Statistical Analysis of Nutrient Content in Skadar Lake Waters

1. STATISTICAL CHARACTERISTICS OF NUTRIENT CONTENTS DATA SERIES IN THE WATERS OF SKADAR LAKE AND ITS MAIN TRIBUTARIESPavle Djuraskovic, Aleksandar KojovicHydrometeorological Institute, Podgorica, S&M Balwois, Ohrid 2006

2. STATISTICS OF NUTRIENTS DATA IN SKADAR LAKE WATERS INTRODUCTION • Skadar Lake is very important object because of its ecological characteristics, economical potential and anthropogenic impact along the catchment area. • Waters of Skadar Lake are very interesting in scientific sense, because of kind, amount and direction of chemical and biological transformation of water pollutants are very different during the year and from point to point of Lake. • Data of many-years water quality investigations by HMI were been used in this paper. • In focus was statistical distribution and other characteristics of available data series of nutrient contents in Skadar lake waters.

3. Period Nitrates Ammonia Phosphates Crnojevića river 1985-2005 1986-2005 1986-2005 Moraca 1985-2005 1986-2005 1985-2005 Bojana 1985-2005 1986-2005 1985-2005 Skadar lake Kamenik 1990-2005 1990-2005 1990-2005 Plavnica 1985-2005 1986-2005 1985-2005 Middle part of the lake 1998-2005 1999-2005 1999-2005 Ckla 1990-2005 1990-2005 1990-2005 STATISTICS OF NUTRIENTS DATA IN SKADAR LAKE WATERS WORK METHOD • Used data are from database of Hydro-meteorological Institute, Podgorica • Measurement places shown on Figure 1.: -Tributaries : Moraca (Grbavci village), Crnojevica river (Hyd. station) -Outflow: Bojana (Fraskanjel village) -Skadar Lake: Kamenik, Plavnica, The Middle of Lake, Ckla • Nutrients : Nitrates, Ammonia, orto-Phosphates • Measurement period

4. STATISTICS OF NUTRIENTS DATA IN SKADAR LAKE WATERS

5. STATISTICS OF NUTRIENTS DATA IN SKADAR LAKE WATERS WORK METHOD • Used statistical elements: - Basic statistical characteristics, - Correlation between appropriate measurement places, - Testing of average differences, - Determination of type of data distribution.

6. STATISTICS OF NUTRIENTS DATA IN SKADAR LAKE WATERS RESULTS AND DISCUSION • According the average, content of nutrient is low (especially at the pelagial of Lake and Bojana). In first part of the period, concrete values very often were below detection limit. Nitrates • The content of nitrate was the highest in the Crnojevica river. • Data series shown relative big variation, the smallest for Moraca, and approximately central way of distribution, with smaller or bigger deviation. • The difference of average was tested for pairs: Moraca-Kamenik, Plavnica and Ckla; Plavnica-Middle of Lake and Ckla; Middle of Lake-Ckla. The difference wasn’t statistical significant only for pairs Moraca-Plavnica and the Middle of Lake-Ckla. • The correlation between content of NO3 in pelagial was strong to very strong. The correlation between Moraca and Plavnica was established. The correlation between Crnojevica river and Kamenik was of low significance and negative. • The testing of distribution type shown that tributaries, especially Crnojevica river submit to the normal distribution, with very good confirmation. Bigger or smaller deviation shown data for Skadar Lake (negative arc) and Bojana (positive arc).

7. STATISTICS OF NUTRIENTS DATA IN SKADAR LAKE WATERS RESULTS AND DISCUSION Ammonia • Values of central tendency measure, standard deviation and variation coefficient shown very low concentration, and very high variation of data. The content of NH4 was equalized at all localities. The Middle of Lake shown the opposite results from other places. • The testing shown that the difference of average wasn’t statistical significant for pairs: Moraca-Plavnica, the Middle of Lake, Ckla, and Ckla-Bojana. • The strongest correlation was established for lake pelagial waters. The strong correlation between Moraca and all lake places (littoral and pelagial) point out significant influence of Moraca’s waters on Lake. The influence of Crnojevica river waters isn’t significant, considering the ammonia. The correlation between Ckla and Bojana was strong, too. • The testing of distribution type shown mainly irregular distribution, because many values are under detection limit in the first part of period. In the rest part, the distribution was approximately normal, with positive arc.

8. STATISTICS OF NUTRIENTS DATA IN SKADAR LAKE WATERS RESULTS AND DISCUSION o-Phosphates • The data shown that the Crnojevica river was main donor of phosphates in the Skadar Lake water. The central tendency measures shown that the data are classified asymmetrical, on the right side, especial for Lake pelagial and Bojana river. The most frequent data value were bellow detected limit. The variation of data was relative big, the biggest for pelagial and the smallest for Crnojevica river. • The average difference of data for the Middle of Lake and Ckla wasn’t statistical significant, established shown by testing. Also, the average difference of data for Crnojevica river and Kamenik was statistical significant. • Phosphates in Crnojevica river have strong correlation with those at Kamenik. The correlation between waters of Moraca and Kamenik was low and negative, but the same correlation between Ckla and Bojana didn’t exist. The highest (very strong) correlation existed again between different pelagial places. • The data for rivers submitted to the normal distribution, the best for Crnojevica river. But, the data for Lake shows deviation from normal distribution, especial for the Middle area.

9. STATISTICS OF NUTRIENTS DATA IN SKADAR LAKE WATERS Figure 2.1. Figure 2.2. Figure 2.3. Figure 2.4 F igure 2.5. Figure 2.6. .

10. Figure 3.1. Figure 3.2. STATISTICS OF NUTRIENTS DATA IN SKADAR LAKE WATERS Figure 3.3. Figure 3.4. Figure 3.5. Figure 3.6.

11. Figure 4.1. Figure 4.2. STATISTICS OF NUTRIENTS DATA IN SKADAR LAKE WATERS Figure 4.3. Figure 4.4. Figure 4.5. Figure 4.6.

12. STATISTICS OF NUTRIENTS DATA IN SKADAR LAKE WATERS Figure 2.7. Figure 3.7. Figure 4.7.

13. STATISTICS OF NUTRIENTS DATA IN SKADAR LAKE WATERS CONCLUSION • The analyses of many-years data shown that content of nutrients in Skadar Lake waters was relative low, in measuring period, but in tributaries was higher. • The variability of the data in Lake waters was bigger then in tributaries. That fact, together with another, show low influence from tributaries to nutrient contents and Lake waters, during vegetation period. • The causality of Moraca’s waters and Plavnica area, for NO3 and NH4, as well as Ckla area and Bojana’s waters, for NH4, was established by testing of average difference. • The strong correlation between pairs Crnojevica river-Kamenik (for PO4), Moraca-Plavnica (for NO3, NH4) and Ckla-Bojana (for NH4) was established at the confidence level 0.05. • The data of nutrient contents in rivers are classified by normal distribution. The fitting of experimental curve was quit good for Crnojevica river, but for Bojana was some worse. A big deviation of data from normal distribution for Skadar Lake waters, was established. • Many data values below detection limit, in first part of the period, had influenced on the statistical characteristics and type of distribution.

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