Academic literature on the topic 'Lake (Vic ) Regulation'

Stable isotopes of lake waters are widely used to identify the relative importance of hydrological processes on the lake water balance across the ungauged landscape via the coupled-isotope tracer model. The isotopic compositions of twenty shallow freshwater lakes across the mid-lower reaches of Yangtze floodplain (MLY) were investigated in January and May of 2018. The lake-specific input water (δI) and evaporation-to-inflow (E/I) ratios were estimated to explore the specific lake hydrology across the MLY. Results showed that distinct isotopic enrichment trends in May compared with those in January, which was indicative of stronger evaporation in May. The δ18OI values of specific lakes exhibited large variability across the MLY, which may be related to the watershed properties, such as watershed area and elevation, and rainfall. The estimated E/I ratios of lakes across the MLY were below 1, which suggested that these lakes (code 1–15) are flood-dominated in the middle reaches of Yangtze River where lakes are susceptible to Three Gorges Dams regulations. By contrast, the relatively lower variability of lake E/I ratios were observed from the Yangtze River Delta (code 17–20) because these lakes with developed river network systems are highly exchanged by artificial regulation. Our investigation of lake types and corresponding isotopic evolution patterns are likely typical of other floodplain landscapes and their identification could be used to better predict hydrological responses to ongoing climate change and artificial regulations by dams.

Desert terminal lakes are important signals to discern ecological degradation crises, particularly in arid areas where an artificial project of ecological water diversion has designated a quota of river water to prevent lake body shrinkage and protect the ecosystem. Knowledge of the minimum ecological water demand (EWD) is thus necessary to ensure the basic health of lake ecosystems. This study analyzed the spatiotemporal evolution of water boundaries using Landsat satellites data via remote sensing technology from 2002 to 2017 in East Juyan Lake, an inland desert terminal lake of the Heihe River in northwest China. The minimum lake water demand was determined using two estimation methods: the lake-evaporation-oriented EWD method and the minimum water level method. In the latter method, both lake topography (using water-level area curves) and biological survival demands (using bighead carps as indicators) were considered to derive the minimum lake EWD. Water diversion to the lake over the past 15 years has increased the lake’s area, but there are still marked intra-annual seasonal variations. The annual minimum lake water demand was suggested to be 54 × 106 m3/year by comparing the different methods; however, it was not satisfied, and the lake survival was endangered when the occurrence frequency of the annual runoff in the Zhengyixia hydrological station exceeded 65%. This study offered promising directions for inland lake water resource management.

Abstract. A one-dimensional (1-D) model for an enclosed basin (lake) is presented, which reproduces temperature, horizontal velocities, oxygen, carbon dioxide and methane in the basin. All prognostic variables are treated in a unified manner via a generic 1-D transport equation for horizontally averaged property. A water body interacts with underlying sediments. These sediments are represented by a set of vertical columns with heat, moisture and CH4 transport inside. The model is validated vs. a comprehensive observational data set gathered at Kuivajärvi Lake (southern Finland), demonstrating a fair agreement. The value of a key calibration constant, regulating the magnitude of methane production in sediments, corresponded well to that obtained from another two lakes. We demonstrated via surface seiche parameterization that the near-bottom turbulence induced by surface seiches is likely to significantly affect CH4 accumulation there. Furthermore, our results suggest that a gas transfer through thermocline under intense internal seiche motions is a bottleneck in quantifying greenhouse gas dynamics in dimictic lakes, which calls for further research.

Globally, many shallow lakes have shifted from a clear macrophyte-dominated state to a turbid phytoplankton-dominated state due to eutrophication. Such shifts are often accompanied by toxic cyanobacterial blooms, with specialized traits including buoyancy regulation and nitrogen fixation. Previous work has focused on how these traits contribute to cyanobacterial competitiveness. Yet, little is known on how these traits affect the value of nutrient loading thresholds of shallow lakes. These thresholds are defined as the nutrient loading at which lakes shift water quality state. Here, we used a modelling approach to estimate the effects of traits on nutrient loading thresholds. We incorporated cyanobacterial traits in the process-based ecosystem model PCLake+, known for its ability to determine nutrient loading thresholds. Four scenarios were simulated, including cyanobacteria without traits, with buoyancy regulation, with nitrogen fixation, and with both traits. Nutrient loading thresholds were obtained under N-limited, P-limited, and colimited conditions. Results show that cyanobacterial traits can impede lake restoration actions aimed at removing cyanobacterial blooms via nutrient loading reduction. However, these traits hardly affect the nutrient loading thresholds for clear lakes experiencing eutrophication. Our results provide references for nutrient loading thresholds and draw attention to cyanobacterial traits during the remediation of eutrophic water bodies.

Abstract. It has become more and more evident that CO2 emission (FCO2) from freshwater systems is an important part in the global carbon cycle. Only few studies addressed the different mechanisms regulating FCO2 from lotic and lentic systems. In a comparative study we investigated how different biogeochemical and physical factors can affect FCO2 from streams and reservoirs. We examined the seasonal variability in CO2 concentrations and emissions from four streams and two pre-dams of a large drinking water reservoir located in the same catchment, and compared them with parallel measured environmental factors. All streams generally were supersaturated with CO2 over the whole year, while both reservoirs where CO2 sinks during summer stratification and sources after circulation. FCO2 from streams ranged from 23 to 355 mmol m–2 d–1 and exceeded the fluxes from the reservoirs (–24 to 97 mmol m–2 d–1). Both the generally high piston velocity (k) and CO2 oversaturation were responsible for the higher FCO2 from streams in comparison to lakes. In both, streams and reservoirs FCO2 was mainly controlled by the CO2 concentration (r = 0.86 for dams, r = 0.90 for streams), which was clearly affected by metabolism and nutrients in both systems. Besides CO2 concentration, also physical factors control FCO2 in lakes and streams. During stratification FCO2 in both pre-dams was controlled by primary production in the epilimnion, which led to a decrease of FCO2. During circulation when CO2 from the hypolimnion was mixed with the epilimnion and the organic matter mineralisation was more relevant, FCO2 increased. FCO2 from streams was physically controlled especially by geomorphological and hydrological factors regulating k, which is less relevant in low wind lakes. We developed a schematic model describing the role of the different regulation mechanism on FCO2 from streams and lakes. Taken together, FCO2 is generally mostly controlled by CO2 concentration in the surface water. Lake stratification is a very important factor regulating FCO2 from lakes via controlling CO2 concentration and metabolism. But FCO2 in heterotrophic streams is generally higher. The higher k values are responsible for the comparable high FCO2. On a Central European landscape scale CO2 emission from streams was more relevant than the CO2 flux from standing waters.

Abstract. The competition for scarce water resources in the Upper Klamath River Basin, Oregon has generated conflict among its stakeholders, as demonstrated by recent regulations on withdrawals from Upper Klamath Lake. Information on agricultural water usage can help assess the hydrologic impacts of irrigation and support operational decisions. This paper presents an experimental satellite-based evapotranspiration estimation system that is combined with the Variable Infiltration Capacity (VIC) hydrological model to estimate irrigation consumption, which is then used to assess the effects of irrigated agriculture on lake storage volumes and water levels. The hydrological model is calibrated with streamflow observations and used to estimate unmeasured lake inflows and guide water balance calculations. When combined with the VIC model, the satellite-based evapotranspiration estimation system shows that irrigation caused a decline of 0.3 m in average annual water levels and 0.5 m in mean October water levels, and an increase of 0.5 m in annual water level ranges at the lake from 2001 to 2005. The results demonstrate the potential of satellite data for agricultural water resource management at the regional scale.

Abstract. Competition for scarce water resources in the Upper Klamath River Basin, Oregon has generated conflict among its stakeholders, as demonstrated by recent regulations on withdrawals from Upper Klamath Lake. Information on agricultural water usage can help assess the hydrologic impacts of irrigation and support operational decisions. This paper presents an experimental satellite-based evapotranspiration estimation system that is combined with the Variable Inflitration Capacity (VIC) hydrological model to estimate irrigation consumption, which is then used to assess the effects of irrigated agriculture on lake storage volumes and water levels. The hydrological model is calibrated with streamflow observations and used to estimate unmeasured lake inflows and guide water budget calculations. When combined with the VIC model, the satellite-based evapotranspiration estimation system shows that irrigation caused a decline of 0.3 m in average annual water levels and 0.5 m in mean October water levels, and an increase of 0.5 m in annual water level ranges at the lake from 2001 to 2005. The results demonstrate the potential of satellite data for agricultural water resource management at the regional scale.

Efforts to understand the ecological regulation of species diversity via bottom-up approaches have failed to yield a consensus theory. Theories based on the alternative of top-down regulation have fared better. Paine’s discovery of keystone predation demonstrated that the regulation of diversity via top-down forcing could be simple, strong, and direct, yet ecologists have persistently failed to perceive generality in Paine’s result. Removing top predators destabilizes many systems and drives transitions to radically distinct alternative states. These transitions typically involve community reorganization and loss of diversity, implying that top-down forcing is crucial to diversity maintenance. Contrary to the expectations of bottom-up theories, many terrestrial herbivores and mesopredators are capable of sustained order-of-magnitude population increases following release from predation, negating the assumption that populations of primary consumers are resource limited and at or near carrying capacity. Predationsensu lato(to include Janzen–Connell mortality agents) has been shown to promote diversity in a wide range of ecosystems, including rocky intertidal shelves, coral reefs, the nearshore ocean, streams, lakes, temperate and tropical forests, and arctic tundra. The compelling variety of these ecosystems suggests that top-down forcing plays a universal role in regulating diversity. This conclusion is further supported by studies showing that the reduction or absence of predation leads to diversity loss and, in the more dramatic cases, to catastrophic regime change. Here, I expand on the thesis that diversity is maintained by the interaction between predation and competition, such that strong top-down forcing reduces competition, allowing coexistence.

AbstractCichlid fishes provide textbook examples of explosive phenotypic diversification and sympatric speciation, thereby making them ideal systems for studying the molecular mechanisms underlying rapid lineage divergence. Despite the fact that gene regulation provides a critical link between diversification in gene function and speciation, many genomic regulatory mechanisms such as microRNAs (miRNAs) have received little attention in these rapidly diversifying groups. Therefore, we investigated the posttranscriptional regulatory role of miRNAs in the repeated sympatric divergence of Midas cichlids (Amphilophus spp.) from Nicaraguan crater lakes. Using miRNA and mRNA sequencing of embryos from five Midas species, we first identified miRNA binding sites in mRNAs and highlighted the presences of a surprising number of novel miRNAs in these adaptively radiating species. Then, through analyses of expression levels, we identified putative miRNA/gene target pairs with negatively correlated expression level that were consistent with the role of miRNA in downregulating mRNA. Furthermore, we determined that several miRNA/gene pairs show convergent expression patterns associated with the repeated benthic/limnetic sympatric species divergence implicating these miRNAs as potential molecular mechanisms underlying replicated sympatric divergence. Finally, as these candidate miRNA/gene pairs may play a central role in phenotypic diversification in these cichlids, we characterized the expression domains of selected miRNAs and their target genes via in situ hybridization, providing further evidence that miRNA regulation likely plays a role in the Midas cichlid adaptive radiation. These results provide support for the hypothesis that extremely quickly evolving miRNA regulation can contribute to rapid evolutionary divergence even in the presence of gene flow.

Maternal influences on age-0 walleye (Sander vitreus (Mitchill, 1818)) recruit abundance and survival from egg to fall were observed in Escanaba Lake, Wisconsin, in 1957–2015. Annual egg production best explained variation in age-0 recruitment, compared with female relative abundance, and adult abundance (sexes combined). Age-0 recruitment was not significantly correlated with any temperature metric tested or our index of yellow perch (Perca flavescens (Mitchill, 1814)) abundance. Survival of walleye from egg to fall age-0 was positively correlated with the percent contribution of large females (>55.9 cm) to annual egg production. Mean size diversity of females by length class did not influence age-0 recruit abundance or survival over time. Evidence for maternal effects via size- and age-specific influences on fecundity and age-0 walleye survival suggest that exploitation may influence natural recruitment by altering adult female size structure. Given recent declines observed in walleye natural recruitment in the upper Midwestern USA, understanding the roles of maternal drivers and exploitation on recruitment is critical for sustainable walleye management.

Focusing on a few key passages, derived principally from law codes and literary sources, this chapter sketches out the legal situation of collegia vis-à-vis “the state”. However, this material is weighed against the rich epigraphic evidence (i.e. inscribed documents) that suggests the widespread and, in practical effect, unrestricted nature of Roman associations. It suggests that the appearance of governmental interference and regulation, from the late Republic throughout the Principate, was itself merely a pretext, as the government continued to encourage the development and proliferation of collegia as a means of social and political control. It questions whether the senate and the emperors had an interest in actually regulating and licencing collegial assembly, and whether legal texts can be reconciled with the inscriptional material attesting extensive collegial organisation, particularly in Italy and the Empire’s western provinces.

Cyber is an integration of computation, communication, and control systems. Physical means natural and human-made systems that are managed and governed by the physics regulations and functioning in constant time. In Cyber Physical Systems, the cyber and physical systems are those firmly incorporated at all stages and dimensions. Starting in late 2006, the US National Science Foundation (NSF) and other United State federal agencies sponsored several workshops on CPSs. In 2007, the NSF identified CPSs as a key area of research. CPS uses embedded computers and networks to compute, communicate, and organize physical actions. Simultaneously, a CPS receives feedback on how physical events impact computations and vice versa. Through the Internet and how people communicate with each other, CPSs will change the way people interrelate with the world around them. This chapter explores CPSs.

Abstract Over the last few decades, China has experienced tremendous growth and socioeconomic development. This has also been a period of significant transformations in many social and economic sectors, including water management. Starting from revision of policies and regulatory frameworks, modifications of water engineering approaches have been introduced, together with broadening the overall management of river basins and water resources to encompass ecological and other nature services, next to considerations for economic benefits. These water management transformations have also been facilitated and enabled by introducing novel information and communication technologies, very much along the lines that Mike Abbott predicted and promoted as he was developing the field of hydroinformatics. In fact, he was always considering China as a country that would greatly benefit from hydroinformatics technologies as it has been going through rapid socioeconomic development, and, that the field itself would then make progress via novel Chinese applications. This chapter briefly introduces the main water management transformations and challenges that China has faced over the past few decades, and proceeds with presentation of hydroinformatics tools and technologies in the sequence of data→models→knowledge→decision-support applications, as they have been deployed in China. To showcase the use of such technologies in actual water management activities, the example of Changjiang River basin is presented as a case study, with demonstration of applications on flood management. These applications integrate monitored data with a suite of different models for flood forecasting and regulation of water infrastructure - particularly large scaled reservoir groups, where flood management is addressed in conjunction with other water resources functions. Decision support applications, such as to enable broader stakeholder and public participation - the platform serving for river/lake chief system - are also presented.

Our themes have so far been commodity frontiers, the transformation of nature, the beginnings of imperial environmental regulation, and the spatial dimensions of colonial cities. In this chapter we open an interrelated enquiry—into disease, specifically the third pandemic of plague. The link between environments and disease has long been made. By the late nineteenth century, as parasitology and tropical medicine made rapid strides, the precise causes of life-threatening maladies could be identified with increasing accuracy. Ross pinpointed mosquitoes as bearers of malaria and yellow fever; Bruce and others discovered the trypanosome borne by tsetse flies (see Chapter 11). Such discoveries gave environmental investigation and understanding a new urgency. They also provided arguments and scientific rationales for environmental regulation that seemed to offer the possibility of controlling disease. State intervention in controlling disease had a profound impact on some colonial environments, both urban, in this case, and rural (Chapter 11). While environmental controls were conceived as beneficial, both for British and indigenous people, they were also one way in which imperial subjects experienced political and social domination. Medical management of environmentally related diseases was sometimes strongly contested by the colonized. The same dilemma is explored in relation to conservation (Chapter 16). In a seaborne empire, as we have noted, ports were often critical sites for urban development, and formed the fundamental web of early empire. Cities, especially ports, were also centres of disease. Infections were brought into them, both by ships and from their hinterlands. They provided large concentrations of people in which disease could easily take hold, especially in the absence of efficient sanitation and healthcare. More people were becoming urbanized, living on top of one another in unsanitary and overcrowded conditions that were ideal spawning grounds for new and old infections. By the 1890s, Mumbai, a major centre of infection in India, had about 800,000 people—along with Kolkata this was a new scale of ships ‘the most convenient way to travel’, and can easily scramble on board via mooring ropes. Other factors in its spread included the bigger size of ships (hence larger colonies of rats), the large shipments of grain (which provided food and nests), and the passing of infection from ships’ rats to susceptible populations of wild rodents in California, Argentina, and South Africa.

In 1966 a retired British Major named Paddy Roy Bates took a liking to a small, abandoned concrete platform in the North Sea nicknamed “Rough’s Tower.” Rough’s Tower was a World War II gun tower used by the British to fire at German bombers on their way to London. By 1966, nobody wanted the rusting contraption, so Bates renamed it the “Principality of Sealand” and declared independence from the United Kingdom, six miles away. He awarded himself the title of Prince Roy, and proceeded to issue Sealand passports and Sealand stamps with pictures of his wife, Joan, an ex-beauty queen. Sealand has had a colorful history, but before 1999, nothing suggested that a chunk of concrete and steel off the English coast might have anything to do with the history of the Internet. That year, Bates agreed to let a young man named Ryan Lackey move to Sealand and begin transforming it into a “data haven.” Lackey’s company, “HavenCo,” equipped Sealand with banks of servers, and Internet links via microwave and satellite connections. Borrowing an idea from cyberpunk fiction, HavenCo aimed to rent computer space on Sealand to anyone who wanted to escape the clutches of government. It promised potential clients—porn purveyors, tax evaders, Web gambling services, independence movements, and just about any other government-shy Internet user—that data on Sealand servers would be “physically secure against any legal action.” HavenCo, the company boasted, would be “the first place on earth where people are free to conduct business without someone looking over their shoulder.” HavenCo was the apotheosis of the late 1990s belief in the futility of territorial government in the Internet era. Lackey’s company was premised on the commonplace assumption that governments cannot control what happens beyond their borders, and thus cannot control Internet communications from abroad. “If the king’s writ reaches only as far as the king’s sword, then much of the content of the Internet might be presumed to be free from the regulation of any particular sovereign,” wrote Duke law professor James Boyle, generalizing the point.

<i>Abstract</i>.—The Vindel River (Vindelälven), Sweden, is 450 km long with a mean annual discharge of 190 m³/s and runs through sparsely populated areas in northern Sweden, joining the Ume River near the Baltic Sea. A severe decline in Atlantic Salmon <i>Salmo salar</i> and Brown Trout <i>S. trutta</i> during the past century was caused by (1) intense timber-floating activities starting in the mid-1800s, which degraded stream habitat; (2) hydropower development in the early 1900s, which limited or blocked upstream migration; and (3) an expanded coastal/ocean fishery after 1950, which overharvested anadromous populations. Restoration efforts during the 1970s and 1980s failed due to low efficacy of stocking programs and insufficient habitat restoration. A legislative reform to unify the fishery right owners (FROs) along the river helped initiate restoration efforts in the late 1990s, focusing on improving fish migration past a hydropower station and restoring degraded habitat. Sweden’s membership in the European Union made large funding for restoration projects possible. The number of returning Atlantic Salmon increased significantly after migration conditions improved around the hydropower station and with stricter regulations on the offshore fishery. Successful habitat restoration was based upon gaining trust from landowners and FROs via extensive communication to gain access to their land. Restoration work was adaptive and experiences gained were incorporated into restoration guidelines. Involvement of universities, as a provider of expertise and as an unbiased interpreter of data, provided support to legal processes and when evaluating restoration measures. During the course of the restoration work, managers learned that stocking often did not produce satisfactory results. By studying historical documents from the timber-floating era, managers learned that the scope of modifications of the tributaries had been much greater than previously thought and that habitat restoration needed to be extensive. In many tributaries, the number of juvenile Brown Trout increased significantly after habitat restoration, sometimes dramatically exceeding expectations, which made the managers question the validity of established production estimates for northern boreal streams. The experience and knowledge gained from the Vindel River restoration served as the catalyst for many other major restoration projects in rivers emptying into the Baltic Sea.

Research Questions/Objective In the context of autonomous and connected vehicle technology, this research aims to develop an environment-on-board predictive braking control system, regulating the vehicle velocity to a desired value, in order to maintain and enhance path-following performance and vehicle stability when a vehicle is driven on a path where the road friction coefficient changes suddenly on a curve. If the vehicle enters a wet road from a dry road and moves on to a dry road at a high velocity, the vehicle suffers unexpected lateral disturbances, thereby causing it to destabilize and leading to deviation from the lane. Therefore, in this research, it is important to find a velocity, which the vehicle can turns on a curve that has an arbitrary curvature radius and wet road friction coefficient without deviating from the lane. Methodology In order to design the predictive braking control, the desired velocity needs to be calculated. By transforming the equation of simplified linear two-degree-of-freedom bicycle model the velocity can be expressed in terms of the curvature radius, road friction coefficient, lateral deviation and each vehicle parameter. Hence, if the definition of lane deviation is that lateral deviation is equal to 0.85 m, substituting its value gives the desired velocity that should be decelerated before entering a wet road. In addition, PID control is used to follow that velocity. The effectiveness of this control system is verified using a nonlinear four-degree-of-freedom four-wheel model and a full vehicle model of the IPG CarMaker under various conditions. Results To verify the effectiveness of the proposed control system, simulations of a vehicle driving through a curve which has a wet road surface are performed at various conditions that the wet road position, wet road friction coefficient and initial velocity differ from each other. Furthermore, the vehicle behavior such as side slip angle and lateral deviation, and the tire workloads are analyzed to evaluate vehicle stability and path-following performance. The results of these analysis show that the vehicle can be stabilize and it can be prevented from deviating from the lane by applying the control which decelerates the vehicle to the desired velocity before entering a wet road. Conclusions Based on the long-horizon road friction and curvature information from infrastructure together with connectivity between intelligent vehicles, the environment-on-board predictive braking control is developed to prevent vehicles from deviating from the lane even when the road friction coefficient changes suddenly on a sharp curve, and its effectiveness is verified through full-vehicle simulation. This system improves the vehicle stability and path-following performance under various conditions, including the position of a wet road.

The main goal of this research plan was to elucidate regulatory mechanisms controlling the development, function of the bovine corpus luteum (CL). The CL contains two different sterodigenic cell types and therefore it was necessary to obtain pure cell population. A system was developed in which granulosa and theca interna cells, isolated from a preovulatory follicle, acquired characteristics typical of large (LL) and small (SL) luteal cells, respectively, as judged by several biochemical and morphological criteria. Experiments were conducted to determine the effects of granulosa cells removal on subsequent CL function, the results obtained support the concept that granulosa cells make a substaintial contribution to the output of progesterone by the cyclic CL but may have a limited role in determining the functional lifespan of the CL. This experimental model was also used to better understand the contribution of follicular granulosa cells to subsequent luteal SCC mRNA expression. The mitochondrial cytochrome side-chain cleavage enzyme (SCC), which converts cholesterol to pregnenolone, is the first and rate-limiting enzyme of the steroidogenic pathway. Experiments were conducted to characterize the gene expression of P450scc in bovine CL. Levels of P450scc mRNA were higher during mid-luteal phase than in either the early or late luteal phases. PGF 2a injection decreased luteal P450scc mRNA in a time-dependent manner; levels were significantly reduced by 2h after treatment. CLs obtained from heifers on day 8 of the estrous cycle which had granulosa cells removed had a 45% reduction in the levels of mRNA for SCC enzymes as well as a 78% reduction in the numbers of LL cells. To characterize SCC expression in each steroidogenic cell type we utilized pure cell populations. Upon luteinization, LL expressed 2-3 fold higher amounts of both SCC enzymes mRNAs than SL. Moreover, eight days after stimulant removal, LL retained their P4 production capacity, expressed P450scc mRNA and contained this protein. In our attempts to establish the in vitro luteinization model, we had to select the prevulatory and pre-gonadotropin surge follicles. The ratio of estradiol:P4 which is often used was unreliable since P4 levels are high in atretic follicles and also in preovulatory post-gonadotropin follicles. We have therefore examined whether oxytocin (OT) levels in follicular fluids could enhance our ability to correctly and easily define follicular status. Based on E2 and OT concentrations in follicular fluids we could more accurately identify follicles that are preovulatory and post gonadotropin surge. Next we studied OT biosynthesis in granulosa cells, cells which were incubated with forskolin contained stores of the precursor indicating that forskolin (which mimics gonadotropin action) is an effective stimulator of OT biosynthesis and release. While studying in vitro luteinization, we noticed that IGF-I induced effects were not identical to those induced by insulin despite the fact that megadoses of insulin were used. This was the first indication that the cells may secrete IGF binding protein(s) which regonize IGFs and not insulin. In a detailed study involving several techniques, we characterized the species of IGF binding proteins secreted by luteal cells. The effects of exogenous polyunsaturated fatty acids and arachidonic acid on the production of P4 and prostanoids by dispersed bovine luteal cells was examined. The addition of eicosapentaenoic acid and arachidonic acid resulted in a dose-dependent reduction in basal and LH-stimulated biosynthesis of P4 and PGI2 and an increase in production of PGF 2a and 5-HETE production. Indomethacin, an inhibitor of arachidonic acid metabolism via the production of 5-HETE was unaffected. Results of these experiments suggest that the inhibitory effect of arachidonic acid on the biosynthesis of luteal P4 is due to either a direct action of arachidonic acid, or its conversion to 5-HETE via the lipoxgenase pathway of metabolism. The detailed and important information gained by the two labs elucidated the mode of action of factors crucially important to the function of the bovine CL. The data indicate that follicular granulosa cells make a major contribution to numbers of large luteal cells, OT and basal P4 production, as well as the content of cytochrome P450 scc. Granulosa-derived large luteal cells have distinct features: when luteinized, the cell no longer possesses LH receptors, its cAMP response is diminished yet P4 synthesis is sustained. This may imply that maintenance of P4 (even in the absence of a Luteotropic signal) during critical periods such as pregnancy recognition, is dependent on the proper luteinization and function of the large luteal cell.

Banco de la República provides a comprehensive overview of Colombia’s finan¬cial infrastructure in its Payment Systems Report, which is an important product of the work it does to oversee that infrastructure. The figures published in this edition of the report are for the year 2020, a pandemic period in which the con¬tainment measures designed and adopted to alleviate the strain on the health system led to a sharp reduction in economic activity and consumption in Colom¬bia, as was the case in most countries. At the start of the pandemic, the Board of Directors of Banco de la República adopted decisions that were necessary to supply the market with ample liquid¬ity in pesos and US dollars to guarantee market stability, protect the payment system and preserve the supply of credit. The pronounced growth in mone¬tary aggregates reflected an increased preference for liquidity, which Banco de la República addressed at the right time. These decisions were implemented through operations that were cleared and settled via the financial infrastructure. The second section of this report, following the introduction, offers an analysis of how the various financial infrastructures in Colombia have evolved and per¬formed. One of the highlights is the large-value payment system (CUD), which registered more momentum in 2020 than during the previous year, mainly be¬cause of an increase in average daily remunerated deposits made with Banco de la República by the General Directorate of Public Credit and the National Treasury (DGCPTN), as well as more activity in the sell/buy-back market with sovereign debt. Consequently, with more activity in the CUD, the Central Securi¬ties Depository (DCV) experienced an added impetus sparked by an increase in the money market for bonds and securities placed on the primary market by the national government. The value of operations cleared and settled through the Colombian Central Counterparty (CRCC) continues to grow, propelled largely by peso/dollar non-deliverable forward (NDF) contracts. With respect to the CRCC, it is important to note this clearing house has been in charge of managing risks and clearing and settling operations in the peso/dollar spot market since the end of last year, following its merger with the Foreign Exchange Clearing House of Colombia (CCDC). Since the final quarter of 2020, the CRCC has also been re¬sponsible for clearing and settlement in the equities market, which was former¬ly done by the Colombian Stock Exchange (BVC). The third section of this report provides an all-inclusive view of payments in the market for goods and services; namely, transactions carried out by members of the public and non-financial institutions. During the pandemic, inter- and intra-bank electronic funds transfers, which originate mostly with companies, increased in both the number and value of transactions with respect to 2019. However, debit and credit card payments, which are made largely by private citizens, declined compared to 2019. The incidence of payment by check contin¬ue to drop, exhibiting quite a pronounced downward trend during the past last year. To supplement to the information on electronic funds transfers, section three includes a segment (Box 4) characterizing the population with savings and checking accounts, based on data from a survey by Banco de la República con-cerning the perception of the use of payment instruments in 2019. There also is segment (Box 2) on the growth in transactions with a mobile wallet provided by a company specialized in electronic deposits and payments (Sedpe). It shows the number of users and the value of their transactions have increased since the wallet was introduced in late 2017, particularly during the pandemic. In addition, there is a diagnosis of the effects of the pandemic on the payment patterns of the population, based on data related to the use of cash in circu¬lation, payments with electronic instruments, and consumption and consumer confidence. The conclusion is that the collapse in the consumer confidence in¬dex and the drop in private consumption led to changes in the public’s pay¬ment patterns. Credit and debit card purchases were down, while payments for goods and services through electronic funds transfers increased. These findings, coupled with the considerable increase in cash in circulation, might indicate a possible precautionary cash hoarding by individuals and more use of cash as a payment instrument. There is also a segment (in Focus 3) on the major changes introduced in regulations on the retail-value payment system in Colombia, as provided for in Decree 1692 of December 2020. The fourth section of this report refers to the important innovations and tech¬nological changes that have occurred in the retail-value payment system. Four themes are highlighted in this respect. The first is a key point in building the financial infrastructure for instant payments. It involves of the design and im¬plementation of overlay schemes, a technological development that allows the various participants in the payment chain to communicate openly. The result is a high degree of interoperability among the different payment service providers. The second topic explores developments in the international debate on central bank digital currency (CBDC). The purpose is to understand how it could impact the retail-value payment system and the use of cash if it were to be issued. The third topic is related to new forms of payment initiation, such as QR codes, bio¬metrics or near field communication (NFC) technology. These seemingly small changes can have a major impact on the user’s experience with the retail-value payment system. The fourth theme is the growth in payments via mobile tele¬phone and the internet. The report ends in section five with a review of two papers on applied research done at Banco de la República in 2020. The first analyzes the extent of the CRCC’s capital, acknowledging the relevant role this infrastructure has acquired in pro¬viding clearing and settlement services for various financial markets in Colom¬bia. The capital requirements defined for central counterparties in some jurisdic¬tions are explored, and the risks to be hedged are identified from the standpoint of the service these type of institutions offer to the market and those associated with their corporate activity. The CRCC’s capital levels are analyzed in light of what has been observed in the European Union’s regulations, and the conclusion is that the CRCC has a scheme of security rings very similar to those applied internationally and the extent of its capital exceeds what is stipulated in Colombian regulations, being sufficient to hedge other risks. The second study presents an algorithm used to identify and quantify the liquidity sources that CUD’s participants use under normal conditions to meet their daily obligations in the local financial market. This algorithm can be used as a tool to monitor intraday liquidity. Leonardo Villar Gómez Governor