Inorganic Turbidity Research Articles

Vertical distribution of picocyanobacteria in deep lakes: the influence of inorganic turbidity

Vertical distribution of picocyanobacteria in deep lakes: the influence of inorganic turbidity

Utilization of Thermophilic Aerobic Oxidation and Electrocoagulation to Improve Fertilizer Quality from Mixed Manure Influent

Thermophilic aeration and electrochemical reactions are well-established methods for wastewater treatment to reduce metallic content, organic and inorganic matter, turbidity, coloration, and nutrient levels. In this study, thermophilic aerobic oxidation (TAO) and electrocoagulation (EC) were implemented together to improve the quality of liquid fertilizer by reducing the nutrient load and toxicity of swine manure. The influent in this study was prepared by mixing anaerobic digestate and liquid swine manure at a 1:9 ratio and treating it for 3 days at 50–60 °C in a field-scale TAO system. The TAO effluent was then processed in an EC reactor for 180 min with a 30 V electric supply through two sets of iron and aluminum hybrid electrodes. The combined TAO and EC processes led to a germination index of 133% using the final efflux. The high retention of important nutrients such as total nitrogen and potassium, combined with the 100% reduction in heavy metals, over 60% reduction in trace minerals, and 89% reduction in pollutants in the final product, helped to achieve a higher germination index. Overall, the combination of TAO and EC was demonstrated to be an effective technique for enhancing the quality of liquid fertilizer derived from swine manure.

Responses of Phytoplanktonic Chlorophyll-a Composition to Inorganic Turbidity Caused by Mine Tailings

Inorganic turbidity can limit light penetration in water and reduce phytoplankton photosynthesis. Anthropogenic activities such as mining can produce or augment the amount of suspended inorganic particles in water. Recent mining disasters in Brazil have released tons of mine tailings into aquatic ecosystems, with known and unknown negative consequences for aquatic life, biodiversity, and ecosystem services beyond the human and material losses. Here, we investigated the effects of inorganic turbidity on phytoplankton chlorophyll content and composition caused by sediments from two areas in Lake Batata, one natural and the other impacted by bauxite tailings. We experimentally compared the effects of different levels of turbidity (12, 50, and 300 NTU) caused by the addition of sediments from the two lake areas on a chlorophyll-a gradient (5, 15, and 25 μg/L). Inorganic turbidity did not consistently reduce chlorophyll-a concentrations. In treatments with high chlorophyll-a, high turbidity was associated with lower chlorophyll-a concentrations at the end of the experiment. On the other hand, in low-chlorophyll treatments, high turbidity was associated with higher chlorophyll-a concentrations. In treatments with sediments from the natural area, overall chlorophyll-a levels were higher than in treatments with sediments from the impacted area. Phagotrophic algae dominated both in treatments with sediments from the impacted area (Chrysophyceae 34%, Chlorophyceae 26%, and Cyanobacteria 22% of total density) and in treatments with sediment from the natural area (Euglenophyceae 26%, Chrysophyceae 23%, and Chlorophyceae 20%). We conclude that high turbidity does not lead to a reduction in chlorophyll-a concentrations and sediment from the natural area allowed higher chlorophyll-a levels, indicating that impacted area sediment affected more phytoplankton.

Identifying Inorganic Turbidity in Water Samples as Potential Loss Factor During Nucleic Acid Extraction: Implications for Molecular Fecal Pollution Diagnostics and Source Tracking.

Molecular diagnostic methods are increasingly applied for food and environmental analysis. Since several steps are involved in sample processing which can affect the outcome (e.g., adhesion of DNA to the sample matrix, inefficient precipitation of DNA, pipetting errors and (partial) loss of the DNA pellet during DNA isolation), quality control is essential at all processing levels. In soil microbiology, particular attention has been paid to the inorganic component of the sample matrix affecting DNA extractability. In water quality testing, however, this aspect has mostly been neglected so far, although it is conceivable that these mechanisms have a similar impact. The present study was therefore dedicated to investigate possible matrix effects on results of water quality analysis. Field testing in an aquatic environment with pronounced chemo-physical gradients [total suspended solids (TSS), inorganic turbidity, total organic carbon (TOC), and conductivity] indicated a negative association between DNA extractability (using a standard phenol/chloroform extraction procedure) and turbidity (spearman ρ = −0.72, p < 0.001, n = 21). Further detailed laboratory experiments on sediment suspensions confirmed the hypothesis of inorganic turbidity being the main driver for reduced DNA extractability. The observed effects, as known from soil samples, were also indicated to result from competitive effects for free charges on clay minerals, leading to adsorption of DNA to these inorganic particles. A protocol modification by supplementing the extraction buffer with salmon sperm DNA, to coat charged surfaces prior to cell lysis, was then applied on environmental water samples and compared to the standard protocol. At sites characterized by high inorganic turbidity, DNA extractability was significantly improved or made possible in the first place by applying the adapted protocol. This became apparent from intestinal enterococci and microbial source tracking (MST)-marker levels measured by quantitative polymerase chain reaction (qPCR) (100 to 10,000-fold median increase in target concentrations). The present study emphasizes the need to consider inorganic turbidity as a potential loss factor in DNA extraction from water-matrices. Negligence of these effects can lead to a massive bias, by up to several orders of magnitude, in the results of molecular MST and fecal pollution diagnostics.

Industrial wastewater treatment by electrocoagulation powered by a solar photovoltaic system

ABSTRACT Textile wastewater is hazardous to the environment due to their high pollution and toxicity. Some non-biodegradable compounds have a significant impact on BOD and COD levels in wastewater bodies. Dyes extracted from wastewater treatment plants that come from textile industry wastewater are carcinogenic, mutagenic, or teratogenic. Certain bacteria, fungi, activated carbon, and carbon nanotubes (CNTs) can be used to treat wastewater by using biological processes. There are a lot of inefficiencies and problems associated with these approaches due to higher cost. Therefore, the current study introduces a research work on cloth textile industries’ wastewater using electrocoagulation cell (EC) powered by solar photovoltaic system. Through a new experimental treatment, the effects of current density, electrolysis time, electrode material (Al or Fe), initial wastewater acidity pHo, and settling age on the elimination of total suspended organic and inorganic matters (SS), turbidity (Tur), and chemical oxygen demand (COD) have been investigated. The handling process was efficient when higher current densities and/or long electrolysis, settling periods, and pHo = 7 irrespective of the electrode material were applied. It was found that the most suitable operating conditions to meet requirements of international laws concerning the discharge of public sewer scheme at a reasonable operating charge with current density, electrolysis time, and settling period were 75 Am−2, 45 min, and 45 min, respectively, without pHo adjustment and iron electrodes. Moreover, in the present work, the removal efficiencies achieved for total suspended organic and inorganic matters (SS), turbidity (Tur), and chemical oxygen demand (COD) were 55%, 82%, and 52%, respectively. The study reveals that the whole electrocoagulation (EC) cell arrangement is simple in design and operation and can be applied to clean the water as per the parameters suggested by the developed countries. It was also found that the used water treatment method was highly efficient and comparatively fast for dye removal from aqueous textile water solutions.

Comparison of floc properties of coagulation systems: Effect of particle concentration, scale and mode of flocculation

This study is aimed to ascertain the influence of varying quantum of organic and inorganic colloids on parameters like floc size, fractal dimension and residual particle size, under alkaline conditions for water treatment by coagulation. Synthetic sample waters were prepared by using humic acid and kaolin for simulating organic matter and inorganic turbidity respectively. PACl (Poly aluminium chloride) was used as a coagulant. Image analysis for floc size measurement and box-counting method for fractal dimension measurement has been used. A batch jar test reactor and two continuous flow pilot-scale reactors: 1. Conventional clariflocculator (CC) and 2. Sludge blanket clarifier (SBC) were studied to evaluate the effect of scale-up on floc properties. The pilot systems differed in the mode of flocculation, as CC used a mechanical impeller and SBC used hydraulic mode for flocculation. For CC, the trendlines indicated a decrease in the size of flocs with increasing organic concentration. The order of floc size was: SBC > jar test > CC. The average fractal dimension of flocs in jar test was 1.28 which was lesser than that in CC (1.51) indicating more filament-like structure of flocs in jar test. The floc sizes and fractal dimensions depended on the scale and mode of flocculation. The size of residual particles in the treated water was quite similar irrespective of the scale and mode of flocculation. However, the trends were opposite with increasing input TOC. For jar test, the residual particle sizes decreased and for pilot-scale, it increased with increasing input TOC.

Cascading effects of predation risk under high organic and inorganic turbidity: impacts on individuals and shoals of a mesopredator fish

We tested whether changes in water transparency caused either by precipitation-mediated sedimentation (inorganic turbidity) or eutrophication (organic turbidity) differently interact with top predator presence to determine predation rates, and individual decisions of mesopredators between foraging and avoiding predators. We tested the hypothesis that fear-induced cascade effects are more pronounced in organic turbid water through an experiment in which we manipulated turbidity (clear water and organic/inorganic turbid water) and predation risk (presence/absence of a top predator) in a 3 × 2 factorial design. We assessed prey consumption, prey selection (benthic and planktonic invertebrates) and food partitioning among individuals within shoals of an invertivorous fish, Moenkhausia forestii. The overall prey consumption by mesopredators was similar with and without top predator in clear water, but the presence of a top predator resulted in decreased invertebrate consumption in turbid waters, with no difference between organic and inorganic turbidity. Also, fear-induced cascade effects caused a strong preference of planktonic prey over benthic in inorganic turbidity and decreased evenness in prey consumption among individuals. Our findings suggest that the interactive effects of turbidity and top predator presence on mesopredator foraging depend on prey type and highlight individual differences in foraging behaviours among shoal members. Increased anthropogenic impacts on aquatic environments could have lasting long-term population impacts for fishes in terms of foraging and predator avoidance behaviour.

Optimized coagulation of humic acid and mineral turbidity at alkaline pH using high basicity PACl

Abstract In this study, the simultaneous removal of inorganic turbidity and organics was investigated at alkaline pH to avert the need for pH adjustment and overdosing. The aim was to compare the doses for conventional and enhanced coagulation and, consequently, arrive at optimized coagulation where both had synergistic maximum removal. High basicity PACl was used to coagulate simulated waters prepared by humic acid (HA) and kaolin. The removal of turbidity, total organic carbon (TOC), dissolved organic carbon (DOC) and UV254 was evaluated. The impact of varying input concentrations of HA and turbidity on doses was studied. The enhanced coagulation doses were higher than conventional ones. However, with an increase in input TOC, the difference between enhanced and conventional doses narrowed. The doses for optimized coagulation ranged from 2 to 9 mg Al/L. At optimized coagulation, the removal of TOC, DOC and UV254 varied from 30–85%, 30–89% and 73–91% respectively. Fourier transform infrared (FTIR) spectroscopy revealed the presence of Si-O-C bond. The interactions of unsaturated bonds of hydrophobic organics to inorganic clay were possibly favoured over hydrophilics. HA agglomeration reduced coagulant consumption as the input TOC increased. It was concluded that instead of a stoichiometric approach, a modified dosing approach can be applied for limiting underdosing and overdosing while ensuring maximum removal of impurities.

Comparison of different trophic state indices applied to tropical reservoirs

AbstractReservoirs represent impoundments of river flows for multiple human purposes, including hydropower generation and industrial, recreational and agricultural activities. In considering the current state of dammed rivers and future projects, there is a major concern in tropical areas regarding the water quality of these aquatic ecosystems, most being subjected to eutrophication process. To this end, the Carlson (1977), Toledo (1983), Lamparelli (2004) and Cunha (2013) trophic state indices were applied and compared in six interconnected reservoirs from the Paraíba do Sul Ecoregion in Brazil that differ in their morphometry, nutrient loadings, water retention times and altitudes. Limnological variables were measured in an extensive monitoring programme carried out from 2011 to 2014 during both the rainy and dry seasons. Application of the different numerical models resulted in different trophic state classifications. Toledo's trophic state index was considered the best for assessing the trophic state of the study reservoirs since it under‐evaluates water transparency, which can be related more to inorganic turbidity rather than to phytoplankton biomass in tropical water systems. The Carlson index, developed for temperate zone lakes, resulted in higher trophic classifications, thereby not being considered a reliable model for the study reservoirs. Both the Lamparelli and Cunha indices generally classified the study reservoirs as being in an oligotrophic state, thereby underestimating their trophic status. All the trophic state indices varied seasonally, with water transparency being the only variable significantly affected by rainfall variations. Based on the results of the present study, it was concluded that an arbitrary choice of existing trophic state indices to evaluate the water quality in tropical environments might lead to erroneous conclusions regarding the actual trophic conditions of tropical waterbodies. Further, the weak correlation observed between total phosphorus and chlorophyll‐a concentrations indicates total phosphorus might not be a key factor limiting algal growth in tropical water systems, thereby meriting more research focusing on tropical reservoirs, as well as development of new trophic state indices, including consideration of other potentially limiting factors.

Mosquito larvae consumption in turbid waters: the role of the type of turbidity and the larval stage in native and invasive fish

Agricultural runoff and biological invasions alter native species interactions with implications for the management of pests. Here, we used live larvae of common house mosquito Culex pipiens to test the efficiencies of the invasive fish Gambusia holbrooki and the IUCN endangered fish Aphanius iberus to manage mosquitoes at three ecologically relevant concentrations of algae and clay. Both species reduced mosquito abundance in aquaria and outdoor mesocosms though A. iberus reduced it at a slower pace. However, G. holbrooki preferentially captured larger larvae at all fish sizes, whereas smaller individuals of A. iberus captured higher number of smaller larvae. Algal turbidity, but not clay, reduced the efficiency of both species, probably because of an adaptation to inorganic turbidity. Fish efficiency was not reduced in mesocosms where fish captured mosquito larvae interacting with natural invertebrate assemblages. Managers should maintain algal turbidity at < 10 FTU based on the visual detection threshold for both species. Our study shows that algal turbidity threatens the potential of waterbodies to naturally control mosquitoes and discusses why the faster foraging rates of alien species such as G. holbrooki should not be used to justify more introductions.

Time Delay Evaluation on the Water-Leaving Irradiance Retrieved from Empirical Models and Satellite Imagery

Temporal delays and spatial randomness between ground-based data and satellite overpass involve important deviations between the empirical model output and real data; these are factors poorly considered in the model calibration. The inorganic matter-generated turbidity in Lake Chapala (Mexico) was taken as a study case to expose the influence of such factors. Ground-based data from this study and historical records were used as references. We take advantage of the at-surface reflectance from Landsat-8, sun-glint corrections, a reduced NIR-band range, and null organic matter incidence in these wavelengths to diminish the physical phenomena-related radiometric artifacts; leaving the spatio-temporal relationships as the principal factor inducing the model uncertainty. Non-linear correlations were assessed to calibrate the best empirical model; none of them presented a strong relationship (&lt;73%), including that based on hourly delays. This last model had the best predictability only for the summer-fall season, explaining 71% of the turbidity variation in 2016, and 59% in 2017, with RMSEs &lt; 24%. The instantaneous turbidity maps depicted the hydrodynamic complexity of the lake, highlighting a strong component of spatial randomness associated with the temporal delays. Reasonably, robust empirical models will be developed if several dates and sampling-sites are synchronized with more satellite overpasses.

Environmental constraint of intraguild predation: Inorganic turbidity modulates omnivory in fairy shrimps

Abstract Omnivory is widespread in food webs, with an important stabilising effect. The strength of omnivorous trophic interactions may change considerably with changes in the local environment. Shallow temporary waters are often characterised by high levels of inorganic turbidity that may directly limit the food uptake of filter‐feeding organisms, but there is little evidence on how it might affect omnivorous species. Anostracans are key species of temporary waters and recent evidence suggests that these organisms are omnivorous consumers of both phyto‐ and zooplankton. Using Branchinecta orientalis as a model species, our aim was to test how turbidity affects the feeding of an omnivorous anostracan. To do this, we used short‐term feeding experiments and stable isotope analyses, with animals collected from soda pans in eastern Austria. In the feeding experiments, algae and zooplankton were offered as food either separately or in combination. The prey type treatments were crossed with turbidity levels in a factorial design. There was a pronounced decrease in the ingested algal biomass with increasing turbidity. Conversely, ingestion rates on zooplankton were less affected by turbidity. Stable isotope analyses from field material supported our experimental results by showing a positive relationship of the trophic position of anostracans and the trophic niche of the communities with turbidity. Our results show that turbidity modulates the intraguild trophic relationship between anostracans and their prey by shifting the diet of anostracans from more herbivorous in transparent to more carnivorous in turbid waters. Thus, inorganic turbidity might also have a community‐shaping role in plankton communities of temporary waters through altering trophic relationships.

Fish-mediated zooplankton community structure in shallow turbid waters: a mesocosm study

Turbidity influences the success of fish feeding, but little is known about the difference in the effects of turbidity as a result of organic and inorganic matter. To assess the feeding behaviour of a native fish, Goodea atripinnis, under turbid conditions (up to 120 NTU) generated by Microcystis aeruginosa or silt, we conducted mesocosm experiments for 25 days using 40-L plastic mesocosms. Each tank received two G. atripinnis individuals (predators) with a mean total length 61 mm and cladoceran zooplankton (prey) (Alona glabra, Chydorus sphaericus, Moina macrocopa, Simocephalus vetulus, Ceriodaphnia dubia, and Daphnia pulex) of 100 ind. L−1. Filtered water from Xochimilco Lake was used to fill the mesocosms. Goodea atripinnis had a selective effect on the zooplankton community in the form of a decrease in the number of pelagic cladocerans. The zooplankton composition, which was least affected by the fish, included small-sized (400–480 µm) benthic cladocerans (e.g. Chydorus sphaericus) and copepods (both calanoids and cyclopoids). Prey consumption by the fish was highest under conditions with inorganic turbidity, while in the fishless treatments, small cladocerans (along with calanoids) had a high density. Organic turbidity offered refuge against fish predation to A. glabra, C. sphaericus, Daphnia pulex, M. alburquerquensis and A. americanus, whereas inorganic turbidity allowed only both test copepods to coexist in the presence of fish. The results suggest that fish predation is a powerful factor regulating zooplankton communities, even in highly turbid waters.

The freshwater biome gradient framework: predicting macroscale properties based on latitude, altitude, and precipitation

AbstractUnderstanding global ecological patterns and processes, from biogeochemical to biogeographical, requires broad‐scale macrosystems context for comparing and contrasting ecosystems. Climate gradients (precipitation and temperature) and other continental‐scale patterns shape freshwater environments due to their influences on terrestrial environments and their direct and indirect effects on the abiotic and biotic characteristics of lakes, streams, and wetlands. We combined literature review, analyses of open access data, and logical argument to assess abiotic and biotic characters of freshwater systems across gradients of latitude and elevation that drive precipitation, temperature, and other variability. We explored the predictive value of analyzing patterns in freshwater ecosystems at the global macrosystems scale. We found many patterns based on climate, particularly those dependent upon hydrologic characteristics and linked to characteristics of terrestrial biomes. For example, continental waters of dry areas will generally be widely dispersed and have higher probability of drying and network disconnection, greater temperatures, greater inorganic turbidity, greater salinity, and lower riparian canopy cover relative to areas with high precipitation. These factors will influence local community composition and ecosystem rates. Enough studies are now available at the continental or global scale to start to characterize patterns under a coherent conceptual framework, though considerable gaps exist in the tropics and less developed regions. We present illustrative global‐scale trends of abiotic, biotic, and anthropogenic impacts in freshwater ecosystems across gradients of precipitation and temperature to further understanding of broad‐scale trends and to aid prediction in the face of global change. We view freshwater systems as occurring across arrays of multiple gradients (including latitude, altitude, and precipitation) rather than areas with specific boundaries. While terrestrial biomes capture some variability along these gradients that influence freshwaters, other features such as, slope, geology, and historical glaciation also influence freshwaters. Our conceptual framework is not so much a single hypothesis as a way to logically characterize patterns in freshwaters at scales relevant to (1) evolutionary processes that give rise to freshwater biodiversity, (2) regulatory units that influence freshwater ecosystems, and (3) the current scope of anthropogenic impacts on freshwaters and the vital ecosystem services they provide.

Great Lakes coastal fish habitat classification and assessment

Abstract Basin-scale assessment of fish habitat in Great Lakes coastal ecosystems would increase our ability to prioritize fish habitat management and restoration actions. As a first step in this direction, we identified key habitat factors associated with highest probability of occurrence for several societally and ecologically important coastal fish species as well as community metrics, using data from the Great Lakes Aquatic Habitat Framework (GLAHF), Great Lakes Environmental Indicators (GLEI) and Coastal Wetland Monitoring Program (CWMP). Secondly, we assessed whether species-specific habitat was threatened by watershed-level anthropogenic stressors. In the southern Great Lakes, key habitat factors for determining presence/absence of several species of coastal fish were chlorophyll concentrations, turbidity, and wave height, whereas in the northern ecoprovince temperature was the major habitat driver for most of the species modeled. Habitat factors best explaining fish richness and diversity were bottom slope and chlorophyll a. These models could likely be further improved with addition of high-resolution submerged macrophyte complexity data which are currently unavailable at the basin-wide scale. Proportion of invasive species was correlated primarily with increasing maximum observed inorganic turbidity and chlorophyll a. We also demonstrate that preferred habitat for several coastal species and high-diversity areas overlap with areas of high watershed stress. Great Lakes coastal wetland fish are a large contributor to ecosystem services as well as commercial and recreational fishery harvest, and scalable basin-wide habitat models developed in this study may be useful for informing management actions targeting specific species or overall coastal fish biodiversity.

Drivers of cyanobacteria dominance, composition and nitrogen fixing behavior in a shallow lake with alternative regimes in time and space, Laguna del Sauce (Maldonado, Uruguay)

Laguna del Sauce, one of the main drinking water sources in Uruguay, is an eutrophic shallow lake with high temporal variation of inorganic turbidity caused by extreme wind events. During low turbidity periods, high phytoplankton biomass can be reached, frequently associated to cyanobacteria blooms, which can cause interferences in the water supply. In this study, we assessed the environmental drivers of cyanobacteria dominance, composition, and nitrogen-fixation behavior. For this, we analyzed the spatial and temporal phytoplankton composition, physical and chemical variables performing weekly samplings during two summers: 2015–2016 and 2016–2017. When inorganic turbidity was high (above 30 NTU), phytoplankton biomass was controlled, below this threshold, temperature, secchi depth and nutrients played key factors controlling cyanobacteria biomass and composition. Blooms of N2-fixing cyanobacteria (Dolichospermum crassum, Aphanizomenon gracile, and Cuspidothrix issatschenkoi) were promoted by low N:P ratios (average 11.5) and wide TN range (286–1300 µg l−1). Non-heterocystous cyanobacteria blooms occurred above TN 1000–1200 µg l−1. The N2-fixing behavior (heterocytes:vegetative cell ratio) depended on TN, it was highest at low TN (< 700 µg l−1) but null above ca. 1000 µg l−1. While low inorganic turbidity allowed cyanobacteria blooms in Laguna del Sauce, its composition and N2-fixation behavior depended on the TN and TP levels.

Effect of organic and inorganic turbidity on the zooplankton community structure of a shallow waterbody in Central Mexico (Lake Xochimilco, Mexico)

Effect of organic and inorganic turbidity on the zooplankton community structure of a shallow waterbody in Central Mexico (Lake Xochimilco, Mexico)

Multi-model approach to predict phytoplankton biomass and composition dynamics in a eutrophic shallow lake governed by extreme meteorological events

A multi-model approach to predict phytoplankton biomass and composition was performed in a eutrophic Uruguayan shallow lake which is the second drinking water source of the country. We combined statistical (spectral analysis and Machine learning techniques) and physically based models to generate, for the first time in this system, a predictive tool of phytoplankton biomass (chlorophyll-a) and composition (morphology-based functional groups). The results, based on a 11-year time series, revealed two alternating phases in the temporal dynamics of phytoplankton biomass. One phase is characterized by high inorganic turbidity and low phytoplankton biomass, and the other by low inorganic turbidity and variable (low and high) phytoplankton biomass. A threshold of turbidity (29 TNU), above which phytoplankton remains with low biomass (<15–20ug/l) was established. The periods of high turbidity, which in total cover 30% of the time series, start abruptly and are related to external forcing. Meteorological conditions associated with the beginning of these periods were modeled through a regression tree analysis. These conditions consist of moderate to high wind intensities from the SW direction, in some cases combined with high antecedent precipitation or low water level. The results from the physically-based modeling indicated that the long decaying time-scale of turbidity and intermediate resuspension events could explain the prolonged length of the high turbidity periods (∼1.5 years). Random Forests models for the prediction of phytoplankton biomass and composition in periods of low turbidity resulted in a proportion of explained variance and a classification error over a test sample of 0.46 and 0.34 respectively. Turbidity, conductivity, temperature and water level were within the most important model predictors. The development and improvement of this type of modeling is needed to provide management tools to water managers in the current water supply situation.

Climate change mitigation: potential benefits and pitfalls of enhanced rock weathering in tropical agriculture.

Restricting future global temperature increase to 2°C or less requires the adoption of negative emissions technologies for carbon capture and storage. We review the potential for deployment of enhanced weathering (EW), via the application of crushed reactive silicate rocks (such as basalt), on over 680 million hectares of tropical agricultural and tree plantations to offset fossil fuel CO2 emissions. Warm tropical climates and productive crops will substantially enhance weathering rates, with potential co-benefits including decreased soil acidification and increased phosphorus supply promoting higher crop yields sparing forest for conservation, and reduced cultural eutrophication. Potential pitfalls include the impacts of mining operations on deforestation, producing the energy to crush and transport silicates and the erosion of silicates into rivers and coral reefs that increases inorganic turbidity, sedimentation and pH, with unknown impacts for biodiversity. We identify nine priority research areas for untapping the potential of EW in the tropics, including effectiveness of tropical agriculture at EW for major crops in relation to particle sizes and soil types, impacts on human health, and effects on farmland, adjacent forest and stream-water biodiversity.

Unusual behaviour of phototrophic picoplankton in turbid waters.

Autotrophic picoplankton (APP) abundance and contribution to phytoplankton biomass was studied in Hungarian shallow lakes to test the effect of inorganic turbidity determining the size distribution of the phytoplankton. The studied lakes displayed wide turbidity (TSS: 4–2250 mg l-1) and phytoplankton biomass (chlorophyll a: 1–460 μg l-1) range, as well as APP abundance (0 and 100 million cells ml-1) and contribution (0–100%) to total phytoplankton biomass. Inorganic turbidity had a significant effect on the abundance and contribution of APP, resulting in higher values compared to other freshwater lakes with the same phytoplankton biomass. Our analysis has provided empirical evidence for a switching point (50 mg l-1 inorganic turbidity), above which turbidity is the key factor causing APP predominance regardless of phytoplankton biomass in shallow turbid lakes. Our results have shown that turbid shallow lakes are unique waters, where the formerly and widely accepted model (decreasing APP contribution with increasing phytoplankton biomass) is not applicable. We hypothesize that this unusual behaviour of APP in turbid waters is a result of either diminished underwater light intensity or a reduced grazing pressure due to high inorganic turbidity.