Increased Water Turbidity Research Articles

Freshwater snail and shrimp differentially affect water turbidity and benthic primary producers

Benthic macroinvertebrates play key roles in shallow aquatic ecosystems and can contribute substantially to aquatic food webs. However, how macroinvertebrates with different behaviors (for example, pertaining to locomotion, foraging and burrowing) impact water quality and primary producers has not been fully explored. Here, we performed two consecutive microcosm experiments to test the effects of (1) macroinvertebrates with different behaviors (a low mobility scraper aquatic snail Bellamya aeruginosa and a high mobility shredder freshwater shrimp Macrobrachium nipponense) and (2) different shrimp biomasses on water clarity and the composition of benthic primary producers. The results showed that presence of snails significantly increased the biomass of filamentous green algae and decreased the biomass of periphyton. In contrast, presence of shrimp significantly decreased the biomass of filamentous green algae and increased the biomass of periphyton, and these effects were biomass dependent. Filamentous green algae disappeared when shrimp biomass reached 9.8 ​g ​m−2. No interactive effects of snail and shrimp presence were found. This could be attributed to different food preferences by the two consumers, with snails preferring periphyton (mainly diatoms) and shrimp preferring filamentous green algae. The presence of snails decreased water turbidity, while shrimp increased water turbidity, which showed a hump-shaped response to shrimp biomass with a peak at 24.2 ​g ​m−2. These results are likely because the snail is a low mobility grazer and can filter suspended particles, while the shrimp is a high mobility shredder with burrows, which can strongly disturb sediment. The decrease in water disturbance at high shrimp biomass might be due to food limitation, thus reducing burrowing and foraging activities. Neither snail nor shrimp affected the biomass of H. verticillata, while the biomass of V. spinulosa increased with shrimp biomass. The reason for this could be that shrimp increased nutrient availability and decreased the growth of filamentous green algae that compete with macrophytes. Our study demonstrated that different macroinvertebrates have complementary functions in benthic habitats; thus, maintaining macroinvertebrate diversity is important for shallow aquatic ecosystems. Furthermore, the freshwater shrimp M. nipponense could be a potential consumer to control filamentous green algal blooms in its native range, but their biomass should be taken into consideration.

Assessment of current and future land use/cover changes in soil erosion in the Rio da Prata basin (Brazil)

In recent years, the Cerrado biome in Brazil (Brazilian savannah) has faced severe environmental problems due to abrupt changes in land use/cover (LUC), causing increased soil loss, sediment yield and water turbidity. Thus, this study aimed to evaluate the impacts of soil loss and sediment delivery ratio (SDR) over the last 30 years to simulate future scenarios of soil losses from 2050 to 2100 and to investigate an episode of sediment delivery that occurred in the Rio da Prata Basin (RPB) in 2018. In this study, the following were used: an estimation of soil losses for 1986, 1999, 2007 and 2016 using the Revised Universal Soil Loss Equation (RUSLE), an estimation of SDR, sediment export and sediment deposition using the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model, an association of RUSLE factor C to LUC data for 2050 and 2100 based on the CA-Markov hybrid model, and an estimation of future soil erosion scenarios for 2050 and 2100. The results show that over the last 30 years (1986–2016), there has been a reduction in the areas of highly intense and severe degrees. Future soil erosion scenarios (2050–2100) showed a 13.84% increase in areas of soil loss >10 Mg ha−1 year−1. The results highlighted the importance of assessing the impacts of LUC changes on soil erosion and the export of sediments to agricultural watersheds in the RPB, one of the best ecotourism destinations in Brazil. In addition, the increase in soil loss in the region intensified sediment yield events and increased water turbidity. Furthermore, riparian vegetation, although preserved, was not able to protect the watercourse, showing that it is essential to adopt the best management practices in the agricultural production areas of the basin, especially where ramps are extensive or the slope is greater than 2%, to reduce the runoff velocity and control the movement of sediments on the surface towards the drainage canals. The results of this study are useful for drawing up a soil and water conservation plan for the sustainable production of agriculture and maintenance of ecosystem services in the region.

Warming alters juvenile carp effects on macrophytes resulting in a shift to turbid conditions in freshwater mesocosms

Abstract Multiple stressors such as climate change and eutrophication are responsible for the global decline in macrophytes in lakes. The loss of this key component can result in turbid conditions and a loss of important ecosystem functions and services, particularly in shallow lakes. Benthivorous fish, which can increase in abundance during eutrophication, can adversely affect macrophytes through physical disturbance, cascading effects on turbidity, suspended and attached algae (phytoplankton and periphyton) and direct consumption. However, whether warming amplifies their effects on macrophytes and can trigger regime shifts remains unexplored. Here, we tested the single and combined effects of warmer water (+4.5°C) and the widespread benthivorous juvenile common carp Cyprinus carpio on two different types of aquatic macrophytes in 24 mesocosms (2,500 L each). We monitored phytoplankton, periphyton, turbidity and the abundance of the submerged curly leafed pondweed Potamogeton crispus and the floating‐leaved water chestnut Trapa bispinosa during their growing season. These species dominated successively in spring and summer. Warming alone advanced the growing season of P. crispus by 17 days. Juvenile carp decreased the abundance of the more palatable P. crispus, but promoted the abundance of T. bispinosa, supporting an ecosystem shift to a dominance of floating‐leaved macrophytes. Fish also substantially increased water turbidity and the biomass of phytoplankton and periphyton. Warming amplified juvenile carp effects on turbidity and submerged macrophytes, but also decreased the abundance of floating‐leaved macrophytes leading to an overall macrophyte decline and increase in water turbidity. Synthesis and applications. Our study provides the first experimental evidence for a warming‐induced regime shift from clear‐water conditions dominated by submerged or floating/floating‐leaved macrophytes to a turbid state in shallow aquatic ecosystems. The regime shift was triggered by the impacts of warming on benthivorous fish (juvenile common carp) rather than on macrophytes. Lowering nutrient loading and other measures to reduce the abundance of benthivorous fish (e.g. fish removal and piscivorous fish restocking) thus may become increasingly important for the management of shallow lakes under global climate change.

Impacts of volcanic eruptions and early recovery in freshwater environments and organisms.

Volcanic eruptions modify environments physically and chemically with serious consequences for the biota. In this review, we analysed 80 papers reporting the effects of volcanic eruptions in freshwater environments and on freshwater organisms. An increase in water turbidity is the most common reported physical effect while increases in concentrations of inorganic elements, many representing nutrients for primary producers, are the most common chemical effects. Bacterial growth is usually stimulated, while autotrophs can be either positively or negatively affected depending on the type of impact. A persistent effect reported in the biota is changes to the assemblage, which could generate further changes in terms of ecosystem functions. This analysis also identifies some information gaps, particularly involving the effects of eruptions on heterotrophic biofilms in streams and on invertebrates and fish in lakes. Most studies were carried out soon after the volcanic eruption, so it is difficult to assess the recovery of the ecosystems. Eruptions present unique opportunities for scientific discovery, although such studies are often hindered by a lack of pre-eruption data, which would allow for a more comprehensive assessment of the effects.

Mapping total suspended matter along Moroccan coast using satellite data series

Remote-sensing techniques are a powerful technique for monitoring turbidity over the whole littoral areas. Different sensors can be used to quantify and analyze water quality parameters such as colored dissolved organic matter, total suspended sediments, chlorophyll-a, and pollutants. Therefore, the goal of this paper is to investigate the inter-annual and spatio-temporal variability’s of total suspended matter (TSM) concentration in the water surface layer. The coastal of the Atlantic Ocean, Morocco is taken an application area. The results show that high TSM (18 g m−3) is observed during winter season, and lower TSM (2 g m−3) is observed during summer season. In addition, the relationship between TSM and wind speed; and with ocean current was analyzed, and the results show that: (1) sand dredging areas usually coincide with region that have high TSM levels; (2) the wind and ocean current were both important to TSM variation; (3) the increased level of sand dredging in response to rapid economic growth has deeply influenced the TSM pattern since 2012 due to the resuspension of sediment in some areas. Visual interpretation of location led to the conclusion that the dredging activities were more located on the northern and western Morocco. Time series of MODIS images revealed a significant increase in water turbidity from 2012 onwards on the northern Morocco. Moreover, strong wind events in the northern Sahara can significantly increase the TSM in turbid coastal waters.

Features of the restoration of biological communities after the technogenic transformation of the estuary area of the Pregolya River (the Baltic Sea basin)

The structural parameters of plankton, benthos and macrophytes after large-scale technogenic transformation of the mouth area of the river were studied. Pregolya. A decrease in the species richness and area of growth of macrophytes, a simplification of the structure of communities was noted. The renewal of plant communities in the places of their origin was recorded, primarily due to the species resistant to biogenic pollution. A decrease in the abundance of submerged species with wide leaves was revealed, which is an indicator of an increase in water turbidity. The species were found in the phyto- and zooplankton community, living in conditions of an increased content of nutrients and suspended matter. There was no significant decrease in the species diversity of summer plankton and benthos, and the quantitative indicators are comparable with the data before the work. A feature of the restoration of the zooplankton and benthic community was the appearance of brackish-water species in the river branches, which were not previously recorded there, incl. alien species of mollusks and polychaetes.

A preliminary study on visibility improvement of turbid underwater images for dismantling of nuclear facilities

Video monitoring environment of underwater cutting objects is rapidly deteriorated due to the increasing water turbidity in proportion to cutting operation. Precise monitoring of the cutting area is one of keys to improve work efficiency. In this paper, we studied a visibility improvement technique based on an artificial neural network for monitoring objects in a turbid underwater cutting site. In order to improve visibility in turbid water, a deep learning neural network that learned two types of visibility enhancement process was adopted. The first type is to train to restore an ideal underwater image with the best visibility from a turbid underwater image, and the second type is to train to restore an image with improved visibility using the conventional visibility improvement technique.We adopted two types of training real images based on the GAN (generative adversarial networks) model for the corresponding turbid input images. The first training image is the histogram-equalized image of a clear underwater image. If the first training image does not exist, an image with improved visibility by using histogram equalization for the turbid input image itself was used as the second training image. Experiments demonstrated that the trained neural network provided significantly improved clarity in turbid images compared to that of the conventional improving technique.

The impact of turbidity on foraging and risk taking in the invasive Nile tilapia (Oreochromis niloticus) and a threatened native cichlid (Oreochromis amphimelas)

Anthropogenic activity can increase water turbidity, changing fish behaviour by reducing visibility. The spread of invasive species is also facilitated by human activity, further increasing the pressure on native species. In two experiments, we measured the foraging efficiency, risk perception and inter-individual consistency of risk-taking (personality variation in boldness) of an invasive species, the Nile tilapia (Oreochromis niloticus), and a threatened tilapia, the Manyara tilapia (Oreochromis amphimelas), in clear and turbid water. In experiment one, O. niloticus was faster to initiate feeding, encountered more food items and consumed more than O. amphimelas. The latency to start foraging by O. niloticus decreased in turbid water. Turbidity did not affect the latency to start foraging in O. amphimelas but the number of food items they encountered was highest at the intermediate turbidity. There was however no significant effect of turbidity in either species on the total food consumed. In contrast to this foraging context, in experiment two with a refuge and no food available, risk taking behaviour was similar in both species and they both responded with similarly reduced risk taking in turbid water. Evidence of personality variation was weak, being observed only in O. amphimelas when first leaving the shelter in turbid water. Overall, species differences were greater in the foraging context but turbidity was more important in the risk-taking context. O. amphimelas is more sensitive to turbidity during foraging, and O. niloticus is likely to have a competitive advantage in foraging situations, especially in degraded turbid habitats.Significance statementUnder human-induced environmental change, native species are often exposed to multiple stressors. Here, we tested the responses of two cichlid fish to increasing turbidity, the Nile tilapia (Oreochromis niloticus), which is invasive throughout the tropics, and the Manyara tilapia (Oreochromis amphimelas), a threatened species, indigenous to Tanzania. We found that turbidity was beneficial to the foraging of O. niloticus, which in both clear and turbid water consumed and encountered more food than O. amphimelas. In contrast, without food present, both species displayed similar responses of increased risk perception in turbid water with little evidence of personality variation between individuals in either species. Our results suggest that invasive species tolerant of degraded habitats may outcompete less well-adapted native species for food.

Assessment of the Impact of the Nile Flood on Food Chain in Lake Nasser—Egypt, with Special Reference to Turbidity

This study aimed to assess the impact of the Nile flood with special reference to turbidity on the food chain in Lake Nasser water as one of the largest man-made lakes in Africa before the flood (BF) and after the flood (AF) seasons. To achieve that aim, subsurface water samples were collected from 11 sampling stations along the lake before and after the flood for analyzing the water turbidity, total suspended solids, and total phosphorus, as well as chlorophyll-a and zooplankton to represent the food chain in the lake. Results showed an increase in water turbidity after the flood than that before the flood. Total suspended solids concentration displayed a similar trend as water turbidity. Chlorophyll-a concentration increased in AF all over the lake except at the entrance of the lake, as compared to the BF season. Zooplankton count was represented by copepods, cladocerans, and rotifers with the dominance of copepods in AF and rotifers in BF. The density of zooplankton was higher in the AF than the BF season. The negative impact of flood turbidity had appeared on crustacean organisms.

ДИНАМІКА МУТНОСТІ РІЧКОВОЇ ВОДИ ЛІВОБЕРЕЖНИХ ПРИТОК ДНІПРА (НА ПРИКЛАДІ СУМСЬКОЇ ОБЛАСТІ)

The article is devoted to the study of sediment runoff, especially one of the characteristics that reflects erosion processes in the catchment area, water turbidity using the example of the rivers of the Sumy region. The main purpose of the article is the spatial and temporal analysis of the turbidity indicators of the rivers of the Sumy region (left-bank tributaries of the Dnieper). The article highlights information on the sediment runoff of the rivers in the region for the entire period of observations, describes modern own studies of the turbidity of river water and establishes the features of the formation of sediment runoff in the rivers of the region. It was found that the indicators of turbidity of river water grow in the direction from north to south of the study area, in the zone of mixed forests are minimal, and in the forest-steppe – maximum; high values of the average turbidity index characteristic of small rivers in the region, аmong the average rivers, the maximum values were recorded for the Sula and Vorskla rivers; during floods, turbidity values are maximum, and during low water periods, they are minimal; there is a tendency to an increase in the indicators of maximum and average turbidity of river water. Particular attention is paid to the influence of river regulation on turbidity indicators. It was found that the deceleration of water exchange is facilitated by the accumulation of sediments in the channel above the dam (high indicators of the thickness of the silt layer), and also below the dam (the creation of a channel island, probably due to the uneven throughput of the dam’s gate valves, which creates a different flow rate from the right and left banks). Decreased flow velocity, increased water turbidity and, as a consequence, siltation, deterioration of river water quality (appearance of swamp odor, decrease in transparency, color change) leads to changes in the species composition of aquatic organisms, extinction of river species and the appearance of atypical river species, overgrowth. In their conclusions, the authors argue that sediment runoff is formed mainly due to washout from the surface of the catchment area, high turbidity indicators in rivers whose basin is more prone to erosion, where the indicators of plowing of the basin surface are maximum, water protection zones and coastal protective belts are destroyed, but when studying the turbidity of river water it is necessary take into account additional factors.

ВЛИЯНИЕ АБИОТИЧЕСКИХ ФАКТОРОВ НА ОСОБЕННОСТИ И ДИНАМИКУ РАСПРЕДЕЛЕНИЯ РЫБ В МАЛОМ ПРИТОКЕ РЕКИ ИРТЫШ

The article focuses on the studies carried out in the flooded floodplain of the small river Varpak in the basin of the lower Irtysh during the spring flood (in May). The influence of abi-otic factors on the distribution of fish, including juveniles of cyprinids, percids and pike was analyzed. It was found that during the research period there was a direct correlation between the fish density and the temperature and water level, i.e. the fish density increased, as well as the mentioned indicators. There was found the regularity of decreasing the proportion of percids and fish density along with increasing water turbidity in the periods of the southern (S) and south-western (SW) winds, which is stipulated by the wind and wave fish set-down and their independent movement to the shallow areas of the flooded floodplain; In the periods of the north (N) and northeast (NE) winds the fish density increased along with water turbidity, i.e. the fish moved from the shallow water zones to the open water area. The investigated section of the Varpak River is open to the winds of the mentioned directions due of its location and relief. When considering the direction of the fish density distribution during the period of wind events S, SW, N and NE, there has been registered the similarity between the wind direction and the fish distribution in the water area of the floodplain. As a result of the analysis during the observation period the influence of the turbidity factor on the distribution of fish is noted; the greater turbidity, the greater the proportion of cyprinids and the lower the proportion of percids, which can be explained by the specific behavior of these groups of fish. Thus, there is a direct and indirect effect of a number of environmental factors (temperature and water level, wind phenomena and turbidity) on the characteristics and dynamics of fish distribution in the flooded floodplain of the river in the spring period

Sediment carbon storage increases in tropical, oligotrophic, high mountain lakes

• El Sol and La Luna are valuable sentinels of global change by displaying detectable signs of anthropic disturbances from 1950 onwards. • The higher mass accumulation rates and organic carbon burial rates from 1950 onwards are result of human activities and atmospheric dust deposition. • Sharing the same climatic conditions, climate change unlikely caused the recent higher organic carbon burial observed in both lakes. High mountain lakes are valuable sentinels of global change because they are sensitive to environmental stress and integrate changes in the atmosphere and their catchment areas. This study tested the hypothesis that local and regional anthropogenic stressors have affected productivity, sedimentation, and organic carbon burial in two tropical high mountain lakes in central Mexico. We studied changes in the water column (Secchi disc depth, total suspended solids (TSS), and chlorophyll- a concentrations) and surface sediments (chlorophyll- a and organic carbon concentrations) in El Sol Lake and La Luna Lake during the period 2000–2018, and organic carbon burial rates in sediment cores (∼1884–2014) dated with lead-210 ( 210 Pb). We observed increasing water turbidity, TSS, and organic carbon in surface sediments in El Sol Lake. Different responses of the two lakes were caused by lower pH in La Luna Lake and a threefold residence time of TSS in El Sol Lake compared to La Luna Lake, mostly attributable to their different surface/volume ratios. Organic carbon burial rates were slightly higher at La Luna Lake until 2000, when they became higher at El Sol Lake due to increasing sediment accumulation and organic carbon concentrations. In both lakes, results show significantly higher organic carbon burial rates since the 1950s, likely resulting from the deposition of human-induced wind-blown particles derived from activities at the volcano slopes and long-distance transport from highly urbanized areas. Anthropogenic impacts rather than climate change, therefore, caused the recent higher organic carbon burial rates observed in both lakes. Methods and findings from this study provide a valuable basis for comparing changes in other high mountain lakes worldwide.

Changes in survival and growth in response to different combinations of turbidity and duration in eelgrass Zostera marina plants

Increased water turbidity is considered a primary cause of the loss of seagrass meadows. This paper first quantified the interactive influence of different combinations of turbidity and duration on the responses of Zostera marina plants in terms of survivorship, morphology and growth. The recovery potential of Z. marina plants, as well as the degrees of potential correlations between key factors induced by the increased turbidity and the survival and growth variables, were assessed. The LT50 (lethal time that caused an increase in mortality to 50% of that of the control) and EC50 (effect concentration, i.e., turbidity level that caused a decrease in growth to 50% of that of the control) were calculated to reveal the quantitative relationship between turbidity and duration that resulted in limiting effects on the survival and growth of Z. marina plants. Z. marina plants were exposed to different combinations of water turbidity [4 (control), 50, 100, 200, 300 and 400 NTU] and duration (5, 10, 15 and 20 days), and then the plants were transferred to the control condition for over 30 days under laboratory conditions. The results showed that the recovery effort (the percentage of the survival of plants at the end of recovery to that of plants at the end of direct turbidity stress) of Z. marina exposed to different combinations of turbidity and duration was lower than 100%, indicating that short-term periods of increased water turbidity would lead to long-term effects on the survival of Z. marina plants. Water turbidity and duration displayed a significant interactive effect on the survival and growth of Z. marina plants. Regression analysis revealed that the relationship between water turbidity and duration that resulted in limiting effects on the survival and growth of Z. marina could be described as a strong inverse function. Spearman correlation analysis showed that the decrease in survival and growth of Z. marina plants was mostly caused by increased silt load in turbid waters, and subsequently by light reduction. This study will further develop our understanding of the degradation and disappearance of seagrass meadows induced by increased turbidity.

Rapid shoreline flooding enhances water turbidity by sediment resuspension: An example in a large Tibetan lake

ABSTRACTRapid water level rise due to climate change has the potential to remobilize loose sediments along shorelines and increase the turbidity of nearshore waters, thereby impacting water quality and aquatic ecosystem health. Siling Lake is one of the largest and most rapidly expanding lakes on the Tibetan Plateau. Between 2000 and 2017, this lake experienced an increase in water level of about 8 m and a doubling in water turbidity. Here, using this lake as a study site, we used a wave model and high‐resolution remote sensing of turbidity (Landsat‐8) to assess the potential connection between water‐level rise, enhanced wind‐driven sediment resuspension and water turbidity. Our analysis revealed that strong bottom shear stresses triggered by wind‐generated waves over newly flooded areas were related to an increase in water turbidity. The spatial variability of Siling Lake turbidity showed a strong dependence on local wind characteristics and fetch. Two factors combined to drive the increase in turbidity: (1) high wave energy leading to high bottom shear stresses, and (2) flooding of unvegetated shallow areas. Using a new relationship between wave energy and turbidity developed here, we expect the increase in turbidity of Siling Lake to taper off in the near future due to the steep landscape surrounding the lake that will prevent further flooding. Our results imply that rising water levels along the coast are not only expected to influence terrestrial ecosystems but could also change water quality. The methodology presented herein could be applied to other shorelines affected by a rapid increase in water level. © 2020 John Wiley & Sons, Ltd.

Influence of Potamogeton crispus on Lake Water Environment and Phytoplankton Community Structure

The decomposition of submerged macrophytes is generally associated with dramatic changes in the water environment, such as the large release of nutrients (e.g., nitrogen and phosphorus) and organic carbon to the surrounding waters, which may result in significant changes in phytoplankton community structure. In this study, Potamogeton crispus, physicochemical variables, and phytoplankton samples were collected in 14 shallow lakes in the middle and lower Jianghuai Plain in spring (growing period of P. crispus) and summer (decomposition phase of P. crispus) of 2018. The effects of the decline of P. crispus on water quality and phytoplankton community structure were quantified. The results showed that water transparency increased significantly in spring because the growth of P. crispus inhibits sediment resuspension and macrophytes can transport the nutrients from the water column to the sediment. The values of dissolved oxygen and pH also increased significantly due the photosynthesis by macrophytes. In contrast, the decomposition of P. crispus during summer months caused a significant increase in water turbidity and organic matter. There were considerable differences in phytoplankton biomass and cyanobacterial biomass in the sites with or without P. crispus, and the corresponding ratios of cyanobacterial biomass to the total algal biomass were 18.96% and 34.05%, respectively. Higher values of cyanobacterial biomass were observed with the decomposition of P. crispus than its counterpart in summer because ① the decomposition of macrophytes provided sufficient organic matter and nutrient (nitrogen and phosphorus) resources for cyanobacterial growth; ② P. crispus decline in summer significantly increased water turbidity, which makes cyanobacteria occupy a better ecological niche and more efficiently utilize nitrogen and phosphorus.

Influences of claywater and greenwater on the skin microbiome of cultured larval sablefish (Anoplopoma fimbria)

BackgroundThe skin microbiome of marine fish is thought to come from bacteria in the surrounding water during the larval stages, although it is not clear how different water conditions affect the microbial communities in the water and, in turn, the composition and development of the larval skin microbiome. In aquaculture, water conditions are especially important; claywater and greenwater are often used in larval rearing tanks to increase water turbidity. Here, we explored the effects of these water additives on microbial communities in rearing water and on the skin of first-feeding sablefish larvae using 16S rRNA gene sequencing. We evaluated three treatments: greenwater, claywater, and greenwater with a switch to claywater after 1 week.ResultsWe observed additive-specific effects on rearing water microbial communities that coincided with the addition of larvae and rotifer feed to the tanks, such as an increase in Vibrionaceae in greenwater tanks. Additionally, microbial communities from experimental tank water, especially those in claywater, began to resemble larval skin microbiomes by the end of the experiment. The differential effects of the additives on larval sablefish skin microbiomes were largest during the first week, post-first feed. Bacteria associated with greenwater, including Vibrionaceae and Pseudoalteromonas spp., were found on larval skin a week after the switch to claywater. In addition to additive-specific effects, larval skin microbiomes also retained bacterial families likely acquired from their hatchery silos.ConclusionsOur results suggest that larval sablefish skin microbiomes are most sensitive to the surrounding seawater up to 1 week following the yolk-sac stage and that claywater substituted for greenwater after 1 week post-first feed does not significantly impact skin-associated microbial communities. However, the larval skin microbiome changes over time under all experimental conditions. Furthermore, our findings suggest a potential two-way interaction between microbial communities on the host and the surrounding environment. To our knowledge, this is one of the few studies to suggest that fish might influence the microbial community of the seawater.

Marine zooplankton dynamics after a major mining dam rupture in the Doce River, southeastern Brazil: Rapid response to a changing environment

Zooplankton were sampled five days after the tailings from the Samarco dam rupture reached the ocean in the coastal region at the mouth of the Doce River. This was one of the largest environmental disasters in Brazilian history, and the impacts on the marine biota are not yet fully understood. This study aimed to evaluate the zooplankton community short term responses to the metal enrichment after the tailings reached the coastal region in different scenarios. Our results showed an acute impact on the zooplankton community, which peaked in abundance (222,958.60 ind/m3) and decreased in diversity (H′ = 1.23) near the river mouth. Two copepod species, Parvocalanus sp. and Oithona nana, composed up to 61% of the total abundance and they were correlated with concentrations of Fe, Pb, Cu and Zn in particulate fraction. These species feed opportunistically on nanophytoplankton, which dominated the autotroph community, possibly in response to the iron enrichment caused by the mud flow. A shift on zooplankton species composition was also observed. During the first three days, we found the presence of oceanic species in the 20 and 30 m isobaths during an incomplete upwelling event, which directly correlated with the presence of Calanoides carinatus. However, only three days later, following a cold front passage and consequent increase of water turbidity, those species were already absent, and the zooplankton community was significantly altered (PERMANOVA, df = 1, pseudo-F = 9.2247, p = .001). Zooplankton responded quickly to the environmental changes detected during our sampling period and proved to be key factors in costal monitoring, especially in dynamic oceanographic areas such as the Doce River coastal region.

Effects of Crucian Carp (Carassius auratus) on Water Quality in Aquatic Ecosystems: An Experimental Mesocosm Study

The presence of omnivorous fish is known to affect aquatic ecosystems, including water quality. The effect, however, depends on the species in question, and our knowledge is limited on the effect of omnivorous crucian carp (Carassius auratus), a common and often the most numerous fish species in eutrophic shallow lakes in China. We conducted a 70-day outdoor experiment in mesocosms with and without crucian carp to examine whether this species adversely affects water quality by increasing the levels of total nitrogen (TN) and total phosphorus (TP), thereby stimulating the biomass of phytoplankton and increasing water turbidity. Compared with carp-free controls, the presence of crucian carp resulted in higher TN and TP in the water column, greater phytoplankton biomass and lower periphyton biomass, measured as chlorophyll a. Total suspended solids (TSS) also increased in the presence of fish. We conclude that crucian carp can increase TN and TP, enhance phytoplankton biomass, and increase water turbidity, thereby contributing significantly to the deterioration of the water quality. In addition to controlling external nutrient loading, the removal of crucian carp may help to improve water quality in warm shallow eutrophic lakes.

Soil erosion-prone area identification using multi-criteria decision analysis in Ethiopian highlands

Soil erosion is a very complex natural process that refers to the detachment and transportation of topsoil from the land surface by natural agents like water, wind, and others. This process has an effect on the environment including loss of soil fertility, reduction of water bodies' depth (lakes, ponds, reservoirs, etc.), increase in water turbidity, flood hazard problems, etc. Identifying the erosion hotspot areas using different techniques is an essential tool for sustainable natural resources management. This study focusses on the mapping of soil erosion-prone areas of Ribb watershed, Upper Blue Nile, Ethiopia. This study aimed to identify the erosion of hotspot areas for the setting of effective soil and conservation strategies. Different soil erosion contributing factors, viz. Slope, land use, soil, rainfall, and stream power index, were integrated on ArcGIS 10.3 environment for determining the erosion-prone areas. Multi-criteria decision analysis (MCDA) technique was used to develop erosion hotspot areas using thematic layers pair-wise comparison tool. The weights for each thematic layer and feature were decided based on the expert's judgment and review of the literature. Hence, the results of soil erosion map showed very high, high, moderate, low, and very low vulnerability to erosion with areal coverage of 7.04%, 20.40%, 17.60%, 32.01%, and 22.95%, respectively. The findings of this study will help decision-makers to plan and carry out effective soil and water conservation practices in highly vulnerable areas to soil erosion. MCDA was found as a basic tool for determining erosion-prone areas coupled with GIS. The spatial distribution map indicated that most of the erosion-prone areas were found in northern, eastern, and northeastern parts of the watershed due to the steep slope and agricultural practice which needs integrated soil and water conservation practice.

Acute Toxicity of Cypermethrin to Freshwater Fish Oreochromis niloticus: Influence of Aquatic Weed and Turbidity of Water

Cypermethrin is a common pollutant of freshwater ecosystem in India. In this study, static bioassays were conducted to evaluate how toxicity of Cypermethrin to freshwater fish Oreochromis niloticus changed with hydro-biological conditions of water. 72-h LC50 of Cypermethrin to O. niloticus was found as 5.05 µg/L. The LC50 value significantly increased in the presence of the aquatic weed Azolla pinnata (150 g/10L). Toxicity of Cypermethrin to fish also reduced with the increase in turbidity of water. It was concluded that determination of lethality of Cypermethrin to fish should be based on ambient conditions of the medium.