Environ Sci Pollut Res DOI 10.1007/s11356-012-1351-9

PROCESSES AND ENVIRONMENTAL QUALITY IN THE YANGTZE RIVER SYSTEM

Case study on rehabilitation of a polluted urban water body in Yangtze River Basin Juan Wu & Shuiping Cheng & Zhu Li & Weijie Guo & Fei Zhong & Daqiang Yin

Received: 29 August 2012 / Accepted: 20 November 2012 # Springer-Verlag Berlin Heidelberg 2012

Abstract In the past three decades, the fast development of economy and urbanization has caused increasingly severe pollutions of urban water bodies in China. Consequently, eutrophication and deterioration of aquatic ecosystem, which is especially significant for aquatic vegetation, inevitably became a pervasive problem across the Yangtze River Basin. To rehabilitate the degraded urban water bodies, vegetation replanting is an important issue to improve water quality and to rehabilitate ecosystem. As a case study, a representative polluted urban river, Nanfeihe River, in Hefei City, Anhui Province, was chosen to be a rehabilitation target. In October 2009 and May 2010, 13 species of indigenous and prevalent macrophytes, including seven species emergent, one species floating leaved, and five species submersed macrophytes, were planted along the bank slopes and in the river. Through 1.5 years’ replanting practice, the water quality and biodiversity of the river had been improved. The concentrations of total nitrogen (TN), total phosphorus (TP), and ammonia nitrogen (NH4+–N) declined by 46.0, 39.5, and 60.4 %, respectively. The species of macrophytes increased from 14 to 60, and the biodiversity of phytoplankton rose significantly in the river (p<0.05). The biomasses of zooplankton and benthos were also improved after the vegetation replanting. The study confirmed that vegetation replanting could alleviate the increasing water pollution and rehabilitate the degraded aquatic ecosystem. The case study would be an example for polluted Responsible editor: Hailong Wang J. Wu : S. Cheng (*) : F. Zhong : D. Yin College of Environmental Science and Engineering, Key Laboratory of Yangtze River Water Environment, Ministry of Education, Tongji University, 1239 Siping Road, Shanghai 200092, China e-mail: [email protected] Z. Li : W. Guo Chinese Academy of Sciences, Institute of Hydrobiology, Wuhan 430072, China

urban waters restoration in the middle–downstream area of Yangtze River Base. Keywords Yangtze River Basin . Urban water bodies . Vegetation replanting . Rehabilitation . Water quality . Aquatic ecosystem . Biodiversity

Background, aim, and scope The Yangtze River is the third largest river in the world with a mean annual water discharge of 29,400 m3 s−1 and a sediment load of 500 Mt year−1 (Zhang 1995). Its watershed (∼1.8×106 km2) is home to 400 million people and is one of the cradles of Chinese culture. However, as one of the fastest developing areas in China, the middle and down reaches of Yangtze River Basin has been suffering extensive and ever-increasing severe water pollution. Receiving industrial, domestic, and agriculture wastewaters leave the Yangtze River as one of the most seriously polluted rivers in the world, even polluted by pesticides, herbicides, and heavy metals (Wong et al. 2007; Hu et al. 2008). To date, 60 % of the main river channel has been affected by the various pollutants some even are widespread in the middle and down reaches, in which areas there are high population densities (Liu and Wu 2006). Chaohu Lake, which links to Yangtze River, is the fifth largest freshwater lake in China with 756 km2 and a mean water depth of 2.69 m in the down reach of Yangtze River Basin (Wang and Dou 1998). Unfortunately, the severe deterioration of water quality and ecological functions exert negative influences on its social and economic value. As long ago as 1996, Chaohu Lake was identified as one of the top three priority pollutioncontrolled lakes in China. Considered a serious situation, central and local governments both had put a lot of human and material resources in the prevention and control of water pollution of Chaohu Lake area.

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Nanfeihe River, in Hefei City, Anhui Province, as a tributary and the biggest pollution source of Chaohu Lake, contributes 21.3 % of COD, 24.8 % of total phosphorus (TP), and 8.8 % of total nitrogen (TN) annual input into the whole lake. In 2008, the average water quality of Nanfeihe River was lower than grade V under the China’s Environmental Quality Standards for Surface Water (GB38382002), which is also a typical polluted urban river in Yangtze River Basin. A further result of the intensified eutrophication and ecological degradation in urban water bodies is the widespread declines of aquatic vegetation cover and drastic changes in plant communities progressively occurring (Ni 2001; Peng et al. 2004). The pre-survey verified Nanfeihe River was also suffering such progress with degradation of vegetation. The ecological rehabilitation aims to regain the original components and function of the ecosystems, including macophytes, which are characteristic features of shallow aquatic systems (Coops et al. 2002; Janauer 2006). Rehabilitation of degraded urban waters has become a research highlight in recent years, in which recovery of aquatic vegetation is an important component of the issue (Brouwer et al. 2002; Dai et al. 2012). In this study, Nanfeihe River was selected as the objective of the present case study on pollution control and ecological rehabilitation in urban water bodies, and a vegetation replanting practice was conducted in the river. The purpose of this study was to determine whether vegetation rehabilitation can successfully alleviate the increasing pollution and reestablish the impaired ecosystem of urban water bodies.

Materials and methods Study site Nanfeihe River, located the northwest of Chaohu Lake, is the largest of 33 tributaries of the lake, with a total length of Fig. 1 Sampling sites for monitoring of chemical and biological parameters along the demonstrated reach of Nanfeihe River

70 km and catchment area of 1,640 km2. It contributed 8.6 % water quantity, 21.3 % of COD, 24.8 % of TP, and 8.8 % of TN input of the lake in 2006. It receives water mainly from the Dongpu Reservoir and tributaries such as Silihe River, Banqiaohe River, Ershibuhe River, and Dianbuhe River, and the effluent from wastewater treatment plants. From 2009, the up reach of urban section of the river, with a length of 4.3 km, which is from the headwater to Qianshan Road (Fig. 1), was conducted with a vegetation replanting practice for water body rehabilitation.. Vegetation replanting A pre-replanting survey of vegetation was done at the initiation of the practice, and it was found that the objective area, including both riparian areas and water bodies, had a relatively low biodiversity and abundance of vegetation. Hence, the vegetation replanting attempted to recover the plant species diversity in the area was greatly required, not only habitats recovery but also indigenous species reestablishment. In October 2009 and May 2010, a vegetation replanting was conducted respectively, each replanting lasting 3 to 5 days. A total of 13 species of indigenous and prevalent macrophytes, including seven emergent species, one floating-leaved species, and five submersed species, were planted by band along the bank slopes and in the river (Table 1). The species were chosen because of their original presences in this area before the ecological degradation with high resistance to environmental hardship and habitat disturbance, in addition with contributing to the scenic effects (e.g., water lily, iris, canna, and willow herb). All emergent species were planted with over 1-year-old seedlings in three to five tillers, floating-leaved species (water lily) with tubers, and submersed species interpolated with apical shoots. In August 2010, the vegetation developed and was surveyed.

Environ Sci Pollut Res Table 1 Plant species replanted in the vegetation rehabilitation practice

Species

Replanting area (m2)

Species

Emergent species Pontederia cordata Thalia dealbata Iris pseudacorus Canna generalis Acorus calamus Lythrum salicaria Cyperus alternifolius

3,500 3,000 3,200 2,500 3,900 3,500 3,800

Floating-leaved species Nymphaea tetragona Submersed species Potamogeton crispus Ceratophyllum demersum Vallisneria natans Myriophyllum spicatum Hydrilla verticillata

Water quality monitoring and bioassay

Results

From the upper stream to downstream of the demonstrated river section, eight typical sites with around same distance for each other were selected along the demonstrated river section for water quality monitoring and ecological survey in the river (Fig. 1). From August 21st 2009 to September 23rd 2011, the water samples were collected monthly for water physicochemical analyses. Total nitrogen (TN), total phosphorus (TP), ammonia nitrogen (NH 4 + –N), and chemical oxygen demand (CODCr) in the water were analyzed based on standard methods (China Environmental Protection Administration 2002). Samples of phytoplankton, zooplankton, and benthos at the sites were also obtained seasonally generally. The species of each were identified by microscopic observation and the biomass was also calculated (China Environmental Protection Administration 2002).

Vegetation

Statistical analysis Shannon–Wiener Index (Eq. 1) was calculated for the species diversity of phytoplankton. Shannon
Wiener Index ðHÞ ¼


X

Pi lnðPi Þ

ð1Þ

where Pi is the proportion of the ith species in the sample For comparison of water quality variables (TN, TP, COD, and NH 4+ –N) and Shannon–Wiener Index of phytoplankton before and after the vegetation rehabilitation practice (August 2010 as the turning point), twotailed t tests were used. Homogeneity of variance was tested with Levene’s test, and logarithmically, transformations of the data were made when necessary. The differences of species richness and biomass of zooplankton and benthos before and after the rehabilitation were also tested with two-tailed t test. Statistical analyses were performed with SPSS 17.0 (SPSS Inc., Chicago, IL, USA).

Replanting area (m2)

3,200 2,500 2,000 2,000 1,500 1,600

Prior to the vegetation replanting, the riparian areas in the demonstrated section were almost covered with herbaceous vegetation communities dominated by the Gramineae, Cyperaceae, Polygonaceae, and Amaranthaceae families. Dominant species were Beckmannia spp., Alternanthera philoxeroides, and Scripus triqueter, and mixed with knotgrass (Paspalum distichum), vetches (Vicia spp.), and goosegrass (Eleusine spp.). Emergent macrophytes were dominated by common reed (Phragmites communis) and Typha angustifolia. Floating-leaved plant was dominated by Marsilea quadrifolia (four-leaf clover). Floating plants were dominated by duckweed (Lemna minor), and only one submerged species, Ceratophyllum demersum, was found. The vegetation-covered area was limited to a strip (1 or 2 m wide) along the river, with a total area less than 8,000 m2. Vegetation rehabilitation succeeded after the replanting practice. The covered area of vegetation increased to 36,200 m2, including 23,400 m2 of emergent macrophytes 9,600 m2 of submersed ones and 3,200 m2 of floatingleaved ones (Table 1 ). The species diversity has increased in the first year after the practice, more surprisingly some new species appeared (new species marked with a superscripted letter “a” in Table 2). The total plant species increased from 14 to 60 according to our vegetation surveys; among them, terrestrial species increased from 5 to 35, emergent macrophyte was from 6 to 15, submersed macrophyte was from 1 to 6, and floating-leaved macrophyte species was from 2 to 4 (Table 2). The species diversity at site 5 was the most abundant with 30 species among the sites, followed by sites 2 and 3 with 15 species for each other. All of the newly present submersed species and seven of the nine new emergent ones were planted. Furthermore, the two new floating-leaved species Nymphaea tetragona (water lily) and Nymphaea peltata were planted, too. The rest of increased species were composed of terrestrial plants, which appeared naturally.

Environ Sci Pollut Res Table 2 Vegetation list in the demonstrated section of Nanfeihe River after the vegetation replanting practice

Family

Species

Family

Species

Equisetaceae Marsileaceae Nymphaeaceae

Equisetum ramosissimuma Marsilea quadrifolia Nelumbo nucifera Nymphaea tetragona Ceratophyllum dedemersum Ranunculus japonicusa Humulus scandens Broussonetia kazinoki Ranunculus sceleratus Pterocarya stenoptera Alternanthera philoxeroides Malachium aquaticum Polygonum lapathifolium Polygonum orietanlea

Plantaginaceae Rubiaceae

Plantago asiatica Galium aparine Galium spurium Artemisia princeps Cephalanoplos segetum Eclipta prostrata Erigeron acer Erigeron annuus Hydrilla verticillata Vallisneria natans Potamogeton crispus Acorus calamusa Lemna minor Commelina communis

Ceratophyllaceae Ranunculaceae Moraceae

Juglandaceae Amaranthaceae Caryophyllaceae Polygonaceae

Cruciferae Rosaceae Leguminosae Haloragidaceae Lythraceae Vitaceae Meliaceae Geraniaceae Umbelliferae Convolvulaceae Labiatae a

New species that appeared naturally

Polygonum perfoliatum Rumex japonicusa Rorippa montanaa Duchesnea indica Vicia cracca Vicia sativa Myriophyllum spicatum Lythrum salicaria Ampelopsis japonica Cayratia japonica Toona sinensis Geranium carolinianum Oenanthe javanicaa Calystegia hederacea Salvia plebeian Prunella vulgaris

Newly planted species developed well in the demonstrated river section. For example, Potamogeton crispus developed extensively and was quite abundant with average water surface cover of over 80 % at sites 1, 2, and 3 during winter and spring after the replanting, and has now become a dominant species in the river. Contrary to the increasing pattern of planted species, the abundance of two species C. demersum and L. minor, which were observed predominately with a cover of 30–50 % before the replanting practice, decreased significantly to 20–30 % after the practice, especially at sites 1, 2, and 3. The vegetational coverage percentage also increased, especially for the river water surface occupation by submersed macrophytes. In May 2011, the river sections of sites 1 to 4 were covered by P. crispus and the coverage percentage reached 80–85 % at sites 1 to 3 and 65 % at site 4, respectively. However, from sites 5 to 8, submersed macrophyte coverage decreased gradually with occasional presence of C. demersum along the river shore.

Asteraceae

Hydrocharitaceae Potamogetonaceae Araceae Lemnaceae Commelinaceae Juncaceae Cyperaceae

Poaceae

Typhaceae Cannaceae Marantaceae Amaryllidaceae Iridaceae

Juncus effusesa Carex dimorpholepis Cyperus alternifolius Scirpus tabernaemontani S. triqueter Pontederia cordata Beckmannia syzigachne Imperata cylindrica Lolium perenne Paspalum distichum Phragmites communis Typha angustifolia Canna generalis Thalia dealbata Zephyranthes candidaa Iris pseudacorus

Water quality From the monitoring results of chemical parameters, water quality of the river reach was improved as a result of the vegetation replanting practice in general. And some fluctuations detected in all the nutrients concentrations could be attributed to seasons, precipitation, non-point farmland runoff, or other factors. The changes in TN, TP, CODCr, and NH4+–N concentrations with time at the sampling sites (sites 2, 5, 6, and 8) were shown in Figs. 2 and 3. Before August 2010, the average concentration of TN at all the eight sites was 5.87 ± 2.15 mgL−1, while after then the average value in the rest monitoring time was reduced to 3.14 ±1.33 mgL−1, with a reduction of 46.0 % (p<0.01). The reduction trend was especially obvious at site 8, the TN concentration decreased from 9.64±3.37 to 4.11±1.96 mgL−1. Similarly for TP, the average concentration was 0.23 ± 0.12 mgL−1 after the replanting, reduced by 39.5 % compared

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Fig. 2 Changes in concentration of total nitrogen (TN) and total phosphorus (TN) with time at sites 2, 5, 6, and 8

to the average value (0.38±0.12 mgL−1) before the replanting (p<0.05). Apart from the changes with time, the distance from river head also had influences on water quality. Before the replanting, the average concentrations of TN and TP were 1.5–3 times higher at sites 5 to 8 than those at sites 1 to 4, which was mainly related to increasing pollution inputs from agricultural runoff and sewage discharges along the river. After the replanting, the differences of the TN and TP concentrations between the sites became slighter, which might be interpreted by that the vegetation rehabilitation could alleviate the deterioration of water quality along the river reach. The average concentrations of CODCr in the sites ranged between 31.1 and 61.6 mg L−1 throughout the practice (Fig. 3). In comparison with TN and TP, the effect of the vegetation replanting practice on CODCr was not significant (p>0.05). However, the concentrations of ammonia (NH4+– N) were significantly reduced by 60.4 %, with a mean value of 3.76±1.34 mgL−1 before the practice vs 1.49±0.58 mg L−1 after the practice (p<0.05).

Fig. 3 Changes in concentration of chemical oxygen demand (CODCr) and ammonia (NH4+–N) with time at sites 2, 5, 6, and 8

Phytoplankton According to the taxonomic identification of phytoplankton from the eight sites, the community structure and biomass of phytoplankton in the demonstrated section strongly varied both with season and site. The dominant phytoplankton species in spring and summer were green algae, diatom, and cyanobacteria, mainly consisting of Chlorella spp., Cyclotella spp., Microcystis spp., etc., while those species were relatively few in winter. However, the increasing trend in species richness was obvious as a function of the rehabilitation, the average Shannon–Wiener Index for all sites was improved by 22.3 % from 1.80±0.21 before Aug. 2010 to 2.21±0.21 after the date (p< 0.05, Fig. 4), although the increase in species richness was site dependent, it was 60.1 % at site 5 and only 2.9 % at site 2. Zooplankton Four times of zooplankton surveys at sites 1, 3, 6, and 8 were conducted in August and December 2009, and March and August 2011, respectively. The biodiversity of zooplankton

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Benthos Biomass and species richness of benthos at sites 1, 3, 6, and 8 were monitored from March 2010 to September 2011, seasonally. A total of 53 benthos species were observed, the dominant species mainly included Limnodrilus hoffmeisteri, Tanypus spp., and Bellamya aeruginosa. The average biomass and species numbers of benthos for the four sites were shown in Fig. 6 and it was found that the biomass varied dramatically with seasons, which was abundant in summer and less in autumn. After the vegetation replanting practice, the highest average biomass of benthos in the sites was 63.37±27.74 gm−2 in June 2011, which was about ten times higher than that in June 2010.

Fig. 4 Changes in Shannon–Wiener index of phytoplankton with time at sites 2, 5, 6, and 8

was successfully elevated although the increased extent of species richness depended on the sampling sites. From the surveys, 97 zooplankton species were observed, of them 70 species were Rotiferas, 19 were Cladocera, and 8 were Copepoda. The dominant species mainly included Brachionus angularis and Filinia maior over the survey period. The zooplankton biomasses for the four sites were shown in Fig. 5, and the average biomass increased by 29.8 % from 2.71±2.67 mgL−1 in Aug. 2009 to 3.85±1.48 mgL−1 in Aug. 2011. The biomass of zooplankton at site 8 in Aug. 2011 was extremely high (18.75 mgL−1) compared to other sites and sampling dates. However, the species characterizing eutrophic habitats was not changed by the vegetation rehabilitation at sites 6 and 8. The seasonal variation of zooplankton biomass was obvious for sites 3, 6, and 8, the biomasses were particularly low in Dec. 2009 compared to other seasons.

Fig. 5 Biomass of zooplankton in different monitoring time at sites 1, 3, 6, and 8

Discussions In many previous studies on riverine ecological rehabilitation, hydrological techniques and socioeconomical strategies were

Fig. 6 Biomass and species richness of benthos in different monitoring time at sites 1, 3, 6, and 8

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discussed frequently. The hydrological techniques included reconnection of systems of rivers and lakes, multiplechanneling, water allocation, flood management, and establishment of wide riparian buffer zones or wetlands (Jensen et al. 2006; Luderitz et al. 2011). Most of the studies and/or engineering were conducted with low pollution loading or even no pollution input, so the rehabilitation of riverine ecosystem was mainly depended on natural processes. In this case, the rehabilitation became relatively easy if a long term was guaranteed. But in the present study, non-point pollution from farmlands and imperfection of sewage system made it impossible to remove the pollution loading completely, and the natural eco-rehabilitation processes could hardly occur without any artificial interference. Therefore, replanting some pioneer macrophyte species to improve the water quality and ameliorate the aquatic habitats became the key step. From the change trend of nutrient concentrations (TN, TP, and NH4+–N) in such a short period (2 years), we could conclude that the vegetation replanting practice implemented in the upper urban section of Nanfeihe River has obtained a preliminary success, neglecting the less satisfactory CODCr concentrations. Frequently, improvement of water quality is not only the goal of the practice, to reestablish river ecosystem and recover its function is also considered as the more desirable and ultimate purpose. The short-term (1 to 2 years) monitoring of vegetation showed that after the replanting practice a rapid plants expansion and heightened species richness occurred in the riparian areas and river water body. However, the macrophytes species composition in the river changed few, ignoring the newly planted ones. Some eutrophic plant species dominating before practice (e.g., C. demersum and L. minor) remained the status, although the declined abundance was observed. Another short-term and more accurate monitoring illustrated a very clear effect of rehabilitation on vegetation indicators that eutrophic plant species, which dominated before rehabilitation, almost disappeared and were replaced by numerous mesotrophic ones (Henry et al. 1995). The discrepancy might be due to that the present study water body still was a eutrophic habitat. Through a 5-year survey after a 17-year rehabilitation, Henry et al. (2002) found that longterm studies on monitoring the effects of rehabilitation on the biota were very important, particularly after a disturbing event for instance a restoration experiment. Therefore, a long-term monitoring need be continued in our practice. A few previous studies focused on the utilizing original seed or propagule bank in river sediment to rehabilitate vegetation (Mauchamp et al. 2002; Pedersen et al. 2007). In some wetland or riparian restoration projects, seed or prapagule banks in soil and sediment were utilized to recover vegetation through appropriate ecological engineering measures (Lu et al. 2012; Van-Zuidam et al. 2012). In our study, the reoccurrences of the species which might existing before river degradation were most likely attributable to the germination of seeds or propagules

(e.g., turions of P. crispus) reserved in the soil or sediment of the river. The improvement of water quality and environment certainly provided prerequisite for the germinations. However, Rosenthal (2006) found that a large species pool (e.g., as a consequence of moderate human alterations to the river) was important for the restoration success of riparian wetlands. From the present study, it seemed that the reintroduction of indigenous plant species through planting could be an alternative measure to construct species pool over a relatively short term. The improvement of water quality and reestablishment of vegetation can provide better habitats for other organisms. Wang et al. (2008) employed benthic macro-invertebrate as indicator to evaluate the effect of ecological rehabilitation and found that biodiversity and number density of macroinvertebrate in rehabilitation reaches remained high levels compared to reference reaches of East River. The present results also showed that the species richness and biomass of phytoplankton, zooplankton, and benthos increased after the rehabilitation of vegetation. To distinguish that the post-rehabilitation state is selfsustainable for further developing of eutrophication processes, continuous biota monitoring would be necessary. When a selfsustainable state (stable and persistent state) is achieved, longer-term monitoring could be less detailed and less intensive, but it is still needed to detect all those events which enable to influence the ecosystem. With major external pollution sources removed, the replanted pioneer species will successfully establish and colonize, then play indispensable roles in ameliorating water quality, especially creating and maintaining clear water states. The improved water environment is essential for the appearances of new plant species that may be relatively sensitive to the original awful living environment. During the period when water quality improved from eutrophic state back to the pre-degradation state, the long-term and gradual succession of species and community occurs naturally under undisturbed conditions, which eventually results in a stable and resistant ecosystem. However, in order to accelerate these processes and avoid major external damages, some adequate measures can be applied at initial post-replantation processes, including restricting nuisance eco-intruders’ spreading. More importantly, when the water environment becomes more favorable for growth of meso- or oligotrophic species, subsequent replanting of these species increases biodiversity and system complexity, which really matters for ecosystem stability and resistance. In conclusion, the results of the study confirmed the hypothesis that rehabilitation in urban polluted waters based on that vegetation replanting could alleviate the increasing pollution and be capable of rehabilitating the degraded aquatic ecosystem. The case rehabilitation project implemented in Nanfeihe River was successful. It would be an example for polluted urban waters restoration in the middle–downstream

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area of Yangtze River Base. Certainly, a long-term ecological monitoring and ecosystem stabilizing measures were recommended in post-rehabilitation processes. Acknowledgments This study was supported by the projects of National Major Program of Science and Technology (2008ZX07316004 and 2011ZX07303-002) and National Natural Science Foundation (51108334). The authors are also grateful to Ms. Wang Yanyan and Ye Yanting for their plankton taxonomic identification.

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