Reservoirs In Semi-arid Regions Research Articles

Method of 210Pb geochronological to estimate sedimentation rate in water reservoir in the Brazilian semiarid region

Dams are important reservoirs in semiarid regions providing the needs of the population and agricultural activities in an area in which intermittent rivers predominate. These reservoirs are subject to erosion processes that can cause sedimentation and affect the quality of the water in them. The method of dating sediments using 210Pb is well known and is used to establish a precise chronology of the sediments in places where abrupt changes in sedimentation conditions do not occur. The work aims to determine the sedimentation rate in five main tributary points of the dam located in the semiarid region of the state of Pernambuco, Brazil, using the geochronologic dating of the sediments by measuring 210Pb activity. The method used was the Constant Rate of Supply (CRS) model. Dating coincides with the date of the conclusion of the construction of the dam. The sedimentation rate grew with the increase in depth and presented a decline in both the rate and flow of the sediments over time. The most recent results presented a decrease in sedimentation rates. The greatest occurrence of the sedimentation rate was identified at points located at the entrance of the dam, which could be justified by the reduction in the average speed of final drainage due to the existence of the reservoir itself.

Critical load of phosphorus in reservoirs of a tropical semi‐arid region

The over-enrichment of water bodies by nutrients and the increase in primary production is a natural process that happens slowly, however, this process has been occurring in recent decades rapidly, due to the increase in the external load of anthropogenic nutrients, mainly phosphorus. Lake and reservoir eutrophication models seeking to calculate the critical load of phosphorus often do not consider the temporal variation in water volume. In this study, a dynamic model was used to estimate critical loads of phosphorus from six reservoirs in Brazil's semi-arid region, all of which experience great water volume variation, to describe the variation in water balance together with the variation in phosphorus mass balance. The critical load of phosphorus was defined as the load that guaranteed total phosphorus concentrations of up to 30 mg/m3 throughout 90% of the simulation period. A total of 40 scenarios were simulated and combined two vertical flows of phosphorus, five concentrations of phosphorus in the affluent volumes, and four water demands. Results revealed that the critical load of phosphorus was strongly affected by water demand, what pose a strong dilemma toward the operation of reservoirs in the semi-arid region of Brazil between rationing stored water for use in long periods of drought or stimulating water use to increase water turnover rates. The critical load of phosphorus was also affected by phosphorus concentration in affluent volumes, and the vertical flow of phosphorus between the sediment and water columns. The findings of this study can help for better understanding of the impact of temporal variations in lake and reservoir water volumes to define critical loads of phosphorus more accurately and control eutrophication more effectively in these environments.

Institutions for reoperating reservoirs in semi-arid regions facing climate change and competing societal water demands: insights from Colorado

ABSTRACT Reservoir reoperation is analysed from the perspective of institutions (rules) governing water resources. A new definition is provided, going beyond ‘modifying dam operations’ found in the literature to instead focus on changes to the allocation of water stored and released from a reservoir. Through interviews and archival research, we assess 32 large reservoirs in the US state of Colorado. Using tools from institutional analysis, we find that reoperation is often the result of institutional ‘crafting’ by reservoir managers and water users, that property rights strongly influence outcomes, and that well-designed policy can promote water sharing in otherwise rigid institutional settings.

Evaporation Suppression From Small Reservoirs Using Floating Covers—Field Study and Modeling

AbstractEvaporative losses from small seasonal water reservoirs in semiarid regions may significantly diminish storage and water availability to rural communities. Motivated by finding effective and economically feasible measures for suppressing evaporation, we study the efficacy of self‐assembling floating covers in suppressing evaporation under field conditions and potential ecological ramifications of the covers. We conducted a multi‐season study with eight identical small reservoirs (13.5 m2 area and 1.5 m deep) using ethylene‐vinyl acetate foam disks (200 mm in diameter, 15 mm thick) in white and black to cover six reservoirs (cover fraction of 91%), leaving two uncovered reservoirs for control. Physical attributes such as evaporative losses, radiative balance, temperature, and heat fluxes were measured and compared with modeling results. Evaporation suppression under field conditions ranged between 65% and 80% in the summer. Despite significant differences in energy partitioning, evaporation from white and black disks were relatively similar (∼20% for white and ∼30% evaporation for black disks compared to uncovered reservoir). Replacing black disks with water filled black polyethylene balls improved suppression efficiency and diminished seasonal variations (∼80% suppression irrespective of season). We developed a physically based model to describe and extend the experimental findings by exploring effects of reservoir management regimes on evaporation and to optimize cover and reservoir characteristics for different climatic conditions.

Distribution of small seasonal reservoirs in semi-arid regions and associated evaporative losses

To support the increasing demand of a growing population for freshwater, small-sized (<0.1 km2) water reservoirs are necessary in areas with limited infrastructure, especially in water-stressed regions having seasonal and variable precipitation. Seasonal storage in small reservoirs is often overlooked in present inventories. Accordingly, we assessed the current state in semi-arid regions using highly resolved Sentinel-2 satellite imagery. Globally, about 3 million small reservoirs are in operation in semi-arid regions having a total water surface area of 17 800 km2 and seasonal storage of 37 km3, supporting 15% of the world’s population in semi-arid regions. Estimated upper-bound of evaporative losses represent 38% (14 km3) of storage during dry season. The study estimates the evaporation suppression using floating covers and lays foundation to assess the feasibility of this technical solution to increase water savings. Significance and originality statement This study provides new insights into the distribution of seasonal freshwater storage in water stressed regions that support large rural population. We provide the first baseline dataset of this distributed freshwater resource to better assess the sustainability of communities in semi-arid regions with chronic water shortages. Water storage in semi-arid regions is subject to potential evaporative losses of nearly 40% of the stored water. We analyzed conditions where evaporative losses could be significantly reduced using floating covers, a simple and scalable solution suitable for regions with underdeveloped economies. The study as well ranks regions with highest potential benefits from evaporation suppression measures.

Balance of nitrogen and phosphorus in a reservoir in the tropical semiarid region

In relation to the process of eutrophication of water reservoirs, it is necessary to understand the nitrogen and phosphorus supply, as well as they support the process of eutrophication. In seeking to quantify the balance of nitrogen and phosphorus, as well as to identify the effect of climatic seasonality on their dynamics, 21 campaigns were carried out for water collection. The campaigns took place from April 2008 to December 2012 at the Oros reservoir, located in the semi-arid region of Brazil in the south-central part of the State of Ceara. Based on dataset it was possible to calculate the inflow and outflow of total nitrogen (TN) and total phosphorus (TP). The reservoir becoming a storage place for the nutrients transported by the flow of water from the drainage network. A total of 176 tons of nitrogen and 230 tons of phosphorus were retained in the reservoir. The TN and TP retained in the reservoir can lead to the water being compromised by eutrophication, increasing the financial cost of water treatment and compromising water availability for consumption use. Because it is a predominantly agricultural basin, and the nutrients show a similar input trend in the reservoir, it is believed that the primary source of nutrients is agriculture and livestock. There has been an increase in nutrient input of over time. Reservoirs in semi-arid regions are unique as regards nutrient load during dry periods, since even without fluvial input, nutrient concentrations generally remain steady or increase.

Effects of temperature increase and nutrient enrichment on phytoplankton functional groups in a Brazilian semi-arid reservoir

Abstract Aim Our study aimed to evaluate changes in the phytoplankton functional groups brought about by increases in temperature and nutrients predicted by the Intergovernmental Panel on Climate Change (IPCC) scenario for semi-arid regions. Methods Two experiments were performed, one in the rainy season and another in the dry season. The nutrient enrichment was based on the annual mean values (August 2012-August 2013) of soluble reactive phosphorus and nitrate verified in the reservoir. The microcosms were exposed to two different temperatures, the five-year average of air temperature in the reservoir (control) and 4°C above the control temperature (warming). The experiment was conducted over 12 days; every three days water samples of approximately 60 mL in volume were taken from the reservoir for chemical and phytoplankton analysis. All species were classified by Reynolds Functional Groups (RFG). Results The functional groups H1, X1, LO and S1 were the most representative in both seasons (rainy and dry). Our results showed that bloom-forming cyanobacteria, in particular the species of functional groups H1 and M, commonly reported in reservoirs in semi-arid regions of Brazil, were not significantly benefited by the warming and nutrient enrichment. The recruitment of other blue-green species, as well as diatoms and green algae, could be observed. Conclusions The effects of warming and/or nutritional enrichment can change the structure of the phytoplankton community. However, as not expected as the pessimist scenario, in our study the bloom-forming phytoplankton functional groups did not show changes in relative biomass. Instead, the recruitment of diatoms and green algae currently found in enriched environments was verified, specifically in the rainy period, when nutrient dilution typically occurs.

Functional attributes of Chironomidae for detecting anthropogenic impacts on reservoirs: A biomonitoring approach

Organisms display sets of functional attributes that reflect local environmental conditions and can be used in environmental quality assessments. We analyzed the functional attributes of Chironomidae in reservoirs in the Brazilian semiarid region with different levels of anthropic disturbances. We examined the relationships of functional feeding groups, feeding strategies, body size, and the morphological adaptations of chironomid larvae with the environmental quality of 94 sites. The sites were classified according to their levels of anthropic disturbance based on environmental characteristics. To observe the relationship between the functional attributes of Chironomidae and the different levels of anthropic disturbance, we performed an RLQ. To test differences between the functional categories of Chironomidae, we use an analysis of variance (ANOVA). The functional categories of Chironomidae that indicated anthropic disturbances were: collector group, reduced pseudopods, abdominal tubule, and gatherers. The least disturbed sites showed higher relative abundances of engulfers, predators, organisms with elongated heads, and small body size. The observed relationships between Chironomid functional attributes and the levels of anthropic impacts on reservoirs in the semiarid region of Brazil allow their use as a tool for assessing the environmental qualities of lentic aquatic ecosystems.

Application of a statistical model for the assessment of environmental quality in neotropical semi-arid reservoirs

The aim of this study was to develop a statistical model to assess the environmental quality of reservoirs located in semi-arid region using metrics of anthropogenic disturbance, water quality variables, and benthic macroinvertebrate communities as indicators. The proposed model was applied to 60 sites located in three reservoirs in the Paraíba river basin, Brazilian semi-arid region. Collections were made in December 2011. In each site, we collected one sample of benthic macroinvertebrates and one water sample for the determination of physical and chemical parameters. Characterization of the landscape was made through application of 10 physical habitat protocols on each site for the collected information on disturbance and subsequent calculation of disturbance metrics. The results showed the formation of two groups: group 1, consisting of 16 minimally altered sites, and group 2, with 44 severely altered sites. The proposed statistical model was sensitive enough to detect changes. In the minimally altered group, the Chironomids Aedokritus and Fissimentum were dominant, indicating a higher environmental quality, while Coelotanypus and Chironomus were abundant in severely altered sites with lower environmental quality. The conservation and management of reservoirs in semi-arid regions should be intensified in view of the need to maintain the environmental quality of these ecosystems.

Assessment of sedimentation in Tuli Makwe Dam using remotely sensed data

A remote sensing approach was used to assess sedimentation in Tuli-Makwe Dam in the semi-arid Mzingwane Catchment in the Matebeleland South province of Zimbabwe. The loss in reservoir gross capacity due to sediment deposition for a period of 47 years since the construction of the dam in 1966 to 2013 was determined to be 3.371 Mm3 which translate to 40.84 % gross capacity loss. The revised capacity of the dam is estimated at 4.883 Mm3. The annual rate of sedimentation was calculated to be 0.87 % per annum which translates to 0.0717 Mm3 per annum. The specific sediment yield over Tuli-Makwe catchment was calculated to be 110.63 tonnes / km2 / year. The result of the sedimentation analysis is typical of small reservoirs in semi-arid regions in Southern Africa. The sedimentation results for Tuli-Makwe reservoir using the remote sensing approach for 2013 are comparable with the sedimentation results from the 2012 hydrographic survey. The results further confirm the applicability of remote sensing for sedimentation analysis for small reservoirs in semi-arid regions. Assuming a uniform sedimentation rate, current trends suggest that Tuli-Makwe reservoir may be filled up in the next sixty eight years from 2013, however the useful capacity of the reservoir may be lost in much less time. Key words: Reservoir sedimentation, remote sensing, reservoir capacity loss.

Water level fluctuations in a tropical reservoir: the impact of sediment drying, aquatic macrophyte dieback, and oxygen availability on phosphorus mobilization.

Reservoirs in semi-arid areas are subject to water level fluctuations (WLF) that alter biogeochemical processes in the sediment. We hypothesized that wet-dry cycles may cause internal eutrophication in such systems when they affect densely vegetated shallow areas. To assess the impact of WLF on phosphorus (P) mobilization and benthic P cycling of iron-rich sediments, we tested the effects of (i) sediment drying and rewetting, (ii) the impact of organic matter availability in the form of dried Brazilian Waterweed (Egeria densa), and (iii) alternating redox conditions in the surface water. In principle, drying led to increased P release after rewetting both in plant-free and in plant-amended sediments. Highest P mobilization was recorded in plant amendments under oxygen-free conditions. After re-establishment of aerobic conditions, P concentrations in surface water decreased substantially owing to P retention by sediments. In desiccated and re-inundated sediments, P retention decreased by up to 30% compared to constantly inundated sediments. We showed that WLF may trigger biochemical interactions conducive to anaerobic P release. Thereby, E. densa showed high P release and even P uptake that was redox-controlled and superimposed sedimentary P cycling. Macrophytes play an important role in the uptake of P from the water but may be also a significant source of P in wet-dry cycles. We estimated a potential for the abrupt release of soluble reactive phosphorus (SRP) by E. densa of 0.09-0.13 g SRP per m(2) after each wet-dry cycle. Released SRP may exceed critical P limits for eutrophication, provoking usage restrictions. Our results have implications for management of reservoirs in semi-arid regions affected by WLF.

A water balance approach for quantifying subsurface exchange fluxes and associated errors in hill reservoirs in semiarid regions

AbstractHill reservoirs are rain water‐harvesting structures that have been increasingly adopted in arid and semi‐arid regions, such as North Africa, to capture and conserve runoff water and for use as alternative water resources in agricultural development. Currently, process‐based information on reservoir hydrology is needed to improve reservoir management practices.The study aims to develop an approach to estimate the reservoir–subsurface exchange flux and its associated error at the annual, monthly, and intra‐monthly time scales to better understand the hydrological functioning and dynamics of hill reservoirs. This approach is based on a hydrological water balance of the hill reservoir by considering all water input and output fluxes and their associated errors.The results demonstrate the ability and relevance of the approach in estimating the net reservoir–subsurface exchange flux and its error estimations at various time scales. Its application on the Kamech catchment (Northern Tunisia) for the 2009–2012 period demonstrates that the net reservoir–subsurface exchange flux is positive, i.e. the infiltration from the hill reservoir to the aquifer dominates over the discharge from the aquifer to the reservoir. Moreover, reservoir–subsurface exchange constitutes the main output component in the water balance. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Assessment of the water quality in a large reservoir in semiarid region of Brazil

The aim of this study was to identify spatial and temporal variations in water quality of Orós reservoir, Ceará, Brazil, as well as the sources of contamination. To get this information the Principal Component Analysis (PCA) and Cluster Analysis (CA) was used. Water samples were collected at seven (geo-referenced) points, from April 2008 to March 2011, totalling 4,032 samples. The following attributes of the waters were analysed: temperature, pH, CE, Ca2+, Mg2+, Na+, K+, Cl-, HCO3-, SO4--, turbidity, colour, Sechi transparency, TS, TVS, TFS, TSS, VSS, FSS, TDS, DO, BO5D, total phosphorus, soluble orthophosphate, EC, TTC, total ammonia, TKN, nitrate, SAR and chlorophyll-a. The PCA promoted the reduction from the 32 initial variables to 14, accounting for 84.39% of the total variance. The major factors responsible for water quality composition are: the natural weathering of geological soil components; the entrainment of suspended solids through surface runoff from agricultural areas; and anthropogenic action in the Upper Jaguaribe basin in Ceará. The similarity of the water of the Orós reservoir allows a reduction in the number of sampling points, which may result in significant cost savings without sacrificing the water quality monitoring. The similarity of the waters was influenced by anthropic activities being carried out near the reservoir and all along the watershed.

Zooplankton assemblages in eutrophic reservoirs of the Brazilian semi-arid

Species composition, density, and temporal dynamics of zooplankton were studied in six reservoirs in a semi-arid region in tropical northeastern Brazil (Rio Grande do Norte state). All the reservoirs are highly eutrophic, with high contents of total nitrogen (minimum of 1200 µg.L(-1)) and total phosphorus (minimum of 10 µg.L(-1)), and extremely high algal biomass was registered (surpassing 20 µg Chl a.L(-1)). All the reservoirs showed an enduring condition of high turbidity and phytoplankton assemblages dominated by cyanobacteria. Zooplankton also showed quantitative patterns suggestive of eutrophic conditions, expressed by high densities, mainly in Passagem das Traíras and Sabugi reservoirs. A spatial differentiation in the composition of the zooplankton community was registered. Rotifers (especially Keratella tropica, Brachionus havanensis, and Keratella americana) were the dominant forms in the zooplankton community of Itans, Passagem das Traíras, and Sabugi reservoirs, while calanoid copepods (mainly Notodiaptomus cearensis) dominated in the Armando Ribeiro, Gargalheiras, and Parelhas systems. The existence of novel relationships in zooplankton community composition in eutrophic reservoirs in this tropical semi-arid region must be considered in designating zooplankton indicators of eutrophic conditions.

Cyanobacterial blooms in stratified and destratified eutrophic reservoirs in semi-arid region of Brazil

This study investigated the dynamics of cyanobacteria in two deep, eutrophic reservoirs in a semi-arid region of Brazil during periods of stratification and destratification. Four collections were carried out at each reservoir at two depths at three-month intervals. The following abiotic variables were analyzed: water temperature, dissolved oxygen, pH, turbidity, water transparency, total phosphorus, total dissolved phosphorus, orthophosphate and total nitrogen. Phytoplankton density was quantified for the determination of the biomass of cyanobacteria. The data were analyzed using CCA. Higher mean phytoplankton biomass values (29.8 mm(3).L(-1)) occurred in the period of thermal stratification. A greater similarity in the phytoplankton communities also occurred in this period and was related to the development of cyanobacteria, mainly Cylindrospermopsis raciborskii (>3.9 mm(3).L(-1)). During the period of thermal destratification, this species co-dominated the environment with Planktothrix agardhii, Geitlerinema amphibium, Microcystis aeruginosa and Merismopedia tenuissima, as well as with diatoms and phytoflagellates. Environmental instability and competition among algae hindered the establishment of blooms more during the mixture period than during the stratification period. Thermal changes in the water column caused by climatologic events altered other physiochemical conditions of the water, leading to changes in the composition and biomass of the cyanobacterial community in tropical reservoirs.

Preliminary Observations on Nutrient Enrichment of Semi-arid, Manmade Lakes in the Northern and Southern Hemispheres

ABSTRACT This paper is part of a multi-step assessment of the hypothesis that subtropical, semi-arid impoundments may respond differently to increasing nutrient enrichment than similar northern temperate waterbodies (primarily natural lakes) from which the classical lake eutrophication concept has been derived. Common physicochemical indicators of eutrophication are referenced, including nutrient status, phytoplankton biomass (chlorophyll), and hypolimnetic deoxygenation. Data from 89 reservoirs in the southwestern United States and southern Africa were used to examine the eutrophication-related limnology of these lakes. In particular, the effects of a large catchment area:lake surface area ratio (AD:A) on the turbidity, nutrient status, and phytoplankton standing crop were highlighted as distinct features relevant to semi-arid lake classification. The responses of reservoirs in semi-arid regions of the northern and southern hemispheres to nutrient enrichment are contrasted with responses of temperate lak...