Seasonal Variation of Temperature, pH, and Dissolved Oxygen Concentration in Lake Rosu, Romania

Gheorghe T. Romanescu

Cristian C. Stoleriu

University ‘‘Al.I.Cuza’’ of Iasi, Faculty

of Geography and Geology,

Department of Geography, Iasi,

Romania

Research Article

Seasonal Variation of Temperature, pH, andDissolved Oxygen Concentration in Lake Rosu,Romania

Lake Rosu (Red Lake) in the Hasmas (Curmaturii) Mountains was created by the natural

barrage of the Bicaz River, a tributary of the Bistrita River, in 1837. Measurements in

2009 were performed, using the Hach Lange multi-parameter meter, to determine

physical and chemical parameters of water. Basic parameters for the analysis of the

ecological conditions were assessed: temperature, dissolved oxygen and pH. Surface

water temperature was 2–38C lower in summer and higher in winter (except during the

period of ice cover) compared with spring and autumn data. At depths <7 m, the

temperature showed constant values of 4–68C with nearly the same values in autumn

and spring. pH values lied between 7 and 8 at the surface as well as in depth. During the

summer, pH values decreased from 8 to 7 in the depth. In spring and autumn, the pH

values remained constant and identical. The value of dissolved oxygen was good

throughout the year. The surface reached values of 10 mg O2/L annually at depths

>7–8 m with a limit of 0 mg O2/L. Lake Rosu becomes a mountain aquatorium which

attracts many tourists. However, its degree of pollution is extremely low.

Keywords: Ecological factors; Limnoecology; Physical and chemical parameters; Water quality

Received: March 20, 2011; revised: January 15, 2012; accepted: November 17, 2012

DOI: 10.1002/clen.201100065

1 Introduction

Lake Rosu (Red Lake) is the best-known Romanian aquatorium

formed following a slippage in the terrain, which barred the course

of the Bicaz River.

Armed with extremely exact equipment of the latest generation

and personnel qualified to carry out measurements of great delicacy,

a series of measurements was done to ascertain the physical-

chemical parameters of Lake Rosu.

Although references in the Romanian literature are extremely

rare, they are nevertheless relevant, with a special examination of

some aspects, which can be attached to those looking at the physical

and chemical characteristics of the lake water [1–13]. Useful data

about temperature, pH, and dissolved oxygen have also been taken

from huge international literature [14–37].

The research attempts, on the basis of our interdisciplinary work,

to delimit, for the first time, the thermal stratification of the water

based on physical and chemical characteristics.

1.1 Geographical location

Lake Rosu is located in the Central Group of the Eastern Carpathians,

within Hasmasu Mare (Haghimas) Massif (Fig. 1). Its main tributaries

are the Oii, Verescheu, Licos, and Suhard brooks.

A natural barrage lake, Lake Rosu, was created in the summer of

1837, when, following a period of abundant rain, a landslide dilu-

vium detached from Ghilcos (Ucigasu) Mountain and created a bar-

rage in the course of the River Bicaz, a tributary of the Bistrita.

Behind the wave of the landslide, a lake was created. This lake

inherited the tree trunks of the forest covering the sliding slope [4].

The geographical coordinates of the lake are: 468470000N latitude in

the southern sector, 4684703700N latitude in the northern sector,

258470000E longitude in the north-western sector and 2584703000E

longitude in the eastern sector [3].

In the Carpathian Mountains, several lakes were formed as a result

of landslides which created a barrage in the course of the rivers

(Crucii, Balatau, Dracului, Iezerul Sadovei, Bolatau, etc.), but the

best-known and most studied is the Lake Rosu [2, 23].

The name ‘‘rosu’’ (red) comes from the fact that at sunrise, the

sun’s rays directly fall on the reddish clays of the western slope

(Piciorul Licos) and are reflected on the relatively clear water of this

aquatorium [9].

2 Materials and methods

In order to have a complete picture of the limno-ecological con-

ditions, 17 measuring and sampling points were chosen. The points

chosen covered the whole of the bathymetric and morphological

spectrum of the lake. The Hach Lange multi-parameter meter was

used for a rapid analysis of physical and geographical factors.

Advanced digital HQd portable meters offer highly accurate

measurements and exceptional reporting capabilities in a rugged

IP67-rated waterproof housing. These multi-parameter meters

Correspondence: Dr. G. T. Romanescu, University ‘‘Al.I.Cuza’’ of Iasi,Faculty of Geography and Geology, Department of Geography,Bd.Carol I, 20A, 700505, Iasi, RomaniaE-mail: [email protected]

236

� 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com Clean – Soil, Air, Water 2013, 42 (3), 236–242

measure pH, dissolved oxygen or biochemical oxygen demand (BOD)

using LDO technology, temperature, etc. utilize the rugged, ultra, or

standard probes. Rugged Probe: IP68-rated SS body and polymer sensor

shroud, a steel-sheathed cable and waterproofness to 30 m. Ultra Probe:

higher accuracy and faster response time compared to Standard Probe.

Standard and Ultra pH Probe: ZeonorTM body and built-in ATC. Hach’s

LDO and LBOD Probes: patented luminescence DO technology. LBOD

Probe: equipped with a stirrer for fastest results.

Measurements were carried out both on the surface and on the

bottom meter by meter. All measurements were repeated in every

season, spring, summer, autumn, and winter. In this way, sufficient

data was obtained for the correct analysis regarding the variation in

living conditions of the water table.

At the same time, the sampling points were chosen especially in

order to register variations for water from streams.

The positioning of the sampling points was carried out by GPS.

Measurements at the same point could not always be carried out as a

result of the existence of aquatic currents on the surface, but more

especially of those at the bottom. For this reason, seasonal measure-

ments did not always attain the same bathymetric values. Sampling

took place in the daytime between 10 am and 4 pm.

3 Results

The thermal values of the pH and the dissolved oxygen were regis-

tered for the entire vertical section of the lake basin: from the

surface to a maximum depth of 10.5 m (Fig. 2).

The lowest depths were found at the two extremities, where the

Suhard si Oii streams are ebbing and formations of the fan-delta type

are formed. Maximum depths were found at the river mouth,

where the present River Bicaz is formed. In reality, the sector with

the greatest depths corresponds to the confluence between the two

brooks, a favorable location for the formation of one eddy current,

which agitates the bottom of the lake basin. As a consequence of

their origins, the lateral sections of the ‘‘bowl’’ present depths,

which are still high from the shore, especially on the rocky, steep,

western slopes [13].

On the surface, the maximum temperature of 17.88C could be

measured in summer and continued until autumn. The minimum

temperature (0.138C) in wintertime favored the formation of ice

bridges, which could reach dimensions of 20–70 cm. In winter

2009, the maximum dimension was 24 cm. In spring, a minimum

temperature of 48C was registered (Fig. 3).

At a depth of 10 m, the maximum temperature was 68C with a

minimum of 48C. The temperature maintained between 4 and 68C.

From the thermal point of view, Lake Rosu behaves like a dimictic

aquatorium with a direct thermal stratification in summer and the

opposite in winter.

Figure 1. Geographical location of the LakeRosu on the territory of Romania.

Figure 2. Bathymetric map of Lake Rosu.

Seasonal Variation of Temperature, pH, and Dissolved Oxygen in Lake Rosu 237


On the surface, the pH values rose to a maximum of 8.5 in spring-

time with a minimum of 6.5 in wintertime. The values usually

maintained between 7 and 8.2 (Fig. 4). At a depth of 10 m a maximum

of pH 7.6 is maintained in autumn and a minimum of 7.2 in spring-

time. Overall, the values maintained between 7.2 and 7.8.

The quantity of dissolved oxygen from the lake water depended on

temperature, circulation, water quality, etc. [24, 30] (Fig. 5). On the

surface, a maximum of 10.6 mg O2/L has been registered in

wintertime. The minimum produced in summer was 7 mg O2/L.

The values for spring and autumn were intermediate, between

7 and 10 mg O2/L. A lack of dissolved oxygen started at a depth of

8 m. At the bottom of the lake dissolved oxygen was totally lacking.

4 Discussion

The fact that Lake Rosu is located in the interior of a mountainous

depression of small dimensions, almost completely closed, favors the

frequent appearance of thermal opposites as a consequence. This is

the reason why the values of water temperatures do not connect

correctly with the air temperatures at the meteorological stations

nearby. Unfortunately, there is no meteorological station in the

mountainous depression to make the correlations between the

mean water value and water temperature values.

On the surface, the maximum temperatures are achieved in spring

and summer. These are specific to the central zones, where lateral

water tributaries originating from the brook (Fig. 6a and b) are

lacking. Temperature in summertime and spring follows this trend

and are related. The maximum temperature of the water is low

(2–38C) compared to air temperature.

In autumn, temperature fluctuated between values of 6 and 88C(Fig. 6c). In wintertime, bridges of ice are formed (Fig. 6d) and could

reach dimensions of up to 70 cm. The dimensions of the ice bridges

were usually uniform on the whole surface of the lake. This fact is

favored by the existence of fossilized tree trunks spread across

almost the entire surface of the lake.

In summer, the temperature fell relative quickly to a depth of

3.5 m. The thermal homogenization of the water determined the

existence of relatively uniform temperature. At 3.5 m, the tempera-

ture was 13–148C. Below this depth, the temperature dropped rap-

idly with a minimum value of 68C at the greatest depth.

In spring, this tendency is respected. The only difference lied in the

fact that the temperature was lower, approximately 1–28C, com-

pared with summer.

Figure 3. Seasonal distribution (vertical) ofthermal values in Lake Rosu (samplecharacteristics).

238 G. T. Romanescu and C. C. Stoleriu


An extremely interesting fact featured the vertical homogeni-

zation of temperature in autumn. The temperature maintained

values of 6–78C from the surface until 5 m depth. At depths

>10 m, it reached a maximum of 88C. Homogenization could be

by coincidence of the existence of the greater debits of brooks during

autumn, some local winds which came down from the slopes, and

the disappearance of vegetation, which results in an almost perfect

homogeneity of the water mass.

In winter, heat homogeneity is lower and was between 0 and 48C.

Up to a depth of 1 m, the temperature remained at the value of 08C as

a result of the influence represented by the ice bridge. At the depth of

3.5 m, temperature rose relatively quick to 2–2.58C. Between 3.5 m

depth and the bottom of the lake (10.5 m) the temperature was 48C.

Thus, the phenomenon of thermal inversion appeared to be more

obvious in winter and less intense in autumn. In summer and spring

the normal phenomenon of lower values varied by depth.

At the surface, the pH value varied between 6.5 and 8.5. In winter

and springtime the values were almost identical, and fluctuate

between 6.4 and 7.5; the lowest values are recorded in wintertime.

A slight change on the vertical of about 5–6 m could be noticed

in summer, autumn, and springtime. The range of annual variation

in depth of pH values is about 1.6. The lowest pH measured was 6.9 in

winter at 3 m depth.

The only difference in pH could be seen during winter compared

with the other seasonal thermal pH values. The pH values in winter-

time are maintained at about 7. During spring, summer, and

autumn, the pH decreased slightly with depth, in winter it increased,

reaching values of 7.5. The highest value of 8 could be measured at

sampling point 12. Sampling point 12 shows maximum depth and

two currents come together and determine the existence of the

Suhard and Oii streams.

The pH of the water is found to be slightly alkaline throughout the

year with ranging from 7.5 to 8.0 (Fig. 7). Very rarely, in certain

conditions, the pH value fell within the circumneutral category.

The existence of dissolved oxygen is essential for the water table

[14, 15, 18]. Even given this, Lake Rosu shows no extraordinary

biological diversity resulting from the fact that its existence is

relatively new.

The highest values of dissolved oxygen could be registered in

winter, when water, at its coldest, produces the most important

distortions of the thresholds. In summer, the values are reduced,

although they are sufficient for the maintenance of optimum eco-

logical conditions [19, 33, 35]. These values are specific to mountain-

ous water, especially rivers. The high value of dissolved oxygen is due

to the streams feeding the aquatorium. This gives rise to currents,

which clear the surface water.

Between summer and winter there is an important difference of

dissolved oxygen values once depth increases. In summer, at a depth

of 4 m, the values fall beneath 4%. In winter, these values fall at a

depth of 7–8 m. For certain intermediary seasons (spring and

autumn) the lowest values begin at a depth of 6 m.

In the sectors with the greatest depths and where the meeting

of two currents produce two streams (Suhard and Oii), the most

important distortion of the threshold limits occur. In this case the

thresholds are greatly expanded to values between 4 and 7 m. It

should be noted that in this sector the water is being continuously

agitated (with the exception of the appearance of ice bridges) by

the oars of tourist boats, which provide boat rides in this area.

Figure 4. Seasonal distribution (vertical) ofthe pH in the waters of Lake Rosu (samplecharacteristics).



Throughout the whole year, a good correlation with the three

values (temperature, pH, dissolved oxygen) can be observed. They

drop from the surface to depths in three seasons: spring, summer

and autumn (Fig. 8). These values are unbalanced in wintertime,

especially by the presence of ice bridges, which are formed every year

and can remain for between 20 and 80 days per year. The extremely

long existence of ice bridges is due to the formation of inverse

thermal conditions in winter, which favor the installation of a

table of cold air at the bottom of the depression [1, 2].

Ice bridges are relatively uniform with a size proportional to the

entire surface of the lake and with values, which can vary between

15 and 70 cm, the most frequent being those limited to 20 cm. The

size depends on the thermal values of the air and their duration.

They are larger in years in which thermal inversions take place,

which led the minimum temperature to values of �378C.

5 Conclusions

Lake Rosu falls into the category of mountain lakes. It offers the

picture of an aquatorium with unusual characteristics as a result

of its genesis and an unusual geographical position. Its location

within a closed mountainous depression, enclosed by high ridges,

Figure 5. Seasonal distribution (vertical) of dissolved oxygen in Lake Rosu(sample characteristics).

Figure 6. Vertical distribution of temperature, pH and dissolved oxygen in(a) springtime, (b) summertime, (c) autumn, and (d) wintertime.

Figure 7. Vertical distribution of annual temperature average, pH anddissolved oxygen in Lake Rosu.



determines the appearance of a microclimate, which influences the

thermal parameters.

From the thermal point of view, Lake Rosu is directly influenced by

the specific climate in the mountainous area of which it forms a part.

It functions as an aquatorium with direct thermal stratification

in summer and the opposite in winter (a dimictic lake).

The main tributaries, and those of an intermittent nature, empty

an important quantity of water, a fact, which makes circulation,

especially at the surface layer, extremely important. For this reason,

a weak stratification of pH values is also present. The water of the

lake is usually alkaline.

The quantities of dissolved oxygen from the water of Lake Rosu are

specific to the water of mountain streams and not to some closed

lakes. This fact is due to the feeding by intermediate streams and the

elimination of water, which enter the main river in this sector.

Between thermal values, pH and those of dissolved oxygen, in the

framework of the four seasons, there is a conjunction with variations

in the decrease or increase in temperature and depth. The only

season in which these values are unbalanced is in winter. The

principal reason is the existence of ice bridges.

Acknowledgments

Our thanks go to the Geo-archaeology Laboratory within the Faculty

of Geography and Geology, University Alexandru Ioan Cuza of Iasi,

which provided the instruments and carried out the processing of

the data. The Ministry of Education and Research paid for the

measurements and the publication through CNCSIS grant no. 426,

for the period 2007–2010, with Professor Gheorghe Romanescu, PhD

as a grant director.

The authors have declared no conflict of interest.

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Seasonal Variation of Temperature, pH, and Dissolved Oxygen Concentration in Lake Rosu, Romania

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