Implications of species addition and decline for nutrient dynamics in freshwaters.

In terrestrial and aquatic ecosystems, organisms directly affect nutrient storage and cycling by sequestering nutrients via growth and remineralizing nutrients via excretion and egestion. Therefore, species introductions and extirpations can profoundly affect nutrient storage and remineralization rates, and present a challenge for conserving ecosystem function in fresh waters. The literature of consumer-driven nutrient dynamics is growing rapidly, but studies of consumer effects on nutrient storage and remineralization across species and among ecosystems are limited. We compared the effects of 3 grazing taxa, nonnative armored catfish in Mexican streams, native mussels in Oklahoma streams, and native tadpoles in Panamanian streams, on nutrient storage and remineralization. We examined interactions among organismal stoichiometry and biomass, nutrient storage, remineralization rates, and ecosystem size across these 3 groups following species decline (tadpoles and mussels) or introduction (armored catfish) to gain a better understanding of organism-specific effects on nutrient dynamics among freshwater ecosystems. Collectively, our results suggest that the ecosystem-level effect of consumer-driven nutrient dynamics is strongly influenced by environmental variables and is taxon specific. Major changes in biomass of stoichiometrically distinctive organisms can lead to subsequent changes in the flux and storage of elements in an ecosystem, but the overall effect of aquatic animals on nutrient dynamics also is determined by discharge and nutrient-limitation patterns in streams and rivers

Investigação gravimétrica do complexo alcalino de Ipanema, São Paulo, Brasil

O Complexo Alcalino de Ipanema localizado na província alcalina de mesmo nome (23°27,5' S e 47°38' W) dista aproximadamente 140 km de São Paulo, e há 40 anos foi tema de estudo geofísico em programa de Doutorado. Os métodos empregados foram o gravimétrico, o magnetométrico, e o eletrorresistivimétrico (SEV). Entretanto, os dados gravimétricos então levantados não foram referenciados à Rede Gravimétrica Fundamental Brasileira, nem à Rede de Nivelamento do IBGE, o que impossibilita sua integração e utilização com outros bancos de dados. Optou-se, então, por efetuar um novo levantamento na área e adjacências, de forma a integrá-lo aos dados de levantamentos geofísicos próximos referidos às duas redes citadas, uma vez que o complexo alcalino em questão é parte de um estudo integrado desses corpos na região S-SE do Brasil. O presente estudo concentra-se no método gravimétrico, tendo como resultados a geometria do corpo em subsuperfície bem como o cálculo de seu volume.The Ipanema Alkaline Province (23°27.5'S/47°38'W), approximately 140 km west of the city of São Paulo, was the subject of a previous doctoral study employing geophysical (gravimetry, magnetics and electro-resistivity) methodologies. The gravimetric data, however, were neither referred to the Fundamental Brazilian Gravimetric Network (ON) nor to the Brazilian Reference Leveling Network (IBGE), thus preventing their integration with other data bases. As this alkaline complex is one of a number of such bodies presently under analysis in S-SE Brazil, new gravimetric data were obtained in the same and neighboring areas for integration with other geophysical surveys referred to both networks. The present study determined the geometry and volume of the buried body using solely on the basis of the gravimetric method

Métodos elétricos, eletromagnéticos e gamaespectrométricos integrados ao complexo alcalino de Pariquera-Açu (SP)

The Pariquera-Açu Alkaline Complex, located in the city of Pariquera-Açu (State of São Paulo), is one of the Brazilian alkaline complexes which has considerable mining potential. The combined use of several methods helped to determine possible areas for exploration. Geophysical prospecting methods were used to assess the exploration potential of these areas. The methods used in this study were gamma-spectrometry, induced polarization and electrical survey. Previous geophysical studies were carried out to better understand the structural evolution of the complex and were not limited to the study of the lithological variation. Gravimetric studies showed a zone of intense fenitization, which is consistent with alkaline complexes with carbonatites. A dipole-dipole survey conducted in the central part of the complex indicated the presence in the subsurface of a resistive lithology with high chargeability. These factors, together with other studies on the alkaline complex, suggest the presence of carbonatite in the area, which is corroborated by gamma spectrometry data, given the concentrations of Th (8 ppm) and U (3.5 ppm) and considering that the measurements were performed over a non-radioactive sedimentary cover.O complexo alcalino de Pariquera-Açu, localizado no município de mesmo nome (SP) representa um dos complexos alcalinos brasileiros com possibilidade de prospecção mineral. A aplicação de vários métodos integrados contribui para o conhecimento das possíveis regiões de exploração. Nesse contexto foram empregados métodos geofísicos de prospecção visando seu estudo. Os métodos aplicados nesse estudo foram o gamaespectrométrico, o eletromagnético e o elétrico. Estudos geofísicos anteriores visaram o estudo estrutural do complexo, não se atendo a delimitação das variações litológicas. Esses estudos indicaram a presença de uma forte zona de fenitização que geralmente ocorre em complexos alcalinos com presença de carbonatito. Na porção central do complexo alcalino foram aplicados os o métodos Eletrorresistivo e de Polarização Induzida (IP), com arranjo dipolo-dipolo, no qual se obteve uma imagem da resistividade e cargabilidade em subsuperfície. Os resultados do método dipolo-dipolo indicam a presença de uma litologia resistiva e com alta cargabilidade. Esses fatores somados sugerem, conjuntamente a outros estudos do complexo alcalino, a presença do carbonatito nesse local. A gamaespectrometria subsidia essa afirmação através dos valores de concentração dos elementos radioativos, sendo de 8 ppm para o Tório, e de 3.5 ppm para o Urânio, mesmo sendo tomadas medidas sobre a cobertura sedimentar, de baixa radioatividade

Resultados geofísicos integrados de um corpo com geometria 3D sem manifestação superficial

O levantamento aerogeofísico SP-RJ do Serviço Geológico do Brasil (CPRM) evidencia uma anomalia magnética, sem correspondentes geológicos em superfície, mas com feições semelhantes àquelas observadas para os complexos alcalinos que afloram na mesma região. Diante da ausência de elementos superficiais, foram utilizadas diferentes técnicas geofísicas para caracterizar a fonte dessa anomalia. Entre as diferentes metodologias, utilizou-se a análise de imagens de satélite para diferentes bandas espectrais, sondagens sísmicas, levantamento gravimétrico e correspondente magnético em superfície ao longo de um perfil que corta a anomalia, além de medidas de densidade e susceptibilidade das diferentes litologias da área. As informações resultantes da aplicação dessas técnicas serviram como vínculos para modelar simultaneamente os dados gravimétricos e magnéticos de superfície com geometria 2½D, e para modelar os dados magnéticos do levantamento aéreo com geometria 3D. Os resultados obtidos convergem para um corpo intrusivo máfico de cerca 3,3 x 10(9) t, próximo da superfície (~ 40 m) e estendendo-se até a profundidade máxima de 1 km.Airborne geophysical data of the SP-RJ survey carried out by the Brazilian Geological Survey (CPRM) reveal a magnetic anomaly without geological expression at the surface. The anomalous features are similar to those associated with alkaline complexes that outcrop in the same region. The absence of surface elements motivated the use of different geophysical methods to characterize the magnetic anomaly source. Among these methods, satellite images for different spectral bands were used, seismic sounding, gravity and ground magnetic surveys along a profile crossing the anomaly were performed, and density and susceptibility measurements of different rock types in the area were made. The obtained results were used to constrain 2½D simultaneous gravity and magnetic modeling and 3D airborne magnetic modeling. Both results indicate the presence of a body of about 3.3 x 10(9) metric tons, having its top at 40 meters from the surface and extending to a maximum depth of 1 km

Neotropical freshwater crabs (Decapoda: Pseudothelphusidae) shred leaves

Freshwater crabs are macroconsumers that are commonly found in Neotropical headwater streams that may play a key role in energy flow and nutrient cycling in detrital food webs. Although studies have examined the feeding habits of trichodactylid crabs, little is known of this behavior in pseudothelphusid species, and specifically whether they actually consume leaf material. We conducted three nine-day laboratory trials with pseudothelphusid crabs (Ptychophallus tumimanus (Rathbun, 1898)) and leaves (Koanophyllon pittieri) to investigate whether crabs shred leaves. We hypothesized that leaf mass loss would be faster with crabs present relative to control tanks with only leaves. Leaf mass loss was significantly higher (p < 0.001) in tanks with crabs (0.49 ± 0.07 g, mean ± 1 SD) compared to control tanks (0.31 ± 0.05 g). We observed crabs manipulating, shredding, and consuming leaves, with leaf fragments and egesta present in tanks with crabs but not in control tanks. Their consumption and egestion activity may affect nutrient availability and transformation by stimulating microbial activity during leaf breakdown and converting coarse particulate organic matter (CPOM) to fine particulate organic matter (FPOM). Therefore, freshwater crabs need to be considered when studying energy flow and nutrient cycling in detrital food webs of Neotropical headwater streams.UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR)UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Evidence for the Persistence of Food Web Structure After Amphibian Extirpation in a Neotropical Stream

Species losses are predicted to simplify food web structure, and disease‐driven amphibian declines in Central America offer an opportunity to test this prediction. Assessment of insect community composition, combined with gut content analyses, was used to generate periphyton–insect food webs for a Panamanian stream, both pre‐ and post‐amphibian decline. We then used network analysis to assess the effects of amphibian declines on food web structure. Although 48% of consumer taxa, including many insect taxa, were lost between pre‐ and post‐amphibian decline sampling dates, connectance declined by less than 3%. We then quantified the resilience of food web structure by calculating the number of expected cascading extirpations from the loss of tadpoles. This analysis showed the expected effects of species loss on connectance and linkage density to be more than 60% and 40%, respectively, than were actually observed. Instead, new trophic linkages in the post‐decline food web reorganized the food web topology, changing the identity of “hub” taxa, and consequently reducing the effects of amphibian declines on many food web attributes. Resilience of food web attributes was driven by a combination of changes in consumer diets, particularly those of insect predators, as well as the appearance of generalist insect consumers, suggesting that food web structure is maintained by factors independent of the original trophic linkages

Geophysical investigation of alkalis rocks in south and southeast from Brazil

Os complexos alcalinos de forma geral geralmente apresentam trabalhos de cunho geológico. Raramente são apresentados estudos que englobam vários complexos alcalinos. Almeida e Ulbrich são autores que conseguiram realizar o estudo de vários complexos do ponto de vista tectônico e petrográfico. Este trabalho teve como objetivo analisar, do ponto de vista geofísico, vários complexos alcalinos. Como o número de complexos localizados no Brasil é enorme, houve uma dificuldade em analisar um numero muito grande, haja visto que para analisar os complexos é necessário coletar dados sobre os corpos. Nesse trabalho são apresentados dados gravimétricos e magnéticos sobre 12 complexos alcalinos. Em alguns casos não houve resposta gravimétrica de alguns complexos alcalinos, no entanto o magnético geralmente apresentou resposta, já que a maior parte desses complexos é enriquecido em minerais ferrimagnéticos. Poços de Caldas foi uma exceção não apresentando resposta magnética equivalente aos demais complexos estudados. Alguns parâmetros como massa e volume foram determinados através do modelamento 3D dos dados gravimétricos e magnéticos. A distribuição de massa para cada complexo alcalino modelado indica a tendência de alojamento de cada corpo ao longo de estruturas como falhas, zonas de charneira, arcos, entre outros. Cada complexo foi estudado independentemente formando capítulos independentes.The alkaline complexes are show in this work, bring of geophysical analyses. Rarely are presented studies that encompass several alkaline complexes. Almeida and Ulbrich are authors who have achieved the study of various complexes of the viewpoint, and tectonic petrographic. This study aimed to analyze several complex using geophysical methods, as well as, gravity, magnetics, radiometric and remote sensor. As the number of complex located in Brazil is enormous, there a difficulty in analyzing a very large number, knowing that to analyze complexes is necessary to collect data on the bodies. In this work are presented on gravity and magnetic data 12 alkaline complexes. In some cases there was no response gravimetric some complexes alkali, but the magnetic usually presented response, since most of these complexes is enriched in minerals ferrimagnetic. Wells Caldas was an exception showing no response magnetic equivalent to the other complexes studied. Some parameters such as mass and volume were determined via 3D modeling of gravity and magnetic data. The mass distribution for each modeled alkaline complex indicates the tendency of each housing body over structures such as faults, zones hinge arches, among others. Each complex was studied independently forming chapters independente

INFLUENCES OF DISEASE-DRIVEN AMPHIBIAN DECLINES ON ECOSYSTEM STRUCTURE AND FUNCTION IN PANAMANIAN HEADWATER STREAMS

Understanding relationships between biodiversity and ecosystem function is a critical challenge, particularly in freshwater ecosystems where species losses are occurring at unprecedented rates. There is a particular need to examine these relationships in natural settings at large spatial scales. Ongoing, disease-driven amphibian declines may influence the structure and function of stream ecosystems, but little is known of the potential roles of stream-dwelling tadpoles in consumer-resource dynamics, ecosystem functions such as decomposition, and ecosystem-level biogeochemical cycling. Tadpoles in tropical streams likely regulate flows and ratios of nitrogen (N), phosphorus (P), and carbon (C), influencing ecosystems by altering nutrient supplies to other animals and their food resources. I used ecological stoichiometry as a framework to assess how the sudden loss of consumer biodiversity in neotropical headwater streams affected ecosystem function. I quantified N and P excretion and C:N:P ratios of tadpoles, macroinvertebrates, and food resources in healthy sites (pre-decline) and sites where disease-driven amphibian declines had occurred (post-decline). I tested the hypothesis of consumer homeostasis (i.e., that organisms maintain consistent body nutrient ratios by altering excretion chemistry) over a range of taxa and size classes. I also used mesocosms in a natural stream setting to quantify the effects of grazing tadpoles, shredding macroinvertebrates and a combination of the two on leaf decomposition and associated microbial activity. Finally, I examined macroinvertebrate community structure and quantified biomass and nutrient storage in tadpoles, macroinvertebrates, and basal resources in pre-decline and post-decline sites. I also measured excretion rates, volumetric excretion, and nutrient turnover for both tadpoles and macroinvertebrates. Patterns of consumer-resource stoichiometry varied with the presence or absence of tadpoles. There were higher concentrations of C, N, and P in basal resources in pre-decline sites compared to post-decline sites, but little variation in elemental ratios among sites. Elemental composition and molar ratios in grazers and shredders varied, with pronounced differences in %N for gatherers and filterers across sites. Macroinvertebrate grazer elemental composition was higher for all elements and had lower C:N, N:P, and C:P molar ratios in pre-decline sites compare to grazers in post-decline sites, while shredders showed the opposite pattern. There were differences in both taxon-specific allometric and stoichiometric relationships in tadpoles and macroinvertebrates between pre- and post-decline sites. Body P content was a good predictor of tadpole P excretion and tadpoles in pre-decline sites excreted more P per unit body P than those in post decline sites. Individuals deviated from strict homeostasis, and the degree of deviation varied among taxa. Tadpoles also affected leaf decomposition by influencing microbial communities and altering shredding macroinvertebrate feeding. Higher respiration rates of leaf discs in chambers with tadpoles suggested that tadpoles enhanced microbial activity by excreting nutrients through feeding and excretion. Shredders alone had little effect on respiration rates, indicating that tadpoles play an important and unique role in enhancing microbial activity and litter decomposition. Leaf area loss was greatest when tadpoles and macroinvertebrates were together, indicating facilitation. Macroinvertebrates are important nutrient recyclers in neotropical headwater streams, but their role is greatly decreased in the absence of larval amphibians. I measured ~80% lower standing stocks and storage of C, N, and P in basal resources in post-decline compared to pre-decline sites. Storage of C, N, and P in both tadpoles and macroinvertebrates also decreased in post-decline sites. I also observed 98% decreases in tadpole nutrient excretion and egestion rates, and an additional decrease in macroinvertebrate excretion rates (~80%) for both N and P in post-decline versus pre-decline sites. These decreases led to \u3e8,000% increase in the distance that it took tadpoles to turn over the ambient N pools in post-decline sites, and a 130% increase for macroinvertebrates. Similar patterns were evident for P turnover, with turnover distance increasing by 6,000% and 400% in post-decline sites for tadpoles and macroinvertebrates, respectively. My results indicate that N and P excretion by both tadpoles and macroinvertebrates constitute significant nutrient fluxes in these headwater streams. Both tadpole and macroinvertebrate communities were excreting nutrients at similar rates in pre-decline sites, suggesting that they were playing equally significant roles in their contribution to ecosystem demand. My results demonstrate that tadpoles are important consumers in Neotropical headwater streams and their loss significantly alters stream food webs and ecosystem functions

Geophysical investigation of alkalis rocks in south and southeast from Brazil

Os complexos alcalinos de forma geral geralmente apresentam trabalhos de cunho geológico. Raramente são apresentados estudos que englobam vários complexos alcalinos. Almeida e Ulbrich são autores que conseguiram realizar o estudo de vários complexos do ponto de vista tectônico e petrográfico. Este trabalho teve como objetivo analisar, do ponto de vista geofísico, vários complexos alcalinos. Como o número de complexos localizados no Brasil é enorme, houve uma dificuldade em analisar um numero muito grande, haja visto que para analisar os complexos é necessário coletar dados sobre os corpos. Nesse trabalho são apresentados dados gravimétricos e magnéticos sobre 12 complexos alcalinos. Em alguns casos não houve resposta gravimétrica de alguns complexos alcalinos, no entanto o magnético geralmente apresentou resposta, já que a maior parte desses complexos é enriquecido em minerais ferrimagnéticos. Poços de Caldas foi uma exceção não apresentando resposta magnética equivalente aos demais complexos estudados. Alguns parâmetros como massa e volume foram determinados através do modelamento 3D dos dados gravimétricos e magnéticos. A distribuição de massa para cada complexo alcalino modelado indica a tendência de alojamento de cada corpo ao longo de estruturas como falhas, zonas de charneira, arcos, entre outros. Cada complexo foi estudado independentemente formando capítulos independentes.The alkaline complexes are show in this work, bring of geophysical analyses. Rarely are presented studies that encompass several alkaline complexes. Almeida and Ulbrich are authors who have achieved the study of various complexes of the viewpoint, and tectonic petrographic. This study aimed to analyze several complex using geophysical methods, as well as, gravity, magnetics, radiometric and remote sensor. As the number of complex located in Brazil is enormous, there a difficulty in analyzing a very large number, knowing that to analyze complexes is necessary to collect data on the bodies. In this work are presented on gravity and magnetic data 12 alkaline complexes. In some cases there was no response gravimetric some complexes alkali, but the magnetic usually presented response, since most of these complexes is enriched in minerals ferrimagnetic. Wells Caldas was an exception showing no response magnetic equivalent to the other complexes studied. Some parameters such as mass and volume were determined via 3D modeling of gravity and magnetic data. The mass distribution for each modeled alkaline complex indicates the tendency of each housing body over structures such as faults, zones hinge arches, among others. Each complex was studied independently forming chapters independente