Environmental change in Jiaozhou Bay recorded by nutrient components in sediments Su Mei Liu a, * , Bing De Zhu a , Jing Zhang b , Ying Wu b , Guang Shan Liu c , Bing Deng b , Mei-Xun Zhao a , Guan Qun Liu d , Jin Zhou Du b , Jing Ling Ren a , Gui Ling Zhang a a Key Laboratory of Marine Chemistry Theory and Technology Ministry of Education, College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China b State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200062, China c Oceanography Department, Xiamen University, 422 Siming Road South, Xiamen 361005, China d College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China article info Keywords: Carbon Nitrogen Phosphorus Silicon Environmental change Jiaozhou Bay abstract Inorganic or bulk organic chemical indicators, including organic carbon (OC), total nitrogen, organic nitro- gen (ON), fixed ammonium (N fix ), exchangeable ammonium, exchangeable nitrate, organic phosphorus (OP), inorganic phosphorus (IP), and biogenic silica (BSi), were examined in a 3-m core collected in Jiaoz- hou Bay (JZB) to decipher how the environment has changed during the preceding two centuries of increasing anthropogenic influence in this region. Concentrations of BSi, OC, and OP reveal overall increases to ca.30 cm (1984), then decreased toward the surface, probably reflecting a decrease in the productivity of overlying waters since 1984. Aquaculture might play an important role in the decrease of nutrient elements in the upper layers recorded in sediments. The decreased molar BSi/OC ratios upcore may be due to a change in dominance from large- to small-sized diatoms, as shown in other research. However, the shift may also be related to changes from heavily-silicified to lightly-silicified dia- toms or to non-siliceous forms such as dinoflagellates. ON concentrations increased towards the surface sediment, which is most likely consistent with the increase in fertilizer application and wastewater dis- charge. Concentrations of IP, total P, and N fix all decreased conspicuously upcore at 41 cm depth (1977), and were largely consistent with the decrease in rainfall and freshwater discharge to JZB. Our data sug- gest that the environment has significantly changed since the1980s. Anthropogenic activities in the watersheds may exert a substantial influence on carbon cycling processes in estuaries and potentially the coastal ocean. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Global nutrient cycles have been greatly altered by land-use changes resulting from human disturbance over the last century (Vitousek et al., 1997; Bennett et al., 2001). Excessive nutrient dis- charges and changes in their relative concentrations have been known to result in eutrophication, hence modifying aquatic food webs and causing severe hypoxic events in coastal environments (Humborg et al., 1997; Ragueneau et al., 2002; Turner and Rabalais, 1994; Turner, 2002; Piehler et al., 2004). Even though monitoring programs and historical data are not sufficient to establish the anthropogenic effects on the ecology of coastal areas, stratigraphic records preserved in the sediments can be used to reconstruct environmental changes in coastal areas (e.g., anoxia and eutrophi- cation) (Cooper and Brush, 1993; Gooday et al., 2009). The objective of this study is to assess how human-induced activities and the impact of changing environmental conditions in JZB are recorded in sediments, and to elucidate the changing nature of nutrient composition including the forms of the nutrients deposited during the last century in order to understand changes in the trophic state of JZB in relation to changes in land use and water, sediment, and nutrient delivery to JZB. The results of sedi- mentary paleoindicator studies help validate the need for manage- ment of nutrient loads for a system where nutrient-related problems are difficult to identify, based on limited water quality data. 2. Study site JZB is a typical semi-enclosed water body with a channel of 2.5 km width connected with the Yellow Sea, with an area of 390 km 2 and an average water depth of 6–7 m. Almost one fifth of the bay area is intertidal. The southeast and southwest shores 0025-326X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2010.04.003 * Corresponding author. Tel.: +86 532 66782005; fax: +86 532 66781810. E-mail address: sumeiliu@ouc.edu.cn (S.M. Liu). Marine Pollution Bulletin 60 (2010) 1591–1599 Contents lists available at ScienceDirect Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul