Phytoplankton dynamics and renewable energy potential induced by the environmental conditions of Lake Burullus, Egypt.

Abstract

The research evaluates the spatio-temporal phytoplankton community structure and abundance along with the pollution sources and the lake bioenergy potential, primarily in order to better understand the interplay of the environmental factors affecting them in inland coastal waters. Burullus Lake, located in the north of the Nile Delta of Egypt, is selected as a case study area. Field investigations along with sampling of lake water from 55 sites in the period 20-25 September 2020 are performed. The physicochemical analysis is carried out for the lake water bathymetry, temperature (T°C), pH, salinities (total dissolved solids (TDS) and electric conductivity), and nutrient contents (nitrate, nitrite, ammonia, and phosphate). Phytoplankton identification and biological analysis are used to document the taxa and abundance along with their contents of chlorophyll-a, protein, carbohydrates, and lipids. Then, the trophic index (TRIX), along with the total phytoplankton biomass and the energy potentials, is estimated. Statistical analyses were appraised for the univariate summary statistics, correlation analysis, regression analysis, multivariate statistical analysis including principal component analysis (PCA), and clustering techniques (both geographic position and the k-means clustering) which were conducted using the PAST 4.03 package. The geostatistical modeling of the ordinary kriging implemented in the ArcGIS 9.3 package was appraised for mapping the studied parameters. Results clarified ranges with wide variations for the water depth of 0.90-2 m (av. 130.5 cm), T°C of 26.6-30.20°C (av. 28.3 °C), alkaline pH of 7.78-8.92 (av. 8.6), and TDS of 0.3-17.09 (av. 4.33) gm/l. Ranges of nutrients (mg/l) are also widely varied with nitrates of 0.44-8.36 (av. 3.5), nitrites of 0.004-7.45 (av. 0.4), ammonia range of 0.03-8.54 (av. 1.4), and phosphate of 0.1-4.9 (av. 0.9). A much-diversified phytoplankton community showed maximum counts of 1005 × 103 units.l-1 to a minimum of 340 × 103 units.l-1 for a total of 145 taxa from 61 genera and six classes typically of freshwater forms. The largest biomass (3.06 × 10-3 kg/m3) and energy potential (19.87 × 10-3 kWh/kg) marked the downstream area of the Brimbal Canal, followed by the area located in front of the eastern Burullus and El-Gharbiya drains, which exhibited 2.76 × 10-3 kg/m3 and 17.96 × 10-3 kWh/kg, for the biomass and the energy potential, respectively. Geographic position and k-means clustering techniques distinguished three homogenous classes of marked intra-class variations. PCA analysis distinguished three principal components summed for about 95% of the variations. Intense environmental pollution at the drain downstream areas is indicated by many fish mortality occurrences that were related to the blooms of the toxic Microcystis aeruginosa among the cyanophyte species, and also due to the dominance of the Euglena spp. and Phacus spp. of the Euglenophyceae, which assimilate lots of organic matters in these areas. Lake water movement in the form of turbulent flows and mixing regimes is affected by wind direction and the amount of flows from the sea drains. The estuarine Nile canal has a great effect on the water's physicochemical properties, particularly the nutrient loads, inducing the phytoplankton composition and abundance, total biomass, and the biological contents hence the energy potential. Nutrient load from discharged water from drains was a major contributor to raising the total algae counts and their corresponding contents of the carbohydrates, lipids, proteins, and the chlorophyll-a, which arranged in decreasing order of influence. Phytoplankton dynamics are mostly linked to climatic, hydrologic fluctuation of the drain water flows, and hence, the associated nutrient load discharged from land use changes to fish farms and the related agricultural practices south of the lake. The adopted integrated analyses proved promising, which confirmed the combined effects of environmental factors on lake pollution and the bioenergy potentials.