CHARACTERIZATION of SPATIO-TEMPORAL

Chem. Monica RADU, Chem. Petra IONESCU, PhD. DEAK György, PhD. Elena DIACU

University "Politehnica" of Bucharest, Faculty of Applied Chemistry and Materials Science, 1 -7 Polizu Str., 011061, Bucharest, Romania National Institute for Research & Development in Environmental Protection Spl. Independentei No. 294, 6th District, Bucharest, Romania

18th Romanian International Conference on Chemistry and Chemical Engineering, September 4-7, 2013, Sinaia, Romania

Study

The Danube River

 Eutrophication of large river systems, as a result of the increasing content of nutrients, is one of the major issues of water quality facing authorities in European countries. In the same time, this phenomena represent a significant problem of environment with profound effects on biodiversity of aquatic ecosystems, still not yet fully understood.  The present study is based on characterization of spatiotemporal trend of nutrient pollution as the Danube River level during one year period, September 2011 - September 2012 for the Calarasi-Braila stretch km 375 – km 175.  Also is evaluated the degree of eutrophication for 10 monitored locations and the relationships between physico-chemical parameters as a general consequence of hydrotechnical works.

 one of the most important inland waterway of Europe;  a natural support for many species of flora and fauna;  the second largest river in Europe, with a length of 2857 km and a drainage area of the hydrographic basin of almost 801 500 km2;

 2414 km navigable - is classified as European artery E80 by European Agreement on Main Inland Waterways of International Importance, which was adopted by the Interior Transport Committee of the UNECE and ratified by the Romania's Government in 1998.

In the area where monitoring stations are located, Danube Commission's recommendations to maintain minimum depths during dry seasons for normal navigation, weren’t met. This is the reason for which were applied hydrotechnical works improve navigation conditions, works that may have a potential negative impact on water quality and biodiversity.

Figure 1 – L2 area - Epurasu Arm 18th Romanian International Conference on Chemistry and Chemical Engineering, September 4-7, 2013, Sinaia, Romania

Sampling    



water samples - monthly from 10 locations (Table 1) of the lower section of the Danube (Figure 2) in period September 2011 (Month 1) - August 2012 (Month 12); nutrients: nitrogen forms - nitrogen (TN), ammonia nitrogen (NH4-N), nitrites (NO2-N), nitrates (NO3-N) phosphorus forms - orthophosphates (PO4-P) and total phosphorus (TP); variation of flow rate (Q); samples - collected from the left bank, right bank and the center and preserved according to standard methods for surface water; indicators - average values.

Reagents and methods    

reagents (Merck) - analytical purity; water flow rate - measurements of level; TP and PO4-P – spectrophotometrically; NO3-N, NO2-N and NH4-N – spectrophotometrically;  TN – titrimetric. The nitrogen and phosphorus forms were analyzed in dissolved status and results being corroborated with the ones from the annual ICPDR reports. All absorbances were measured spectrophotometrically, using a UV-Vis spectrometer Cary 300 Bio, and the values obtained were processed for establishing the average values.

Table 1 – locations of monitoring, their general characteristics and the geographical coordinates of sampling stations Watercourse

Area Bala

Epurasu Island

Lupu Island

Notation of sampling site

Lenght (km)

Average flow (m3·s-1)

347

4654

L2

345

3087

L3

344

1580

L4

343

3514

340

1361

L6

341

219

L7

334

1576

197

2713

L9

196

1645

L10

195

4367

L1

L5

L8

Geographical coordinates Longitude

27˚34'9.549''

27˚37'2.349''

27˚54'27.93''

Latitude

44˚11'24.35''

44˚11'59.10''

45˚4'0.316''


Figure 2 - The map of profiles where the investigation of the Danube water quality


Chemical Speciation  In Danube River, particles released from the decomposition of macrophyte species are partially stored in sediments and in suspended matter, and thus significant amounts of inorganic and organic nutrients are exported in the Nord-West Black Sea.  For characterizing the share of all the forms of nitrogen in total nitrogen, and of the orthophosphates (the most easily assimilated form in the process of photosynthesis) as total phosphorus, were calculated specific weightings which are shown in Table 2, the values were calculated as the average of three measurements.

Table 2 - The weighting of the forms of nutrients

Table 2 shows that the TIN represents about 75 % of TN, being expected that approximately 25 % (organic nitrogen) to be found in suspended matter, respectively in sediments. Therefore, from the point of view of the eutrophication, only 75 % of the TN is bio-available for assimilation and formation of chlorophyll ”a”. In the TIN level, the major share returns NO3-N (about 63 %) and ions NH4-N (33 %), in that balance NO2 -N being situated below the threshold of 4 %. PO4-P have a share of about 40 % in TP. It is emphasized that these values were calculated at level of all locations throughout all the period of investigation.

Nutrients

Weighting (%)

TIN in TN

74,78

NO2-N in TIN

3,73

NO3-N in TIN

62,91

NH4 -N in TIN

33,36

PO4-P in TP

39,55


Results and Discussion

Eutrophication potential, characterized by the ratio TN/TP, has a lower relevance to the investigated sections of the Danube River, aspect highlighted in the Figure 3, where are presented the temporal variations of the concentrations of Chlorophyll ”a”, TN and TP. It is thus observed that higher values of concentrations of Chlorophyll ”a” are recorded during the months May to August, in the same time registering an increase in concentrations of TN. This growth is observed in Figure 4, where there is a temporal variation of nutrients ratio.

Figure 3 - Temporal variation of nutrients and Chlorophyll ”a” concentration

In spatio-temporal terms, the Chlorophyll ”a” presents an increase in concentration for the monitoring area L6, area where the water flow is lower due to construction works in progress (Figure 5). It was found that on the Danube River, loading with nutrients is higher in spring and early summer mainly because of variations in river flow which is increased due to snowmelt. Figure 4 - Temporal variation of nutrients ratio

Figure 5 - Spatial variation of Chlorophyll ”a” concentration.


Interdependences and mutual conditionings between nutrients Variation of Chlorophyll ”a” concentration in function of the water flow presents a slight increase, even that there isn’t a significant correlation (Figure 6), and the ratio TN/TP versus the concentration of Chlorophyll ”a” presents seasonal variability, being increased in warm season and decreased in cold season, fact shown in Figure 7. In Figure 8 is presented the ratio TN/TP which increases with water flow due to the fact that at higher water flows, the share of diffuse pollution increases. Figure 6 - Variation of Chlorophyll ”a” concentration as a function of the water discharge

Figure 7 - Variation of the TN/TP ratio as a function of the Chlorophyll ”a” concentration

Figure 8 - Dependence of N/P ratio on flow rate


Results and Discussion Interdependences and mutual conditionings between nutrients Results presented in Figure 9 a-f show that NO3 -N are increasing with the water flow, while PO4-P are decreasing. Also NO2-N and TN increases with the water discharge, and TP has very low concentrations. The explanation for this differentiation lies in the fact that at high rainfall increases the share of diffuse pollution, and thus the input of nutrients from topsoil.

Also, is observed that the monitored nutrients content have recorded a relatively low variability, mainly dependent by the sampling time (seasonal variability). Depending on the content of nutrients, the river water quality was within the first and second classes, according to Order 161/2006.

(a)

(b)

(c)

(d)

(e)

(f)

Figure 9 a-f - Temporal variation of nutrient concentrations connected with flow water and the respective water quality classes 18th Romanian International Conference on Chemistry and Chemical Engineering, September 4-7, 2013, Sinaia, Romania

Results and Discussion The ratio TN/TP highlights the variation of the eutrophication potential, values obtained for this ratio TN/TP is > 10, what indicates the increasing of eutrophication potential. This ratio can be interpreted from two points of view. Thereby, from the temporal point of view, this ratio decreases in cold season and implicitly a decrease of the potential of eutrophication, as seen from Figure 10. And, from the spatially point of view, it can be observed a decrease from upstream to downstream (comes loaded from upstream), except the location L6, where the flow is small and implicitly, the potential of eutrophication increases. - Figure 11. The hydrological regime of the Danube River on the monitored sector presents a seasonal variability (Figure 12), being recorded maximum flows in period January - February, exception making the monitoring location L6, where the river water flow was very small due to the hydrotechnical constructions. A comparison of this phenomenon observed in L6 location with the other 9 locations monitored is shown in Figure 13.

Figure 10 - N/P ratio depending on time

Figure 12 - Monthly average flow across total section of monitoring

Figure 11 - N/P ratio depending on space

Figure 13 - The monthly flow water of sections monitored


The results of water analyses show that the variation of indicators is due to the actual ecological status of the Danube River as a results of environmental conditions in the period 2011-2012, and not to the hydrotechnical works that occurred during this time. It was found that on the Danube River, loading with nutrients is higher in spring and early summer mainly because of variations in river flow which is increased due to snowmelt, so is a seasonal variation. Based on corroboration of indicators quality data with water flow can be estimated that the potential impact of hydrotechnical works will reflect with priority over the changing of nutrients (N and P forms) transfer balance as insoluble form (suspended solids and sediments). Since both PO4-P, and soluble forms of N are not influenced, it can be expected that hydrotechnic works specified above will not influence directly the eutrophication potential. From the water quality point of view, it can be concluded that the actual ecological status of the Danube in terms of nutrients can be classified between good and moderate, appreciation which enroll in the appropriate range of historical data. The method used for parametric correlation of studied indicators is accessible, easy and provides a global picture of surface water quality. 18th Romanian International Conference on Chemistry and Chemical Engineering, September 4-7, 2013, Sinaia, Romania
