Phosphorus Release Rates Research Articles

Culture of denitrifying phosphorus removal granules with different influent wastewater

Fed with three different kinds of influent, i.e. sodium acetate-based synthetic wastewater, synthetic wastewater with 10-mg L−1 Ca2+ ions, and raw domestic wastewater, respectively, compact of different influent wastewater on aerobic granulation was investigated in three sequencing batch reactors (corresponding to R1–R3) operating in an alternating anaerobic/oxic/anoxic mode. As a result, denitrifying phosphorus removal granules with an average diameter above 600 μm were successfully cultivated within 42 d when inoculated with flocculent sludge. The granules showed some characteristics, e.g. low in moisture content, high in specific gravity, and specific oxygen uptake rate. Reactors’ performance throughout operation presented that effluent concentration of COD was always lower than 40-mg L−1; TN, NH4+-N, and TP was often lower than 1-mg L−1. In addition, cycle test displayed that efficiencies of COD, NH4+-N, TN, and TP removal in R1–R3 reached up to 90.25, 92.98, 92.96%; 99.29, 99.57, 91.70; 90.83, 92.80, 89.56%; 94.06, 96.76, 90.71%, respectively, the maximal specific phosphorus release rate was 14.34, 8.32 and 2.32 mg P g MLVSS−1 h−1 in R1–R3, respectively, and the maximal specific phosphorus uptake rate was 14.13 mg P g MLVSS−1 h−1 in R1 and 2.34 mg P g MLVSS−1 h−1 in R2, respectively.

Does infection tilt the scales? Disease effects on the mass balance of an invertebrate nutrient recycler.

While parasites are increasingly recognized as important components of ecosystems, we currently know little about how they alter ecosystem nutrient availability via host-mediated nutrient cycling. We examined whether infection alters the flow of nutrients through hosts and whether such effects depend upon host diet quality. To do so, we compared the mass specific nutrient (i.e., nitrogen and phosphorus) release rates, ingestion rates, and elemental composition of uninfected Daphnia to those infected with a bacterial parasite, P. ramosa. N and P release rates were increased by infection when Daphnia were fed P-poor diets, but we found no effect of infection on the nutrient release of individuals fed P-rich diets. Calculations based on the first law of thermodynamics indicated that infection should increase the nutrient release rates of Daphnia by decreasing nutrient accumulation rates in host tissues. Although we found reduced nutrient accumulation rates in infected Daphnia fed all diets, this reduction did not increase the nutrient release rates of Daphnia fed the P-rich diet because infected Daphnia fed this diet ingested nutrients more slowly than uninfected hosts. Our results thus indicate that parasites can significantly alter the nutrient use of animal consumers, which could affect the availability of nutrients in heavily parasitized environments.

Application of the DYRESM–CAEDYM model to the Sau Reservoir situated in Catalonia, Spain

The aim of this work was to apply to the Sau Reservoir a one-dimensional hydrodynamic DYRESM model linked to the water quality CAEDYM model. And how hydrodynamic affects water quality in reservoirs, especially when have been used for water supply purposes. Thus, simulations were undertaken for 2 years between 2000 and 2001 with the aim of predicting thermal structure and water quality variables such as dissolved oxygen, dissolved inorganic phosphorus and chlorophyll in the reservoir. Inputs were meteorological data, river inflow and outflow data, morphometry parameters, an initial profile and file configuration data. The CAEDYM model also requires a configuration file and initial profiles for all the water quality data, as well as the calibration of different parameters such as sediment-dissolved oxygen, the sediment flux release rate of phosphorus and the maximum potential growth rate of phytoplankton. Temperatures simulation shows clearly a good agreement with the observed one during the stratification period starting from July to the end of September. Also, the model gives a good prediction of dissolved oxygen, however, for simulated dissolved inorganic phosphorus, and chlorophyll exhibits the same trend as measured values. Hence, coupling of those models explains in better way how water quality may be affected by hydrodynamic and could be used as an adequate tool for water quality management purposes.

TMDL reevaluation: reconciling internal phosphorus load reductions in a eutrophic lake

Total maximum daily loads (TMDLs) are assigned to impaired waterbodies and provide a prescription for recovery. It is implicit that both the existing conditions and targets identified in a TMDL are based on credible and accurate information, ensuring that management actions directed to recovery are appropriate and effective. We evaluated the TMDL for phosphorus in Bear Lake, Michigan, to assess if the prescribed reduction was appropriately based on existing annual internal loads. We developed 5 different annual internal load scenarios based on phosphorus release rates from laboratory-based sediment incubations and diel dissolved oxygen measurements, ranging from very conservative to very liberal estimates of phosphorus release. The most realistic scenarios indicate that the previously established TMDL for internal phosphorus loading is 3–7 times greater than what actually occurs in Bear Lake. Based on our assessment, Bear Lake is likely already meeting the TMDL internal loading target, without the implementation of any management action. Thus, management efforts aimed at reducing the water column phosphorus concentration to reach the TMDL target should instead be directed at controlling the external phosphorus load.

Impacts of hydrodynamic disturbance on sediment resuspension, phosphorus and phosphatase release, and cyanobacterial growth in Lake Tai

The objective of this study was to link hydrodynamic disturbance with sediment resuspension, phosphorus release, and algal growth in Lake Tai, a typical shallow lake located in the south of the Yangtze River Delta in China. With this regard, a sediment–water-algae laboratory experiment was conducted and extrapolated to the real situation in terms of field observations. The results show that the algal growth rate synchronically increased with dissolved total phosphorus (DTP) release rate. The DTP decreased with increase of bottom flow velocity, indicating that the phosphorus release rate was lower than its transfer rate into algal biomass. While all levels of hydrodynamic disturbances could increase sediment resuspension and phosphorus release, a low to moderate disturbance was beneficial, but a strong disturbance was harmful for algal growth. Also, a low to moderate disturbance caused the dissolved alkaline phosphatase activity (DAPA) to increase with time, which provided the enzyme for hydrolyzing a variety of organic phosphorus compounds from bed sediment into algae-needed nutritional DTP. The experiment proved to be an efficient means to understanding eutrophication mechanisms of large shallow lakes such as Lake Tai.

Effect of Nitrite and External Carbon Source on the Via Nitrite Biological Phosphorus Removal

The via nitrite biological phosphorus removal was investigated in batch experiments using biomass collected from a sequencing batch reactor (SBR) treating low strength nitrogenous effluents. The effect of the initial nitrite concentration and the external carbon source characteristics on the via nitrite specific phosphorus uptake rate (sPUR) was investigated. The external carbon sources that were applied consisted of fermented liquid produced from the organic fraction of municipal solid waste (OFMSW FL), fermented liquid produced from vegetable and fruit waste (VFW FL) and VFW enriched with propionic acid and/or butyric acid. The type and composition of the applied external carbon source critically impacted the via nitrite sPUR. The addition of OFMSW FL resulted in very high via nitrite sPUR (7.25 mgP/(gVSS∙h)) and specific phosphorus release rates (sPRR=5.11 mgP/(gVSS∙h)). The presence of propionic acid and butyric acid in OFMSW FL promoted phosphorus uptake. The short chain fatty acids (SCFAs) in the VFW FL consisted mainly of acetic acid and resulted in lower sPUR. Furthermore, increased concentration of SCFAs in the mixed liquor enhanced the via nitrite phosphorus removal. The presence of nitrite in the mixed liquor did not adversely impact the phosphorus uptake mechanism up to the concentration range of 50-70 mg/L. However, higher nitrite levels (100-120 mg/L) resulted in some sPUR inhibition.

Effects of sediment physical properties on the phosphorus release in aquatic environment

Particle size, porosity, and the initial phosphorus concentration in sediments are the main factors affecting phosphorus release flux through the sediment-water interface. Sediments can be physically divided to muddy and sandy matters, and the adsorption-desorption capacity of sediment with phosphorus depends on particle size. According to phosphorus adsorption-desorption experiments, phosphorus sorption capacity of the sediment decreases with the increase of particle dimension. But among the size-similar particles, sediment with a bigger particle size has the larger initial phosphorus release rate. In terms of muddy and sandy sediments, there are inversely proportional relationships between the release rate and the flux. Due to the contact of surface sediment and the overlying water, the release flux from the sediment is either from direct desorption of surface sediment layer or from the diffusion of pore water in the sediment layer, which is mainly determined by sediment particle size and porosity. Generally, static phosphorus release process may include two stages: the first is the initial release. As for coarse particles, phosphorus is desorbed from surface sediment. And for fine particles, phosphorus concentration in water often decreases, mainly from pore water by the molecular diffusion. During the second stage, pore water flows faster in coarse sediment, and phosphorus is easy to desorb from the surface of the particles as diffusion dominates. For the smaller liquid-solid ratio of fine particles and the larger amount of phosphorus adsorption, the release flux from pore water due to diffusion is very small with longer sorption duration.

Operation performance and microbial community dynamics of phosphorus removal sludge with different electron acceptors.

Operation performances of phosphorus removal sludge with different electron acceptors in three parallel SBRs were firstly compared in the present study, and the effect of post-aeration on denitrifying phosphorus removal was also studied. Moreover, community dynamics of different phosphorus removal sludge was systematically investigated with high-throughput sequencing for the first time. TP removal rates for nitrate-, nitrite-, and oxygen-based phosphorus removal sludge were 84.8, 78.5, and 87.4%, with an average effluent TP concentration of 0.758, 0.931, and 0.632mg/l. The average specific phosphorus release and uptake rates were 20.3, 10.8, and 21.5, and 9.43, 8.68, and 10.8mgP/(gVSSh), respectively. Moreover, electron utilization efficiency of denitrifying phosphorus removal sludge with nitrate as electron acceptor was higher than nitrite, with P/e(-) were 2.21 and 1.51mol-P/mol-e(-), respectively. With the assistance of post-aeration for nitrate-based denitrifying phosphorus removal sludge, settling ability could be improved, with SVI decreased from 120 to 80 and 72ml/g when post-aeration time was 0, 10, and 30min, respectively. Moreover, further phosphorus removal could be achieved during post-aeration with increased aeration time. However, the anoxic phosphorus uptake was deteriorated, which was likely a result of shifted microbial community structure. Post-aeration of approximately 10min was proposed for denitrifying phosphorus removal. Nitrate- and nitrite-based denitrifying phosphorus removal sludge exhibited similar community structure. More phosphorus accumulating organisms were enriched under anaerobic-aerobic conditions, while anaerobic-anoxic conditions were favorable for suppressing glycogen-accumulating organisms. Significant differences in pathogenic bacterial community profiles revealed in the current study indicated the potential public health hazards of non-aeration activated sludge system.

Effects of mechanical disintegration of activated sludge on the activity of nitrifying and denitrifying bacteria and phosphorus accumulating organisms

The purpose of the study was to analyse the impact of hydrodynamic disintegration of thickened excess activated sludge, performed at different levels of energy density (70, 140 and 210 kJ/L), on the activity of microorganisms involved in nutrient removal from wastewater, i.e. nitrifiers, denitrifiers and phosphorus accumulating organisms (PAOs). Ammonium and nitrogen utilisation rates and phosphorus release rates for raw and disintegrated sludge were determined using batch tests. The experiment also included: 1) analysis of organic and nutrient compound release from activated sludge flocs, 2) determination of the sludge disintegration degree (DD), and 3) evaluation of respiratory activity of the biomass by using the oxygen uptake rate (OUR) batch test. It was shown that the activity degree of the examined groups of microorganisms depended on energy density and related sludge disintegration degree, and that inactivation of individual groups of microorganisms occurred at different values of DD. Least resistant to the destruction of activated sludge flocs turned out to be phosphorus accumulating organisms, while the most resistant were denitrifiers. A decrease of 20–40% in PAO activity was noted already at DD equal to 3–5%. The threshold values of DD, after crossing which the inactivation of nitrifiers and denitrifiers occurred, were equal to 8% and 10%, respectively. At lesser DD values an increase in the activity of these groups of microorganisms was observed, averaging 20.2–41.7% for nitrifiers and 9.98–36.3% for denitrifiers.

The regularity of wind-induced sediment resuspension in Meiliang Bay of Lake Taihu.

Contaminants released by wind-induced sediment resuspension could influence the water quality in shallow lakes. This study aims to reveal the quantitative relationship between wind speed (v) and sediment resuspension rate (r) in Meiliang Bay of Lake Taihu. The study was conducted in three steps. First, the in situ wind speed and current velocity were measured over a period of 2 days in Meiliang Bay to establish the relationship between wind and hydrodynamic conditions; second, an indoor experiment was conducted in a cylindrical simulator with sediment from the study area to determine sediment resuspension rates under different hydrodynamic conditions; and third, linkages between sediment resuspension and wind were determined. The average sediment resuspension rate was highly correlated with the wind speed (R(2) = 0.99), and was expressed by r = 20.72v(2.034) at wind speeds in the range of 0-14 m/s. The critical wind speed for sediment resuspension is about 7 m/s. Under these conditions, the average resuspension rate could reach 1,000 g/(m(2)d), with a total phosphorus release rate of 1.1 g/(m(2)d) and a total nitrogen release rate of 18.1 g/(m(2)d).

Comparison of biochemical characteristics between PAO and DPAO sludges

A successful enhanced biological phosphorus removal (EBPR) was observed in both anaerobic-aerobic sequencing batch reactor (An-Ox SBR) to induce growth of phosphorus accumulating organism (PAO) and anaerobic-anoxic (An-Ax) SBR to induce growth of denitrifying PAO (DPAO). Although the EBPR performance of An-Ox SBR was higher by 11.3% than that of An-Ax SBR, specific phosphorus release rates in the An-Ax SBR (22.8 ± 3.5 mg P/(g VSS·hr)) and the An-Ox SBR (22.4 ± 4.8 mg P/(g VSS·hr)) were similar. Specific phosphorus uptake rates under anoxic and aerobic conditions were 26.3 ± 4.8 mg P/(g VSS·hr) (An-Ax SBR) and 25.6 ± 2.8 mg P/(g VSS·hr) (An-Ox SBR), respectively, which were also similar. In addition, an analysis of relationship of poly-β-hydroxyalkanoates (PHA) synthesized under anaerobic conditions with phosphorous release (Preleased/PHAsynthesized) and of PHA utilized under anoxic and aerobic conditions with phosphorous uptake (Puptaked/PHAutilized) verified that biological activities of EBPR per unit biomass between DPAO and PAO were similar. An analysis of the specific denitrification rate of DPAO showed that NO−3-N can be denitrified at a rate that does not substantially differ from that of an ordinary denitrifier without additional consumption of organic carbon when the PHA stored inside the cell under anaerobic conditions is sufficiently secured.

Phosphorus release from anaerobic peat soils during convective discharge — Effect of soil Fe:P molar ratio and preferential flow

Phosphorus (P) accumulation in drained agricultural lowlands causes a risk for P pollution to the aquatic environment following wetland restoration. While extensive knowledge is available on P sorption and desorption from anaerobic soils, very limited information is available on the interacting influence of soil geochemistry and local scale active flow volume. Combining batch incubation experiments and continuous column discharge experiments, we investigated iron (Fe) reduction and P release from 10 anoxic Fe-dominated (oxalate extractable Fe (Feox) from ~5500 to 50,000mgkg−1) lowland peat soils (TOC from 5 to 39%) with a gradient in Fe:P molar ratio (molar ratio between bicarbonate dithionite extractable Fe and P (FeBD:PBD) from 3 to 112) and degree of non-equilibrium (preferential) flow. Short-term batch incubation experiments (21days) indicated that concurrent Fe and P release was controlled by reductive Fe(III) dissolution, and was well predicted from the soil FeBD:PBD molar ratio. Continuous convective column discharge with oxygen-free deionised water at 1mmh−1 for 10 effluent pore volumes resulted in highly variable in situ redox potential (Eh from −200 to 300mV), effluent Fe(II) concentrations (23 to 2000μM) and effluent dissolved reactive phosphorus (DRP) concentrations (<6.5 to 316μM). Effluent P forms changed from dominantly particular P/dissolved organic P (PP/DOP) to dominantly DRP as Eh decreased in all soils. Total phosphorus (TP) release rates during convective discharge (3–66μmolkg−1day−1) were negatively non-linearly correlated with the soil FeBD:PBD molar ratio, which explained 71–73% of the variability, and with FeBD:PBD of 10 as a critical threshold ratio. Fe and P release rates from batch experiments were poorly correlated with convective discharge Fe and P release rates, indicating the overall influence of soil structure. Diffusion was found to be the rate-limiting step for P release after prolonged leaching. Although the soil FeBD:PBD molar ratio turned out as a key explanatory parameter in predicting P release rates following rewetting of these peat soils, the results did indicate the influence of preferential flow in decreasing P release rates. Although, sufficient available P is present for leaching in the initial phase after rewetting P enriched lowland soils, we do expect that soils with pronounced preferential flow will become more rapidly exhausted in available P, and hence limit P release after prolonged discharge.

On the potential release rates of nutrient from internal sources: A comparative study of typical dredged and un-dredged areas, northwestern Lake Taihu

Simulated research of internal loading release was carried out to assess the effects of sediment dredging on internal source release,and the basic properties of dredged and un-dredged sediments was also analyzed in this study. Intact sediment cores were collected from dredged and un-dredged sites in four areas including Bafang Port,Lvjiang Port,Moon Bay and Zhushan Bay,northwestern Lake Taihu. The results showed that the potential release rates of sediments can be efficiently prevented by dredging because of the internal loadings such as the loss on ignition,total nitrogen and ammonium nitrogen which were significantly lower after dredging. The potential release rates of ammonium in dredged sites of Bafang Port,Moon Bay and Zhushan Bay was 65. 3%,88. 8% and 21. 9%,respectively. The potential release rates of phosphorus in dredged sites of Bafang Port even showed negative(- 0. 35 mg/( m2·d)) which means the diffusion direction of phosphorus was from overlying water toward sediments. The release rates of phosphorus in dredged sites of Moon Bay and Zhushan Bay was 11. 3% and 50. 2% of the corresponding un-dredged sites.We also found that the potential release rates of ammonium and phosphorus in dredged sites of Lvjiang Port was significantly higher than those in un-dredged sites,which may be accounted for the reducing environment of water body and the high content of organic matter in sediments.

Longitudinal Variability of Phosphorus Fractions in Sediments of a Canyon Reservoir Due to Cascade Dam Construction: A Case Study in Lancang River, China

Dam construction causes the accumulation of phosphorus in the sediments of reservoirs and increases the release rate of internal phosphorus (P) loading. This study investigated the longitudinal variability of phosphorus fractions in sediments and the relationship between the contents of phosphorus fractions and its influencing factors of the Manwan Reservoir, Lancang River, Yunnan Province, China. Five sedimentary phosphorus fractions were quantified separately: loosely bound P (ex-P); reductant soluble P (BD-P); metal oxide-bound P (NaOH-P); calcium-bound P (HCl-P), and residual-P. The results showed that the total phosphorus contents ranged from 623 to 899 µg/g and were correlated positively with iron content in the sediments of the reservoir. The rank order of P fractions in sediments of the mainstream was HCl-P>NaOH-P>residual-P>BD-P>ex-P, while it was residual-P>HCl-P>NaOH-P>BD-P>ex-P in those of the tributaries. The contents of bio-available phosphorus in the tributaries, including ex-P, BD-P and NaOH-P, were significantly lower than those in the mainstream. The contents of ex-P, BD-P, NaOH-P showed a similar increasing trend from the tail to the head of the Manwan Reservoir, which contributed to the relatively higher content of bio-available phosphorus, and represents a high bio-available phosphorus releasing risk within a distance of 10 km from Manwan Dam. Correlation and redundancy analyses showed that distance to Manwan Dam and the silt/clay fraction of sediments were related closely to the spatial variation of bio-available phosphorus.

Three-dimensional lake water quality modeling: sensitivity and uncertainty analyses.

Two sensitivity and uncertainty analysis methods are applied to a three-dimensional coupled hydrodynamic-ecological model (ELCOM-CAEDYM) of a morphologically complex lake. The primary goals of the analyses are to increase confidence in the model predictions, identify influential model parameters, quantify the uncertainty of model prediction, and explore the spatial and temporal variabilities of model predictions. The influence of model parameters on four model-predicted variables (model output) and the contributions of each of the model-predicted variables to the total variations in model output are presented. The contributions of predicted water temperature, dissolved oxygen, total phosphorus, and algal biomass contributed 3, 13, 26, and 58% of total model output variance, respectively. The fraction of variance resulting from model parameter uncertainty was calculated by two methods and used for evaluation and ranking of the most influential model parameters. Nine out of the top 10 parameters identified by each method agreed, but their ranks were different. Spatial and temporal changes of model uncertainty were investigated and visualized. Model uncertainty appeared to be concentrated around specific water depths and dates that corresponded to significant storm events. The results suggest that spatial and temporal variations in the predicted water quality variables are sensitive to the hydrodynamics of physical perturbations such as those caused by stream inflows generated by storm events. The sensitivity and uncertainty analyses identified the mineralization of dissolved organic carbon, sediment phosphorus release rate, algal metabolic loss rate, internal phosphorus concentration, and phosphorus uptake rate as the most influential model parameters.

Optimization of a full-scale Unitank wastewater treatment plant for biological phosphorus removal

The Unitank process combines the advantages of traditional continuous-flow activated sludge processes and sequencing batch reactors, and has been extensively employed in many wastewater treatment plants (WWTPs) in China. Biological phosphorus removal (BPR) of a full-scale Unitank WWTP was optimized by increasing anaerobic time from 80 to 120 min in an operation cycle of 360 min and reducing solid retention time (SRT) from 21.3 to 13.1 d. The BPR efficiency of the full-scale Unitank system increased from 63.8% (SRT of 21.3 d) to 83.2% for a SRT of 13.1 d. When the anaerobic time increased from 80 to 120 min, the net anaerobic phosphorus release amount increased from 0.25 to 1.06 mg L−1, and sludge phosphorus content rose from 13.8 to 15.0 mgP·(gSS)−1. During half an operation cycle, the average specific phosphorus release rate increased from 0.097 mgP·(gVSS·h)−1 in 0–40 min to 0.825 mgP·(gVSS·h)−1 in 40–60 min. Reducing SRT and increasing anaerobic time account for 84.6% and 15.4% in the total increment of phosphorus removal of 1.15 mg L−1.

Effect of MLSS on Nitrosation Denitrifying Phosphorus Removal System

The influence of MLSS on nitrosation denitrifying phosphorus removal (NDPR) process was investigated through the experiments of anaerobic-anoxic NDPR and anoxic NDPR. Experimental results show that the higher MLSS is, the bigger COD removal rate is, and the higher the rates of anaerobic phosphorus release and anoxic phosphorus absorption are. Low carbon sewage will easily lead to insufficient inner carbon source in the system with high MLSS. High concentration of carbon source in the raw water with high MLSS will bring considerable difficulties to returned sludge and sludge treatment. Moreover, excessive MLSS will result in phosphorus release in the later anoxic stage, and lower MLSS can prolong the time of denitrification and phosphorus removal. The system with 5200 mg/L MLSS has the best effect of nitrogen and phosphorus removal.

Interaction between nitrogen and phosphorus cycles in mining-affected aquatic systems—experiences from field and laboratory measurements

The main objectives of this study were to (a) study the interaction between N and P cycles in mining-affected aquatic systems and (b) to quantify release rates of sedimentary soluble reactive phosphorus (SRP) that may be related to this interaction. Sediment cores and water from Lake Bruträsket (Boliden, northern Sweden) were collected and a time series of water sampling and flow measurements was conducted in the Brubäcken stream connected to the lake. Factors affecting SRP release were studied in a sediment incubation experiment and water column experiments. Field and laboratory measurements indicated that pH and dissolved oxygen are two important factors for SRP release. At the end of the low-oxygen incubation, an SRP concentration of 56 μg L(-1) resulted in a sedimentary flux of 1.1 mg SRP m(-2) day(-1). This is ~10 times higher than the flux of 0.12 mg SRP m(-2) day(-1) obtained from depth integration of vertical SRP profiles measured in the lake, and ~100 times higher than the external flux of 0.014 mg SRP m(-2) d(-1) into the lake (based on catchment area). Field measurements indicated that oxidation of organic matter and mining-related chemicals (ammonium and thiosulphates) may result in increased internal SRP flux from the sediment. Increased P loading in the lake as a result of low-oxygen conditions could change water column total nitrogen/total phosphorus ratios from 27 to 17, consequently changing the lake from being P-limited to be co-limited by N and P. The obtained findings point to possible interaction between the cycles of nitrogen (oxygen consumption) and P (flux from sediment) that may be important for nutrient regulation in mine water recipients.

Seasonal fluxes of phosphate across the sediment-water interface in Edku Lagoon, Egypt

Edku Lagoon is a shallow, brackish, coastal wetland located in the north-western part of the Nile Delta. It suffers from a high level of eutrophication, owing to the heavy load of nutrients, especially phosphorus. The purpose of this paper was to study the flux rates of organic and inorganic phosphorus across the sediment water interface in Edku Lagoon. Both the organic and inorganic phosphorus of surface sediments, pore water and their concentrations in the water just above the sediments were used to calculate the flux rates and to derive the geochemical models. These suggest that, at present, the flux of inorganic and organic phosphorus is from water to sediments via the sedimentation of inorganic particles and organic matter. The results show that phosphorus deposition to the sediments exceeds the rate of inorganic phosphorus release from the sediments to the water column. In a steady state, the rates of organic phosphorus release more or less match the rates of deposition. These reflect the imbalance (accumulation) of phosphorus in the geochemical cycle in the lagoon and its highly eutrophic status. Efforts to control the eutrophication of Edku Lagoon have focused on reducing the phosphorus input.

Evaluation of internal loading and water level changes: implications for phosphorus, algal production, and nuisance blooms in Kabetogama Lake, Voyageurs National Park, Minnesota

Hydrologic manipulations have the potential to exacerbate or remediate eutrophication in productive reservoirs. Dam operations at Kabetogama Lake, Minnesota, were modified in 2000 to restore a more natural water regime and improve water quality. The US Geological Survey and National Park Service evaluated nutrient, algae, and nuisance bloom data in relation to changes in Kabetogama Lake water levels. Comparison of the results of this study to previous studies indicates that chlorophyll a concentrations have decreased, whereas total phosphorus (TP) concentrations have not changed significantly since 2000. Water and sediment quality data were collected at Voyageurs National Park during 2008–2009 to assess internal phosphorus loading and determine whether loading is a factor affecting TP concentrations and algal productivity. Kabetogama Lake often was mixed vertically, except for occasional stratification measured in certain areas, including Lost Bay in the northeastern part of Kabetogama Lake. Stratification, higher bottom water and sediment nutrient concentrations than in other parts of the lake, and phosphorus release rates estimated from sediment core incubations indicated that Lost Bay is one of several areas that may be contributing to internal loading. Internal loading of TP is a concern because increased TP may cause excessive algal growth including potentially toxic cyanobacteria.