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The aim of this study was to test the hypothesis that a widespread non-native fish species in Brazil displays opportunistic feeding behavior and changes its diet according to environmental conditions. We compared the diet, feeding selectivity, carbon assimilation, trophic niche, and trophic level of Knodus moenkhausii (a small non-native characid fish species of Upper Parana River) in streams surrounded by natural riparian vegetation (natural cover streams) and in streams impacted by pasture. We analyzed stomach contents and stable isotopes (carbon and nitrogen), simultaneously. Overall, insects were the most common food items (> 65%). In natural cover streams, K. moenkhausii showed higher selectivity among aquatic macroinvertebrates consumed, while in pasture streams, they fed on the most abundant groups. The proportion of feeding groups assimilated by K. moenkhausii and the proportion of primary sources consumed by each feeding group of macroinvertebrates also varied between natural cover and pasture streams, as indicated by stable isotopes. In natural cover streams, fine and coarse particulate organic matter accounted for approximately 80% of K. moenkhausii’s diet, while in pasture streams, algae and periphyton also contributed greatly. As a result, K. moenkhausii occupied a higher trophic level and exhibited a broader niche width in pasture streams. We conclude that K. moenkhausii presents feeding selectivity with capacity to alter the trophic niche depending on environmental conditions. Such opportunism could be one of the reasons underpinning the abundance and wide distribution of this invasive species.

Eutrophic estuaries receive organic matter (OM) inputs from multiple sources. This study evaluated the distribution and origin of sedimentary OM in an eutrophic estuary (Pina Sound, NE Brazil). Thirteen samples were collected in the sublittoral in addition to major local sources. Biochemical (chlorophyll - Chl), elemental [(C/N)a and C/S ratios] and isotopic (δ 15N and δ 13C) analyses were carried out for characterizing OM and redox conditions. The SIAR mixing model was used to quantify contribution from main sources. At Pina Sound, distribution of OM is associated with mud, reflecting the hydrodynamics control on deposition of suspended particles. Microphytobenthic production is limited ([Chl a] < 1000 µg/g organic carbon) in the sublittoral where the Chl degradation products prevail (mean [Pheopigments] = 2643 ± 958 µg/g organic carbon). Anoxic conditions (C/S ratio ≈ 2) are typically observed in sediments of deeper portions of Pina Sound. Such sediments receive high organic loads and are subject to poor water renewal. According to SIAR mixing model, sedimentary OM of Pina Sound is composed of, on average: 50% phytoplankton, 24% sewage and 26% C3 plants. This reflects fertilization of Pina Sound with high loads of untreated sewage. Pina Sound has a great potential to retain sewage-derived OM.

Integrated farming systems are sustainable strategies to intensify land productivity by combining annual crop, livestock and/or forestry activities in different spatio-temporal arrangements. Therefore, they may help tackle global food and energy insecurity and climate change in the coming decades. We investigated the effects of integrated crop-livestock (ICL) and integrated crop-livestock-forestry (ICLF) systems on quantity, quality, and origin of soil organic matter (SOM) in southeastern Brazil. A native forest and an extensive low-grazing intensity pasture system were used as references. In integrated systems, corn (Zea mays) was alternated with two consecutive years of piata grass (Urochloa bryzantha) for cattle grazing. In ICLF, eucalyptus trees (Eucalyptus urograndis) were planted in simple rows of 15 × 2 m. Soil sampling was performed three times; in 2014, after two years of grazing; in 2015, after crop cultivation; and in 2016, after a successive grazing year, to evaluate chemical and physical composition changes of organic matter (C, N, δ13C, δ15N, and organic matter fractions) with time. Our findings showed that from 2010 to 2016, all systems (extensive grazing, ICL and ICLF) promoted increments on soil C and N stocks. However, land intensification converting extensive low-grazing intensity pasture to ICL was the most promising strategy, increasing soil C stocks at the rate of 0.28 Mg C ha−1 yr−1 from 2010 to 2016. Annual crop cultivation (corn intercropped with piata grass) promoted high organic matter inputs on the soil, increasing the amount of soil labile organic matter fractions, which presented higher δ13C and lower δ15N values over time. SOM in the integrated farming systems was originated mainly from C4 plants. Therefore, optimizing development of piata grass and corn increases organic residue inputs and then, soil C and N stocks. In addition, the crop period increased soil fertility parameters, which favors plant growth, thus providing high labile C inputs to the soil. In contrast, land intensification by adding the forestry component into the system (i.e., conversion from ICL to ICLF) reduced soil C (-0.22 Mg C ha−1 yr−1) and N (-0.03 Mg N ha−1 yr−1) stocks from 2010 to 2016, likely due to the reduction of C and N inputs to the soil caused by limited growth of annual crop and grass species under tree shades. In conclusion, land use intensification through ICL system contributes towards a more efficient and low-C agriculture, whereas the studied ICLF system did not bring further benefits to increase the quantity and/or quality of SOM.

The origin of the organic matter was assessed in two estuaries in Eastern Amazon, Brazilian Northern Coast, under different hydrodynamic conditions. The isotopic composition ( δ 13 C; δ 15 N) and the elementary ratio (C/N) were determined in the sediments, in the suspended particulate material (SPM), as well as in the phytoplankton, plants and oysters. The ( δ 13 C) values have indicated that the sedimentary organic matter is a terrestrial–marine mix composed of terrigenous organic matter (75%) in the Para River estuary, as well as of marine organic matter (60%) in the Mocajuba River estuary. The estimates of sources recorded through δ 13 C data were partially confirmed through the correlation ( δ 15 N) versus C/N, which reflects the action of diagenetic and biological processes on the organic matter composition control. On the other hand, the high carbon content ( δ 13 C) found in Para River estuary samples is conclusive because it shows isotopic changes due to the anthropogenic processes in the region.

The aim of this study was to evaluate how distinct land uses can alter the trophic structure of fish communities in streams. For this purpose, nine streams under the influence of three distinct land uses (pasture, sugarcane, and natural cover) were evaluated. The structure and isotopic niche of the fish communities were investigated by calculating descriptive community-wide metrics based on stable isotopes of δ13C and δ15N. The largest isotopic niche was observed in fish communities in pasture streams, and the smallest in sugarcane streams. Pasture streams exhibited greater ranges of carbon sources exploited by fishes, higher trophic diversity, and lower trophic redundancy. In contrast, sugarcane streams had greater ranges of nitrogen exploited by fishes and showed the smaller trophic diversity, higher trophic redundancy, and uniformity. Sugarcane was also the only land use that exerted a negative influence on community isotopic niche width. Natural cover streams in turn, showed lower trophic uniformity and exhibited intermediate values for all remaining metrics. We conclude that fish communities residing in streams influenced by pastures displayed characteristics that led to greater trophic diversity, and fish communities influenced by sugarcane plantations were more negatively affected by this land use.

This study investigated two estuaries on the northern coast of Brazil submitted to different anthropic activities. The main objective was to assess the use of oysters (Crassostrea gasar and Paxyodon ponderosus) and phytoplankton as bioindicators of environmental contamination. Water, sediments, phytoplankton and oysters were chemically analyzed by ICP-OES and ICP-MS. The source for metal bioaccumulation in oysters and phytoplankton was assessed using BSAF (Biota Sediment Accumulation Factor) and the isotropic relations of stable carbon ( δ 13 C and δ 15 N). The oyster-sediment BSAF showed bioaccumulation of Mn, Cu, Zn, Se, Sr, As, Cd and Ba, which was supported by the correlations of Fe, Mn, Cu, Zn, Se, Sr, Al, Ba and Pb with the isotopes ( δ 15 N and δ 13 C), which confirmed bioaccumulation as well as biodilution and biomagnification in oysters and phytoplankton. That reflects the efficiency of organisms in bioconcentrating metals and their capacity as bioindicators of contamination.

The aim of this study was to test if changes in land use alter the isotopic signature of fish species, promoting changes in the trophic position and food resource partitioning between these consumers. Three different systems were investigated: pasture streams (n = 3), streams in sugar cane plantations (n = 3) and reference streams (n = 3). Fish species Aspidoras fuscoguttatus, Astyanax altiparanae, Characidium zebra, Hisonotus piracanjuba and Knodus moenkhausii were selected, and their nitrogen and carbon isotopic compositions were estimated to assess changes in the trophic level and partitioning of food items consumed. The composition of δ(13) C (‰) only differed among the land use categories for A. altiparanae, H. piracanjuba and K. moenkhausii. Resource partitioning was different for all species, with changes in the sources or proportions they consumed in each land use category, but only A. altiparanae introduced new food sources in large quantity in altered land uses. It is important to note, however, that the results from the resource partitioning analysis are limited due to large overlapping of isotopic signatures between the analysed food resources. All fish species exhibited variation in δ(15) N (‰), with the highest values found in streams under sugar cane or pasture influence. Despite the variation in nitrogen isotopic values, only C. zebra and H. piracanjuba displayed changes in trophic level. Therefore, it is believed that the increase in the δ(15) N (‰) value of the individuals collected in streams under the influence of sugar cane or pasture was due to the greater influence of livestock dung and chemical and organic fertilizers. The results also highlight the importance of studying consumer species along with all forms of resources available at each location separately, because the signatures of these resources also vary within different land uses.

Made available in DSpace on 2018-12-11T17:16:15Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-01-01 The vegetation of the Cerrado has been replaced by pastures and agriculture, affecting the stock and dynamic of soil organic matter (SOM). The present study was conducted in a cultivated chronosequence with a mixed system (agriculture+pasture for 15 years; Agric+P15) and cultivated pasture (30 years; P30), taking the native Cerrado as a reference to assess changes in the stock of SOM, the dynamics (δ13C) and the carbon replacement derived from the C3 in native vegetation to C4 in cultivated vegetation. Compared to Cerrado, there was a reduction in C stock in cultivated soils at 0-15-cm depth (reduction of 26.5% in Agri+P15 and 6% in P30). The close similarity between Cerrado and P30 indicates that the pasture management enhanced the stock relative to Agri+P15, but was not effective in sequestering C. Only in the 0-15cm depth was there a marked replacement of C derived from the C3 of Cerrado plants associated with cultivation time. In the chronosequence, the isotopic signature of C4 plants dominated in the soil below 30cm depth, suggesting a paleoclimatic effect on SOM. Universidade Federal de Uberlândia (UFU), Avenida João Naves de Ávila Universidade Estadual Paulista (UNESP) Instituto de Geociências e Ciências Exatas (IGCE), Avenida 24A Food and Agriculture Organization of the United Nations (FAO), Viale delle Terme di Caracalla Universidade de São Paulo (USP) Centro de Energia Nuclear Na Agricultura (CENA), Avenida Centenário Centro de Estudos Ambientais (CEA)/UNESP, CEA24A, 1515 Universidade Estadual Paulista (UNESP) Instituto de Geociências e Ciências Exatas (IGCE), Avenida 24A Centro de Estudos Ambientais (CEA)/UNESP, CEA24A, 1515

Wetlands have been identified as key elements of global carbon budgets. Today, due to increasing anthropogen- ic carbon emissions, the carbon storage capacity of these ecosystems has become of global interest. The focus of this research was to determine the storage capacity and mecha- nisms ofcarbonsequestration ofNeotropical seasonalshallow lakes (SSLs), assessing their flood pulse, biomass, geomor- phology and sediment composition. We applied a standard- ized and extensive sampling to five SSLs from the Colombian Orinoco-Llanos and five from the Brazilian Pantanal, during both flooded and non-flooded seasons. We found that sedi- ment organic carbon (SOC) storage capacity in SSLs is sig- nificantly driven by the number of flooded days (p-value= 0.0057) ratherthanbytheir biomassproduction.TheOrinoco- Llanos and Pantanal lakes differ in morphology, and thus in their inundation patterns. SSLs of the Orinoco-Llanos are more concave, having a significantly higher number of flooded days/year than SSLs from Pantanal. These hydrologic differences affect SOC storage, resulting in a significantly higher SOC storage in SSLs from Orinoco-Llanos than in Pantanal. A synopsis of data from both regions suggests the existence of a critical threshold between "non-flooded season losses"and "non-flooded seasonstorage"ofSOC inSSLsina range of 225-275 flooded days/year.

Stomach content and stable isotopes of tambaqui, Colossoma macropomum (Cuvier), were use to determine seasonality of energy sources in a floodplain lake in the central Amazon. The turnover time of carbon in young tambaqui was fast enough to detect a broad seasonal variation both in stomach content and tissue isotopic signal of carbon and nitrogen. The relative importance of food items varied with water level. C3 plants (seeds and fruits) contributed between 55% and 95% of the biomass fraction of tambaqui. Zooplankton contributed a minimum of 26% of the nitrogen fraction during periods of flooding, and a maximum of 67% in the dry season. C4 plants (macrophyte leaves and roots) contributed a maximum of 26% of the biomass fraction and 13% of the N fraction mainly during the flooding period. The feeding habits and behaviour of tambaqui are complex and linked to the flood pulse.

Este trabalho discute os efeitos das mudanças do uso do solo na biogequímica dos rios da bacia de drenagem do rio Ji-Paraná (Rondônia). Nesta região, a distribuição espacial do desmatamento e das propriedades do solo resultam em sinais diferentes, possibilitando a divisão dos sistemas fluviais em três grupos: rios com águas pobres em íons e baixo impacto; rios com conteúdo iônico intermediário e impacto médio e rios com elevados conteúdo iônico e impacto antropogênico. As características biogeoquímicas dos rios têm relação significativa com a área de pasto, melhor parâmetro para prever a condutividade elétrica (r² = 0,87) e as concentrações de sódio (r² = 0,75), cloreto (r² = 0,69), potássio (r² = 0,63), fosfato (r² = 0.78), nitrogênio inorgânico (r² = 0.52), carbono inorgânico (r² = 0.81) e carbono orgânico (rain ² = 0.51) dissolvidos. Cálcio e magnésio tiveram sua variância explicada pelas características do solo e pastagem. Nossos resultados indicam que as mudanças observadas na micro-escala constituem "sinais biogeoquímicos" gerados pelo processamento do material nas margens dos rios. A medida em que os rios evoluem para ordens superiores, os sinais persistentes nos canais fluviais estão mais associdados às características da bacia de drenagem (solos e uso da terra). Apesar dos efeitos das mudanças observadas no uso do solo não serem ainda detectáveis na macro-escala (bacia amazônica), a disrupção da estrutura e funcionamento dos ecossistemas é detectável nas micro e meso escalas, com alterações significativas na ciclagem de nutrientes nos ecossistemas fluviais. In this article we present the results of the effects of land use change on the river biogeochemistry of the Ji-Paraná basin (Rondônia). In this region, the spatial distribution of deforestation and soil properties result in different biogeochemical signals, allowing the division of the fluvial systems into three groups: rivers with low ionic concentration and low impact; rivers with intermediate ionic content and medium impact; and rivers with high ionic content and anthropogenic impact. River biogeochemical characteristics present a significant correlation with pasture area, the best predictor for electric conductivity (r² = 0,87), sodium (r² = 0,75), chloride (r² = 0,69), potassium (r² = 0,63), phosphate (r² = 0,78), and dissolved inorganic nitrogen (r² = 0,52), inorganic carbon (r² = 0,81) and organic carbon (r² = 0,51). For calcium and magnesium, both soil properties and pasture explained most of the observed variability. Our results indicate that the changes observed at the micro-scale constitute "biogeochemical signals" generated by the material processing at the riparian zones. As the rivers evolve to higher orders, the persistent signals in the fluvial channels are very closely related to the drainage basin characteristics (soils and land use), which, in turn, become the determinant of these systems dynamics. While at the macro-scale (the whole basin) the effects of land use changes are not yet detectable in the Amazon, the disruption of the structure and functioning is occuring at the micro and meso scales, with significant alterations of nutrient cycling in fluvial ecosystems

We investigated the forms and composition of dissolved and particulate organic matter in rivers of the Ji-Parana Basin, which is situated at the southern limit of the Amazon lowlands and has experienced extensive deforestation in the last three decades (∼35 000 km2). Our objective was to investigate how extensive land-use changes, from forest to cattle pasture, have affected river biogeochemistry. We measured a series of chemical, biochemical, and isotopic tracers in three size classes of organic matter within five sites along Ji-Parana River and eight more sites in six tributaries. The results were compared with C4 leaf and pasture soils end members in order to test for a pasture-derived signal in the riverine organic matter. The coarse size fraction was least degraded and derived primarily from fresh leaves in lowland forests. The fine fraction was mostly associated with a mineral soil phase, but its ultimate source appeared to be leaves from forests; this fraction was the most enriched in nitrogen. The ultrafiltered dissolved organic matter (UDOM) appeared to have the same source as the coarse fraction, but it was the most extensively degraded of the three fractions. In contrast to Amazon white-water rivers, rivers of the Ji-Parana Basin had lower concentrations of suspended solids with a higher carbon and nitrogen content in the three size fractions. However, principal component analyses showed a correlation between areas covered with pasture and the δ13C values of the three size fractions. The highest δ13C values were observed in the ultrafiltered dissolved organic matter of the Rolim-de-Moura and Jaru rivers, which have the highest areas covered with pasture. The lower the order of the streams and the higher the pasture area, the greater is the possibility that the C4-derived organic matter signal will be detected first in the faster-cycling fraction (UDOM). The large change in land use in the Ji-Parana Basin, replacement of primary forests by C4 pastures for cattle feeding, that has taken place in the last 30–40 yr, has already changed the characteristics of the composition of the riverine organic matter.

This study evaluated the water uptake patterns of a primary forest and of the savanna-like vegetation of an abandoned pasture in an eastern Amazon site. We used natural stable isotope abundance in the soil profile, as well as plots irrigated with deuterated water to determine time and depth of soil water uptake by plants in different functional groups. Natural isotopic abundance was not suitable for identification of depth of water uptake by plants, but experiments using labeled water were. We found that the label percolation rate in the soil profile of the forest was lower than that observed in the pasture. Fourteen months after application, the label peak was located at 1.8 m depth in the forest and at 3 m depth in the pasture. Isotopic analysis of sap water from trees and lianas in the forest during the dry season showed that trees acquired labeled water at a deeper level in the soil profile compared to that acquired by lianas. Depth of water uptake by lianas seems to vary on a seasonal basis. In the pasture the ‘colonizer’ shrub (Solanum crinitum Lamb.) took up labeled water only from the surface layer of the soil profile (∼20%), whereas the most abundant coexisting grass (Panicum maximum Jacq.) acquired it from the top meter. None of the pasture plants were able to acquire labeled water after one rainy season when the label pulse was deep in the soil (>1 m deep). These results have implications for studies of forest water cycle in which the soil volume used as source of water for plant transpiration is still unknown, and for an understanding of plant succession in the forest regeneration process of abandoned pastures in the eastern Amazon.

Sustainable management for existing Amazonian forests requires an extensive knowledge about the limits of ecosystem nutrient cycles. Therefore, symbiotic nitrogen (N2) fixation of legumes was investigated in a periodically flooded forest of the central Amazon floodplain (Várzea) over two hydrological cycles (20 months) using the 15N natural abundance method. No seasonal variation in 15N abundance (delta 15N values) in trees which would suggest differences in N2 fixation rates between the terrestrial and the aquatic phase was found. Estimations of the percentage of N derived from atmosphere (%Ndfa) for the nodulated legumes with Neptunia oleracea on the one side and Teramnus volubilis on the other resulted in mean %Ndfa values between 9 and 66%, respectively. More than half of the nodulated legume species had %Ndfa values above 45%. These relatively high N gains are important for the nodulated legumes during the whole hydrological cycle. With a %Ndfa of 4-5% for the entire Várzea forest, N2 fixation is important for the ecosystem and therefore, has to be taken into consideration for new sustainable land-use strategies in this area.

We analyze the interannual monthly variability of oxygen isotope ratios in data from IAEA stations along the Atlantic coast of South America between 238 and 348 S to evaluate the influence of parameters such as temperature, rainfall amount and moisture source contribution on meteoric water recharging two karst systems in subtropical Brazil. In addition, a 2 year monitoring program performed on soil and cave drip and rimstone pool waters from sampling sites with contrasting discharge values and located at 100 and 300 m below the surface in the Santana Cave System (24831V S; 48843V W), is used to test the influence of hydrologic and geologic features on the temporal variations of seepage water d 18 O. Interannual monthly variations in d 18 O of rainfall reflect primarily regional changes in moisture source contribution related to seasonal shifts in atmospheric circulation from a more monsoonal regime in summer (negative values of d 18 O) to a more extratropical regime in winter (positive values of d 18 O). Variations in groundwater d 18 O indicate that the climatic signal of recent rainfall events is rapidly transmitted through the relatively deep karst aquifer to the cave drip waters, regardless of location of collection in the cave. In addition, the data also suggest that water replenishment in the system is triggered by the increase in hydraulic head during periods when recharge exceeds the storage capacity of the soil and epikarst reservoirs. Significant perturbations in the groundwater composition, characterized by more positive values of d 18 O, are probably connected to an increased Atlantic moisture contribution associated with extratropical precipitation. This implies that the d 18 O of speleothems from caves in this region may be a suitable proxy for studying

About 35km south of the city of Sao Paulo, near Colonia, within Precambrian crystal line basement rocks, there is a well-defined ring feature, with 3.64km in diameter and filledby at least 263m of sediments, which corresponds to a probable astrobleme. It is defined by a hilly circular outer rim up to 125m higher than an inner alluvial plain presently occupied by a large swamp. This paper explains the regional geology of the area and discusses the different hypothesis as to the origin of the structure as well as the morphological parameters pertinent to an understanding of this feature. Preliminary vibrocore data are also presented

(1) Our objective was to measure the stable carbon isotope composition of leaf tissue and CO2 released by respiration (dr), and to use this information as an estimate of changes in ecosystem isotopic discrimination that occur in response to seasonal and interannual changes in environmental conditions, and land-use change (forest-pasture conversion). We made measurements in primary forest and pastures in the Amazon Basin of Brazil. At the Santarem forest site, dr values showed a seasonal cycle varying from less than 29% to approximately 26%. The observed seasonal change in dr was correlated with variation in the observed monthly precipitation. In contrast, there was no significant seasonal variation in dr at the Manaus forest site (average dr approximately 28%), consistent with a narrower range of variation in monthly precipitation than occurred in Santarem. Despite substantial (9%) vertical variation in leaf d 13 C, the average dr values observed for all forest sites were similar to the d 13 C values of the most exposed sun foliage of the dominant tree species. This suggested that the major portion of recently respired carbon dioxide in these forests was metabolized carbohydrate fixed by the sun leaves at the top of the forest canopy. There was no significant seasonal variation observed in the d 13 C values of leaf organic matter for the forest sites. We sampled in pastures dominated by the C4 grass, Brachiaria spp., which is planted after forest vegetation has been cleared. The carbon isotope ratio of respired CO2 in pastures was enriched in 13 C by approximately 10% compared to forest ecosystems. A significant temporal change occurred in dr after the Manaus pasture was burned. Burning removed much of the encroaching C3 shrub vegetation and so allowed an increased dominance of the C4 pasture grass, which resulted in higher dr values. INDEX TERMS: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 1610 Global Change: Atmosphere (0315, 0325); 1615 Global Change: Biogeochemical processes (4805); 3309 Meteorology and Atmospheric Dynamics: Climatology (1620); KEYWORDS: carbon cycle, global change, tropical ecosystems, atmospheric carbon dioxide

The stable carbon isotopic composition of methane ( δ 13 C-CH 4 ) gas bubbles formed in the sediments of three Amazonian streams was determined over a 5-yr period. The study sites were two ‘ varzea ’ floodplain (Acu and Maica) and one ‘ terra-firme ’ (Jamaraqua) streams. The δ 13 C of sedimentary organic matter (SOM) from the surrounding vegetation and bottom sediments were also determined. The mean δ 13 C value of SOM was lower in the terra-firme (−29.6‰) than in the varzea stream (−23.8‰) as a result of less C 4 plant deposition in the former. The δ 13 C-CH 4 values varied systematically both seasonally and spatially among the sites during all 5 yr of the study, in association with changes during hydrologic cycle. Overall, the variation in values of δ 13 C-CH 4 during the high water phase covered a narrower range of values, −63 to −56‰. Contrastively, during the low water phase the δ 13 C-CH 4 values for varzea and terra-firme streams are different and are in direct opposition. At this phase, the δ 13 C-CH 4 at terra-firme stream is at least 20‰ depleted of 13 C compared to varzea streams. Changes in organic matter sources, water levels and associated microbial degradation processes control the observed seasonal and spatial variations in net stable carbon isotopic composition of methane. DOI: 10.1111/j.1600-0889.2007.00322.x