Reynaldo L. Victoria

Autotrophic Carbon Sources for Fish of the Central Amazon

Effective management of the Amazons commercial fish populations requires an understanding of the factors controlling their production. A fundamental step in the investigation of fish production is to identify the plant groups that contribute energy to fish foodwebs. Stable isotope data for plants and 35 fish species were used to identify autotrophic carbon sources for the central Amazon fish community. Adult fish, aquatic macrophytes, tree parts, periphyton, and phytoplankton were collected in lakes and other flooded environments along the central Amazon floodplain and analyzed for carbon stable isotope composition (°13C) by mass spetroscopy. °13C values for plants ranged from —39.4 to —11.9% with averages of —33.3, —28.8, —27.6, —26.2, and —12.8% for phytoplankton, flooded forests trees, C3 aquatic macrophytes, periphyton, and C4 macrophytes, respectively. The average for all C3 plants (phytoplankton, trees, C3 macrophytes, and Periphyton) was —29.1%, while the average for C4 plants (mainly C4 macrophytes) was —12.8%. Mean °13C values for adult fish ranged from —37.0 to —19.8% with an average of —28.8%. Fish and plant data were used in an isotope mixing model to estimate the relative contribution of different plant groups to fish carbon. C4 macrophytes, which contributed over half of the primary production on the floodplain, accounted on average for only 2.5—17.6% (minimum to maximum) of the carbon in fish. The C3 plants, as a group, were the primary carbon source for 34 fish species, and accounted for an average of 82.4—97.5% of the carbon in all species. Phytoplankton, a minor C3 producer, accounted for a minimum of 36.6% of fish carbon on average, and was the principal carbon source for the commercially important characiform detritivores. Several alternative hypothese are proposed to explain the apparent selective transfer of C3 carbon through Amazon fish foodchains.

Energy sources for detritivorous fishes in the Amazon.

Detritivorous fishes form an important part of the ichthyomass in the Amazon basin. Most of these fishes are contained in the orders Characiformes and Siluriformes (catfishes). The Characiformes constitute more than 30% of the total fish yield in the Amazon basin, whereas the catfishes are of minor importance. Stable isotope data indicate that Characiformes species receive most of their carbon through food chains originating with phytoplankton, while the Siluriformes receive a significant part of their energy from other plant sources.

Chemical composition of rainwater and anthropogenic influences in the Piracicaba River Basin, Southeast Brazil

Abstract The influences of different kinds of anthropogenic activities on rainwater chemistry in a tropical area were studied during one uninterrupted year at Piracicaba River Basin (Southeast Brazil). A total of 272 rainwater samples collected continuously from August 1997 to July 1998 at four different sites were analyzed for F − , CH 3 COO − , HCOO − , MSA, Cl − , NO 2 − , Br − , NO 3 − , SO 4 2− , C 2 O 4 2− , PO 4 3− , Na + , NH 4 + , K + , Mg 2+ , Ca 2+ , DOC (dissolved organic carbon), DIC (dissolved inorganic carbon), pH and conductivity. The most abundant ion was H + and rain acidity was significant at all sampling sites (average pH of 4.4–4.5). The sources of this free acidity differ among sites and appear to be correlated to the different land-uses. The composition of rainwater appeared to be controlled mostly by three sources: soil dust, sugar cane burning and industrial emissions.

EFFECTS OF URBAN SEWAGE ON DISSOLVED OXYGEN, DISSOLVED INORGANIC AND ORGANIC CARBON, AND ELECTRICAL CONDUCTIVITY OF SMALL STREAMS ALONG A GRADIENT OF URBANIZATION IN THE PIRACICABA RIVER BASIN

In Brazil most of the urban sewage is dumped without treatment into rivers. Because of this, it is extremely important to evaluate the consequences of organic matter rich sewage on the structure and functioning of river ecosystems. In this study we investigated the effects of urban sewage on the dissolved oxygen (O2), dissolved inorganic (DIC) and organic carbon (DOC), and electrical conductivity (EC) in 10 small streams of the Piracicaba River basin, southeast region of Brazil. In the Piracicaba River basin, which is one of the most developed regions of the country, only 16% of the total sewage load generated is treated. These streams were classified into two groups, one with heavy influence of urban sewage and another with less influence. Both concentrations and seasonal variability were distinct between the two groups. The streams that received sewage effluent had a combination of low O2 with high DIC, DOC, and EC. In the polluted streams, concentrations of dissolved carbon forms and EC were higher and O2 concentration lower during the low water period. In the less polluted streams seasonal variations in concentrations were small. We also investigated the efficiency of a sewage treatment plant installed two years ago in the catchment of one of these streams. It was observed an increase in the O2 concentration after the beginning of the treatment, and a decrease of DIC and DOC concentrations especially during the low water period. However, no significant change was observed in the EC, suggesting that the concentrations of major ions is still unaltered, and that a secondary treatment is necessary in order to reduce ion load into the stream.

Control of cation concentrations in stream waters by surface soil processes in an Amazonian watershed.

The chemical composition of ground waters and stream waters is thought to be determined primarily by weathering of parent rock. In relatively young soils such as those occurring in most temperate ecosystems, dissolution of primary minerals by carbonic acid is the predominant weathering pathway that liberates Ca2+, Mg2+ and K+ and generates alkalinity in the hydrosphere. But control of water chemistry in old and highly weathered soils that have lost reservoirs of primary minerals (a common feature of many tropical soils) is less well understood. Here we present soil and water chemistry data from a 10,000-hectare watershed on highly weathered soil in the Brazilian Amazon. Streamwater cation concentrations and alkalinity are positively correlated to each other and to streamwater discharge, suggesting that cations and bicarbonate are mainly flushed from surface soil layers by rainfall rather than being the products of deep soil weathering carried by groundwater flow. These patterns contrast with the seasonal patterns widely recognized in temperate ecosystems with less strongly weathered soils. In this particular watershed, partial forest clearing and burning 30 years previously enriched the soils in cations and so may have increased the observed wet season leaching of cations. Nevertheless, annual inputs and outputs of cations from the watershed are low and nearly balanced, and thus soil cations from forest burning will remain available for forest regrowth over the next few decades. Our observations suggest that increased root and microbial respiration during the wet season generates CO2 that drives cation-bicarbonate leaching, resulting in a biologically mediated process of surface soil exchange controlling the streamwater inputs of cations and alkalinity from these highly weathered soils.

Trends in hydrological parameters of a southern Brazilian watershed and its relation to human induced changes

The Piracicaba river basin is a subtropical watershed located in the southeastern region of Brazil. With an area of 12 400 km2, the basin is a typical example of new landscape resulting from development in tropical and sub-tropical regions: establishment of intensive industrial and agricultural processes were followed by significant population growth and water management. This scenario has led to significant increase in water demand and decrease in water quality. The main objective of this study is the detection of changes in the patterns of flow and precipitation in the basin, and its possible relation to man-induced changes. Statistical analyses were performed on records of precipitation, evapotranspiration and streamflow, from 1947 to 1991. Precipitation and evapotranspiration totals showed significant increasing trends for the entire basin. From eight streamflow gauge stations, half showed significant decreasing trend. The most probable cause of such trends is the export of water from the basin to the metropolitan region of São Paulo city.

Land use and nitrogen export in the Piracicaba River basin, Southeast Brazil

Anthropogenic N inputs and riverine export were determined for a meso-scale river basin in one of the most developed and economically important regions of South America. The Piracicaba River basin is located in southeastern Brazil and drains into a tributary of the Paraná River. The basin supports over 3 million people (about 2% of the population of Brazil) with intensive agricultural and industrial activities. During two years from 1995 to 1997, biweekly samples were collected at 10 stations along the Piracicaba River and its tributaries for analyses of dissolved and particulate N. The average annual flux of dissolved inorganic N and total N increased by a factor of 15 and 20 times, respectively, from the headwaters to the lower reaches of the main channel, whereas discharge increased by only 7 times. On a per area basis, the export of TN varied according to land use and was significantly correlated to the net input of anthropogenic N. Among 10 sub-catchments composing the basin, areas mostly covered by pasture and forest had the lowest export, whereas more agricultural and urban areas had higher export. The amount of N exported from each sub-catchment varied widely, but inputs were consistently higher than fluvial outputs. Losses and retention of N occurred throughout the basin but were especially high in the sub-catchment with a main-stem reservoir, suggesting that aquatic processing plays an important role in controlling riverine N export. Total net anthropogenic input to the Piracicaba River basin was 4,500 (± 900) kg N km−2 yr−1 of which about 40% was exported via fluvial outputs.

Using stable isotopes to determine sources of evaporated water to the atmosphere in the Amazon basin

Abstract The return of water in vapor form from the land to the atmosphere, via plant transpiration and evaporation, is fundamental for the maintenance of the regional water cycle in the Amazon basin. Whereas transpiration, the dominant process, has the extensive vegetation cover as a large single source, evaporation can have several sources, and their relative importance and location are poorly known. The isotopic composition (δ 18 O and δD) of water from various sources was used to see whether or not specific sources of water vapor to the atmosphere could be determined. It is well established that natural waters fall on a line called the meteoric water line (MWL; the regression of δ 18 O × δD), with slope equal to eight and an intercept equal to ten. When a water body loses water via evaporation the slope become smaller than eight, typically 5–6. We estimated the slope of the regression of δ 18 O × δD for several potential sources. We analyzed 1273 samples: 500 of rainfall, 409 of river water, 134 of lake water, 164 of soil water, 40 of throughfall and stemflow water, and 26 of shallow ground-water. We found that large rivers and lakes are likely contributors of evaporated water to the atmosphere. However, as they cover only a small area of the basin, other sources are needed. Probably, evaporated water originates from several small sources that were not detected by the isotopic composition of our data.

Agricultural use of treated sewage effluents: agronomic and environmental implications and perspectives for Brazil

In many studies worldwide the use of treated sewage effluents (TSE) as water and nutrient sources in agricultural irrigation have been introduced as a viable alternative for wastewater destination in the environment. Considering agronomic and environmental aspects the objectives of this review were: (i) to present an overview of TSE irrigation on different agro-systems (annual crops, orchards, forests and forages); and (ii) to show the principal changes on chemical, physical and microbiological soil characteristics after TSE application. Various studies have revealed that the nutrient supply only by TSE irrigation was not sufficient to meet plant nutrient requirements resulting in yield decreases. The problem could be solved by an adapted effluent/fertilizer management. Moreover, TSE could generally substitute efficiently freshwater for irrigation. Regarding soil quality conditions, TSE irrigation affected mainly: (i) total soil carbon and nitrogen, and mineral nitrogen in soil solution; (ii) microbial activity, composition of microbial communities and their function; (iii) exchangeable calcium and magnesium; (iv) salinity, sodicity, clay dispersion and hydraulic conductivity. Other soil parameters considered in this review (e.g. heavy metals) did not present significant changes over short and medium terms. Due to the often observed accumulation of sodium and nitrogen losses (leaching, volatilization and denitrification) after TSE irrigation, the monitoring of these components is of crucial importance for a sustainable use. Finally, further studies on the technical-economical-environmental viability of TSE irrigation are required to establish reliable recommendations for TSE use particularly in Brazilian agro-systems.

Stable carbon and nitrogen isotopic composition of bulk aerosol particles in a C4 plant landscape of southeast Brazil

Abstract The carbon and nitrogen isotopic compositions of aerosol particles collected in the Piracicaba region, where C4 plants like sugarcane and pasture dominate the land cover, were measured. For comparison, aerosol particles were also analyzed from the Santarem region, Amazon basin, where the main land cover is primary forest. The average δ 13 C value of samples collected in Piracicaba was equal to −20.9±0.8‰. The average δ 13 C of samples collected in Santarem was almost 5‰ smaller than in Piracicaba (−25.8±0.5‰). This difference between the two sites was attributed to the presence of C4 material in Piracicaba aerosol particles. On the other hand, there was no statistical difference between the average δ 15 N values observed in Piracicaba (10.6±2.8‰) and Santarem (11.5±2.1‰). The δ 13 C and δ 15 N values of aerosol particles collected in Santarem were higher than vegetation tissues and soil organic matter, which are the potential sources of organic matter to aerosol particles.