Water quality, nutrient budget, and pollutant loads in Chinese mitten crab (Eriocheir sinensis) farms around East Taihu Lake

Abstract

To understand the factors causing frequent outbreaks of harmful algae blooms in the Taihu Lake, China, we studied water quality and nutrient budget in Chinese mitten crab (Eriocheir sinensis) farm ponds in the eastern part of the lake from November 2007 to December 2009. We estimated the nitrogen (N), phosphorus (P), and chemical oxygen demand (COD) loads. Materials input and output ponds, water exchange, and applied management practices of 838.5-hm 2 crab ponds were surveyed using questionnaires. Water quality of 12 ponds, which were located no more than 2 km from East Taihu Lake, were monitored. The results show that water quality in the crab ponds was better than reference data. Feeds, including corn seed, commercial feed, trash fish, and gastropod, were the major sources of N and P input in the crab ponds, contributing 88.7% and 94.9%, respectively. In total, 60.5% of N and 37.3% of P were sequestered by macrophytes, and only 15.7% and 8.5% of them were discharged as effluent. The net loads of N and P in effluent were 16.43 kg/ hm 2 /cycle and 2.16 kg/ hm 2 /cycle, respectively, while the COD load was -17.88 kg/hm 2 /cycle. This indicated that crab farming caused minor negative impact on the trophic status of the lake area, which was attenuated by macrophytes. However, wastewater purification is still necessary in crab faming.

Farming system transformation yields significant reduction in nutrient loading: Case study of Hongze Lake, Yangtze River Basin, China

“…Information on nutrients inputs (feed added) and nutrients removed (gain in weight of harvested mitten crab) were used as indices of TNL and TPL. The N and P contents of each types of feed and mitten crab were based on published information Dai et al, 2010;Cai et al, 2012b). The amounts of each types of feed, biomass stocked and yield of mitten crab were obtained from our previous study (Wang et al, 2016).…”

“…The net N and P in effluent discharged took into account that 8.3% of N and 5.1% of P from total feed input were discharged in the effluent in mitten crab farming (Cai et al, 2012b).…”

“…Aquaculture like other animal-production sectors generates waste (Amirkolaie, 2011). As intensification of aquaculture is driven by the increasing demand for food fish, there have been increasing critiques of Chinese aquaculture practices because of the perceived negative environmental impacts (Xie and Yu, 2007;Cai et al, 2012aCai et al, , 2012bHerbeck et al, 2013;Zeng et al, 2013). It is alleged that a large amount of waste from aquaculture is released into environments that causes deterioration of aquatic ecosystems or wetlands (Amirkolaie, 2008;Verdegem, 2013), and at times being health hazards (Qin et al, 2007;Cai et al, 2012a).…”

Sustainable farming practices of the Chinese mitten crab (Eriocheir sinensis) around Hongze Lake, lower Yangtze River Basin, China

“…The lowest net loading of total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD), and total suspended solids (TSS) have been observed in mitten crab farming compared to other farmed freshwater species, such as grass carp (Ctenopharyngodon idellus), black carp (Mylopharyngodon piceus), river prawn (Macrobrachium nipponensis), shrimp (Penaeus vanmamei), and soft-shelled turtle (Trionyx sinensis) (Cai et al 2012a). The contribution to low volumes and concentrations of pollutants in effluents of mitten crab farming are mainly attributed to the common practice of transplanting aquatic macrophytes to regulate water quality rather than through water exchange (Cai et al 2012b). Therefore, mitten crab farming is considered to be relatively more environmentfriendly than most other practices.…”

Estimation of the lower practical limit of aquatic plant coverage in intensive Chinese mitten crab ( Eriocheir sinensis ) rearing ponds using an unmanned aerial vehicle

“…Importantly, the outlet waters from these intensive‐rearing CMC ponds contain high abundances of nutrients (e.g. nitrogen and phosphorus) that may pollute natural rivers or lake waters (Cai et al, ; Chen, Hu, Qu, & Fan, ; Wang, Li, et al, ).…”