Megacity development and the demise of coastal coral communities: Evidence from coral skeleton δ15N records in the Pearl River estuary. (16th January 2020)

• Record Type: Journal Article
• Authors: Duprey, Nicolas N.; Wang, Tony X.; Kim, Taihun; Cybulski, Jonathan D.; Vonhof, Hubert B.; Crutzen, Paul J.; Haug, Gerald H.; Sigman, Daniel M.; Martínez‐García, Alfredo; Baker, David M.
• Is Part Of: Global change biology. Volume 26:Number 3(2020)
• Page Start: 1338
• Page End: 1353
• Publication Date: 2020-01-16
• Subjects: corals -- eutrophication -- megacities -- stable nitrogen isotopes -- urbanization; Climatic changes -- Environmental aspects -- Periodicals; Troposphere -- Environmental aspects -- Periodicals; Biodiversity conservation -- Periodicals; Eutrophication -- Periodicals; 551.5
• DOI: 10.1111/gcb.14923
• Languages: English
• ISSNs: 1354-1013

Abstract

Abstract: Historical coral skeleton (CS) δ 18 O and δ 15 N records were produced from samples recovered from sedimentary deposits, held in natural history museum collections, and cored into modern coral heads. These records were used to assess the influence of global warming and regional eutrophication, respectively, on the decline of coastal coral communities following the development of the Pearl River Delta (PRD) megacity, China. We find that, until 2007, ocean warming was not a major threat to coral communities in the Pearl River estuary; instead, nitrogen (N) inputs dominated impacts. The high but stable CS‐δ 15 N values (9‰–12‰ vs. air) observed from the mid‐Holocene until 1980 indicate that soil and stream denitrification reduced and modulated the hydrologic inputs of N, blunting the rise in coastal N sources during the early phase of the Pearl River estuary urbanization. However, an unprecedented CS‐δ 15 N peak was observed from 1987 to 1993 (>13‰ vs. air), concomitant to an increase of NH4 + concentration, consistent with the rapid Pearl River estuary urbanization as the main cause for this eutrophication event. We suggest that widespread discharge of domestic sewage entered directly into the estuary, preventing removal by natural denitrification hotspots. We argue that this event caused the dramatic decline of the Pearl River estuary coral communities reported from 1980 to 2000. Subsequently, the coral record shows that the implementation of improved wastewater management policies succeeded in bringing down both CS‐δ 15 N and NH4 + concentrations in the early 2000s. This study points to the potential importance of eutrophication over ocean warming in coral decline along urbanized coastlines and in particular in the vicinity of megacities. Abstract : What are the respective roles of eutrophication and ocean warming in the decline of coastal coral communities along expanding urban centers? Here, we use historical coral geochemical records from a heavily urbanized area, the Pearl River Delta (PRD), China, to formalize the link between urbanization‐driven eutrophication and coral reef ecosystems decline. Our study reveals that ocean warming had no measurable influence on the decline of the coral communities located in the estuary, whereas the development of the PRD megacity in the 1980s–1990s was linked to an unprecedented eutrophication event that triggered a major coral die‐off in the estuary.