An alternative fish feed based on earthworm and fruit meals for tilapia and carp postlarvae

(Uma ração alternativa baseada em farinha de minhoca e frutas para alevinos de tilápia e carpa). A busca por fontes proteicas e lipídicas alternativas na nutrição de organismos aquáticos em cativeiro é de extrema importância à luz da sustentabilidade e conservação de ecossistemas. Nós investigamos o potencial de uma nova ração alternativa, baseada em frutas, farinha de minhoca e soja, na nutrição de alevinos de duas espécies de grande interesse comercial mundial – Oreochromis niloticus (L.) e Cyprinus carpio (L.), i.e. tilápia e carpa. Os alevinos alimentados com a ração alternativa exibiram crescimento e ganho de peso similares àqueles alimentados com uma ração comercial baseada em farinha de peixe.  Embora as concentrações de minerais e de proteínas totais tenham sido maiores na ração comercial do que na ração alternativa, a concentração de lípides foi maior nesta última. As concentrações de minerais, proteínas e lípides nos tecidos dos alevinos, por outro lado, não diferiram significativamente entre os animais alimentados com a ração comercial e a ração alternativa. Este resultado sugere uma elevada eficiência de assimilação da ração alternativa comparada à ração comercial. A ração alternativa testada em nosso estudo provou ser eficiente em promover crescimento e ganho de peso de alevinos de tilápia e carpa. Devido à sua formulação simples, baseada em ingredientes comumente encontrados em países tropicais, a ração alternativa aqui proposta oferece uma alternativa economicamente viável e ecologicamente sustentável para pequenos proprietários e fornecedores de alevinos nestes países

A global synthesis of human impacts on the multifunctionality of streams and rivers

Human impacts, particularly nutrient pollution and land-use change, have caused significant declines in the quality and quantity of freshwater resources. Most global assessments have concentrated on species diversity and composition, but effects on the multifunctionality of streams and rivers remain unclear. Here, we analyse the most comprehensive compilation of stream ecosystem functions to date to provide an overview of the responses of nutrient uptake, leaf litter decomposition, ecosystem productivity, and food web complexity to six globally pervasive human stressors. We show that human stressors inhibited ecosystem functioning for most stressor-function pairs. Nitrate uptake efficiency was most affected and was inhibited by 347% due to agriculture. However, concomitant negative and positive effects were common even within a given stressor-function pair. Some part of this variability in effect direction could be explained by the structural heterogeneity of the landscape and latitudinal position of the streams. Ranking human stressors by their absolute effects on ecosystem multifunctionality revealed significant effects for all studied stressors, with wastewater effluents (194%), agriculture (148%), and urban land use (137%) having the strongest effects. Our results demonstrate that we are at risk of losing the functional backbone of streams and rivers if human stressors persist in contemporary intensity, and that freshwaters are losing critical ecosystem services that humans rely on. We advocate for more studies on the effects of multiple stressors on ecosystem multifunctionality to improve the functional understanding of human impacts. Finally, freshwater management must shift its focus toward an ecological function-based approach and needs to develop strategies for maintaining or restoring ecosystem functioning of streams and rivers

Simulating rewetting events in intermittent rivers and ephemeral streams: A global analysis of leached nutrients and organic matter

Climate change and human pressures are changing the global distribution and the ex‐ tent of intermittent rivers and ephemeral streams (IRES), which comprise half of the global river network area. IRES are characterized by periods of flow cessation, during which channel substrates accumulate and undergo physico‐chemical changes (precon‐ ditioning), and periods of flow resumption, when these substrates are rewetted and release pulses of dissolved nutrients and organic matter (OM). However, there are no estimates of the amounts and quality of leached substances, nor is there information on the underlying environmental constraints operating at the global scale. We experi‐ mentally simulated, under standard laboratory conditions, rewetting of leaves, river‐ bed sediments, and epilithic biofilms collected during the dry phase across 205 IRES from five major climate zones. We determined the amounts and qualitative character‐ istics of the leached nutrients and OM, and estimated their areal fluxes from riverbeds. In addition, we evaluated the variance in leachate characteristics in relation to selected environmental variables and substrate characteristics. We found that sediments, due to their large quantities within riverbeds, contribute most to the overall flux of dis‐ solved substances during rewetting events (56%–98%), and that flux rates distinctly differ among climate zones. Dissolved organic carbon, phenolics, and nitrate contrib‐ uted most to the areal fluxes. The largest amounts of leached substances were found in the continental climate zone, coinciding with the lowest potential bioavailability of the leached OM. The opposite pattern was found in the arid zone. Environmental vari‐ ables expected to be modified under climate change (i.e. potential evapotranspiration, aridity, dry period duration, land use) were correlated with the amount of leached sub‐ stances, with the strongest relationship found for sediments. These results show that the role of IRES should be accounted for in global biogeochemical cycles, especially because prevalence of IRES will increase due to increasing severity of drying event

Nutrient uptake in tropical rivers receiving wastewater treatment plant discharge : high mass removal but low nutrient uptake efficiencies

Wastewater treatment plants (WWTPs) have eliminated many problems related to sewage inputs to aquatic systems. However, the treated effluents still affect river and stream ecosystems. Yet, very limited information is available about the fate of treated effluents in tropical receiving water bodies. Here, we examined the longitudinal changes in ammonium (NH4-N), nitrate (NO3-N), and soluble reactive phosphorus (SRP) concentrations in reaches downstream from chronic WWTP inputs in three receiving rivers in São Paulo state (Southeastern Brazil). The studied WWTPs were not designed or operated to have specific tertiary treatment for nutrient removal at the time of the study. We conducted a total of five sampling campaigns between 2019 and 2021. We applied the nutrient spiraling approach to these high-magnitude nutrient additions to examine net nutrient uptake. Changes in nutrient loads along the reaches were also examined. Overall, nutrient concentrations and loads were considerably increased by WWTP discharges. Net uptake lengths (SW-net) for NO3-N, NH4-N, and SRP ranged from 1.2 to 13.6, 1.5–infinity (uptake coefficient < 0), and 1.2–7.5 km, respectively. Net uptake velocities (Vf-net) varied between 0.7–2.5, −0.4 to 4.1, and 0.2–10.2 mm/min, respectively. Areal net uptake rates (Unet) ranged from 0.78 to 10.7, −20.08–45.8, and 0.18–4.4 g/m2/min for NO3-N, NH4-N, and SRP, respectively. High export (long SW-net) and limited net uptake along the reaches (low Vf-net) indicated that nutrients were transported downstream for long distances without efficient removal (nutrient availability higher than demand) despite the high mass removal (high Unet). These results suggest that the export of nutrients is substantial, potentially creating water quality impairments to downstream ecosystems. Our study highlighted that WWTPs with limited nutrient removal have considerable effects on water chemistry, nutrient cycling and loading in tropical receiving freshwaters

Land-use effects on river habitat quality and sediment granulometry along a 4th-order tropical river

Land-use change, i.e., the transformation of natural land into agricultural and urban area is among the most important human impacts on habitat quality and species diversity. In this study, we investigated the effects of land use on river habitat quality and sediment granulometry in a larger tropical river, affected by urbanization and agricultural land use. We selected 15 representative sampling reaches in the Rio das Mortes basin, 12 of them along the main river from its headwater to its mouth, and 3 in major tributaries. A habitat survey was conducted in these reaches in the dry season 2010 and sediment samples were taken for granulometry analyses. Sub-basin land cover of reaches was dominated by natural vegetation (41.6 to 60.2% of total land cover), followed by agricultural land cover (38.4% to 56.9%) and urban land cover (1.4% to 5.6%). Sediments were dominated by poorly to moderately sorted silts to sands, little conducive to diverse biological communities. According to the river habitat survey, all investigated river reaches exhibited moderately to totally disturbed habitat integrity, due to diverse and often co-occurring human impacts, such as riparian deforestation, water abstraction, sand and gravel extraction, and margin erosion. Only one of the investigated sampling reaches exhibited the minimum riparian forest corridor width demanded by the Brazilian Forest Code. Our results indicated that river habitat and sediment quality mainly depended on conditions in the direct vicinity of river reaches. Accordingly, initial cost-effective restoration of aquatic habitats could be achieved by relatively simple channel restoration measures and the protection of the riparian corridor in the investigated tropical river

Contrasting effects of agriculture and urban land use on macroinvertebrate secondary production in Neotropical streams

We compared the structural and functional attributes of Neotropical macroinvertebrate communities between two natural, two agricultural, and two urban streams. We quantified food resource availability, community structure, secondary production, and consumer–resource interaction strength, attributing them to environmental characteristics. In agricultural streams, secondary production was significantly reduced compared to natural streams, reaching the lowest reported estimates for tropical streams (0.08–0.69 g DW·m−2·year−1 in agricultural streams vs. 1.1–15.8 g DW·m−2·year−1 in natural streams). This decline was primarily attributed to habitat degradation caused by siltation and channelization, alongside stronger top-down pressure in agricultural streams. Conversely, urban streams exhibited a substantial increase in secondary production, ranking among the highest estimates for tropical streams (25.6–191.2 g DW·m−2·year−1). The high secondary production in urban streams was primarily due to substantial increases in fine benthic organic matter, likely originating from poorly treated wastewater. Along with higher resource availability, we also observed a lack of, or insufficient, top-down control by macroinvertebrate predators or fish, which may have promoted higher secondary production in urban streams. This study is the first to quantify land use impacts on energy flows in stream communities in a region particularly threatened by land use change. Future studies should address multifunctional responses to land use changes in both the tropical and temperate realms to shed new light on how stream ecosystem functions in different biomes respond to human impacts. Our findings highlight the urgent need for effective management strategies tailored to address the environmental characteristics of tropical stream ecosystems

An alternative fish feed based on earthworm and fruit meals for tilapia and carp postlarvae

(Uma ração alternativa baseada em farinha de minhoca e frutas para alevinos de tilápia e carpa). A busca por fontes proteicas e lipídicas alternativas na nutrição de organismos aquáticos em cativeiro é de extrema importância à luz da sustentabilidade e conservação de ecossistemas. Nós investigamos o potencial de uma nova ração alternativa, baseada em frutas, farinha de minhoca e soja, na nutrição de alevinos de duas espécies de grande interesse comercial mundial – Oreochromis niloticus (L.) e Cyprinus carpio (L.), i.e. tilápia e carpa. Os alevinos alimentados com a ração alternativa exibiram crescimento e ganho de peso similares àqueles alimentados com uma ração comercial baseada em farinha de peixe.  Embora as concentrações de minerais e de proteínas totais tenham sido maiores na ração comercial do que na ração alternativa, a concentração de lípides foi maior nesta última. As concentrações de minerais, proteínas e lípides nos tecidos dos alevinos, por outro lado, não diferiram significativamente entre os animais alimentados com a ração comercial e a ração alternativa. Este resultado sugere uma elevada eficiência de assimilação da ração alternativa comparada à ração comercial. A ração alternativa testada em nosso estudo provou ser eficiente em promover crescimento e ganho de peso de alevinos de tilápia e carpa. Devido à sua formulação simples, baseada em ingredientes comumente encontrados em países tropicais, a ração alternativa aqui proposta oferece uma alternativa economicamente viável e ecologicamente sustentável para pequenos proprietários e fornecedores de alevinos nestes países

From intermittent to persistent cyanobacterial blooms: identifying the main drivers in an urban tropical reservoir

Eutrophication has impacted water bodies around the world. Knowledge on how to manage and restore these systems is urgently needed in order to maintain adequate water quality. However, causes and consequences of eutrophication may differ among lakes located in tropical and temperate regions. The eutrophication process is better understood for temperate lakes due to the availability of a larger number of studies and longer time-series of data sets. In tropical regions, long-term studies are rare, but could exemplify the particularities of eutrophication speed under conditions of higher temperatures. The purpose of this work was to analyze the evolution of the eutrophication process in an urban tropical reservoir, using a 15-year time series (with occasional interruptions). The dataset comprised monthly sampling of several environmental variables and the phytoplankton community. We found a continuous process of water quality deterioration, mainly related to increasing levels of nutrient and phytoplankton biomass, as well as decreasing water transparency, even after the installation of a municipal wastewater treatment plant. The ongoing eutrophication resulted in a steep trend of increasing cyanobacteria biomass that turned from a seasonal appearance into more persistent blooms in the most recent decades, while the relative contribution of other algal phyla to total phytoplankton biomass declined, which resulted in a loss of phytoplankton diversity. Phosphorus was the major determinant of the persistent blooms. Even though nitrogen concentrations were very high in this system, they were not significantly correlated with phytoplankton or cyanobacteria biomass. Total-P concentrations increased about three times during the study period, indicating that the reservoir did not respond to recent restoration efforts. The average water temperature, always sufficiently high to allow phytoplankton growth all year round, is an additional factor that makes tropical reservoirs especially sensitive to eutrophication. In contrast to temperate systems, the constantly favorable temperatures in the tropics may facilitate the persistence and dominance of cyanobacteria in the plankton community.</p

Global effects of agriculture on fluvial dissolved organic matter

Agricultural land covers approximately 40% of Earth's land surface and affects hydromorphological, biogeochemical and ecological characteristics of fluvial networks. In the northern temperate region, agriculture also strongly affects the amount and molecular composition of dissolved organic matter (DOM), which constitutes the main vector of carbon transport from soils to fluvial networks and to the sea and is involved in a large variety of biogeochemical processes. Here, we provide first evidence about the wider occurrence of agricultural impacts on the concentration and composition of fluvial DOM across climate zones of the northern and southern hemispheres. Both extensive and intensive farming altered fluvial DOM towards a more microbial and less plant-derived composition. Moreover, intensive farming significantly increased dissolved organic nitrogen (DON) concentrations. The DOM composition change and DON concentration increase differed among climate zones and could be related to the intensity of current and historical nitrogen fertilizer use. As a result of agriculture intensification, increased DON concentrations and a more microbial-like DOM composition likely will enhance the reactivity of catchment DOM emissions, thereby fuelling the biogeochemical processing in fluvial networks and resulting in higher ecosystem productivity and CO2 outgassing