下载掌阅APP，畅读海量书库
立即打开
Farm ponds in conjunction with the surrounding woods, farmlands, cottages, and water courses, constitute a unique pastoral landscape of small farms in southern China (Fig. 2.4). While storing rainwater, farm ponds can profoundly alter the hydrologic and nutrient cycling in the watershed, and, as a consequence, lead to idiosyncratic riparian conditions to host flora and fauna.They also offer considerable social and cultural benefits, including improving physical and mental well-being and increasing awareness of environmental conservation at larger scales. The benefits of farm ponds are summarized in Table 2.1 and discussed in the sub-sections below.
Fig. 2.4 A typical landscape with small, scattered farm ponds from low mountains to plains.
Table 2.1 Benefits of farm ponds in southern China
Farm ponds provide disproportionate contributions to hydrological and ecological functions that have lag, sink, and source effects on the physical,chemical, and biological status of downstream waters (Rains et al., 2016).Rainfall initially fills ponds and then runs off along the surface. This process helps to reduce flood peaks, contributes to groundwater recharge and discharge, and provides stream base flow for irrigation. In addition to the qualitative descriptions in ancient literature, such as in The Odes of Chen, Classic of Poetry , on-site monitoring and numerical assessment have quantified those hydrological functions. For example, in the Liuchahe watershed, Anhui Province, the 193 farm ponds that accounted for 6.2% of the total watershed area were observed to reduce irrigation water shortages from 333 mm to 138 mm in wet years and from 280 mm to 41 mm in dry years. During a heavy rainfall storm event (141 mm), the ponds reduced the flood peak from 2.5 to 0.3 m 3 /s (Yin and Shan, 2001). Pond parameters, such as shape, area, and depth, determine their water retention in the catchment, while their spatial distribution is important to the water storage capacity and utilization of rainwater in the watershed (Verhoeven et al., 2006; Fang et al., 2014).
Farm ponds can reduce diffuse pollutants from agricultural drainage via many processes including interception and precipitation, plant uptake,microbial degradation, and sediment adsorption. Capps et al. (2014) discovered that oxygen transport through the stems of emergent and floating plants can create an aerobic environment at their root surface, where organic matters can be decomposed by aerobic microorganisms and ammonia can be nitrified by nitrifying bacteria. In the low-oxygen areas of the deep root zone, where anaerobic fermentation is prevalent, organic matters can be denitrified into carbon dioxide and methane. Moreover, farm ponds can remove the particle-bound phosphorus in runoff through sedimentation and enhance the binding of soluble inorganic phosphate to Al 3+ and Fe 3+ in the sediments (Liu et al., 2009).A two-year monitoring in the irrigated area of Gaoyou county, Jiangsu Province,revealed that the concentration of total nitrogen and total phosphorus were reduced by 64.5 and 54.4%, respectively, by the groups of ponds and ditches(Peng et al., 2013). The reduction rate is determined by their connectivity,vegetation coverage and dredging operations (Mitsuo et al., 2014; Hansen and Dolph, 2018; Chen et al., 2018).
As an essential component of the circular“crop-livestock-fish”production system, farm ponds increase biodiversity from within-pond to regional scale.While crops are used to feed poultry and livestock, a large proportion of the manure produced by the poultry and livestock is applied into the ponds to promote fish growth, and the sediments in the ponds are returned to the land to improve soil fertility for crop production (Ongley et al., 2010; Chen et al.,2016a). Although most of the manure is consumed by fish, it provides large amounts of nutrients for accelerating the phytoplankton and zooplankton growth and supplies substrates for decomposing microorganisms. These increased biomasses, in turn, serve as food for a wide range of wildlife. In the ponds of the Liuchahe watershed, for example, Han and Sun (2007) reported a total of eight types of aquatic vegetation, including emergent plants, floating leaved plants, and submerged plants. The vegetation covered approximately 12.6% of the pond surface area and formed different communities from the village, the farmland and the hillslope nearby. In the Taoyuan tableland, Huang et al. (2012) detected 94 bird species in pond areas. Serving as stepping stones between larger freshwater habitats, these ponds provide both a stopover site during winter migration for shorebirds and seabirds and attract many wetland birds to feed and nest. In addition, farm ponds are reported to provide habitats for many amphibians, such as frogs and toads, tortoises, and insects, including dragonflies, caddisflies, and midges. This even includes some species on the International Union for Conservation of Nature's Red List, which rely on the humid environment and abundant carbon resources in riparian areas, especially during the spawning and incubation periods (Raebel et al., 2012; Capps et al.,2014).
Awealth of socioeconomic benefits stem from farm ponds. As enumerated above, the hydrological regulation and flood alleviation services contribute to social stability, and the improved nutrient cycling, particularly in the“crop-livestock-fish”system, is beneficial to agricultural production and farm economy. In a three-year study on abandoned ponds near Wuhan city, Hubei Province, for example, it was found that the annual fish production amounted 2.2 to 2.6 kg/m 2 . This generated a profit of $1.96 to $2.55 (13.5 to 17.6 RMB,$1≈6.90 RMB) per square meter (Zhou et al., 2016b), and the whole city was estimated to benefit approximately $145 million (1 billion RMB) from the industry of pond aquaculture. Besides, Phragmites at the water's edge are reaped as raw material for papermaking in Hunan Province (Tian et al.,2011). Combined with farmlands, woods, and streams, farm ponds constitute a harmonious and nature-based rural residential scenery. For thousands of years,they have served as a traditional exchange place for neighbors’communicating and sharing life stories while washing, swimming and fishing. Such a water-centric lifestyle remains in the present, despite environmental and water quality deterioration due to nutrient enrichment from fertilizers and pesticides.In addition, these aquatic features may provide educational and recreational opportunities nationally and even globally. For example, Quebei has been honored as China's Key Relic Protection Unit since 1988 and a World's Heritage Irrigation Structure since 2015, attracting more than 100,000 domestic and foreign tourists annually (Zhou et al., 2016a). Although farm ponds triggered conflicts between different ethnic groups in northern Taiwan in the 1900s,a recent TV series called Beitang has aroused an appreciation of these land and water resources and introspection on their degradation in the Chinese community.