Purpose In this study, the effects of the distribution of phosphorus fractions, enrichment, and type of bottom sediment of small retention reservoirs on the internal supply of phosphate were determined in aerobic and anoxic environments under simulated resuspension conditions. Materials and methods Tests were carried out on undisturbed sediment cores from twelve test sites at five small retention reservoirs in Poland. The potential internal phosphate supply capacity of the bottom sediments was evaluated by determining the equilibrium phosphate concentration at the zero point (EPC0) in aerobic and anoxic environments. The sediment cores were subjected to resuspension (10 min) and resedimentation (110 min) using different concentrations of P-PO43- in the solution. Based on the concentrations of P-PO43- in the solution at the beginning (Ci) and end (Cf) of the exposure, EPC0 was determined as the zero point of the linear function Ci-Cf = f(Ci). The obtained EPC0 equations and the mean phosphate concentration in the reservoir water were used to estimate the potential internal phosphorus load [mgP m-2 d-1] under simulated sediment resuspension conditions. Results and discussion The internal phosphate supply capacity of the sediments of the small reservoirs was affected by the enrichment in phosphorus, its mobile fractions, and organic matter and was only indirectly related to granulometry. The EPC0 values ranged from 0.049 to 0.344 mgP dm-3 under aerobic conditions and from 0.220 to 4.84 mgP dm-3 under anoxic conditions. Under anoxic conditions, the EPC0 values were 1.5 to 16 times higher than those obtained under aerobic conditions. The estimated internal loads of the resuspended sediments ranged from 58 to 326 mg m-2 d-1 under aerobic conditions and from 385 to 4638 mg m-2 d-1 under anoxic conditions. Anoxic conditions significantly influenced the capacity of sediments to release phosphate, except for clay sediments rich in calcium (high proportion of AP = 38% (apatite phosphorus), high Ca/P = 135 and high Ca/AP = 351). Conclusions The distribution of phosphorus and organic matter is important, but not a decisive factor in the internal supply. The high ratio of metals to P fractions limits an internal load under anoxic conditions. Three types of sediments were identified in terms of internal supply risk, including two types (I and II) associated with a high risk of enhanced trophic degradation of the corresponding reservoir. In reservoirs with favourable conditions for phytoplankton growth, the internal load may be higher than that in reservoirs with high-risk sediments (types I and II).

The importance of phosphorus fraction distribution, enrichment, and type of bottom sediment for internal loading in small retention reservoirs

期刊论文
发表日期：

2026年1月14日

查看全文

Lilianna Bartoszek,
Piotr Koszelnik,
Małgorzata Miąsik

摘要

Purpose

In this study, the effects of the distribution of phosphorus fractions, enrichment, and type of bottom sediment of small retention reservoirs on the internal supply of phosphate were determined in aerobic and anoxic environments under simulated resuspension conditions.

Materials and methods

Tests were carried out on undisturbed sediment cores from twelve test sites at five small retention reservoirs in Poland. The potential internal phosphate supply capacity of the bottom sediments was evaluated by determining the equilibrium phosphate concentration at the zero point (EPC₀) in aerobic and anoxic environments. The sediment cores were subjected to resuspension (10 min) and resedimentation (110 min) using different concentrations of P-PO₄^3- in the solution. Based on the concentrations of P-PO₄^3- in the solution at the beginning (C_i) and end (C_f) of the exposure, EPC₀ was determined as the zero point of the linear function C_i-C_f = f(C_i). The obtained EPC₀ equations and the mean phosphate concentration in the reservoir water were used to estimate the potential internal phosphorus load [mgP m^-2 d^-1] under simulated sediment resuspension conditions.

Results and discussion

The internal phosphate supply capacity of the sediments of the small reservoirs was affected by the enrichment in phosphorus, its mobile fractions, and organic matter and was only indirectly related to granulometry. The EPC₀ values ranged from 0.049 to 0.344 mgP dm^-3 under aerobic conditions and from 0.220 to 4.84 mgP dm^-3 under anoxic conditions. Under anoxic conditions, the EPC₀ values were 1.5 to 16 times higher than those obtained under aerobic conditions. The estimated internal loads of the resuspended sediments ranged from 58 to 326 mg m^-2 d^-1 under aerobic conditions and from 385 to 4638 mg m^-2 d^-1 under anoxic conditions. Anoxic conditions significantly influenced the capacity of sediments to release phosphate, except for clay sediments rich in calcium (high proportion of AP = 38% (apatite phosphorus), high Ca/P = 135 and high Ca/AP = 351).

Conclusions

The distribution of phosphorus and organic matter is important, but not a decisive factor in the internal supply. The high ratio of metals to P fractions limits an internal load under anoxic conditions. Three types of sediments were identified in terms of internal supply risk, including two types (I and II) associated with a high risk of enhanced trophic degradation of the corresponding reservoir. In reservoirs with favourable conditions for phytoplankton growth, the internal load may be higher than that in reservoirs with high-risk sediments (types I and II).