Impact of damming the Mogi-Guaçu River (São Paulo State, Brazil) on reservoir limnological variables

This study examined the effects of the damming of the Mogi‐Guaçu River (São Paulo State, Brazil) on the surface current velocity, water temperature, Secchi disc transparency, turbidity, colour, conductivity, pH and concentrations of nutrients and pigments. Surface‐water samples were taken before, during and after the reservoir was filled. Three sampling sites were established, one in the upper reach of the reservoir, one in the central area of the reservoir and one downstream from the dam. An additional sampling site was established on the Peixe River, the major tributary of the Mogi‐Guaçu in the study area. After filling of the reservoir, the surface current velocity tended to decrease, excepting downstream of the dam. The pH, and the Kjeldahl nitrogen, ammonia and chlorophyll‐a concentrations, tended to increase. The nitrite concentrations increased mainly in the upper reach and central area of the reservoir. The Secchi disc transparency and colour tended to decrease. A decreasing trend in dissolved oxygen concentration was observed mainly at the central area of reservoir. The conductivity tended to decrease, later returning to levels observed prior to reservoir filling. The nitrate, total phosphorus and orthophosphate concentrations exhibited an increasing trend after reservoir filling, followed by a decreasing concentration, reaching lower levels than those found prior to reservoir filling. High phaeophytin concentrations were measured for the filling phase. The observed water quality changes for Mogi‐Guaçu Reservoir generally were not as extreme as those observed for other tropical reservoirs. This trend was related to the operation of the reservoir. As Mogi‐Guaçu Reservoir is a run‐of‐the‐river reservoir with a short water retention time, the flooded area is not extensive and the retention of material and sedimentation upstream from the dam is not remarkable. These facts explain the small water quality changes observed for most of the variables after reservoir filling. The water quality decreased at the in‐lake site in the central part of the reservoir, attaining a hypereutrophic condition. This fact was related to the ageing of the reservoir and to cultural eutrophication.     

Impact of climate on the vertical water column structure of Lajes Reservoir (Brazil): A tropical reservoir case

Ribeirão das Lajes Reservoir was constructed in 1905 for energy production, and is now used as a domestic water supply for about 1 million people. The reservoir was considered as being general monomictic, exhibiting water column mixing in the winter. Water column mixing, however, did not occur in the deepest parts of the reservoir in the warm year of 2005. Nevertheless, the long stratification period leads to an anoxic, nutrient-rich hypolimnion that exhibits poor water quality in the deepest part. The meteorological events of cold front passages in the reservoir region were not able to disrupt the water column stability, or affect its water quality for domestic supply. Maintenance of thermal stratification over most of the year was likely because of the low influence of wind, long water retention time, and the input of cold water from the tributary and from rain directly draining into the metalimnion.     

Turbid flow through a tropical reservoir (Lake Dalrymple, Queensland, Australia): Responses to a summer storm event

The first flood event following a prolonged dry period is described for an impoundment, Lake Dalrymple, in tropical north‐eastern Australia. The event, in January 1996, generated substantial flow in the two main inflow sources: the Burdekin River from the north and the Suttor River from the south. Flow through the Burdekin River peaked early and then subsided to a lower level, but flow through the Suttor River persisted at a moderate level for over 15 days after the initial inflow. An extensive water quality survey was conducted on 16 January 1996 (seven days after the initial dam overflow) to determine the nature of the inflows originating from the two major subcatchments feeding the reservoir as they entered and passed through the impoundment. The inflow comprising waters of high turbidity and low conductivity occupied the mid‐column region along the two major inflow channels through the impoundment to the dam wall. The suspended particulate material in the form of silt and clay sized particles remained in suspension as the flow passed through the reservoir, due in part to the low ionic strength of the inflow and the relative densities of the inflowing and receiving waters. For both river sources, more than 50% of the total nitrogen and almost all of the total phosphorus were bound to the suspended particulate matter. Much of this was exported in the flow over the spillway. The highly turbid nature of the inflow resulted in strong attenuation of down‐welling photosynthetically active radiation (up to maximum attenuation values of 12.24 m^–1 in the reservoir where the euphotic depth was only 0.38 m). The irradiance reflectance and the scattering coefficient were considerably higher than any reported for other Australian inland waters. Concentrations of viable chlorophyll a in the surface waters were very low (maximum value 3.4 μg L^–1) because of the highly turbid conditions and extensive dilution by the inflow. The results of this study provide an example of the significant impact a large inflow of turbid, low conductance water can have on a large reservoir in the arid tropics following a prolonged dry period. During inflow events such as the one described in this paper, the reservoir becomes riverine in nature, and large amounts of suspended particulate matter and associated nutrients are transported through the reservoir.     

Adaptation of the Reservoir Fish Assemblage Index (RFAI) for assessing the Barra Bonita Reservoir (São Paulo,Brazil)

In order to evaluate the environmental condition of the Barra Bonita Reservoir, we adapted the Index of Biotic Integrity (IBI). We chose 24 sampling sites in which three types of habitats were sampled: the mouths of tributaries, the central reservoir and the lateral reservoir. Fish were caught in two seasons (dry and rainy) using 10 gillnet gangs, with meshes ranging from 3 to 12 cm between opposite knots, and funnel traps. Abiotic and biotic variables were measured. Due to the artificial nature of the reservoir, the term biotic integrity was considered inappropriate and the term RFAI (Reservoir Fish Assemblage Index) was adopted. Twelve metrics from sixteen possibles were selected using the Pearson correlation coefficient. The reference conditions were set up based on the criteria of the best condition observed. For each metric, a score of 1, 3 or 5 was assigned as it strongly departs (1), slightly departs (3) or approaches (5) the reference condition. The index value is the sum of the metrics partial scores and ranges from 12 to 60. To evaluate the importance of the unit of measurement of the metric, the index was calculated in fish number (RFAI_N) and in weight (RFAI_W). The correlation between RFAI_N and RFAI_W was very high ( r = 0.90, n = 46) indicating that the unit of measurement does not influence the final result of the index. Most of the sampling sites were classified in the ‘reasonable’ RFAI category. Only the central sites were classified as ‘poor’. To validate the RFAI, another index, the Habitat Quality Index (HQI), was built starting from the physiochemical and habitat variables collected. The correlation of the RFAI with the HQI was highly significant (RFAI_N, r = 0.37; RFAI_W, r = 0.47; n = 46), indicating that they respond in the same way to environmental degradation. The HQI metrics which most affect RFAI were depth, surrounding landscape and macrophyte presence/absence. Copyright © 2007 John Wiley & Sons, Ltd.     

Discharge pulses of hydroelectric dams and their effects in the downstream limnological conditions: a case study in a large tropical river (SE Brazil)

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.     

A preliminary hydrosedimentary view of a highly turbid,tropical, manmade lake: Cointzio Reservoir (Michoacán,Mexico)

This study represents the first limnological assessment of Cointzio Reservoir (Michoacán, Mexico). A full three‐dimensional scan of temperature, conductivity and turbidity was done for the reservoir during two field surveys at the end of the 2005 rainy season (December 2005), and before the beginning of the next season (May 2006). These parameters also were measured continuously during the 2006 rainy season. Analysis of data within the context of local climate trends at a multidecadal scale indicates the reservoir can amplify seasonal features because of its morphometric properties. Between June to December, the reservoir behaved as a fluvial system, exhibiting a rapid, efficient mixing of the water column. Between January to May, the reservoir developed substantial stratification, and exhibited typical lacustrine characteristics. These alternate phases of fluvial and lacustrine regimes, associated with a high water turbidity throughout the year (Secchi depth of ≈0.2 m) contributes to stress on this aquatic ecosystem.     

The role of the hyporheic zone in the nitrogen dynamics of a semi‐arid gravel bed stream located downstream of a heavily polluted reservoir (Tafna wadi,Algeria)

Nitrogen retention was measured along the Tafna wadi downstream of a heavily polluted reservoir in North‐West Algeria to understand the role of the hyporheic zone (HZ) in nitrogen dynamics. Nutrient concentrations were measured monthly for 2 years within the bed sediments of a 300 m reach located 20 km downstream from the dam. Due to strong hydrological fluctuations hyporheic water was analysed during natural low and high water (HW) periods, and during water reservoir releases. Nutrient concentrations in surface water (SW) increased during water releases and in the HZ during the low water (LW) periods. Surface/hyporheic water interactions were characterized by determining the vertical hydraulic gradient (VHG) and the chemical signature of the ground water (GW). The latter was obtained from regional GW monitoring. Hyporheic chemistry was strongly influenced by patterns of surface flow. Hyporheic and SWs had similar chloride concentrations during high flow when they were significantly lower than those of the regional GW. GW was generally richer in nitrates and nitrites, but was lower in ammonium concentrations than interstitial and river waters. Nitrates decreased significantly from upstream to downstream within the HZ throughout the hydrological period even though temporal fluctuations were high. Ammonium concentrations in interstitial water (IW) were significantly higher than in SW and generally increased from upstream to downstream. This study demonstrates the importance of the HZ in altering the dissolved inorganic nitrogen composition and concentrations of heavily polluted arid streams. The study is of interest because it documents a large ‘natural experiment’ that being the effect of periodic water release from a reservoir with serious water quality problems on the water quality dynamics (particularly nitrogen) of subsurface and SWs downstream. Copyright © 2008 John Wiley & Sons, Ltd.     

Water quality assessment of a recently refilled reservoir: The case of Bütgenbach Reservoir, Belgium

Bütgenbach Reservoir is situated in the High Ardennes plateau in eastern Belgium (50°25′N; 6°13′E). It is used principally for flood control and for production of hydroelectric energy. It has been subjected to a previous series of studies because of its eutrophication problems and their impacts on the local economy. Bütgenbach Reservoir was emptied during spring 2004 for dam restoration, being refilled in mid‐September of the same year. Selected physicochemical and biological parameters (temperature, dissolved oxygen, pH, inorganic and organic nutrients, chlorophyll‐a) were measured fortnightly during the lake's productive season (mid‐April to mid‐October 2005) at three sampling sites throughout the water column. The water quality conditions after refilling of the lake were compared to previous studies accomplished at the same sampling sites (prior to emptying the lake). The actual trophic status was mesotrophic to eutrophic, based on the combination of total phosphorous and chlorophyll‐a concentrations, as well as water transparency. Bütgenbach Reservoir generally exhibits good water quality, based on the French water quality system SEQ‐eau. A longitudinal decrease in water quality was observed from upstream to downstream, because mainly of the differences in lake bottom morphology and water residence time, and their impacts on nutrient distribution in the lake.     

Estimation of bacterial production through the coupling of (methyl 3H) Thymidine incorporation and several parameters over a Microcystis aeruginosa bloom in a hypereutrophic reservoir

The coupling of the changes in bacterial quantitative and metabolic aspects during Microcystis aeruginosa bloom conditions together with several environmental parameters was studied in the hypereutrophic Villerest reservoir, France. Bacterial abundance varied from 5.20 to 21.28 × 10⁶ bacteria-mL^?1, while bacterial biomass ranged between 75 and 507 μg C mL^?1. These results confirmed the highly eutrophic status of the Villerest reservoir. The relative quantitative importance of attached bacteria increased as Microcystis proliferated. Methyl-³H incorporation and D-(U-¹⁴C) glucose uptake varied from 8.99 to 60.57 × 10⁶ cells-mL^?1, and 0.016 to 1.587 μg CL^?1 h^?1, respectively. Correlations between several abiotic and biotic parameters showed that phytoplankton regulated bacterial growth by releasing organic carbon which is directly uptaken by heterotrophic bacteria. In the hypolimnion, the sedimentation of decaying algae represented a substantial substrate for bacterial growth.     

A multi‐tracers analysis of sources and transfers of particulate organic matter in a tropical reservoir (Petit Saut,French Guiana)

We measured the organic carbon (OC) content, the isotopic composition, the C/N ratios and the photosynthetic pigment composition of suspended matter, sediments, sediments traps and epiphytic and epilithic biofilms at the tropical Sinnamary River system (French Guiana). Our sampling included the mid‐stream reservoir lake (Petit Saut) and the estuary on the Atlantic coast. These tracers were complementary and allowed identifying different sources of particulate organic matter (POM) in the system. We found a δ¹³C–C/N signature of POM close to that of soils and litters collected in the surrounding forest, both for water column and sediment at the upstream station as well as for the sediment in a littoral zone of the reservoir, which thus indicated a terrestrial origin. Plankton communities at the centre of the reservoir were dominated by Chlorophyceae (chlorophyll a (Chl a), chlorophyll b (Chl b) and lutein) in the oxic epilimnion and by anoxygenic phototrophic bacteria, namely Chlorobiaceae (bacteriochlorophyll d (BChl d) and bacteriochlorophyll c (BChl c)) at and below the oxycline (6 m depth). In addition, this planktonic material was slightly ¹³C‐depleted due to a contribution of methanotrophic bacteria. Phytoplankton and bacterioplankton were the major source of settling material collected in the traps at all depths in the centre of the reservoir. In the traps, POM was subject to intense degradation, as revealed by C/N and isotopic data and by the presence of pheopigments. In the river downstream of the dam, Chl b, lutein, BChl c and d originating from the reservoir progressively decreased downstream as the result of mineralization. At the estuarine mouth, fucoxanthin showed the presence of diatoms and the δ¹³C‐C/N signature matched that of POM carried by the Amazonian coastal mobile mud belt. By analysing sedimentation rates in the reservoir and its outflow into the river, we were able to provide a first estimates of POM transfers in this system during the sampling period. Copyright © 2008 John Wiley & Sons, Ltd.     

An alternative approach to the operation of multinational reservoir systems: Application to the Amistad &; Falcon system (Lower Rio Grande/Río Bravo)

An optimization approach for the operation of international multi-reservoir systems is presented. The approach uses Stochastic Dynamic Programming (SDP) algorithms – both steady-state and real-time – to develop two models. In the first model, the reservoirs and flows of the system are aggregated to yield an equivalent reservoir, and the obtained operating policies are disaggregated using a non-linear optimization procedure for each reservoir and for each nation's water balance. In the second model a multi-reservoir approach is applied, disaggregating the releases for each country's water share in each reservoir. The non-linear disaggregation algorithm uses SDP-derived operating policies as boundary conditions for a local time-step optimization. Finally, the performance of the different approaches and methods is compared. These models are applied to the Amistad-Falcon International Reservoir System as part of a binational dynamic modeling effort to develop a decision support system tool for a better management of the water resources in the Lower Rio Grande Basin, currently enduring a severe drought.     

Temporal and spatial patterns based on sediment and sediment–water interface characteristics along a cascade of reservoirs (Paranapanema River, south-east Brazil)

Physical and chemical characteristics of the sediments in a cascade of eight reservoirs located in the Paranapanema River (south‐east Brazil) were analysed during two consecutive years during summer (January), autumn (April), winter (July) and spring (October) of 2000 and 2001, respectively. The granulometric texture, organic matter content and nutrient concentration (total nitrogen and phosphorus) were determined in the superficial sediment of 19 sampling stations, as well as the temperature, dissolved oxygen, pH, conductivity and redox potential in the bottom layer of the water column. Seasonal and spatial changes were observed for both years, especially for organic matter and nutrient concentrations. Three different areas could be identified along the river, which corresponded to the upper, middle and lower Paranapanema basin. The first area was characterized by an increase of nutrients and organic matter in the sediments and a decrease of temperature and dissolved oxygen in the downstream direction. The second one represented a region where fluctuations in nutrient and organic matter concentrations and a reduction in dissolved oxygen were observed. In the third area, there was an increase in nutrient and organic matter in the sediments and also an increase in temperature and dissolved oxygen towards the river mouth. The results of the principal components analysis, using water and sediments variables, showed the ordination of sampling stations by periods: wet (January–April) and dry (July–October) during 2000. This pattern was also verified during 2001, but with slight changes, probably due to the increase in the rains which would have produced certain homogenization effects along the river.     

Seasonal and spatial variation in algal growth potential and growth-limiting nutrients in a shallow endorheic lake: Lake Pátzcuaro (Mexico)

The present research focused on the functional role of the phytoplankton of an economically important endorheic tropical lake from the perspective of algal growth bioassays. The algal growth potential of the lake water was compared for littoral and pelagic sites during the wet and dry seasons. Algal growth potentials at open waters reached minimum and maximum values following the seasonal alternation of dilution (by rain) and concentration (by evaporation) respectively. Conversely, at southern littoral stations high algal growth responses related to the availability of nutrients from point contamination sites. There was no such effect at nearby offshore sites or elsewhere in the lake which suggests filtration and competitive interactions for these nutrients between phytoplankton and littoral macrophytes. Nitrogen and phosphorus both acted consistently as limiting nutrients at open waters by colimitation. Nitrogen to phosphorus ratios seemed to approach equilibrium where limitation easily shifted to one element or the other temporally and spatially.     

Spatial and temporal distribution of ichthyoplankton during an unusual period of low flow in a tributary of the São Francisco River,Brazil

Flow‐dependent fish specialists require specific conditions for reproduction, so the success and reproductive intensity of these animals are determined by the flood regime. Thus, this study investigated the spatial and temporal reproductive patterns of fish, especially migratory Prochilodus species (flow‐dependent specialists) in an unusual period of low flow in the Pará River sub‐basin, one of the main tributaries of the upper São Francisco River. For this, ichthyoplankton collections were carried out between November 2013 and February 2014. Data were analysed considering the spatial and temporal variations in density of eggs and larvae for the upper, middle, and lower portions of the Pará River sub‐basin, and correlating this to some environmental variables. The results showed that the small headwater stretch of the Pará River is one relevant spawning area for migratory fish species. However, this area is isolated by the Cajuru reservoir, which makes it uncertain the recruitment of these embryos, due to interruption of natural drift between spawning/nursery areas caused for reservoirs. Larvae of newly hatched migratory species found in tributaries of the lower Pará River sub‐basin also indicate these species use these tributaries as spawning grounds and migratory routes. The period in which the research was conducted represented the most atypical low flow, one in the last 75 years, resulting in the low variability in the environmental parameters. Although few parameters increased briefly in this low flow period influenced by greater rainfall in December, this precipitation was possibly responsible for the final gonadal maturation and spawning of migratory species.     

Sediment greenhouse gases (methane and carbon dioxide) in the Lobo-Broa Reservoir, São Paulo State, Brazil: Concentrations and diffuse emission fluxes for carbon budget considerations

Carbon gases (methane, CH₄, and carbon dioxide, CO₂) were measured for the first time in sediments of the Lobo‐Broa Reservoir, near São Carlos in São Paulo State, Brazil. It is believed these are the first measurements of this kind in any of the many reservoirs located in Brazil. Even though the Lobo‐Broa Reservoir is classified as oligotrophic, the sediment gas concentrations were exceedingly high, ranging from 0.4–3 mmol L^?1 for CH₄ and 1–9 mmol L^?1 for CO₂. Both gases exceeded their in situ gas saturation values at these shallow water depths (7 m in central basin; 11 m at dam), resulting in numerous sediment bubbles. Organic matter was highly concentrated in the reservoir sediments, averaging 25.5% loss on ignition (LOI) (dam) to 26.9% LOI (central basin) for the 0–12 cm depth interval, with values as high as 29–30% LOI (12% organic carbon) in the surface 0–5 mm layer. The theoretical flux of dissolved pore water carbon gases to the sediment–water interface (SWI) averaged 3.4 mmol L^?1 m^?2 day^?1 CH₄ and 7.3 mmol L^?1 m^?2 day^?1 CO₂ for the surface 0–10 mm. From gas emission measurements at the water surface, it was calculated that 90% of CH₄ is consumed either at the SWI or in the water column, resulting in a loss of 0.31 mmol L^?1 m^?2 day^?1 of CH₄ to the atmosphere. However, only 20% of the total CO₂ gas transported across the water–atmosphere interface (36.3 mmol L^?1 m^?2 day^?1, or 1600 mg CO₂ m^?2 day^?1) was produced in the sediments. The remaining 80% of CO₂ probably comes from other carbon sources. With CH₄ oxidation in the aerobic water column, close to 30% of the carbon gas flux to the atmosphere could be accounted for by gas production of CO₂ and CH₄ in the sediments and their diffuse transport to the water column.     

Seasonal variation in the phytoplankton of a saline lowland river (Buenos Aires,Argentina) throughout an intensive sampling period

The aim of this survey was to analyse seasonal variations in phytoplankton composition and abundance with respect to temperature and conductivity values at two sampling sites in the Salado River's lower basin: El Destino and Guerrero. Samples were taken twice a week from 9 March 2004 to 20 July 2004. A total of 145 and 143 species were identified for these two sites, respectively. Infrequent species were discarded to avoid statistical misinterpretations. Autocorrelation analyses (Ljung‐Box Q‐statistic) were performed in order to establish seasonal patterns for species abundance. Similar significant (p < 0.05) autocorrelation patterns were observed for phytoplankton species composition, temperature and conductivity, thus, illustrating correlations with seasonal behaviour. On the basis of these data, species were grouped as (1) late‐summer: with 34 species well represented in warm waters (>22°C) (e.g. Planctonema lauterbornii and Chroococcus spp.); (2) winter: with 10 species that reached their highest densities in cold waters (<12°C) (e.g. Binuclearia eriensis and Microcystis firma); (3) transitional: of only four species with abundance peaks during intermediate conditions (15.5°C average) such as Closteriopsis acicularis and Nodularia spumigena and (4) independent: with 22 species of random behaviour whose autocorrelations remain within confidence limits. These four classifications pertain to species with similar presence at both sampling sites; the rest of the species evinced slightly different patterns. An apparent season‐associated succession of species was detected with those adapted to the warm, stagnant water of the late summer being replaced by others acclimated to the cold water of the winter. Copyright © 2009 John Wiley & Sons, Ltd.