2. Materials and Methods
3.1. Spatial statistics
33 Figure 3.1. Vector scheme of water objects of the Lena Delta and Bykovsky peninsula.
Scale 1: 1 750 000
34 Tab. 3.1 Spatial distribution characteristics of lakes in the study region
Total lakes area [km²]
Number of lakes
Percentage of lake number fraction
[%]
Area of terraces [km²]
Areal fraction of
lake coverage
per region[%]
Percentage of lake areal
fraction[%]
Entire Lena Delta
3408.02 188966 100 23813** 11.7% 100
First terrace
2239.8 132798 70.3 15840.1* 14.1% 65,7
Second terrace
1052.19 52158 27.6 6098.6* 17.3% 30.9
Third terrace
97.86 4010 2.1 1711.6* 5.7% 2.9
BYK*** 16.41 (18.17)****
345 (526)****
172.5*** 9.5%
*According Morgenstern, (2005); ** According Schneider et al., (2009); ***Bykovsky Peninsula according Grosse et al., (2005); **** with adjacent part of Khorogor Valley
Figure 3.2. Percent of total terrace area covered by lakes 0%
5%
10%
15%
20%
Entire Delta 1 Terrace 2 Terrace 3 Terrace 12%
14%
17%
6%
% of Area
35 Figure 3.3. Lakes covered area by terraces. BYK – Bykovsky peninsula
The results show that percentage of the Lena Delta territory covered by lakes is 12%. This areal fraction is considerably higher than, for example, the percent of territory covered by lakes in Russia is near to 2.5% (http://water-rf.ru). Among the Lena Delta terraces, values are particularly high for the first and especially for the second terraces (tab. 3.1, fig.3.2). The percentage of open water covered area on the third terrace is much lower in comparison with the whole Lena Delta. In absolute terms, the greatest contribution to the lacustrine area is due to the first terrace with almost 133 000 of lakes covering a total area of 2240 km². Although 70% of the total amount of lakes is concentrated on this terrace, their areal fraction is somewhat lower at around two-third of the total lake area in the Lena Delta (fig. 3.3, tab. 3.1).
Tab 3.2 Statistical characteristics of the lakes elevation and area by terraces in the Lena Delta
1st terrace 2nd terrace 3rd terrace entire Delta area, m² elev., m area, m² elev., m area, m² elev., m area, m² elev., m
mean 16866.3 4.4 20173.1 8.9 24402.9 20.3 17938.9 5.9
std 114026.4 3.3 267460.4 6.2 136179.4 11.8 171109.1 5.5
median 1550.0 3.8 1625.0 8.0 1600.0 19.0 1575.0 4.6
max 2239.8 1052.19 2584500.
0
64.3 24318275 .0
64.3
min 125.0 0 125.0 0 225.0 0 125.0 0.0
Tab 3.3 Statistical characteristics of lake elevations and surface areas on Bykovsky Peninsula area, m²* elevation, m* area, m² elevation, m
mean 34538.6 8.6 47592.1 10.5
mode 400.0 0.0 400.0 3.1
std 273113.7 10.8 335739.9 12.6
median 2550.0 3.4 2550.0 3.4
0,0 1000,0 2000,0 3000,0 4000,0
1 Terrace 2 Terrace 3 Terrace Entire Delta BYK 2 240
1 052
98
3 390
18 S km²
36
max 5903000.0 40.2 5903000.0 40.2
min 225.0 0 225.0 0
* including adjacent part of Khorogor Valley
As described in the methods, this study only considers lakes with an area of more than 100 m², because of technical and methodical limitations. Average lake size in the study region is about 1.8 ha, while maximum size is up to 25 km² (tab. 3.2). The high standard deviation of ±17.1 ha is also reflected in a considerably lower median size of 1.6 ha. The third terrace is characterized by the largest (24.4 ha) and the first terrace by the smallest mean size of lakes (16.9 ha). However, the median size is relatively similar across all terraces. Standard deviations of lakes areas are highest for the second terrace two times higher as for other terraces moreover it is quite high when considering lakes of the entire delta.
Figure 3.4. Lakes mirror size in the Lena Delta and Bykovsky Peninsula. a – number of lakes in each group relatively to lakes area. B - lakes covered area relatively to lakes area (1 <0.001 km²; 2. 0.001 – 0.25 km²; 3. 0.25 - 1 km²; 4. 1 – 5 km²; 5. 5 – 10 km²; 6. > 10 km²)
General distribution of lakes area over the entire Lena Delta is displayed in the Fig.3.4 Grouping by area for analysis is based on Bolshiyanov et al. (2013) with adding a special group of lakes with area under 1000 m². Majority of lakes in the delta 117623 have an area between 0.25 - 1 km² (fig.3.4a). Herewith only a minor part of lakes can be considered as large, with an area more than 1 km². Fig. 3.4b shows that although quantity of ponds and small lakes in the first group stays on the second place, an area which is covered by this group is least in comparison with other groups. For the second group the number of lakes correlates well with a territory occupied by this group. It should be noted that small number of relatively major lakes plays a great role in the
69617 117623 1796
421 40 461
a
<0.001 km² 0.001 - 0.25
0.25 - 1 1 - 5
> 5 km²
37,57
1452,19
838,54 739,17 209,79
130,79
b
<0.001 km² 0.001 - 0.25 0.25 - 1 1 - 5 5 - 10
> 10 km²
37 water area distribution. For example number of lakes in the third group is about four times more than in the fourth group, but values of filed areas are very similar.
Distribution territory covered by lakes relatively to terraces is considered (fig.3.5) according grouping of lakes area based on the work of Boike et al. (2013), where lakes divided on three groups according area: polygonal ponds, polygonal lakes, thermokarst lakes. In this work one more category is added: large thermokarst lakes, with an area of more than 1 km². The major area is occupied by thermokarst lakes (third group) for total area as well as for the first and the third terraces. Moreover area of the third group exceeds a total area of other groups, for the third and first terraces as well as in general. The second terrace differs from the other terraces, because major part of the entire lake area is occupied by large lakes with an area more than 1 km². However, figure 14 demonstrates that the largest amount of all lakes is situated on the first terrace, across all lake size classes.
Figure 3.5. Distribution of territory covered by lakes relatively to 4 lakes size groups and terraces. 1. Area
<0.001 km² (polygonal ponds); 2. 0.001 – 0.01 km² (polygonal lakes); 3. 0.01 - 1 km² (thermokarst lakes);
area>1 km² (large thermokarst lakes)
The most common lake size all over the delta generally as well as separately for each terrace are polygonal lakes according to classification of Boike et al. (2013), which have an area between 1000 m² and 1 ha (fig. 3.6). Especially on the first and particularly on the second terrace they account for around a half of all lakes, with 45.8% and 52%, respectively (fig. 3.6). Water bodies from the third and the fourth groups with an area of more than 1 ha (thermokarst lakes) are relatively sparse (fig. 3.6), only 29541 from 188968 lakes in total within the delta, according to 16%. However, as it was mentioned before they are responsible for the majority of areal lake coverage in the delta (fig.3.5), where 3060.9 out of 3389.89 km² are covered by these lake types, corresponding to 90%
0 500 1000 1500 2000 2500
1 2 3 4
lakes area, km²
groups terrace 1 terrace 2 terrace 3
38 areal fraction. In contrast, small water bodies like ponds with an area between 100 m² and 1 ha occupy the smallest territory despite of their number, where a huge amount of polygonal lakes with 48% of all lakes in delta corresponds to a relatively small areal fraction of only 9%. The shape and the size of polygonal ponds are defined by ice- wedge structures (Boike et al., 2013).
Figure 3.6. Number of lakes by size. Groups: 1. area <0,001 km²; 2. area between 0,001 and 0,01 km²; 3.
0,01 and 1 km²; 4. area>1 km²
Figure 3.7. Distribution of lakes by area on Bykovsky Peninsula A: Total lakes area for each group; B:
Number of lakes in each group. Groups: 1. area <0,001 km²; 2. area between 0,001 and 0,01 km²; 3.
0,01 and 1 km²; area>1 km²
Lakes on Bykovsky Peninsula were considered together with Lena Delta. Figure 3.7a shows that the distribution of lakes by groups on the base of covered area as well as distribution of groups by quantity of water bodies in each group is similar to allocation in Lena Delta (fig. 3.5; 3.6). On the other side relative quantity of polygonal lakes is higher comparatively to Lena Delta terraces.