential risk assessment of sediment PAEs was evaluated by adopting the total risk quotient (TRQ) method. The total PAEs concentrations (∑PAEs) in the sediments of the Fengshan River system are between 490–40,190 ng/g dw, with an average of 8418 ± 11,812 ng/g dw. Diisononyl phthalate (38.1%), bis(2-ethylhexyl) phthalate (36.9%) and di-isodecyl phthalate (24.3%) accounted for more than 99.3% of ∑PAEs. The concentration of ∑PAEs in sediments at the river channel stations is higher during the wet season (616–15,281 ng/g dw) than that during the dry season (490–1535 ng/g dw). However, in the downstream and estuary stations, the wet season (3975–6768 ng/g dw) is lower than the dry season (20,216–40,190 ng/g dw). The PAEs in sediments of the Fengshan River may have low to moderate potential risks to aquatic organisms. The TQR of PAEs in sediments at the downstream and estuary (TQR = 0.13) is higher than that in the upstream (TQR = 0.04). In addition, during the wet season, rainfall transported a large amount of land-sourced PAEs to rivers, leading to increased PAEs concentration and potential ecological risks in the upper reaches of the river.

Nitrogen Removal by River Systems of the Feng River Basin in China

2014 ◽  
Vol 1015 ◽  
pp. 631-634
Author(s):  
Jian Hui Zhi ◽  
Ai Zhong Ding ◽  
Shu Rong Zhang
Keyword(s):  
Water System ◽  
River System ◽  
Dry Season ◽  
River Network ◽  
Nitrogen Loading ◽  
Combined Processes ◽  
River Systems ◽  
N Removal ◽  
N Input ◽  
The Impact

As human activities continue to alter the global nitrogen cycle, the ability to predict the impact of increased nitrogen loading to river systems is becoming more and more important. Nitrogen retention is of particular interest because it is through its combined processes that local and downstream nitrogen concentrations are reduced. To determine the potential for N removed from Feng River network, we used stream chemistry and hydrogeo-morphology data from 17 stream and river sites to estimate NO3-–N removal in Feng River system of China. We used a N removal model to predict NO3-–N input and removal in December of 2011. NO3-–N input ranged from 0.06 to 20 kg km-1d-1in the Feng River system. Cumulative river network NO3-–N input was 446 ton year-1 in dry season in whole water system. NO3–N removal based on the model ranged from 0.04 to 4.2 kg km-1d-1 December of 2011 for Feng River. Cumulative river network NO3-–N removal predicted by the model was 58 ton year-1 in dry season. Proportional NO3–N removal (PNR) ranged from 0.2 to 0.6 in this time. PNR was negatively correlated with both stream orders.

scholarly journals Viral infection switches the balance between bacterial and eukaryotic recyclers of organic matter during algal blooms

2021 ◽  
Author(s):  
Flora Vincent ◽  
Matti Gralka ◽  
Guy Schleyer ◽  
Daniella J Schatz ◽  
Miguel Cabrera-Brudau ◽  
...  
Keyword(s):  
Organic Matter ◽  
Viral Infection ◽  
Algal Blooms ◽  
Large Scale ◽  
Deep Ocean ◽  
Trophic Levels ◽  
Microbiome Composition ◽  
Carbon Release ◽  
Open Question ◽  
The Impact

Algal blooms are hotspots of marine primary production and play central roles in microbial ecology and global nutrient cycling. When blooms collapse, organic carbon is transferred to higher trophic levels, microbial respiration or sinking in proportions that depend on the dominant mortality agent. Viral infection can lead to bloom termination, but its impact on the fate of carbon remains an open question. Here, we characterized the consequences of viral infection on the microbiome composition and biogeochemical landscape of marine ecosystems by conducting a large-scale mesocosm experiment. Moniroting of seven induced coccolithophore blooms, which showed different degrees of viral infection, revealed that only high levels of viral infection caused significant shifts in the composition of free-living bacterial and eukaryotic assemblages. Intriguingly, viral infection favored the growth of eukaryotic heterotrophs (thraustochytrids) over bacteria as potential recyclers of organic matter. By combining modeling and quantification of active viral infection at a single-cell resolution, we estimate that viral infection can increase per-cell rates of extracellular carbon release by 2-4.5 fold. This happened via production of acidic polysaccharides and particulate inorganic carbon, two major contributors to carbon sinking into the deep ocean. These results reveal the impact of viral infection on the fate of carbon through microbial recyclers of organic matter in large-scale coccolithophore blooms.

scholarly journals Viral infection switches the balance between bacterial and eukaryotic recyclers of organic matter during algal blooms

2021 ◽  
Author(s):  
Flora VINCENT ◽  
Matti Gralka ◽  
Guy Schleyer ◽  
Daniella Schatz ◽  
Miguel Cabrera-Brufau ◽  
...  
Keyword(s):  
Organic Matter ◽  
Viral Infection ◽  
Algal Blooms ◽  
Large Scale ◽  
Deep Ocean ◽  
Trophic Levels ◽  
Microbiome Composition ◽  
Carbon Release ◽  
Open Question ◽  
The Impact

Abstract Algal blooms are hotspots of marine primary production and play central roles in microbial ecology and global nutrient cycling. When blooms collapse, organic carbon is transferred to higher trophic levels, microbial respiration or sinking in proportions that depend on the dominant mortality agent. Viral infection can lead to bloom termination, but its impact on the fate of carbon remains an open question. Here, we characterized the consequences of viral infection on the microbiome composition and biogeochemical landscape of marine ecosystems by conducting a large-scale mesocosm experiment. Moniroting of seven induced coccolithophore blooms, which showed different degrees of viral infection, revealed that only high levels of viral infection caused significant shifts in the composition of free-living bacterial and eukaryotic assemblages. Intriguingly, viral infection favored the growth of eukaryotic heterotrophs (thraustochytrids) over bacteria as potential recyclers of organic matter. By combining modeling and quantification of active viral infection at a single-cell resolution, we estimate that viral infection can increase per-cell rates of extracellular carbon release by 2-4.5 fold. This happened via production of acidic polysaccharides and particulate inorganic carbon, two major contributors to carbon sinking into the deep ocean. These results reveal the impact of viral infection on the fate of carbon through microbial recyclers of organic matter in large-scale coccolithophore blooms.

The impact of socioeconomic system on the river system in a heavily disturbed basin

2019 ◽  
Vol 660 ◽  
pp. 851-864 ◽  
Author(s):  
Zengliang Luo ◽  
Qiting Zuo ◽  
Quanxi Shao ◽  
Xiangyi Ding
Keyword(s):  
River System ◽  
Socioeconomic System ◽  
The Impact

scholarly journals Effects of the Marine Biotoxins Okadaic Acid and Dinophysistoxins on Fish

2021 ◽  
Vol 9 (3) ◽  
pp. 293
Author(s):  
Mauro Corriere ◽  
Lucía Soliño ◽  
Pedro Reis Costa
Keyword(s):  
Okadaic Acid ◽  
Harmful Algal Blooms ◽  
Algal Blooms ◽  
Current Knowledge ◽  
Global Climate ◽  
Scientific Evidence ◽  
Shellfish Poisoning ◽  
Morphological Alterations ◽  
The Impact ◽  
Dsp Toxins

Natural high proliferations of toxin-producing microorganisms in marine and freshwater environments result in dreadful consequences at the socioeconomically and environmental level due to water and seafood contamination. Monitoring programs and scientific evidence point to harmful algal blooms (HABs) increasing in frequency and intensity as a result of global climate alterations. Among marine toxins, the okadaic acid (OA) and the related dinophysistoxins (DTX) are the most frequently reported in EU waters, mainly in shellfish species. These toxins are responsible for human syndrome diarrhetic shellfish poisoning (DSP). Fish, like other marine species, are also exposed to HABs and their toxins. However, reduced attention has been given to exposure, accumulation, and effects on fish of DSP toxins, such as OA. The present review intends to summarize the current knowledge of the impact of DSP toxins and to identify the main issues needing further research. From data reviewed in this work, it is clear that exposure of fish to DSP toxins causes a range of negative effects, from behavioral and morphological alterations to death. However, there is still much to be investigated about the ecological and food safety risks related to contamination of fish with DSP toxins.

scholarly journals Enhanced Viral Activity in the Surface Microlayer of the Arctic and Antarctic Oceans

2021 ◽  
Vol 9 (2) ◽  
pp. 317
Author(s):  
Dolors Vaqué ◽  
Julia A. Boras ◽  
Jesús Maria Arrieta ◽  
Susana Agustí ◽  
Carlos M. Duarte ◽  
...  
Keyword(s):  
Environmental Factors ◽  
Food Web ◽  
Physicochemical Characteristics ◽  
The Arctic ◽  
Microbial Food Web ◽  
Surface Microlayer ◽  
Polar Regions ◽  
Nutrient Inputs ◽  
Viral Activity ◽  
The Impact

The ocean surface microlayer (SML), with physicochemical characteristics different from those of subsurface waters (SSW), results in dense and active viral and microbial communities that may favor virus–host interactions. Conversely, wind speed and/or UV radiation could adversely affect virus infection. Furthermore, in polar regions, organic and inorganic nutrient inputs from melting ice may increase microbial activity in the SML. Since the role of viruses in the microbial food web of the SML is poorly understood in polar oceans, we aimed to study the impact of viruses on prokaryotic communities in the SML and in the SSW in Arctic and Antarctic waters. We hypothesized that a higher viral activity in the SML than in the SSW in both polar systems would be observed. We measured viral and prokaryote abundances, virus-mediated mortality on prokaryotes, heterotrophic and phototrophic nanoflagellate abundance, and environmental factors. In both polar zones, we found small differences in environmental factors between the SML and the SSW. In contrast, despite the adverse effect of wind, viral and prokaryote abundances and virus-mediated mortality on prokaryotes were higher in the SML than in the SSW. As a consequence, the higher carbon flux released by lysed cells in the SML than in the SSW would increase the pool of dissolved organic carbon (DOC) and be rapidly used by other prokaryotes to grow (the viral shunt). Thus, our results suggest that viral activity greatly contributes to the functioning of the microbial food web in the SML, which could influence the biogeochemical cycles of the water column.

scholarly journals Seasonal feeding plasticity can facilitate coexistence of dominant omnivores in Neotropical streams

2021 ◽  
Author(s):  
Mayara P. Neves ◽  
Pavel Kratina ◽  
Rosilene L. Delariva ◽  
J. Iwan Jones ◽  
Clarice B. Fialho
Keyword(s):  
Seasonal Variation ◽  
Fish Species ◽  
Resource Availability ◽  
Seasonal Changes ◽  
Dry Season ◽  
Diet Overlap ◽  
Isotopic Niche ◽  
Neotropical Streams ◽  
Feeding Plasticity ◽  
The Impact

AbstractCoexistence of ecomorphologically similar species in diverse Neotropical ecosystems has been a focus of long-term debate among ecologists and evolutionary biologists. Such coexistence can be promoted by trophic plasticity and seasonal changes in omnivorous feeding. We combined stomach content and stable isotope analyses to determine how seasonal variation in resource availability influences the consumption and assimilation of resources by two syntopic fish species, Psalidodon aff. gymnodontus and P. bifasciatus, in the Lower Iguaçu basin. We also tested the impact of seasonality on trophic niche breadth and diet overlap of these two dominant omnivores. Seasonal changes in resource availability strongly influenced the consumption and assimilation of resources by the two fish species. Both species exhibited high levels of omnivory, characterized by high diversity of allochthonous resources in the wet season. Terrestrial invertebrates were the main component of diet during this season. However, in the dry season, both species reduced their isotopic niches, indicating diet specialization. High diet overlap was observed in both seasons, but the isotopic niche overlap was smaller in the dry season. Substantial reduction in the isotopic niche of P. bifascistus and a shift toward aquatic invertebrates can facilitate coexistence during this season of resource shortage. Feeding plasticity allows omnivorous fish to adjust their trophic niches according to seasonality, promoting the exploitation of different resources during periods of greater resource diversity. This seasonal variation could be an important mechanism that contributes to the resource partitioning and coexistence of dominant omnivores in Neotropical streams.

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