Colonization of benthic invertebrates on artificial and natural substrate in a Neotropical lotic environment in Southern Brazil

The objective of this research was to validate the colonization process on natural and artificial substrates by benthic invertebrates in a tropical stream in South Brazil. The samples were performed in July and August-2012, and 32 samplers were used, being 16 natural and 16 artificial substrates. In each sample, two replicas were taken for each substrate at the 2th, 4th, 7th, 14th, 21th28th, 35th and 42thdays of colonization. The organisms were identified to the lowest possible taxonomic level. In both substrates 3,070 benthic invertebrates were detected, of which 1,753 individuals were collected on the natural substrate, and 1,317 on the artificial substrate. From the identified taxa 8.5% were not dominant (Anacroneuria, Orthocladiinae, Tupiara, Smicridea, Baetodes, Tupiperla, Macrogynoplax, Gripopteryx, Cylloepus, Macrelmis, Microcylloepus, Hetaerina, Argia, Coryphaeschna, Atopsyche, Pomacea, Corydalus, Leptohyphes and Eccoptura), and31.5% were dominant (Tanypodinae, Chironominae, and Paragripopteryx). The genus Simulium was very common, dominant and abundant, representing 65% of the collected individuals. No significant difference was found in the abundance and species composition between artificial and natural substrates. On the natural substrate, the higher colonization index was at the 35th day with 459 individuals, and the lowest was at the 14th day, with 87. On the artificial substrate the highest index was at the 42thday with 337 individuals, and the lowest was at the 4th day, with 85. Both natural and artificial substrates are efficient in characterizing the benthic community. In the evaluation of the ecological succession, it was not possible to observe a pattern that described the process, since the composition was nearly constant throughout the study period.

Distribution and abundance of freshwater decapods in an Atlantic rainforest catchment with a dammed future / Distribuição e abundância de decápodes de água doce e sua associação com variáveis ambientais em uma bacia hidrográfica de Mata Atlântica que será represada

Abstract Variations in physical characteristics along the course of a river influence habitat availability which reflects in species distribution. Knowledge of ecology and diversity of lotic species is important for evaluating how river ecosystems will respond to environmental impacts. Freshwater decapods are a group of high ecological and economic importance, but the knowledge about factors influencing their distribution is scarce in Brazil. We performed a survey of decapods to describe their abundance and distribution as well as to study their relationships with stream physical variables and especially their association with different substrates types. We studied 23 sites located in 15 tributaries of Guapiaçú River, RJ, where we collected decapods in different substrates types and measured a set of physical variables. We found five decapods species, including amphidromous and non-amphidromous shrimps and crabs. Decapods were strongly associated with leaf-litter substrates and their abundance was related to a multivariate axis describing longitudinal changes in stream characteristics. We concluded that decapods occurring in the Guapiaçú catchment inhabit mainly small streams with preserved riparian forests where they find shelter and potential prey of invertebrates. The ongoing project to build a dam on the Guapiaçú River will have negative consequences to migrating shrimps and we strongly recommend that mitigating actions, such the construction of structures to allow the passage of migrating fauna, should be taken.

Resumo Variações nas características físicas de um rio ao longo do seu curso influenciam a disponibilidade de habitas e dessa forma a distribuição de espécies. O conhecimento sobre a ecologia e diversidade de espécies lóticas é importante para avaliar como esses ecossistemas responderão a impactos ambientais. Decápodes de água doce são um grupo de grande importância ecológica e econômica, contudo o conhecimento sobre fatores influenciando sua distribuição ainda é escasso no Brasil. Nós realizamos um levantamento de decápodes para descrever sua abundância e distribuição, bem como estudar sua relação com características físicas dos rios, especialmente sua associação com tipos diferentes de substrato. Nós estudamos 23 localidades distribuídas em 15 rios tributários do Rio Guapiaçú, RJ, onde coletamos decápodas em diferentes tipos de substratos e medimos um conjunto de variáveis físicas. Nós encontramos cinco espécies de decápodas incluindo camarões anfídromos e não anfídromos e caranguejos. Esses organismos foram fortemente associados a substratos de folhiço alóctone e sua abundância foi relacionada com um eixo PCA que descreve as mudanças nas características físicas longo do curso do rio. Nós concluímos que os decápodas que ocorrem na bacia do Rio Guapiaçú habitam principalmente pequenos córregos com mata ciliar preservada, onde podem encontrar abrigo e um potencial campo de caça onde predam invertebrados. O projeto atualmente em curso para a construção de uma represa no Rio Guapiaçú irá afetar negativamente a fauna de camarões anfídromos, assim nós recomendamos fortemente que ações mitigadoras, como a construção de estruturas para permitir a passagem da fauna migrante sejam tomadas.

Temperatura y emergencia diaria de siete géneros de Ephemeroptera(Insecta) en un río de la Selva Nublada de los Andes Tropicales / Temperature and daily emergence of seven genera of Ephemeroptera (Insecta) in a cloud forest stream of tropical Andes

ResumenLa emergencia diaria de los efemerópteros de ríos neotropicales y sus causas, han sido poco estudiadas. En zonas templadas, este proceso es mejor conocido y atribuido a diversos factores. En este trabajo, estudiamos la emergencia diaria de subimagos de varios géneros de Ephemeroptera en un río en una selva nublada andina venezolana, y sus posibles relaciones con cambios diarios de la temperatura ambiente. Cuatro trampas de emergencia fueron colocadas en un tramo de 50m del río, y cada una se examinó cada dos horas durante 24 horas para recolectar los subimagos recién emergidos. Este procedimiento fue repetido en ocho fechas, entre noviembre-2007 y febrero-2008, para un total de 32 observaciones en cada hora de muestreo. Los subimagos fueron criados hasta adultos e identificados hasta género. Para cada género y hora de muestreo calculamos la densidad relativa de emergencia por trampa. La temperatura del agua y del aire fueron medidas cada hora del ciclo diario de observación y, para cada hora calculamos la temperatura promedio y los gradoshoras promedio del aire y del agua, de las ocho fechas estudiadas. Se identificaron siete géneros: Leptohyphes Eaton, 1882 y Haplohyphes Allen, 1966 (Leptohyphidae); Prebaetodes Lugo-Ortiz y McCafferty, 1996, Andesiops Lugo-Ortiz y McCafferty, 1999, Baetodes Needham y Murphy, 1924 y Americabaetis Kluge, 1992 (Baetidae); y Thraulodes Ulmer, 1920 (Leptophlebiidae); siendo más abundantes Leptohyphes (38.4 %) y Thraulodes (20.5 %). La emergencia ocurrió entre las 11:00 am y 23:00 pm, y mostró lo siguiente: a) una emergencia iniciada en horas diurnas, por organismos de Leptohyphes, Prebaetodes y Haplohyphes; b) una emergencia nocturna, realizada por Thraulodes, Andesiops, Baetodes y Americabaetis; y c) dos máximos, uno diurno producido por Leptohyphes, y otro nocturno con predominancia de Thraulodes. Estos resultados son los primeros registros sobre la emergencia diaria diurna en Andesiops, Prebaetodes, Americabaetis, Haplohyphes y Leptohyphes; así como, de la emergencia nocturna en Thraulodes. Se evidenció que Leptohyphes, con ninfas pequeñas (ancho cefálico promedio = 1.05 mm), necesitó acumular menos grados-horas para iniciar la emergencia que los requeridos por Thraulodes, cuyas ninfas son más grandes (ancho cefálico promedio = 2.01 mm). Esta disparidad en los requerimientos energéticos para la emergencia, debe ser consecuencia de diferencias entre los tamaños de las ninfas maduras de ambos géneros; hechos que se apoyan sobre la constancia de tamaños que muestran ambos taxa en un gradiente térmico-altitudinal, y en la poca variabilidad diaria y estacional de la temperatura del agua en el río La Picón. En el lapso diario de emergencia, las temperaturas promedios del aire y del agua fueron superiores a aquellas registradas dentro del lapso de no-emergencia; en consecuencia, se propone que durante el lapso diario en el que ocurre este proceso, el ambiente es térmicamente favorable para la emergencia de los subimagos y su supervivencia fuera del agua.

AbstractDaily emergence of mayflies in Neotropical rivers and their causes have been poorly studied. In temperate zones, this process is better known and attributed to several factors. In this work, we studied the daily emergence of subimagines of several Ephemeroptera genera in La Picón River of a Venezuelan Andean cloud forest and its relation with changes of environmental temperature. Four emergence traps were placed along a reach of 50 m of the stream, each one was examined each two hours in a 24 hr cycle to capture the newly emerged subimagos. This procedure was repeated for eight dates between November-2007 and February-2008 for a total of 32 observations in each sampling hour. The subimagos were reared to adults and identified to genus. The relative density of emergence per trap was calculated for each genus and sampling hour. Water and air temperature were measured each hour during the daily cycle of observation, and the averages of temperature and hour-degrees of air and water were calculated for each hour from the eight dates studied. Seven genera were identified: Leptohyphes Eaton, 1882 and Haplohyphes Allen 1966 (Leptohyphidae); Prebaetodes Lugo-Ortiz and McCafferty, 1996, Andesiops Lugo-Ortiz and McCafferty, 1999, Baetodes Needham and Murphy, 1924 and Americabaetis Kluge, 1992 (Baetidae); and Thraulodes Ulmer, 1920 (Leptophlebiidae); being the more abundant Leptohyphes (38.4 %) and Thraulodes (20.5 %). The emergence occurred between 11:00 am and 23:00 pm showing the following: a) an emergence initiated during daylight hours by organisms of Leptohyphes, Prebaetodes and Haplohyphes; b) a nocturnal emergence, in Thraulodes, Andesiops, Baetodes and Americabaetis; and c) two peaks: one diurnal produced by Leptohyphes and other nocturnal with predominance of Thraulodes. These results are the first records on the diurnal daily emergence in Andesiops,Prebaetodes,Americabaetis, Haplohyphes, and Leptohyphes, as well as the nocturnal emergence in Thraulodes. It was evidenced that Leptohyphes, with small nymphs (average head width = 1.05 mm) needed to accumulate less hourdegrees to initiate the emergence than those required by Thraulodes whose nymphs are larger (average head width = 2.01 mm). This disparity in the emergence energy requirements must be consequence of differences between the sizes of mature nymphs of both genera; facts which rely on the constancy of sizes shown by these taxa along an altitudinal-thermal gradient and the little daily and seasonal variability of water temperature in La Picón River. In the daily lapse when the emergence occurred, the air and water average temperatures were higher than those registered in the no-emergence lapse; therefore; it is suggested that during the daily lapse, when this process occurs, the environment is thermally favorable for the emergence of subimagos and their survival out of water. Rev. Biol. Trop. 64 (1): 117-130. Epub 2016 March 01.

Effects of insect and decapod exclusion and leaf litter species identity on breakdown rates in a tropical headwater stream

High species richness of tropical riparian trees influences the diversity of organic detritus entering streams, creating temporal variability in litter quantity and quality. We examined the influence of species of riparian plants and macroinvertebrate exclusion on leaf-litter breakdown in a headwater stream in the Luquillo Mountains of Puerto Rico. Leaf litter of Dacryodes excelsa (Burseraceae), Guarea guidonia (Meliaceae), Cecropia scheberiana (Moraceae), Manilkara bidentata (Sapotaceae), and Prestoea acuminata (Palmae) were incubated in litter bags in a pool of Quebrada Prieta. Fine mesh bags were used to exclude macroinvertebrates during leaf breakdown, and coarse mesh bags allowed access to decapod crustaceans (juvenile shrimps and crabs) and aquatic insects (mainly mayflies, chironomids, and caddisflies). D. excelsa and G. guidonia (in coarse- and fine-mesh bags) had significantly higher breakdown rates than C. scheberiana, M. bidentata, and P. acuminata. Breakdown rates were significantly faster in coarse-mesh bag treatments for all leaf types, thus indicating a positive contribution of macroinvertebrates in leaf litter breakdown in this headwater stream. After 42 days of incubation, densities of total invertebrates, mayflies and caddisflies, were higher in bags with D. excelsa and G. guidonia, and lower in P. acuminata, C. scheberiana y M. bidentata. Decay rates were positively correlated to insect densities. Our study highlights the importance of leaf identity and macroinvertebrate exclusion on the process of leaf litter breakdown in tropical headwater streams. Rev. Biol. Trop. 62 (Suppl. 2): 143-154. Epub 2014 April 01.

La gran variedad de especies vegetales junto a los ríos tropicales afecta la diversidad de detritos orgánicos que llegan a los arroyos, creando variaciones temporales en cantidad y calidad de hojarasca. Examinamos la influencia de las especies vegetales y de la exclusión de macroinvertebrados sobre la descomposición de hojarasca en la parte alta de un arroyo en las montañas Luquillo de Puerto Rico. Incubamos hojarasca de Dacryodes excelsa (Burseraceae), Guarea guidonia (Meliaceae), Cecropia scheberiana (Moraceae), Manilkara bidentata (Sapotaceae) y Prestoea acuminata (Palmae) en bolsas descomposición que colocamos en una poza de Quebrada Prieta. Usamos bolsas de malla fina para excluir los macroinvertebrados y de malla gruesa para permitir la entrada a crustáceos decápodos (camarones y cangrejos jóvenes) e insectos acuáticos (principalmente efemerópteros, quironómidos y tricópteros). D. excelsa y G. guidonia (en ambos tipos de malla) tuvieron tasas de descomposición más altas que C. scheberiana, M. bidentata y P. acuminata. La descomposición fue más rápida para todas las especies de hoja con la malla gruesa, resaltando el papel de los descomponedores en este hábitat. Tras 42 días de esta incubación, las densidades totales de invertebrados, efemerópteros y tricópteros fueron mayores en las bolsas con hojas de D. excelsa y G. guidonia, e inferiores en P. acuminata, C. scheberiana y M. bidentata. A mayor densidad de insectos hubo mayor tasa de descomposición. Nuestros resultados indican la importancia de la especie de las hojas y de la presencia de macroinvertebrados en el proceso de descomposición de hojarasca en partes altas de arroyos tropicales.

Índice de calidad ecológica con base en macroinvertebrados acuáticos para la cuenca del río Negro (ICE RN-MAE), Colombia

Aquatic Ecological Index based on freshwater (ICE RN-MAE) for the Río Negro watershed, Colombia. Available indices to assess the ecological status of rivers in Colombia are mostly based on subjective hypotheses about macroinvertebrate tolerance to pollution, which have important limitations. Here we present the application of a method to establish an index of ecological quality for lotic systems in Colombia. The index, based on macroinvertebrate abundance and physicochemical variables, was developed as an alternative to the BMWP-Col index. The method consists on determining an environmental gradient from correlations between physicochemical variables and abundance. The scores obtained in each sampling point are used in a standardized correlation for a model of weighted averages (WA). In the WA model abundances are also weighted to estimate the optimum and tolerance values of each taxon; using this information we estimated the index of ecological quality based also on macroinvertebrate (ICE RN-MAE) abundance in each sampling site. Subsequently, we classified all sites using the index and concentrations of total phosphorus (TP) in a cluster analysis. Using TP and ICE RN-MAE, mean, maximum, minimum and standard deviation, we defined threshold values corresponding to three categories of ecological status: good, fair and critical. Rev. Biol. Trop. 62 (Suppl. 2): 233-247. Epub 2014 April 01.

Los índices disponibles para la evaluación del estado ecológico de los ríos en Colombia están basados principalmente en hipótesis subjetivas generalizadas acerca de la toleración de los macroinvertebrados, un proceso que presenta limitaciones. En este estudio se presenta la aplicación de un método para establecer un índice de calidad ecológica para sistemas lóticos, basado en abundancia de macroinvertebrados y variables fisicoquímicas. Se tomó como caso de estudio la cuenca del rio Negro (Colombia). Este nuevo índice se ha formulado como alternativa al BMWP-Col y consiste en la determinación de un gradiente ambiental a partir de un Análisis de Correspondencia Canónica de correlaciones entre abundancias y registros fisicoquímicos. Los puntajes de las estaciones -obtenidos en las correlaciones- son estandarizados y usados en un modelo de Promedios Ponderados (WA); en el modelo se ponderan también las abundancias para estimar los valores óptimos y de tolerancia de cada taxón. Con ellos y la abundancia se calcula los valores del Índice de Calidad Ecológica con base en macroinvertebrados acuáticos para la cuenca del rio Negro (ICE RN-MAE). Se utilizan los valores del índice junto con las concentraciones de fósforo total (FT) en un análisis de agrupamiento, para así clasificar los sitios de estudio. De ahí se obtienen finalmente los valores medios, máximos, mínimos y de desviación estándar del ICE RN-MAE y FT. Con ellos se definen los umbrales que corresponden a diferentes categorías de calidad ecológica (buena, regular y crítica).

Grupos funcionales alimentarios de macroinvertebrados acuáticos en el río Gaira, Colombia

Functional feeding groups of macroinvertebrates in Gaira river, Colombia. Tropical rivers are frequently described on their biodiversity but few studies have considered the ecological value of this richness in their food webs. We determined the trophic structure of aquatic macroinvertebrate communities (expressed in the richness and abundance of taxa and biomass proportions of different functional feeding groups) at the level of the river, stretch and microhabitats (functional units - UFs). We evaluated the spatial and temporal variation of these descriptors during wet and dry events, and selected three sites associated with different altitudinal belts. We reported 109 taxa, with 11 167 individuals who contributed 107.11g of biomass. Density of macroinvertebrates was favored with increasing height, and biomass showed the opposite pattern (K-W=10.1, d.f.=1, p<0.05), due to the addition of large crustaceans (Macrobrachium), and the taxa diversity was higher in the middle stretch of the river (H’=3.16). The Gaira stream runs through a mid-sized river basin, for this reason we found mainly bedrock (epilithon=50.5%), gravel and sand (43.7%). The functional unit with more habitat and food resources that contains a higher abundance of leaf litter macroinvertebrates was foliage followed by epilithon, fine sediment and gravel-sand (K-W=25.3, d.f.=3, p<0.05). The biomass values of these organisms were higher in leaves followed by gravel-sands, epilithon and sediment (K-W=15.3, d.f.=3, p<0.05). Autochthonous biomass input by different functional feeding groups can be considered very low, but they define the functionality of the stream, being represented almost exclusively by shredders (Macrobrachium, 73%), present only in the lower reaches, followed by shredder Leptonema with 15%, located mostly in the upper reaches and predatory stoneflies of the genus Anacroneuria to 6.56%, which dominated in the middle stretch of stream. Excluding Macrobrachium from the analysis, there was dominance of Anacroneuria in the lower reaches. Between rainfall and drought events, biomass of functional feeding groups was higher in rain (W=10.1, d.f.=1, p<0.05), favoring the growth of decapods, but the abundance was much higher during drought events. Rev. Biol. Trop. 59 (4): 1537-1552. Epub 2011 December 01.

Para Colombia, la información sobre grupos funcionales alimentarios de macroinvertebrados acuáticos es muy escasa. Por lo tanto, en este estudio se determinó la riqueza, abundancia y biomasa de los GFAs de estos organismos a escala de río, tramo y unidades funcionales, con el objeto de evaluar su variación espacio-temporal. Se seleccionaron tres tramos de 200m. En total se reportan 109 táxones, con una abundancia de 11 167 individuos que aportaron una biomasa de 107.11g. La densidad de los macroinvertebrados se vio favorecida con el incremento en la altura, la biomasa presentó un patrón inverso pues fue mayor hacia el tramo bajo y la diversidad de táxones fue mayor en el tramo medio del río (H’=3.16). Los valores de biomasa de estos organismos fueron mayores en hojarasca seguida de gravas-arenas, epiliton y sedimento. El tramo bajo fue dominado por Macrobrachium con el 73%, seguido de Leptonema con el 15 % en el tramo alto y Anacroneuria con el 6.56 %, en el tramo medio del río. Entre eventos de lluvia y sequía, la biomasa aportada por los grupos funcionales alimentarios fue mayor en lluvia, pero la abundancia fue muy superior durante eventos de sequía.

Mesohabitat indicator species in a coastal stream of the Atlantic rainforest, Rio de Janeiro-Brazil

The Mato Grosso is a typical Atlantic Forest stream located on the East coast of Brazil, approximately 70km from Rio de Janeiro city. From its source at about 800m a.s.l, the stream drains a 30km² area of the Northwestern part of the municipality of Saquarema, state of Rio de Janeiro and flows into the Saquarema Lagoon system. We hypothesized that fish species occupy distinct mesohabitats, with the prediction that their occurrences and densities differ among the microhabitats of riffles, runs and pools. A 250m-long stretch of the stream located in its uppermost part was selected for this study, where it becomes second-order. Mesohabitat description and their fish characterization were undertaken. Fish sampling was conducted by electroshocking and after their identification and counting, they were returned to the stream. For mesohabitat characterization, a Discriminant Function Analysis (DA) was applied. The total number of samples was estimated by the Zippin method and the recorded densities were used as an Indicator Species Analysis (ISA), followed by a Monte Carlo test for 1 000 permutations. The DA significantly separated the three predetermined mesohabitats (pool, riffle and run) (WL=0.13, F=187.70, p=0.001). We found five species of fishes, belonging to four families and three orders. The fishes Rhamdia quelen, Phalloceros harpagos, Pimelodella lateristriga and Astyanax taeniatus are indicators of the pool environment in the Mato Grosso stream, whereas Characidium cf. vidali is an indicator of the riffle environment. The Monte Carlo test detected non-random mesohabitat use only for P. lateristriga and A. taeniatus in the pools and for Characidium cf. vidali in the riffles. We concluded that the Mato Grosso stream contains three well-defined mesohabitats, with indicator species present in two of these mesohabitats. Rev. Biol. Trop. 58 (4): 1479-1487. Epub 2010 December 01.

El estudio se realizó en el Río Mato Grosso (22º55‘ S-42º35‘ W), donde se encontraron cinco especies de peces, pertenecientes a cuatro familias y tres órdenes. Teniendo en cuenta la distancia filogenética y la evidente diferencia morfológica externa entre ellos, nuestra hipótesis es que ellos ocupan distintos mesohabitats y que las ocurrencias y densidades difieren entre mesohabitats, previamente definidos como corriente, rápido y remanso. La colección de peces fue realizada por pesca eléctrica, los peces fueron identificados, contados y devueltos al arroyo. Para la caracterización de mesohabitats se aplicó un análisis de función discriminante (AD). El número total de ejemplares fue calculado por el método de Zippin y las densidades fueron utilizadas para un análisis de especies indicadoras (AIE), seguido de la prueba MonteCarlo para 1 000 permutaciones. Los tres mesohabitats fueron separados de manera significativa por AD (WL=0.13, F=187.70, p=0.00), siendo las especies Phalloceros harpagos, Pimelodella lateristriga, Rhamdia quelen y Astyanax taeniatus indicativas del ambiente de remanso, mientras que Characidium cf. Vidali del ambiente rápido. Podemos concluir que este arroyo presenta tres mesohabitats bien definidos con la presencia de especies indicadoras en estos dos mesohabitats.

Nutrient addition does not enhance leaf decomposition in a Southeastern Brazilian stream (Espinhaço mountain range)

A decomposition experiment using eucalyptus leaves was carried out in a Southeastern Brazilian mountain stream located at the transition between the Cerrado and the Atlantic Forest to test whether nutrient addition increases microbial and invertebrate colonisation and accelerates breakdown rates. The results show that none of the tested variables was significantly affected by nutrient addition, despite the average increase in ATP concentrations and invertebrate colonisation observed in the fertilised leaf bags. This could mean that breakdown in the stream was already at its maximum due to the relatively high water temperature and nutrient content, or that the breakdown rate of eucalyptus leaves was too fast to allow the detection of any effects of nutrient addition. Breakdown rates of eucalyptus leaves were much faster than the values reported in literature for most species in Brazilian Cerrado streams, suggesting that the replacement of the natural vegetation by eucalyptus may affect nutrient dynamics in the region.

Um experimento de decomposição de folhas de eucalipto foi efetuado em um riacho do sudeste do Brasil, localizado na transição entre o Cerrado e a Mata Atlântica para testar se a adição de nutrientes aumenta a colonização das folhas por microrganismos e por invertebrados e se acelera a sua taxa de decomposição. Nenhuma das variáveis testadas foi significativamente afetada pela adição de nutrientes, apesar do aumento médio verificado nas concentrações de ATP e na colonização por invertebrados dos sacos contento detritos fertilizados. Isto pode significar que a decomposição no riacho já ocorria à taxa máxima devido à temperatura e concentração de nutrientes relativamente elevadas da água ou que a taxa de decomposição das folhas de eucalipto foi demasiado rápida para permitir detectar qualquer efeito da adição de nutrientes. Os coeficientes de decomposição das folhas de eucalipto (0,1127 - 0,1192 dia-1) foram mais elevados que os verificados na literatura para a maioria das espécies em riachos do Cerrado, sugerindo que o reflorestamento com eucalipto pode alterar a dinâmica dos nutrientes na região.