Tropical Water Bodies Research Articles

Dynamics and source characterization of chromophoric dissolved organic matter (CDOM) in a tropical monsoon driven lagoon

While there is a significant body of research on the dynamics of chromophoric dissolved organic matter (CDOM) in coastal and offshore waters, our understanding of CDOM dynamics in tropical inland water bodies remains limited. To bridge this knowledge gap, a monthly in-situ investigation was carried out at 33 stations along a monsoon driven lagoon, Chilika, on the southeast coast of India for one year i.e., from July 2018 to June 2019. CDOM absorption at 440 nm [aCDOM(440)] data were analyzed as a proxy for CDOM concentration which varied between a range of 0.04–65.14 m−1 with an average value of 2.77 ± 5.23 m−1. A gradient in aCDOM(440) was observed from the river discharge dominated shallower northern sector (4.91 ± 8.32) m−1 to the more isolated and less fresh water influenced deeper southern sector (1.21 ± 1.55) m−1. Spectral slope (S), spectral slope ratio (SR), and molecular weight proxy (M) were computed to understand the possible source and fate of CDOM in the lagoon. The average spectral slope of S280–500 and S350–500 vary between 0.002 and 0.096 nm−1 and 0.001–0.095 nm−1, respectively. The (SR) and (M) values ranged between of 0.01–6.81 and 0.31–52.28. It was observed that large-sized, high molecular weight CDOM from terrestrial origin was prevalent during monsoon with lower (S280–500), (SR), and (M)values. In contrast, lower molecular weight CDOM fractions were prevalent during pre- and post-monsoon which were mainly of autochthonous origin with higher (S350–500), (SR), and (M) values. Our findings indicate significant spatio-temporal variations of CDOM in Chilika Lagoon, influenced by the monsoon-driven influx of freshwater and the mixing of fresh and marine water. In-situ changes in CDOM are likely shaped by microbial breakdown and photodegradation.

Distribution of Recent Benthic Foraminifera from the Outer Channel in and Around Gabakund Sea Mouth of Chilika Lagoon

Chilika (19°28’ to 19°54’ N; 85°54’N to 85°38’ E) lagoon situated in the east coast of India is considered to be one of the largest tropical coastal brackish water bodies in Asia. The unique setup of 60 km long narrow strip of sand barriers and swampy islands separating the area from the sea with few mouths of interconnections in the east and draining of tributaries of the river Mahanadi in the west while its environmental condition governed by tidal inflows and the southwest monsoon.The study of features of benthic foraminiferal tests, morphology, and abundance shed light upon paleoclimatic changes like monsoon variability, salinity, temperature, etc. Ten sediment samples were collected from the outer channel of Chilika lagoon in and around the Gabakund area and processed for species level study and SEM imaging following standard procedures. Sand dominates as the substrate towards the mouth at Gabakund area and silty to clayey sand towards the southern part of the Outer Channel. A total of 13 genera of benthic foraminifera belonging to 36 species were documented at the sampling stations. In the current study the species diversity and richness on the basis of the physico-chemical attributes of sea and river water incursion during pre-monsoon time in the outer channel of the lagoon is reported. In this region calcareous benthic foraminiferal are dominant while few agglutinated foraminifera have found their unusual niche.

Sustainable aquatic resource management and inland fisheries in tropical Asia: Interdisciplinary and transdisciplinary approaches

The intensive utilization of tropical inland water bodies for multiple and sometimes competing activities underlines the necessity for their integrated and holistic co-management. This paper presents our synthesis on lake and reservoir fisheries in South and Southeast Asia as social–ecological systems, based on a synopsis of our research findings from a previous EU-funded research programme in Sri Lanka, Thailand and the Philippines (FISHSTRAT project). The paper attempts to merge our results with recent developments in research, policy and practice. We explore the effects of the main external and internal control mechanisms of the trophic state and pinpoint to the high production potential of traditionally unexploited small indigenous fish species. The limitations of conventional centralized management systems highlight the importance of introducing transdisciplinary approaches which integrate limnology, fish ecology and fisheries with the interests of other resource using stakeholders and decision makers in order to develop locally appropriate co-management strategies for sustainable aquatic resource use.

Implementation of remote sensing algorithms to estimate TOC, Chl-a, and TDS in a tropical water body; Sanalona reservoir, Sinaloa, Mexico.

The present study implements a methodology to estimate water quality values using statistical tools and remote sensing techniques in a tropical water body Sanalona. Linear regression models developed by Box-Cox transformations and processed data from LANDSAT-8 imagery (bands) were used to estimate TOC, TDS, and Chl-a of the Sanalona reservoir from 2013 to 2020 at five sampling sites measured every 6 months. A band discriminant analysis was carried out to statistically fit and optimize the proposed algorithms. Coefficients of determination beyond 0.9 were obtained for these water quality parameters (r2TOC = 0.90, r2TDS = 0.95, and r2Chl-a = 0.96). A comparison between the estimated and observed water quality was carried out using different data for validation. The validation of the models showed favorable results with R2TOC = 0.8525, R2TDS = 0.8172, and R2Chl-a = 0.9256. The present study implemented, validated, and compared the results obtained by using an ordered and standardized methodology proposed for the estimation of TOC, TDS, and Chl-a values based on water quality parameters measured in the field and using satellite images.

Reconstructing the paleoenvironment of an oxygenated Mesoproterozoic shoreline and its record of life

The Nonesuch Formation microbiota provide a window into ca. 1075 Ma life within the interior of ancient North America. The Nonesuch water body formed following the cessation of widespread volcanism within the Midcontinent Rift as the basin continued to subside. In northern Michigan and Wisconsin, USA, the Copper Harbor Conglomerate records terrestrial alluvial fan and fluvial plain environments that transitioned into subaqueous lacustrine deposition of the Nonesuch Formation. These units thin toward a paleotopographic high associated with the Brownstone Falls angular unconformity. Due to these “Brownstone Highlands,” we were able to explore the paleoenvironment laterally at different depths in contemporaneous deposits. Rock magnetic data constrain that when the lake was shallow, it was oxygenated as evidenced by an oxidized mineral assemblage. Oxygen levels were lower at greater depth—in the deepest portions of the water body, anoxic conditions are recorded. An intermediate facies in depth and redox between these endmembers preserves detrital magnetite and hematite, which can be present in high abundance due to the proximal volcanic highlands. This magnetic facies enabled the development of a paleomagnetic pole based on both detrital magnetite and hematite that constrains the paleolatitude of the lake to 7.1 ± 2.8°N. Sediments of the intermediate facies preserve exquisite organic-walled microfossils, with microfossils being less diverse to absent in the anoxic facies where amorphous organic matter is more likely to be preserved. The assemblage of cyanobacteria and eukaryotes (both photoautotrophs and heterotrophs) lived within the oxygenated waters of this tropical Mesoproterozoic water body.

Physicochemical Characteristics of a Tropical Seasonal Water Body: Ikoro Stream, Edo State, Nigeria

The objective of this paper is to evaluate the physicochemical characteristics of a tropical seasonal water body- Ikoro stream, Edo State, Nigeria using standard methods. The results obtained from the physical and chemical analyses showed that the range of values were: 23oC - 30oC for air temperature, 22oC - 29oC for water temperature, 1.28NTU - 14.48NTU for turbidity, 1mg/l - 10mg/l for total dissolved solid, 4.01 - 6.43 for pH, 2.3µScm-1 - 21.7µScm-1 for conductivity, 4.00mg/l - 13.00mg/l for dissolved oxygen, 0.005mg/l - 0.227mg/l for Sulphate, 0.004mg/l - 0.047mg/l for nitrate, 0.05mg/l - 0.15mg/l for phosphate, 0.49mg/l - 2.43mg/l for magnesium, 2.41mg/l - 8.02mg/l for calcium, 0.19mg/l - 8.71mg/l for ammonium, 14.3mg/l - 22.3mg/l for chloride, 1.33mg/l - 2.57mg/l for sodium, 0.76mg/l - 1.46mg/l for potassium, 10.18mg/l - 26.88mg/l for silicate, 18.30mg/l - 42.70mg/l for total alkalinity 2.90mg/l - 9.64mg/l for total hardness. The parameters fluctuated in all three stations throughout the period of study while only turbidity showed a seasonal pattern of increasing trend from dry season to rainy season. The stream had low nutrients level but high ammonium in one of the stations which clearly exceeded the WHO guideline for drinking water.

Ecological importance of rare phytoplankton species revealed by their high contribution to unsaturated fatty acids in tropical waters

Abstract There is increasing evidence that rare species play an important role in trophic interactions, but the function of rare species with low biomass in these processes remains unclear. Phytoplankton is placed at the base of lentic and marine food webs and is characterised by a few dominant species and many rare species. While the dominant species contribute most to the primary production, they are often low‐quality food for primary consumers. The rare species may instead provide the essential biochemical nutrients for consumers, especially in eutrophic waters. We hypothesised that the biomass of rare eukaryotic phytoplankton species significantly determines the concentrations of sestonic long‐chain highly unsaturated fatty acids, directly linking them to the functioning of aquatic ecosystems. We applied redundancy analysis and Lasso regression models to identify the species whose population dynamics explain the variations of sestonic fatty acids concentrations in tropical reservoirs and lakes. The lasso models predicted that the dominant phytoplankton species determined the concentration of saturated sestonic fatty acids and that rare phytoplankton species were the main determinant for polyunsaturated fatty acids, which are critical for the food quality of consumers such as zooplankton and promote the energy transfer from primary producers to higher trophic levels in natural waters. In particular, the biomass of the rare species Scenedesmus obliquus was a key variable explaining the variations of α‐linolenic acid, α‐linoleic acid, γ‐linolenic acid, and eicosapentaenoic acid concentrations. We conclude that the population dynamics of rare phytoplankton species can define the food quality associated with eicosapentaenoic acid for consumers and thus play a critical role in the trophic transfer in the food webs of tropical waterbodies.

Anatomical Features and Antimicrobial Activity of Duckweed

Duckweeds are common floating flowering plants belonging to Lemnaceae. Five main genera known as duckweed are found in tropical water bodies mostly under eutrophic condition. Despite of their minute size, duckweeds exhibit distinction as per morpho-anatomical characterisation and production of secondary metabolites, that show antimicrobial potentialities. Connective stalk of duckweeds is an organ of attachment between the mother and daughter fronds, whose anatomy has been studied here in details. The present study focuses on the critical anatomical differences between Lemna minor L. and Spirodela polyrrhiza (L.) Schleid. using scanning electron microscope. The antimicrobial potency especially against Gram-negative bacteria were studied using duckweeds biomass collected from Indian aquatic environment, which were cultured in laboratory conditions. Activity against fish pathogen like Aeromonas sp. were investigated also. Bangladesh J. Bot. 52(1): 105-110, 2023 (March)

Toward eDNA‐based bioassessment of freshwater reservoirs with small volumes of water: Robust molecular protocols

AbstractBioassessment of freshwater quality with eDNA is a powerful alternative to traditional methods involving collecting, sorting, and identifying metazoan taxa with morphology (e.g., macroinvertebrates). Particularly attractive for routine monitoring would be an eDNA method that uses a remote‐controlled boat for collecting small volumes of water without filtration in order to simplify sampling. Such a method would not likely capture eDNA signals for all metazoan species, but may nevertheless allow for cost‐effective, and frequent monitoring of water quality, which is important for tropical waterbodies that require year‐round surveillance. We here optimize a molecular protocol for capturing metazoan signatures based on eDNA obtained from 15 ml of water. To test the robustness of the method, we used samples from two tropical reservoirs with known differences in water quality to optimize molecular procedures so that they yield repeatable results. Each reservoir was sampled at three sites (“biological replicates”) and each water sample was subsampled twice before extracting the eDNA using ethanol precipitation for both subsamples (“technical replicates”). We then tested how much DNA (0.1 ng to 15 ng) and how many PCR cycles (25 or 35) minimized the variance of the metazoan eDNA signal between biological and technical replicates. For this purpose, we amplified a 313 bp COI minibarcode using a universal metazoan primer pair. We found that regardless of template amounts or PCR cycle numbers, the eDNA signatures for both reservoirs were distinct because only 17 of 59 mOTUs (mainly planktonic crustaceans and rotifers) were shared. We also found that template amounts between 0.5 and 15 ng yielded overall similar results, but the use of 35 PCR cycles significantly depressed the number of detected species (p‐value < 0.05). Fortunately, the differences between the detected metazoan community of the reservoirs were so strong that all biological and technical replicates could be assigned unambiguously to their source reservoir although the variance between technical replicates remained high for all PCR experiments (Bray‐Curtis dissimilarity: 5%–20%; Jaccard distance: 10%–40%).

Identification of Microcrustaceans as Potential Bioindicators of Arsenic in Tropical Water Bodies.

We investigated microcrustaceans inhabiting arsenic contaminated and non-contaminated freshwater to identify potential bioindicators of arsenic contamination in the tropical freshwater of Matehuala in northern Mexico. We collected water, sediment, and zooplankton, at five sampling points during three sampling campaigns. We determined water temperature, pH, electrical conductivity, dissolved oxygen, alkalinity, salinity, and total arsenic concentration in water. Additionally, we determined total arsenic and arsenic speciation in sediment samples. We identified microcrustaceans and determined abundance, richness, and Shannon Index. We also investigated relationships and correlations between physiochemical and ecological variables. Results showed that arsenic concentrations in freshwater ranged from 0.001 to 53.23mg/L, while total arsenic in sediments ranged from 10.37 to 2472.84mg/kg as As + 5. Six microcrustacean species were found in highly and moderately contaminated water (Latonopsis australis, Eucyclops chihuahuensis, Acanthocyclops americanus, Pleuroxus (Picripleuroxus) quasidenticulatus, Macrocyclops albidus, and Paracyclops chiltoni), while five species were found in arsenic-free water (Simocephalus punctatus, Alona glabra, Eucyclops leptacanthus, M. albidus, and P. quasidenticulatus). An inverse relationship was observed between microcrustacean richness and arsenic. However, the scope of the data did not allow for a strong and significant correlation. Nevertheless, among the species inhabiting As-free water, S. punctatus showed potential to be further tested as a bioindicator of As contamination in Matehuala. Identification of potential bioindicators could help monitor water quality and increase understanding of the incorporation and toxicity of As in freshwater-sensitive and freshwater-metallotolerant microcrustaceans, which, in turn, might help us to understand As incorporation in the food web.

Seasonality in Environmental Conditions Drive Variation in Plankton Communities in a Shallow Tropical Lake

Factors influencing the spatio-temporal dynamics of plankton communities in small tropical lakes are not well-understood. This study assessed plankton communities in response to spatial (six sampling sites) and seasonal (wet vs. dry seasons) changes in environmental variables in Lake Kanyaboli, a small satellite lake on the northern shores of Lake Victoria, Kenya. Water quality variables, including pH, conductivity (EC), dissolved oxygen (DO), temperature, Secchi depth (SD), nitrates (NO3-), nitrites (NO2-), ammonium (NH4+), soluble reactive phosphorus (SRP), total nitrogen (TN), total phosphorus (TP), and chlorophyll-a(Chl-a), were monitored monthly at six sites spread throughout the lake for 1 year. Phytoplankton and zooplankton samples were collected and analyzed for taxon composition and abundance. Two-way ANOVA showed no significant interaction between site and season for all variables. Likewise, there were no significant spatial differences for all variables except Chl-a. At-test showed significant seasonal differences in SD, DO,NH4+,NO3-,NO2-, and TN. Thirty phytoplankton genera were identified belonging to Bacillariophyceae, Chlorophyceae, Cryptophyceae, Cyanophyceae, Euglenoidae, Trebouxiophyceae, and Zygnematophyceae, with Chlorophyceae being the most dominant (42.30%). Zooplankton comprised of 15 genera, belonging to Copepoda (55.4%), Rotifera (27.9%), and Cladocera (16.7%). Two-way ANOVA for plankton abundance showed no significant interaction between site and season, but there were significant differences in community composition between the wet and dry seasons. Canonical correspondence analysis identified water clarity (Secchi depth) and concentrations of dissolved fractions of nitrogen and phosphorus as the major water quality variables driving variation in the composition of plankton communities in the lake. This study showed that seasonality was a major driver of changes in plankton community composition between dry and wet seasons through changes in the concentrations of nutrients (NH4+,NO3-,NO2-, TN, and TP). Lake Kanyaboli's phytoplankton community indicated a non-equilibrial state, perhaps due to short residence times of water, especially during the wet season, and dense macrophytes fringing the lake that increase nutrient uptake and limit the dominance of select phytoplankton species. This study shows the importance of long-term studies covering dry and wet seasons to understand the dynamics of plankton communities and their drivers in small tropical waterbodies to inform management and conservation.

Multi-class secondary metabolites in cyanobacterial blooms from a tropical water body: Distribution patterns and real-time prediction

Cyanobacterial blooms that produce toxins occur in freshwaters worldwide and yet, the occurrence and distribution patterns of many cyanobacterial secondary metabolites particularly in tropical regions are still not fully understood. Moreover, predictive models for these metabolites by using easily accessible water quality indicators are rarely discussed. In this study, we investigated the co-occurrence and spatiotemporal trends of 18 well-known and less-studied cyanobacterial metabolites (including [D-Asp3] microcystin-LR (DM-LR), [D-Asp3] microcystin-RR (DM-RR), microcystin-HilR (MC-HilR), microcystin-HtyR (MC-HtyR), microcystin-LA (MC-LA), microcystin-LF (MC-LF), microcystin-LR (MC-LR), microcystin-LW (MC-LW), microcystin-LY (MC-LY), microcystin-RR (MC-RR) and microcystin-WR (MC-WR), Anatoxin-a (ATX-a), homoanatoxin-a (HATX-a), cylindrospermospin (CYN), nodularin (NOD), anabaenopeptin A (AptA) and anabaenopeptin B (AptB)) in a tropical freshwater lake often plagued with blooms. Random forest (RF) models were developed to predict MCs and CYN and assess the relative importance of 22 potential predictors that determined their concentrations. The results showed that 11 MCs, CYN, ATX-a, HATX-a, AptA and AptB were found at least once in the studied water body, with MC-RR and CYN being the most frequently occurring, intracellularly and extracellularly. AptA and AptB were detected for the first time in tropical freshwaters at low concentrations. The metabolite profiles were highly variable at both temporal and spatial scales, in line with spatially different phytoplankton assemblages. Notably, MCs decreased with the increase of CYN, possibly revealing interspecific competition of cyanobacteria. The rapid RF prediction models for MCs and CYN were successfully developed using 4 identified drivers (i.e., chlorophyll-a, total carbon, rainfall and ammonium for MCs prediction; and chloride, total carbon, rainfall and nitrate for CYN prediction). The established models can help to better understand the potential relationships between cyanotoxins and environmental variables as well as provide useful information for making policy decisions.

Isolated and combined effects of a submerged macrophyte and a cladoceran on the interactions between Microcystis aeruginosa (Cyanobacteria) and Raphidocelis subcapitata (Chlorophyta)

Introduction: Cyanobacterial blooms in tropical water bodies are increasingly common, because of eutrophication and rising temperatures. Consequently, many freshwater systems are affected, by reducing water quality, biodiversity, and ecosystem services. With the increased frequency of harmful algal blooms, the development of biological tools to improve water quality is an urgent issue. Objective: To evaluate the effects of a submerged macrophyte and a cladoceran on the microcystin-producing cyanobacteria Microcystis aeruginosa (NPLJ-4) and the chlorophyte Raphidocelis subcapitata (BMIUFRPE-02) in mixed cultures. Methods: Two parallel experiments were carried out for ten days to evaluate the effects of the submerged macrophyte Ceratophyllum demersum and the cladoceran Moina micrura on microalgal interactions. Microalgal strains were cultivated in the ASM1 culture medium, under controlled laboratory conditions. The first experiment presented four treatments: M (C. demersum), Z (M. micrura), MZ (C. demersum and M. micrura), and C (control). Meanwhile, the second experiment consisted of five treatments, in which the microalgae were cultivated together at different Microcystis:Raphidocelis ratios: 1:0, 3:1, 1:1, 1:3, and 0:1. Biomass and growth rates of the strains were evaluated every two days, which were statistically treated with three-way or two-way repeated-measures ANOVA. Results: In the first experiment, M. aeruginosa was significantly inhibited in M and MZ treatments from the second day, and Z from the fourth, while R. subcapitata showed no reduction in its biomass in any treatment. On the other hand, R. subcapitata was stimulated from the eighth and tenth days in M treatment and only on the eighth day in Z treatment. In the second experiment, M. aeruginosa was significantly inhibited when cultivated with R. subcapitata in low ratios (Microcystis:Raphidocelis ratio of 1:3) throughout the experiment, while the chlorophyte was stimulated in that treatment. Conclusions: The coexistence of a cyanobacterium with a green alga did not alter the main negative response of M. aeruginosa to the submerged macrophyte and zooplankton but stimulated the green alga. Accordingly, the introduction of submerged macrophytes and cladocerans already adapted to eutrophic conditions, both isolated and combined, proved to be a good method to control cyanobacterial blooms without negatively affecting other coexisting phytoplankton species.

Population and molecular responses to warming in Netzelia tuberspinifera – An endemic and sensitive protist from East Asia

With the effects of global warming becoming ever more obvious, biodiversity conservation is facing severe challenges. Currently, a deeper understanding the mechanisms of the effects of warming on sensitive species has become an important topic in aquatic biodiversity and ecological management. Our study first overcame the “challenge” for a sensitive indicator species (Netzelia tuberspinifera, an endemic testate amoeba species in East Asia) of culturing under laboratory conditions, and then explored its molecular response mechanisms to warming using transcriptomic analysis. Our data indicate that temperature mainly drove the geographical and seasonal variation of N. tuberspinifera populations. Transcriptomic results indicate that when the temperature is <25 °C, rising temperature triggers the biosynthesis of ribosomes; while the temperature is >25 °C, it triggers molecular processes related with cell division, test formation and general biomass increase. However, once the temperature exceeds 40 °C, N. tuberspinifera is unable to survive. Following from these results, the distribution of N. tuberspinifera might expand towards higher altitude or latitude regions under global warming. For the first time, our study showed direct evidence for sensitive protozoa species that presents a very narrow adaptation mechanism to local climate. Our work provides fundamental data for regional biodiversity conservation and scientific reference in subtropical and tropical waterbodies.

Limnological responses of a shallow tropical reservoir to recent incidence of hydro-climatic anomaly suggest potential challenges of future restoration efforts.

The impact of El Niño-induced drought (2015/2016) on the limnology of Koka Reservoir was studied through a 1-year sampling with emphasis on nutrient concentration. The monthly concentration of riverine input of TP varied between 400 and 2872 mg/m3, with a total annual load to the reservoir of 482012 × 106 mg. This resulted in annual areal load to the reservoir of 2410 mg/m2. The mean annual in lake concentration of total phosphorus as predicted by the trophic state model specifically developed for warm tropical water bodies by Salas and Martino in 1991 was 146.6 mg/m3. This is only 24% of the observed concentration of 609 mg/m3 suggesting that internal recycling is sufficient to supply much of the phosphorus that sustain cyanobacterial growth. Koka Reservoir is a highly productive water body exhibiting a thick recurrent cyanobacterial bloom exclusively dominated by Microcystis spp. Mineralization of the Microcystis-bound phosphorus could be the major mechanism of phosphorus recycling following the collapse of the bloom. High water temperature and frequent mixing may have promoted this mechanism of phosphorus recycling from autochthonous sources. In our related study, we also reported the emergence and unusual dominance of diazotrophic cyanobacteria following the climate anomaly and the consequent severe nitrogen limitation. The emergence of cyanobacteria that can fulfill their nitrogen requirement from the atmospheric nitrogen (N2) and the possibility of large phosphorus reserve in the sediment could make future restoration efforts very challenging.

Prey preference of Stenostomum cf. virginianum Nuttycombe, 1931 (Platyhelminthes); a case study in the littoral zone of a tropical reservoir

In aquatic systems, littoral zones provide heterogeneous environments where turbellarians can reach densities of up to 40,000 ind. m−2 . To reach such high densities turbellarians need to feed on a variety of prey items. Very little information is available on the feeding ecology of Stenostomum spp. in natural conditions. The objective of this work was to determine the food preference of Stenostomum virginianum based on the density and physical characteristics of prey present in the littoral zone of the Benito Juárez reservoir (Mexico) associated with the macrophyte Egeria densa by analyzing the gut content of the turbellarians. We found that 58% of turbellarians contained rotifers in their gut. The thickness of rotifer lorica did not limit the selection, but the size and availability of the species did. The preferred rotifer prey included Trichocerca porcellus, Lecane closterocerca and Colurella obtusa. This work demonstrates that turbellarians feed on rotifers but are often overlooked in freshwater trophic analyses. They need be considered together with other invertebrate predators such as Asplanchna and cyclopoid copepods because of their impact on rotifer communities in tropical and temperate water bodies.

Characterizing Trophic State in Tropical/Subtropical Reservoirs: Deviations among Indexes in the Lower Latitudes.

Trophic state indexes (TSI) guide management strategies regarding eutrophication control worldwide. Such indexes usually consider chlorophyll-a (Chl-a), total phosphorus (TP), and Secchi disk depth (SDD) as independent variables for estimating aquatic productivity and the degree of impairment. TSIs for each of these components are frequently averaged to produce a single TSI value associated with a trophic state classification (e.g., oligotrophic, mesotrophic, or eutrophic). The potential divergence among equations and classification systems originally developed for temperate lakes or tropical/subtropical reservoirs might be particularly relevant in the tropics, where there is a lack of data and the use of equations originally developed for temperate systems may be inappropriate. We calculated two widely used TSIs for temperate lakes (TSItemp) or tropical reservoirs (TSItrop) and explored the deviations among TSI components in Brazilian reservoirs. When applied to our tropical/subtropical reservoirs, the TSItemp provided a conservative approach, with lower limits anticipating increasing trophic state classification. TSI components for Chl-a and SDD significantly deviated for both sets of equations, and these discrepancies were related to turbidity, water temperature, and cyanobacterial biomass. For TSItemp, but not for TSItrop, TSI values in relation to Chl-a and TP were also significantly different. All such deviations have important management implications especially when Chl-a, TP, and SDD are averaged in a single TSI, representing loss of information and less useful trophic state classifications. Our results demonstrate that tropical water bodies may respond to drivers of eutrophication differently than temperate systems, highlighting the need for more data to better inform management of these understudied ecosystems. As managers collect data from more tropical water bodies, regional models may offer even better understanding of factors influencing trophic state.

Dynamics of Vibrio cholerae in a Typical Tropical Lake and Estuarine System: Potential of Remote Sensing for Risk Mapping

Vibrio cholerae, the bacterium responsible for the disease cholera, is a naturally-occurring bacterium, commonly found in many natural tropical water bodies. In the context of the U.N. Sustainable Development Goals (SDG) targets on health (Goal 3), water quality (Goal 6), life under water (Goal 14), and clean water and sanitation (Goal 6), which aim to “ensure availability and sustainable management of water and sanitation for all”, we investigated the environmental reservoirs of V. cholerae in Vembanad Lake, the largest lake in Kerala (India), where cholera is endemic. The response of environmental reservoirs of V. cholerae to variability in essential climate variables may play a pivotal role in determining the quality of natural water resources, and whether they might be safe for human consumption or not. The hydrodynamics of Vembanad Lake, and the man-made barrier that divides the lake, resulted in spatial and temporal variability in salinity (1–32 psu) and temperature (23 to 36 °C). The higher ends of this salinity and temperature ranges fall outside the preferred growth conditions for V. cholerae reported in the literature. The bacteria were associated with filtered water as well as with phyto- and zooplankton in the lake. Their association with benthic organisms and sediments was poor to nil. The prevalence of high laminarinase and chitinase enzyme expression (more than 50 µgmL−1 min−1) among V. cholerae could underlie their high association with phyto- and zooplankton. Furthermore, the diversity in the phytoplankton community in the lake, with dominance of genera such as Skeletonema sp., Microcystis sp., Aulacoseira sp., and Anabaena sp., which changed with location and season, and associated changes in the zooplankton community, could also have affected the dynamics of the bacteria in the lake. The probability of presence or absence of V. cholerae could be expressed as a function of chlorophyll concentration in the water, which suggests that risk maps for the entire lake can be generated using satellite-derived chlorophyll data. In situ observations and satellite-based extrapolations suggest that the risks from environmental V. cholerae in the lake can be quite high (with probability in the range of 0.5 to 1) everywhere in the lake, but higher values are encountered more frequently in the southern part of the lake. Remote sensing has an important role to play in meeting SDG goals related to health, water quality and life under water, as demonstrated in this example related to cholera.

Elimination of Congo Red Dyes From Aqueous Solution Using Eichhornia Crassipes

Water hyacinth (Eichhornia crassipes) is a free-floating plant, growing plentifully in the tropical water bodies. It is being speculated that the large biomass can be used in wastewater treatment, heavy steel and dye remediation, as a substrate for bioethanol and biogas production, electrical energy generation, industrial uses, human food and antioxidants, medicines, feed, agriculture, and sustainable improvement. In this work, the adsorption of Congo Red (CR) from aqueous solution onto EC biomass was investigated through a series of batch experiments. The effects of operating parameters such as pH (3-9), dosage (0.1-0.9 g. /100 ml), agitated velocity (100-300), size particle (88-353μm), temperature (10-50˚C), initial dye concentration (50-500) mg/l, and sorption–desorption were investigated to assess the efficiency of EC-elimination from aqueous solution. Different pre-treatments, alkali, and acid were achieved to increase the adsorption uptake. The optimum conditions for maximum removal of CR from an aqueous solution of 50 mg/L were as follows: pH (6), particle size (88 μm), stirring speed (200 rpm), and dose (0.3 g). The experimental isotherms data were analyzed using Langmuir, Freundlich, and Temkin isotherm equations and the results indicated that the Langmuir isotherm showed a better fit for CR adsorption with a higher adsorption uptake of 92.263mg/g, and the kinetic data were fitted well with pseudo-second-order kinetic model. Thermodynamic parameters were calculated from Van’t Hoff plot, confirming that the adsorption process was spontaneous and endothermic. Data show that the adsorption-desorption process lasts for four cycles before losing its efficiency and the recovery efficiency increased up to 76.63%.

Qualitative Tests of Secondary Metabolite Compounds in Ethanol Extract of Spirulina platensis from Karimun Jawa Sea, Indonesia

Spirulina platensis is a spiral green-blue algae that is abundant in the subtropical and tropical water bodies. S. platensis has several potentials to be used in the medical fields due to its wound healing and antitumor potentials. This research aimed to evaluate the secondary metabolite compounds contained in the ethanolic extract of S. platensis from Karimun Jawa Sea, Indonesia. The dried S. platensis was macerated and extracted using ethanol, then was filtered using Whatman filter paper. A series of tests has been done to determine the secondary metabolites in the ozonated oil using several chemistry tests and reagents in the ethanol extract of S. platensis. The tests found that S. platensis microalgae harvested from Karimun Jawa sea contains alkaloid, saponin, flavonoid, and quinone. As S. platensis from different region contains different substances, this research shows the substances contained in S. platensis from Karimun Jawa sea. With this research, we knew that S. platensis from Karimun Jawa islands contains alkaloid, saponin, flavonoid, and quinone which can be used as a medicinal ingredient.