RESEARCH ARTICLE
Abiotic factors controlling the seasonal and spatial patterns of
phytoplankton community in the Tigris River, Turkey
M. Varol
1
|
B.
Ş
en
2
1
Faculty of Fisheries, Department of Basic
Aquatic Sciences, Inonu University, Malatya,
Turkey
2
Faculty of Fisheries, Department of Basic
Aquatic Sciences, F
ı
rat University, Elaz
ığ
,
Turkey
Correspondence
Memet Varol, Faculty of Fisheries, Department
of Basic Aquatic Sciences, Inonu University,
Malatya, Turkey.
Email: mvarol23@gmail.com; memet.
varol@inonu.edu.tr
Funding information
The Scientific and Technological Research
Council of Turkey, Grant/Award Number:
107Y216
Abstract
In this study, the seasonal and spatial dynamics of the phytoplankton community in the Tigris
River (Turkey) and the relationships with environmental factors were analysed. Bacillariophyta
were the most important taxonomic group both in terms of abundance and species number.
Phytoplankton abundance increased from winter to autumn associated with a decline in dis-
charge and an increase in nutrient concentrations and water temperature. There was a down-
stream increase in phytoplankton abundance and species number in the river. Similar spatial
and seasonal patterns were observed in chlorophyll
a
concentration and phytoplankton abun-
dance. Redundancy analysis and correlation analysis revealed that chemical variables, mainly
nutrients were the most important abiotic factors controlling phytoplankton abundance in the
Tigris River.
KEYWORDS
abiotic factors, chlorophyll
a
, phytoplankton, redundancy analysis, Tigris River
1
|
INTRODUCTION
In terms of changes in species composition and density, seasonal and
spatial patterns of phytoplankton community variability have been
the subject of many studies (Bazzuri, Gabellone, & Solari, 2010).
Although phytoplankton dynamics have been studied extensively in
lakes and reservoirs, considerably less research has focused on under-
standing the species composition and community structure of phyto-
plankton in streams and rivers (Bazzuri et al., 2010; Piirsoo, Pall,
Tuvikene, & Viik, 2008; Reynolds, 1988; Wu, Schmalz, & Fohrer,
2011). Therefore, more studies are needed to clarify general patterns
in phytoplankton community structure in relation to different river
types and hydrological regimes (Salmaso & Braioni, 2008).
Factors regulating phytoplankton abundance and diversity in
rivers may be physical (light, water temperature), chemical (inorganic
nutrient concentrations), hydrological (discharge, water residence
time), or biological (grazing, competition). Hydrological factors such
as discharge or water residence time are thought to be of greater
importance to planktonic development in rivers than in lakes
(Hamilton, Lavoie, Ley, & Poulin, 2011; Pace, Findlay, & Lints, 1992;
Wu et al., 2011). During high river discharge periods, phytoplankton
biomass decreases, and relatively few species dominate phytoplankton
communities, whereas biomass and species diversity tend to be higher
during low discharge periods (Sullivan, Prahl, Small, & Covert, 2001;
Tavernini, Pierobon, & Viaroli, 2011; Wehr & Descy, 1998). However,
some studies have concluded that river phytoplankton is more strongly
regulated by nutrient availability. A significant positive relationship
between river phytoplankton abundance or biomass and total phos-
phorus concentration has been observed in several studies (Basu &
Pick, 1996; Hamilton et al., 2011; Wu et al., 2011). Phytoplankton is
also susceptible to light limitation due to high turbidity caused by
resuspension of solids in turbulent waters (Zalocar de Domitrovic,
Devercelli, & Forastier, 2014). Clearly, many factors may control the
development of phytoplankton in rivers, and there is no clear consen-
sus as to which factors regulate river phytoplankton communities
(Tavernini et al., 2011; Wu et al., 2011).
The Tigris River is one of the most important transboundary
rivers in Turkey. Until now, only one study (Varol &
Ş
en, 2014)
documented the phytoplankton composition of the river within the
borders of Turkey, but this did not provide detailed data of the sea-
sonal and spatial variations of the phytoplankton community. Thus,
this represents a significant gap in the understanding of river phyto-
plankton structure and environmental factors regulating phytoplank-
ton development.
In the present study, we assessed the seasonal and spatial
dynamics of the phytoplankton community in the Tigris River and
analysed the main physical, chemical, and hydrological factors control-
ling the phytoplankton community structure. The river was regularly
Received: 9 January 2017 Revised: 7 September 2017 Accepted: 13 September 2017
DOI: 10.1002/rra.3223
River Res Applic
. 2018;
34
:13
23.
Copyright © 2017 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/rra
13
monitored for a period of 1 year at seven different stations spread over
500 km.
2
|
MATERIALS AND METHODS
2.1
|
Study area
The Tigris River is a transboundary river in Turkey with a catchment
area of about 57,614 km
2
and a length of 1,900 km, of which
523 km is inTurkey. TheTigris River originates in theToros mountains
of Turkey and continues to Cizre, where it forms the Turkish
Syrian
border before entering Iraq. There are two connected reservoirs in
the upper part of the main section of the Tigris River in Turkey: the
Kralk
ı
z
ı
and the Dicle (Varol, Gökot, Bekleyen, &
Ş
en, 2012).
The highest flows occur from February to April, and the lowest
flows occur from August to October. The river discharge varies consid-
erably at different locations and increases towards its downstream
region with the input from its tributaries. The average annual flow of
the river in Diyarbak
ı
r and Cizre has been determined to be 28.3 and
211.8 m
3
/s, respectively (Varol et al., 2012).
Although the climate of the Tigris Basin is continental, it is more
similar to that of the Mediterranean region, comprising hot and dry
summers and milder winters than those of the Eastern Anatolia Region.
The annual total rainfall along the river during the study period
decreased in the downstream direction, whereas the annual air tem-
perature increased in the downstream direction. The highest annual
total rainfall value was 611.1 mm in Maden (Station 1), whereas the
lowest annual total rainfall of 294.1 mm was in Cizre (Station 7). About
82% of the annual precipitation occured between October and April.
The annual mean air temperature ranged from 14.6 °C (Station 1) to
21.8 °C (Station 7) (Varol et al., 2012).
2.2
|
Sampling
The locations of the sampling stations are shown in Figure 1. Phyto-
plankton and water samples were collected from seven stations along
the Tigris River at monthly intervals between February 2008 and
January 2009. One sampling station (Maden) was located upstream
of Kralk
ı
z
ı
and Dicle dam reservoirs, while six stations (E
ğ
il, Diyarbak
ı
r,
Bismil, Batman, Hasankeyf and Cizre) were located downstream of the
reservoirs. For the taxonomic analysis of phytoplankton, samples were
collected with a plankton net. For the quantitative analysis of phyto-
plankton, river water samples were collected in 250 ml polyethylene
bottles. All samples were preserved with formaldehyde in the field.
Water samples for hydrochemical analyses were also taken simulta-
neously with phytoplankton sampling. Concurrently, at each station,
water temperature (WT), dissolved oxygen (DO), pH, and electrical
conductivity (EC) were measured in the field with a portable
multimeter. In this study, river discharge data were only available for
two gauging stations
Diyarbak
ı
r (Station 3) and Cizre (Station 7).
2.3
|
Analysis
For quantitative phytoplankton analysis, phytoplankton cells were
counted with an inverted microscope (Olympus CKX
41), using
Utermöhl's sedimentation method (Utermöhl, 1958). Unicellular,
colonial, and filamentous taxa were counted as individual cells. For
qualitative analysis, the samples were examined with an Olympus
BX51 microscope.
FIGURE 1
Sampling stations location on the Tigris River [Colour figure can be viewed at wileyonlinelibrary.com]
14
VAROL AND
Ş
EN