Trophic state index

Résumé

The Trophic State Index (TSI) is a classification system designed to rate water bodies based on the amount of biological productivity they sustain. Although the term "trophic index" is commonly applied to lakes, any surface water body may be indexed. The TSI of a water body is rated on a scale from zero to one hundred. Under the TSI scale, water bodies may be defined as:

oligotrophic (TSI 0–40, having the least amount of biological productivity, "good" water quality);
mesotrophic (TSI 40–60, having a moderate level of biological productivity, "fair" water quality); or
eutrophic to hypereutrophic (TSI 60–100, having the highest amount of biological productivity, "poor" water quality).

The quantities of nitrogen, phosphorus, and other biologically useful nutrients are the primary determinants of a water body's TSI. Nutrients such as nitrogen and phosphorus tend to be limiting resources in standing water bodies, so increas

Source officielle

https://en.wikipedia.org/wiki/Trophic_state_index

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The rates of gross primary production (GPP), ecosystem respiration (R), and net ecosystem production (NEP) provide quantitative information about the cycling of carbon and energy in aquatic ecosystems. In lakes, metabolic rates are often diagnosed from diel oxygen fluctuations recorded with high-resolution sondes. This requires that the imprint of ecosystem metabolism can be separated from that of physical processes. Here, we quantified the vertical and temporal variability of the metabolic rates of a deep, large, mesotrophic lake (Lake Geneva, Switzerland–France) by using a 6-month record (April–October 2019) of high-frequency, depth-resolved (0–30 m) dissolved oxygen measurements. Two new alternative methods (in the time and frequency domain) were used to filter low-frequency basinscale internal motions from the oxygen signal. Both methods proved successful and yielded consistent metabolic estimates showing net autotrophy (NEP = GPP − R = 55 mmol m−2 day−1) over the sampling period and depth interval, with GPP (235 mmol m−2 day−1) exceeding R (180 mmol m−2 day−1). They also revealed significant temporal variability, with at least two short-lived blooms occurring during calm periods, and a vertical partitioning of metabolism, with stronger diel cycles and positive NEP in the upper ∼10 m and negative NEP below, where the diel oxygen signal was dominated by internal motions. The proposed methods expand the range of applicability of the diel oxygen technique to large lakes hosting energetic, low-frequency internal motions, offering new possibilities for unveiling the rich spatiotemporal metabolism dynamics in these systems.

2021

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3D water quality modelling of a eutrophic lake

Christel Marie Chappuis

In an environment subject to anthropogenic pressures, the understanding of lakes is crucial as they are essential for ecosystems and represent a source of the scarce accessible freshwater existing on Earth. Water quality management is especially designed to protect this precious resource and relies on monitoring programs and model simulations. Case study of this project, Greifensee is a small eutrophic lake located in the northern plateau of Switzerland (ZH). For decades, it has been subject to nutrient-‐rich runoff from agricultural activities in its catchments, consequence of the fast population growth in the area. These considerable human-‐related pressures have led to a strong process of eutrophication and significantly altered its water quality. In recent years, although nutrient inputs have been reduced, the lake has still not fully recovered and remains classified as eutrophic. This project developed a 3D coupled hydrodynamic-‐biological model for Greifensee using the software Delft-‐3D from Deltares in the Netherlands. Delft-‐3D has been widely applied in various situations and validated, which makes it an excellent tool for such project. Moreover, the development of the model also relies on two monitoring campaigns, from the Eawag institute and Zürich Kanton. Finally, while the model provides an almost full spatio-‐temporal representation of the processes happening in this lake, final results simulated fairly well the general trends of chlorophyll-‐a, dissolved oxygen, orthophosphate and ammonium in terms of mass content and depth distribution. Understanding the ecological dynamics of a eutrophic lake using such kind of simulation will hopefully contribute, on a longer-‐term perspective, to the better management of the lake towards the recovery of its former ecological status.

2017

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Accelerated Water Quality Improvement during Oligotrophication in Peri-Alpine Lakes

Beat Mueller, Alfred Johny Wüest

Monitoring of four eutrophic Swiss lakes undergoing oligotrophication during more than 25 years (i.e., gradually decreasing nutrient loading, productivity, and associated symptoms of eutrophication) revealed that phosphorus (P) net sedimentation rates (the fraction of a lake's total P content that is buried within its sediments each year) and P export rates (the fraction of the lakes' total P content that is exported via the outlet each year) increased as the lakes' P contents decreased. These findings are of scientific as well as practical interest because they imply that, contrary to the hitherto prevailing view, the P concentration of eutrophic lakes will decrease more than proportional to the reduction of their external P load, and faster than predicted by the linear (eutrophic state-based) models.

Amer Chemical Soc2014

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