Abstract
China is facing intense coastal eutrophication. Large-scale seaweed aquaculture in China is popular, now accounting for over 2/3’s of global production. Here, we estimate the nutrient removal capability of large-scale Chinese seaweed farms to determine its significance in mitigating eutrophication. We combined estimates of yield and nutrient concentration of Chinese seaweed aquaculture to quantify that one hectare of seaweed aquaculture removes the equivalent nutrient inputs entering 17.8 ha for nitrogen and 126.7 ha for phosphorus of Chinese coastal waters, respectively. Chinese seaweed aquaculture annually removes approximately 75,000 t nitrogen and 9,500 t phosphorus. Whereas removal of the total N inputs to Chinese coastal waters requires a seaweed farming area 17 times larger than the extant area, one and a half times more of the seaweed area would be able to remove close to 100% of the P inputs. With the current growth rate of seaweed aquaculture, we project this industry will remove 100% of the current phosphorus inputs to Chinese coastal waters by 2026. Hence, seaweed aquaculture already plays a hitherto unrealized role in mitigating coastal eutrophication, a role that may be greatly expanded with future growth of seaweed aquaculture.
Highlights
The magnitude of nutrient removal by Chinese seaweed aquaculture is dependent on the yield and the nutrient concentration in the seaweed tissues, which depends, in turn, on the species composition
We calculate that one km[2] of seaweed farm removes the annual N and P inputs received by 17.8 km[2] and 126.7 km[2] of Chinese coastal waters, respectively (Table 1), providing an estimate of the nutrient removal footprint area of Chinese seaweed farms
We demonstrate here that seaweed aquaculture has reached a scale in China where it is already delivering considerable environmental benefits in terms of nutrient removal from coastal waters
Summary
The magnitude of nutrient removal by Chinese seaweed aquaculture is dependent on the yield and the nutrient concentration in the seaweed tissues, which depends, in turn, on the species composition. Provided a mean (±SE) reported nitrogen (N) and phosphorus (P) concentration for the dominant species in Chinese aquaculture of 3.71 ± 1.15N % DW and 0.52 ± 0.23P % DW for Saccharina japonica, 4.53 ± 0.43N % DW and 0.34 ± 0.05P % DW for Gracilariopsis spp., and an estimated average concentration of 3.52 ± 0.40N % DW and 0.38 ± 0.14P %
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