Phytoplankton blooming in Lake Qarun in relation to chlorophyll a measured by fluorometric and spectrophotometric techniques

Abstract

Lake Qarun is a closed saline lake in the northern part of El-Fayoum Depression of Egypt. The objective of this work is to give a complete picture of lake biotic factors to alarm on dinoflagellates blooming phenomenon and to compare between chlorophyll a values measured by Fluorometer and Spectrophotometer. Monthly patterns in Chlorophyll a concentrations were measured during the period from May 2015 to April 2016, using two different methods; by fluorometric and spectrophotometric techniques. Phytoplankton species in Lake Qarun are heterogeneously distributed all over the year; dinoflagellates were the main dominant group, chlorophyll a frequently accumulated as distinct peak (336 μgl-1) in July 2015. The phenomenon of dinoflagellated blooming of Prorocentrum micans, Gymnodinium lantzschii and Exuviaell aapora that turning the lake water to brown in colour, is recorded annually. The two methods used in detection of chlorophyll a during this work are accurate and simplified bring the picture in Lake Qarun. Actually, results of fluorometer are more sensitive and higher than those of spectrophotometer. In fact, high salinity, agricultural drainage water from drains and aquaculture activities turned the lake to variable, sensitive aquatic ecosystem, affecting significantly on phytoplankton structure and blooming dynamics determination. There is no record of toxicity effects or mass fish mortality in the lake due to this phenomenon.

Trophic state and potential productivity assessment for Qaroun Lake using spatial techniques

“…The chlorophyll levels ranged between 51.9 and 335.8 µg/L which exceeded the standard chlorophyll-a levels for the lake’s water, where the normal levels are ranging between 4.49 and 69.50 μg/L (Saeed & Mohammed, 2012 ). It is worthy mentioned that the chlorophyll levels are proportionally increasing during the last 8 years where in 2008, the average chlorophyll-a concentration was 201.5 µg/L, while in March 2015, the recorded CHL-a average reaches its maximum value 336 μg/L showing a blooming phenomenon (Hussein et al, 2008 ; Zaher & Ibrahim, 2018 ). High CHL-a concentrations give alarm to increase lake eutrophication where chlorophyll- a is positively correlated to enriched nutrient concentrations which forms a blooming, poor water quality and the presence of harmful species of algal.…”

“…Napiórkowska-Krzebietke et al ( 2016 ) recorded Mugil cephalus and Solea spp as dominant fish types, while Tilapia zillii and Engraulis encrasicolus were found in the east and the middle of the Lake. Qaroun Lake drainage system is consisting of twelve drains; the main drains are El-Bats and Al-Wadi (Mehanna, 2020 ; Zaher & Ibrahim, 2018 ). It receives a massive amount of wastewater reaching 450 mm 3 /year from agricultural sector, sewage water, and excessive nutrient salts from aquaculture drainage dominating the southern part of the lake (Elsayed et al, 2021 ).…”

Characterization of cyanobacterial isolates from freshwater and saline subtropical desert lakes

“…Salinity in Lake Qarun varies between 14.24 and 39.8 g/l (Abd El-Aal et al 2020). The main phytoplankton fractions in Lake Qarun have been found to belong to diatoms, dinoflagellates, and Cyanobacteria (Abd El-Karim 2012;Zaher and Ibrahim 2018). Cyanobacterial fraction constituted about 26.8% of the total phytoplankton cell concentration in Lake Qarun (Flefil and Mahmoud 2021).…”