Levels Of Suspended Solids Research Articles

Seasonal water quality and trophic status of shallow lentic waters and their association with water levels

Extreme hydro-climatic changes associated with floods and drought greatly influence the ecosystem dynamic of tropical lakes in Malaysia, resulting in negative impacts on their water quality and trophic status. This study examined the seasonal changes in water quality and trophic state connected to hydro-ecological changes in a natural lake and two reservoirs. Water levels in the three water bodies varied with changes in rainfall regime, and water regulation for irrigation or water supply. Multivariate analysis of variance showed a significant relationship between season and temperature, pH, conductivity, total nitrogen and chlorophyll-a (p < 0.05). Drought events and the associated period of low water levels were characterized by high temperature, conductivity and chlorophyll-a levels in these shallow lakes, which probably led to high photosynthetic rates with concomitant increase in dissolved oxygen and pH and decrease in total nitrogen concentration. Elevated chlorophyll-a and total phosphorus concentrations were also associated with drought events and the decrease in water level in Bukit Merah Reservoir, possibly due to the release of phosphorus from internal loading resulting from sediment re-suspension by wind. Salinity increase in Durian Tunggal Reservoir during dry season was possibly due to seawater intrusion into river. During the rainy season, transparency in Bera Lake and Bukit Merah Reservoir was strongly influenced by the influxes of the main river that transported elevated levels of suspended solids and nutrients.

The influence of dam construction on water quality in the lower Geum River, Korea

AbstractThe Geum River has been faced with extreme environmental change due to the construction of three dams in midstream since 2012 (Four Major River Restoration Project). We hypothesized that suspended solids (SS) and total particulate phosphorus (TPP) decreased after the dam construction. To test our hypothesis, we investigated the influence of the dam construction on water quality by measuring possible impacts of decreasing SS, total phosphorus (TP), and TPP on the ecosystem in the lower Geum River and the Geum River estuary. For this study, we chose one site to compare the monthly water quality data pre‐construction (2008) and post‐construction (2015). Dissolved oxygen and pH were not significantly different between pre‐ and post‐construction, while electric conductivity (EC) increased. The increase in the EC may be related to a decrease in river discharge (RD) after the dam construction. As we expected, TP and TPP decreased post‐construction, but SS did not show significant differences between pre‐ and post‐construction. This suggests that the decline of TPP concentrations post‐construction were not related to SS levels. The explosive algal bloom and sedimentation of the algae may be an important factor in explaining the decrease in TP and TPP. The decline of SS, TP, and TPP flux to the lower Geum River was observed. This could be a potential reason for the erosion of the mud flat of the Geum River estuary in the future. Therefore, to determine the long‐term effects of the SS and the phosphorus fluxes to the lower Geum River, these factors should be monitored periodically over longer periods of time than this study.

Effect of Grit Chamber Configuration on Particle Removal: Using Response Surface Method

In recent years ever-increasing industrial growth has resulted in a significant increase in the production of wastewater, this wastewater sometimes contains high levels of suspended solids. Therefore, the need to formulate an appropriate course of action for managing this wastewater has reached a critical level. In this study, the removal of suspended particles in wastewater that were a byproduct of an idustrial cut stone production process were investigated. For these purposes, a laboratory grit chamber was employed, and response surface methodology (RSM) was used to simulate the contributing parameters in the settling process. In order to study the performance of the grit chamber, factors such as flow rate, inlet location and mesh size, parameters of pH, COD, BOD, TSS and turbidity in influent and effluent were monitored. Results indicated that values of pH, COD and BOD in raw wastewater were within the standard range of discharging wastewater. The results indicated that the model with a high correlation of 0.95 was able to simulate the process. In addition, turbidity removal was found to be affected by three parameters among which mesh size and its interaction with the flow rate were the most influential ones.

Relationship among physicochemical conditions, chlorophyll-a concentration, and water level in a tropical river–floodplain system

The free-flowing Usumacinta River maintains an average annual water-level fluctuation of 6.7 m. This study evaluated relationships between 14 physicochemical and biological variables and key factors in four water-level conditions in a river–floodplain system. The analysis incorporated intra-annual variation in all variables, with each selected in accordance with multiple statistical and physicochemical criteria. Possible correlations were examined as a function of various physicochemical and biological factors at each water level. Within the study area, defined by a temporal gradient in principal component 1, the yearly river overflow above the bankfull stage is characterized by water with a low level of total suspended solids. Data on riverine wetlands suggest that seasonal changes are key to determining intra- and inter-annual chlorophyll-a levels and water clarity. However, opposite trends are observed for high and low water-level conditions. Nutrient enrichment cannot be taken as the key physicochemical factor of water level, under either water-level conditions, due to the lack of a temporal gradient in principal component 2 and the high biochemical variability of nitrate and orthophosphate levels. In conclusion, the hypothesis was accepted for the production of phytoplankton biomass and light attenuation at low and high water levels, as both were dependent on intra-annual changes. The increases in chlorophyll-a related to the minimal variability at the lowest water level open the opportunity to gauge this relationship as a possible environmental predictor for river–floodplain systems.

Distribution of Anticancer Drugs in River Waters and Sediments of the Yodo River Basin, Japan

This article reviews the pollution status of anticancer drugs present in the Yodo River basin located in the Kansai district of Japan, covering both the soluble and insoluble (adsorbed on the river sediments and suspended solids) levels. Procedures ranging from sampling in the field and instrumental analytical methods to the data processing for mass balance estimation of the target basin are also described. All anticancer drugs concerned with this article were detected in sewage and river waters, where the presence of bicalutamide (BLT) was identified at considerably high concentrations (maximum 254 ng/L in the main stream, 151 ng/L in tributaries, and 1032 ng/L in sewage treatment plant (STP) effluents). In addition, sorption distribution coefficient (logKd) values showed a tendency to become higher in the silty sediments at Suita Bridge than in the sandy sediments at Hirakata Bridge; these trends were supported by the results of the laboratory-scale sorption experiment. STPs were concluded to be the main sources of the anticancer drug load in the river, and a mass flux evaluation revealed that the effect of attenuation in the river environment was small. The effectiveness of ozonation in the sewage treatment process for removal of these anticancer drugs was further confirmed. The present article should be of value for facilitating the environmental risk assessment of a wide range of drugs in a broader geographical area.

Reconstruction of Water Infiltration Rate Reducibility in Response to Suspended Solid Characteristics Using Singular Spectrum Analysis: An Application to the Caspian Sea Coast of Nur, Iran

Drawing a distinction between the suspended solid size and concentration impacts on physical clogging process in the Managed Aquifer Recharge (MAR) systems has been fraught with difficulties. Therefore, the current study was then aimed to statistically investigate and differentiate the impacts of clay-, silt- and sand-sized suspended solids at three concentration levels including 2, 5 and 10 g/L, compared with the clean water (0 g/L), on infiltration rate reducibility. The treatments were compared by virtue of Cohen’s d effect size measure. Furthermore, the competency of Singular Spectrum Analysis (SSA) was evaluated in reconstruction of infiltration rate. Results showed that clay-sized suspended solids were found to be the most important determining factor in physical clogging occurrence. The effect size measure highlighted that a lower concentration level of clay-sized suspended solids, that is, 2 g/L could be more important in trigging the physical clogging than a higher concentration level of silt-sized suspended solids namely 5 g/L. Also, we recognized that concentration level of clay-sized suspended sediments could non-linearly decrease the infiltrability. Also, findings revealed that SSA represented a high level of competency in reconstruction of the infiltration rate under all treatments. Hence, SSA can be quite beneficial to MAR systems for forecasting applications.

A Source Pollution Control Measure Based on Spatial-Temporal Distribution Characteristic of the Runoff Pollutants at Urban Pavement Sites

The concentrations of pollutants in urban pavement runoff are normally higher than those in other urban surface runoff, which causes serious problems in protecting the environment of receiving water and soils. The purpose of this study was to propose a source pollution control measure based on the spatial-temporal distribution characteristics of the runoff pollutants at urban pavement sites. Therefore, samples from pavement runoff were collected and tested for analyzing the spatial-temporal distribution characteristics. Then, infiltration tests were conducted on selected purification materials to evaluate their purification ability to the simulated pavement runoff. Results indicated that heavy metals Zn and Pb were at high concentrations near the intersection, the reason being the frequent braking of vehicles at this site. The level of suspended solids was far higher than the limitation in the standard near the site where massive human activities occurred. Besides, the cumulative amounts of all kinds of pollutants tended to be stable with the extension of rainfall duration. The logarithmic function was found to fit the experimental data well. Finally, the pavement runoff was categorized into different situations. The combinations of purification materials were recommended and integrated into a source control measure for the treatments of different pollution situations, which made the most use of each purification material and ensured the high elimination efficiency of different pollutants.

Formation and prevention of biofilm and mineral precipitate clogging in drip irrigation systems applying treated wastewater

Pressure-irrigation systems and, in particular, micro-irrigation provide an effective methodology for increasing irrigation efficiency. However, emitter clogging is a major problem in micro-irrigation systems, especially under irrigation with treated wastewater (TWW). Currently, farmers treat their irrigation system by periodical application of solutions of chemicals or washing the lateral lines. The aim of this study was to characterize treatments for the prevention of clogging in drip irrigation systems utilizing different qualities of TWW (secondary and tertiary TWW). A model system was designed and assembled to compare the flow rate (FR), fouling accumulation and fouling composition in laterals and drippers subjected to different treatments. Under irrigation with secondary TWW, control treatment function decreased rapidly while chemical treatment prolonged proper function of the drippers by maintaining a normal FR and coefficient of variation (CV). Wash treatment improved to some extent the irrigation function. Under irrigation with tertiary TWW the function of all treatments was significantly better than that of the secondary treatments. The total suspended solids level was found to be a significant factor in the mechanism of clogging formation according to biofouling development. The deposit chemical characterization could shed light on the mode of growth mechanism and properties of the biofouling. In general, oxidation treatments using hydrogen peroxide or hypochlorite acid were found to eliminate biofouling and in accordance also prevented clogging.

Assessment of the quality of SOBO industrial wastewater and its impact on water quality in Nankhaka River

An assessment of the quality of industrial (effluent) from soft drink manufacturer Southern Bottlers (SOBO) factory in Lilongwe was carried out to determine the impact of pollution in Nankhaka River. Both the effluents and the water samples at selected points in the river were analysed for pH, suspended solids (SS), total dissolved solids (TDS), phosphate, nitrates, dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD) and faecal coliform (FC) using standard methods. The levels of SS, TDS, phosphate, BOD and COD with mean values of 111, 803, 4.61, 186 and 570 mg/ℓ respectively, in the SOBO industrial wastewater were outside the Malawi Standard recommended limits for effluents discharged into inland waters. However, the levels of pH (8.29) and nitrates (0.031 mg/ℓ) were within the recommended limits whereas the levels of faecal coliform (42,900 counts /100 mℓ) and DO (2.50 mg/ℓ) were not specified in the standard. The variation in water quality between upstream and downstream parameters was statistically significant (p < 0.05) at 95% confidence level. The results suggest that SOBO effluent pollutes the water in the river rendering it unfit for human consumption. It is therefore recommended that the discharge of poor quality effluents should be discouraged. Authorities should enforce the laws governing the disposal of wastes to protect the lives of the people who use the water in Nankhaka River.

Performance of an outdoor membrane photobioreactor for resource recovery from anaerobically treated sewage

Abstract The objective of this work was to evaluate the performance of a pilot scale membrane photobioreactor (MPBR) for treating the effluent of an anaerobic membrane bioreactor (AnMBR) system. In particular, new experimental data on microalgae productivity, nutrient recovery, CO2 biofixation and energy recovery potential was obtained under different operating conditions, which would facilitate moving towards cost-effective microalgae cultivation on wastewater. To this aim, a 2.2-m3 MPBR equipped with two commercial-scale hollow-fibre ultrafiltration membrane modules was operated treating the nutrient-loaded effluent from an AnMBR for sewage treatment. The influence of several design, environmental and operating parameters on MPBR performance was studied. Among the conditions evaluated, variations in solar irradiance significantly affected the nutrient recovery rate (NRR). Operating at temperatures above 25 °C and high biomass concentrations, which increased light shading effect, negatively affected biomass production and NRR. Maximum biomass productivity of 66 mg VSS L−1 d−1 (areal productivity of 15.78 g VSS m−2 d−1) and NRR of 7.68 mg N L−1 d−1 and 1.17 mg P L−1 d−1 were achieved when operating at 4.5 days of biomass retention time. These results would outcome maximum theoretical energy recoveries and CO2 biofixations of about 0.43 kWh and 0.51 kg CO2 per m3 of treated water, respectively. Moreover, the excellent quality permeate that was produced (i.e. negligible levels of pathogens and suspended solids) represents a reclaimed water source.

Physiological consequences of chronic exposure of rainbow trout (Oncorhynchus mykiss) to suspended solid load in recirculating aquaculture systems

High levels of suspended solids, especially fines, are widely regarded as harmful to fish, particularly in recirculating aquaculture systems (RAS) where accumulation of particles is likely. However, little is known about the consequences of chronic exposure to system-related particles on the stress-levels, well-being and health of fish. In this study, the chronic effects of suspended solids on the physiology and performance of rainbow trout were investigated over the growout period, uncoupled from other potentially confounding water parameters. Compared with fish in a control system with a total suspended solid (TSS) load of 3.9mg/L, fish in an otherwise comparable treatment system exposed to minimum particle concentrations of more than 30mg/L exhibited no observable difference in hematological variables (differential leukocyte count, RBC and WBC counts, hematocrit), gill histology, fin condition, or heat shock protein 70 concentrations in gill, liver, skin and head kidney tissues. Slight alterations in feeding behavior and a slight increase in bacterial load on fish and in system water were observed in the treatment RAS, but without any apparent effect on fish performance or health. Furthermore, no significant difference in mortality occurred. The absence of expected effects across a wide range of physiological criteria after long-term exposure suggests that suspended solid levels over 30mg/L are within the physiological tolerance of this species.

Migration of two antibiotics during resuspension under simulated wind–wave disturbances in a water–sediment system

In this study, the migration of antibiotics (norfloxacin, NOR; and sulfamethoxazole, SMX) under simulated resuspension conditions across the sediment-water interface were quantified for two locations in China: point A, located in Meiliang Bay of Lake Taihu, and point B, located in Dapukou of Lake Taihu. The concentrations of suspended solids (SS) in the overlying water amounted to 100, 500, and 1000 mg/L during background, moderate, and strong simulated wind–wave disturbances, respectively. At each SS level, the initial concentrations of the two antibiotics were set to 1, 5, and 10 mg/L. The results showed that both resuspended SS and the initial concentration of antibiotics could influence the migration of NOR in the water–sediment system. Specifically, both higher SS and initial antibiotic concentrations were associated with higher rates of migration and accumulation of NOR from water to sediment. In contrast, the migration of SMX in the water–sediment system was not impacted by SS or initial antibiotic concentration. The adsorption capacities of sediments for NOR and SMX were significantly different at both locations, possibly reflecting differences in cation exchange capacity (CEC) and organic material (OM) contents. In general, higher CEC and OM values were found in sediments with a higher adsorption capacity for the antibiotics. When CEC and OM values of sediments were higher, the adsorption capacity reached up to 51.73 mg/kg. Large differences in the migration from water to sediment were observed for the two antibiotics, with NOR migration rates higher than those of SMX. The accumulation of NOR in surface sediment during resuspension was about 14 times higher than that of SMX. The main reason for this is that the chemical adsorption of NOR is seldom reversible. Overall, this study demonstrates that resuspension of NOR and SMX attached to sediments under simulated wind–wave disturbances can promote the migration of the antibiotics from water to sediment; these results could be useful for assessing the migration and fate of commonly used antibiotics in water–sediment systems.

Use of a filtering process to remove solid waste and antibiotic resistance genes from effluent of a flow-through fish farm

The objective of this study was to investigate reduction in antibiotic resistance genes (ARGs) via targeting solid waste in effluent from a flow-through aquaculture in South Korea. The level of suspended solids in the filtrates was approximately 12.5±2.3mg/L, corresponding to a removal efficiency of 68.8±5.7% irrespective of variations in the size of the filter pores. The total number of particles in the effluent was reduced to the lowest numbers of particles using a filter pore size of 25μm, corresponding to a removal efficiency of 40.3%. Among the 23 ARGs conferring resistance to tetracyclines, beta-lactam antibiotics, sulfonamides, quinolones, macrolides, florfenicol and multidrug, tetracycline resistance genes were the most prevalent with a relative abundance of 67.5%. Of eleven tetracycline resistance genes (tetA, tetB, tetD, tetE, tetG, tetH, tetM, tetQ, tetX, tetZ, tetB/P) analyzed, the relative abundance of tetG was the highest in the effluent. The removal efficiency of the total number of particles showed similar patterns to the removal efficiency of ARGs depending on the size of the filter pores. Levels of ARGs in the filtrates were reduced to approximately 60.5% of those of the ARGs in the effluents. With a filter pore size of 25μm, a maximum removal efficiency of 66.0% was achieved. In particular, the relative abundance of detected tetracycline resistance genes decreased only after passing through the filters, perhaps reflecting the presence of high quantities of tetracycline resistance genes in particles from the fish farm. Using Illumina sequencing based on a 16S rRNA gene, the dominant phyla were found to be Bacteroidetes, Proteobacteria, Planctomycetes and Verrucomicrobia in the effluent. Although the overall composition of the bacterial communities was not significantly changed via filtering tests, only the relative abundance of Bacteroidetes and Proteobacteria was changed. These results demonstrate that a filtering process in aquaculture facilities can be used to reduce solid waste as well as ARGs from aquaculture farms.

Initial impacts of rain gardens’ application on water quality and quantity in combined sewer: field-scale experiment

Green infrastructures such as rain gardens can benefit onsite reduction of stormwater runoff, leading to reduced combined sewer overflows. A pilot project was conducted to evaluate the impact of rain gardens on the water quality and volume reduction of storm runoff from urban streets in a combined sewer area. The study took place in a six-block area on South Grand Boulevard in St. Louis, Missouri. The impact was assessed through a comparison between the pre-construction (2011/2012) and the post-construction (2014) phases. Shortly after the rain gardens were installed, the levels of total suspended solids, chloride, total nitrogen, total phosphorous, zinc, and copper increased. The level of mercury was lower than the detection level in both phases. E. coli was the only parameter that showed statistically significant decrease following the installation of rain gardens. The likely reason for initial increase in monitored water quality parameters is that the post-construction sampling began after the rain gardens were constructed but before planting, resulted from soil erosion and wash-out from the mulch. However, the levels of most of water quality parameters decreased in the following time period during the post-construction phase. The study found 76% volume reduction of stormwater runoff following the installation of rain gardens at one of studied sites. Statistical analysis is essential on collected data because of the encountered high variability of measured flows resulted from low flow conditions in studied sewers.

Factors related to Secchi depths and their stability over time as determined from a probability sample of US lakes.

A probabilistic sample of lakes in the 48 coterminous US lakes was made by the United States Environmental Protection Agency in the 2007 National Lakes Assessment. Because of the statistical design, the results of our analyses of Secchi depths (SD) apply to a population of 45,265 lakes. We found statistically significant differences in mean Secchi depths between natural (1.57m) and man-made lakes (1.18m). The most important variable correlated with SD was turbidity, an optical measure related to suspended particles in the water column. For most lakes, chlorophyll a was highly correlated with both turbidity and SD, but several lakes had more turbidity and lower SD than expected based on chlorophyll a alone, indicating that non-algal suspended solids were an important factor. On an ecoregion basis, the non-algal suspended solids in the lake waters were related to the average levels of suspended solids in streams located in that ecoregion, and the non-algal suspended solids were more important in man-made than natural lakes. Phosphorus and nitrogen were directly correlated with chlorophyll a and turbidity and inversely correlated with SD. Based on diatom-inferred Secchi depths for the tops and bottoms of sediment cores from lakes in Ecoregions VIII and VII (excluding lakes in Minnesota) representing 40% of the natural lakes in the US, there has been no decrease in water transparency in that population of lakes in the past 70 or more years when the US population increased by 134%. We do not have information to determine if the other 60% of lakes have or have not changed.

Fate of selected pharmaceutically active compounds in the integrated fixed film activated sludge process.

The potential for integrated fixed film activated sludge (IFAS) processes to achieve enhanced transformation of pharmaceuticals relative to conventional activated sludge (CAS) processes was assessed. Previous studies have focused on direct comparisons of parallel reactors with and without fixed film carriers and little information is available on the impacts of how varying operating parameters impact the differences in observed pharmaceutical compound (PC) transformation capabilities between CAS reactors and those equipped with both an activated sludge (AS) and fixed film carriers. The testing was carried out using bench scale sequencing batch reactors fed with authentic municipal wastewater and operated at selected combinations of temperature and solids retention time (SRT). PC transformation efficiencies were assessed in a 22 factorial design that employed the IFAS and CAS processes, operated in parallel under identical process conditions. Nitrification rate testing that was conducted to obtain insight into the biomass activity demonstrated that IFAS consistently had improved nitrification kinetics despite lower mixed liquor volatile suspended solids levels thereby demonstrating the contribution of the biofilm to nitrification. Increased transformation of atenolol (ATEN; ranging from 10-60%) and trimethoprim (TRIM; ranging from 30-50%) in the IFAS equipped reactors relative to their respective activated sludge (AS) controls was observed under all experimental conditions. Negligible transformation of carbamazepine was observed in both reactors under all conditions investigated. More than 99% of acetaminophen was transformed in both configurations under all conditions. There was no correspondence between nitrification activity and TRIM removal in the control AS while conditions that stimulated nitrification in the control AS also resulted in enhanced removal of ATEN. The results of this study indicate that the integration of biofilms in AS processes enhances transformation of some PCs.

Treatment of Potato FarmWastewater with Coagulation

Abstract. The processing wastewater from an on-farm potato storage facility contains substantial concentrations of colloidal particles that are hard to remove through sedimentation alone. This study evaluated coagulation as a potential approach for reducing total suspended solid levels. Wastewater was coagulated with two proprietary Nalco polymers, as well as aluminum sulfate (alum) and ferric chloride (FeCl 3 ). One of the Nalco polymers required the smallest volume to achieve 50%, 75%, or 90% total suspended solids removal. However, alum was consistently the least expensive product, despite the larger volume required. Although cost is an important factor for farmers, the convenience of using a smaller volume and the effects of coagulation on pH are also important factors to consider. Both polymers had minimal effect on pH, whereas alum and FeCl 3 resulted in a pH below 6 at high concentrations. In consequence, alum and FeCl 3 require additional chemicals to maintain a biologically neutral pH, thus also requiring extra work and expense. Future research should focus on on-farm coagulant trials to verify laboratory results and optimize protocols for on-farm use.

Effect of the exposure to suspended solids on the enzymatic activity in the bivalve Sinonovacula constricta

Aquatic animals are susceptible to sudden changes of their living environment but they adopt strategies to cope with adverse environmental challenges. Contamination by suspended solids, often associated with a dramatic change in the concentrations of important water-quality variables is a frequent occurrence in China's coastal waters and estuaries. Here we studied the impact of suspended solids on the activities of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT), as well as adenosine triphosphates (including Na+ K+-ATPase, Mg+ +-ATPase, Ca+ +-ATPase) and H+ K+-ATPase in the gills and visceral mass tissues of the molluscan bivalve Sinonovacula constricta exposed (4, 8, 12, 16, 20, and 24 days) to various concentrations of suspended solids. Our results showed that the antioxidant enzymes cooperated closely to effectively scavenge superoxide anion free radicals and H2O2 (which can ultimately inhibit gill activity) through the modification of SOD and/or CAT enzymatic activities. ATPases activity (considered to be a sensitive indicator of toxicity) could play an effective role in the maintenance of functional integrity of the plasma membranes as well as some other intracellular functions. After the exposure, a decrease in the Na+ K+-ATPase, Mg+ +-ATPase, and Ca+ +-ATPase activity of the gills was observed suggesting that they were inhibited by the treatments. These results also indicated that, from day 4 to day 16, exposure to high concentrations of suspended solids had an inhibitory effect on the activity of H+-K+-ATPase in the visceral mass of S. constricta. However, after a period of adaptation the H+-K+-ATPase activity was restored to original levels. Our results suggest that long-term exposure to high levels of suspended solids disturb osmoregulation, gastric acid secretion and digestion, cause oxidative damage, as a consequence of antioxidant enzymes inactivation which eventually damages the gills, affect the food intake and transformation, ultimately resulting in systems failure and eventually death.

Relationship between nutrients and plankton biomass in the turbidity maximum zone of the Pearl River Estuary

Nutrients, dissolved and particulate organic carbon and plankton (bacterio-, phyto- and zoo-) were compared in the turbidity maximum zone (TMZ) and adjacent areas (non-TMZ) in the Pearl River estuary. Our results showed that high levels of suspended substances had marked effect on dynamics of nutrients and plankton in the TMZ. Based on the cluster analysis of total suspended solids (TSS) concentrations, all stations were divided into two groups, TMZ with average TSS of 171mg/L and non-TMZ of 45mg/L. Suspended substances adsorbed PO43− and dissolved organic carbon, resulting in higher particulate phosphorus and organic carbon (POC) and lower PO43− and DOC in the TMZ, compared to the non-TMZ. However, suspended substances had limited effect on nitrogenous nutrients. Phytoplankton growth was light-limited due to high concentrations of suspended substances in the TMZ and a peak of phytoplankton abundance appeared in the non-TMZ. In contrast, the highest bacterial abundance occurred in the TMZ, which was likely partly responsible for low DOC levels. Two peaks of zooplankton abundance observed in the TMZ and non-TMZ in the Pearl River estuary were primarily supported by bacteria and phytoplankton, respectively. Our finding implied that high levels of suspended solids in the TMZ affect the trophic balance.

Understanding the creek dynamics and environmental characteristics that determine the distribution of mangrove and salt marsh communities at Nahoon Estuary

The southern distributional limit for mangroves on the east coast of Africa is thought to be at the planted mangrove forest at Nahoon Estuary (33° S) in the Eastern Cape, South Africa. This study investigated the influence of a tidal creek on the intertidal zone and the physical and biological differences between the salt marsh and mangrove forest communities at Nahoon Estuary. Three transects were established across the tidal creek and one transect in each of the following habitats mangrove, mangrove–salt marsh, and the salt marsh area. The tidal creek introduced oxygenated (~6mg.l−1) and saline water with high levels of total suspended solids (120–424g.l−1) into the intertidal zone. In areas where tidal water was retained, algal mats formed over pneumatophores during summer. The vegetation distribution in the mangrove–salt marsh community was significantly affected by elevation, ammonium concentration, and porewater temperature while the salt marsh vegetation distribution was influenced by porewater salinity, sediment, pH and the percentage of sand content. Porewater nitrogen was mostly present as ammonium, and phosphate concentrations were moderate ranging from 1.3μM in the salt marsh to 3.7μM in the mangrove community. Mangrove and salt marsh communities are clearly constrained by the physical characteristics of the intertidal area (elevation) and this will ensure that both communities will be maintained at Nahoon Estuary. However with climate change and sea level rise, this may change in the long term with mangroves expanding into elevated areas.