Bengt Boström

Exchange of phosphorus across the sediment-water interface

In this article, principles of phosphorus retention and phosphorus release at the sediment-water interface in lakes are reviewed. New results and hypotheses are discussed in relation to older models of phosphorus exchange between sediments and water. The fractional composition of sedimentary phosphorus is discussed as a tool for interpretation of different retention mechanisms. Special emphasis is given to the impact of biological, particularly microbial, processes on phosphorus exchange across the sediment-water interface and to the significance of biologically induced CaCO3 precipitation to phosphorus retention in calcareous lakes.

Bioavailability of Different Phosphorus Forms in Freshwater Systems

The recent literature on the bioavailability of different forms of P in freshwater systems is reviewed. Bioavailable P is defined as the sum of immediately available P and the P that can be transformed into an available form by naturally occurring processes. Methods used to estimate the bioavailable P pool, which vary between studies largely depending on the time perspective applied, are critically evaluated. Most studies on particulate P aim to determine the potentially available P pool. Potential bioavailability of particulate P is normally analysed in bioassays with algal yield determinations and the available P fraction is characterized from interpretations of results of sequential chemical extractions. NaOH-extractable P is in most studies the most algal-available P fraction. For soil samples and tributary water particulate matter, NaOH-P has often been found to be equal to algal extractable P. In other studies depletions of NaOH-P have accounted for the algal P uptake, but only a minor proportion of the fraction has been utilized. Organic P in lake water particulate matter and bed sediments of eutrophic lakes can also be algal-available to a significant extent.Studies on the bioavailability of dissolved P have often been concerned with immediate availability, or the minimum amount of available P. Such studies need other types of experimental design and normally assays with radiotracers are used. Immediately available P is frequently found to be less than P chemically assessed as dissolved reactive P (DRP) at low (< 10 µg DRP·l-1) concentrations. However, immediate availability may also approach or exceed DRP concentrations, especially at higher concentrations. Potential bioavailability, assayed as for particulate P, may generally render higher bioavailability than P assayed as immediately available. Large fractions of dissolved P remain unutilized and are primarily found in the high molecular weight fraction of dissolved P.

Phosphorus in Sediments — Speciation and Analysis

Characterization of sediment phosphorus is commonly based on sequential chemical extractions, in which phosphorus is supposed to be selectively removed from different compounds in the sediments. The first extraction schemes were designed to quantify discrete chemical or mineralogical compounds. As extraction schemes have been tested on different sediments, several systematic errors have been detected and the schemes have been modified and simplified accordingly. Other chemical extractions or treatments have attempted to determine phosphorus bound to particles with a certain strength or binding energy, the purpose being to determine the labile, loosely bound, exchangeable, mobile or algal-available fraction of sediment phosphorus. All extraction procedures yield operationally defined fractions and cannot be used for identification of discrete phosphorus compounds. The many methodological modifications make it necessary to be cautious when comparing results from the literature in this field.

Different patterns of phosphorus release from lake sediments in laboratory experiments

The phosphorus release from surface sediments of eight lakes, mainly shallow lakes in agricultural areas, was studied in laboratory batch experiments with additions of acetate and/ or nitrate. The lake sediments could be separated into three categories. Some sediments did not release phosphorus under any conditions. The second category showed a high phosphorus release rate when acetate was added, in order to stimulate bacterial activity and oxygen consumption. The addition of nitrate, only, stabilized the redox conditions and prevented phosphorus release. This pattern followed the classical theories of Einsele and Mortimer. The third sediment category released phosphorus up to some level which remained constant throughout the experiment, and was independent of acetate and/or nitrate additions.Several extraction procedures and adsorption-desorption experiments were performed in order to characterize the sediment phosphorus and thus explain the different behaviours of the three sediment categories.

Interstitial water concentrations of phosphorus, iron and manganese in a shallow, eutrophic swedish lake—Implications for phosphorus cycling

Abstract The seasonal variation of ferrous iron, manganese and phosphate concentrations in the interstitial water (0–30 cm), ETS activities in the surface sediments (0–10 cm) and water quality properties were studied in 1983, in the polymictic, eutrophic Lake Vallentunasjon, Sweden. In addition, phosphorus release experiments using intact sediment cores were performed in the laboratory. Ferrous iron was generated to the interstitial water in two layers, namely in the surface sediments and at ≈ 10–30 cm down in the sediment. Manganese in a reduced form was mobilized in a single layer close to the sediment-water interface, while phosphate was generated at a sediment depth of 3–8 cm in shallow areas (2 m) and in deeper sediment layers ( > 25 cm ) at a water depth of 4m. A mobilization of both ferrous iron and phosphate in the interstitial water mainly during periods of high water temperature and ETS activity in the surface sediments, suggests that microbial processes were involved in the liberation. Reduction of ferric iron-phosphorus complexes could account for only a minor proportion of the phosphate mobilization in the interstitial water as demonstrated by the P/Fe molar ratios. In accordance, ferric iron formation, caused by ferrous iron diffusion from deeper sediment layers and oxidation at the sediment surface, could only partially retain the diffusive phosphate flux towards the sediment-water interface. The phosphorus retention capacity appears to be low in Lake Vallentunasjon sediments, even at high bottom water oxygen concentrations.

Coupling between benthic biomass of Microcystis and phosphorus release from the sediments of a highly eutrophic lake

Variations in microbial biomass and activity in the sediments of hypereutrophic Lake Vallentunasjon were followed during a period of 5 years. The data were compared to the calculated release of phosphorus from the sediments during the same period. A strong co-variation was found between biomass of Microcystis, heterotrophic bacterial activity in the sediments and internal phosphorus loading. These parameters exhibited mainly a declining trend during the investigation period. A pronounced stability of the sediment chemistry, including the fractional composition of the sediment phosphorus, during the studied period indicates that microbial activity affected the phosphorus release from the sediments. Calculations of the percentage of sediment bacteria that was associated to the mucilage of Microcystis colonies imply, together with the specific bacterial production, that Microcystis in the sediment stimulates bacterial production. In the highly phosphorus-saturated sediments of Lake Vallentunasjon this would ultimately lead to an increased release of phosphorus from the sediment. Lake Vallentunasjon does not follow the common pattern of recovery after reduction of external phosphorus loading. The large biomasses and long survival of Microcystis in the sediment are probably important reasons for the delayed recovery of the lake.

Phosphorus Exchange Between Sediment and Water in Lake Balaton

A cooperative Hungarian-Swedish research program on Lake Balaton was initiated in 1979. The studies primarily concerned the exchange of phosphorus (P) between sediments and lake water. This contribution summarizes results from laboratory experiments on P release from sediments, and determinations of the distribution of P forms in the sediments. These results are, in combination with other available data, used to discuss and revise an existing model of phosphorus cycling in Lake Balaton.

Simultaneous Nitrification and Denitrification in Lake Erken Sediments

The nitrification-denitrification sequence in surface sediments was studied in situ using 15N-technique. The rates of denitrification were independent of whether ammonium or nitrate was added as labelled source. The denitrification subsesuentlto nitrification decreased from July to December from 9 to 1 mg.m−2.d−1 of N2. The balance between the two processes under various conditions is discussed. A comparison with observed changes in the nitrate content of the lake water during the same period is made.