Phosphorus Concentrations In Sediments Research Articles

River Sediments Downstream of Villages in a Karstic Watershed Exhibited Increased Numbers and Higher Diversity of Nontuberculous Mycobacteria

The impact of residential villages on the nontuberculous mycobacteria (NTM) in streams flowing through them has not been studied in detail. Water and sediments of streams are highly susceptible to anthropogenic inputs such as surface water flows. This study investigated the impact of seven residential villages in a karst watershed on the prevalence and species spectrum of NTM in water and sediments. Higher NTM species diversity (i.e., 19 out of 28 detected) was recorded downstream of the villages and wastewater treatment plants (WWTPs) compared to sampling sites upstream (i.e., 5). Significantly, higher Zn and lower silicon concentrations were detected in sediments inside the village and downstream of the WWTP’s effluents. Higher phosphorus concentration in sediment was downstream of WWTPs compared to other sampling sites. The effluent from the WWTPs had a substantial impact on water quality parameters with significant increases in total phosphorus, anions (Cl–and N-NH3–), and cations (Na+ and K+). The results provide insights into NTM numbers and species diversity distribution in a karst watershed and the impact of urban areas. Although in this report the focus is on the NTM, it is likely that other water and sediment microbes will be influenced as well.Graphical

Effect of the control area layout on the impact evaluation of cage culture

Spatial comparison is widely used to assess cage culture impact, which requires accurate evaluation. It is difficult to guarantee that the differences between cage culture zones and control areas are caused by cage culture instead of natural variables, which implies that the control area layout affects impact evaluation. To test this hypothesis, the effect of the control area layout on the impact evaluation of cage culture in Maniao Bay, Hainan, China, was analyzed, during which the total phosphorus content in sediment was used as the environmental indicator, and the difference between the cage culture area and control area was compared through the Mann-Whitney U test. The impact evaluation varied with control areas, which means that the impact assessment is biased by spatial comparison alone. Impact assessments only based on spatial comparison and without removing the bias of the comparison might be necessary reassessed if the homogeneity of the regions compared, such as the cage culture area and the control area, is difficult to meet, and it is necessary to construct a reasonable evaluation system.

Assessment of Phosphorus Mobilizing Capacity of Bacillus spp. Isolated from Mangrove Rhizospheric Sediment and its Potential Application in Aquaculture

Background: Phosphatase producing bacteria (PPB) plays a major role in mineralising organic P into inorganic form. Though application of bacterial biofertilizers are practiced in agriculture, their application is very limited in aquaculture. Method: The PPB isolates were screened and isolated from rhizospheric sediment of mangrove, Avicennia marina of Ennore creek, Tamil Nadu. Their P transformation potential and the possibilities of their application in aquaculture to mineralise organic P to inorganic P were studied. Result: Twenty PPB isolates were screened in the study site and their Alkaline Phosphatase (ALP) activity was in the range of 13.6-20.4 µmol.ml-1.hr-1. Out of this, five Bacillus sp isolates were selected to assess their P transformation potential at various salinity. The P mobilizing potential of these isolates were compared with the commercial PPB following a microcosm study for a period of 14 days. During the study period, there is a significant increase in phosphorus in water as well as ALP activity and available phosphorus concentrations in sediments were observed between control and treatment tanks. Among the treatment groups, B. subtilis treatment tanks showed maximum P in water ie. 1.60mg.L-1, followed by B. altitudinis –1.49mg.L-1; B. pumilus –1.47mg.L-1; the soil ALP activity was in the order of commercial P products greater than B. pumilus greater than B. subtilis greater than B. paramycoides greater than B. altitudinis greater than B. aryabhattai. In terms of available phosphorus content in sediments on 14th day, there is no significant difference observed between B. pumilus and commercial product with respect to available P content of sediment.

Phosphorus concentrations in sediments from the equatorial Amazon estuary, Furo of Muriá, Pará State, Brazil

We characterized the spatial and seasonal distributions of different phosphorus fractions in surface sediments from the Furo of Muriá estuary by chemical fractionation. Five phosphorus species were successfully separated: phosphorus bound to Fe/Al oxyhydroxides (non-apatite inorganic phosphorus (NAIP) ranging from 164.54 to 280.32 μg g-1), phosphorus bound to calcium (apatite phosphorus (AP) ranging from 63.02 to 102.80 μg g-1), inorganic phosphorus (IP, ranging from 227.21 to 378.61 μg g-1), organic phosphorus (OP, ranging from 30.33 to 135.88 μg g-1) and total phosphorus (TP, ranging from 257.54 to 507.73 μg g-1), in which 88% of TP is constituted by IP. Statistical results showed that seasonality was not a major factor influencing phosphorus concentrations. Considering the classification of estuarine sediment conditions, we can conclude that the TP concentrations found in Furo of Muriá do not yet indicate the risk of environmental deterioration.

Understanding how nutrient limitation and plant traits influence carbon in mangrove‐seagrass coastal ecosystems

AbstractMangrove forests and seagrass meadows provide critical ecosystem services, including the accumulation of “blue carbon.” Plants' functional traits could influence this blue carbon accumulation. To test for interactions among functional traits and blue carbon accumulation, we conducted a study in connected mangrove‐seagrass coastal ecosystems in southeast Florida (USA). We quantified how plants' above‐ground traits correlated with sediment nutrient content, and how changes in traits along inland‐to‐coastal gradients influenced inorganic and organic carbon storage potential. Physical traits of Thalassia testudinum were higher at sites with higher sediment phosphorus (SP) and nitrogen (SN) concentrations. Sediment organic carbon concentrations were positively correlated to T. testudinum physical traits. Root density, pneumatophore abundance, specific leaf area, leaf toughness, leaf nitrogen, and phosphorus content were positively correlated with SN concentrations in the mangrove forest coastal fringe. Mangrove leaf thickness and root complexity index were negatively correlated with SP concentrations in the coastal fringe. Our results also indicate that seagrass above‐ground traits and blue carbon were strongly correlated in areas with higher sediment nutrient concentrations. Moreover, mangrove root complexity is coupled with phosphorus limitation, whereby highly complex root systems develop with decreasing phosphorus concentrations. Distinct functional traits of plants drive variation in carbon retention capacity even in interconnected ecosystems.

Connecting sources, fractions and algal availability of sediment phosphorus in shallow lakes: An approach to the criteria for sediment phosphorus concentrations

Although point and nonpoint sources contribute roughly equal nutrient loads to lakes, their relative role in supporting algae growth has not been clarified. In this research, we have established a quantitative relationship between algae-available phosphorus (P) and P chemical fractions in sediments; the latter indicates the relative contribution of point versus nonpoint sources. Surface sediments from three large shallow lakes in eastern China, namely, the Chaohu, Taihu and Hongzehu Lakes, were sampled to assess their algae-available P and chemically extracted P fractions. The algae-available P primarily comes from iron/aluminium (hydr)oxide-bound P (Fe/Al-bound P), 45% of which is algae-available P. The ratio of Fe/Al-bound P to calcium compound-bound P (Ca-bound P) indicated the relative contribution of point to nonpoint sources, with the point sources contributing the majority of increased Fe/Al-bound P in sediments. Therefore, the reduction of point sources from urbanized areas, rather than nonpoint sources from agricultural areas that primarily contribute to the Ca-bound P fraction, should be prioritized to alleviate cyanobacterial algal blooms (CyanoHABs) in shallow lakes with sediment P as a potential source to support algae growth. With these important results, we proposed a conceptual model for “P-pumping suction” from sediments to algae to aid in the development of the criteria for sediment P concentrations in shallow lakes.

Nutrient and physicochemical properties as potential causes of stress in mangroves of the central Red Sea.

Mangrove ecosystems are some of the most productive and important sinks for sediment globally. Recently, there has been an increasing interest in possible causes of stress in mangroves, such as nutrient limitation, high salinity, solar radiation and temperature. We measured different factors casing stress and determined how they influenced oxidative stress and growth biomarkers in six study sites dominated by mangroves; Al Lith, South Jeddah, Dahban, Thuwal, Rabigh and Mastorah. Significant differences (P < 0.05) were recorded in water salinities and temperatures, nitrogen and phosphorus content in sediments, and antioxidant enzyme activities in different study sites. The highest salinity (40.75 ‰) and temperature (29.32°C) were recorded in the Rabigh mangrove stand, which corresponds to the lowest dissolved oxygen (5.21 mg/L). Total organic carbon, total nitrogen and total phosphorus in sediment across the study areas were in the order Rabigh>Thuwal>Dahban>Al Lith>South Jeddah>Mastorah. Total nitrogen in mangrove leaves at Rabigh was the highest and about 1.3 times higher than the total nitrogen in South Jeddah mangrove ecosystem, very different from the ratio of total nitrogen in the sediments at Rabigh and South Jeddah mangrove ecosystems. The average values of δ13C (-17.60‰) and δ15N (2.84‰) in the six mangrove ecosystems, and the highest δ13C (-13.62‰) and δ15N (4.39‰) at Rabigh in the sediments suggest that nutrient input differed among study sites. Higher nutrient levels at Rabigh mangrove ecosystem were attributed to restricted circulation, camel grazing and land runoff with agricultural waste during seasonal flooding events. However, N limitation and possibly salinity contributed to stress in Al Lith, South Jeddah, Dahban, Thuwal, Rabigh, and Mastorah mangrove ecosystems. Salinity (r = 0.9012) contribute more to stress at Rabigh.

Effect of Myriophyllum verticillatum on controlling phosphorus release from sediment for water environment purification

Eutrophication is one of the most common water pollution problems in the world. In this paper, the effects of Myriophyllum verticillatum on phosphorus content in water and sediment were studied. The results showed that Myriophyllum verticillatum had the strongest purification effect on water sample. Under the condition of sufficient light, suitable temperature and environmental factors not affected by the external environment, the phosphorus content in the overlying water increased first and then decreased. In addition to the external factors, the phosphorus content in the water decreased. The results show that the growth of Myriophyllum verticillatum depends on the change of phosphorus concentration in water. The increase of phosphorus concentration in water will increase the phosphorus concentration in plants and accelerate the growth of Myriophyllum verticillatum. However, the growth of Myriophyllum verticillatum will consume more phosphorus. Myriophyllum verticillatum in sufficient light, suitable temperature, environmental factors are not affected by the outside world. The contents of phosphorus in the sediments showed a downward trend. In addition to the external factors, the phosphorus content in the sediment was reduced by Myriophyllum verticillatum. The relationship between the growth of Myriophyllum verticillatum and the total phosphorus concentration in sediments is interdependent. The release of phosphorus in sediment will increase the phosphorus content in water, which will lead to the enrichment of phosphorus in plants and accelerate the growth of Myriophyllum verticillatum. The growth of Myriophyllum verticillatum will make Myriophyllum verticillatum need more phosphorus, which will accelerate the absorption of phosphorus in water and release more phosphorus from sediment. This is the reaction mechanism of phosphorus removal by Myriophyllum verticillatum; Under the conditions of sufficient light, warm climate and environmental factors not affected by the external environment, the total phosphorus content of Myriophyllum verticillatum was on the rise.

Distribution and Pollution Evaluation of Nitrogen and Phosphorus of Sediments in Zhangze Reservoir

The nitrogen and phosphorus pollution of sediments has increasingly become the main cause of eutrophication in reservoir. The temporal-spatial distribution features and pollution level of nitrogen and phosphorus of sediments were revealed in Zhangze Reservoir. The nitrogen and phosphorus content of 16 sediment samples were detected, as well as sediment oxygen demand. The temporal-spatial changing rules of nitrogen and phosphorus of sediments were analyzed. The pollution level of sediments was evaluated. The results showed that the total nitrogen content of sediments varied from 506 mg/kg to 4411 mg/kg, the total phosphorus content of sediments varied from 160 mg/kg to 961 mg/kg, and the sediment oxygen demand varied from 1295.7 mg/(m2•d) to 2957.6 mg/(m2•d). The nitrogen and phosphorus content of sediments in north and south section was larger than that in middle section. The temporal variation rule of nitrogen and phosphorus content was that it increased obviously in flood season and decreased obviously in freezing stage. The nitrogen pollution level of most of the sediments was severe pollution, with the most serious pollution near the dam and at the end of the reservoir. The phosphorus pollution level of most of the sediments was mild pollution, with moderate and severe pollution near the dam and at the end of the reservoir.

Effect of addition of lanthanum-modified bentonite(Phoslock&lt;sup&gt;&amp;#174;&lt;/sup&gt;) in sediments on growth of &lt;i&gt;Hydrilla verticillata&lt;/i&gt; under different water nutrient concentration

轮叶黑藻（Hydrilla verticillata）是我国浅水湖泊常见的沉水植物，经常用于湖泊生态修复工程.然而在生态修复中后期，轮叶黑藻又往往会过度繁殖，影响其他湖泊功能的发挥.镧改性膨润土（锁磷剂）可以有效地降低沉积物中生物可利用磷含量，近年来被用于控制湖泊沉积物磷释放，其对轮叶黑藻生长和形态的影响还有待阐明.本研究在2种不同上覆水营养盐浓度条件下，设置添加和不添加锁磷剂2种处理，探究沉积物添加锁磷剂对轮叶黑藻生长及形态特征的影响.结果表明：1）沉积物添加锁磷剂之后，铁锰结合态磷、有机磷、铝结合态磷等生物可利用磷浓度显著降低，而生物不可用磷，如钙结合态磷浓度显著升高；2）沉积物添加锁磷剂显著降低了轮叶黑藻的生物量和生长率.添加锁磷剂的处理组植物的株高、地上部分生物量均明显低于无锁磷剂组；相反，添加锁磷剂显著增加了植物的根长和地下部分生物量，进而提高了植物的根冠比；3）锁磷剂对轮叶黑藻生长的影响程度与水体营养盐浓度有关，在低营养盐浓度水体中锁磷剂对植物生长和形态特征的影响更为显著.本研究表明，锁磷剂的添加能降低沉积物中生物可利用磷浓度，抑制轮叶黑藻的生长，同时这种影响程度与在水体营养盐浓度有关.;Hydrilla verticillata is a common submerged plant in shallow lakes in China, and is often used as a pioneer species in lake ecological restoration projects. However, the Hydrilla verticillata tends to overgrowth, forming a canopy which affects other functions of lakes. Lanthanum-modified bentonite (Phoslock^®) can effectively reduce the bioavailable phosphorus content in sediments. In recent years, it has been used to control phosphorus release from lake sediments. Its impact on the growth and morphology of Hydrilla verticillata remains to be clarified. In this study, two treatments with and without Phoslock^® in the sediments were set up to investigate the effects of Phoslock^® on the growth and morphological characteristics of Hydrilla verticillata under two different water nutrient concentrations. The results show that:1) After adding Phoslock^® to the sediments, the bioavailable phosphorus concentration, such as Fe/Mn combined phosphorus (BD-P), organic phosphorus (Org-P), Aluminum-bound phosphorus (Al-P), is significantly reduced, while the non-bioavailable phosphorus concentration, such as Calcium-bound phosphorus (Ca-P), is significantly increased. 2) The addition of Phoslock^® in the sediments significantly reduced the biomass and growth rate of the Hydrilla verticillata. The plant height and aboveground biomass of Phoslock^® group were significantly lower than those without Phoslock^®; on the contrary, the addition of Phoslock^® significantly increased the root length of the plant and the underground biomass, and increased the plant's root-shoot ratio. 3) The effect of Phoslock^® on the growth of Hydrilla verticillata is related to the concentration of nutrients in the water, and the effect of Phoslock^® on plant growth and morphological characteristics is more significant in low-nutrient water. Overall, this study shows that the addition of Phoslock^® can effectively reduce the concentration of bioavailable phosphorus in sediments and inhibit the growth of Hydrilla verticillata, and this effect is more significant when the concentration of nutrients in the water is reduced.

Spatial distribution of sediment phosphorus in a Ramsar wetland

Eutrophication is a significant threat to surface water biodiversity worldwide, with excessive phosphorus concentrations being among the most common causes. Wetland ditches under these conditions shift from primarily submerged aquatic vegetation to algae or duckweed dominance, leading to excessive shading and anoxic conditions. Phosphorus, from both point (e.g. wastewater treatment works) and diffuse (largely agricultural runoff) sources, is currently the central reason for failure in the majority of surface water bodies in England to meet required water quality guidelines. This study assesses phosphorus storage in the ditch systems at West Sedgemoor, a designated site of special scientific interest. Elevated phosphorus concentrations in sediment was observed across the Moor up to 4220 mg Kg−1, almost 10 times that which may be expected from background levels. The highest concentrations were generally observed at the more intensively farmed sites in the north of the moor, near key inlets and the outlet. Based upon their chemical and physical properties, clear distinction was observed between sites outside and within the Royal Society of the Protection of Birds nature reserve, using principal component analysis.

Spatio-temporal changes in surface water quality and sediment phosphorus content of a large reservoir in Turkey

The Keban Dam Reservoir, located on the Euphrates River, is the second largest reservoir of Turkey. Water quality of this reservoir is of great importance because it is widely used for recreation, aquaculture production, fishing, and irrigation. In this study, discriminant analysis, principal component analysis (PCA), factor analysis (FA) and cluster analysis (CA) were conducted to evaluate the seasonal and spatial variations in surface water quality of the reservoir. Also, total phosphorus (TP) content in sediments, water type and trophic status of the reservoir were determined. For this, 19 water quality variables and TP in sediments were monitored seasonally at 11 sampling stations on the reservoir during one year. Hierarchical CA classified 11 stations into three groups, i.e., upstream (moderate polluted), midstream (low polluted) and downstream (clean) regions. PCA/FA allowed to group the variables responsible for variations in water quality, which are mainly related to mineral dissolution (natural), organic matter and nutrients (anthropogenic), and physical parameters (natural). Discriminant analysis (DA) gave better results for both data reduction and spatio-temporal analysis. Stepwise temporal DA identified eight variables: water temperature (WT), chemical oxygen demand (COD), nitrate nitrogen (NO3–N), soluble reactive phosphorus (SRP), chlorophyll-a (Chl-a), potassium (K+), magnesium (Mg2+), and calcium (Ca2+), which are the most significant variables responsible for temporal variations in water quality of the reservoir, while stepwise spatial DA identified three variables: K+, chloride (Cl−), and sulphate (SO4−2), which are the most significant variables responsible for spatial variations. According to Ontario sediment-quality guidelines, sediments of the reservoir can be considered as unpolluted in terms of mean TP content. The water type of the reservoir was calcium-bicarbonate. According to trophic state index values based on TP and Chl-a, upstream region (moderate polluted) of the reservoir was in the eutrophic status, whereas other regions were in the mesotrophic status.

Quality Assessment of Some Freshwater Resources Located in Bucharest and Surrounding Areas. III. Case Study: Trophic Status Assessment of Mogosoaia, Herastrau and Pantelimon Lakes

The aim of this paper is the evaluation of the trophic status of three lakes riparian to the Colentina River, namely Mogosoaia, Herastrau, Pantelimon, as Part III of an extended study on evaluation of the freshwater resources quality in Bucharest and surrounding areas [1, 2], supplementing the general quality assessment based on indices and indexes presented in Part I with a more in depth analysis of nutrient speciation and partitioning between water and upper sedimentary layers. Water and sediment samples were taken from the inlet and outlet areas of each lake in two sampling campaigns in July 2016 and September 2016. Some of the nutrient related water quality parameters presented in Part I of this series have been used here, together with the analysis of total nitrogen and total phosphorus content in sediments, to assess the general trophic state of the lakes and to highlight the relationships between the nitrogen and the phosphorus content from water and sediments.The studied lakes were found to be eutrophic, Mogosoaia and Pantelimon being in the most advanced state. A significant amount of nitrogen and phosphorus was detected in all sediments analysed, constituting a high accumulation of nutrients from anthropogenic activities. Actions to improve local sanitation infrastructure and to prevent anaerobic leakage of nutrients from sedimentary deposits are recommended.

Quality Assessment of Some Freshwater Resources Located in Bucharest and Surrounding Areas. III. Case Study: Trophic Status Assessment of Mogosoaia, Herastrau and Pantelimon Lakes

The aim of this paper is the evaluation of the trophic status of three lakes riparian to the Colentina River, namely Mogosoaia, Herastrau, Pantelimon, as Part III of an extended study on evaluation of the freshwater resources quality in Bucharest and surrounding areas [1, 2], supplementing the general quality assessment based on indices and indexes presented in Part I with a more in depth analysis of nutrient speciation and partitioning between water and upper sedimentary layers. Water and sediment samples were taken from the inlet and outlet areas of each lake in two sampling campaigns in July 2016 and September 2016. Some of the nutrient related water quality parameters presented in Part I of this series have been used here, together with the analysis of total nitrogen and total phosphorus content in sediments, to assess the general trophic state of the lakes and to highlight the relationships between the nitrogen and the phosphorus content from water and sediments.The studied lakes were found to be eutrophic, Mogosoaia and Pantelimon being in the most advanced state. A significant amount of nitrogen and phosphorus was detected in all sediments analysed, constituting a high accumulation of nutrients from anthropogenic activities. Actions to improve local sanitation infrastructure and to prevent anaerobic leakage of nutrients from sedimentary deposits are recommended.

Effects of decabromodiphenyl ether on activity, abundance, and community composition of phosphorus mineralizing bacteria in eutrophic lake sediments

Polybrominated diphenyl ethers (PBDEs) are typical persistent organic pollutants (POPs) in the environment. However, little is known about their effects on phosphorus mineralizing bacteria (PMB) in eutrophic lake sediments, despite the critical role of PMB in phosphorus (P) biogeochemical cycling. In this study, we carried out a 60-day microcosm experiment to understand the effects of 2 and 20 mg kg−1 dry weight decabromodiphenyl ether (BDE-209) on the activity, abundance, diversity, and community composition of PMB in the sediment of Taihu Lake, a typical eutrophic lake in China. The results showed that BDE-209 contamination, regardless of the contamination levels, significantly increased the orthophosphate concentration in overlying water and available phosphorus concentration in sediments on day 60. Such increases may be explained by the stimulatory effects of BDE-209 on alkaline phosphatase (ALP) activity and PMB abundance. Moreover, based on Miseq sequencing of the phoD gene encoding ALP, Actinobacteria was the dominant PMB phylum in all treatments, and BDE-209 significantly increased the diversity of PMB and altered their community composition. In particular, the relative abundances of some PMB genera such as Bradyrhizobium were increased significantly after 60 days of the High treatment. A co-occurrence network analysis further revealed that the high level of BDE-209 contamination strengthened the connectivity and interspecific co-operative relationships in the PMB community. These results will help us to understand the effects of POPs on P biogeochemical cycling in eutrophic lakes and the associated microbial mechanisms.

Effects of Exogenous Carbon Addition on Equilibrium Phosphate Concentration and Risk of Phosphorus Release from Sediments in the Shiwuli River, Chaohu Lake Basin

Five surface sediment samples were collected every two months from the Shiwuli River along an urban-rural gradient, Chaohu Lake Basin, from July 2017 to May 2018. Sediment phosphorus fractions were investigated, and equilibrium phosphate concentration (EPC0) and its response to exogenous carbon (sodium acetate) addition were explored. Moreover, the risk of phosphorus release from sediment into water column was also evaluated. Results show that the Shiwuli River was seriously polluted by phosphorus. The average values of total phosphorus content in sediments ranged from 915.04 to 1205.31 mg·kg-1, and it decreased slowly along the urban-rural gradient, while the bio-available phosphorus content remained stable. Exogenous carbon addition not only reduced the EPC0 values of sediments (about 29%), but changed the order of EPC0 values among the five sampling sites as well. In general, the ratio of overlying water SRP (soluble reactive phosphorus) concentration to EPC0 value was 66.7%, and phosphorus adsorption-desorption equilibrium saturation EPCsat<-20% accounted for about 60.0%, indicating that the surface sediments in the Shiwuli River were dominated by phosphorus adsorption, namely, keeping the phosphorus "sink" state. The inputs of exogenous carbon addition increased the proportion of EPCsat<-20% from 60.0% to 73.3%, which lowered the risk of phosphorus release from sediments.

Study on spatial-temporal distribution of different forms of phosphorus in wetland sediments

As an important factor for controlling phosphorus adsorption and release in wetland system, the forms of phosphorus in sediment has a decisive effect on phosphorus retention and release. Four different wetland systems were selected to study the phosphorus status and its environmental effects in wetland sediment. Phosphorus forms in sediments were related to aquatic plant characteristics. In the Vallisneria Linn. wetland system, the content of Ca-P of sediment was higher than the other systems because of its higher pH of the water. The maximum phosphorus adsorption capacity is 766.82-840.27 mg/kg. The content of Ca-P and TP have very good correlation with Smax. When the phosphorus concentration in the water is lower than 0.1mg/L, the surface sediment is no longer a “sink” of phosphorus but a “source” of phosphorus. The changes of TP in four wetland sediments basically follow a similar trend. The phosphorus content in the sediment decreased during the growth period of aquatic plants, and the wetland sediment as the phosphorus “source” provided the biomass for the growth of the aquatic plants. In autumn and winter, phosphorus in plants is released into wetland again with the decay of plants, resulting in the increase of phosphorus content in sediment.

Vertical change of cladoceran ephippial densities in the sediments of Lake Nanyi and its correlation with the nutrients

We examined the vertical variations of cladoceran ephippia in the sediments (1-28 cm) of Lake Nanyi. Nine cladoceran ephippia (Daphnia similoides sinensis, Daphnia galeata, Daphnia pulex, Ceriodaphnia sp., Moina micrura, Bosmina sp., Scapholeberis sp., Leydigia leydigii and Chydorus sp.) were identified. The ephippial densities of Daphnia species and small cladocerans ranged from 0 to 2.0 ind&middot;g-1 DM and from 0 to 10 ind&middot;g-1 DM, respectively. D. similoides sinensis and Ceriodaphnia sp. were respectively dominant species of large and small cladocerans in the sediments of Lake Nanyi. The ephippial densities of D. similoides sinensis had a significant negative correlation with total phosphorus content of sediments in the 1# sampling site of Lake Nanyi and had positive correlations with total nitrogen and total phosphorus contents in the 3# sampling site. In three sampling sites (except for total nitrogen contents in the 2# sampling site), there were significant positive relationships between the ephippial densities of Ceriodaphnia sp. and both total nitrogen and total phosphorus contents. Our results suggested that eutrophication and fish predation affected the historical succession of cladoceran community structure in Lake Nanyi.

Distribution of Phosphorus Fractions in Surface Sediments of Minjiang Mainstreams

In recent years, the total phosphorus pollution in Minjiang River was serious, and the surface sediments of the Minjiang River also threatened water quality. To study the spatial distributions of phosphorus in the surface sediments of the Minjiang River, samples of surface sediments were collected upstream (Aba District) and downstream (Yibin District) of the Minjiang River in December, 2016. The sediments were analyzed with the modified sequential extraction method (SEDEX) to obtain six forms of phosphorus, including exchangeable phosphorus (Ex-P), exchangeable organic phosphorus (Org-P), iron-bound phosphorus (Fe-P), authigenic phosphorus (Ca-P), detrital phosphorus (De-P), and refractory phosphorus (Res-P). The results indicated that the contents of total phosphorus (TP) in surface sediments ranged from 522.17 μg ·g-1 to 979.22 μg ·g-1, which were far more than the soil phosphorus background values (700 μg ·g-1). The spatial distribution characteristics of the TP of surface sediments indicated that the TP concentrations in sediments at the Meishan sections (the middle reach of the Minjiang River) were higher than those in the other sections. This was related to the smaller particle size and higher OM contents in sediments in the Meishan sections. The main phosphorus forms in the sediments in the Minjiang River were Ca-P and De-P, with their concentrations accounting for 75% of TP in the sediments. The bio-available phosphorus, which included Ex-P, Org-P, and Fe-P, accounted for 0.31%-29.62% of TP in the sediments of the Minjiang River. The concentrations of bio-available phosphorus in sediments at the Meishan sections and Leshan sections (the middle reach) were highest, indicating that bio-available phosphorus in the surface sediments was high, and its potential environmental impact risks were higher.

Mechanisms driving phosphorus release during algal blooms based on hourly changes in iron and phosphorus concentrations in sediments

Algal growth causes a drastic change in aquatic conditions over a diel cycle, which may induce sensitive feedback systems in sediments, causing P release. In this study, a microcosm experiment was performed using a suction sampler (Rhizon) to observe changes in soluble reactive phosphorus (SRP) and soluble Fe(II) concentrations in the top 20 mm sediment layer on a 3-h time interval, at different phases of harmful algal bloom (HAB) development. The results showed that the algal blooms prevailed up to 15 days after incubation, after which the process of bloom collapse proceeded until the 70th day. The concentrations of pore-water soluble Fe(II) and SRP increased throughout the incubation period. Compared to day 1, maximum increases of 214% in soluble Fe(II) and 387% in SRP were observed at night during the bloom and collapse periods, respectively. The diffusive fluxes of Fe and P at the sediment-water interface (SWI) generally corresponded to their changes in concentrations. Hourly fluctuation in soluble Fe(II) and SRP concentrations were observed with two distinct concentration peaks occurred at 21:00 p.m. and 06:00 a.m. (or 03:00 a.m.), respectively. These findings suggest that Fe-P coupling mechanisms are responsible for the release of P from sediments. During the collapse period, soluble Fe(II) concentrations were suppressed by the increase of labile S(-II) at night. Meanwhile, SRP concentrations were decoupled from Fe cycling with small fluctuations (<11% RSD) on an hourly timescale, and the decomposition of algae was a dominant source contributing to the release of P from sediments. These results significantly improved the understanding of processes and mechanisms behind the stimulated release of P from sediments during HABs.