Thank you Ehsan, however, can we measure this using remote sensing? I mean is there any standard which tells us how much aquatic vegetation is good for a lake and the threshold beyond which the lake can be termed as eutrophicated?

Yes ocan color sensors (or other sensors in the visible) can allow the chlorophyll concentration, as well as, turbidity index, to be retrieved. These two parameters are directly related to the eutrophisation state of surface waters (eutrophisation can also be a natural event, for instance due to intense phytopplankton blooms, which can be due to natural or anthropogenic causes).

Thanks Prof Hubert. However I wanted to know if there is some published material regarding the parameters and thresholds based on which a lake can be stated as eutrophicated. Also, the lake I am talking about is an inland freshwater lake covering an area of only 4.5 sq km. So as far ocean colour sensor are considered they are very low resolution and please advice if they are even good for studying these inland wetlands.

The US/EPA has published specific ranges of chlorophyll concentrations defining levels of eutrophication between oligotrophic and eutrophic.

Was that the US/EPA ranges of chlorophyll concentrations (to defining level of eutrophication) can be use globally, or just site specific (in US)?

A eutrophic lake is one with an excessive growth of algae. Algae contains significant amounts of Chlorphyll a which can be measured from remote sensing. The difficult question is at what threshold does the lake turn eutrophic, it may require some fieldwork to determine the point where the water turns from oxygen surplus to deficit if you could determine the % of Chlorophyll at this turning point you could estimated for other lakes (im pretty sure this must have been done)

Some definitions are given in the following paper:

Klemas,V. (2012). Remote sensing of algal blooms: An overview with case studies. Journal of Coastal Research, 28, 34-43.

Water eutrophication has become a worldwide environmental problem in recent years, and understanding the mechanisms of water eutrophication will help for prevention and remediation of water eutrophication. In this paper, recent advances in current status and major mechanisms of water eutrophication, assessment and evaluation criteria, and the influencing factors were reviewed. Water eutrophication in lakes, reservoirs, estuaries and rivers is widespread all over the world and the severity is increasing, especially in the developing countries like China. The assessment of water eutrophication has been advanced from simple individual parameters like total phosphorus, total nitrogen, etc., to comprehensive indexes like total nutrient status index. The major influencing factors on water eutrophication include nutrient enrichment, hydrodynamics, environmental factors such as temperature, salinity, carbon dioxide, element balance, etc., and microbial and biodiversity.

It has been shown that the eutrophication or red tide occurs when N concentration in water reaches 300 μg/L and P concentration reaches 20 μg/L. Richardson et al.(2007) reported that exceeding a surface water mean TP threshold concentration of 15 μg/L causes an ecological imbalance in algal, macrophyte and macroinvertebrate assemblages as well as slough community structure in the Everglades areas. Therefore, it is considered that a threshold zone (12~15 μg/L) of TP may be more realistic and protective for all trophic levels.

Although there are many different assessment parameters, the concentrations of total nitrogen and phosphorus are the two basic ones. Cheng and Li (2006) used total nutrient status index (TNI) to assess eutrophication status of lakes. The calculation of total nutrient status index is as follows:

TNI=∑WjTNIj

Wj=r2ij/∑r2ij

where, TNI is the sum of indexes of all nutrient parameters, TNIj is the TNI of j parameter, Wj is the proportion of j parameter in the TNI, and rij is the relation of chlorophyll a (Chla) to other parameters. The available parameters concerned include total nitrogen (TN), total phosphorus (TP), Chla, dissolved oxygen (DO), chemical oxygen demand by K2MnO4 oxidation method (CODMn), biological oxygen demand (BOD5), etc., and TN, TP and Chla are selected for calculating the TNI (Cheng and Li, 2006).

The criteria of surface water quality for lakes or reservoir is given by

CNEPA (Environmental Protection Agency of China) Environmental Quality Standard for Surface Water. GB 3838-2002. 2002. (Available from: http://www.cc.ln.gov.cn/lncj./shownews.asp?)

Therefore you may classify the water bodies by the above formuleas and then you can match the color of your RS with various euthropication levels to varify the concentration. That means you need to have a one year field work to finally come up with right conclusions.

The biomass of phytoplankton algae in surface waters can be measured as ’chlorophyll-a-like pigments’ by remote sensing. Enhanced levels of these pigments, compared to natural background concentrations of chlorophyll-a, are an indication for

eutrophication.

By knowing the primary productivity of water body,if the primary productivity of water body is >2500mgc/cubic meter/day the water turns into eutrophic