Phytoplankton as an Indicator of Improving Water Quality in the Golden Horn Estuary

Abstract

The variation in phytoplankton community as a response to improving water quality has been studied in the severely polluted Golden Horn Estuary (GHE). Phytoplankton data collected monthly for 4 years and a detailed set of environmental parameters clearly showed the remarkable change in the GHE. The GHE ecosystem did not respond to numerous rehabilitation efforts to improve water quality, unless strict measures were taken to enhance water circulation. The opening of a bridge operating on large buoys and release of high amounts of fresh water from a dam acted as the turning point for the whole system. The weakening of light limitation and anoxia at upper regions is followed by consecutive blooms of different species/groups and resulted in supersaturated dissolved oxygen concentrations and a significant decrease in nutrient concentrations. When compared to the pre-remediation period, average total eukaryotic phytoplankton abundance increased 11-fold in the lower estuary, while the increase in the upper estuary was over 3×10 4 in the post-remediation period. In addition, species richness continuously increased through the study period and community structure showed very strong variability. Since the estuarine ecosystem is controlled by precipitation in the last decade, the increase in anthropogenic/terrestrial inputs following heavy rainfall had adversely affected water quality and phytoplankton.

Potentially harmful microalgae and algal blooms in a eutrophic estuary in Turkey

“…Dinoflagellates showed a wider distribution throughout the study area than diatoms. The third group, including all phytoflagellates, played an important role particularly in the upper part of the estuary, as reported in an earlier work (Tas et al, 2009). A wide distribution and high abundances of mixotrophic flagellates in the upper estuary indicates the suitability of trophic conditions for mixotrophy.…”

“…Considering the seasonality of different harmful species, it appears that spring and summer poses a higher risk for the occurrence of harmful conditions , as reported in previous studies at the region (Tas et al, 2009) and elsewhere (Zingone et al, 2006). Moreover, water discolorations caused by mostly different dinoflagellates and phytoflagellates, were observed in spring and summer depending on the water column stability.…”

“…During monthly samplings in 1998-2002, 17 potentially harmful and/or bloom-forming species were reported by Tas et al (2009), while 23 potentially harmful and/or bloom-forming species in the total phytoplankton community were observed in this study period. The high nutrient concentrations originating from the upper estuary supported a diverse harmful algal species in the LE together with a better mixed upper layer due to Strait's currents and increased light penetration.…”

“…Dense blooms continued until the end of 2001. At times, different groups such as euglenophytes dominated the phytoplankton in this period (Tas et al, 2009).…”

Spring bloom of the raphidophycean Heterosigma akashiwo in the Golden Horn Estuary at the northeast of Sea of Marmara

“…The previous studies on phytoplankton carried out in this study area, when it was extremely polluted, demonstrated that phytoplankton abundance was very low and even they were absent particularly at the upper estuary (Uysal and Unsal, 1996;Tas and Okus, 2003;Tas et al 2009). During rehabilitation of the GHE (after 2000), phytoplankton abundance increased and dense blooms of phytoplankton occurred in spring and summer Tas and Okus, 2011;Tas, 2015).…”