Tropical Water Bodies Research Articles

An application of a water assessment and simulation model in the remediation of the eutrophication capacity of a tropical water system: Case study the Lake Obili in Yaounde (Cameroon)

Abstract Lake Obili is one of the most famous lakes in the city of Yaounde, Cameroon. Studies carried out in this lake showed that it was hyper eutrophic and therefore it represents a great danger because it is used for aquaculture, tourism and a suitable laboratory for hydro-biological engineering. It is thus very vital to restore this lake ecosystem that singles itself in the heart of the city of Yaounde. This can be greatly facilitated through the use of Water Quality Analysis Simulation Program (WASP) of the United State Environmental protection Agency (USEPA). The outcomes of the previous results obtained from EUTRO, a Subroutine of the WASP model specialised in determining eutrophication level have proven that the remediation of this lake can be achievable through the implementation of a wet dredging, the construction and restoration of a wastewater treatment plant, the implementation of environmental incentive policies and the arrangement of the access to the lake. The application of the model is a contribution to the scientific mastery of nutrient flow, lake functioning and possibilities of restauration of highly polluted tropical water bodies subjected to domestic and industrial pollution.

The efficiency of combined coagulant and ballast to remove harmful cyanobacterial blooms in a tropical shallow system

We tested the hypothesis that a combination of coagulant and ballast could be efficient for removal of positively buoyant harmful cyanobacteria in shallow tropical waterbodies, and will not promote the release of cyanotoxins. This laboratory study examined the efficacy of coagulants [polyaluminium chloride (PAC) and chitosan (made of shrimp shells)] alone, and combined with ballast (lanthanum modified bentonite, red soil or gravel) to remove the natural populations of cyanobacteria collected from a shallow eutrophic urban reservoir with alternating blooms of Cylindrospermopsis and Microcystis. PAC combined with ballast was effective in settling blooms dominated by Microcystis or Cylindrospermopsis. Contrary to our expectation, chitosan combined with ballast was only effective in settling Cylindrospermopsis-dominated blooms at low pH, whereas at pH≥8 no effective flocculation and settling could be evoked. Chitosan also had a detrimental effect on Cylindrospermopsis causing the release of saxitoxins. In contrast, no detrimental effect on Microcystis was observed and all coagulant-ballast treatments were effective in not only settling the Microcystis dominated bloom, but also lowering dissolved microcystin concentrations. Our data show that the best procedure for biomass reduction also depends on the dominant species.

Water hardness determines 226Ra uptake in the tropical freshwater mussel

Chemical data for freshwater mussels (Velesunio spp.) and water from 15 sampling sites in the Alligator Rivers Region and Rum Jungle uranium provinces in tropical Northern Australia were analysed to develop a predictive model of radium-226 (226Ra) bioaccumulation for variable water calcium (Ca) and magnesium (Mg) concentrations. Application of the model as a 226Ra screening approach for freshwater mussels in tropical waterbodies potentially impacted by operational or remediated uranium mine sites is discussed in relation to Mudginberri Billabong, located approximately 12 km downstream of Ranger uranium mine in the Alligator Rivers Region.

Influence of environmental factors on cyanobacterial biomass and microcystin concentration in the Dau Tieng Reservoir, a tropical eutrophic water body in Vietnam

Cyanobacterial blooms can be harmful to environmental and human health due to the production of toxic secondary metabolites, known as cyanotoxins. Microcystins (MCs), one of the most widespread class of cyanotoxins in freshwater, have been found to be positively correlated with cyanobacterial biomass as well as with nitrogen and phosphorus concentrations in temperate lakes. However, in tropical water bodies, cyanobacterial density and cyanotoxin correlation to environmental factors is not fully understood. In the present study, we examined the effects of total nitrogen and total phosphorus (TP) concentrations among other environmental parameters on cyanobacterial community structure and MC concentrations in the Dau Tieng reservoir, a tropical, eutrophic water body in Southern Vietnam. Cyanobacterial biomass and MC content were monitored monthly from March 2012 to February 2013, when MCs were present in the Dau Tieng Reservoir. The highest concentrations of intracellular MCs were found in September and February when cyanobacteria biomass reached maximum values, with 2.50 and 2.13 μg MC.L–1 , respectively. Principle component analysis and redundancy analysis showed that MC concentration was positively correlated with the biomass of the cyanobacterial order Chroococcales, whereas TP was the primary abiotic factor influencing cyanobacterial biomass and MC concentrations in the Dau Tieng Reservoir. In addition, Bayesian model average analysis was used to construct a prediction model of MCs using cyanobacterial biomass and environmental variables revealing a suite of useful predictive factors for MCs in the Dau Tieng Reservoir, including water temperature, TP and the biomass of Chroococcales.

Characterization of Musty Odor-Producing Actinomycetes from Tropics and Effects of Temperature on the Production of Musty Odor Compounds.

Geosmin and 2-methylisoborneol (MIB) outbreaks in tropical water bodies, such as Southeast Asia, by actinomycetes have not yet been elucidated in detail. Six Streptomyces isolates from lowland environments in Malaysia were selected and evaluated for their odor production under different temperatures. The gene responsible for the production of geosmin, geoA, was detected in all isolates, while only two isolates harbored tpc, which is responsible for 2-MIB production. This result suggested that geosmin and 2-MIB synthesis pathway genes already existed in the environment in the Tropics of Southeast Asia. Furthermore, our isolates produced musty odor compounds at 30°C, and differences were observed in musty odor production between various temperatures. This result indicated the potential for odor episodes in water bodies of the tropical countries of Southeast Asia throughout the year due to the mean annual ambient temperature of 27°C in the lowlands.

Organochlorine Pesticides (OCPs) in Sediment and Fish of Two Tropical Water Bodies Under Different Land Use.

In this study we quantified and compared bioaccumulated OCPs in target fish species Cichlasoma urophthalmus (Mayan cichlid) and Oreochromis niloticus (Nile tilapia) and sediment in two lentic systems neighboring areas with different land use (Xnoha=agricultural/Mocu=nature reserve). Fish at both sites showed the same number of pesticide compounds (17) while in sediment were 17 and 20, respectively. ∑chlordane concentrations were significantly higher in Xnoha in both fish and sediment (1.0 and 0.17µg/g, respectively). Here higher concentrations of o,p'DDT were found in fish than in sediments, this was similarly demonstrated in Mocu but to a lesser extent. The proportion of endosulfan sulfate was lower in Xnoha (<20%) than in Mocu (<50%) compared to the original product. Detected concentrations of ∑DDT and chlordane exceed international permissible limits. Results indicate that OCPs were present in both aquatic systems regardless of the differences in land use.

Occurrence of Mass Swarming of Family Acartiidae (Calanoid Copepods) (Zooplankton) in Ashtamudi Estuary, Kerala

Aggregation and swarming of different species of zooplankton has been reported worldwide from estuaries and coastal systems. But such swarming behaviors are seldom reported from tropical water bodies. Mass swarming and aggregation of Acartia species (91%) in mesozooplankton were observed in Ashtamudi estuary on the west coast during late monsoon season (2015). The mesozooplankton density recorded was 106,578 ind.m -3 ; composed of calanoid copepods dominated by females (97%), fish eggs (2.4%) and cyclopoids (0.2%). Even though swarming of copepods appears to be a common phenomenon in temperate shallow waters, reports from tropical estuaries are less. Here, females were outnumbering males, with sex ratio of 1:3 (male to female) and observed with spermatophore in the collections suggesting aggregation of copepods that might be for mating purpose. Since the males are usually short lived, swarming will facilitate high rate of fertilization and it helps the copepods in existence and propagation. They are also able to disperse easily by producing resting eggs leading to their sudden appearance in water column when temperature rises and salinity increases. Presence of such swarms indicates habitat shifts due to climatic change, water pollution and eutrophication issues in the coastal environment.

Assessment of the Effects of Light Availability on Growth and Competition Between Strains of Planktothrix agardhii and Microcystis aeruginosa

In this study, we tested the hypothesis that Planktothrix agardhii strains isolated from a tropical water body were better competitors for light than Microcystis aeruginosa strains. These cyanobacteria are common in eutrophic systems, where light is one of the main drivers of phytoplankton, and Planktothrix is considered more shade-adapted and Microcystis more high-light tolerant. First, the effect of light intensities on growth was studied in batch cultures. Next, the minimum requirement of light (I*) and the effect of light limitation on the outcome of competition was investigated in chemostats. All strains showed similar growth at 10 μmol photons m(-2) s(-1), demonstrating the ability of the two species to grow in low light. The optimum light intensity was lower for P. agardhii, but at the highest light intensity, Microcystis strains reached higher biovolume, confirming that P. agardhii has higher sensitivity to high light. Nonetheless, P. agardhii grew in light intensities considered high (500 μmol photons m(-2) s(-1)) for this species. M. aeruginosa showed a higher carrying capacity in light-limited condition, but I* was similar between all the strains. Under light competition, Microcystis strains displaced P. agardhii and dominated. In two cases, there was competitive exclusion and in the other two P. agardhii managed to remain in the system with a low biovolume (≈15%). Our findings not only show that strains of P. agardhii can grow under higher light intensities than generally assumed but also that strains of M. aeruginosa are better competitors for light than supposed. These results help to understand the co-occurrence of these species in tropical environments and the dominance of M. aeruginosa even in low-light conditions.

Impact of terrestrial runoff on organic matter, trophic state, and phytoplankton in a tropical, upland reservoir

The impact of organic matter inputs from agricultural, forest and domestic sources on aquatic processes has been considerably less studied in tropical reservoirs relative to temperate systems despite the high number of these small aquatic systems in the tropics. Here we present the results of an in situ mesocosm study that examined the impact of allochthonous organic matter on a headwater reservoir in Northern Vietnam. We examined the impact of wastewater and soils from floodplain paddies, Acacia mangium plantations and from upland slopes on the metabolic status of the reservoir. The addition of floodplain paddy soils to the reservoir water led to a rapid switch in metabolic status from net autotrophic to net heterotrophic. In contrast, the addition of wastewater in low concentrations had less impact on the metabolic status of the reservoir, reflecting the low population density in the area. The addition of floodplain paddy soils also increased phytoplankton diversity and evenness relative to the control. In summary, soils from floodplain paddies and from A. mangium plantations had the highest impact on the reservoir, with upland soils and wastewater having less of an impact. We also found that primary production in this reservoir was nitrogen limited. In order to avoid accelerating the impact of runoff on the reservoir, future management options should perhaps focus on minimizing water and sediment runoff from upstream paddy fields and from A. mangium plantations. These results also underline the importance of studying these upland tropical water bodies that can contribute an important but, on the whole, ignored part of the global carbon balance.

Fecal pollution source tracking in waters intended for human supply based on archaeal and bacterial genetic markers.

The determination of fecal pollution sources in aquatic ecosystems is essential to estimate associated health risks. In this study, we evaluate eight microbial source tracking (MST) markers including host-specific Bacteroidales and Methanobrevibacter spp. for discrimination between human, bovine, equine, and swine fecal contamination in waters intended for human supply. Overall, the novel host-specific archaeal and bacterial primers proposed in this study demonstrated high sensitivity and specificity. Markers for the Archaea domain were more prevalent in the fecal and water samples studied. We conclude that the investigations regarding the sources of fecal pollution in public water supplies can contribute to improve the quality of human health. To our knowledge, this is the first analysis using both archaeal and bacterial fecal MST markers on tropical water bodies of Rio de Janeiro city, Brazil.

Ecotoxicological risks of calcium nitrate exposure to freshwater tropical organisms: Laboratory and field experiments

This study aimed to analyze laboratory and field data to assess the ecotoxicological risks of calcium nitrate exposure to freshwater tropical biota. Short-term laboratorial tests resulted in estimated EC50 values of 76.72 (67.32–86.12)mg N-NO3-L−1 for C. silvestrii and 296.46 (277.16–315.76)mg N-NO3-L−1 for C. xanthus. Long-term laboratorial tests generated IC25 values of 5.05 (4.35-5.75) and 28.73 (26.30–31.15)mg N-NO3-L−1 for C. silvestrii and C. xanthus, respectively. The results from in situ mesocosm experiments performed in the Ibirité reservoir (a tropical eutrophic urban water body located in SE Brazil) indicated that C. silvestrii and C. xanthus were not under severe deleterious acute impact due to the treatment because the higher nitrate concentrations determined were 5.2mg N-NO3-L−1 (t=24h; sediment-water interface) and 17.5mg N-NO3-L−1 (t=600h; interstitial water). However, an abrupt decrease in the densities of Cyanophyceae members and other benthic taxa was observed. In summary, the present work contributes greatly to the toxicity data linked to two taxonomically distinct organisms that have never been screened for calcium nitrate sensitivity. Furthermore, considering the problem of the management and restoration of eutrophic environments, our study reports a comprehensive field assessment that allows the elucidation of the possible toxic impacts caused by the addition of calcium nitrate (a remediation technique) on aquatic and benthic organisms as well as the implications on the aquatic ecosystem as a whole, which may greatly allow expanding the current knowledgebase on the topic.

Tilapia rendalli increases phytoplankton biomass of a shallow tropical lake

AIM: This study aimed to experimentally test the influence of a planktivorous filter-feeding fish (Tilapia rendalli) on the phytoplankton dynamics of a small and shallow tropical reservoir (Lake Monte Alegre, Brazil). Adults of T. rendalli of this lake feed preferentially on phytoplankton, and we hypothesize that: I) adults of T. rendalli will decrease the phytoplankton biomass and composition through direct herbivory, and II) as it is a eutrophic system, fish would not have strong influence on phytoplankton through nutrient cycling. METHODS: To evaluate these different effects on algae, a field experiment was performed in the summer period for 15 days, in mesocosms isolated from the sediment, using a control group (no fish) and a treatment group (with one fish in each mesocosm). Physical and chemical variables and phyto- and zooplankton were evaluated at the start, middle, and end of the experiment. RESULTS: At the end of the experiment, it was observed a significant increase in ammonium concentrations and total phytoplankton biomass, Cyanobacteria and Zygnemaphyceae and all size classes except class II (20-30 µm) in the treatment group (with fish). The biomass increase of the potentially toxic cyanobacterium Cylindrospermospsis raciborskii was also observed in the fish treatment at the end of the experimental period. CONCLUSION: This study did not support both initial hypotheses. It supports the assertion that in tropical water bodies, with similar characteristics to the environment studied, planktivorous filter-feeding fish, such as T. rendalli, are not effective in reducing phytoplankton biomass through direct grazing, even when phytoplankton is one of their main food items. T. rendalli can contribute to the increase of phytoplankton biomass and can promote or increase the eutrophication of aquatic systems.

Competitive outcome between the rotiferBrachionus calyciflorusand the cladoceranMoina macrocopadepends on algal density but not temperature

The rotifer Brachionus calyciflorus often occurs simultaneously with the cladoceran Moina macro- copa in tropical water bodies. We studied the effects of temperature (20, 25 and 30 xC) and algal density (0.5, 1.0 and 3.0r 10 6 cells.mL x1 Scenedesmus obliquus) on the outcome of competition and duration of coex- istence between B. calyciflorus and M. macrocopa using population growth experiments. The results showed that regardless of temperature, M. macrocopa outcompeted B. calyciflorus at the lowest algal density (0.5r 10 6 cells.mL x1 ), whereas B. calyciflorus outcompeted M. macrocopa at the higher algal densities (1.0 and 3.0r 10 6 cells.mL x1 ). The duration of coexistence shortened with increasing temperature when M. macrocopa outcompeted B. calyciflorus, and those with increasing temperature and algal density when B. calyciflorus outcompeted M. macrocopa. Our results suggested that the competitive outcome between the rotifer B. calyciflorus and the cladoceran M. macrocopa was dependent on algal density but not temperature, the duration of coexistence between them was dependent on algal density and temperature, and the exploitative competition of M. macrocopa over B. calyciflorus may be more important than the interference competition.

Zooplankton, fish communities and the role of planktivory in nine Ethiopian lakes

Fish and zooplankton populations of nine Ethiopian freshwater lakes were quantitatively sampled along a North–South gradient. Differences in altitude and latitude resulted in a temperature gradient from North to South. We tested three hypotheses: (1) the degree of zooplanktivory decreases with water temperature, i.e. from North to South; (2) the degree of zooplanktivory increases with the abundance of large-bodied zooplankton; and (3) the pattern of zooplanktivory in eutrophic Ethiopian water bodies differs from other tropical and temperate water bodies. Proportions of zooplanktivory in the fish communities did not show a geographical trend, but mainly depended on fish species, zooplankton density and the availability of large-bodied cladocerans. The degree of zooplanktivory in eutrophic Ethiopian water bodies differs from other eutrophic water bodies, both temperate and tropical. In Ethiopia, the degree of zooplanktivory can be both low and high, in contrast with other tropical water bodies where zooplanktivory is generally low and with temperate eutrophic water bodies where it is generally high. As a result, predation pressure on zooplankton by fish varies dramatically amongst Ethiopian water bodies.

A First Account of Freshwater Potamolepid Sponges (Demospongiae, Spongillina, Potamolepidae) from the Middle Eocene: Biogeographic and Paleoclimatic Implications

We report the oldest fossil occurrence of freshwater potamolepid sponges (Demospongiae, Spongillina, Potamolepidae) to date, originating from middle Eocene lake sediments accumulated in the Giraffe kimberlite maar, northern Canada. Sponges are represented by strongyle spicules that are gemmuloscleres. These are described herein as belonging to a new species,Potamophloios canadensis. Because the most similar extant potamolepid sponges inhabit subtropical to tropical water bodies, these observations provide further evidence of biogeographic reorganizations in response to warm high-latitude Eocene paleoclimates.

Threats, management and envisaged utilizations of aquatic weed Eichhornia crassipes: an overview

Eichhornia crassipes or water hyacinth is a free-floating plant, growing plentifully in the tropical water bodies. This invasive weed poses multiple hazards ranging from ecological and economical to social. It tends to endanger biodiversity, cause eutrophication, shelter pests, clog fresh waterways, affect agriculture and aquaculture, hamper shipping and recreational activities. Existing control methods have been insufficient to contain its aggressive propagation. Recently, it has been envisaged that successful utilization of this weed can solve the associated problems associated with them. It is being speculated that the huge biomass can be used in waste water treatment, heavy metal and dye remediation, as substrate for bioethanol and biogas production, electricity generation, industrial uses, human food and antioxidants, medicines, feed, agriculture and sustainable development. Towards this quest many approaches have been undertaken and partial success is achieved. If harnessed properly, this weed-based green technology can solve many of the issues our society faces now. In this context, the papers published in recent years have been reviewed, with the objective of creating public awareness and bolstering management and utilization of this cumbersome invasive weed.

Predation on the eggs and larvae of invasive cane toads (Rhinella marina) by native aquatic invertebrates in tropical Australia

An invasive species is less likely to flourish if it is vulnerable to the predators it encounters in its newly-colonised range. The success of cane toads (Rhinella marina) in invading Australia has been attributed to the toads’ powerful chemical defences, which render this toxic invader invulnerable to most vertebrate predators. However, invertebrate predators have been largely ignored. Our laboratory studies show that at least three invertebrate species (one coleopteran, two hemipterans) are unaffected by the toads’ bufadienolide defences, and consume aquatic stages of the cane toad life history. The water beetle Cybister godeffroyi consumed eggs, hatchlings and tadpoles of R. marina, whereas the water bugs Diplonychus rusticus and Lethocerus insulanus consumed toad tadpoles but not eggs. In choice tests, C. godeffroyi and D. rusticus preferred cane toad tadpoles to simultaneously available native tadpoles or fish, possibly reflecting the smaller size and/or slower swimming speeds of larval cane toads. Rates of predation on cane toad tadpoles were high (e.g., a single water beetle often consumed five tadpoles per day in a complex environment). These abundant, voracious invertebrate predators could reduce cane toad recruitment success in some tropical waterbodies. Future research could usefully examine whether densities of water beetles and water bugs increase after toad invasion (potentially explaining why toad numbers often decline post-colonisation).

Morphological and molecular studies of Sphaerospermopsis torques-reginae (Cyanobacteria, Nostocales) from South American water blooms

Werner V.R., Laughinghouse IV H.D., Fiore M.F., Sant'Anna C.L., Hoff C., Santos K.R.d.S., Neuhaus E.B., Molica R.J.R., Honda R.Y. and Echenique R.O. 2012. Morphological and molecular studies of Sphaerospermopsis torques-reginae (Cyanobacteria, Nostocales) from South American water blooms. Phycologia 51: 228–238. DOI: 10.2216/11-32.1Sphaerospermopsis torques-reginae (Komárek) Werner, Laughinghouse IV, Fiore & Sant'Anna comb. nov. was originally described as Anabaena torques-reginae Komárek from planktonic populations of Cuban eutrophic environments, characterized by twisted trichomes with spherical akinetes adjacent to the heterocytes. Recently, using molecular analyses, all planktonic Anabaena Bory ex Bornet & Flahault morphospecies were transferred into the genus Dolichospermum (Ralfs ex Bornet & Flahault) Wacklin et al., including Dolichospermum torques-reginae (Komárek) Wacklin et al. However, by a polyphasic characterization of strains of Anabaena reniformis Lemmermann and Aphanizomenon aphanizomenoides (Forti) Horecká & Komárek (=Anabaena aphanizomenoides Forti), these planktonic species were reclassified into Sphaerospermopsis Zapomělová et al. Our study's main objective was to characterize morphologically and molecularly cyanobacterial populations identified as Dolichospermum torques-reginae, observed in different aquatic ecosystems in South America. The 16S rRNA gene of two Dolichospermum torques-reginae strains (ITEP-024 and ITEP-026) was sequenced and phylogenetically analyzed for the first time. The morphological and phylogenetic analyses demonstrated the affiliation of the studied populations with the genus Sphaerospermopsis and, consequently, were denominated as Sphaerospermopsis torques-reginae. Furthermore, geographic distribution, ecology, and toxicity of the species are discussed. It was observed in different aquatic environments, natural and artificial, tropical and subtropical in Brazil, temperate in Argentina, and tropical in Colombia, suggesting a wide distribution in South America. It normally occurred in dense freshwater blooms, although it was also found in water with low salinity. Sphaerospermopsis torques-reginae toxic blooms have been reported in tropical water bodies in northeastern Brazil.

Gene expression in caged fish as indicators of contaminants exposure in tropical karstic water bodies

Karstic areas in Yucatan are very permeable, which allows contaminants to move rapidly into the aquifer. In the present study, we evaluated gene expression of vitellogenin (VTG) and cytochrome P-450 1A (CYP1A) in caged juvenile zebrafish deployed for 15 days in 13 different water bodies, cenotes and aguadas, throughout karstic region of the Yucatan peninsula. Gene expression was evaluated using qRT-PCR. Results indicated induction of VTG in 7 water bodies with respect to reference cage. The highest relative VTG expression, about 3000 times higher than reference cage, was found in an aguada close to a cattle farm. CYP1A induction with respect to reference cage was observed in 3 water bodies, all of them located near villages or used for tourist activities. Pollutants and biomarkers of effect should be monitored in these water bodies in order to have a better understanding of the actual levels of pollutants that are present at Yucatan’s aquifer and the potential risk to human and environmental health.

Remote sensing of water quality in an Australian tropical freshwater impoundment using matrix inversion and MERIS images

The purpose of this study was to investigate how semi-analytical inversion techniques developed for the remote sensing of water quality parameters (chlorophyll a, tripton and coloured dissolved organic matter (CDOM)) in inland waters could be adapted or improved for application to Australian tropical and sub-tropical water bodies. The Matrix Inversion Method (MIM) with a semi-analytic model of the anisotropy of the in-water light field was applied to MERIS images of Burdekin Falls Dam, Australia, a tropical freshwater impoundment. Specific attention was required to improve the atmospheric correction of the MERIS data. The performance of the conventional three band exact solution of the MIM was compared to that of over-determined solutions that used constant and differential weighting for each sensor band. The results of the application of the MIM algorithm showed that the best weighting scheme had a mean chlorophyll a retrieval difference of 1.0 μgl − 1 , the three band direct matrix inversion scheme had a mean difference of 4.2 μgl − 1 and the constant weight scheme had a mean difference of 5.5 μgl − 1 . For tripton, the best performed weighting scheme had a mean difference of 1.2 mgl − 1 , the three band scheme had a mean difference of 3.4 mgl − 1 and the constant weight scheme had a mean difference of 1.8 mgl − 1 . For the CDOM retrieval, the mean difference was found to be 0.12 m − 1 for the best performed weighting scheme, 0.25 m − 1 for the three band scheme and 0.52 m − 1 for the constant weight scheme. It was found that significant improvements in the accuracy and precision of retrieved water quality parameter values can be obtained by using differentially weighted, over-determined systems of equations, rather than exact solutions. These more reliable estimates of water quality parameters will allow water resource managers to improve their monitoring regimes.