Sandbar Opening Research Articles

Development of an acceleration method for sediment transport analysis with suspended load and bedload in an integrated river channel and coastal region

ABSTRACT To analyze sediment dynamics in estuaries during floods, a method capable of three-dimensional flows for high-resolution calculations is essential. However, such calculations are computationally intensive for midium to long term periods. We developed a high-speed calculation method for temporal variations in river bed topography and sediment discharge from river basins based on the average component acceleration (ACA) method by shortening the duration of floods. In the ACA method, the local components remained unchanged, and the temporal variation in the average components was amplified. This study developed the ACA method to calculate sediment transport, including bedload and suspended load, around an estuary. The ACA method enabled five times faster than the analysis of riverbed variations and the amount of sediment discharge compared to the conventiola non-accelerated analysis. It also accurately captured the widening of the estuarine sandbar opening during a flood demonstrating its utility for medium- to long-term riverbed-change analysisand its advantage over the other acceleration methods.

Effects of recent urbanization on carbon and nitrogen burial rates of sedimentary records in a tropical coastal lagoon (Brazil)

Land use and land cover changes (LULCC) are a global environmental issue that has impacted biogeochemical cycles worldwide. Sedimentary records can demonstrate the effects of LULCC on aquatic ecosystems, where the recent urbanization has been linked to changes in carbon and nitrogen burial. In this study, we reconstructed long-term LULCC and sedimentary records of carbon (C), nitrogen (N), phosphorus (P), and sediment burial rates in a eutrophic tropical coastal lagoon affected by recent urban expansion. Based on analyses of 30 years of satellite imagery and sedimentary records from 1932 to 2013, we revealed that urban expansion over low-productivity agricultural-pasture areas increased siltation and C, N, P concentrations and fluxes in the coastal lagoon. Large temporal variability of such parameters revealed not only the effects of LULCC on the lagoon's burial rates, but also the influence of artificial sand barrier openings, which connect the studied lagoon to the sea, reducing C, N, P, and particle deposition in the sediment. Our results support multi-proxy methods to assess the relationships between recent urbanization, rising C, N, and P burial rates, and the eutrophication process. We highlight that artificial sandbar openings, the current eutrophication management strategy for coastal lagoons, are ineffective in reducing the eutrophication state, even in the recent scenario of decreasing C, N, and P burial rates.

LONG-TERM CHANGES IN SANITARY CONDITIONS AND ZOOPLANKTON COMMUNITY IN THE IMBOASSICA LAGOON (RIO DE JANEIRO, BRAZIL): EFFECTS OF SANDBAR OPENINGS

The present study investigated the intra-ecosystem variability of nutrient enrichment (nitrogen -N- and phosphorus -P-), density of faecal coliforms (i.e., as a proxy of sanitary conditions), and ecological responses of the zooplankton community structure in a tropical urban coastal lagoon, following eutrophication, changes in rainfall, and episodic sandbar openings. Surface waters were monthly taken over 14 years (1992-2005) within the long-term monitoring program ECOlagoas from two sampling stations at the Imboassica lagoon (Northern of the Rio de Janeiro State, Brazil): near a domestic wastewater channel (SEWAGE station), and at the limit to the sea (SANDBAR station). Changes in faecal coliforms and nutrient concentration reduced water quality due to untreated sewage inputs, which was intensified by artificial sandbar openings mainly under low rainfall, such as observed in February 2001. Indeed, a greater depth and subsequent volume of water of the Imboassica lagoon during the acidification period (i.e., attributed to the increased rainfall, and lower frequency of sandbar openings) contributed to dilute the faecal coliform only in the SANDBAR station. In turn, the zooplankton community structure showed that episodic sandbar openings promoted the loss of their functional features derived from a reduction and replacement of species over time, even in the period of lower frequency of sandbar opening and dilution of nutrient concentrations. Our findings indicate that sandbar openings are not the best management practice when facing coastal eutrophication, once it may cause harmful effects on sanitary conditions and ecological community related to zooplankton, mainly in periods of decline in rainfall.

Effects of a recent urbanization event on coastal groundwater in the southeastern coast of Brazil: a case study of the Macaé municipality

Coastal groundwater is extremely vulnerable to land-based human activities and seawater intrusion. In Brazil, a developing country, several coastal cities are undergoing recent urbanization with no planning, giving rise to problems such as groundwater overexploitation, sanitation, and chemical contamination. This study provides seasonal and spatial groundwater chemical and microbiological characterization of a recently urbanized coastal region, discussing contamination and salinization. The recent urbanization event affected both shallow and deep wells represented by the extensive presence of Escherichia coli on groundwater and nitrate, ammonium, arsenic, and lead (NO3-, NH4+, As and Pb) levels above groundwater safety guidelines. In contrast, iron and manganese (Fe and Mn) concentrations above the safety limit were associated with lithological enrichment, but might also restrict groundwater consumption. In addition to chemical and microbiological contamination, salinization of coastal aquifers did not pose a threat in this shoreline, but brackish groundwater was found in one well influenced by a coastal lagoon sandbar opening that allowed seawater to enter the aquifer.

Assessment of a coastal lagoon metal distribution through natural and anthropogenic processes (SE, Brazil)

The present study intends to assess the metal pollution of a eutrophic coastal lagoon, analyzing the long-term and actual metal content in surface sediments, suspended particles, aquatic macrophyte and fish species, and the loads emitted from natural processes and anthropogenic sources, including the relative emission of domestic untreated sewage. Distribution indicated contamination of suspended particles with Cd and the predominance of Pb in the bioavailable form in surface sediments which may explain Cd and Pb contamination in fish. Domestic untreated sewage was an important source of Cu and due to the lagoon's management, this source may be increasing the metal content in the lagoon's surface sediments. Soil loss, atmospheric deposition and solid waste disposal also contributed to metal inputs to the lagoon. Extensive contamination has been prevented by the lagoon's management such as sandbar opening. Metal retention within the watershed soils reduce the effective metal transference and lagoon pollution.

Short-Term Changes in Two Tropical Coastal Lagoons: Effects of Sandbar Openings on Fish Assemblages

ABSTRACT Camara, E.M.; Caramaschi, E.P.; Di Dario, F., and Petry, A.C., 2018. Short-term changes in two tropical coastal lagoons: Effects of sandbar openings on fish assemblages. Sandbar openings (SBOs) are among the largest possible disturbances in coastal lagoons. This study investigated the mechanisms of the responses of fish assemblages to short-term environmental changes resulting from several SBOs during 1 year in two coastal lagoons in southeastern Brazil. Lagoons were sampled monthly in sites closer to, and more distant from, the sandbars. A principal component analysis summarized limnological differences between periods of contact and isolation from the sea, and site- and lagoon-based variation partitioning and independent redundancy analyses (RDAs) quantified the unique and shared effects of limnology, space, and period on species and groups of species (marine, estuarine, and freshwater). Limnological differences between periods were associated with a higher marine influence during SBOs and an i...

Effects of an artificial and annual opening of a natural sandbar on the fish community in a coastal lagoon system: a case study in Lagoa do Peixe floodplains, southern Brazil

Summary Two hypotheses were tested: that the artificial sandbar opening decreases the richness, diversity and abundance of fishes and alters the fish composition in floodplain ponds; that the salinity variations influence fish richness, diversity, abundance, as well as composition. Results suggest that artificial sandbar openings did not reduce the richness or diversity of freshwater fishes in southern Brazil floodplain ponds. Nevertheless, this process causes an increase in salinity, which determines significant differences in species composition between natural and managed areas. In this sense, the artificial sandbar opening must be considered with caution, since the area of study is one of the most important conservation units in wetland systems of southern Brazil.

The ethnoecological knowledge of fishermen from three coastal lagoons in the northern of the State of Rio de Janeiro, Brazil

The current study investigated the ethnoecological knowledge developed by fishermen through their fishing activities and searched for ways to match such knowledge to empirical data available in the scientific literature. The research involved fishermen from three coastal lagoons in the northern region of the State of Rio de Janeiro, Brazil, who were consulted through semi-structured interviews after the establishment of a trustful relationship over a period of three years with the interviewer. Their knowledge, in addition to its cultural and historical importance to these populations’ survival, in many ways matches scientific studies based on an ethnoecological approach. Their knowledge considers reproductive aspects, feeding habits, and migratory fishing as well as the consequences and the importance of sandbar openings to estuarine-dependent species and the understanding of the consequences of sandbar openings to lagoon trophic state and other organisms’ control (such as macrophytes). This set of data can contribute to the construction of plans for managing these ecosystems, in which fishermen may have a more important role than at present.

Salinity as a Major Driver for Submerged Aquatic Vegetation in Coastal Lagoons: a Multi-Year Analysis in the Subtropical Laguna de Rocha

This paper analyses 6 years of temporal and spatial dynamics of submerged aquatic vegetation (SAV) in a subtropical choked coastal lagoon in Uruguay. In this lagoon, macrophyte proliferation is frequently observed. Nutrient inputs and a highly dynamic salinity regime may be promoting the observed changes in SAV. We explored the main potential factors causing plants proliferation. We took seasonal samples of SAV biomass and physicochemical variables in vegetated areas of the entire lagoon and analysed the spatial distribution with correspondence analysis. Generalised linear models were used to quantify the contribution of physicochemical variables to SAV species biomass, total biomass and richness. Salinity was the most important factor determining SAV structure, causing a decrease of richness and biomass at salinity values higher than ca. 10. The SAV temporal and spatial dynamics were also determined by the species life strategies. Freshwater and slightly brackish conditions allowed competitive species to develop high biomass and cover, while marine water declined biomass and richness promoting stunted species dominance. The wide variation of salinity resulted in a highly dynamic SAV community, and the artificial opening of this coastal lagoon sand bar could therefore have strong effects on SAV. Further eutrophication due to land use intensification might enhance SAV variability and the alternating dominance of submerged angiosperms, macroalgae and phytoplankton.

Intermittently Closed Estuaries and Tadpole Communities: Influence of Artificial Breaching

Naturally or mechanically opening the sand bar of intermittently closed estuaries (ICEs) plays an important role in the proper functioning of these systems. In this study, the impacts of artificial breaching of a coastal lagoon on anuran communities (composition, richness, and abundance) were investigated in the Lagoa do Peixe National Park floodplains, southern Brazil, from 2007 to 2009. The sampling period included two lagoon openings and occurred four times when the lagoon was open and four when it was closed. Artificial opening of the lagoon considerably changed the salinity and availability of temporary ponds in the estuary floodplains. Tadpole species richness and abundance were higher in areas influenced by the sand bar opening than in floodplain areas not influenced by this management. Although salinities were higher when the lagoon was open, only species that do not reproduce explosively occurred in significantly lower abundance. Multivariate analyses demonstrated that anuran species composition differed between areas affected and not affected by the lagoon opening. The composition gradient was associated with conductivity, hydroperiod, and floodplain management. These differences likely relate to individual traits of each species (e.g., habitat preference and reproductive mode). The study suggests that amphibian communities in the Peixe lagoon floodplains are resistant to oligohaline conditions when the lagoon is open. However, projected sea level rise and planned increasing drainage of freshwater wetlands could raise the salinity levels in floodplains to polyhaline or even euhaline conditions. Thus, artificially opening the sand bar for fishery management should be done with caution.

Effects of sandbar openings on the zooplankton community of coastal lagoons with different conservation status

AIM: Artificial sandbar openings are a common management practice in coastal lagoons but they can be a threat when negative effects to the quality of water and to the aquatic biota are observed. The current study compared sandbar opening effects in two coastal lagoons located close to each other, but differing on trophic status and on sandbar openings' background. METHODS:Limnological variables and zooplankton community were recorded monthly during one year before and one year after sandbar openings that occurred in the same month for both lagoons, giving 24 samples. We compared the effects of sandbar opening on response variables, according to the two types of system. RESULTS: The sandbar openings determined changes in some limnological features - depth and salinity - but such effects were different in the two types of system. The zooplankton structure displayed dramatic changes in the eutrophic and commonly opened lagoon. The occurrence and abundance of some species were closely related to changes in limnological variables. CONCLUSIONS: Our data indicated that zooplankton communities are more resistant to sandbar openings in coastal lagoons historically less disturbed. The direction and magnitude of changes promoted by sandbar openings might be specific to each lagoon, due to different backgrounds of disturbances that, in the long term, modify the water quality and the structure of zooplankton communities, and consequently, their resistance and resilience.

An update on the fish composition (Teleostei) of the coastal lagoons of the Restinga de Jurubatiba National Park and the Imboassica Lagoon, northern Rio de Janeiro State

AIM: We present an update on the composition of the fish species of the Restinga de Jurubatiba National Park and the Imboassica Lagoon, in the northern portion of Rio de Janeiro State, based on collecting efforts of almost two decades, historical museum records, and a review of the literature. METHODS: Specimens were collected using a variety of techniques, mostly between 1994 and 2012, and were fixed with the use of a 10% solution of formalin and subsequently stored in 70% alcohol solution. All specimens examined are deposited in the fish collections of the Nucleo em Ecologia e Desenvolvimento Socioambiental de Macae, Universidade Federal do Rio de Janeiro (NPM), and Museu Nacional, Universidade Federal do Rio de Janeiro (MNRJ). Continental (freshwater) fishes and some marine or estuarine species frequently collected were regarded as Resident, whereas marine species collected only sporadically were regarded as Occasional. Possible associations between the orientation of the lagoons and the composition of Resident fishes were explored through a Correspondence Analysis (CA). RESULTS: A total of 100 species, belonging to 19 orders and 41 families of the Teleostei were recorded. When both Resident and Occasional species are considered, families Carangidae and Engraulidae, with nine and eight species respectively, are the most representative. When only Resident species are considered, the Gerreidae and Gobiidae, both with seven species, are the most representative families. The Imboassica Lagoon, with 76 species, has the highest species richness among lagoons included in this study. A total of 81 species were recorded in the Restinga de Jurubatiba National Park, a number two times higher than reported on previous studies. An identification key, including 57 Resident species, is also presented. CONCLUSIONS: Parallel lagoons were characterized by a small group of continental species presumably of marine ancestry (Secondary Division), while marine species were more representative in Orthogonal lagoons. The higher frequency of marine species in Orthogonal lagoons is possibly associated with sandbar openings. Temporary and sporadic connections between Parallel lagoons during periods of higher rainfall may promote a higher similarity in terms of species composition.

Does the Lagoa do Peixe sandbar opening influence the macrophyte richness and composition in Southern Brazil wetlands?

The Lagoa do Peixe has its connection with the sea artificially opened every year at the end of winter. However, this management has been carried out without the evaluation of the impact of this opening in the aquatic biodiversity. This information is crucial for the management of the natural resources of the Lagoa do Peixe National Park, the unique Ramsar site in Southern Brazil. The following questions were analyzed: (1) Do richness and composition of aquatic macrophytes from Lagoa do Peixe floodplain varies temporarily according to the sandbar opening and closing? (2) Does the variation pattern of the macrophyte community changed according to the sandbar opening and closing? A set of eight sampling sites of 1ha were selected over the Lagoa do Peixe floodplain: four sites not influenced by the artificial sandbar opening and four sites influenced by this event, being two sites closer to the sandbar opening and the two sites distant to the sandbar opening. The samplings were carried out between November 2007 and October 2009. The results show that although the artificial sandbar breaching does not affect the aquatic macrophyte richness at the floodplain, it affects the dynamics of species composition. The hydrological variation related to this management can be the main factor of the continuous change in the species composition in the floodplain, especially in the Southern portion. In order to avoid impacts in the macrophyte conservation, the artificial sandbar opening should be considered carefully, since the area of study is one of the most important conservation units to wetland systems in Southern Brazil.

The effects of artificial sandbar breaching on the macrophyte communities of an intermittently open estuary

Artificial sandbar opening of intermittently open estuaries is a practice utilised worldwide to improve water quality, fishing, and recreational amenities and to prevent the flooding of adjacent properties. Breaching causes the water level to drop drastically, exposing plants to two water level extremes. With some exceptions, estuarine communities are adversely affected by this practice. Although breaching can happen naturally, artificial breaching is on the rise, and the impact of manipulating water levels on estuarine communities needs to be investigated. In this work, we described the breaching cycles of the Massaguaçu River Estuary and proposed flooding scenarios for the estuary's macrophyte banks based on our data. We calculated the relationship between plant distribution and flooding conditions and used our calculations to predict the estuary community's composition depending on the water level at breaching time. We discovered a strong relationship between plant distribution and flooding conditions, and we predicted that the estuarine community would be markedly different between flooding scenarios. Low frequency flooding scenarios would be related to submerged macrophytes and, as the flooding frequency increases, macrophytes would be replaced by amphibious plants, and eventually by the arboreal stratus. Therefore, we concluded that an increase in artificial breaching cycles would have a detrimental impact on the estuary community.

Does the management of sandbar openings influence the macroinvertebrate communities in southern Brazil wetlands? A case study at Lagoa do Peixe National Park – Ramsar site

This study assessed the influence of an artificial sandbar opening on the macroinvertebrate richness, abundance and composition of the Lagoa do Peixe floodplains in the only Ramsar site in southern Brazil. The Lagoa do Peixe has its connection with the sea artificially opened every year at the end of winter. However, this management intervention has been carried out without the evaluation of the impact of this opening in the aquatic biodiversity. Six samplings were carried out over two years (from March 2008 to October 2009) which encompassed two artificial sandbar openings. The mean richness and abundance were lower in the floodplain sites influenced by the artificial sandbar opening (opened wetlands) than in the floodplain sites not influenced by this event (natural wetlands). Water salinity was higher in opened wetlands than in natural wetlands during the open sandbar samplings. The richness was negatively associated with water salinity, and the abundance was positively associated with hydroperiod, and negatively associated with conductivity. The composition of macroinvertebrate taxa was different between opened and natural wetlands. Our results suggest that artificial sandbar openings have a negative impact on freshwater macroinvertebrate communities in southern Brazil floodplain wetlands. Hydrologic variation and increase of salinity related to this management may be the main factors of the change in the richness, abundance and composition in opened wetlands. We concluded that the artificial sandbar opening should be carefully re-analysed or forbidden, since this management practice may be jeopardizing the aquatic macroinvertebrate community in a National Park and Ramsar site, where the biodiversity conservation is a priority and protected by Brazilian laws.

Abundance, composition and spatial variation in the egg bank of a tropical zooplankton community

Resting eggs have important ecological roles in zooplankton communities, but characterizations of egg banks in tropical systems remain scarce. Here, we describe the abundance, composition and spatial variation in the egg bank of a tropical zooplankton community in a shallow aquatic system (Imboassica lagoon, Brazil). Due to sporadic disturbances by sandbar openings at this system, we hypothesized that the abundance and species richness close to the sandbar is lower when compared to other sites. Sediment samples were collected at four sampling stations, and the egg bank was analyzed using ex situ hatching experiments. Hatchlings from 21 rotifer and five cladoceran species were identified considering all sampling stations. The number of hatchlings at the sampling stations ranged from 14.2 (± 3.8 SE) to 192.8 (± 37.1), whereas species richness ranged from 3.6 (± 0.7) to 12.2 (± 0.5) in 100 g of wet sediment. Abundance and species richness were similar at three of the sampling stations, suggesting low spatial variations in the egg bank of shallow systems. Significantly lower values for abundance and species richness were found close to the sandbar when compared to the other sampling stations, probably as a result of local and recurrent disturbances due to artificial sandbar openings. The presence of an egg bank is a possible mechanism for facilitating the reestablishment of active populations after disturbances by sandbar openings and consequent increases in salinity at Imboassica lagoon. Os ovos de resistência apresentam importantes funções ecológicas para as comunidades zooplanctônicas, mas a caracterização do banco de ovos de sistemas tropicais permanece escassa. Nesse estudo nós descrevemos a abundância, a composição e a variação espacial do banco de ovos de uma comunidade zooplanctônica tropical oriunda de um sistema aquático raso (lagoa Imboassica, Brasil). Devido a eventuais distúrbios ocasionados por aberturas de barra nesse sistema, nós hipotetizamos que a abundância e a riqueza de espécies próximo à barra de areia são menores quando comparadas a outros locais. Amostras de sedimento foram coletadas em quatro estações amostrais, e o banco de ovos foi analisado através de experimentos de eclosão ex situ. Através dos organismos eclodidos dos ovos foram identificadas 21 espécies de rotíferos e cinco de cladóceros, considerando todas as estações amostrais. O número de organismos eclodidos nas estações amostrais variou de 14.2 (± 3.8 EP) a 192.8 (± 37.1), enquanto a riqueza de espécies variou de 3.6 (± 0.7) a 12.2 (± 0.5) em 100 g de sedimento úmido. A abundância e a riqueza de espécies foram similares em três das estações amostrais, sugerindo uma baixa variação espacial no banco de ovos de sistemas rasos. Valores significativamente menores de abundância e riqueza de espécies foram encontrados próximo à barra de areia, quando comparados com as outras estações, provavelmente como resultado de distúrbios locais e recorrentes devido às aberturas artificiais da barra de areia. A presença de um banco de ovos é um possível mecanismo facilitador do restabelecimento das populações ativas após distúrbios ocasionados por aberturas de barra e consequentes aumentos da salinidade na lagoa Imboassica.

Environmental status of a tropical lake system

Eutrophication has become a serious threat to the lake systems all over the world. This is mainly due to the pollution caused by anthropogenic activities. Carlson trophic state index (CTSI) is commonly used for the classification of trophic conditions of surface waters. The study is conducted to assess the trophic status of a tropical lake (Akkulam-Veli lake, Kerala, India) using CTSI based on Secchi disc depth (SD), total phosphorus (TP) and chlorophyll-a. The TSI values based on SD and TP are high (>70), indicating the hypereutrophic state which needs urgent action for the restoration of the fragile ecosystem. The higher TP in both lakes, and the lower value of chlorophyll-a in the Akkulam part, warrant explanation, are discussed here. The influence of other biochemical parameters in both the Akkulam and the Veli part of the lake has been assessed. Correlation analysis is conducted to study the effect of various water quality parameters. The variation in the water quality before and after the opening of sand bar is studied using paired t test. As almost all the lakes in the world are experiencing similar situation of extinction, this study is helpful to have an insight in the hydrochemistry of the lake as well as to identify the worst affected areas of the lakes.

Management Proposal for an Intermittently Closed Coastal Lagoon Using a Wave-Driven Seawater Pump and a Volume–Salinity Box Model

Abstract A SIBEO (Spanish acronym for sistema de bombeo por energia de oleaje) wave-driven seawater pump is proposed for managing the volume and salinity of a coastal lagoon on the Mexican Pacific coast. The observed variation in volume and salinity of the Lagartero lagoon during most of the year when the sandbar is closed is adequately reproduced by a model that assumes an evaporation–precipitation controlled closed basin. The model was employed to examine the use of a SIBEO for controlling the lagoon volume and salinity. Continuous seawater pumping maintains a water level that favors the greatest number of sandbar openings at the end of the rainy season and thus the intake of shrimp larvae, while not significantly affecting the observed yearly salinity cycle. The possible effects of the SIBEO seawater pumping on lagoon eutrophication and shrimp production are discussed in this article. It seems likely that SIBEO seawater pumping will help curb eutrophication and significantly increase shrimp production ...

Spatio-temporal variation of the pink shrimp Farfantepenaeus paulensis (Crustacea, Decapoda, Penaeidae) associated to the seasonal overture of the sandbar in a subtropical lagoon

On the southern Brazilian coast, the penaeid pink shrimp Farfantepenaeus paulensis (Pérez-Farfante, 1967) is intensively captured by both artisanal and industrial fisheries. In the Ibiraquera Lagoon, artisanal fishing of juvenile stocks has declined sharply over the last 15 years. The traditional management methods used by fishermen are no longer sustainable due to conflicts with the demands of tourism and weak environmental and public agencies. The dynamics of the timing of the artificial opening and natural reformation of a sandbar across the mouth of the lagoon are regarded as a central socio-ecological problem. We evaluated the abundance and biomass variation of F. paulensis throughout the year and along a spatial gradient measured from the sandbar into the lagoon. We also explored the influence of opening the sandbar on the shrimp population. Samples were collected monthly from February 2004 to February 2005, using a 27 mm mesh cast net, in four different areas, with three sites being sampled per area. Small numbers of large shrimps were captured in the upper area, while greater biomass and abundance of small shrimps were observed near the sandbar, suggesting the role of the inner area as a refuge for growing. The highest records for biomass and abundance were recorded during warm months, regardless if the lagoon was open or closed by the sandbar. The Ibiraquera Lagoon could be more productive for fishermen if the sandbar opening was coincident to the period of natural post-larvae influx. Furthermore, coastal stocks could be improved by opening the sandbar again during summer in conjunction with fishing quotas.

Interactive effects of environmental variability and human impacts on the long-term dynamics of an Amazonian floodplain lake and a South Atlantic coastal lagoon

Human activities are exposing freshwater ecosystems to a wide range of stressors, whose direct and indirect effects can be alleviated or exacerbated through interactive effects with dynamic environmental drivers. This study used long-term data from two Neotropical lacustrine freshwater systems (Batata Lake, an Amazonian floodplain lake and Imboassica lagoon, an Atlantic coastal lagoon) subjected to different kinds of environmental fluctuations (i.e., flood pulse and sandbar opening) and anthropogenic impacts (i.e., siltation and eutrophication). Our objective was to determine whether the effects of human perturbations are contingent on modifications of important biotic and abiotic characteristics through environmental variability. For both ecosystems, environmental variability consistently interacted with anthropogenic perturbations to alter most of the variables analyzed, such as nutrient dynamics, chlorophyll- a concentration, zooplankton and benthic invertebrate species richness, and temporal community stability, which indicates that interactive effects between environmental variability and anthropogenic perturbations may impact a myriad of ecosystem properties. Furthermore, the nature of these interactive effects was highly dependent on the variable considered and on the ecosystem analyzed. For example, at Imboassica lagoon, sandbar openings interacted synergistically with trophic state to increase the phosphorus concentration in the water column. At Batata Lake, flooding generally alleviated the negative effects of siltation on species richness by both diluting inorganic suspended material concentration and by promoting local recruitment from the regional species pool. Such results indicate that our ability to understand and predict the outcome of anthropogenic impacts on inland aquatic systems can be hampered if we consider human stressors as “static” phenomena disconnected from dynamic interactions with major local environmental drivers.