Abstract
This study was a laboratory investigation of the rates and mechanisms of the aerobic release of phosphorus and silicon from the sediments of Lough Neagh, Northern Ireland. The topic was chosen as it is important in the lake nutrient-trophic status relationship, in paleolimnological reconstruction, in lake recovery after eutrophication and in Lough Neagh.The investigation was carried out using two main experimental methods. From the variation of release rate with pH, temperature, season, sediment disturbance and concentration in undisturbed sediment-water systems (sediment cores), the sediment release process was inferred. The solid-solution reactions of phosphorus and silicon were more directly characterized in homogeneous sediment-water systems (suspensions).
The release rate of silicon was determined mainly by temperature. pH and the. time since a sedimentary input of biogenic silica were of lesser importance and sediment disturbance and maintenance of low concentration increased the release rate. Sedimentary biogenic silica (diatoms) was the source of the release and diffusion in the sediment pore solution was the rate determining step of the release process. The magnitude of the-9 2 -1 inferred apparent diffusion coefficient (4.9 x 10 em s ato 3 to 25 C), much lower than that expected for molecular di~fusion, was proposed to be due to chemical interaction with a sediment component. A kinetic model for silicon in Lough Neagh sediment. Based on first order dissolution from biogenic silica and parabolic uptake by kaolinite and/or illite, was proposed. Linear concentration-time relationships were observed in the cores and these were proposed to be due to concave pore water concentration-depth profiles which were produced in the lough by water movements and/or the irrigational activities of benthic organisms.
The release rate of phosphorus was determined by pH and temperature. Sediment disturbance and maintenance of low concentration increased the release rate. Desorption of phosphorus from hydrous ferric oxide at increased pH by a ligand exchange reaction was the source of the release and the desorption reaction was the rate determining step of the release process. On the basis of the characterization of the solid-solution reactions of phosphorus, it was proposed that the interactions of phosphorus with Lough Neagh sediment can be abstracted to those of phosphorus with goethite.
The description of the laboratory release processes allowed proposals to be made about the sediment-water interactions of phosphorus and silicon in Lough Neagh, and the field evidence supported the proposals. The chemical behavior of the Fe (lll)-P system accounted for the winter phosphorus concentrations in Lough Neagh and the sedimentary FejP ratio appeared to be a control on the trophic status of lakes in general. The rate determining factor for silicon release in Lough Neagh was proposed to be the irrigational activities of the benthic fauna, specifically, the 4th ins tar of Chironomus anthracinus.
| Date of Award | Sept 1980 |
|---|---|
| Original language | English |
| Supervisor | Brian Wood (Supervisor) |
Keywords
- Lough Neagh
- lake sediments
- sediment
- phosphorus release
- silicon release