Table 4
Chemical parameters of the surface and near-bottom water of Lake Gulbinas during the different study periods (mean values ± SD for May, August and September). Asterisks indicate significant differences (Kruskal-Wallis test, p ≤ 0.05) in each chemical parameter between two study periods, urban (2014–2015) and agriculture (1987–1989).
| Parameter | Period, years | ||||
|---|---|---|---|---|---|
|
|
|||||
| Agriculture | Transitional | Urban | |||
|
|
|
||||
| 1962 | 1987–1989 | 2001–2002 | 2007 | 2014–2015 | |
| Inorganic nitrogen (mg L−1) |
0.4 ± 0.2
0.8 ± 0.0 |
1.3 ± 0.2
3.4 ± 0.3 |
1.3 ± 0.1
1.8 ± 0.1 |
0.8 ± 0.5
2.4 ± 0.2 |
0.7 ± 0.2*
2.3 ± 0.1* |
| Total nitrogen (mg L−1) | – |
2.2 ± 0.2
4.3 ± 0.2 |
1.9 ± 0.1
2.2 ± 0.2 |
1.7 ± 0.4
3.6 ± 0.7 |
1.6 ± 0.2*
3.5 ± 0.1* |
| Inorganic phosphorus (mg L−1) | – |
0.03 ± 0.01
0.04 ± 0.01 |
0.01 ± 0.0
0.03 ± 0.0 |
0.01 ± 0.0
0.06 ± 0.0 |
0.01 ± 0.00*
0.07 ± 0.01* |
| Total phosphorus (mg L−1) | – |
0.06 ± 0.00
0.08 ± 0.00 |
0.05 ± 0.04
0.06 ± 0.01 |
0.03 ± 0.01
0.09 ± 0.02 |
0.03 ± 0.01*
0.1 ± 0.00* |
| Dissolved organic carbon (mg L−1) |
9.6 ± 3.5
9.8 ± 1.9 |
9.4 ± 1.0
9.5 ± 1.4 |
10.5 ± 1.3
10.5 ± 1.0 |
10.4 ± 1.6
10.8 ± 0.4 |
10.3 ± 0.2
10.1 ± 0.5 |
| Biochemical oxygen demand (mg O2 L−1) | – |
4.8 ± 0.1
4.3 ± 0.2 |
5.7 ± 0.1
4.8 ± 0.0 |
7.5 ± 0.9
7.4 ± 1.0 |
6.8 ± 0.4*
9.4 ± 0.5* |
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