Floodplain Lagoons Research Articles

Influência do ciclo hidrológico sobre a abundância de desmídias em uma lagoa rasa de planície de inundação do semiárido brasileiro

Abstract Aim Knowledge of hydrological characteristics is essential for understanding ecological processes in floodplains, which can support sustainable management. We evaluated environmental variations in a shallow floodplain lagoon located in the Chapada Diamantina, Andaraí, Bahia. We aim to identify phases of the hydrologic cycle and their influence on desmid density, which is a group of algae known for its potential as bioindicator of trophic changes. Methods Bimonthly samplings were performed at four points in the lagoon. Abiotic (temperature, conductivity, pH, transparency, depth, dissolved oxygen, total and dissolved nutrients) and biotic (macrophyte cover, phytoplankton chlorophyll-a, and desmid density) variables were determined. The Trophic State Index (TSI) was calculated based on phytoplankton chlorophyll-a, and total phosphorus concentration. Results The lagoon was characterized by well-oxygenated, slightly acidic waters with low electrical conductivity. According to the TSI, the lagoon varied from mesotrophic to hypereutrophic during the study period. The driest months (August and October) were marked by high water transparency, low depth, nitrogen concentration, and macrophyte coverage. The highest value of accumulated precipitation was registered in December, when there was an increase in depth and a decrease in electrical conductivity and PT concentration. Two phases of the hydrologic cycle were evidenced and determined by the depth and nutrient concentrations. The highest abundance of desmids occurred at the end of the rainy season when the nutrient availability and pH were higher, and the depth was reduced. Conclusions Our results suggest that the flood pulse was the determining factor of the local environmental conditions and that, together with the macrophyte morphological traits, it influenced desmid abundance and distribution in a floodplain lagoon in the semiarid region.

Essential and toxic elements in juvenile migratory commercial fish species in the Paraná River alluvial valley (South America): an approach for aquatic environmental monitoring.

The Paraná River is the sixth largest in the world, and the lower section of the river is one of the largest and most productive floodplain wetlands in South America. The alluvial plain is an important habitat for nursery and feeding areas for commercial fish; however, it has been heavily anthropized due to industries, agricultural activities, and the growth and expansion of metropolitan areas. The aim of this study was to determine element accumulation (As, Cd, Cr, Cu, Fe, Mn, Pb, and Zn) in young-of-the-year fish muscle from a floodplain lagoon of the lower Paraná River (Argentina) during summer and winter seasons, in relation with abiotic matrices (water and sediment). Four commercial fish species were assessed: sábalo (Prochilodus lineatus), boga (Megaleporinus obtusidens), dorado (Salminus brasiliensis), and pirapitá (Brycon orbignyanus). The concentrations of eight elements were detected by quadrupole inductively coupled plasma mass spectrometry. In water samples, Cd, Cr, Mn, Fe, and Zn levels were under the permissible limits for aquatic biota protection in both seasons, except for Pb (> 1 μg L-1) and Cu (> 2 μg L-1). In sediment, the average concentrations of all elements were under the limits set by national and international regulatory authorities. Differences in elemental concentrations between species and seasons were found. In general, the levels of elements in water were higher in summer than in winter, while in sediment, the lowest concentrations of elements were detected during the summer. The order of element concentration in fish muscle was Cd (0.01-0.04 μg g-1) < As (0.02-0.16 μg g-1) < Pb (0.03-0.23 μg g-1) < Mn (0.77-4.32 μg g-1) < Cu (1.01-4.07 μg g-1) < Cr (1.09-4.30 μg g-1) < Zn (15.8-31.7 μg g -1) < Fe (12.6-49.7 μg g-1). The accumulation assessment showed that the four fish species significantly accumulate Cr, Cu and Zn, and As and Zn from water and sediment, respectively. The correlation analysis showed a relationship between fish size and As, Cr, Cu, Fe, Mn, and Zn concentrations. Similarly, the highest values of element concentrations in muscle were detected during the summer when the fishes are early juveniles. The level of As, Cd, and Pb detected in B. orbignyanus, M. obtusidens, and P. lineatus juveniles suggested that these species had the potential to be used as biomarkers for assessing accumulation of toxic elements in the environment. Also, this study reveals that the accumulation patterns differ between size and fish species, which should be a considered insight at the moment of selecting a bioindicator to monitor pollution in the ecosystem.

Otolith microchemistry highlights the importance of extensive connectivity for conservation of an iconic migratory fish in a large tropical river basin

Abstract Migratory fishes exert important influences on tropical river food webs, but these species are often most vulnerable to environmental change. Movement patterns of fishes in tropical rivers are also generally poorly understood, hindering conservation efforts. Common snook, Centropomus undecimalis, depend on connected coastal habitats for reproduction and growth and can migrate extensively up rivers when not hindered by barriers to movement. In southern Mexico, they are frequently captured 300 river km or more upstream from the delta of the Usumacinta River. The Usumacinta is a large river system with no mainstem dams, providing an expansive network of connected river, stream and wetland habitats which form a much larger migratory domain that exists in many other systems where common snook have been studied. To assess whether fish captured in different zones were associated with different natal habitats or distinct migratory patterns, variation in common snook otolith chemical signatures was examined in the Usumacinta River from the Gulf of Mexico coast to as far as 600 river km upriver. Otolith microchemistry was useful for characterizing migratory histories of individuals, but there was no clear evidence that fish captured in different river zones used different types of natal habitats. Based on lifetime Sr:Ca in otoliths, a diverse array of movement patterns was evident in the Usumacinta system, with 97% of common snook showing evidence of freshwater habitat use. Prevalent use of riverine habitats by common snook far from the coast reinforces the need to preserve connectivity in the Usumacinta River and other undammed systems supporting migratory species. The natural flow regime and lack of barriers allow for longitudinal and lateral connectivity in this system, providing pathways for migratory species to move extensively and have access to an array of habitats, including productive floodplain lagoons.

Assessment of cardinal temperatures of Egeria najas Planchon and its potential growth in a tropical floodplain lagoon

Assessment of cardinal temperatures of Egeria najas Planchon and its potential growth in a tropical floodplain lagoon

Assembleia de peixes e status atual da planície de inundação da bacia do alto rio São Francisco

Abstract: Aim This study aimed to evaluate whether the upper São Francisco River basin floodplain is still used as a nursery by migratory fish and present the current status of the area’s ichthyofauna after almost 40 years since the only survey was conducted in the region. Methods Sampling occurred in seven perennial lagoons and six temporaries from São Francisco River or its direct tributaries using gillnets and trawls. Temperature, pH, and transparency of each lagoon were measured. The estimated richness was calculated, and the fish assemblage from both perennial and temporary lagoons was compared using NMDS and ANOSIM. Results Forty species were captured, of which four were non-native and three were migratory. Although there was a low abundance of migratory species, most captured individuals were juveniles. Moreover, the perennial lagoons showed higher species richness. Conclusions After almost 40 years, the floodplain lagoons of the upper São Francisco basin remain important for the recruitment of migratory species and harbor an impressive proportion of fish fauna in the upper São Francisco area. However, the reduction of migratory species and the presence of non-natives may be a sign of the degradation of these environments, emphasizing the need for conservation measures in this area.

The ichthyofauna of the Rio Carinhanha basin, one of the main tributaries of the Rio São Francisco

The ichthyofauna of the Rio São Francisco basin is relatively well-documented. However, most of this knowledge is concentrated at the upper stretch of its catchment area. In this study, we compile a list of species encompassing almost the entire length of the Rio Carinhanha, an important tributary from upper-middle section of the Rio São Francisco, including a comprehensive diversity of environments. A total of 99 species from 8 orders and 27 families were recorded. Five species are considered non-native, six classifieds as long distance migrants, and three as vulnerable. The orders with the greatest richness of native species were Characiformes and Siluriformes. Characidae was the most represented family, followed by Loricariidae. The main river channels were the richest environments sampled, followed by floodplain lagoons, veredas, and streams. The Carinhanha basin has important lotic remnants, thus it has several migratory fish populations as well as endangered species. This study demonstrates the importance of cataloguing the still poorly explored tributaries of the upper-middle section of the Rio São Francisco basin.

Integrating freshwater wetland science into planning for Great Barrier Reef sustainability

Abstract The paper ‘Biodiversity values of remnant freshwater floodplain lagoons in agricultural catchments: evidence for fish of the Wet Tropics bioregion, northern Australia’, published in Aquatic Conservation: Marine and Freshwater Ecosystems in 2015, has contributed in several ways to the integration of freshwater wetland science within new catchment management policies and practices for Great Barrier Reef (GBR) sustainability. The Tully–Murray biodiversity study developed novel protocols to sample larval, juvenile, and adult fish life‐history stages in floodplain lagoons using a combination of boat‐based backpack electrofishing and fyke netting. In addition, hydrological and hydrodynamic models were applied in a completely new way to quantify the timing, extent, and duration of water connectivity across floodplain streams, cane drains, and wetlands. Combining the two novel approaches enabled an analysis of lagoon fish assemblage patterns in relation to environmental gradients, especially floodplain hydrology, connectivity patterns, and measures related to agricultural land use. In demonstrating the importance of different levels of connectivity for different biodiversity outcomes in freshwater floodplain lagoons of the Tully–Murray catchment, the subject paper established that floodplain connectivity needs to be taken into consideration in wetland management practices. The timing of the subject publication was fortuitous. It coincided with the preparation of the evidence‐based 2017 Scientific Consensus Statement on land‐based water quality impacts on the GBR. As one of the few freshwater wetland ecology publications for the catchments of the GBR at that time, this paper played an important role in demonstrating freshwater wetland values, fish conservation options, and management imperatives to sustain wetland ecological health and services in GBR catchments. By advancing the understanding of factors driving biodiversity patterns, and the importance of connectivity and ecohydrological processes in freshwater floodplain wetlands of the GBR catchment, the Tully–Murray study helped to drive new policy directives for the protection and restoration of catchment, floodplain, and estuary functions, and connectivity, now embedded in the Reef 2050 Long‐Term Sustainability Plan 2018, an overarching strategy for managing the GBR over the next 35 years, and complementary Queensland environmental legislation.

Temporal and spatial variability of heavy metals in bottom sediments and the aquatic macrophyte Paspalum repens of the Orinoco River floodplain lagoons impacted by industrial activities.

This study investigated the water parameters and the levels of several heavy metals in leaves and roots of the aquatic macrophyte Paspalum repens and in bed sediments of one unpolluted lagoon and two polluted lagoons of the Orinoco River floodplain to know the impact of the alumina refining wastes on these ecosystems. The sampling was performed during four hydrological periods, covering one hydrological year. Chemical parameters in water (pH, conductivity, and total dissolved solids) and the levels of Al, Pb, Cr, and Cu in sediments were the highest in Macanillal (LMaca) lagoon, whereas sediments of Punta Cuchillo (LPC) lagoon also had elevated concentrations of Al and Fe in comparison with Las Aruhacas (LArh) lagoon (unpolluted lagoon). Chemical parameters in waters returned almost to natural values during high water stage because of the huge inundation of the Orinoco River during the high discharge periods. The solid/liquid discharges of industrial effluents over these systems also affected the grain size distribution of sediments in the lagoons. In all the studied lagoons, the distribution of elements in leaves of P. repens was in the order K ≥ Cr > Ca > Mg > Al > Fe > Mn > Cu > Pb, whereas Al was found to be the more abundant element in roots. The high abundance of Cr in P. repens was related with the high Cr accumulation potential shown by aquatic macrophytes. Despite this, the concentration of elements in P. repens did not show differences between the plants collected in the polluted lagoons versus the plants collected in the unpolluted lagoon. This suggests that P. repens is unsuitable for bio-monitoring studies of heavy metals in these aquatic environments impacted by alkaline residues.

ISOLATION AND LAGOON MORPHOMETRY DEFINE FISH DIVERSITY AND COMPOSITION IN NEARSHORE AREAS OF FLOODPLAIN LAGOONS OF THE SOUTHERN PANTANAL

Floodplain lagoons support high fish diversity, but the role of local vs. regional factors in structuring assemblages is little studied in the Brazilian Pantanal. Aiming to understand the importance of limnological, biological, and regional characteristics shaping fish assemblages in the Pantanal floodplain, we sampled 26 lagoons in the Rio Negro floodplain from September 2005 through November 2006. Our results suggest that widely distributed species are also more abundant locally. Fish species richness is defined by a combination of isolation level, area and mean depth of lagoons, while evenness is determined mainly by macrophyte richness, lagoon area, water conductivity and distance to the river. Distribution of the most abundant fish species in sampled lagoons was explained by macrophyte biomass, lagoon area, shoreline development index and macrophyte richness. Overall, a general pattern of species diversity and distribution was primarily defined by a regional characteristic, namely, isolation, interacting with lagoon morphometry, and secondarily by biotic characteristics.

Conservation status and regional habitat priorities for the Orinoco crocodile: Past, present, and future.

Conservation of large predator species has historically been a challenge because they often overlap in resource utilization with humans; furthermore, there is a general lack of in-depth knowledge of their ecology and natural history. We assessed the conservation status of the Orinoco crocodile (Crocodylus intermedius), defining regional habitat priorities/crocodile conservation units (RHP/CCU) and regional research priorities (RRP) for this species. We also estimated a species distribution model (SDM) to define current suitable areas where the species might inhabit and/or that might be successfully colonized. The SDM area obtained with a suitable habitat probability ≥ 0.5 was 23,621 km2. Out of 2,562 km2 are included within protected areas in both Colombia (1,643 km2) and Venezuela (919 km2), which represents only 10.8% of C. intermedius’ potential range. Areas such as Laguna de Chigüichigüe (flood plain lagoon) exhibited an increase in population abundance. In contrast, localities such as the Cojedes and Manapire Rivers reported a significant reduction in relative abundance values. In Colombia, disparity in previous survey methods prevented accurate estimation of population trends. Only one study in this country described an increase over a 13 years span in the Ele, Lipa, and Cravo Norte River populations based on nest surveys. We defined 34 critical areas (16 in Colombia, 17 in Venezuela, and one covering both countries) where we need to preserve/research/monitor and/or generate management actions, 10 RHP/CCU (six from Venezuela and four from Colombia) and 24 RRP (11 from Venezuela, 12 from Colombia, and one in both countries). Caño Guaritico (Creek) and the Capanaparo River in Venezuela and the Ele, Lipa, Cravo Norte River System and the Guayabero River in Colombia were defined as areas with the most optimal conditions for long-term preservation and maintenance of C. intermedius populations. We conclude that the conservation status of this species is still critical, which implies the necessity to increase efforts to recover the species, especially in Colombia, to guarantee its survival as a structural and functional component of the ecosystems it inhabits.

Typification of Lymans of the North-Western Black Sea According to the Recommendations of the Eu Water Framework Directive

Purpose. Typification of limans in the north-western Black Sea coast (NWBS) (so called “marine lagoons”) according to the EU Water Framework Directive methodological approaches on hydrological, morphometric, hydrochemical and genesis characteristics. Methods. Comparative &amp; geographical, generalization, cluster analysis. Results. Five groups of limans have been determined by analysis of their crucial parameters: mean annual salinity, depth fluctuation, fresh water influx, water bodies’ and their catchments’ genesis, which were taken from the historical sources and from researches of the Odessa I.I. Mechnikov National University. The selected groups comprised water bodies having similar properties in their water balance regime, origin and hydrochemical regime. Brief description of properties for the each group of water bodies has been formulated. A comparison of the typification results with the work of another team on these objects has been conducted. Conclusions. Five types of limans have been identified in the NWBS: 1) floodplain lagoons, oligogaline, shallow, without free connection to the sea; 2) polygaline shallow sea lagoons; 3) very elongated deep mesohaline floodplain water bodies; 4) estuaries of large rivers with permanent connection to the sea; 5) floodplain shallow hyperhaline water bodies, without a natural connection to the sea. The typification performed makes it possible to use modern monitoring programs for large groups of water bodies in NWBS taking into account the European experience.

Contribution of humic substances as a sink and source of carbon in tropical floodplain lagoons

Purpose We evaluated the decay of humic (HA) and fulvic acids (FA) in order to discuss the contribution of these substances as a sink and source of carbon in a tropical lagoon.

Fish larvae and recruitment patterns in floodplain lagoons of the Australian Wet Tropics

Floodplain lagoons in the Queensland Wet Tropics bioregion, Australia, are important and threatened habitats for fish. As part of studies to assess their ecological condition and functions, we examined patterns of occurrence of fish larvae, juveniles and adults in 10 permanent lagoons on the Tully–Murray floodplain. Lagoons contained early life-history stages of 15 of the 21 native species present, including 11 species that complete their life cycle in fresh waters and 4 that require access to saline habitats for larval development. Lagoon connectivity to the rivers, distance from the coast and flood dynamics influenced temporal variation in fish abundance, population size structures and recruitment patterns. This study and the literature show that wet, post-wet and dry-season habitats are utilised by small opportunists (e.g. Melanotaenia splendida), an equilibrium species (Glossamia aprion) and larger periodic strategists (neosilurid catfishes). Maintenance of natural seasonal patterns of flow and connectivity, and active protection of permanent floodplain lagoons from riparian and land-use disturbance, will be essential if their roles in fish recruitment are to be sustained.

Subsurface constraints of an active detachment fault in Laguna Salada Basin, Baja California, México, from interpretation of seismic-reflection profiles

The Laguna Salada Basin in northeastern Baja California, Mexico, is an active half-graben with subsidence principally controlled by two major faults along the eastern basin margin—the Canada David detachment fault and the dextral oblique Laguna Salada fault. Active-source, seismic-reflection data constrain the geometry of the active detachment fault and indicate two structural domains. The south domain is a supradetachment basin controlled by the Canada David detachment fault. Two seismic profiles indicate the detachment fault dips 17°–20° west, has a minimum of 10.1 km of slip, and accumulates a sedimentary wedge more than 2.5 km thick in the west-central part of this basin domain. This estimation indicates that the subsurface portion of the Canada David detachment accommodates 24% of extension in the western main plate boundary zone. The north domain is a dilatational stepover (or pull apart) controlled by the northwest-trending, west-dipping, dextral-oblique Laguna Salada fault and the north-trending, dip-slip Canon Rojo fault, which defines the south boundary of the pull-apart basin domain. The Canon Rojo fault accumulates more than 2 km of subsidence, but geometric considerations indicate that the basement in the hanging wall of the Laguna Salada fault projects to a depth of ∼3.8 km and intersects the 70° west-dipping Laguna Salada fault. Several faults cut the west margin of the floodplain lagoon and the hanging wall of both the Canada David detachment and the Laguna Salada fault. The largest fault is west dipping and produces ∼500 m of vertical offset. Its location projects south of the Canon Rojo fault, and we speculate these two faults may correlate. Seismic facies reflect its sedimentary environment and processes. Seismic facies 1 is high-amplitude, laterally continuous reflectors that represent flooding and prolonged lacustrine conditions. Seismic facies 2 is high- to low-amplitude, laterally discontinuous reflectors also representing flooding conditions. Seismic facies 3 is low-amplitude, poorly contrasted continuous to discontinuous reflectors interpreted as subaerial distal fan sandstone deposits. Seismic facies 4 is high-amplitude, discontinuous, imbricated to a chaotic pattern of reflectors. We interpret facies 4 as coarse-grained, high-energy alluvial fan deposits prograding over the basin floor from the west in the range front of Sierra Juarez. Seismic facies 1 and 2 predominate in the east and central portions of seismic profiles where the depocenter accumulates thicker sedimentary sequences.

Nonlinear effect of density on trophic niche width and between‐individual variation in diet in a neotropical cichlid

AbstractDensity‐dependent dynamics have considerable effects in many ecological processes and patterns that characterize natural populations. In the present study, we aim at evaluating the effect of density on the diet width and between‐individual variability in nine different pike cichlid Crenicichla lepidota populations dwelling in floodplain lagoons. Our results indicated that low‐density populations exhibit small diet breadth as well as small between‐individual variability in their diet. In addition, these populations were characterized by a nested diet pattern, where the diet of specialist individuals represented a subset of the food items consumed by generalist individuals. Populations with intermediate densities had a larger populational diet breadth while the individual diet breadth remained unchanged. This pattern was due to an increase in between‐individual variability in diet, which consequently decreases the diet overlap among individuals and thus lower diet nestedness. Finally, under high densities, the niche width at the population level decreased because of lower between‐individual variability and higher diet overlap. Together, these results showed that niche width exhibits a non‐linear function with density. At first, an increase in density increased the niche width because of greater between‐individual diet variability. However, after a threshold density value, the effect was reversed, and the niche width decreased because of a higher diet overlap among individuals.

Proposal of a non-lethal visual census method to estimate freshwater stingray abundance

&lt;p&gt;There is not a current method to estimate South American freshwater stingray’s abundance. Therefore we designed a census method and tested it in the field. It consists of making nocturnal surveys by boat in large rivers (&amp;gt;25m width) and floodplain lagoons of varying sizes, along transects of 100m x 10m (1000 m2). We applied this method in the Tomo River, a tributary of the Orinoco River in Colombia. 110 transects were surveyed in 200 runs. A total of 149 rays of four species were recorded: &lt;em&gt;Potamotrygon motoro, Potamotrygon orbignyi, Potamotrygon schroederi&lt;/em&gt; and &lt;em&gt;Paratrygon aiereba. P. motoro&lt;/em&gt; was the most abundant with a density of 0.31 individuals /1000 m2 (SD=0.5). This method gave optimal results when applied to habitats with high transparency and shallow depth (&amp;lt; 1m) since it permitted the identification of both adults and juveniles present.&lt;/p&gt;

Status of the Endangered Yellow Chat Epthianura crocea tunneyi on the western South Alligator River floodplain, Kakadu National Park

The current status of the Endangered Yellow Chat Alligator Rivers subspecies Epthianura crocea tunneyi is poorly known. A survey of Kakadu National Park floodplains, Northern Territory, in 2004 identified the western floodplain of the South Alligator River as a key population area. To provide preliminary information on the status of the subspecies in Kakadu National Park, this floodplain was intensively surveyed over a 4-day period in September 2014 and compared with the 2004 survey, which was undertaken at a similar time of year (late dry season: October–November). Despite covering considerable areas of floodplain habitat over nearly 40 hours of surveying, Yellow Chats were recorded in only one area in 2014; 27 Yellow Chats from nine observations were recorded over 2 days, with a minimum number of 17 individual birds (16 adult and 1 juvenile) observed. This compared with a total of 65 Yellow Chats from 2 days of surveying in 2004, clustered around five areas of the western floodplain of the South Alligator River. Habitat in 2014 comprised predominantly dry floodplain lagoon, consistent with previous surveys. Feral animals (in particular Feral Pigs Sus scrofa ) were regularly observed throughout the surveys, as was significant feral-animal damage to wet floodplain areas. Although these results suggest a possible decline on the western South Alligator River floodplain over a 10-year period, a comprehensive survey is required of all floodplains within the subspecies’ range to assess overall population status. This could inform the establishment of annual monitoring sites in order to evaluate long-term population trends, essential data for management of threatened species.

Influence of water fluctuations on the limnological characteristics of two floodplain lagoons (Ribeira do Iguape Valley, state of São Paulo, Brazil)

Abstract Aim: Current study assessed the influence of hydrometric levels on the limnological characteristics of two river floodplain systems in the Ribeira do Iguape Basin (state of São Paulo, Brazil). Methods: Rainfall data were collected dailyfrom an automatic weather station in Jacupiranga SP Brazil and daily hydrometric level records were obtained from automatic linigraphs installed on the two adjacent rivers. Moreover, pH, electrical conductivity and dissolved oxygen were measured by a multiparametric probe. Water samples were collected to analyze nitrate, ammoniac nitrogen, total nitrogen and phosphorus, total alkalinity and suspended material. The samplings were carried out in April and July, representative months for low and high water periods, respectively. Results and Conclusions: Statistical analysis highlighted the “effect of homogenization”, attributed to the hydrological pulses in several studies carried out in river-floodplain systems. This effect in current study was more underscored at Lagoon 2, which remained connected for a longer period with the adjacent river, when compared to Lagoon 1- River Jacupiranguinha system. Higher dissolved oxygen concentrations at Lagoon 2, in contrast with the Lagoon 1 featuring anoxia during the whole period under analysis, were also attributed to the above-mentioned greater hydrological connectivity. Current study highlights that the water-mediated transferences during the high water period may contribute not only towards the fertilization of marginal lagoons (inputs of nutrients and organic matter) but also to significant pollutant loads, according to land use along the watersheds. In the case of Lagoon 1- River Jacupiranguinha system, even though further studies are needed and strongly recommended, it is reasonable to assume that the discharges of mining effluents into the river may result in ecological damage not only to the receiving water body but also to the connected ecosystems.

Evaluation of alternative macroinvertebrate sampling techniques for use in a new tropical freshwater bioassessment scheme

Aim: The study aimed to determine the effectiveness of benthic macroinvertebrate dredge net sampling procedures as an alternative method to kick net sampling in tropical freshwater systems, specifically as an evaluation of sampling methods used in the Zambian Invertebrate Scoring System (ZISS) river bioassessment scheme. Tropical freshwater ecosystems are sometimes dangerous or inaccessible to sampling teams using traditional kick-sampling methods, so identifying an alternative procedure that produces similar results is necessary in order to collect data from a wide variety of habitats.MethodsBoth kick and dredge nets were used to collect macroinvertebrate samples at 16 riverine sites in Zambia, ranging from backwaters and floodplain lagoons to fast flowing streams and rivers. The data were used to calculate ZISS, diversity (S: number of taxa present), and Average Score Per Taxon (ASPT) scores per site, using the two sampling methods to compare their sampling effectiveness. Environmental parameters, namely pH, conductivity, underwater photosynthetically active radiation (PAR), temperature, alkalinity, flow, and altitude, were also recorded and used in statistical analysis. Invertebrate communities present at the sample sites were determined using multivariate procedures.ResultsAnalysis of the invertebrate community and environmental data suggested that the testing exercise was undertaken in four distinct macroinvertebrate community types, supporting at least two quite different macroinvertebrate assemblages, and showing significant differences in habitat conditions. Significant correlations were found for all three bioassessment score variables between results acquired using the two methods, with dredge-sampling normally producing lower scores than did the kick net procedures. Linear regression models were produced in order to correct each biological variable score collected by a dredge net to a score similar to that of one collected by kick net sampling.ConclusionsThe use of a dredge net in macroinvertebrate bioassessment schemes is an effective, alternative method in certain environments when site conditions prohibit the use of the preferred kick net sampling method. The results of this study can be used to aid in the development of other tropical freshwater bioassessment schemes around the world, including Brazil.

Impact of the Red Mud Disposal on Several Floodplain Lagoons of the Lower Orinoco River

This paper identifies the effects of red mud spills on several lagoons of the Orinoco River located surrounding the red mud deposits. Chemical and mineralogical analyses of sediments indicate that the geochemical signature of red mud is evident in Los Caribes and Guadita lagoons, with elevated concentrations of Fe, Al, and Na and the presence of goethite and hematite as the major mineral phases. Water quality analyses indicate that these lagoons have elevated values of dissolved oxygen, pH, conductivity, and dissolved Ca, Na, Ni, and Al. Also, elevated concentrations of Ca, Mg, and Mn in sediments suggest the precipitation of calcite, brucite a Mn-oxyhydroxides due to high pH values. Although Los Cardonales lagoon also showed evidence of red mud deposition, the enrichment of Mn, Zn, Ni, and Cd in sediments from this lagoon could be associated with wastewaters coming from landfills. The absence of vascular plants and the low abundance of fish communities in several lagoons can be related with the high pH values and the elevated concentrations of dissolved Al. The high concentrations of Fe and Mn in sediments of these lagoons can have adverse effects on benthic organisms, according to International Guidelines. Even though this lagunar system is impacted by red mud spills, hyperalkaline conditions (pH > 13) were not found in superficial waters. Thus, dissolved trace element concentrations (Fe, Zn, Mn, Cr, Cu, Cd, and Pb) in waters were not high, mainly due to trace elements are immobilized by sorption or coprecipitation at circum-neutral pH.