Monitoring: Water Quality and Biocoenosis

17.4.1.1 Water Quality

Eight water samples were obtained 0.5 m underwater and determined according to the National Surface Water Environmental Quality Standard (GB3838-2002). The parameters were measured as follows: total phosphorus (TP) using the ammonium molybdate spectrophotometric method; total nitrogen (TN) via the alkaline potassium persulfate digestion-UV spectrophotometric method; chemical oxygen demand (COD) by the dichromate method; dissolved oxygen (DO) using the iodimetric method; Chlorophyll-a via spectrophotometry; and water transparency by Secchi disc.

17.4.1.2 Aquatic Plants

The fresh weight was measured with three replications by harvesting all plants in a square of 1 m2 in each season. After that, fresh samples were air-dried, smashed and sieved for later determination. Total phosphorus and total nitrogen were measured using the perchloric acid-sulfuric acid solution method.

17.4.1.3 Aquatic Animals

Samples of zoobenthos were collected by 1/16 m2 Peterson grab at three points. Samples of fish were obtained by fishing in a certain location. The fresh weight was measured after washing and identification.

Monitoring Results

17.4.2.1 Variation of Water Quality

In general, water quality was improved from below Class V to Class II based on the National Surface Water Environmental Quality Standard (GB3838-2002) (Table 17.5). TN, TP, COD, and Chlorophyll-a were greatly decreased. From 2003 to 2007, the transparency increased from 20–40 to 80–100 cm. The DO was low with an average value less than 5 mg/L and a minimum of 0.8 mg/L in summer 2003, increasing to 9.09–11.18 mg/L in November 2007. The concentration of

Chlorophyll-a decreased from an average level of 19.41 μg/L to around 7.86 μg/L. Algae was remarkably inhibited after introducing H. molitrix and A. novilis. In addi-

tion, inhibition of algal growth via competition from aquatic plants was immeasurable (Chen et al. 2009).

Table 17.5

Water quality of Liwa River

Date

Engineering phase

TN

(mg/L)

TP

(mg/L)

COD

(mg/L)

Chlorophyll-a (μg/L)

2003.10

Before treatment

11.34

1.13

58.9

123.52

2005.11

Traditional treatment

1.85

0.23

33.3

completed

2006.11

Near-natural restoration completed

0.89

0.19

20.2

19.41

2007.11

One year later

0.41

0.03

21.5

7.86

17.4.2.2 Biocoenotic Dynamics

The distribution and biomass of each introduced species was recorded monthly for 2 years after restoration (Table 17.6). In comparison with their areas in 2006, the ranges of P. crispus, N. nucifera, and Ceratophyllum demersum expanded 96 %, 100 %, and 84 %, respectively. In contrast, Vallisneria asiatica and Iris tectorum lost 72 % and 50 % of their ranges, respectively. Range shrinkage of V. asiatica was observed only in deep-water areas, which suggests that the decrease in V. asiatica was mainly due to insufficient light (Li et al. 2008).

Most aquatic species, such as V. asiatica and C. demersum, attained maximum biomass in summer and fall, except for P. crispus. Therefore, P. crispus played an important role in removing nutrients, filtering particles, and replenishing oxygen in winter when the other species lost vitality. As a result, the aquatic vegetation had an observable effect on the removal of excess nutrients throughout the whole year and provided habitats and sufficient food for fish even in the winter.

Most aquatic plants reached the highest fix rate of nitrogen and phosphorus in fall, but P. crispus and N. nucifera were the highest in spring and in summer respectively. Calculations based on data collected showed that 12.8 kg of N and 1.6 kg of P could be removed from the water by harvesting P. crispus in May and N. nucifera in November every year (Table 17.7). The effect would be even better if N. nucifera was harvested in summer. The data indicated that harvesting aquatic vegetation was an effective treatment for urban river eutrophication (Graneli and Solander 1988; Meuleman et al. 2004).

Two years after the restoration, native zoobenthos species Radix swinhoei and Planorbidae spp, and native fish Saurogobio dumerili were found in addition to the species artificially introduced. Invertebrates in particular were thriving in the flourishing macrophyte communities. The number of B. quadrata, R. swinhoei and Planorbidae spp increased to 82.5, 151.5, and 19.3 m3, respectively. These increases showed that food chains had reestablished with increased species richness in the restored river.

Table 17.6 Distribution and biomass of aquatic plants

Table 17.7 Nitrogen and phosphorus fixed by aquatic plants

Table 17.8 Comparison of expenses for removing nitrogen and phosphorus between traditional treatment and near-natural restoration engineering

Assessment of Near-Natural River Construction

The total cost of comprehensive treatment in Liwa River was RMB 5.617 million. The cost of near-natural restoration was RMB 0.199 million, accounting for only

3.5 % of the total cost (Table 17.8).

There were only a few additional expenses for post-restoration management involving macrophyte vegetation harvesting every half year. Other methods typically cost four to six times more than near-natural restoration to remove the same amount of nutrients. This is because near-natural restoration almost exclusively uses solar energy, a very diffuse but sustainable and free energy source (Seidel 1976). Photosynthesis and renewable energy utilization are economical by nature. But it cannot be doubted that it would be a cheaper and more effective treatment for seriously polluted rivers to employ near-natural restoration after traditional environmental engineering techniques that are considered more likely to have an immediate effect.

Concluding Remarks

Near-natural restoration is both a method and a theory. Its meaning surpasses ecology, embracing a philosophy of “harmony between man and nature.” Since the era of the Warring States (720–221 bc), the Chinese have investigated the harmonious relationship among Tian (heaven or universe), Di (earth or resource), and Ren (people or society), advocating the union of man and nature. From these investigations, a systematic set of principles for managing the relationship between man and the environment was developed. In particular, principles of holism, symbiosis, circulation and self-reliance were emphasized (Wong and Bradshaw 2008).

In successive phases, appropriate native species were selected, relevant communities from the pioneer to senior phase were built, and each phase of the food cycle was connected, to enable the forest or water system to become a self-maintaining, recycling, living ecosystem. Numerous restoration projects and studies have shown that near-natural restoration could provide ample ecological benefits and enhance environmental quality with minimal human maintenance and a small initial investment. Within Shanghai, in addition to the construction of green space in urban areas and greenbelts along the outer circle line, the near-natural forest method could be widely recommended for a number of purposes, including the following: restoring vegetation in garbage disposal fields, creating environmental protection forests in large industrial areas including those occupied by corporations such as the Shanghai Petrochemical Co., Ltd., planting coastal protection forests, creating forest networks within farms, and providing forests for ecological education and research. The method could be regarded as a new means of constructing urban forests, and as central to the construction of urban environments (Da and Song 2008). When planning urban river restoration projects, it is advisable to take advantage of near-natural restoration techniques adapted to local conditions. In most cases, the ecological functioning of river systems can be improved, while simultaneously minimizing the impacts of development and adding genuine social and economic value to the urban environment (Findlay and Taylor 2006).

However, there are still barriers to using near-natural methods in urban areas for restoration purposes, especially the need for management after the restoration, and unfavorable public perceptions. It is recommended that near-natural restoration be pursued through active collaboration with a range of other disciplines in order to improve restoration efforts on multiple fronts.

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