Lagoa Santa Karst Research Articles

Groundwater flow modelling in Neoproterozoic carbonate karst based on dye tracer pathways

The current study consisted of the development of a hydrogeological numerical model in the Lagoa Santa Karst Environmental Protection region, in order to represent the conduit-flow karst springs in the most well-studied karst system in Brazil. Once carbonate aquifers are characterized by a complex 3D pattern with a combination of a double porosity of matrix and conduits, two different modelling approaches were used: Equivalent Porous Medium (EPM), based on Darcy’s law, to represent laminar flow in the fractured massif and Conduit Network (CN), using Manning-Stricker Law and the discrete feature tool, to represent the karst conduits with turbulent flow. Modeling was calibrated in a steady-state and simulations of groundwater flow and an evaluation of water exchanges between the karstic aquifer and the other hydrogeological units, were conducted. The model was developed based on data available for many studies carried out in the area, including tracer-derived route data. The calibration results for spring discharges, water levels and mass balance were satisfactory and aligned with modeling good practices. In turn, the hydraulic conductivities and recharge rates obtained by back-analysis were in agreement with literature references. The regional groundwater flow was well represented and indicated how external water entrances can be relevant to explain the higher discharge rates observed in some karstic springs. In addition, the representation of conduits allowed for the simulation of tracer pathways, enabling the inference of potential flow rates to the karstic springs from the particle simulations.

Two new cavernicolous species of Pseudochthonius Balzan, 1892 (Pseudoscorpiones, Chthoniidae) from Lagoa Santa karst, Minas Gerais, Brazil

Two new pseudoscorpion species of the genus Pseudochthonius Balzan, 1892 are described from caves in the Lagoa Santa karst area in Southeast Brazil. Pseudochthonius limettioides sp. nov. was collected in ten caves and is a troglobite that lacks eyes and body pigmentation. Pseudochthonius lundi sp. nov. was collected in three caves and is considered a troglophile with only one pair of eyes. Both species might be threatened by mining projects and more studies are needed to better understand many aspects of their biology.

Characterization and classification of lakes based on geospatial analyses in the karst hydrogeological system of the Bambuí group, Lagoa Santa, Minas Gerais, Brazil

The karst of Lagoa Santa is a protected area located near the city of Belo Horizonte, in Minas Gerais state (Brazil), namely Lagoa Santa Karst Environmental Protection Area (EPA), one of the main research areas related to archeology, paleontology, speleology and hydrogeology in the Brazilian territory. The region is comprised by several lakes, because of its complex water system due to karst evolution. In addition, the karstic nature of the rocks in the region allows the existence of several other typical dissolution morphologies, such as: caves, speleothems, sinkholes, uvalas, among others. The morpho-structural characteristics, combined with the local geology, can provide important information about the behavior of lakes in view of the cycles of expansion and retraction of the water surface. Thus, this work aims to understand the water dynamics of the lakes present in the Karst of Lagoa Santa through analysis of spatial data between the years 1984 and 2020. Based on the surveys, 153 lakes were identified in the study region in the last 35 years: 40 perennial lakes, 89 intermittent lakes, 19 new lakes and 5 lakes that dried up completely. Also, this study compares the relationship of each lake with the type of relief depressions (Sinkhole or Uvala), rock masses and the main negative structural lineaments. The data obtained allowed the identification of which characteristics are diagnostic for perenniality or intermittence of existing lakes in the region, as well as the grouping of existing lakes into subgroups with similar geological and morpho-structural characteristics. The most important characteristics to define the water dynamics on lakes are the evolutionary state in karst depressions and the presence of structural lineaments, in which in more evolved depressions (uvalas) the lakes tend to be intermittent and in less evolved depressions (sinkholes) the lakes tend to be perennial. Finally, the water bodies associated with structural lineaments may be the condition for the permanence of water in some depressions, mainly in lakes over non-carbonate formations existing in the region.

Evaluation of recharge estimation methods applied to fissure and karst aquifers of the Lagoa Santa Karst Environmental Protection Area, Brazil

AbstractThe Lagoa Santa Karst Environmental Protection Area is known worldwide as the place where the oldest human fossil in the Americas was found. Beyond its archaeological richness is speleological, faunistic and floristic richness across this remarkable karstic landscape. It is also a region with important aquifers for public and private water supply. Located in the state of Minas Gerais, Brazil, despite its environmental relevance, the area is characterized by increased anthropic environmental impacts. Regarding the relationship between surface water and groundwater, in order to investigate the annual input of water into the aquifers, this study aimed to estimate the annual recharge rate in the hydrological years 2017 to 2021 using three methods: the recession curve displacement method of Rorabaugh (International Association of Scientific Hydrology, 1964, 63:432–441), the recursive digital filter method by Lyne and Hollick (Institute of Engineers Australia National Conference, 1979, pp. 89–93), and the method based on water‐table fluctuation in tubular wells proposed by Healy and Cook (Hydrogeology Journal, 2002, 10(1):91–109). The average percentage of rainfall that is recharged into the aquifer, considering the overall period studied from 2017 to 2021, found with the three methods was 13%, 9% and 9%, respectively, which indicates that recharge rates within the study area are low and that higher values are observed within karst basins in comparison with basins located in pelitic zones. Overall, the methods yielded coherent values among each other and were compared with previous studies in the area. In relation to the automatized recursive digital filter method, the automatized recession curve displacement method was more adherent because it considers daily streamflow measurements. The WTF method was handy for the local recharge rate analysis and enabled an evaluation of recharge rates in each aquifer unit. Despite the similarity of the values obtained in the methods, they are likely underestimated due to the high pumping rates of groundwater. Furthermore, it is recommended to deepen the correlation between lithotype, karst geomorphology, and its dissolution processes to improve the understanding of recharge processes.

Cervidae and Tayassuidae of the Late Pleistocene from the Cuvieri Cave, Eastern Brazil

The Pleistocene of the eastern Brazilian territory is characterized by a great diversity of extinct and living mammals. The Cuvieri Cave, part of the Lagoa Santa karst complex, presents an abundant amount of osteological material dated from the Pleistocene, resulting in an important record of changes in faunal composition and environmental settings. In this cave, Cervidae are represented by two extant species: Mazama americana and Mazama cf. gouazoubira, while the Tayassuidae family is the most abundant of Pleistocene macrovertebrates and is represented by two species. One of the species was identified as Dicotyles tajacu, showing anatomical features larger than recent specimens from the same region, but similar in size to Amazonian specimens. The most common observed species could not be identified and is much larger than the living Tayassu pecari, the largest Tayassuidae in the region and to the Pleistocene deposits of Cuvieri Cave. The Cervidae species are the same observed in the Holocene, but the differences of the Tayassuidae in relation to the living specimens suggest that paleoenvironmental changes occurred after the deposition.

Características do solo na APA Carste de Lagoa Santa (MG) e seu papel na infiltração de potenciais contaminantes

Os solos podem ser conceituados de acordo com o ramo da ciência que o estuda. Entretanto, é ponto comum o fato de que é formado sob influência do clima, organismos, material de origem, relevo e tempo e o fato de recobrirem as rochas, mantendo a vida animal e vegetal na biosfera. Em muitos casos, o material de origem ou rocha matriz é fator de formação de maior importância. No entanto, quando se trata de solos sobre o carste, sua formação ainda é motivo de controvérsias. No caso dos solos da APA Carste de Lagoa Santa, percebe-se que são solos profundos, de estrutura granular e ultra fina granular. Também se apresentam em blocos cuja relação sólido-vazios é bem diferenciada dos solos de influência direta dos carbonatos. Na região, em geral, possuem pH majoritariamente ácido que, aliados à dominância da caulinita e oxi-hidróxidos de ferro e alumínio na mineralização da fração argila, proporcionam taxas de infiltração da ordem de 10-3 a 10-5 cm.s-1 , fato que pode levar a um risco adverso muito maior às águas subterrâneas. Assim sendo, é objetivo desta pesquisa a discussão desses pontos.

Comportamento hídrico das depressões cársticas da região de Lagoa Santa, MG

As depressões cársticas se configuram como importantes feições dissolutivas presentes principalmente em regiões calcárias. À luz da típica geomorfologia e hidrogeologia cárstica, este trabalho apresenta as investigações realizadas nas depressões cársticas situadas sobre as rochas pelito carbonáticas do Grupo Bambuí, localizadas nos arredores da Área de Proteção Ambiental (APA) Carste Lagoa Santa (MG). As investigações tiveram como principal objetivo a compreensão do comportamento e desempenho hídrico das 393 depressões cársticas detectadas a partir de Modelo Digital de Elevação (MDE) derivado de uma imagem do satélite ALOS PALSAR. As etapas se constituíram fundamentalmente de geoprocessamento em ambiente SIG, foto observação através de imagens do Google Earth Pro, classificação supervisionada em imagens multiespectrais dos satélites Landsat registradas em quatro períodos hidrológicos distintos (ano com índice pluviométrico normal e ano atipicamente seco). O coeficiente de Kappa e acurácia geral indicaram que as classificações supervisionadas realizadas obtiveram resultados excelentes. As análises estatísticas multivariadas revelaram que a presença de lagoas no interior das depressões cársticas após o período de estiagem em ano hidrológico normal ou em ano de excepcional stress hídrico está relacionada com a morfologia e morfoestrutural. Isto é, as depressões maiores, com grandes profundidades, altos índices de eixos de alongamento e grandes áreas de maciços calcários em seus interiores são aquelas mais favoráveis a possuírem água em seus interiores.

Análise dos fluxos nos aquíferos cárstico-fissurais da região da APA Carste de Lagoa Santa, MG

A área de estudos, que engloba a Área de Proteção Ambiental (APA) Carste de Lagoa Santa, se estende por 504 km2. Nesta região, ocorrem os metacalcários da Formação Sete Lagoas, composta pelos membros Pedro Leopoldo e Lagoa Santa, os quais acomodam os aquíferos cárstico-fissurais. O método de estudo envolveu o levantamento de estruturas rúpteis e de dissolução cárstica em uma malha de 9.000 m2, escala 1:300.000, com a finalidade de analisá-las e associá-las com as direções de cavernas e com direções de fluxos da água subterrânea comprovadas por testes de traçadores corantes (E-W, NE e SE), de sentido oriental. Por toda a área, a preponderância sistemática de cavernas e paleocondutos reliquiares na direção N70-90W, com caimento suave para leste, indica que esses paleocondutos resultam da dissolução ao longo da interseção das fraturas E-W, de alto ângulo, com o plano de acamamento suave, de direção NNW. Fraturas de alto ângulo de direção NE e SE também são frequentes, contudo, são raras as exposições dos paleocondutos e cavernas correlatos. Em contrapartida, embora as cavernas N-S se destaquem como mais persistentes e alongadas, assim como as E-W, não se observaram fluxos de água naquela direção (N-S). Os resultados demonstram que os parâmetros estruturais primordiais, as fraturas de alto ângulo e o acamamento, condicionam os fluxos subsuperficiais em condutos de cavernas ainda ativos no sentido oriental. No entanto, não se descarta a possibilidade de ocorrerem circulações profundas em segmentos N-S não observáveis nas zonas superiores.

New fossil remains of Quaternary capybaras (Rodentia: Caviomorpha: Caviidae) from the intertropical region of Brazil: morphology and taxonomy

In this work, new fossils of Hydrochoerinae rodents (Caviomorpha: Caviidae: Hydrochoerinae) from the Quaternary of the intertropical region of Brazil are described, almost 180 years after the first fossils of these animals were found in Lagoa Santa, Minas Gerais. The fossils studied herein were collected in caves of States of Bahia (Toca dos Ossos and Lapa dos Brejões) and Minas Gerais (Lapa Vermelha cave, Lagoa Santa karst). The analyzed material is assigned to the extinct large rodent Neochoerus sulcidens and is composed of skull portion, upper and lower cheek teeth, mandible, humerus, innominate, femur, tibia, and calcaneus. The specimens were assigned to this taxon based on the presence of an M3 with 14 prisms; incisor alveolus reaching the pr. II do m2; anteriormost level of the palatine at the level of the Pr. II of the M2; and larger size than the living species. The p4 is mesiodistally longer than the m1 and m2, distinct from previous interpretations in which the mesiodistal length of the p4 of N. sulcidens would be smaller than the m2, indicating the presence of a variable character. Except for the differences in size, the postcranial bones of N. sulcidens are quite similar to H. hydrochaeris.

Cave protection as a Karst conservation tool in the environmentally sensitive Lagoa Santa Karst, Southeastern Brazil

Karst areas in densely populated and industrialized areas in Brazil are under severe environmental pressure due to urbanization, quarrying, groundwater pollution, groundwater overpumping and cave vandalism. Although karst terrains receive no specific protection according to Brazilian environmental law, caves, regardless of rock type, are classified as belonging to the society, and must be studied in detail to have their significance (and related level of protection) determined. Most caves (>90 %) are of either maximum or high significance, which results in protection of not only the cave but also of an associated buffer zone. Given the very conservative definition of cave (a natural void large enough to allow a human being to enter), hundreds of caves will exist in any given outcrop and the amalgamation of buffer zones tends to yield an integrated area that covers most of the karst surface. In the Lagoa Santa Karst, Brazil’s most urbanized and industrialized karst area, cave preservation is presently the most effective approach to protecting karst heritage. However, other karst features not connected to existing caves (e.g., covered karst, karst aquifers with no accessible caves, dolines with no associated caves) receive no specific protection. Although this heterogeneous level of protection may yield non-preserved karst areas, the remaining zones tend to be surrounded by protection belts, imposing severe restrictions on urban and mining development and associated sources of potential damage.Key words: Environmental policy, cave protection, karst preservation, Lagoa Santa Karst.

Solanum lagoense (Solanaceae, Geminata clade), a new species from Lagoa Santa, Minas Gerais State, Brazil.

A new species of Solanum (Solanaceae) from the Geminata clade is described for the Brazilian flora. Solanum lagoense Stehmann is only known from Lapinha, a rocky massif located in the Lagoa Santa karst region of Minas Gerais State. The flora of this area, including Solanaceae, was studied in detail in the second half of the 19th century by the Danish botanist Eugene Warming. The species differs from other members of the Geminata clade in Brazil in its geminate leaves of different sizes, simple multicellular trichomes present on the new growth and young stems, short extra-axillary inflorescences with few (1-3) flowers, and its stellate corollas with cucullate and strongly reflexed lobes. Here we present a description, taxonomic comments and a preliminary assessment of conservation status of this critically endangered species.

The Oldest Case of Decapitation in the New World (Lapa do Santo, East-Central Brazil).

We present here evidence for an early Holocene case of decapitation in the New World (Burial 26), found in the rock shelter of Lapa do Santo in 2007. Lapa do Santo is an archaeological site located in the Lagoa Santa karst in east-central Brazil with evidence of human occupation dating as far back as 11.7–12.7 cal kyBP (95.4% interval). An ultra-filtered AMS age determination on a fragment of the sphenoid provided an age range of 9.1–9.4 cal kyBP (95.4% interval) for Burial 26. The interment was composed of an articulated cranium, mandible and first six cervical vertebrae. Cut marks with a v-shaped profile were observed in the mandible and sixth cervical vertebra. The right hand was amputated and laid over the left side of the face with distal phalanges pointing to the chin and the left hand was amputated and laid over the right side of the face with distal phalanges pointing to the forehead. Strontium analysis comparing Burial 26’s isotopic signature to other specimens from Lapa do Santo suggests this was a local member of the group. Therefore, we suggest a ritualized decapitation instead of trophy-taking, testifying for the sophistication of mortuary rituals among hunter-gatherers in the Americas during the early Archaic period. In the apparent absence of wealth goods or elaborated architecture, Lapa do Santo’s inhabitants seemed to use the human body to express their cosmological principles regarding death.

Early Holocene human skeletal remains from Cerca Grande, Lagoa Santa, Central Brazil, and the origins of the first Americans

We present the results of comparative multivariate morphological analyses based on nine skulls from Cerca Grande. The site is in the Lagoa Santa karst in Central Brazil, a key area for understanding the peopling of the Americas. The region has several archaeological sites with excellent preservation of late Pleistocene and early Holocene material culture and human skeletal remains. Stratigraphic association and direct dating of the Cerca Grande human skeletons place them definitely in the Early Holocene (c. 9000 bp uncalibrated). Principal components analysis and Mahalanobis distances reveal that these skeletons have no morphological affinities with present-day Native Americans or East Asians. These results agree with other studies and suggest that the skeletons may derive from a wave of migrants that entered the New World before the characteristic 'Mongoloid' morphology spread throughout East Asia.