Lake Jingpo is a typical alpine barrier lake. Further, it is world’s second largest such lake. It is located in northeast China (N 43°46´-44°18´, E 128 °30’-129°30’); the lake area is in Heilongjiang province, but most of the catchment area is in Jilin Province (Fig. 1). The total area of the Lake Jingpo catchment measures 11,664.67 km2, of which 79.8% is in Jilin Province (9,312.39 km2), while the remaining 20.2% is in Heilongjiang Province (2,352.28 km2). Lake Jingpo is in a deep mountain valley with an elevation range of 339.17-1,260.7 m. Some of this area is covered by extinct volcanos. The lake itself was formed by several volcanic eruptions that intercepted the Mudanjiang River, which is both the outflowing and largest inflowing river.
Lake Jingpo catchment is located in a temperate continental monsoon climate zone. It is characterized by windy and rainless weather in spring, concentrated rainfall in summer, a cool climate, short autumn, and cold winter. There is a large temperature difference between daytime and nighttime. The annual average temperature is 3.5 °C, while the highest is 38 °C, and the lowest is − 40.1 °C. Annual average precipitation measures 549 mm, which is normal for a temperate humid climate. The distribution of precipitation varies significantly during the year. For instance, summer precipitation (June-August) accounts for approximately 61% of the annual total. There are only short durations of sunshine, while the wind direction is stable, the three-dimensional climate characteristics are remarkable, and temperatures vary with altitude. The snowfall period lasts from October to March of the following year; the average snowfall period is 172 days. It usually begins to freeze during mid-to-late October and gradually begins to melt in March of the following year.
The literal meaning of Lake Jingpo translates as “lake as clear as a mirror.” This reflects that its water quality was once very good. Lake Jingpo is still a tourist attraction and a shining pearl in northeast China. As recently as 2012, it was designated as a “good water quality lake” by the Ministry of Ecology and Environment, China. However, the recent expansion of local farmlands, economic growth of the upstream area, and vigorous development of tourism have caused nutrient concentrations in the lake’s water to rise. This is especially evident during the summer rainfall flooding period (July to September), when the concentrations of both total nitrogen (TN) and total phosphorus (TP) can exceed 2 mg/L and 0.2 mg/L, respectively. Similar, TN and TP concentrations also begin to peak during the spring freshet period. However, they do not reach the same levels seen during the summer rainfall flooding period. The deteriorating water quality at Lake Jingpo has caused concern among various environmental protection departments. As such, significant efforts will be made to protect Lake Jingpo over the next few years.
Lake Jingpo has a water area of 91.5 km2 and a water storage capacity of 11.8 × 108 m3. The water exchange period totals 116.7 days (3.13 times per year). The annual variation characteristics of Lake Jingpo’s water level are as follows: The highest water level mainly occurs during the main rainfall period (from August to September), while the lowest water level mainly occurs from March to April, the annual average water level is 347.95 m, the highest water level is 354.43 m, and the lowest water level is 339.17 m. A total of 11 main inflowing rivers enter Lake Jingpo. The upper reaches of the Mudanjiang River are its main source of water inflow. The surface of Mudanjiang River measures about 50–150 m wide, while its normal water depth is 1.0–2.0 m, and the maximum and minimum velocities have been rated at 2.75 m/s and 0.09 m/s, respectively. Lake water is mainly recharged by surface runoff; the Mudanjiang River inflows an average of 2.53 billion m3/a each year. Indeed, it accounts for 68.6% of the total river inflow into the lake, which is 2.18 times the total inflow of all other rivers. The outflowing water from Lake Jingpo is mainly used to generate hydraulic power. After discharging from the power plant, water enters the outflowing Mudanjiang River through an underground passage. Further, part of the water body flows into the Mudanjiang River through the Diaojiaolou Fall at the northern end of the lake. A map of the water system is available in Fig. 2.
Figure 3 shows land use in the Lake Jingpo catchment. Here, forestlands account for 70.7%, arable lands account for 23%, grasslands account for 3.4%, the water system accounts for 1.7%, gardens accounts for 0.3%, town, village, industrial, and mining lands account for 0.2%, traffic lands account for 0.3%, and other lands account for 0.4%. The total population of the Lake Jingpo catchment is approximately 466,500. Most people are concentrated in Dunhua City of Jilin Province and Ningan City of Heilongjiang Province.