Lakes & Reservoirs: Science, Policy and Management for Sustainable Use

Delazari‐Barroso, Alessandra; Barroso, Gilberto Fonseca; De Moraes Huszar, Vera Lúcia; De Oliveira e Azevedo, Sandra Maria Feliciano

doi: 10.1111/j.1440-1770.2009.00409.xpmid: N/A

The water‐mixing regime, light availability, nutrient limitation and trophic state were evaluated for the Duas Bocas Reservoir (DBR; Espírito Santo State, southeastern Brazil), a small (0.51 km2), shallow (zmax < 10 m) water supply reservoir located in a conservation area. Monthly water sampling was conducted for the lacustrine zone (zmax = 10 m) next to the water withdrawal tower, during one hydrological cycle (October 2002 to September 2003). Water samples were taken at four depths in this area, including subsurface, Secchi depth, euphotic/aphotic boundary and near the bottom of the lake. The variability of the reservoir’s limnological features defined two periods. Period 1, comprised of the summer months (October to April), was characterized by strong thermal stratification, nutrient limitation in the mixing layer, a metalimnetic biomass maximum and anoxia and high nutrient concentrations in the hypolimnion. Period 2, comprised of the winter months (May to September), was characterized by overturn events during which the phytoplankton population experienced light limitation. The observed water‐mixing regime was characteristic of warm monomictic system, presenting atelomixis, the incomplete vertical mixing of stratified water masses. The average total phosphorus and chlorophyll‐a concentrations suggested a meso‐eutrophic water system. The nutrient concentrations exhibited nitrogen and phosphorus limitation, suggesting that nutrients, rather than light, limit or regulate the phytoplankton biomass in the DBR for most of the year.

Adwubi, Afua; Amegashie, Bright Kofi; Agyare, Wilson Agyei; Tamene, Lulseged; Odai, Samuel Nii; Quansah, Charles; Vlek, Paul

doi: 10.1111/j.1440-1770.2009.00410.xpmid: N/A

Many small dams and dugouts have been constructed in the Upper East Region of Ghana to address the problem of regional water scarcity. The reservoirs were constructed primarily as water supplies for agricultural irrigation and livestock watering, aquaculture and domestic use. However, many of the reservoirs dry up during the dry season, affecting the livelihoods of their basin inhabitants. A major cause for the dried reservoirs is siltation, which reduces the reservoir’s storage capacities. The goal of this study is to quantify the annual siltation rate of four study reservoirs, using a bathymetric survey and reservoir soil sampling. The sediment yield and its relation to catchment area also were assessed. The results of this study indicate that the annual siltation rates are 1272, 3518, 2764 and 6135 t year−1 for Doba, Dua, Zebilla and Kumpalgogo reservoirs, respectively. Analyses of the sediment yield and catchment areas illustrated that the sediment yields decreased with increasing catchment area. All the study reservoirs have lost their dead storage capacity, which was meant to store sediment until the end of their anticipated design lives. The decreasing storage capacity because of siltation will affect the livelihoods of the local basin inhabitants, as the reservoirs will not be able to achieve all their intended purposes. The results of this study indicate that, because siltation is not the only factor threatening the benefits gained from the reservoirs, the integrated assessment of all relevant factors is required.

Gubiani, Éder A.; Gomes, Luiz C.; Agostinho, Angelo A.

doi: 10.1111/j.1440-1770.2009.00411.xpmid: N/A

Length–length and length–weight relationships was estimated for 48 fish species collected in 30 neotropical reservoirs located in the State of Paraná, Brazil. Significant relations were found for all species. The values of the parameter slope (b) in the length–weight relationship ranged from 2.49 to 3.46 for grouped sexes, and from 2.66 to 3.15 for separated sexes. Differences between sexes (indication of sexual dimorphism) were verified for 20 species. Males exhibited greater lengths than females for Astyanax janeiroensis, Bryconamericus iheringii, Geophagus brasiliensis, Glanidium ribeiroi and Hypostomus derbyi, whereas females attained greater lengths than males for the other 15 species examined in this study.

De Oliveira Naliato, Danilo A.; Nogueira, Marcos Gomes; Perbiche‐Neves, Gilmar

doi: 10.1111/j.1440-1770.2009.00414.xpmid: N/A

To address daily fluctuations in electricity demands, the quantities of water passing through the turbines of hydropower plants can vary significantly (up to fourfold) during a 24‐h cycle. This study evaluates the effects of hourly variations in water discharges on the limnological conditions observed in two below‐dam river stretches. The study reservoirs, Capivara and Taquaruçu, are the 9th and 10th reservoirs in a cascade of dams in the Paranapanema River in south‐east Brazil. The reservoirs exhibit different trophic conditions, water retention times, thermal regimes and spillway positions. Capivara Reservoir is deeper, meso‐eutrophic, with a high water retention time and hypolimnetic discharges (32 m) varying between 500 and 1400 m3 s−1. In contrast, Taquaruçu Reservoir is relatively shallow, oligo‐mesotrophic, and has a low retention time, with water discharges varying between 500 and 2000 m3 s−1. Its turbine water intake zone also is more superficial (7 m). For two periods of the year, winter and summer, profiles of limnological measurements were developed in the lacustrine (above‐dam site) zones of the reservoirs, as well as in the downstream river stretches (below‐dam site). In both cases, the sampling was carried out at 4‐h intervals over a complete nictemeral cycle. The results demonstrated that the reservoir operating regime (water discharge variations) promoted significant differences in the conditions of the river below the dams, especially for water velocity, turbidity, and nutrient and suspended solids concentrations. The reservoir physical characteristics, including depth, thermal stratification and outlet structure, are also key factors influencing the limnology and water quality at the below‐dam sampling sites. In the case of Capivara Reservoir, for example, the low dissolved oxygen concentration (<5.0 mg L−1) in its bottom water layer was transferred to the downstream river stretches during the summer. These study results demonstrated that it is important to continue such investigations as a means of verifying whether or not these high‐amplitude/low‐frequency variations could negatively affect the downstream river biota.

Rangel‐Peraza, Jesús Gabriel; De Anda, Jose; González‐Farias, Fernando; Erickson, Dana

doi: 10.1111/j.1440-1770.2009.00412.xpmid: N/A

A statistical assessment was used to assess if a tropical reservoir had reached a stable condition, permitting the use of water quality models to predict the water quality dynamics of a water system under different climatic or management scenarios. This approach was applied to Aguamilpa Reservoir in western Mexico, one of the largest tropical reservoirs in the world. Water quality data collected by the National Water Commission, and hydrological and climatic data from the Federal Electricity Commission from the period of January 2000 to December 2007 served as the data base. Time‐series analysis identified three distinct homogeneous seasonal groups: (i) warm dry season, (ii) rainy season and (iii) cold dry season. The seasonal responses of water quality parameters (temperature, electrical conductivity, total suspended solids concentration, biochemical oxygen demand and total coliforms) were demonstrated through analysis of variance of the principal components.

Nagabhatla, Nidhi; Pattnaik, C.; Sellamuttu, S. Seneratna; Narendra Prasad, S.; Wickramasuriya, R.; Finlayson, Max

doi: 10.1111/j.1440-1770.2009.00413.xpmid: N/A

This study presents a comprehensive site‐scale analysis conducted within the global wetland inventory and mapping (GWIM) project. GWIM was developed and promoted by the International Water Management Institute (IWMI) through global partnerships to investigate wetland analyses at multiple scales. The present study investigates the complexity of an inland freshwater wetland system, presenting a conceptual framework for mapping and monitoring the dynamics of Lake Kolleru (a wetland of international importance, as defined by the Ramsar Convention), utilizing a geospatial platform. Illustrating the pace of land use changes leading to the progressive elimination of the wetland ecosystem of freshwater Lake Kolleru, this study also highlights the impacts of such changes on the socio‐economic system. A comprehensive temporal analysis (1977–2007) provided a structural base to schematically analyse the dynamics of biophysical and ecological changes to the wetland by effectively using a spectrum of remote sensing data. The present status and changing trends in ecological dimensions of Lake Kolleru were illustrated, utilizing information from spatial analyses, complimented with socio‐economic assessment. Attention is drawn to the potential of utilizing earth resources systems in exploring space–time interactions in freshwater ecosystems heavily modified through aquaculture interventions. Further, the spatial derivatives are meant as reference material for local authorities and decision‐makers to rehabilitate the economic livelihood activities to the social community dependent on the lake ecosystem. The disseminated message emphasizes the applicability of geospatial tools to enhance the efficacy of the decision‐making process by facilitating regular monitoring of ecosystem dynamics and providing updated information on wetland patterns and uses.

Nyikahadzoi, Kefasi

doi: 10.1111/j.1440-1770.2009.00415.xpmid: N/A

This study focused on the Kapenta fishing industry at Lake Kariba to illustrate that variations in economic situation, and in biophysical attributes of the resource users, make it difficult to institute collective conformity with fishery management regulations. The paper discusses how the Kapenta fishing companies in the Lake Kariba region have differing preferences regarding fishery resource management, and assign different priorities to various objectives of the resource management. The differences in personal objectives regarding management of the fishery resources, and the differences in the degree of control and access over the fishery, led to situations where users had varying incentive structures. The differences in incentive structures lead to fishery management regulations based on the average characteristics of users and the biophysical environment, fuelling conflicts between fishery resource managers and users. The variations of micro‐biophysical attributes of the resource, combined with the behaviour of the resource users, make it difficult to bring resource users together for developing and initiating collective action.

Lurling, Miquel; Tolman, Yora; Euwe, Marieke

doi: 10.1111/j.1440-1770.2009.00416.xpmid: N/A

This study examined the effects of ‘Effective Microorganisms (EM)’ on the growth of cyanobacteria, and their ability to terminate cyanobacterial blooms. The EM was tested in the form of ‘mudballs’ or ‘Bokashi‐balls’, and as a suspension (EM‐A) in laboratory experiments. No growth inhibition was observed for a laboratory strain of Microcystis aeruginosa and for M. aeruginosa from the field at the recommended dosage of 1 EM‐mudball per square‐metre (≈0.1–0.3 g L−1). Cyanobacteria were inhibited only at very high concentrations (5–10 g L−1 cyanobacteria), and a bloom was reduced, being attributed to the high amount of clay and high water turbidity. For these high dosage treatments, the dissolved oxygen concentration dropped initially to very low levels, with longer incubation indicating that nutrients were released from the material. The EM‐A suspension appeared ineffective in hampering cyanobacterial growths at recommended usage concentrations. EM‐mudballs released phosphate (160 μg P g−1) and metals (aluminium, copper, traces of lead and lanthanum). The results of this study did not support the hypothesis that EM are effective in preventing cyanobacterial proliferation or in terminating blooms, thereby suggesting lake restoration by ‘Effective Microorganisms’ is not a convincing eutrophication control option.