The total incremental ecological service value was obtained by solving the developed FTSCCP model (model 1), with values of 10,912.32 million CNY, 15,400.50 million CNY, and 15,400.50 million CNY under scenarios of low, normal, and high flow levels, respectively. With an increase of available flood water resources under different scenarios, there would be adequate water resources for the planned water supplementation to regional lakes and ponds in the western Jilin Province. In low-flow years, insufficient water resources would lead to an adjustment of the initial water supplement schemes and reduction in ecological service value.
4.1. Incremental Ecological Service Values and Analysis of Restored Areas
describes the total incremental ecological service values of different ecosystems in the western Jilin Province under low, normal, and high flow levels. With the same trend in total incremental ecological service value, the values for fish ponds, crab ponds, reed wetlands, and marsh wetlands under a low flow level would be 2735.88 million CNY, 1056.08 million CNY, 2923.11 million CNY, and 3797.77 million CNY, respectively, which are significantly lower than those obtained for normal and high levels, with reductions of 38.0%, 32.9%, 15.2%, and 27.1% compared to the original planning schemes.
presents the trend in incremental ecological service values based on the ecological service assessment index system under different scenarios in the western Jilin Province. The ecological service values of all assessment indexes would decrease under a low flow level. Taking the third-class indexes as an example, the ecological service values of 10 indexes (e.g., fish, crab, water supply, water storage and regulation, and biodiversity) would significantly decrease with respect to the original planning schemes, with reductions of more than thirty percent. In addition, the value proportions of 9 indexes (fish, crab, and water supply) would decrease from the original levels; the proportion reductions of fish, crab, water supply, water storage and regulation would be 12.5%, 5.3%, 13.7%, 5.8%, and 3.8%, respectively, for biodiversity and all culture service indexes. For the other 6 indexes, the ecological value proportions would have a certain improvement, with values of 19.7% (reeds), 16.2% (carbon sequestration), 16.1% (oxygen release), 8.4% (microclimatic modification), and 9.3% (plant fixation and assimilative capacity). Among these indexes, the proportions of fish, reeds, water supply, carbon sequestration, and oxygen release have larger changes, and the changes in the ecological service value pattern would be highly affected under the low flow level.
Based on the above analysis, the planned scale of ecosystem restoration would not be realized in low flow years because of the decrease in flood water resources, leading to a decrease in ecological service values; furthermore, the values of indexes mainly from water surface ecosystems (e.g., fish, crabs, water supply, water storage and regulation) would present more significant decreasing trends.
presents the restoration of water surface and ecosystem areas by water diversion and supplementation under different scenarios. The restored areas under the low flow level would be far smaller than those under normal and high flow levels, which are equal to the original planning schemes shown in Table 2
. Compared to the original plans, in low-flow years, the areas of water surfaces, fish ponds, crab ponds, reed wetlands, and marsh wetlands would decrease by 39%, 38%, 33%, 15% and 27%, respectively. The water surface area, fish ponds and crab ponds show greater decreases, corresponding to the more significant decreasing trends in the values of indexes mainly from the water surface ecosystem.
and Figure 5
provide comparisons of the restored water surface area (including fish ponds and crab ponds) and wetlands under different scenarios in different regions. The figures show the same trends as those obtained for the whole western Jilin Province: the restored areas of water surfaces and wetlands under normal and high flow levels would be equal to those of the original planning schemes, and there would be decreases of different degrees under low flow levels. For example, in Nong’an County, Songhua River basin (r
= 1), the restored water surface area under the low flow level would be 0.99 × 104
ha, with a decrease of 17.1% compared with the original restored area of 1.20 × 104
ha; in Qianguo County (r
= 2), the restored water surface area under a low flow level would be 2.83 × 104
ha, a decrease of 1.10 × 104
ha or 26.6% with respect to the original plans; and in Tongyu County, Huolin River basin, the reduction would reach 65.1%, representing a decrease from 0.11 × 104
ha to 0.04 × 104
ha. For wetlands, in region 1, the restored area under a low flow level would be 0.61 × 104
ha, a 14.3% decrease compared to that under normal and high levels; in region 6, the decreased area would be 0.23 × 104
ha, 36.7% that of the original planning scheme. However, in regions 2, 3, 4 and 5, there would be no decrease under a low flow level; these results show varying trends in different ecosystems and regions.
and Figure 7
describe the relative decreases in water surface area, fish ponds, crab ponds, reed wetlands, and marsh wetlands under low flow levels. Different ecosystems would show various degrees of decrease in each region. For example, in region 1, the decrease in water surface area, fish ponds, crab ponds, reed wetlands, and marsh wetlands would be 17.2%, 16.9%, 0, 25.1%, and 0, respectively; in region 7, the corresponding relative decreases would be 36.3%, 44.5%, 57.7%, 1.4%, and 0. The main reasons for these results are that (1) the ratio of ecological service value and water demand quota in marsh wetlands is higher than that in other ecosystems, and thus more water resources would be allocated to marsh wetlands when the minimal water requirements of each ecosystem were satisfied; and (2) the development of fish and crab ponds as part of water surface area is different from those in other regions, leading to a difference in the relative decreases in water surface area, fish ponds and crab ponds. However, in regions 4 and 15, the decreases in marsh wetlands would be 100%, because the priority of water supplementation would be water surface area, reed wetlands, and marsh wetlands. In these regions, there would not be adequate water resources to supplement for the water surface area; as a result, no water resources would be supplied to restore wetlands.
In addition, regional ecosystem planning plays a significant role in optimal adjustments to the original ecosystem restoration planning schemes under low flow levels. For example, in regions 5, 6 and 11, there was no fish or crab breeding in the water surface area with a lower ecological service value; thus, water resources would be mainly supplied for reed wetlands and marsh wetlands, combined with different minimal requirements of water surface areas. The decreases in these regions would be 37.6%, 65.2% and 56.2%, respectively. For wetland ecosystems, in region 5, without reed wetland development, there would be no decrease in marsh wetlands; in region 11, the decreases in reed wetlands and marsh wetlands would be 10% and 0, respectively. However, in region 6, there would be a 23.8% and 40.0% decrease in reed wetlands and marsh wetlands, respectively; in this region, the priority of water supplementation and lack of water resources would play the leading role in the adjustment of water supplement schemes for the restoration of ecosystems.
Above all, differences in ecosystem structure would lead to different optimal adjustments of water supplementation planning schemes in lakes and regions. Nevertheless, the amount of flood resources and regional water resource structure for ecosystem water supplementation would be the key factors in adjusting the original water supplement schemes and maximizing the regional ecological service values.
4.2. Water Diversion and Supplement Analysis
presents the water diversion schemes and adjustments to the original ecosystem restoration schemes in 15 regions in western Jilin Province under low flow level. The proportion of flood resources is a significant factor in adjusting the original ecosystem restoration schemes. For example, in region 1, flood resources only account for 20.1% of the total water resources, and there would be only 17.2% and 14.3% reductions in the restored water surface area and wetlands, respectively; in region 7, where the proportions of local water resources and normal supplementation reach 86.5%, the reductions would be 36.3% and 1.2%, respectively. In contrast, in region 6, there is no normal water supplement planning, and the amount of local water resources is only 755 × 104
/year. The reductions in restored water surface area and wetlands would reach 65.2% and 36.8%, respectively.
In addition, as shown in Table 5
, the reductions in water surface area would be higher than the reductions in wetlands in each region. Taking region 1 as an example, Table 6
presents the water diversion schemes and reductions to the original ecosystem restoration schemes in regional lakes and ponds. In lakes 1 and 3, there would be adequate local water resources for the original ecosystem restoration schemes, and flood resources would be allocated to the other lakes with crab ponds and marsh wetlands, e.g., lakes 5 and 7. The flood resources at lakes 5 and 7 would be 484.97 × 104
and 365.89 × 104
, respectively, accounting for 33.0% and 24.9% of the total water resources. There would be no reductions in crab ponds and marsh wetlands, and a 30% reduction in reed wetlands, which would only meet the minimal requirement. Moreover, in lakes 2 and 6, although the ecological service values of the water surface area and fish ponds are lower than that of the reed wetland, because of the higher minimal requirements for water surface area, there would be lower reductions in the water surface area and fish ponds than reed wetlands.
, Figure 9
and Figure 10
show the water diversion schemes of local resources, normal water supplementation and flood resources under different levels. Figure 8
shows that local water resources would have no change under the three scenarios, indicating that local water resources would be utilized prior to the other water resources.
As shown in Figure 9
and Figure 10
, only regions 1, 2, 8, 10, and 12 have planned normal water supplements. Along with the increase in available flood resources, under normal flow level, there would be no change in normal water supplementation and an obvious increase in flood resource utilization compared to those under a low flow level. Under a high flow level, there would be an obvious decrease in normal water supplementation and higher flood resource utilization than under a normal-level scenario. Because the original ecosystem restoration scheme could be realized under both normal- and high-flow-level scenarios, the proposed model would not only reduce normal water supplementation and the cost of water resources but also improve the utilization rate of flood resources, thus realizing higher effective water resource utilization.
However, this model was developed based on meeting the target of ecosystem restoration planning schemes to realize the optimal adjustment of the original plans under the low-flow-level scenario and water diversion schemes under normal- and high-flow-level scenarios, ignoring further developments in terms of ecosystems restoration and higher ecological service values. Meanwhile, this model would fail to make full use of flood resources and avoid possible flood risk under high-flow scenarios.
4.3. Study on the Maximization of Ecological Service Value
Compared to model 1, the total increase in ecological service value obtained by solving model 2 would be 3.2%, 6.9%, and 14.5%, with values of 11,256.79 million CNY, 16,465.11 million CNY, and 17,639.59 million CNY, under low-, normal- and high-flow scenarios, respectively.
provides a comparison of the incremental ecological service value obtained by the two models under different scenarios. Different ecosystems show different variation trends. Compared to model 1, the incremental ecological service values of fish ponds and crab ponds obtained by model 2 would decrease, in contrast to reed wetlands and marsh wetlands. For example, under low-flow scenarios, the ecological values of fish ponds and crab ponds would decrease from 2735.88 million CNY and 1056.08 million CNY to 2423.42 million CNY and 982.49 million CNY, respectively; in contrast, the values of reed and marsh wetlands would increase from 2923.11 million CNY and 3797.77 million CNY to 3204.19 million CNY and 4292.97 million CNY, respectively. The main reason for this difference is that for most lakes in the western Jilin Province, the ecological service value of fish and crab ponds is lower than that of wetlands, so more water resources would be allocated to wetlands after meeting the minimal requirement of each ecosystem to obtain higher ecological service values. In addition, the total ecological value would increase with a gradual increase in available flood resources, although the value of marsh wetlands under the high-flow scenario would be lower than that under the normal flow scenario, indicating that model 2 could realize the maximization of ecological service value through the optimal allocation of water resources under different scenarios.
lists comparisons of the incremental ecological service values of the two models based on assessment indexes. Under low- and normal-flow scenarios, the values of fish, crabs, water supply, water storage, and regulation obtained by solving model 2 would decrease compared to those of model 1. For example, under the normal-flow scenario, the ecological service values of water supply, water storage, and regulation would decrease from 1515.98 million CNY and 1546.01 million CNY to 1300.64 million CNY and 1524.10 million CNY, respectively, mainly because the ecological service values of these four indexes are mainly due to the ecosystems of fish and crab ponds. For the other indexes, because the main service values are generated from wetland ecosystems, the values would have a certain increase under different scenarios. For example, the values of oxygen release would increase from 210.33 million CNY, 255.63 million CNY, and 255.63 million CNY to 231.92 million CNY, 299.87 million CNY, and 335.46 million CNY under low-, normal- and high-flow scenarios, respectively. For biodiversity, ecological service values would increase from 303.36 million CNY, 445.26 million CNY, and 445.26 million CNY to 304.16 million CNY, 453.40 million CNY, and 492.74 million CNY, respectively, with lower relative increases than those obtained for oxygen release. This difference might be because of the approximate equivalent service values among different ecosystems of indexes, such as scientific culture, tourism development, urban landscape, and natural landscape.
and Figure 13
describe the trends in restored water surface area and wetlands based on model 2 in the western Jilin Province under different scenarios. Figure 12
shows that, except for regions 1 and 6, the restored water surface area would increase with a gradual increase in flow levels. For example, in region 2, the restored areas would be 2.33 × 104
ha, 3.36 × 104
ha and 3.77 × 104
ha, and in region 12, the areas would be 0.98 × 104
ha, 0.98 × 104
ha, 1.30 × 104
ha, respectively. In region 6, the restored water surface area under different scenarios would be a consistent 0.04 × 104
ha, mainly because of the lower service value without fish or crab breeding and the high proportion of wetlands in lakes and ponds.
For wetlands, Figure 13
shows a similar trend to that obtained for water surface area, and the restored area would increase as the flow levels gradually increased. However, under normal- and high-flow scenarios, there would be little or no increase in restored wetland areas. For example, in region 2, the restored areas of wetlands would be 1.40 × 104
ha under the three scenarios; in region 12, the restored areas would be 3.33 × 104
ha, 5.47 × 104
ha, and 5.67 × 104
ha under low, normal and high flow scenarios, respectively. This indicates that in the western Jilin Province, more water resources would be allocated to wetland ecosystems to obtain higher ecological service values. In normal-flow years, the restored area of wetlands would approximately reach the maximum planned value; as a result, there would be no obvious increase in high-flow years.
presents adjustments to the original ecosystem restoration schemes of lakes and ponds in Nong’an County, Songhua River basin. In Table 8
, the positive values and negative values represent decreases and increases with respect to the initial planned schemes, respectively. In general, adjustment schemes would mainly comprise an increase in crab ponds or marsh wetlands and a decrease in reed wetlands. For example, in lake 2, the restored area of marsh wetlands would increase by 0.043 × 104
ha under all three scenarios; in low- and normal-flow years, the area of reed wetlands would decrease by 0.08 × 104
ha, and in high-flow years, the area would increase by 0.04 × 104
ha because of abundant water resources. In lake 5, the restored area of marsh wetlands would increase by 0.021 × 104
ha under all three scenarios, and for reed wetlands, the area would decrease by 0.01 × 104
ha in all three scenarios; in low-flow years, because of a lack of water resources, the restored area of crab ponds would decrease by 0.038 × 104
ha, and in normal- and high-flow years, the area would increase by 0.011 × 104
ha. However, in lake 1, different adjustment schemes are shown, with an increase of 0.021 × 104
ha in reed wetlands and a decrease of 0.003 × 104
ha in marsh wetlands under the three scenarios. Combined with water diversion schemes, there were adequate local water resources and no need for other water supplements for original restoration plans in this lake. Model 2 could realize higher ecological service values through the optimal adjustment of water resource allocation. Moreover, in lake 2, adjustments to fish pond restoration would decrease by 0.181 × 104
ha, increase by 0.136 × 104
ha, and increase by 0.06 × 104
ha under low-, normal- and high-flow scenarios, and for reed wetlands, the adjustments would decrease by 0.08 × 104
ha and 0.08 × 104
ha and increase by 0.04 × 104
ha, respectively. Although there would be more available flood resources under a high-flow scenario and the ratio of ecological service value to water demand quota in fish ponds is higher than in reed wetlands, a decrease in fish ponds and an increase in reed ponds appeared compared to normal-flow scenario. This result indicated that some water resources would be transferred from higher-valued ecosystems to lower-valued ecosystems to realize the full use of water resources and maximization of ecological service value by the constraint of the planned lake scale.
provides a comparison of flood resource utilization based on two optimal models under the high-flow scenario. The utilization of flood resources in model 2 would be more than in model 1, indicating the full use of flood resources, and decrease the possible flood risk to a certain extent.