Shallow Tropical Reservoir Research Articles

Environmental Variables Outpace Biotic Interactions in Shaping a Phytoplankton Community

We evaluated the main environmental factors (abiotic and biotic) driving the phytoplankton community in a shallow tropical reservoir located in an environmentally protected area. Phytoplankton samples were collected from the surface and bottom of the reservoir. The phytoplankton samples were later identified at the species level, and the species were further assigned to morphology-based functional groups (MBFGs). Zooplankton were sampled through vertical haul, communities were identified to species level, and functional diversity was estimated based on community-weighted means (CWM). Phytoplankton MBFGs IV, V, and VI contributed the most to the biomass under high light availability coupled with low nutrient availability. Potentially toxic cyanobacteria from MBFG III were observed during thermal stratification. Hydraulic mixing plays a crucial role in reducing the phytoplankton biomass during the warmer/rainy season. Cyclopoid copepods accounted for more than 83% of the zooplankton biomass. There was a weak but significant effect of zooplankton functional diversity on phytoplankton functional diversity, mainly because of the dominance of small zooplankton. Altogether, our findings suggest that environmental filtering plays a greater role than zooplankton grazing in phytoplankton community structure in this shallow tropical reservoir.

Prevalence of Endoparasites and Haematology in Redbelly Tilapia from a Shallow Tropical Reservoir in Ghana

The goal of this study was to assess common endoparasites on Tilapia zillii in the Tono Reservoir, as well as to investigate the mean intensity and prevalence of these parasites. A total of 175 fish specimens were examined during the study. Endoparasites of three metazoans and one protozoan were observed from the Tilapia zillii gills, intestines, and stomach. The findings showed that the most common endoparasites affecting Tilapia zillii are Ichthyopthirius multifiliis, Bothriocephalus sp., Contracaecum sp., and Dactylogyrus sp. Also, Contracaecum sp had the highest prevalence of 29.71, followed by Bothriocephalus sp (18.86), Ichthyopthirius multifiliis (12), and Dactylogyrus sp (6.86). The average quantity of Bothriocephalus sp was 0.84, Contracaecum sp was 1.33, Dactylogyrus sp was 0.31, and Ichthyopthirius multifiliis was 0.54. The reservoir's physicochemical parameters changed every month due to inflows and other runoffs joining. Low levels of these parameters were discovered to influence the prevalence and distribution of these parasites. Haematological parameters showed significant changes between the adult and fingerling groups, where it was observed an improvement in health status in the adult group. It was also observed that fingerlings (0.1–20 g) were more infected, which significantly affected their blood profile.
 Keywords: Tilapia zillii, endoparasite, blood profile, pathogenic effects, environmental stress

Impacts of a floating photovoltaic system on temperature and water quality in a shallow tropical reservoir

A three-dimensional hydrodynamic-ecological lake model combined with field measurements and sampling was applied to investigate the impacts of floating photovoltaic (PV) systems on hydrodynamics and water quality in a shallow tropical reservoir in Singapore. The model was validated using field data and subsequently applied to predict temperature and water quality changes for a hypothetical 42 ha placement of floating photovoltaic panels, covering about 30% of the water surface and capable of generating up to 50 MW of energy. The impact of the panel placement was studied numerically. The area of the reservoir where panels are placed experiences both light limiting and reduced wind stress conditions. The model indicated an average water temperature increase of 0.3 °C beneath the panels, consistent with the field observation from a 1 ha demonstration installation. Comparisons of model results between the uncovered and covered areas reveal greater stability of the water column (increase in Richardson number from 2.3 to 3.3) and reduction in mixing energy (from 9 × 10–7 to 7 × 10–7 W/kg) under the PV panels. Furthermore, the model predicted that chlorophyll a, total organic carbon and dissolved oxygen concentrations would decline by up to 30%, 15% and 50%, respectively, under the photovoltaic panels. Total nitrogen and total phosphorus, averaged over the water column, increased by 10% and 30%, respectively, under the panels. Distant from the floating solar panels, temperature, stability and water quality were unaffected.

Radiation and energy budget dynamics associated with a floating photovoltaic system

Shortwave radiation, longwave radiation, photovoltaic (PV) panel, air and near-surface water temperature data were measured for a floating PV system installed in a shallow tropical reservoir. Similar air and water temperature measurements were conducted in open water (ambient condition) for comparison. The data indicate that shortwave radiation is reduced significantly under the PV panels while the longwave radiation increased, and in fact became higher than the shortwave radiation as compared to open water conditions. The air temperature and the water temperature under the PV panels are higher than in open water. A numerical model was developed to predict the PV panel temperature, air and water temperatures beneath the panels and to investigate the heat balance at the reservoir surface, beneath the panels. The modelled air and PV panel temperatures were in good agreement with the field data. The modelled surface water temperature also replicated field measurements showing an increase of about 0.5 °C as compared to the open water temperature. Heat budget analysis showed that the thermal dynamics under the PV panels is mainly controlled by the longwave radiation from the PV panels and reduction in latent heat flux. The altered flux conditions beneath the panels result in a higher equilibrium temperature near the water surface, compared to open water conditions.

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.

Effects of the manipulation of submerged macrophytes, large zooplankton, and nutrients on a cyanobacterial bloom: A mesocosm study in a tropical shallow reservoir

Biomanipulation is an efficient tool to control eutrophication and cyanobacterial blooms in temperate lakes. However, the effects of this technique are still unclear for tropical ecosystems. Herein, we evaluated the effects of the biomanipulation on cyanobacterial biomass in a tropical shallow reservoir in Northeast Brazil. A mesocosm experiment was conducted in Tapacurá reservoir (Pernambuco) with eight treatments, in which we factorially manipulated the presence of submerged macrophytes (Ceratophyllum demersum), large herbivorous zooplankton (Sarsilatona serricauda), and nutrients (0.4 mg L−1 of nitrogen and 0.5 mg L−1 of phosphorus). On the first, fifth, and tenth days, we analyzed the total biomass of cyanobacteria, and the morphotypes coccoid, heterocyted filamentous, and non-heterocyted filamentous cyanobacteria; these components were compared through a three-way ANOVA. The bloom was composed mainly of five Microcystis morphospecies (coccoids) and Raphidiopsis raciborskii (heterocyted filaments). On the fifth day of the experiment, the combined addition of macrophytes and zooplankton was more efficient at controlling cyanobacterial biomass. On the tenth day, all macrophyte treatments showed significant cyanobacterial biomass reduction, decreasing up to 84.8%. On the other hand, nutrients and zooplankton, both isolated and combined, had no significant effect. Macrophytes also reduced the biomass of coccoids, heterocyted filaments, and non-heterocyted filaments when analyzed separately on the tenth day. Ceratophyllum demersum was more efficient at controlling the bloom than the addition of large herbivorous zooplankton, which could be related to allelopathy since cyanobacterial biomass was also reduced when nutrients were added. The addition of submerged macrophytes with allelopathic potential, associated with the increase of large herbivorous zooplankton, proved to be an efficient technique for controlling tropical cyanobacterial blooms.

The overriding role of hydrological factors on zooplankton community: evidence from a shallow tropical reservoir (Koka, Ethiopia).

Due to changes in global climate and local hydrological variability, land-water interactions are considered the prevailing processes underpinning aquatic ecology. Periodic meteorological conditions could have significant effect upon freshwater plankton communities by modifying the relative influences of biotic and abiotic structuring factors. However, the influence of unusual meteorological events, such as the El-Niño Southern Oscillation cycles, and advection on zooplankton communities of tropical shallow lakes and reservoirs are not fully understood. The present study, therefore, aimed to explore the relationship between hydrological factors and zooplankton community structure in Koka Reservoir, Ethiopia. Field measurements and collection of water samples and zooplankton were performed at monthly intervals from January to August 2016 at three sampling sites along a stretch of the reservoir from the river mouth to the center and the outlet (dam). The results showed post-El-Niño hydrological events (i.e., elevated riverine runoff and higher levels of turbidity) and associated advective losses can disrupt zooplankton community structure at the river mouth site, particularly during the rainy period. The results suggest that integrated watershed management activities are important aquatic resource management options in small- and medium-sized lakes and reservoirs.

Epipelon, phytoplankton and zooplankton responses to the experimental oligotrophication in a eutrophic shallow reservoir

Epipelon can contribute to the maintenance of shallow lake oligotrophication. Herein, we simulated oligotrophication by diluting eutrophic water and evaluated epipelon biomass and structure and potential relationships with phytoplankton and zooplankton communities. Dilutions of 25–75% negatively impacted phytoplankton biomass and zooplankton diversity and increased Rotifera density. Additionally, the 25% dilution increased Copepoda density, but had no effect on Cladocera. On both experimental days, epipelon chlorophyll-a and algal density responded to oligotrophication, but the algal biomass response was less pronounced after 14 days. Ceratium furcoides was dominant in the phytoplankton, while diatom species were dominant in the epipelon. We observed that experimental oligotrophication can influence both the biomass and taxonomic structure of the algal and zooplankton communities. Overall, we concluded that experimental oligotrophication negatively impacted the phytoplankton biomass and favored the development of the phototrophic epipelon; however, a large reduction in eutrophication (>50%) is required for a significant algal response in the benthic environment of a shallow tropical reservoir.

Partitioning the influence of hydrodynamics-induced physical variables and nutrients on phytoplankton assemblages in a shallow tropical reservoir (Koka, Ethiopia)

Ecological processes, population dynamics and species interactions in shallow lakes and reservoirs are affected by seasonal and inter-annual fluctuations in rainfall and runoff. The present study aimed to explore the relationship between riverine runoff and phytoplankton community structure in Koka Reservoir, Ethiopia. Onsite measurements and collection of water samples and phytoplankton were performed at monthly intervals from January to August 2016 at three sampling sites along a stretch of the reservoir running from the river mouth to center and the outlet (dam). The results showed the decline in phytoplankton biomass at the river mouth site. The decline was particularly noticeable during the period of high rainfall and runoff compared to that of the low water period. This was associated with the hydrodynamics-induced high turbidity and reduced euphotic depth. Our results implied that phytoplankton community structure was strongly influenced by flood pulse. The results suggest that river flow and watershed management have the potential to be used more widely as an aquatic resources management option in small and medium-sized lakes and reservoirs.

Relationship between epipelon, epiphyton and phytoplankton in two limnological phases in a shallow tropical reservoir with high Nymphaea coverage

Macrophytes and phytoplankton are recognized as having roles in determining alternative stable states in shallow lakes and reservoirs, while the role of periphyton has been poorly investigated. Temporal and spatial variation of phytoplankton, epipelon and epiphyton was examined in a shallow reservoir with high abundance of aquatic macrophytes. The relationships between algae communities and abiotic factors, macrophyte coverage and zooplankton density were also analyzed. Monthly sampling was performed in three zones of the depth gradient of the reservoir. Two phases of algal dominance were found: a phytoplankton phase and epipelon phase. The phase of phytoplankton dominance was characterized by high macrophyte coverage. Rotifera was the dominant zooplankton group in all the zones. Flagellate algae were dominant in phytoplankton, epipelon and epiphyton. Macrophyte coverage was found to be a predictor for algal biomass. Changes in biomass and species composition were associated with macrophyte cover variation, mainly the Nymphaea. In addition to the abiotic factors, the macrophyte coverage was a determining factor for changes to the algal community, contributing to the alternation between dominance phases of phytoplankton and epipelon. The macrophyte–phytoplankton–periphyton relationship needs to be further known in shallow reservoirs, especially the role of epipelon as an alternate stable state.

Environmental predictors of algal community structure of plankton, epipelon and epiphyton in a shallow tropical reservoir

Structural characteristics of algal communities can be used to access environmental conditions, but there is a great need to identify the drivers of change in all habitats. This study evaluated the spatial and temporal changes in the phytoplankton, epipelon and epiphyton structures in a shallow reservoir. We investigated the determining factors of the structural variability and spatial differences in the species composition and algal density in the three habitats. Bimonthly samplings were carried out for determination of the limnological variables and algal communities. The rainy season was characterized by high nutrient availability and macrophyte coverage, and the communities were dominated by flagellate algae, as Chromulina elegans Doflein. The highest modification rate was found in the phytoplankton structure, followed by epiphyton and epipelon. Despite the species co-occurrence among phytoplankton, epipelon and epiphyton, the descriptor species presented different representativeness in communities. Planktonic and epiphytic algae were more associated with temporal variation in nutrient availability, while depth was more important for epipelic algae structuring. We conclude that the algal community in the plankton, epipelon and epiphyton was structured by different environmental factors, but descriptor species co-occurrence suggested an interrelationship between communities in this shallow reservoir with high abundance of macrophytes.

Circulation patterns in a shallow tropical reservoir: Observations and modeling

The diurnal circulation pattern is deduced in Kranji Reservoir, a shallow, elongated tropical reservoir in Singapore via field observations and results from the 3-D Estuary, Lake, and Coastal Ocean Model (ELCOM) model for the month of July 2012 which is during Singapore’s Southwest Monsoon season. Detailed comparisons of the modeled temperature and velocity fields with field measurements during a dry period of July 21–26 2012 without rainfall or inflow events are presented in terms of point comparisons, longitudinal profiles and cross-reservoir transverse velocity profile, thus providing a good representation of the flow field. Both observation and modeling show that the diurnal circulation pattern is driven by wind and by temperature gradients due to upwelling which depend on the time of the day. There is a daytime circulation pattern characterized by one large loop along the main channel, and a nighttime circulation characterized by two loops: one large loop between the reservoir dam and a location K1 (2500 m upstream from the dam where inflow tributary flows merge), and one small loop between K1 and the tributaries. These circulation patterns are consistent with the observed horizontal distribution of chlorophyll a during the Southwest Monsoon months over years 2008–2012. High chlorophyll a concentration occurs near the dam as expected due to downwelling within the large circulation loop and also close to the tributaries due to the nutrient from the catchments being trapped within the smaller loop. These results demonstrate the contributing effect of hydrodynamic flow on the biomass distribution that can occur in shallow tropical systems and which affects the diurnal and seasonal variation of biomass for such systems.

Dissolved organic N in shallow tropical lakes and reservoirs: Contribution to total dissolved N and relationships with eutrophication

AbstractDissolved organic nitrogen (DON) plays important biogeochemical and ecological roles in aquatic systems. However, little is known about its importance in small tropical lakes and reservoirs. We hypothesized that (a) DON is higher in these systems than dissolved inorganic N (DIN), and that (b) relative contributions of DON and DIN to the total dissolved nitrogen (TDN) pool decrease and increase, respectively, with trophic status. To test these hypotheses, we measured DON and DIN in six lakes and two reservoirs at the Atlantic forest‐Cerrado savanna transition in Southeast Brazil, in the rainy and the dry season. With one exception in each season, all oligo‐ and mesotrophic systems had DON:DIN ratios >1. DON:DIN ratios were negatively correlated with total phosphorus (TP). This pattern was due to high DIN, mainly ammonium, in eutrophic and hypertrophic systems. DON:DIN ratios <1 occurred at TP higher than 103 and 104 µg L−1 in the rainy and dry season, respectively. We found a general dominance of DON in near‐natural lentic systems at the Atlantic forest‐Cerrado savanna transition, which was more pronounced than that reported for other regions. Human alterations to the TDN pool may affect biological communities and ecosystem functioning of these systems.

Epipelon responses to N and P enrichment and the relationships with phytoplankton and zooplankton in a mesotrophic reservoir

The phototrophic epipelon has been suggested to play an important role in ecosystems, especially those with shallow depths; however, only a few studies have investigated this function. Nutrient availability has been shown to be a determining factor for autotrophic interactions and can potentially interfere with the food web, as eutrophication. Thus, we evaluated the responses of epipelon, phytoplankton and zooplankton to combined and isolated N and P addition, during the enrichment period (14 days) and after 12 days with no enrichment. It was hypothesized that P addition (the limiting nutrient) should decrease the photosynthetic potential of the epipelon, due to the rapid increase in phytoplankton and zooplankton biomass, which can strongly attenuate light, and that the opposite effect would be observed after a period with no enrichment. We developed an in situ experiment with combined and isolated N and P enrichment at open-bottom mesocosms. The addition of P, individually and combined, augmented phytoplankton chlorophyll-a concentrations during the enrichment period, while zooplankton density only responded positively after day 14. After 12 days with no enrichment, the phytoplankton chlorophyll-a and zooplankton density decreased. While P enrichment had no significant effect on epipelon chlorophyll-a, there was a significant increase in the photosynthetic potential detected 12 days after the enrichment was stopped. In conclusion, the present study demonstrated that P enrichment reduces the photosynthetic potential of epipelon, and that variations in nutrient availability can modulate relationships among phytoplankton, zooplankton and epipelon. Drastic changes in the growth and development of the phototrophic epipelon, due to the input of nutrients, could directly impact the functioning of shallow tropical lakes and reservoirs.

Vertical mixing in a shallow tropical reservoir

This paper presents observations of diurnal cycles of stratification and vertical mixing in Kranji Reservoir, a shallow tropical reservoir with an average depth of 6.7 m located in the northwest corner of Singapore, via field measurements, focusing on a series of three 24-h self-contained autonomous microprofiler (SCAMP) measurements. This data, representing one of the most complete data sets, shows vertical mixing parameters for a tropical shallow reservoir over a diurnal cycle. Responding to diurnal cycles, the observations indicate that the thermal and flow structures are delineated by two distinct thermoclines: a three-layer structure during the daytime and a two-layer structure during the night-time when the two thermoclines merged into one. The daytime structure consisted of a thin surface mixed layer (SML) above the diurnal thermocline, an intermediate hypolimnion layer with the two thermoclines as its boundaries, and an underflow layer below the secondary thermocline. This underflow is shown to primarily arise from a horizontal temperature gradient generated by the daytime wind and stratification, and maintained by night-time differential cooling. The nocturnal structure is comprised of a SML deepened by penetrative cooling and the underflow layer. Analysis of relevant dimensionless numbers, the turbulent kinetic energy (TKE) budget, and FrT–ReT turbulent phase diagram provide a consistent picture of the different mixing mechanisms within each layer. This short time scale variability of vertical mixing as observed in Kranji Reservoir would be a factor in favouring primary production for such shallow tropical systems.

The influence of El Niño-induced drought on cyanobacterial community structure in a shallow tropical reservoir (Koka Reservoir, Ethiopia)

Koka Reservoir in Ethiopia has been severely impacted by water quality deterioration associated with harmful algal blooms. As a large proportion of the annual nutrient budget of the reservoir is believed to be of riverine origin, nutrient availability is presumably largely influenced by rainfall pattern and hydrological cycles, which are related to changes in climatic conditions such as El Nino-induced drought. The effect of El Nino-induced drought, which occurred in 2015, on the cyanobacterial community structure of Koka Reservoir was, therefore, investigated from May 28, 2015 to April 28 2016. The drought caused the failure of the main rainy season, which expectedly caused reduction in the external input of nutrients and changes in other limnological conditions of the reservoir. These changes, particularly nitrogen limitation, triggered the unusual dominance of the diazotrophic cyanobacterial genus Cylindrospermopsis over the previously persistently dominant nondiazotrophic genus, Microcystis, in the reservoir.

Relationship among carnivorous macrophyte Utricularia foliosa L. and species composition and life forms of periphytic algae community

Abstract Aim Present study evaluated the life forms and taxonomic structure of the periphytic algae community on Utricularia foliosa L. (modified leaf and stem) and artificial substrate during the four seasons in a tropical shallow reservoir. Methods We evaluated the periphyton on natural and artificial substrate in order to evaluate the influence of substrate type on the taxonomic structure of algal community. Monospecific stands of U. foliosa were selected. Water and periphyton sampling were performed within U. foliosa stands in the autumn (April/2010), winter (July/2010), spring (November/2010) and summer (February/2011). Nylon thread was used as the artificial substrate. The community structure was evaluated through life forms, species richness, diversity and species composition. Results Species diversity was significantly different only among seasons. The life forms and species richness were different between substrate types and seasons. Entangled filamentous algae had higher biovolume in the periphyton on artificial substrate and unicellular flagellated algae had higher biovolume on natural substrate. Species composition changed among the seasons and species descriptors differed among substrates types. Species-level taxonomic classification responded clearly to the substrate type. Conclusions We concluded that the taxonomic structure and life forms of periphytic algae on artificial substrate poorly represented the natural periphyton on U. foliosa. The type of substrate strongly influenced the periphyton–Utricularia relationship.

Body Length Determines the Diet and Niche Specialization of Non-Biting Midge Predator (Tanypodinae) Larvae in Shallow Reservoirs.

The functional traits of species respond to environmental gradient changes, which, in turn, are responsible for the niche specialization of species. We analyzed the niche specialization of several Tanypodinae taxa (predatory non-biting midge, 4th instar, n = 693) along the depth zones of the water in six shallow tropical reservoirs. We measured the body length and diet composition of seven Tanypodinae larvae genus. Community-weighted mean (CWM) traits index was utilized to calculate the niche distribution of body length and diet composition. We analyzed the niche distribution of predator larvae, through a simple linear analysis of CWM index and the depth of the water, and by establishing correlations between body length and diet composition. In our study, it was found that the consumption of oligochaete (b = 0.30, SE ± 0.04, t = 7.02, p = 0.0001, R2 = 0.45) and the body length (b = 0.64, SE ± 0.11, t = 5.44, p = 0.0001, R2 = 0.33) increased in deeper zones. We observed a strong and positive relationship between oligochaete consumption and a longer body (r = 0.91, p = 0.0001). We inferred that changes in habitat characteristics, from littoral to deeper zones of the reservoirs, are expected to have influenced the selection of larvae traits predators. We concluded that body length determines the diet consumption and accurately reflects the niche distribution of Tanypodinae assemblages. The functional trait approach proved to be an efficient tool for the analysis of the ecological processes that determine the structure of a non-biting midge predator assemblage.

Phytoplankton species interactions and invasion by Ceratium furcoides are influenced by extreme drought and water-hyacinth removal in a shallow tropical reservoir

This study explored the interactions of phytoplankton species during the invasion of Ceratium furcoides and the environmental variables that contributed to its establishment and ecological success in a shallow eutrophic reservoir (Garcas Reservoir, southeast Brazil), which has been monitored monthly for 20 years (1997–2017). The Ceratium furcoides invasion in September 2014 was preceded by disturbance events (macrophyte removal and a historical drought period), which disrupted the dominance of cyanobacteria by modifying resource availability (high water transparency and soluble reactive phosphorus concentrations) and recruiting other species. Ceratium blooms at the water surface were preceded by high abundance near the bottom, suggesting the importance of the propagule bank. However, the pattern of Ceratium-Microcystis coexistence that is usually recorded in temperate lakes was not observed. Instead, Ceratium replaced Cylindrospermopsis raciborskii in mixing periods with high light and nitrogen availabilities, significantly influencing the abundance of Trachelomonas spp. Flagellated forms became dominant in the Garcas Reservoir, due to the higher water transparency and relatively lower water-column stability, and alternative states between Ceratium-Trachelomonas in mixing periods and Microcystis-Cryptomonas in stratified periods have been repeated. Since then, cyanobacterial dominance ceased, and the “skillful” Ceratium apparently has come to stay, influencing interactions among phytoplankton species.

Associations between epiphyton species composition and macrophyte diversity in a shallow tropical reservoir

Associations between epiphyton species composition and macrophyte diversity in a shallow tropical reservoir