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Measuring Phosphorus Release in Laboratory Microcosms for Water Quality Assessment
Published on: July 22, 2019
6.6K
Water depth determines spatial and temporal phosphorus retention by controlling ecosystem transition and P-binding
Zhiyuan Ren1, Jia He2, Haichao Zhao3
1State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, 8 Dayangfang, Beijing 100012, China; National Engineering Laboratory for Lake Pollution Control and Ecological Restoration, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; Institute of Water Environment Research, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
Water Research
|May 14, 2022
Summary
Different mechanisms control phosphorus retention in shallow and deep lake areas. Water depth is key to restoring sediment phosphorus preservation and macrophyte ecosystems, crucial for preventing eutrophication.
Area of Science:
- Environmental Science
- Geochemistry
- Limnology
Background:
- Shallow lakes are more prone to eutrophication than deep lakes.
- The specific geochemical and biogeochemical mechanisms governing phosphorus (P) retention in lakes of varying depths are not fully understood.
- Erhai Lake, a degrading ecosystem, provides a case study for investigating these mechanisms.
Purpose of the Study:
- To investigate the combined phosphorus retention mechanisms in both shallow and deep areas of Erhai Lake.
- To analyze the roles of phosphorus fractions, water depth, metal element distribution, and macrophyte coverage in controlling phosphorus retention.
- To understand how hydrological engineering and water depth variations impact lake ecosystem transitions and phosphorus dynamics.
Main Methods:
- Analysis of phosphorus fractions and P-binding metal elements (Al, Fe, Mn).
- Assessment of water depth, macrophyte coverage, total organic carbon (TOC), calcium (Ca) distributions, and turbulence.
- Examination of historical records and core samples to reconstruct ecosystem changes.
- Quantification of labile organic phosphorus (NaOH25-nrP) and BD-P release from sediments.
Main Results:
- Distinct P retention mechanisms operate in shallow (biogeochemical, influenced by TOC, Ca, turbulence) and deep (physicochemical, influenced by Al, Fe) areas.
- Manganese (Mn) acts as a potential indicator for the release and re-adsorption of redox-sensitive P (BD-P) in deep zones.
- Water depth variation, driven by hydrological engineering, created an intermediate zone favoring macrophytes only at low water levels.
- Increased water levels in the 1990s shifted the ecosystem from macrophyte-dominated to a mixed algal-macrophyte state, reducing stable P fraction accumulation.
- Macrophytes previously preserved P in biomass, but post-deterioration, sediments released significantly more NaOH25-nrP (150%) and BD-P (72%).
Conclusions:
- Water depth is a critical factor for restoring both sediment phosphorus preservation and macrophyte ecosystem health.
- Hydrological engineering projects must consider the ecosystem transition induced by water-level variations to effectively manage phosphorus and prevent eutrophication.
- Understanding the interplay between water depth, macrophytes, and geochemical processes is essential for rehabilitating degraded lake ecosystems.
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