The impact of solid and liquid wastes from a rural town on the Chorobamba River Oxapampa, Peruvian Amazon

The goal of this study was to determine the instantaneous vs. integrated effects of waste on the water quality of the Chorobamba River. I sampled 9 stations upstream and downstream of the Town of Oxapampa, Peru during the dry season (June-August) of 2004. I measured in-situ parameters such as pH, DO, temperature, etc. as well as vegetation, riverbank erosion, nutrients (N03, NH4, P04), coliform bacteria and macroinvertebrate communities to determine the current conditions of the river, as well as the integrated effects of pollution. Although water quality conditions remained stable, high fecal coliform concentrations and macroinvertebrate communities indicate deterioration in river health over a longer period of time. If riparian areas along the Chorobamba continue to decrease and if inputs of sewage into the rivers continue to increase, as a function of population, then, conditions will continue to deteriorate in the coming years.

A Modeling Approach to Determine the Impacts of Land Use and Climate Change Scenarios on the Water Flux of the Upper Mara River

With the flow of the Mara River becoming increasingly erratic especially in the upper reaches, attention has been directed to land use change as the major cause of this problem. The semi-distributed hydrological model Soil and Water Assessment Tool 5 (SWAT) and Landsat imagery were utilized in the upper Mara River Basin in order to 1) map existing field scale land use practices in order to determine their impact 2) determine the impacts of land use change on water flux; and 3) determine the impacts of rainfall (0%, ±10% and ±20%) and air temperature variations (0% and +5%) based on the Intergovernmental Panel on Climate Change projections on the water flux of the 10 upper Mara River. This study found that the different scenarios impacted on the water balance components differently. Land use changes resulted in a slightly more erratic discharge while rainfall and air temperature changes had a more predictable impact on the discharge and water balance components. These findings demonstrate that the model results 15 show the flow was more sensitive to the rainfall changes than land use changes. It was also shown that land use changes can reduce dry season flow which is the most important problem in the basin. The model shows also deforestation in the Mau Forest increased the peak flows which can also lead to high sediment loading in the Mara River. The effect of the land use and climate change scenarios on the sediment and 20 water quality of the river needs a thorough understanding of the sediment transport processes in addition to observed sediment and water quality data for validation of modeling results.

Land Use and Climate Change Impacts on the Hydrology of the Upper Mara River Basin, Kenya: Results of a Modeling Study to Support Better Resource Management

Some of the most valued natural and cultural landscapes on Earth lie in river basins that are poorly gauged and have incomplete historical climate and runoff records. The Mara River Basin of East Africa is such a basin. It hosts the internationally renowned Mara-Serengeti landscape as well as a rich mixture of indigenous cultures. The Mara River is the sole source of surface water to the landscape during the dry season and periods of drought. During recent years, the flow of the Mara River has become increasingly erratic, especially in the upper reaches, and resource managers are hampered by a lack of understanding of the relative influence of different sources of flow alteration. Uncertainties about the impacts of future climate change compound the challenges. We applied the Soil Water Assessment Tool (SWAT) to investigate the response of the headwater hydrology of the Mara River to scenarios of continued land use change and projected climate change. Under the data-scarce conditions of the basin, model performance was improved using satellite-based estimated rainfall data, which may also improve the usefulness of runoff models in other parts of East Africa. The results of the analysis indicate that any further conversion of forests to agriculture and grassland in the basin headwaters is likely to reduce dry season flows and increase peak flows, leading to greater water scarcity at critical times of the year and exacerbating erosion on hillslopes. Most climate change projections for the region call for modest and seasonally variable increases in precipitation (5–10 %) accompanied by increases in temperature (2.5–3.5 °C). Simulated runoff responses to climate change scenarios were non-linear and suggest the basin is highly vulnerable under low (−3 %) and high (+25 %) extremes of projected precipitation changes, but under median projections (+7 %) there is little impact on annual water yields or mean discharge. Modest increases in precipitation are partitioned largely to increased evapotranspiration. Overall, model results support the existing efforts of Mara water resource managers to protect headwater forests and indicate that additional emphasis should be placed on improving land management practices that enhance infiltration and aquifer recharge as part of a wider program of climate change adaptation.

Ph.D. student Greg Koch describe his research to the 2009 Midterm Review panel at TS/Ph-3

http://digitalcommons.fiu.edu/fce_lter_photos/1266/thumbnail.jpg

Comparison of Ba/Ca and d18OWATER as freshwater proxies: a multi-species core-top study on planktonic foraminifera from the vicinity of the Orinoco River mouth

Past river run-off is an important measure for the continental hydrological cycle and the as-sessment of freshwater input into the ocean. However, paleosalinity reconstructions applying different proxies in parallel often show offsets between the respective methods. Here, we compare the established foraminiferal Ba/Ca and d18OWATER salinity proxies for their capability to record the highly seasonal Orinoco freshwater plume in the eastern Caribbean. For this purpose we obtained a data set comprising Ba/Ca and d18OWATER determined on multiple spe-cies of planktonic foraminifera from core tops distributed around the Orinoco river mouth. Our findings indicate that interpretations based on either proxy could lead to different conclu-sions. In particular, Ba/Ca and d18OWATER diverge in their spatial distribution due to different governing factors. Apparently, the Orinoco freshwater plume is best tracked by Ba/Ca ratios of G. ruber (pink and sensu lato morphotypes), while d18OWATER based on the same species is more related to the local precipitation-evaporation balance overprinting the riverine freshwater contribution. Other shallow dwelling species (G. sacculifer, O. universa) show a muted response to the freshwater discharge, most likely due to their ecological and habitat prefer-ences. Extremely high Ba/Ca ratios recorded by G. ruber are attributed to Ba2+-desorption from suspended matter derived from the Orinoco. Samples taken most proximal to the freshwater source do not show pronounced Ba/Ca or d18OWATER anomalies. Here, the suspension loaded freshwater lid developing during maximum discharge suppresses foraminiferal populations. Both proxies are therefore biased towards dry season conditions at these sites, when surface salinity is only minimally reduced.

Desenvolvimento e calibração de fotômetro solar para medições da profundidade óptica por aerossóis e coluna de água precipitável

Instrumentation is a tool of fundamental importance for research in several areas of human knowledge. Research projects are often unfeasible when data cannot be obtained due to lack of instruments, especially due to impor ting difficulties and the high costs there associated. Thus, in order to collaborate with the enhancement of a national technology, a multiband hand - held sun p hotometer (FSM - 4) was developed to operate in the 500 nm, 670 nm, 870 nm and 940 nm bands. In the 500 nm, 670 nm and 870 nm bands aerosols are monitored for evaluation of the AOD (Aerosol Optical Depth), and the PWC (Precipitable Water Column) is evaluated in the 940 nm band. For the development of the mech anical and electronic parts for the FSM - 4, th e materials and componen ts should combine low cost and quality of the data collected. The calibration process utilized the Langley method (ML) and Modified Langley Method (MLM). These methods are usually applied at high altitudes in order to provide atmosp heric optical stability. This condition however can be found in low height sites as shown in the research by Liu et al. (2010). Thus, for calibration of the FSM - 4, we investigated the atmospher ic optical stability utilizing the ML and MLM at a site in the cit y of Caicó / RN, located in the s emiarid region in northeastern Brazil. This site lies in a region far aw ay from large urban centers and activities generating anthropogenic atmospheric pollution. Data for calibration of the prototype were collected usin g the FSM - 4 in two separate operations during the dry season, one in December 2012 and another in September 2013. The methodologies showed optical atmospheric instability in the studied region through the dispersion of the values obtained for the calibrati on constant. This dispersion is affected by the variability of AOD and PWC during the appl ication of the above mentioned methods . As an alternative to the descr ibed sun photometer calibration , a short study was performed using the sun photometer worldwide network AERONET/NASA (AERsol RObotic NETwork – US Space Agency), installed in Petrolina / PE in Brazil. Data were collected for three days utilizing the AERONET instruments and the FSM - 4, operating simultaneously on the same site. By way of the ML and MLM techniques, convergent test values were obtained for the calibration constants, despite the low amount of data collected. This calibration transfer methodology proved to be a viable alternative to the FSM - 4 calibration .

Sustentabilidade e gestão da pesca artesanal na costa do Semiárido Potiguar (RN), Brasil

T he socio - economy of the coastal municipalities of Rio Grande do Norte semiarid coast was analyzed th r ou g h by the actors, ant hropogenic implications, fishing environment and composition of its fish fauna, as well as the trend of product ion landed by the artisanal fleet with the aim of identifying the sustainability and management. In this study, were used participatory methodologies, monthly data of rainfall between September 2001 and December 2010; landings of the artisanal fleet during January 2001 to December 2010; and socioeconomic (IBGE, 2002/2010), (IDEMA, 2011/2012), (MPA, 2010; 2012), UNDP and MS (2013). Based on these data, we performed analysis of variance were performed using the method of Analytic Hierarchy Process (HAP) and s tatistical models of multiple regression and time series. It was identified that the occupation of the coastal and marine zone through salt industry, tourism, shrimp farming, oil and gas and wind energy reconfigured the environment and attracted new actors . Rainfall influenced the catches, of which 35% occur in the rainy season, 40% in the dry season and 25% independent. Production increased 55%, in the period analyzed , being landed in 31 ports spread over 11 municipalities, cap tured in environments mangrov e/ estuarine (23%), coastal (46%) and oceanic (31%). Despite market up 41 species, were commercialized in the region production concentrated in eight, mainly landed in Macau and Caiçara North, by vessels of small and medium - sized (motorized and sailboats) . Highlights included three species ( Hirundichthys affins , Coryphaena hippurus and Opisthonema oglinum ), which together accounted for 63.3% of the whole volume. It was found that the motorized vessels tripled in number while sailboats reduced by half. Landin gs by different types of vessels tend to increase over time, while the small sailboats vessels, decrease. The introduction of more new motorized vessels and sailboats also tend to increase production. The study concluded that GDP and HDI of coastal countie s increased however inequality persisted. The potential of artisanal fishing is in the stage “ unfavorable ” of development and the trend in fish production is to grow over time and with the entry of more vessels. However, it is urgent that the state actions to promote and enhance planning to restore fish stocks in a sustainable and profitable fisheries standards. Therefore, it is recommend the strategic use of natural resources in a sustainable development perspective.

Ecologia trófica de uma comunidade de lagartos da caatinga

The trophic ecology studies issues related to the diet of individuals within a community .The relation between the body size of the predator and the prey size, individual specialization and niche breadth are some of the issues that can be discussed by it .I collected the lizards using pitfall trap, glue and active collecting traps in a fragment of Caatinga. The most common species in this community were Tropidurus hispidus, T. semitaeniatus and Cnemidophorus ocellifer. The visits to the farm also relied on collecting invertebrates at each season to understand how the nutritional resources of lizards were presented in each one of them. I tried to answer some questions : 1) If there was a positive relation between body size of the predator and the size of prey of the community ; 2) If in different seasons the relation of body size of the predator and the maximum and/or minimum size of the prey would be positive ; 3) If species with different foraging strategies have positive relation on the size of the predatorprey relation; 4) If the seasonality would influence on the individual expertise of lizards community and more common species; 5) If the breadth of the niche would be influenced by seasonality ; 6) If more individuals with different morphology between them would present less similar diet. I found that there was indeed a positive relationship between size of prey and predator, but nonexistent related to the minimum size of prey; Among the seasons relative size of predators and prey was different for the maximum and minimum size, but was positively related only to the size of the maximum prey. And comparisons between different foraging strategies had the maximum and minimum line inclination greater than zero and different from each other; individual specialization was not influenced by seasonality and the niche breadth was wider in the dry season only to T. semitaeniatus. At last I didn't find a significant negative relationship between morphological dissimilarity and similarity of diet.

Parâmetros biológicos de Herpsilochmus pectoralis Sclater 1857 (Aves: Thamnophilidae) em fragmentos de mata atlântica do Nordeste do Brasil

The study of birds represents an important tool for the understanding of the processes involved in behavioral and morphological patterns. The species we have studied belongs to Thamnophilidae family, the third largest family restricted to the Neotropic ecozone. They are popularly known as antbirds and comprise 209 species. A large portion of the species has cryptic behavior, making the acoustic communication an important tool for maintaining contact among birds. Herpsilochmus pectoralis Sclater 1857 has evident sexual dimorphism, measured between 10 and 12 cm height and it is found in forest fragments in the Northeast and it is also categorized as vulnerable to extinction process. This study was conducted in three sandbank fragments on the east coast of the state of Rio Grande do Norte, Brazil. With the help of tape recordings between 2006 and 2012 it was possible to describe and characterize the sing of H. pectoralis. The sing from male birds has more and longer length than the female sing (16% of dimorphism). No differences were found in the dominant frequency between the sexes. We describe four types of calls from this species repertoire. Through capturing with ornithological nets between 2009 and 2012 it was possible to describe and compare the morphology of H. pectoralis. The species have shown lower corporal mass in the dry season. The young birds showed morphometric similarities in comparison to adults. The species has no accentuated dimorphism in their morphometric characteristics. The young ones with flying capabilities have morphometric characteristics of adults, even though they do not show a characteristic adult plumage. The moult pattern in the species is a characteristic of tropical birds, but it shows short reproductive period, typical of temperate species. Even being in the tropical region, the species suffers with seasonal rainfall, which influences their reproductive phenology and moult (remex and rectrix) cycle. Thus, this dissertation provides information on the biology of H. pectoralis to support the understanding of the relationship of this species to the environment and also to know the variations of morphology and vocal aspects, in order to understand patterns and general characteristics of Thamnophilidae.

Biologia reprodutiva de Mimus gilvus (Aves: Mimidae) em área de restinga no nordeste do Brasil

The thrush beach, Mimus gilvus (Aves: Mimidae) is a passerine widely distributed in Central and South America. In Brazil occurs mainly in the areas of the resting and vegetation near the beach. In southeastern Brazil this species has disappeared, mainly due to urbanization. Many attributes of their reproductive biology are unknown, especially in relation to reproductive success. During the years 2010-2011, 2011-2012 and 2014-2015 were made visits to the area of restinga forest in Centro de Lançamento da Barreira do Inferno (CLBI), located between the cities of Natal and Parnamirim-RN (5 ° 54'S 35 ° 10'W ) where they were made systematic searches to trying describe reproductive biology of the characteristics of M. gilvus, estimate their reproductive success using the Mayfield method, and identify the main factors that influence their reproductive success in environment the resting. For this, forty fifth active nests monitored were used. Only during the breeding season of 2011-2012 and 2014-2015 were made systematic visits to the study area. The reproductive period ranged August to March. Clutch size ranged from two, three and six eggs (n = 22). Broods of two eggs were more common, with an average of eggs laid per nest of 2 ± 0,51 (n = 20 nests). The incubation period was approximately 13 ± 1,9 days (n = 11 nests). The period of stay of the nestlings was approximately 11 ± 1,6 days (n = 9 nests). With approximately 11 days old the nestlings were able to leave the nest. The apparent success was 37,8% and the success estimated by Mayfield method was 26,6%. Predation was the main cause of loss of nests in the study area. The daily survival rates (TDS) were obtained from 0,9593 incubation and 0,9313 for nestling period respectively. Survival estimates for each period was 0,5827 for incubation and 0,4571 for nestling period. The cumulative average rainfall for each month influenced negatively the hatching rates of M. gilvus nests. In addition, the number hatch eggs among the most rainy season (rainy season) and the period of lowest rainfall (dry season) were different. The number of lost nests of M. gilvus was lower in scrubs than cactus, which may account for the largest number of nests of this species found in scrubs. Survival rates in nestling period were lower compared with the incubation period. The fact that the survival rates nests of M. gilvus be lower in the nestling period compared to the incubation period may result from increased activity of adults during this phase of the nest, which in turn would increase predation rates. M. gilvus seems to avoid the rainy season during their reproduction, concentrated most of their nests in periods of low rainfall.

Organic carbon sources and their transfer in a gulf of Mexico coral reef ecosystem

Coral reefs face unprecedented threats throughout most of their range. Poorly planned coastal development has contributed increased nutrients and sewage contamination to coastal waters, smothering some corals and contributing to overgrowth by macroalgae. My approach to assessing the degree to which coral reef ecosystems have been influenced by terrestrial and anthropogenic organic carbon inputs is through the use of carbon (C) and nitrogen (N) stable isotopes and lipid biomarkers in a marine protected area, the Coral Reef System of Veracruz: Parque Nacional Sistema Arrecifal Veracruzano (PNSAV) in the southwest Gulf of Mexico. Firstly, I used a C and N stable isotope mixing model and a calculated fatty acid (FA) retention factor to reveal the primary producer sources that fuel the coral reef food web. Secondly, I used lipid classes, FA and sterol biomarkers to determine production of terrestrial and marine biogenic material of nutritional quality to pelagic and benthic organisms. Finally, I used coprostanol to determine pollutant loading from sewage in the suspended particulate matter. Results indicate that phytoplankton is the major source of essential metabolite FA for marine fish and that dietary energy from terrestrial sources such as mangroves are transferred to juvenile fish, while seagrass non-essential FA are transferred to the entire food web mainly in the rainy season. Sea urchins may be the main consumers of brown macroalgae, especially in the dry season, while surgeon fish prefer red algae in both dry and rainy seasons. C and N isotopic values and the ratio C:N suggest that fertilizer is the principal source of nitrogen to macroalgae. Thus nitrogen supply also favored phytoplankton and seagrass growth leading to a better nutritional condition and high retention of organic carbon in the food web members during the rainy season when river influence increases. However, the great star coral Montastrea cavernosa nutritional condition decreased significantly in the rainy season. The nearest river to the PNSAV was polluted in the dry season; however, a dilution effect was detected in the rainy season, when some coral reefs were contaminated. In 2013, a new treatment plant started working in the area. I would suggest monitoring δ¹⁵N and the C: N ratio in macroalgae as indicators of the nitrogen input and coprostanol as an indicator of human feces pollution in order to verify the efficiency of the new treatment plant as part of the management program of the PNSAV.

Climatologia da pluviosidade na bacia hidrográfica do Rio Paranaíba

The main aim of this research was to study pluviosity in the Paranaíba Riverbasin, especially concerning the variability frame and trends. For this end, we used data from 22 pluviometric stations of the Agência Nacional da Águas- ANA(National Water Agency)spatially distributed throughout the basin area. The data comprised the years 1979-2013, which is a historical series of 35 years, and was downloaded through the ANA website and tabulated using the Hydro 1.2 software (2015) and Excel. After tabulation process were applied based methodologies for statistical analysis of annual variability, monthly, daily and seasonal rainfall in the basin beyond the trend analysis. Results of this research showed that the annual rainfall averageis 1491 mm. Seasonality is a hallmark and rainfall variability occurs spatially and temporally. Rains are accumulated in the rainy season accumulating 85% of the annual volume in the basin. In daily analysis it was found that the daily rainfall above 30 mm occur in only 3% of the time. Dry season comprises 15% of the rainfall. Trend analysis using linear regression pointed to a downward trend in rainfall in 46% of jobs, stability in 18% of posts and increased rainfall by 36%. As for the analysis using the sign test indicated that 32% of the analyzed rainfall stations showed an increasing trend of rainfall over the time series and 68% of stations showed downward trend. This research is important because shows how rainfall worksin the area of the Paranaiba basin, and may be used to develop better management of natural resources and the area through public policies for this purpose.

Prospecção química e avaliação biológica de Banisteriopsis laevifolia (Malpighiaceae)

The Banisteriopsis genus is widespread in traditional medicine. This work aims to contribute with information about the chemical composition and on the evaluation of the biological activity of the essential oil, the ethanol extract of the leaves and partitions of the Banisteriopsis laevifolia. The phytochemical screeningtest of ethanol extract and partitions of leaves indicated the presence of flavonoids, terpenoids, saponins, phenols and steroids compounds. Nitrogenous compounds, characteristic of some species of this family, were not detected. Flavonoids were the predominant metabolite, with the highest concentrations on the partitions ethyl acetate and n-butanol. The antibacterial activity, antifungal and cytotoxicity of the essetial oil, ethanol extract and partitions were assyed by microdilution broth method (MBM), where the minimum inhibitory concentrations (MIC) were calculated. The ethanol extract and partitions did not inhibit growth against to Gram positive bacteria tested, with MIC less than 400 mg L-1. For the Gram negative bacteria tested, the hexane and hydroethanol partitios were more effective against F. nucleatum bacteria (MIC 100 ug mL-1). The ethanol extract showed antifungal activity with MIC of 31.2 mg L-1. Ethyl acetate and n-butanol partitions showed MIC 187.5 mg L-1 and 93.7 mg L-1, respectively, arousing interest for isolation studies. The antioxidant activity was evaluated by the DPPH free radical method. The ethanolic extract, ethyl acetate and n-butanol partitions were active, since they showed EC50 values (4.53 ug mL-1, 4.07 and 8.39 ug mL-1, respectively), values equivalent to the BHT (7.3 mg L-1). The analysis by HPLC-MS/MS of the most active fractions (ethyl acetate and n-butanol) identified phenolic compounds (flavonols and phenolic acids) which exert recognized biological activity. The GC-MS analysis of the essential oils from leaves collected in two periods studied (dry and wet), showed a small variation in the number of compounds. The major classes identified for the oil collected in the dry period were aliphatic alcohols (23,4%), terpenoids (18.7%), sterols (10.4%) and long-chain alkanes (9.2%) compounds. Terpenoids (26.8%) were the major class for the rain season. The major compounds (3Z) -hexenol, phytol and untriacontano are present in the two seasons but in different amounts (19.4%, 9.8% and 7.5% during the dry season, and 17.0 %, 14.9% and 15.3% in the rainy season, respectively). The essential oil from rainy season was not effective against to the oral bacteria Gram positive and Gram negative tested. However, showed significant antifungal activity with MIC 1000 mg L-1 against Candidas. Thus, the promising results with respect to biological assays of ethanolic extract and partitions from B. laevifolia contributed to the chemical and biological knowledge of the species B. laevifolia.

Respostas ecofisiológicas de Cybistax antisyphilitica Mart. (Ipê verde) em função das alterações na intensidade de luz

Light varies widely in both time and space in forest formation of “Bioma Cerrado”. Cybistax antisyphilitica occurs in areas typical of this biome, such as cerrado sensu stricto, “cerradões”, and altered areas. The aim of this study was to understand the morphological and physiological responses of C. antisyphilitica to alterations in light intensity. Juvenile plants (5 month of age) were taken to a fragment of semideciduous forest in Uberlândia-MG, and were divided into three treatments: 50 were maintained under the canopy (UC) 20 were kept in small gap (SG) and 20 were maintained under in full sun (FS). The daily courses of chlorophyll a fluorescence were made at the beginning, middle and end of dry season in 2015. At the end of the experiment measurements of chlorophyll content, gas exchange and growth were made. The plants showed dynamic photoinhibition as exhibited by reductions on Fv/Fm close to midday at the end of the dry season. Regarding the effective quantum yield (ΔF/Fm'), plants under FS showed reduced values that coincided with the higher values of electron transport rates (ETR). Plants under FS showed higher values of net CO2 assimilation rates, stomatal conductance, transpiration rates, water use efficiency and chlorophyll content compared to plants under UC. The stem diameter, dry mass of leaves and stem, total dry mass and relative growth rate were higher in plants under FS than plants under UC. On the other hand, plants under UC showed superior values of height, specific leaf area and leaf area ratio. Our results indicate that C. antisyphilitica has plasticity to survive in the contrasting light environments of the semideciduous forests, but this species was able to growth better under full sun conditions.

Interannual and (multi-)decadal variability in the sedimentary BIT index of Lake Challa, East Africa, over the past 2200 years: assessment of the precipitation proxy

The branched vs. isoprenoid tetraether (BIT) index is based on the relative abundance of branched tetraether lipids (brGDGTs) and the isoprenoidal GDGT crenarchaeol. In Lake Challa sediments the BIT index has been applied as a proxy for local monsoon precipitation on the assumption that the primary source of brGDGTs is soil washed in from the lake's catchment. Since then, microbial production within the water column has been identified as the primary source of brGDGTs in Lake Challa sediments, meaning that either an alternative mechanism links BIT index variation with rainfall or that the proxy's application must be reconsidered. We investigated GDGT concentrations and BIT index variation in Lake Challa sediments at a decadal resolution over the past 2200 years, in combination with GDGT time-series data from 45 monthly sediment-trap samples and a chronosequence of profundal surface sediments.

Our 2200-year geochemical record reveals high-frequency variability in GDGT concentrations, and therefore in the BIT index, superimposed on distinct lower-frequency fluctuations at multi-decadal to century timescales. These changes in BIT index are correlated with changes in the concentration of crenarchaeol but not with those of the brGDGTs. A clue for understanding the indirect link between rainfall and crenarchaeol concentration (and thus thaumarchaeotal abundance) was provided by the observation that surface sediments collected in January 2010 show a distinct shift in GDGT composition relative to sediments collected in August 2007. This shift is associated with increased bulk flux of settling mineral particles with high Ti / Al ratios during March–April 2008, reflecting an event of unusually high detrital input to Lake Challa concurrent with intense precipitation at the onset of the principal rain season that year. Although brGDGT distributions in the settling material are initially unaffected, this soil-erosion event is succeeded by a massive dry-season diatom bloom in July–September 2008 and a concurrent increase in the flux of GDGT-0. Complete absence of crenarchaeol in settling particles during the austral summer following this bloom indicates that no Thaumarchaeota bloom developed at that time. We suggest that increased nutrient availability, derived from the eroded soil washed into the lake, caused the massive bloom of diatoms and that the higher concentrations of ammonium (formed from breakdown of this algal matter) resulted in a replacement of nitrifying Thaumarchaeota, which in typical years prosper during the austral summer, by nitrifying bacteria. The decomposing dead diatoms passing through the suboxic zone of the water column probably also formed a substrate for GDGT-0-producing archaea. Hence, through a cascade of events, intensive rainfall affects thaumarchaeotal abundance, resulting in high BIT index values.

Decade-scale BIT index fluctuations in Lake Challa sediments exactly match the timing of three known episodes of prolonged regional drought within the past 250 years. Additionally, the principal trends of inferred rainfall variability over the past two millennia are consistent with the hydroclimatic history of equatorial East Africa, as has been documented from other (but less well dated) regional lake records. We therefore propose that variation in GDGT production originating from the episodic recurrence of strong soil-erosion events, when integrated over (multi-)decadal and longer timescales, generates a stable positive relationship between the sedimentary BIT index and monsoon rainfall at Lake Challa. Application of this paleoprecipitation proxy at other sites requires ascertaining the local processes which affect the productivity of crenarchaeol by Thaumarchaeota and brGDGTs.