Fish and fisheries of large and medium-sized reservoirs in Vietnam

The study was undertaken in view of the importance of reservoir fisheries for Vietnam, and to fill gaps in the current knowledge in order to introduce affective management measures to optimise the fish yields from the reservoirs. Eight large and medium sized reservoirs , representing a cross section of reservoirs in Vietnam in the different climatic zones were studied.

Observations on metal concentrations in commercial landings of two species of tilapia (Oreochromis mossambicus and Oreochromis niloticus) from reservoirs in six river basins in Sri Lanka

Samples of the muscle of two species of tilapia (Oreochromis mossambicus and O. niloticus; 17-20 cm length) were obtained from at least one reservoir in each of the six river basins (Aruvi Aru, Kala Oya, Kirindi Oya, Ma Oya, Mahaweli, and Walawe Ganga catchments) in Sri Lanka. The metals Ca, Cu, Fe, K, Mg, Mn, Na, and Zn were consistently detected in the muscle tissue. Overall, there were few differences in the concentration of metals between the two species of fish, although there were also some statistically significant differences (p < 0.05) in the concentrations of some metals in fish obtained from some of the reservoirs. Aruvi Aru stands out as a river basin in which the two fish species have significantly lower concentration of metals when compared to other river basins. The concentration of the metals studied were below WHO and FSANZ guideline values for fish, suggesting that the consumption of the metals found in tilapia from these reservoirs poses little risk to human health.

Variations, trends and patterns of fish landings in large tropical reservoirs

Temporal variations of fish yields in four major reservoirs in Thailand (Ubolratana; Sirindhorn; Srinakarin; Vajiralongkorn) were investigated with the use of long-term fish landing data (≥20years). The long-term variations in fish yield, measured as the coefficient of variation of yearly yield, ranged mostly between 50% and 100%. For short-term variations, the means of the relative variation (85%) were larger than the absolute variation (63%). This finding indicates that short-term variations were inversely related to fish yield and that a higher uncertainty occurs when fish catches are low. The stocked exotic species exhibited higher variations than the indigenous species. The trend analyses indicated some species had sharply declined fish landings, while some species were quite stable (i.e. reservoir-adapted species). Stocked species tended to increase in relatively shallow reservoirs, compared to the deep reservoir. Fish landing data for each reservoir were patternized, using the self-organizing map, indicating temporal trends of chronological order. The differences among clusters in each reservoir were with respect to the weight of each species in the fish landings in each year, and temporal changes in species composition in the reservoirs, which would primarily be attributed to the environmental changes followed by anthropogenic pressures. The mean trophic level (τ) fluctuated, resulting from changes in species composition and weight of fish landing, as well as fish stocking programmes.

Optimal sensor placement and measurement of wind for water quality studies in urban reservoirs

We collaborate with environmental scientists to study the hydrodynamics and water quality in an urban district, where the surface wind distribution is an essential input but undergoes high spatial and temporal variations due to the complex urban landform created by surrounding buildings. In this work, we study an optimal sensor placement scheme to measure the wind distribution over a large urban reservoir with a limited number of wind sensors. Unlike existing sensor placement solutions that assume Gaussian process of target phenomena, this study measures the wind which inherently exhibits strong non-Gaussian yearly distribution. By leveraging the local monsoon characteristics of wind, we segment a year into different monsoon seasons which follow a unique distribution respectively. We also use computational fluid dynamics to learn the spatial correlation of wind in the presence of surrounding buildings. The output of sensor placement is a set of the most informative locations to deploy the wind sensors, based on the readings of which we can accurately predict the wind over the entire reservoir surface in real time. 10 wind sensors are finally deployed around or on the water surface of an urban reservoir. The in-field measurement results of more than 3 months suggest that the proposed sensor placement and spatial prediction approach provides accurate wind measurement which outperforms the state-of-the-art Gaussian model based or interpolation based approaches.

Evaluation of community participation for the development of culture-based fisheries in village reservoirs of Sri Lanka

In this paper, an attempt is made to identify the socioeconomic characteristics of a community that influence the development and management of culture-based fisheries in village reservoirs of Sri Lanka. Socioeconomic data were collected from 46 agricultural farming communities associated with 47 village reservoirs in Sri Lanka. Principal component analysis indicated that scores of the first principal component were positively influenced by socioeconomic characteristics that are favorable for making collective decisions. These included leadership of the officers, age of the group, percentage of active members of the group, percentage of kinship of the group, percentage of common interest of the group, and percentage of participation of the group. The size of the group had a negative effect on the first principal component. The principal component scores of communities were positively related to willingness to pay (P < 0.001). The communities with socioeconomic characteristics favoring collective decision making were in favor of culture-based fisheries. Homogeneity of group characteristics facilitated successful development of culture-based fisheries.

Use of geographical information system and remote sensing techniques for planning culture-based fisheries in non-perennial reservoirs of Sri Lanka

 The presence of a wide areal extent of small-sized village reservoirs offers a considerable potential for the development of culture-based fisheries (CBFs) in Sri Lanka. To this end, this study uses geographical information systems (GISs) and remote sensing (RS) techniques to determine the morphometric and biological characteristics most useful for classifying non-perennial reservoirs for CBF development and for assessing the influence of catchment land-use patterns on potential CBF yields. The reservoir shorelines at full water supply level were mapped with a Global Positioning System to determine shoreline length and reservoir areal extent. The ratio of shoreline length to reservoir extent, which was reported to be a powerful predictor variable of CBF yields, could be reliably quantified using RS techniques. The areal extent of reservoirs, quantified with RS techniques (RS extent), was used to estimate the ratio of forest cover plus scrubland cover to RS extent and was found to be significantly related to the CBF yield (R2 = 0.400; P < 0.05). The results of this study indicated that morphometric characteristics and catchment land-use patterns, which might be viewed as indices of biological productivity, can be quantified using RS and GIS techniques. © 2014 Wiley Publishing Asia Pty Ltd.

Demo abstract: wind measurements for water quality studies in urban reservoirs

Water quality monitoring and prediction are critical for ensuring the sustainability of water resources which are essential for social security, especially for countries with limited land like Singapore. For example, the Singapore government identified water as a new growth sector and committed in 2006 to invest S$ 330 million over the following five years for water research and development [1]. To investigate the water quality evolution numerically, some key water quality parameters at several discrete locations in the reservoir (e.g., dissolved oxygen, chlorophyll, and temperature) and some environmental parameters (e.g., the wind distribution above water surface, air temperature and precipitation) are used as inputs to a three-dimensional hydrodynamics-ecological model, Estuary Lake and Coastal Ocean Model - Computational Aquatic Ecosystem Dynamics Model (ELCOM-CAEDYM) [2]. Based on the calculation in the model, we can obtain the distribution of water quality in the whole reservoir. We can also study the effect of different environmental parameters on the water quality evolution, and finally predict the water quality of the reservoir with a time step of 30 seconds. In this demo, we introduce our data collection system which enables water quality studies with real-time sensor data.

Sensor placement and measurement of wind for water quality studies in urban reservoirs

We study the water quality in an urban district, where the surface wind distribution is an essential input but undergoes high spatial and temporal variations due to the impact of surrounding buildings. In this work, we develop an optimal sensor placement scheme to measure the wind distribution over a large urban reservoir using a limited number of wind sensors. Unlike existing solutions that assume Gaussian process of target phenomena, this study measures the wind that inherently exhibits strong non-Gaussian yearly distribution. By leveraging the local monsoon characteristics of wind, we segment a year into different monsoon seasons that follow a unique distribution respectively. We also use computational fluid dynamics to learn the spatial correlation of wind. The output of sensor placement is a set of the most informative locations to deploy the wind sensors, based on the readings of which we can accurately predict the wind over the entire reservoir in real time. Ten wind sensors are deployed. The in-field measurement results of more than 3 months suggest that the proposed sensor placement and spatial prediction scheme provides accurate wind measurement that outperforms the state-of-the-art Gaussian model based on interpolation-based approaches.

Delaware Reservoirs’ Drought Risk Assessment: A Paleo View

The Delaware River provides half of New York City's drinking water, is a habitat for wild trout, American shad and the federally endangered dwarf wedge mussel. It has suffered four 100‐year floods in the last seven years. A drought during the 1960s stands as a warning of the potential vulnerability of the New York City area to severe water shortages if a similar drought were to recur. The water releases from three New York City dams on the Delaware River's headwaters impact not only the reliability of the city’s water supply, but also the potential impact of floods, and the quality of the aquatic habitat in the upper river. The goal of this work is to influence the Delaware River water release policies (FFMP/OST) to further benefit river habitat and fisheries without increasing New York City's drought risk, or the flood risk to down basin residents. The Delaware water release policies are constrained by the dictates of two US Supreme Court Decrees (1931 and 1954) and the need for unanimity among four states: New York, New Jersey, Pennsylvania, and Delaware ‐‐ and New York City. Coordination of their activities and the operation under the existing decrees is provided by the Delaware River Basin Commission (DRBC). Questions such as the probability of the system approaching drought state based on the current FFMP plan and the severity of the 1960s drought are addressed using long record paleo‐reconstructions of flows. For this study, we developed reconstructed total annual flows (water year) for 3 reservoir inflows using regional tree rings going back upto 1754 (a total of 246 years). The reconstructed flows are used with a simple reservoir model to quantify droughts. We observe that the 1960s drought is by far the worst drought based on 246 years of simulations (since 1754).

Migratory and Carnivorous Birds in Brazil: Reservoirs for Anaplasma and Ehrlichia Species?

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Phytoplankton structure in two contrasting cascade reservoirs (Paranapanema River, Southeast Brazil)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Heat budgets, thermal structure and dissolved oxygen in Brazilian reservoirs

A comparison of the thermal regime and oxygen distribution patterns of some Brazilian reservoirs was made. A strong latitudinal dependence of surface temperature, annual mean and annual range was found. Except for Tucurui Reservoir, a reservoir of the Equatorial zone, the lowest surface temperature of the year in the other compared reservoirs was observed from June to August while the highest extended from October to February. The decreasing trend of annual mean temperatures and thermal ranges was due to the increasing seasonal variability of insolation with the latitude. A positive relationship between the increase on thermal surface-bottom differences and the depth of water column was found for reservoirs of similar latitudes. A long thermal stratification (around four months) was evidenced in the lacustrine zone of reservoirs with a residence time higher than 40 days. Low fluctuation (<2%) of the annual variability of heat contents was observed for the Tucurui Reservoir, while in das Garcas Reservoir a manmade lake located in the frontier between tropical and temperate regions, the annual coefficient of variation attained 13%. Concerning the heat budgets, the value for the Tucurui Reservoir was two times higher than in das Garcas Reservoir. Both the morphometric and climatological factors affected the heat contents of the two compared reservoirs. In deep eutrophic reservoirs, a significant reduction on the oxygen concentrations in the hypolimnetic zone was frequently observed. In some oligotrophic stratified reservoirs, a decrease on oxygen with depth occurred when the temperature of the hypolimnion was higher than 20 degrees C and caused a biochemical oxygen demand. In das Garcas Reservoir, the actual oxygen deficits ranged from 0.40 to 1.52 mg.O-2.cm(-2) and appear to be linked to oxygen consumption after the senescence of Microcystis aeruginosa populations in the spring. But, other factors such as the allochthonous loads of organic matter also had an important role on the oxygen balance of das Garcas Reservoir.