Summer Phosphorus Research Articles

New and recycled primary production in an oligotrophic lake: Insights for summer phosphorus dynamics

Primary production that is supported by new inputs of nutrients from outside the system is distinct from production that is supported by remineralization of nutrients within the system. We applied the concept of new production to Mirror Lake, New Hampshire, and our view of P dynamics in this lake was altered dramatically. New production during midsummer put a large demand on P in surface waters, removing 37 µmol P m−2 d−1. Without new inputs of P, the P content of surface waters would drop to zero in < 1 month. There is, however, a slight increase, not a decrease, in P content of surface waters during summer stratification. Inputs to surface waters during summer months must, therefore, be large. We now believe that higher than average P loading to the lake occurs in summer, despite low runoff inputs.

Utility of Layer Aeration for Reservoir and Lake Management

ABSTRACT Layer aeration (U.S. Pat. 4,724,086) is a process that manipulates the heat and oxygen mass of a thermally stratified water body to create a desirable physical/chemical depth profile. Unlike destratification, layer aeration creates an aerobic cool, isothermal layer(s) bounded by several functional thermoclines. The process also enhances stratification and habitat structure. Unlike hypolimnetic aeration, the method redistributes available heat and oxygen and avoids the potentially adverse effects of nitrogen super-saturation, increased diffusional transport to the epilimnion, and metalimnetic anoxia. This paper discusses the chemical, physical, and biological effects of layer aeration in two Connecticut lakes. In Mulberry Reservoir, layer aeration reduced summer phosphorus accumulation by over one-third of pretreatment levels and improved hypolimnetic oxygen levels. Application to Glen Reservoir lowered ferrous iron concentrations and improved dissolved oxygen concentrations. Although further rese...

Phosphorus inactivation in a eutrophic lake by the direct addition of ferric aluminium sulphate changes in phytoplankton populations

SUMMARY. 1. Reduced total phosphorus concentrations in the summer which followed the addition of iron aluminium sulphate to White Lough failed to reduce significantly the phytoplankton. which continued to be dominated by Oscitlatoria agardhii var. isothrix Skuja.This species was present throughout the 4 years studied, forming over 50% of the algal volume in 80% of samples. In contrast, species which occurred principally in the summer months were found to be severely curtailed when sediment release of phosphorus was suppressed.2. The phosphorus: carotenoid ratio was used to assess the extent of phosphorus limitation because laboratory studies on O. agardhii var. isothrix showed that this ratio was a much beter indicator of cell phosphorus content than the phosphorus: chlorophyll a ratio. Reduced summer phosphorus concentrations in White Lough caused a transition from intermittent to continuous phosphorus limitation rather than a proportional reduction in the summer phytoplankton.3. Reduced autumn grazing pressure by Daphnia hyatina Leydig allowed large algal populations to develop in the winters following phosphorus reduction despite a 50% decline in total phosphorus. The combination of increased winter phytoplankton and lower total phosphorus reduced soluble reactive phosphorus concentrations to less than 5,μg P l−1 which in turn curtailed the spring diatom pulse.

A mathematical model of seasonal and spatial variation in phosphorus concentrations in lake memphremagog, Quebec

A mathematical model was formulated to predict monthly and spatial changes in total phosphorus concentrations in the epilimnion of Lake Memphremagog, a long abd narrow lake transversing the Canada-United States border. Computer experiments were designed to elucidate phosphorus loading mechanisms and to assess the effects of tertiary treatment and increased cultural eutrophication. The initial model, based purely on two equations of advective transport, showed a rapid exponential decrease in total phosphorus from the source to the outlet. The pattern was similar to observed trends but predicted values were too low. Possible discrepancies due to (1) convectional mixing, (2) release of phosphorus from the lake sediments, and (3) particle size effects were examined. Characteristics of the model were evaluated using correlation, a ‘predictability’ index, and simple differences between predicted and observed values. Simulations assuming 25% and 100% mixing of the water column predicted total phosphorus levels twice and 1.5 times greater than observed values, respectively. Correlations and predictability were low. Simulations assuming phosphorus release from the sediments (based on temperature and dissolved phosphorus functions reported in the literature) greatly improved the correspondence between measured and predicted values. Correlation and predictability were twice as high for the convectional model and three to ten times as high as for the initial run. Overall correlation and predictability also increased from the initial model if large particle size and rapid settling were assumed. Tertiary treatment resulted in a 49% reduction near the source and a 24% reduction at the far end of the lake. Little reduction occurred in the summer. A 20% increase in cultural eutrophication indicated an annual average increase of 15% could be expected. Summer phosphorus levels increased 25% indicating the effect was concentrated in the growing season. Sensitivity analysis showed that phosphorus loading rate was more important than either sedimentation or phosphorus release rates. Halving each rate resulted in a 35, 34 and 17% change in average total phosphorus concentration.

Sludge dewatering in a conventional plant with phosphorus removal-I: Analysis of additional costs

The aim of this research is to assess the differences in quantity and quality of sludges produced in a conventional activated sludge plant, modified for phosphorus chemical removal. Tests were carried out at the Cesenatico sewage treatment plant, where in summer phosphorus is removed simultaneously to the biological process with the aid of aluminium or ferrous sulphate. Characteristics of the sludge produced with or without phosphorus removal were compared. The sludge was then dewatered by a centrifuge and a filter-press on pilot scale and many tests were carried out under different operating conditions. In this part, the plant's most important performances are discussed with regard to phosphorus removal efficiency, sludge production, characteristics and dewaterability. The experiments showed that phosphorus could be removed up to residual concentration of 1.6 mg 1 −1 without detrimental effects on the biological process, with an increase of sludge production of 21 and 36% using aluminium or ferrous sulphate respectively. On the basis of experimental results a costs analysis was carried out to assess the costs for phosphorus removal, including the additional ones for sludge conditioning, dewatering and cake transport to landfill. It results that additional costs vary from 3290 to 6380 Lit per capita per year (29–54%). The higher costs refer to smaller plants (50,000 inhabitants), in which aluminium sulphate is used and sludge dewatered by centrifuge. The use of ferrous rather than aluminium sulphate allows savings of 1300–1600 Lit per capita per year.