Total Dissolved Phosphorus Research Articles

Effects of soil organic residue amendment on losses of dissolved organic carbon, P, Cu and Zn via surface runoff from arable soils

Dissolved organic carbon (DOC) constitutes the largest carbon pool in surface waters, with soil being its main source via surface and subsurface runoff. Amendment with organic residues can reduce soil erosion and surface runoff, but little is known how this affects the amount and composition of DOC losses via surface runoff and the associated transfer of nutrients and pollutants. In this study, artificial rainfall experiments were conducted on three pairs of soil runoff plots with contrasting organic matter management. A mixture of grass and wheat straw residues was incorporated into the topsoil of one plot in each pair (OI treatment) but not into the other (control). Artificial rainfall was applied onto both treatments at an intensity of 49.1 mm h−1, and surface runoff samples were collected at designated time steps for analysis of DOC, total dissolved phosphorus (TDP), copper (TDCu) and zinc (TDZn) concentrations, as well as for characterization of DOC by UV–vis absorbance (SUVA254 and E2:E3) and fluorescence spectroscopy (FI) indexes. The organic amendment reduced the loss rates of DOC, TDP, TDCu and TDZn by reducing surface runoff, although increasing the concentrations of DOC, TDP and TDCu. Regardless of the treatment, DOC, TDP and TDCu concentrations were always maximal at the onset of runoff and then continuously decreased after the initial flush. The observed relationships of TDP and TDCu concentrations with DOC indicate that the export of “dissolved” P and Cu primarily occurred in DOC-bound form, while the concentration of TDZn was not correlated with that of DOC. Surface runoff from the amended soils generally contained more hydrophilic and low molecular weight DOC (as indicated by low SUVA254 and high E2:E3 and FI values), particularly at high DOC concentrations. The ratio between TDCu and DOC concentration showed a positive relationship to DOC aromaticity (as indicated by SUVA254 values) in the OI treatment. The results indicate that organic amendment can reduce total rates of dissolved element losses with surface runoff, but attention should also be paid to the composition of lost DOC and the concentrations of DOC-associated solutes.

Multi-scale Modeling of Nutrient Pollution in the Rivers of China.

Chinese surface waters are severely polluted by nutrients. This study addresses three challenges in nutrient modeling for rivers in China: (1) difficulties in transferring modeling results across biophysical and administrative scales, (2) poor representation of the locations of point sources, and (3) limited incorporation of the direct discharge of manure to rivers. The objective of this study is, therefore, to quantify inputs of nitrogen (N) and phosphorus (P) to Chinese rivers from different sources at multiple scales. We developed a novel multi-scale modeling approach including a detailed, state-of-the-art representation of point sources of nutrients in rivers. The model results show that the river pollution and source attributions differ among spatial scales. Point sources accounted for 75% of the total dissolved phosphorus (TDP) inputs to rivers in China in 2012, and diffuse sources accounted for 72% of the total dissolved nitrogen (TDN) inputs. One-third of the sub-basins accounted for more than half of the pollution. Downscaling to the smallest scale (polygons) reveals that 14% and 9% of the area contribute to more than half of the calculated TDN and TDP pollution, respectively. Sources of pollution vary considerably among and within counties. Clearly, multi-scale modeling may help to develop effective policies for water pollution.

Nutrient inputs from the leaf decay of Cynodon dactylon (L.) Pers in the water level fluctuation zone of a Three Gorges tributary

Cynodon dactylon (L.) Pers (C. dactylon) is one of the dominant plants in the water level fluctuation (WLF) zone of the Three Gorges Reservoir (TGR) tributaries. However, the leaves of C. dactylon can decay to increase the inputs of nutrients under flood inundation, increasing the risk of eutrophication in the TGR tributaries. Nutrient inputs from the leaf decay of C. dactylon in three interfaces, namely, water-sediment (WS), water-C. dactylon (WC) and water-sediment-C. dactylon (W-S-C), were estimated in a 180 d inundation experiment. The results showed that the kinetic processes of total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) input accorded with the power function equation: y = axb for the WS, WC and W-S-C interfaces (R2s > 0.72, p < 0.001). The cumulative TDN input from leaf decay of C. dactylon in the WC interface was 506.44 mg N kg−1 of biomass, which was significantly higher than that in the W-S-C interface with 422.24 mg N kg−1 of biomass (p < 0.05). However, no significant differences in TDP input were found between the WC and W-S-C interfaces (p > 0.05). The total amounts of TDN and TDP inputs at the 165–175 m altitude were 21,688.81 and 13,121.68 kg year−1, respectively, which were approximately 3.17 times those from the 145–155 m altitude of the WLF zone. The amounts of TDN and TDP inputs from the leaves of C. dactylon for the whole WLF zone were 49,261.65 and 29,803.17 kg year−1, respectively, which were 0.1 and 2.7 times the annual permissible discharge amount of pollutants calculated from a municipal wastewater treatment plant with the peak flow of 60,000 m3/d according to Class I (A) of the Wastewater Discharge Standard (GB18918-2002) in China. Thus, the aboveground part of this perennial herb should be harvested in a timely manner before reflooding, especially at the higher altitudes of the WLF zone to decrease eutrophication risk.

Microbial Community Structure in the Sediments and Its Relation to Environmental Factors in Eutrophicated Sancha Lake.

To study the microbial community structure in sediments and its relation to eutrophication environment factors, the sediments and the overlying water of Sancha Lake were collected in the four seasons. MiSeq high-throughput sequencing was conducted for the V3–V4 hypervariable regions of the 16S rRNA gene and was used to analyze the microbial community structure in sediments. Pearson correlation and redundancy analysis (RDA) were conducted to determine the relation between microbial populations and eutrophic factors. The results demonstrated four main patterns: (1) in the 36 samples that were collected, the classification annotation suggested 64 phyla, 259 classes, 476 orders, 759 families, and 9325 OTUs; (2) The diversity indices were ordered according to their values as with summer > winter > autumn > spring; (3) The microbial populations in the four seasons belonged to two distinct characteristic groups; (4) pH, dissolved oxygen (DO), total phosphorus (TP), and total nitrogen (TN) had significant effects on the community composition and structure, which further affected the dissolved total phosphorus (DTP) significantly. The present study demonstrates that the microbial communities in Sancha Lake sediments are highly diverse, their compositions and distributions are significantly different between spring and non-spring, and Actinobacteria and Cyanobacteria may be the key populations or indicator organisms for eutrophication.

Phosphorus losses under heavy rain from the sloping farmlands in the purple hilly region of Southwestern China

Phosphorus (P) and sediment loss through runoffs to surface and ground water represent a risk to human and environmental health. The objective of this work was to understand the mechanisms of P loss under heavy rain from the purple soil of sloping farmlands. The work was carried out with simulated rainfall experiment at different maize growth stages. The combination of three factors was studied: tillage methods (flat planting, longitudinal ridge, and cross-ridge), slope gradients (10°, 15°, and 20°), and maize growth stages (seedling stage, elongation stage, tasseling stage, and maturity stage). Surface runoff, subsurface runoff, sediment, P content in runoff, and sediment were determined. The rate of sediment yield was positively and non-linearly correlated with the runoff shear force and increased quickly when using the longitudinal ridge tillage method. Longitudinal ridge and 20° slope croplands showed greater erodibility, which resulted in higher runoff, sediment yield, and associated P loss. Total phosphorus (TP) and available phosphorus (AP) losses during the entire growth period were 17.58 mg m−2 and 32.86 mg m−2, in the longitudinal ride on 20° slope. Cross-ridge treatment can effectively prevent the loss of P. The P loss occurred violently on 20° slope, and there was little difference in the P loss between 10° and 15° slopes. Dissolved total phosphorus (DTP) loss dominated the TP loss in runoff, accounting for more than 55.58% of the DTP losses in all the treatments. These results indicate the application of flat planting and cross-ridge tillage in croplands with less than 20° slope, as these will minimize the pollution of soil and water resources by reducing P loss in runoff and sediment.

Analysis of Transport and Transformation Characteristics Between Dissolved Phosphorus and Particulate Phosphorus in Water of the Three Gorges Reservoir

To understand the difference between transport coefficients of water runoff, sand discharge, and phosphorus flux in each subsection of a river, a judgement method for analyzing the characteristics of phosphorus transport and transformation in water of rivers was established in this study. Based on the measured data of water runoff, sand discharge, and phosphorus fraction concentrations in the water of the Three Gorges Reservoir (TGR) in January and July 2015, characteristics of phosphorus transport and transformation in the water were analyzed by using the conceptual method. The results showed that the predominant phosphorus fraction in water of the TGR was total dissolved phosphorus (TDP), which accounted for 51%-96% of total phosphorus in water. The TDP flux relative to runoff in the TGR decreased in January 2015 That was caused by the adsorption of TDP by suspended particles in the dry season. In contrast, TDP flux showed additive effect relative to water runoff in July 2015 due to exogenous water inputs with high TDP concentrations in the wet season. Both sand and total particulate phosphorus (TPP) presence in the water showed obvious sediment and retention characteristics during the two periods. The TPP flux presented an additive effect relative to sand discharge, meaning that the major transformation direction of phosphorus fractions was from TDP to TPP. The subsection between Qingxichang and Wanzhou was the main retention area of water, sand, and phosphorus in the TGR, which can be associated with the enhancement of phosphorus adsorption capacity caused by particle size reduction of suspended particles in the subsection.

Variation in dissolved organic matter (DOM) stoichiometry in U.K. freshwaters: Assessing the influence of land cover and soil C:N ratio on DOM composition

AbstractDissolved organic matter (DOM) plays an important role in freshwater biogeochemistry. To investigate the influence of catchment character on the quality and quantity of DOM in freshwaters, 45 sampling sites draining subcatchments of contrasting soil type, hydrology, and land cover within one large upland‐dominated and one large lowland‐dominated catchment were sampled over a 1‐yr period. Dominant land cover in each subcatchment included: arable and horticultural, blanket peatland, coniferous woodland, and improved, unimproved, acid, and calcareous grasslands. The composition of the C, N, and P pool was determined as a function of the inorganic nutrient species (NO3−, NO2−, NH4+, and PO43−) and dissolved organic nutrient (dissolved organic carbon [DOC], dissolved organic nitrogen [DON], and dissolved organic phosphorus [DOP]) concentrations. DOM quality was assessed by calculation of the molar DOC : DON and DOC : DOP ratios and specific ultraviolet absorbance (SUVA254). In catchments with little anthropogenic nutrient inputs, DON and DOP typically composed &gt; 80% of the total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) concentrations. By contrast, in heavily impacted agricultural catchments DON and DOP typically comprised 5–15% of TDN and 10–25% of TDP concentrations. Significant differences in DOC : DON and DOC : DOP ratios were observed between land cover class with significant correlations observed between both the DOC : DON and DOC : DOP molar ratios and SUVA254 (rs = 0.88 and 0.84, respectively). Analysis also demonstrated a significant correlation between soil C : N ratio and instream DOC : DON/DOP (rs = 0.79 and 0.71, respectively). We infer from this that soil properties, specifically the C : N ratio of the soil organic matter pool, has a significant influence on the composition of DOM in streams draining through these landscapes.

Nutrient biogeochemistry in the Cross River estuary system and adjacent Gulf of Guinea, South East Nigeria (West Africa)

The Cross River, Calabar River, and Great Kwa River together form a network of an estuary system otherwise known as the Cross River Estuary system (CRES). Studies of dissolved nutrients and water mass dynamics were conducted mainly in February 2017. Nutrients measured included NO3−, NO2−, NH4+, dissolved inorganic phosphate (DIP), total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), dissolved organic nitrogen (DON), dissolved organic phosphorus (DOP) and dissolved silicate (DSi). The rivers were enriched with DSi and depleted of DIP. Dissolved nutrients were more elevated in the Great Kwa River than Cross River and Calabar River. The levels of DSi and DIN were less than average global concentrations, and that of river estuaries affected by anthropogenic activities. DON was the major form of TDN in the Calabar River estuary, and averagely accounted for 68–76% of TDN pool, while DOP accounted for ∼ 54–75% of TDP pool. Similarly, DON was the dominant form of TDN, and represented 75–84% of TDN pool in the Cross River estuary. In contrast, TDN was dominated by DIN, which accounted for 76–84% of TDN pool, while DIP accounted for 56–61% of TDP pool in the Great Kwa River estuary. There was a switch from DOP (67% of TDP) dominated river water to DIP (67% of TDP) dominated estuarine water in the Cross River estuary, due to enrichment of DIP in the lower Cross River estuary. The adjacent shelf was dominated by DON (58% of TDN) and DIP (70% of TDP). Based on nutrient molar ratios, primary production was strongly limited by DIP, especially in the riverine regions, and switched to DIN limitation in the adjacent shelf. Nutrients in the CRES behaved non-conservatively, and were affected by biogeochemical and physical processes. Nutrient budgets were estimated using the classical LOICZ steady−state box model. Atmospheric deposition of dissolved nutrients was very limited compared to riverine supply. The exchange time of water between the CRES and adjacent sea was ∼ 3.5 days, and may have affected biotic processes and nutrient transport. The CRES was an important source of DIP (137 × 103 moL day−1), DOP (92 × 103 moL day−1) and DON (4849 × 103 moL day−1) to the adjacent shelf, which was respectively 7, 4 and 2 times higher than the total riverine input. The ecosystem metabolism of the CRES, inferred from the ΔDIPsystem and ΔDINsystem indicated that respiration of organic matter was higher than primary production with respiration rate of −15.7 × 106 mol C day−1 (−58 mmol C m−2 day−1), while nitrogen metabolism was −3.8 × 106 mol N day−1 (−14 mmol N m−2 d−1), suggesting that the CRES was heterotrophic, and denitrifying more than nitrogen fixation during this study.

Long‐term weather, streamflow, and water chemistry datasets for hydrological modelling applications at the upper La Salle River watershed in Manitoba, Canada

AbstractLong‐term weather (1990–2013), streamflow (1990–2013; excluding 7 years with no or poor data), and water chemistry (2009–2013) datasets for hydrological modelling applications were developed using simple methods for the upper La Salle River watershed, in Canada, to address the lack of such datasets in the northern Red River Basin. Weather variables consist of temperature, relative humidity, wind speed, solar radiation, and precipitation disaggregated to an hourly time‐step. The only hydrometric variable included in the dataset is stream discharge in a daily time‐step. Water chemistry data consisted of total nitrogen (TN), total dissolved nitrogen (TDN), total phosphorus (TP), and total dissolved phosphorus (TDP). Samples were collected weekly during the open water season at the same site as the hydrometric gauging station from August 2009 to October 2012 with some gaps (i.e. Fall 2011, Spring 2012, September 2012). In 2013 the sampling frequency was increased to daily or sub‐daily during high stream discharge and weekly during low stream discharge. A data overview indicates values within ranges reported for the area. Mean annual, winter, and summer temperatures were 3.5, −10.7, and 17.2°C, respectively. Annual relative humidity averaged 73.1% but was higher and more homogenous in cold seasons. Wind speed was similar over the year with annual average of 4.3 m/s. Solar radiation followed the typical curve reported for western Canada, with peak daily average values around 250 W/m2 in July. Precipitation records were mostly comprised of dry hours with 75.3% of the events being equal or less than 2 mm/h. Stream discharge was typical of the Canadian Prairies; the average peak discharge over the entire period was larger in April (2.3 m3/s) due to large amounts of snowmelt runoff. Average concentrations of TN, TDN, TP, and TDP of 1.54, 1.35, 0.56, and 0.49 mg/L, respectively, were in agreement with values found in previous studies at the site.Open Practices This article has earned an Open Data badge for making publicly available the digitally‐shareable data necessary to reproduce the reported results. The data is available at https://doi.org/10.23684/odi-2017-00957. Learn more about the Open Practices badges from the Center for Open Science: https://osf.io/tvyxz/wiki.

The prevalence of nonlinearity and detection of ecological breakpoints across a land use gradient in streams

Human activities can alter aquatic ecosystems through the input of nutrients and carbon, but there is increasing evidence that these pressures induce nonlinear ecological responses. Nonlinear relationships can contain breakpoints where there is an unexpected change in an ecological response to an environmental driver, which may result in ecological regime shifts. We investigated the occurrence of nonlinearity and breakpoints in relationships between total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and total dissolved carbon (DOC) concentrations and ecological responses in streams with varying land uses. We calculated breakpoints using piecewise regression, two dimensional Kolmogorov-Smirnov (2DKS), and significant zero crossings (SiZer) methods. We found nonlinearity was common, occurring in half of all analyses, with some evidence of multiple breakpoints. Linearity, by contrast, occurred in less than 14% of cases, on average. Breakpoints were related to land use gradients, with 34–43% agricultural cover associated with DOC and TDN breakpoints, and 15% wetland and 9.5% urban land associated with DOC and nutrient breakpoints, respectively. While these breakpoints are likely specific to our study area, our study contributes to the growing literature of the prevalence and location of ecological breakpoints in streams, providing watershed managers potential criteria for catchment land use thresholds.

Composition and Dynamics of Phytoplankton in the Coastal Bays of Maryland, USA, Revealed by Microscopic Counts and Diagnostic Pigments Analyses

Maryland Coastal Bays (MCBs) have undergone changes in water quality in the past two decades due to nutrient enrichment but the composition and dynamics of the phytoplankton community have not been adequately described. Microscopic counts and photosynthetic pigments of samples collected monthly in 2012 at selected sites in MCBs that differed with regard to the degree of anthropogenic impacts were examined. Sixty-three (63) phytoplankton genera were recorded, of which 40 species are being reported for the first time in the Bays. Among the dominant species were Dactyliosolen fragilissimus (Bacillariophyta), Paulinella ovalis (Cercozoa) and Cryptomonas sp. (Cryptophyta). Bloom densities of Heterocapsa rotundata (Miozoa), which previously had not been reported in the Bays, were observed bay-wide in December, particularly at the mouth of St. Martin River. Diatoms dominated (&gt;40%) the phytoplankton community in winter and decreased in spring (&lt;40%), while Cercozoa and microphytoflagellates (MPF) co-dominated in summer (July). From August to October, diatoms dominated with maximum contributions from an unidentified small (&lt;10 µM) centric species and co-dominated the assemblage with cryptophytes in late fall (November). Canonical correspondence analysis indicated that diatoms were favored by high salinity and total dissolved phosphorus (TDP), cercozoans and chlorophytes by total dissolved nitrogen (TDN) and cryptophytes by dissolved organic carbon. The spatial and seasonal differences in the composition of phytoplankton species, coupled with the occurrence of potentially toxic species and bloom densities of H. rotundata suggest that important changes have occurred in the phytoplankton assemblage that likely have affected the food web of these eutrophic bays.

Distribution and Release Characteristics of Phosphorus in a Reservoir in Southwest China

Dam construction changes the nutrient transport of a river system. Phosphorus is an important fundamental material in the global biochemical cycle and is always a limiting factor in the primary productivity of reservoirs. Extending the study of phosphorus in reservoirs is necessary given the dam construction in southwest China. Zipingpu Reservoir was chosen as the research site in this study. The form and distribution of phosphorus in the reservoir’s surface sediments and overlying water were analyzed. The results showed that overall, the total phosphorus (TP) content of surface sediments in the Zipingpu Reservoir decreased from the tail to the front of the dam. The TP content ranged from 682.39 to 1609.06 mg/kg, with an average value of 1121.08 mg/kg. The TP content at some sampling points was affected by exogenous input. Inorganic phosphorus (IP) was the main form of phosphorus in surface sediments and had a proportion of 89.38%. Among the forms of IP, the content of Ca-P was larger than that of O-P; Ex-P, Fe-P, and Al-P had the lowest contents. Particulate phosphorus (PP) was the main form of phosphorus in the overlying water of the Zipingpu Reservoir and was strongly affected by hydrodynamic conditions. The content of total dissolved phosphorus (TDP) in the overlying water was relatively low. To further understand the risk of phosphorus release in the surface sediments in the reservoir, the rate and flux of phosphorus exchange at the sediment-overlying water interface were investigated through laboratory experiments. The results showed that both water temperature and pH significantly affected the sediment release rate, but the influence of water temperature was more significant. Acidic and alkaline conditions were conducive to the release of phosphorus from sediment, while a neutral environment was not. The release rate significantly increased with increasing water temperature, and a positive linear relationship was found between these two parameters. The sediment exhibited absorption characteristics when the water temperature was extremely low and exhibited releasing characteristics at a high temperature. These results could provide a theoretical basis for the management and protection of reservoir water environments.

CO2 partial pressure and CO2 degassing in the Daning River of the upper Yangtze River, China

Rivers and streams are important agents for global and regional carbon cycle, which represent a nonnegligible carbon source to the atmosphere. However, carbon dioxide (CO2) degassing via water-air interface from inland waters currently has a large uncertainty in estimation. Here we examined the CO2 partial pressure (pCO2) and CO2 degassing in the Daning River, a main tributary of the Yangtze in the Three Gorges Reservoir (TGR) region. The riverine pCO2 showed obvious spatial and temporal variations on the main stem and its tributaries, ranging from 483.2 ± 293.9 μatm (May) to 2183.3 ± 1309.2 μatm (August) with an average of 1198.2 ± 1122.9 μatm. pCO2 increased with the intensive agricultural practices and population on the lower reach of the tributary. The daytime average water-air CO2 flux was 329.8 ± 470.2 mmol/m2/d, and yielded a total CO2 efflux approximately 0.12 Tg CO2/y. The results also indicated that carbon loss via atmospheric exchange accounted for 38.8% of riverine dissolved carbon fluxes. There were close relations between pCO2 and environmental parameters such as total dissolved nitrogen (TDN), total dissolved phosphorus (TDP) and water temperature in the rainy season, but not in the dry season. Our results demonstrated the essential need to highlight the importance of anthropogenic activities on global and regional CO2 outgassing, and it is urgent to underscore the detailed biogeochemical processes in riverine pCO2, as well as the couplings between pCO2 and environmental parameters.

Gcd Gene Diversity of Quinoprotein Glucose Dehydrogenase in the Sediment of Sancha Lake and Its Response to the Environment.

Quinoprotein glucose dehydrogenase (GDH) is the most important enzyme of inorganic phosphorus-dissolving metabolism, catalyzing the oxidation of glucose to gluconic acid. The insoluble phosphate in the sediment is converted into soluble phosphate, facilitating mass reproduction of algae. Therefore, studying the diversity of gcd genes which encode GDH is beneficial to reveal the microbial group that has a significant influence on the eutrophication of water. Taking the eutrophic Sancha Lake sediments as the research object, we acquired samples from six sites in the spring and autumn. A total of 219,778 high-quality sequences were obtained by DNA extraction of microbial groups in sediments, PCR amplification of the gcd gene, and high-throughput sequencing. Six phyla, nine classes, 15 orders, 29 families, 46 genera, and 610 operational taxonomic units (OTUs) were determined, suggesting the high genetic diversity of gcd. Gcd genes came mainly from the genera of Rhizobium (1.63–77.99%), Ensifer (0.13–56.95%), Shinella (0.32–25.49%), and Sinorhizobium (0.16–11.88%) in the phylum of Proteobacteria (25.10–98.85%). The abundance of these dominant gcd-harboring bacteria was higher in the spring than in autumn, suggesting that they have an important effect on the eutrophication of the Sancha Lake. The alpha and beta diversity of gcd genes presented spatial and temporal differences due to different sampling site types and sampling seasons. Pearson correlation analysis and canonical correlation analysis (CCA) showed that the diversity and abundance of gcd genes were significantly correlated with environmental factors such as dissolved oxygen (DO), phosphorus hydrochloride (HCl–P), and dissolved total phosphorus (DTP). OTU composition was significantly correlated with DO, total organic carbon (TOC), and DTP. GDH encoded by gcd genes transformed insoluble phosphate into dissolved phosphate, resulting in the eutrophication of Sancha Lake. The results suggest that gcd genes encoding GDH may play an important role in lake eutrophication.

Phosphorus fractionation in surface water and sediments of industrially polluted freshwater reservoir, India

ABSTRACTIndustrial pollutions are responsible for alterations in biogeochemical cycling of phosphorus (P) in freshwater systems. The objectives of the present study were to quantify the major P forms and assess the relationship between P fractions in water and surface sediments of Govind Ballabh Pant Sagar (GBPS) reservoir, India. Surface water samples (n = 48) and surface sediment samples (n = 48) were collected from six regions of GBPS reservoir in December 2014. The results showed that total particulate phosphorus (TPP) and total dissolved phosphorus (TDP) account for 45%–58% and 42%–55% of total phosphorus (TP) in the surface water. The authigenic-P was found to be more than 84% of the total P in surface sediments. The TPP showed a positive statistical relationship with sedimentary P fractions (authigenic-P, exch-P, and organic-P) indicated the impact of industrial pollution load on inorganic and organic P fractions in water and sediments of GBPS reservoir. The discriminant fraction analysis (DFA) revealed that the exch-P, Fe(III)-bound-P, detrital-P, organic-P, and TPP were sensitive indicators of P dynamics in the industrially polluted GBPS reservoir.

Temporal controls on dissolved organic carbon biodegradation in subtropical rivers: Initial chemical composition versus stoichiometry

Dissolved organic carbon (DOC) plays an indispensable role in biogeochemical cycles and ecosystem services in rivers. However, little is known about the seasonal variations of DOC biodegradation in subtropical rivers. Here, we investigated the concentrations of DOC, dissolved total nitrogen (DTN), and dissolved total phosphorus (DTP), humification index (HIX), fluorescence index (FI), and DOC biodegradation in 57 rivers in the dry and wet seasons in the Three Gorges Reservoir area, China, and the aims were to clarify the temporal changes in DOC biodegradation and its driving factors in these subtropical rivers. Compared with dry season, DTN and DTP concentrations, and HIX value were greater, and FI value was lower in the wet season. However, DOC biodegradation remained unchanged across the two sampling seasons. Further, DOC biodegradation negatively correlated with DOC:DTP ratio, DTN:DTP ratio, and FI in the dry season, but only with HIX in the wet season. These findings emphasis that, despite unchanged DOC biodegradation, the key factors driving DOC biodegradation shift from C:N:P stoichiometry in the dry season to initial chemical composition in the wet season in subtropical rivers. Our results regarding the temporal patterns of DOC biodegradation and the underlying mechanisms bear important implications for a better understanding of C dynamics in subtropical river ecosystems.

Performance of a pilot-scale aquaponics system using hydroponics and immobilized biofilm treatment for water quality control

Aquaponics is considered as a promising approach to mass produce both fish meat and vegetable at high rates without discharge pollutants. A novel aquaponics system is proposed to control water quality and enhance nutrition efficiency with high rate immobilized biofilm units, including mass-bio system (MBS) and fiber biofilter (FB), installed between upstream hydroponics units, which are composed of the media filled beds (MFD) and nutrient film technique (NFT), and downstream aquaculture unit for fish rearing. A pilot test was conducted over 130 d to characterize the performance of proposed system which converted residual nutrients from aquaculture unit into ammonium and nitrate at balanced ratio for aquatic plant growth and then removed residual ammonium or/and nitrite to ensue recycled water quality for fish rearing. The kinetics of organic matter removal and nutrient conversion in hydroponics unit and immobilized biofilm units were determined via batch assays over 24 h in the system. The estimated daily pollutant increments for TAN, NO2−-N, NO3−-N, TN, DTP and TOC in the system were 0.28, 0.17, 0.20, 0.64, 0.56 and 2.19 mg/L, respectively. The results demonstrated that total ammonia nitrogen (TAN), nitrite (NO2−-N), nitrate (NO3−-N), total nitrogen (TN), dissolved total phosphorus (DTP) and total organic carbon (TOC) were maintained at low levels in the system for a long-term. Aquatic plants in MFD and NFT contributed to the removal of TAN, NO2−-N, NO3−-N, TN and DTP. The removal efficiencies of MFD versus NFT for TAN were 71.4% vs 43.5% for TAN and 62.5% vs 52.3% for DTP. MBS and FB performed the removal of TAN, NO2−-N and TOC. The 24 h removal efficiencies of TAN, NO2−-N and TOC were 71.8%, 58.5% and 3.7% for MBS and 15.7%, 7.7% and 27.2% for FB.

Influences of land use metrics at multi-spatial scales on seasonal water quality: A case study of river systems in the Three Gorges Reservoir Area, China

The impact of land use metrics on watershed water quality is scale-dependent on a seasonal - spatial basis. Exploring the associations between land use metrics and riverine water quality provides useful information for effective land use planning for water quality security, whilst, these relationships remain poorly understood. 94 water samples covering entire tributaries in the Three Gorges Reservoir Area were collected and analyzed over the time period of 2015–2016, and consequently, multivariate statistics and empirical models were used for understanding the associations between land use metrics and water quality across multi-scales. Analysis of variance (ANOVA) revealed significant spatial differences in water temperature (WT), potential of hydrogen (pH), dissolved oxygen (DO), total nitrogen (TN), total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), TDN/TDP, nitrate nitrogen (NO3−-N), ammoniacal nitrogen (NH4+ -N) and permanganate index (CODMn). Meanwhile, Oxidation-Reduction Potential (ORP), electrical conductivity (EC), DO, TN, TDN, TP, TDP, NO3−-N, NH4+-N and CODMn generally appeared higher values in the dry season. Redundancy analysis (RDA) showed that the total explained variation of land use metrics on overall water quality was slightly stronger at catchment scale than at 100 m and 500 m buffer scales. The influence of land use metrics on water quality was a little stronger in the dry season than the wet season, but there were multi-spatial scale effects of different land use metrics. Our results can provide important information in land use planning and making multiple scales measures for water quality conservation.

한국 해남 양식장에서 홍조 잇바디돌김의 성장기 아미노산과 광합성 색소 성분 조성

To study the effects of marine environmental on thallus of Pyropia dentata (Rhodophyta), I analyzed water temperature, salinity and water quality at the Haenam aquafarm in southern coast of Korea from September to December, 2016. Composition of amino acid and photosynthesis pigment on growing season of P. dentata were studied. Thallus samples were collected at the aquafarm in October and November. Mean water temperature and salinity ranged from 23.11 to 10.93℃ and 30.89 to 32.53 psu, respectively. Dissolved total nitorgen (DTN), dissolved total phosphorus (DTP), total nitrogen (TN), total phosphorus (TP) and chemical oxygen demand (COD) ranged from 0.108~0.282 mg/L, 0.004~0.017 mg/L, 0.164~0.399 mg/L, 0.007~0.021 mg/L and 0.900~1.500 mg/L, respectively. Concentration of DTN, DTP, TN, TP were highest in September and were lowest in November. Proximate composition, amino acid and photosynthetic pigment with P. dentata sampled from aquafarm in October and November were analyzed. Contents of moisture and crude protein, crude lipid, crude ash, carbohydrate were 11.05±0.04, 34.52±0.61, 0.09±0.01, 20.03±0.18, 34.31±0.67% in October and 14.21±0.21, 27.91±1.41, 0.38±0.09, 12.18±0.28, 45.32±1.69% in November. Photosynthetic pigment of Chl. a, PE and PC concentration of P. dentata thalli were 1.609±0.074, 7.848±3.990, 4.288±1.934 mg/g in October and 0.145±0.013, 6.081±0.393, 3.902±0.227 mg/g in November. The pigment concentration was relatively high in October than November. Total amino acid contents were 24,860.00±911.76 mg/100g in October and 21,039.55±825.53 mg/100g in November. Free amino acid contents were 2,310.52±177.93 mg/100g in October and 2,474.87±141.43 mg/100g in November. These results show that proximate composition, photosynthetic pigment content and amino acid content of P. dentata are affected by changes in marine environment seasonally.

Relationship between phytoplankton community and environmental factors in landscape water with high salinity in a coastal city of China.

Relationship between phytoplankton community and environmental variables was explored in three landscape water bodies (namely Jiyun River Oxbow (JRO), Qingjing Lake (QL), and Jiyun River (JR)) with high salinity, located in Sino-Singapore Tianjin Eco-city of China, using redundancy analysis (RDA). A total of 48 species of phytoplankton were identified during the study period, in which Chlorophyta and Bacillariophyta accounted for 35.42 and 31.25%, respectively. The most dominant species of the studied water bodies were Cyclotella meneghiniana (Bacillariophyta) and Aphanocapsa elachista (Cyanophyta). The diversity index ranged from 0.56 to 1.42, with an average of 1.11, reflecting low biodiversity in the phytoplankton community. Moreover, the average density of phytoplankton was 42.39 × 106cells/L, indicating that those landscape water bodies belonged to moderate eutrophication. The results of RDA revealed that the most significant environmental factors influencing phytoplankton community were water temperature (WT), dissolved total phosphorus (DTP), salinity, and total nitrogen (TN) (p< 0.05, Monte Carlo permutation test). Meanwhile, Aphanocapsa elachista was positively correlated with WT, TN, and salinity, while Cyclotella meneghiniana was positively related to salinity and negatively related to TP. The results suggested that salinity was a non-negligible key factor affecting the phytoplankton community of the water body with high salinity.