poster - International Conference of Agricultural Engineering

About 5.2 billion m3 water is diverted each year from the Yellow River to irrigate this
area (Qu et al., 2003) During the last 10 years, the average water use in the Hetao
area was greatest from April to November (Fig. 2). Although from January to April no
irrigation was carried out, there was still some wastewater discharge into the lake (Fig.
2). A study on impacts of various irrigation scenarios on the groundwater dynamics was
carried out by Xu et al., (2010).
2.2. Sampling, analytical and statistical methods
From 2005 to 2010 (Table 1), twenty-one geo referenced sites with a grid of
about 2×2 km 2 and covering about 85% of the open water, were marked in the
lake. Sites were chosen according to the distribution of pollution sources and
hydrodynamic characteristics of the lake. Water samples were collected at a
depth of 20 cm with polyethylene or glass bottles according to different water
quality indicators, then stored at controlled temperature and analyzed for
chemical, physical and biological parameters, within 24 h.
Table 1 . Sampling times in the WL from 2005 to 2010
Sampling time 2005 2006 2007 2008 2009 2010
January (frozen lake) 8th 7th 14th
May 10th 16th 12th 18th
June 28th 13th 19th 7th 5th 23th
July 20th 19th 16th 8th 27th
August 27th 12th 22th 13th 10th 24th
September 15th & 30th 12th 19th 12th 16th 26th
October 19th 12th 23th 23th 14th 23th
Data was analyzed with excel 2003 and with the Kriging Geostatistical technique of
Geostatistical Analyst Arc GIS 9.3. Maps of concentration for different water quality
indicators were created to show spatial distribution.
3. Result and discussion
3.1. Temporal variability of parameters
Some parameters showed a clear seasonal variability which was repeated over the
years (Fig. 3), while others, namely total nitrogen (N), chlorophyll a and electrical
conductivity, appeared to decrease with time. In contrast, suspended solids, COD and
dissolved organic increased with the years, showing a probable increase in urban
wastewater discharge into the lake. The marked season variability shown in figure 3
suggests a great influence of irrigation on water quality of the lake. In fact, values of total
N (TN) and total phosphorus (TP) were significantly higher in the winter compared with
other seasons. The greater organic load in winter was reflected on a higher
concentration of suspended solids as well as COD. Together, these parameters may
increase the risk for eutrophication of the lake.