Hypereutrophic Waters Research Articles

Pollutants Co-occurring With Microcystins in Hypereutrophic Waters Used for Irrigation: A Case Study of the Crocodile West River Catchment

Pollutants Co-occurring With Microcystins in Hypereutrophic Waters Used for Irrigation: A Case Study of the Crocodile West River Catchment

Impacts of flue gas desulfurization (FGD) gypsum on water quality and the algal community in catfish aquaculture ponds

Catfish aquaculture ponds are at high risk of experiencing excessive algal growth, especially cyanobacteria, that can lead to negative water quality issues due to their consistent input through regular feedings and internal cycling of nutrients. Conventional algaecides used in aquaculture, such as copper sulfate, may be effective in the short-term but can potentially lead to developed resistance in phytoplankton over time or harmful effects on non-target species. An alternative nutrient management strategy, which has traditionally been used in land-based agriculture, is via flue gas desulfurization (FGD) gypsum, a form of calcium sulfate that is created as a by-product of carbon-based energy sources. A six-month field experiment was conducted on active catfish aquaculture ponds at a farm in west Alabama to test the effects of FGD gypsum on water quality, including its ability to manage excessive algal blooms throughout the growing season. In stark contrast to previous results from FGD gypsum application in eutrophic waters, it was discovered that FGD gypsum-treated ponds experienced a large increase in soluble reactive phosphorus (SRP) that led to a spike in phytoplankton abundance, specifically cyanobacteria. Supplementary microcosm experiments aided in determining that FGD gypsum could extract legacy phosphorus out of the nutrient-rich flocculant sediment found in aquaculture ponds. While these results were unexpected and ultimately undesired, we did discover that the use of FGD gypsum at the 500 mg/L concentration does not produce any trace metal contamination in the water column or in the fish tissue. Overall, this experiment discovered new results that FGD gypsum could produce when used in hypereutrophic waters with nutrient-rich sediments and provides the foundation for future research directions to determine the specific mechanisms behind the interaction of FGD gypsum with the sediment.

Water quality improvement using novel attached growth systems

ABSTRACT Excessive growth of microalgae results in the eutrophication and degradation of water quality in lakes and ponds. Microalgae have proved to be very beneficial for sustainable development. Its applications, starting from growth to death, make them a valuable resource for food and energy production. However, presence of microalgae in surface water sources affects water quality and its beneficial uses. The excess nutrient-rich agriculture runoff also adds problems to the downstream systems. Nutrient removal and microalgae harvesting are considered the most problematic task for improving water quality of surface waters. The main objective of the present study was to improve the water quality of nutrient rich waters using attached growth systems. The use of batch and continuous flow baffled attached growth systems has successfully improved the water quality and produced algal biomass that can be utilized or transformed into other valuable products. The performance of continuous flow baffled attached growth system was better and it improved the quality of oligotrophic, mesotrophic, eutrophic and hypereutrophic waters by removing>95% of TN and TP in 35, 63, 63 and 4 days, with biomass productivity of 2.69 ± 0.21, 3.17 ± 0.06, 3.61 ± 0.16 and 4.64 ± 0.3 gDWm−2 day−1, respectively.

Ecological Preferences and Indication Potential of Freshwater Bryophytes-Insights from Croatian Watercourses.

A comprehensive survey of Croatian watercourses covering the whole of the national territory and investigating inherent watercourse heterogeneity was conducted to explore the ecological responses of the most frequent freshwater bryophytes with respect to water chemistry variables and land use within the catchment area. Direct multivariate ordination (CCA) of vegetation data paired with 18 environmental variables revealed that freshwater bryophytes and their assemblages were segregated along the gradients of water chemistry and the proportion of natural and urban area within the catchment. Generalized additive models (GAM) were employed to explore the ecological responses of individual species. The results showed that most of the investigated species preferred natural, clean, well-oxygenated watercourses, with low nutrient and organic matter content, as well as with low electrical conductivity. Species such as Palustriella falcata, Eucladium vertcillatum, Dichodontium flavescens and Jungermannia atrovirens had narrow ecological niches and were restricted to pristine watercourses, while the most frequent and widely distributed species, such as Fontinalis antipyretica, Rhynchostegium riparioides, Cratoneuron filicinum, Fissidens crassipes, Cinclidotus fontinaloides and C. riparius, had a wide ecological tolerance. Riccia fluitans and Leptodyctium riparium had wide ecological ranges, but with optima in hypereutrophic waters with high nutrient and organic content, as well as high electrical conductivity. Furthermore, these two species were frequently associated with a high share of intensive agriculture and a low share of natural land within the catchment.

High taxonomic turnover and functional homogenization of rotifer communities in an amazonian river.

Patterns of beta diversity of plankton communities in rivers have been mainly determined by hydrological factors that alter the dispersion and composition of species and traits. Rotifers in the Guamá River (eastern Amazonian River) were sampled (monthly between October 2017 and June 2019) to analyze the temporal variation of taxonomic and functional beta diversity and its partitions (turnover and nestedness) as well as the effects of temporal, environmental, and seasonal dissimilarities. Taxonomic turnover and functional nestedness over time were observed as well as functional homogenization, which was arguably due to the hypereutrophic condition of the river. There were no seasonal differences in taxonomic and functional beta diversity probably due the low environmental dissimilarity. This study demonstrated that this Guamá River stretch presented low environmental dissimilarity and hypereutrophic waters, which benefited the establishment of a community of species with high taxonomic turnover over time, but with low functional dissimilarity and loss of some functions related to the functional traits evaluated in the ecosystem. It is important to point out that temporal studies should evaluate both taxonomic and functional aspects of communities, mainly because the effect of environmental changes may be more noticeable at the functional level of communities.

Linking land system changes (1980–2017) with the trophic status of an urban wetland: Implications for wetland management

The knowledge on urban ecosystem dynamics is being increasingly felt due to unprecedented symptoms arising out of urbanization. This study is aimed to assess land use-land cover changes (LULCCs) around a wetland ecosystem using high spatial resolution CORONA and Google Basemap satellite imageries. The imageries were processed by digitizing land cover features at 1:3000 scale in ArcGIS 10.1. The imageries were classified into nine classes, and an estimation of accuracy was performed utilizing the Kappa coefficient and error matrices. The overall accuracy obtained was 94% for the 2017 dataset. The key findings indicated a loss of 23% in the wetland area from 1980 to 2017. While in the vicinity, a significant increase in green spaces (706.2%) and roads (89.4%) was observed. Morphometric analysis revealed that the wetland has lost a surface area of 10.2ha from 1980 to 2017. The maximum length (Lmax) of the wetland was reduced by 722m while the maximum width (Wmax) decreased by 78m. Bathymetric analysis revealed that the wetland is shallow with a depth ranging from 10 to 174cm. The Carlson's Trophic State Index (TSI) of wetland ranging from 74 to 87 indicates hyper-eutrophic waters. Overall, the loss of wetland area, together with the reduction in morphometric features, low depth, and higher trophic status speak of anthropogenic pressures that are compromising the ecological integrity of this wetland. Therefore, landscape planning and governance are of pivotal importance for the conservation and management of wetland ecosystems in this region.

Meta-classification of remote sensing reflectance to estimate trophic status of inland and nearshore waters

Common aquatic remote sensing algorithms estimate the trophic state (TS) of inland and nearshore waters through the inversion of remote sensing reflectance (Rrs (λ)) into chlorophyll-a (chla) concentration. In this study we present a novel method that directly inverts Rrs (λ) into TS without prior chla retrieval. To successfully cope with the optical diversity of inland and nearshore waters the proposed method stacks supervised classification algorithms and combines them through meta-learning. We demonstrate the developed methodology using the waveband configuration of the Sentinel-3 Ocean and Land Colour Instrument on 49 globally distributed inland and nearshore waters (567 observations). To assess the performance of the developed approach, we compare the results with TS derived through optical water type (OWT) switching of chla retrieval algorithms. Meta-classification of TS was on average 6.75% more accurate than TS derived via OWT switching of chla algorithms. The presented method achieved > 90% classification accuracies for eutrophic and hypereutrophic waters and was > 12% more accurate for oligotrophic waters than derived through OWT chla retrieval. However, mesotrophic waters were estimated with lower accuracy from both our developed method and through OWT chla retrieval (52.17% and 46.34%, respectively), highlighting the need for improved base algorithms for low - moderate biomass waters. Misclassified observations were characterised by highly absorbing and/or scattering optical properties for which we propose adaptations to our classification strategy.

Active DNRA and denitrification in oxic hypereutrophic waters

Since the start of synthetic fertilizer production more than a hundred years ago, the coastal ocean has been exposed to increasing nutrient loading, which has led to eutrophication and extensive algal blooms. Such hypereutrophic waters might harbor anaerobic nitrogen (N) cycling processes due to low-oxygen microniches associated with abundant organic particles, but studies on nitrate reduction in coastal pelagic environments are scarce. Here, we report on 15N isotope-labeling experiments, metagenome, and RT-qPCR data from a large hypereutrophic lagoon indicating that dissimilatory nitrate reduction to ammonium (DNRA) and denitrification were active processes, even though the bulk water was fully oxygenated (> 224 µM O2). DNRA in the bottom water corresponded to 83% of whole-ecosystem DNRA (water + sediment), while denitrification was predominant in the sediment. Microbial taxa important for DNRA according to the metagenomic data were dominated by Bacteroidetes (genus Parabacteroides) and Proteobacteria (genus Wolinella), while denitrification was mainly associated with proteobacterial genera Pseudomonas, Achromobacter, and Brucella. The metagenomic and microscopy data suggest that these anaerobic processes were likely occurring in low-oxygen microniches related to extensive growth of filamentous cyanobacteria, including diazotrophic Dolichospermum and non-diazotrophic Planktothrix. By summing the total nitrate fluxes through DNRA and denitrification, it results that DNRA retains approximately one fifth (19%) of the fixed N that goes through the nitrate pool. This is noteworthy as DNRA represents thus a very important recycling mechanism for fixed N, which sustains algal proliferation and leads to further enhancement of eutrophication in these endangered ecosystems.

The biological pump effects of phytoplankton on the occurrence and benthic bioaccumulation of hydrophobic organic contaminants (HOCs) in a hypereutrophic lake

The distribution of hydrophobic organic contaminants (HOCs) in eutrophic ecosystems has been widely studied, but how phytoplankton blooms affect their occurrence and benthic bioaccumulation is poorly understood. To fill this knowledge gap, the biological pump effects of phytoplankton on the fate of organochlorine pesticides (OCPs) and polycyclic aromatic hydrocarbons (PAHs) in sediments and benthos (Corbicula fluminea) from Lake Taihu, a hypereutrophic lake in China, were identified. The spatial-temporal distribution of HOCs suggests that higher phytoplankton biomass, coupled with sediment organic matter (SOM) content, greatly increased the concentration of HOCs in sediments in both winter and summer seasons. This could be attributed to the biological pump effects sequestering more HOCs from water to sediments with settling phytoplankton, especially during the summer. The biological pump effects further promoted the uptake of sediment-bound HOCs by benthos. The significant positive relationships between concentrations of HOCs in sediments and benthos were observed during the winter dormancy phase of benthos. Furthermore, the benthic bioaccumulation of HOCs could be strengthened by phytoplankton, due to their contribution to SOM and the following increased bioavailability of HOCs in sediments. Further research is needed to elucidate the phytoplankton biological pump effects on the fate of HOCs in benthic food chain, especially for hypereutrophic waters.

Hyperspectral remote sensing monitoring of cyanobacteria blooms in a large South American reservoir: high- and medium-spatial resolution satellite algorithm simulation

We used hyperspectral remote sensing with the aim of establishing a monitoring program for cyanobacteria in a South American reservoir. We sampled at a wide temporal (2012–16; 10 seasons) and spatial (30km) gradient, and retrieved 111 field hyperspectral signatures, chlorophyll-a, cyanobacteria densities and total suspended solids. The hyperspectral signatures for cyanobacteria-dominated situations (n=75) were used to select the most suitable spectral bands in seven high- and medium-spatial resolution satellites (Sentinel 2, Landsat 5, 7 and 8, SPOT-4/5 and -6/7, WorldView 2), and for the development of chlorophyll and cyanobacteria cell abundance algorithms (λ550 – λ650+λ800) ÷ (λ550+λ650+λ800). The best-performing chlorophyll algorithm was Sentinel 2 ((λ560 – λ660+λ703) ÷ (λ560+λ660+λ703); R2=0.80), followed by WorldView 2 ((λ550 – λ660+λ720) ÷ (λ550+λ660+λ720); R2=0.78), Landsat and the SPOT series ((λ550 – λ650+λ800) ÷ (λ550+λ650+λ800); R2=0.67–0.74). When these models were run for cyanobacteria abundance, the coefficient of determination remained similar, but the root mean square error increased. This could affect the estimate of cyanobacteria cell abundance by ~20%, yet it still enable assessment of the alert level categories for risk assessment. The results of this study highlight the importance of the red and near-infrared region for identifying cyanobacteria in hypereutrophic waters, demonstrating coherence with field cyanobacteria abundance and enabling assessment of bloom distribution in this ecosystem.

Evaluation of Atmospheric Correction Algorithms over Spanish Inland Waters for Sentinel-2 Multi Spectral Imagery Data

The atmospheric contribution constitutes about 90 percent of the signal measured by satellite sensors over oceanic and inland waters. Over open ocean waters, the atmospheric contribution is relatively easy to correct as it can be assumed that water-leaving radiance in the near-infrared (NIR) is equal to zero and it can be performed by applying a relatively simple dark-pixel-correction-based type of algorithm. Over inland and coastal waters, this assumption cannot be made since the water-leaving radiance in the NIR is greater than zero due to the presence of water components like sediments and dissolved organic particles. The aim of this study is to determine the most appropriate atmospheric correction processor to be applied on Sentinel-2 MultiSpectral Imagery over several types of inland waters. Retrievals obtained from different atmospheric correction processors (i.e., Atmospheric correction for OLI ‘lite’ (ACOLITE), Case 2 Regional Coast Colour (here called C2RCC), Case 2 Regional Coast Colour for Complex waters (here called C2RCCCX), Image correction for atmospheric effects (iCOR), Polynomial-based algorithm applied to MERIS (Polymer) and Sen2Cor or Sentinel 2 Correction) are compared against in situ reflectance measured in lakes and reservoirs in the Valencia region (Spain). Polymer and C2RCC are the processors that give back the best statistics, with coefficients of determination higher than 0.83 and mean average errors less than 0.01. An evaluation of the performance based on water types and single bands–classification based on ranges of in situ chlorophyll-a concentration and Secchi disk depth values- showed that performance of these set of processors is better for relatively complex waters. ACOLITE, iCOR and Sen2Cor had a better performance when applied to meso- and hyper-eutrophic waters, compare with oligotrophic. However, other considerations should also be taken into account, like the elevation of the lakes above sea level, their distance from the sea and their morphology.

Comparison of LISAT and Landsat imagery for estimating chlorophyll-a (case study: Jatiluhur Reservoir)

Jatiluhur Reservoir located in Purwakarta Regency, West Java is one of the largest reservoirs in Indonesia. Various studies have been done to determine the quality of water in the reservoir. The presence of locally made satellites, LISAT, can be a tool for monitoring the reservoir’s water constituent using satellite imagery. Our purpose here is to define the spectral reflectance properties on Jatiluhur Reservoir and determine the water column constituents that correlate with the observed lake color. In addition, this study also aims to compare the spatial, temporal, and spectral resolutions of LISAT imagery and Landsat imagery in the Jatiluhur Reservoir region. Based on the table of the relationship between TSI with chlorophyll a parameter, the TSI value is in the range of 80 - 90. TSI 80 value> falls into the category of hypereutrophic waters. The estimated result from Landsat and LISAT imageries still show different results. Chlorophyll-a value from image processing also show significance differences from Chlorophyll-a value derived from laboratory analysis.

Sustained High Nutrient Supply As an Allelopathic Trigger between Periphytic Biofilm and Microcystis aeruginosa.

Allelopathy among aquatic organisms, especially microorganisms, has received growing attention in recent years for its role in shaping interactions with bloom-forming algae. Many studies have shown that allelopathy occurs and increases under nutrient limiting conditions. However, to date there is no reported direct evidence to indicate that allelopathy occurs under the condition of constant high nutrient supply. Here we report the allelopathic action of periphytic biofilm on bloom-forming cyanobacteria (Microcystis aeruginosa), which was triggered by the stress of high nutrient conditions, and continues while nutrients are maintained at high levels (trophic state index at 159 and 171). The experimental evidence indicates that the electron transport from photosystem II (PS II) to photosystem I (PS I) in M. aeruginosa is interrupted by the identified allelochemicals, (9Z)-Octadec-9-enoic acid and (9Z)-Hexadec-9-enoic acid, leading to the failure of photosynthesis and the subsequent death of M. aeruginosa. Our findings indicate that the nutrient stress of constant high nutrient supply may be a newly recognized trigger causing allelopathy between microbial competitors, and therefore opening a new direction for the better management of ecological processes in cyanobacteria-dominated and hyper-eutrophic waters.

The relationship between phytoplankton and fish in nutrient-rich shallow Lake Qarun, Egypt

Abstract The present study focused on the determination of the baseline data and correlations between biological and physicochemical variables, including the assessment of trophic conditions in Lake Qarun. The concentrations of nutrients were high, with the maxima usually in the east subarea (total nitrogen 6.40 mg dm-3, mineral nitrogen 2.34 mg dm-3, orthophosphates 0.22 mg dm-3). A total of 134 phytoplankton species were recorded. Bacillariophyceae and Dinophyceae co-dominated spatially and seasonally in phytoplankton assemblages. The highest phytoplankton density (935 × 104 cells dm-3) and chlorophyll a content (69.3 μg dm-3) were recorded in the east subarea of the lake, whereas the largest total and dominant fish (Mugil cephalus and Solea spp.) were in the west. Tilapia zillii and Engraulis encrasicolus were most abundant in the east and in the middle part, respectively. When phytoplankton density decreased from the east toward the west subarea, the Secchi disk depth increased. The TLI-based assessment indicated hypereutrophic waters at most sites of Lake Qarun. Statistically significant positive or negative correlations were found between the dominant fish species: T. zillii and Solea spp., and the phytoplankton density, Dinophyceae density, concentrations of TP, chlorophyll a, ammonium, nitrite and nitrate. Such correlations may be helpful to better understand how to enhance the sustainable fish production.

Dominance and succession of Microcystis genotypes and morphotypes in Lake Taihu, a large and shallow freshwater lake in China

Lake Taihu, which is the third largest freshwater lake in China, has experienced extensive cyanobacterial (Microcystis spp.) blooms over the past two decades. However, the distribution, dynamics and succession of the blooms have not been fully studied. To better understand the basic characteristics of Microcystis blooms in Lake Taihu, samples were collected from December 2008 to December 2009. The distribution and dynamics of different Microcystis morphotypes were characterized. Microcystis genotypes were analyzed also by sequencing the clone library of the internal transcribed spacer of the rRNA operon (ITS). The abundance of total Microcystis and the proportion of microcystin-producing subpopulation were estimated by using a quantitative PCR assay. Marked succession in both morphotypes and genotypes of the Microcystis population occurred during the course of the Microcystis bloom. The 2337 ITS sequences were obtained and were revealed to contain 618 Microcystis genotypes, which was the highest Microcystis genetic diversity reported in Lake Taihu. The T1 genotype, which was characterized by strains of Microcystis flos-aquae, was the most dominant genotype during winter and spring around the entire lake and likely acted as the main inoculum for forming blooms the following year. Water temperature periodically affected the succession of both Microcystis genotypes and morphotypes, whereas the micro-environment influenced the spatial distribution of Microcystis genotypes and morphotypes. High ratios of mcyD containing Microcystis subpopulations were detected during the onset and later bloom phases. A redundancy analysis (RDA) indicated that the water temperature and PO4-P were the major factors controlling both the total Microcystis abundance and the proportion of microcystin-producing Microcystis in hyper-eutrophic waters.

Assessment of the Physico-Chemical Pollution of a Water Body in a Perspective of Integrated Water Resource Management: Case Study of Nokoué Lake

Nokoue Lake is the most important surface of brackish waters of Benin and one of the biggest West African lagoons, in point of view of its surface (about 150 km2), its productivity and exploitation. The aim of this study is to monitor the temporal and spatial variation of physico-chemical parameters of Nokoue lake water for its sustainable management. A total of twenty (20) points of sampling have been followed during a period of one year. The results of the monitoring reveal low dissolved oxygen and high concentration in phosphorus and chlorophyll a, sign of eutrophication. In addition, nutrient concentrations (nitrites, phosphates, nitrates) responsible for the phenomenon compared to water quality assessment grid of the Organisation for Economic Co-operation and Development, (OECD) used to classify the waters in the range of hyper-eutrophic waters characterized by the proliferation of aquatic plants. So some measures have been proposed to remediate to this pollution in order to an integrated management.

Zooplankton diversity and macrophyte biometry in shallow water bodies of various trophic state

In order to determine whether using indicators of zooplankton diversity and macrophyte parameters (density and biomass) could be a useful tool for diagnosing the water quality of ponds we hypothesised that in various trophic types of shallow water bodies parameters of a macrophyte habitat will reflect zooplankton diversity. Thus, 439 stations (open water, helophytes, elodeids) were studied among 274 pastoral ponds (mid-west Poland). In each trophic state of waters a key predictor of zooplankton diversity was biomass of macrophytes attributed to a variety of ecological types or various species of macrophytes. A shift from the high importance of elodeids (e.g. Myriophyllum, Ceratophyllum demersum) in structuring zooplankton diversity in mesotrophic waters to helophytes (Typha angustifolia, Phragmites australis, Schoenoplectus lacustris) in hypereutrophic ponds was recorded. Hypereutrophy proved to be extremely unfavourable for zooplankton, as reflected in its lowest diversity; rotifers reached their optimum in eutrophy and crustaceans in mesotrophy. Adverse environmental conditions in hypereutrophic waters caused the elimination of macrophyte-dominated refuges, thereby lowering the macrophyte-site share, which ranged from 47% in eutrophy, 40% in mesotrophy to only 20% in hypereutrophy. Therefore, we assume that zooplankton diversity and macrophyte occurrence can be used for quality assessment of small water bodies.

Análisis espectral del Lago de Guadalupe, mediante imágenes de satélite y datos in situ

Lake of Guadalupe is a reservoir located in the neighborhood of Mexico City, and it is one of the few relicts still remaining in the basin of Mexico. This reservoir receives an important volume of waste waters from its surroundings which include urban, forested, recreational and agricultural sites. In this work we present a spectral analysis of this lake utilizing spot imagery and in situ data and the its Trophic State Index (tsi). Measurements were carried out in February and September of 2006. Measured variables include temperature, pH, chlorophyll a, Secchi transparency and quasi-simultaneous satellite data from spot images. Variables were measured at seven sampling sites, strategically located along the lake. This water body has eutrophic characteristics, it has basic pH valúes (6.8 - 11.3), high chlorophyll a concentrations (6.9-112.4μg 1-1) andlow valúes of Secchi transparency. Thermally, the lake is warm monomictic. Results indícate a high degree of eutrophization of the Lake of Guadalupe, due, mainly, to the presence of phytoplankton and submerged and floating vegetation. The presence of aquatic vegetation such as hyacinth and duckweed is apparent at the edge of the lake.In February, the concentration of Chlorophyll a, expressed as biomass, was homogenous in the reservoir with a mean of 9.56±4.26 mg m-3. The mean valué for Secchi transparency was 3.39 (± 1.13) ni, which corresponds to an Extinction Coefficient K=0.50m-1 associated to turbid waters. The pH average of 10.40 indicates alkaline conditions. The TSI, estimated from Secchi transparency was 43.50 (±6.9) indicative of meso-trophic waters, whilst the TSI, estimated for chlorophyll a was 52.16 (± 3.35) corresponds to eutrophic waters characterized by the presence of microphytes.In September the concentration of chlorophyll a had a wide range of values with a mean of 72.90 (± 28.46) mg m-3, which clearly indicates hyper-eutrophic waters. Secchi Transparency La averaged 60.29 (± 0.22) cm, with an Extinction Coefficient K=2.82 m-1. The TSI for this variable was 68.13 (± 5.32) indicative of hyper-eutrophized waters and suggesting anoxic hypolimnia. the TSI estimated from the concentration of chlorophyll a was 71.86 (± 4.62) which is a referent of hyper-eutrophized waters as well.Surface temperature of the reservoir changed from 18.1 in February to 23 in September, pH varied from an alkaline condition >9 in February to a slightly acid pH of 6.8 in September. Chlorophyll a concentration confirm the eutrophication of the dam. Values higher than 5μgl-1 indícate eutrophic conditions, while those higher than 40μgl-1 indícate a high hypertrophic environment. In this work, chlorophyll values varied from 6.9μgl-1 to an a hyper-trophic value of 112.4μgl-1. Water coloration allowed for the selection of an appropriate spectral spot band. The high amount of phytoplankton in the reservoir is useful for a better satellite image interpretation. The use of remote sensed imagery helps for a better monitoring of water quality along with a suitable field work.

Bio-Optical Inversion in Highly Turbid and Cyanobacteria-Dominated Waters

Phytoplankton pigment absorption data from algal-bloom-dominated waters are highly desirable to better understand the primary productivity and carbon uptake by algal biomass in a regional scale. However, retrieving phytoplankton pigment absorption coefficients, in turbid and hypereutrophic waters, from above-surface remote sensing reflectance (Rrs) is often challenging because of the optical complexity of the water body. In this paper, a quasi-analytical algorithm has been parameterized using in situ data to retrieve inherent optical properties from Rrs(λ) in highly turbid productive aquaculture ponds, where the phytoplankton absorption coefficient (3.44-37.67 m-1 ) contributes 54 % of the total absorption at 443 nm (4.99-47.21 m-1). The model was validated using an independent data set by comparing the model-derived optical parameters with in situ measured values. The absolute percentage error (assuming no error in the in situ measurements) of the estimated total absorption coefficient at( λ) varied from 15.22 % to 24.13 % within 413-665 nm, and the overall average error was 19.87 %. Maximum and minimum errors occurred at 443 and 665 nm, respectively. Similarly, the percentage error for the phytoplankton absorption coefficient aφ(λ) varied from 15.9 % to 41.27 % within the 413-665-nm range, and the average error was 27.24 %. The spectral shape of modeled aφ(λ) matched very well (R2 = 0.97) with the measured aφ(λ). A supplementary method was also developed to retrieve first-order estimates of colored detrital matter absorption coefficients aCDM( λ) from subsurface remote sensing reflectance rrs( λ) using an empirical approach. Results reveal that the retrieval accuracy of aφ(λ) improved after incorporating the first-order estimates of aCDM(λ) in the algorithm.

Removal of nitrogen (N) from hypereutrophic waters by ecological floating beds (EFBs) with various substrates

The present experiment tested various EFBs for the purification of hypereutrophic waters under batch and continuous flow conditions. A conventional plant-only EFB (EFB-PO) was used as the control system and compared to EFBs using either rice straw (EFB-RS) or plastic filling (EFB-PF) as a substrate for microorganisms. Under the batch condition, the mean removal rates of the EFB-RS for total nitrogen (TN), ammonium nitrogen (NH4+-N), and nitrate nitrogen (NO3−-N) were, respectively, 76.94, 93.50, 93.18% after 2 days, which represent increases of 43.94%, 19.83%, 75.24% and 34.76%, 24.67%, 34.54% over the same values for EFB-PF and EFB-PO, respectively. The number of total bacteria, nitrifying bacteria, and denitrifying bacteria in the rice straw system, as well as the total amount of biomass, was significantly greater than in the plastic filling system. The results of the continuous flow experiment indicated that the mean removal rates of TN, NH4+-N, and NO3−-N for EFB-RS and EFB-PF were, respectively, 72.21%, 88.88%, and 80.41%, and 51.85%, 86.23%, and 58.62% when the hydraulic retention time (HRT) was 24h. Relative to the EFB-PF system, the EFB-RS system exhibited a lower accumulation of NO2−-N concentration.