Distribution, partitioning and sources of dissolved and particulate nitrogen and phosphorus in the north Yellow Sea

Accepted Manuscript Distribution, partitioning and sources of dissolved and particulate nitrogen and phosphorus in the north Yellow Sea Li-Qin Duan, Jin-Ming Song, Hua-Mao Yuan, Xue-Gang Li, Ning Li PII:

S0272-7714(16)30299-2

DOI:

10.1016/j.ecss.2016.08.044

Reference:

YECSS 5234

To appear in:

Estuarine, Coastal and Shelf Science

Received Date: 2 September 2015 Revised Date:

24 August 2016

Accepted Date: 29 August 2016

Please cite this article as: Duan, L.-Q., Song, J.-M., Yuan, H.-M., Li, X.-G., Li, N., Distribution, partitioning and sources of dissolved and particulate nitrogen and phosphorus in the north Yellow Sea, Estuarine, Coastal and Shelf Science (2016), doi: 10.1016/j.ecss.2016.08.044. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Distribution, partitioning and sources of dissolved and particulate

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nitrogen and phosphorus in the north Yellow Sea

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Li-Qin Duana,b∗, Jin-Ming Songa,b*, Hua-Mao Yuana,b, Xue-Gang Lia,b, Ning Lia,b

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a

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Sciences, Qingdao, 266071, PR China

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b

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Technology, Qingdao, 266237, PR China

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Abstract: Little is known about characteristics of dissolved and particulate N and P forms in the

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north Yellow Sea (NYS). In this study, water and particulate samples were collected from the NYS

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to understand the biogeochemical behaviors, interactions and sources of dissolved and particulate

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N and P. Among the various N and P forms, dissolved organic N (DON) and P (DOP) were the

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predominant forms, accounting for 64% and 65% of total N (TN) and P (TP). Dissolved and

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particulate inorganic N and P displayed a decreasing trend from northwest region to the middle

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region, which was mainly influenced by riverine input along the Liaodong Peninsula coast.

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However, dissolved and particulate organic N and P showed higher values at northwest region and

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southern region, which were dominantly affected by biological activities and the Bohai Sea input.

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Vertical distribution patterns of dissolved and particulate N and P generally displayed the higher

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values at surface and bottom waters, which was the combined result of the influences by

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thermocline, the Yellow Sea Cold Water Mass (YC), biological activities and sediment

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resuspension. There were significant correlations between dissolved and particulate pools and

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Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of

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Marine Ecology and Environmental Science Laboratory, Qingdao National Laboratory for Marine Science and

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Corresponding author. Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, PR China. Tel.:

+86 532 82898583; fax: +86 532 82898583. E-mail addresses: [email protected] (J. Song), [email protected] (L. Duan). 1

ACCEPTED MANUSCRIPT between inorganic and organic forms, indicating their transformations through phytoplankton and

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bacteria activities and adsorption/desorption processes. Budgets suggested that net sink of

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dissolved inorganic N and P in the NYS could be mainly removed from water column. Particulate

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N and P were mainly from phytoplankton productivity, contributing to 84% and 74% of total

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particulate N (TPN) and P (TPP) influx.

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Keywords: Nitrogen; Phosphorus; Partitioning; Sources; the north Yellow Sea

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1. Introduction

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Nitrogen (N) and phosphorus (P) as major bioactive elements, play an essential role in the

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biological productivities, ecosystem functions and biogeochemical processes in marine

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environments (Lin et al., 2012; Loh and Bauer, 2000). In some marine ecosystems, elevated N and

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P inputs to aquatic environment will increase the eutrophication risk on water quality (Yu et al.,

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2012; Zhou et al., 2008), contrarily, the absent N and P will limit algal growth (Worsfold et al.,

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2008). In aquatic environments, N and P exist in both dissolved and particulate pools, each of

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which contains organic and inorganic forms (Loh and Bauer, 2000; Suzuki et al., 2015; Yoshimura

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et al., 2007).

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Dissolved N and P are essential nutrients for the growth of marine primary and secondary

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producers ( Burford et al., 2008; Carpenter and Dunham, 1985; Vegter and De Visscher, 1987).

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Total dissolved N (TDN) and P (TDP) occur in both dissolved inorganic N (DIN) and P (DIP) and

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dissolved organic N (DON) and P (DOP) (Lin et al., 2012; Loh and Bauer, 2000; Shi et al., 2015).

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Among them, DIN, in the form of nitrate (NO3-), nitrite (NO2-) and ammonium (NH4+), is thought

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to be the major bioavailable form of N. DON mainly contains protein, free amino acids, amides,

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vitamin and urea (Berman and Bronk, 2003). A large fraction of DON is now known to be

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ACCEPTED MANUSCRIPT bioavailable and provides the majority of N requirements in certain oligotrophic systems (Doval et

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al., 1999; Worsfold et al., 2008; Moschonas et al., 2015). The DIP pool consists of orthophosphate

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(PO43-), pyrophosphate (pyroP) and polyphosphate (polyP), in which PO43- is the dominant form

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and has high reactivity and can be utilized easily by phytoplankton whereas pyroP and polyP can

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not be absorbed easily by some phytoplankton species (Diaz et al., 2016). DOP comprises a major

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fraction of dissolved P (Karl and Björkman, 2002) and may be utilized by marine photoautotrophs

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as well as by microheterotrophs (Björkman and Karl, 1994; Loh and Bauer, 2000; Orrett and Karl,

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1987).

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Particulate N and P, accounting for a large proportion of total N and P, are essential factors in

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nutrient loading and act as potential sources of dissolved nutrients in the coastal waters (Shen et al.,

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2008; Yu et al., 2012; Zhang et al., 2003). Total particulate N (TPN) and P (TPP) also exist in

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inorganic N (PIN) and P (PIP), and organic N (PON) and P (POP) forms (Labry et al., 2013; Yu et

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al., 2012). PIN is mainly from riverine input and marine source, such as biological debris (Yu et

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al., 2012). Besides, the fine suspended particles can also adsorb some forms of dissolved nitrogen

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and become absorbed nitrogen. At present, the study on the PIN determination method is less and

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mainly based on the extraction method of PIP. This method has been used to extract PIN in the

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East China Sea (Yu et al., 2012). PON consists of organic nitrogen debris, bacteria and

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phytoplankton composition, which can be readily recycled by mineralization, especially in

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maximum turbidity zones of estuaries (Abril et al., 2000). PIP occurs in mineral phases (i.e.,

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orthophosphate, pyrophosphate and polyphosphate), which can be adsorbed to biotic and abiotic

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particles and as intracellular storage products (Yoshimura et al., 2007). POP comprises P

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incorporated in living and detrital organic molecules such as phosphomonoesters and diesters,

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ACCEPTED MANUSCRIPT phosphonates, and nucleotides (Labry et al., 2013). Dissolved and particulate organic N and P

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have been shown to be a significant component (~40%) of the total dissolved and particulate pools

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(Boynton et al., 1995; Loh and Bauer, 2000; Ormaza-González and Statham, 1996). Due to the

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bioavailability and turnover times between inorganic and organic forms of N and P are different,

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thus, it is necessary to research the characteristic and dynamic of each form of N and P, which is

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useful to understand their cycles in aquatic environments.

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Coastal waters are active interfaces between terrestrial and oceanic environments that have a

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large discharge of fluvial materials, complex biogeochemical processes and anthropogenic inputs.

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The north Yellow Sea (NYS), as a semi-closed marginal sea and one of the world’s most

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representative shallow continental shelf oceans (Yang et al., 2010), is rich in natural resources and

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plays an important role in human life and economic exploitation of the Chinese eastern littoral. It

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is also the link for material and energy exchange between the Bohai Sea and South Yellow Sea (Lu

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et al., 2005). Thus, the NYS is a dynamic system governed by riverine input, currents and

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anthropogenic input. At present, due to their high reactivity and easy uptake by marine organisms,

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DIN and DIP and their bioavailability in the NYS have been studied (Li et al., 2013; Zhao et al.,

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2012). However, compared with dissolved inorganic N and P, little is known about the

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corresponding organic and particulate N and P characteristics and fluxes in the NYS. In addition,

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studies examining both dissolved and particulate, and inorganic and organic N and P in the NYS

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are even scarcer. Therefore, this paper investigated inorganic and organic N and P in both

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dissolved and particulate forms in the NYS. The aim was to explore the behaviors, variations,

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interactions and sources of dissolved and particulate N and P in the NYS. This study will provide

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the data base for the future research on N and P cycles in the NYS.

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2. Materials and methods

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2.1. Study area The NYS is a semi-closed marginal sea bordered by the Chinese mainland and the Korean

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peninsula (Fig. 1). It is one of the world’s most representative shallow continental shelf oceans

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with an average depth of about 38 m (Yang et al., 2010). It is separated from the Bohai Sea (BS) to

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the west by the Bohai Strait, and from the South Yellow Sea (SYS) to the south by a line

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connecting the Chengshanjiao of the Shandong Peninsula and the Changshanchuan of the Korean

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Peninsula. Thus, the NYS is the link for material and energy exchange between the BS and SYS

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(Lu et al., 2005). Major rivers discharging into the NYS include rivers along the Liaodong

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Peninsula coast (e.g., the Yalu, Dayang, Zhuang, Biliu and Dengsha Rivers) with sediment

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discharge of 250×104 t/yr, and rivers along the Shandong Peninsula coast (e.g., the Jia River and

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Jie River) with sediment discharge of 140×104 t/yr (Cheng, 2000).

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Fig. 1. Study area and sampling locations of the north Yellow Sea

The circulation patterns in the NYS are dominated by the Yellow Sea Cold Water Mass (YC),

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Yellow Sea Warm Current (YSWC) and coastal currents along the northern and eastern coasts of

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the NYS. The YC is a mixed water of outer seawater and coastal water and has low temperature.

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The YSWC is a branch of the Tsushima Current that flows northwestward into the SYS and carries

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warm and salty water into the Yellow Sea, roughly following the Yellow Sea Trough (Song, 2009).

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Coastal currents include the Liaonan Coastal Current (LCC), west Korean Coastal Current (KC)

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and Yellow Sea Coastal Current (YSCC). The LCC is formed by the flowing water from Yalu

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River southwestward along the south coast of Liaodong Peninsula and has low temperature. The

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KC flows southward along the west coast of Korean Peninsula and has low temperature and low

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ACCEPTED MANUSCRIPT salinity. The YSCC is formed by the cold water masses of Bohai Bay and Laizhou Bay converging

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at the effect of north wind and flows eastward along the north coast of Shandong Peninsula and

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then turns southward in Chengshantou.

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2.2. Sampling

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Seawater and suspended particle samples were collected in September 2012 from cruise of

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“Kexue 3” in the NYS. Thirty-six sampling sites in the NYS were set (Fig. 1). In all the sampling

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sites, seawaters and suspended particles were collected from surface and bottom (2 m above

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sediment) layers. Besides, seawaters and suspended particles at nine stations in two sections

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(BX-5 and NYS1) were collected for determining nutrients at six depths (surface, 5 m, 10 m, 20 m,

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30 m and bottom layers) according to the water depth. Transect BX-5 located in the YC and

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crossing the Zhangzi Island shellfish farms, was typical to present the influence of YC and organic

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detritus discharge of shellfish on the NYS; transect NYS1 located between the BS and NYS, was

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typical to present the influence of Bohai Sea input on the NYS. Seawater samples were collected

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by a CTD-Rosette system using Teflon coated bottles (10 L, Sea Bird Inc., USA) equipped with

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temperature, salinity and fluorescence sensors. Immediately after collection, about 100 ml

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seawaters were directly collected in acid-cleaned HDPE bottles and stored at -20 oC for total N

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(TN) and P (TP) determination; about 2 L seawaters were filtered through pre-acid-cleaned and

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pre-combusted (450 oC for 4 h), 47 mm diameter Whatman GF/F glass fiber filters. The filtrate

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samples for DIP and DIN were collected in acid-cleaned HDPE bottles and stored at -20 oC until

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analysis in the laboratory. The filters were rinsed with distilled water to remove dissolved nutrients

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after filtration, then were folded twice with the loaded surface inside, returned to the plastic Petri

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dishes, and stored at -20 oC for particulate sample analysis. Data of environment conditions,

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including temperature (T), salinity (S) and chlorophyll a (Chl a) were continuously determined by

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temperature, salinity and fluorescence probes installed in CTD.

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2.3. Measurement of dissolved, particulate and total N and P Nitrate (NO3-), nitrite (NO2-), ammonium (NH4+) and DIP were measured with a Skalar

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nutrient autoanalyzer using the standard colorimetric methods according to Aydin-Onen et al.

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(2012). The detection limits were 0.02, 0.02, 0.03 and 0.01 µM for NO3-, NO2-, NH4+ and DIP,

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respectively. The relative standard deviations (RSD) of both repeatability and reproducibility for

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nutrient analysis was <5%. TN and TP were measured by an autoclave-assisted persulfate method

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according to Lin et al. (2012) with some modifications. Briefly, 20 ml of unfiltered seawater

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sample and 5 ml 0.15 mol/L alkaline K2S2O8 solution were added to a Teflon vial with a Teflon

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screw cap. The mixed solution was digested at 124 oC for 1 h in an autoclave. After digestion, TN

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and TP were measured with a Skalar nutrient autoanalyzer. Accuracy of TN and TP was assured

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using the standard addition method of calibration with recoveries of 94-101% and 98-100%, and

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RSD of both repeatability and reproducibility <5%.

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The filters were dried in oven at 60 oC and reweighed for suspended particulate material

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(SPM) determination. Particulate N and P were measured by the method of Yu et al. (2012).

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Briefly, the filters and blank membranes were shaken with 25 ml of 0.1 mol/L HCl for 2 h to

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extract PIN and PIP. Residue was treated with 0.15 mol/L alkaline K2S2O8 solution at 124 oC for 1

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h to digest PON and POP. Reactive N and P in HCl and K2S2O8 were determined with a Skalar

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nutrient autoanalyzer. Accuracies of PIP, POP, PIN and PON were assured using the standard

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addition method of calibration with recoveries of 93-98%, 95-101%, 92-103% and 98-102%, and

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RSD <5%. TPN and TPP were the sum of particulate inorganic and organic N and P. Ten

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particulate samples were analyzed for TPN and TPP using the same procedure as that for PON and

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POP analysis. The recoveries for particulate N and P were calculated as follows: Recovery=(CPIP/PIN+CPOP/PON)/CTPP/TPN×100%

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The recoveries for TPN and TPP were 95-105% and 93-107%, with RSD of both

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repeatability and reproducibility were <10%. Concentrations of DON and DOP were calculated

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from the difference between TN and (DIN+TPN) and between TP and (DIP+TPP). Chl a was

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collected from SeaBird CTD equipped with a fluorescent probe by calibration against discrete

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bottle samples. Bottle samples were collected approximately once every 10 stations in the field.

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Water samples were filtered immediately on board through pre-cleaned Whatman GF/F glass fiber

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filters. Chl a was measured by the method of Duan et al. (2010). Briefly, the filters were placed in

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amber glass vials containing 10 ml of 90% acetone and immediately stored in the dark at 4oC for

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24 h. After warming to room temperature, the soaked solution was analyzed with a fluorescence

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spectrophotometer (Hitachi F4600). The CTD fluorescence was calibrated by the method of

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Holliday et al. (2006). Briefly, calibration of CTD fluorescence was performed by calculating a

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linear fit between all the bottle samples and CTD fluorescence (after initial SeaBird calibration

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from volts to µg/L).

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2.4. Budget calculation

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The box models were used to calculate budgets of dissolved and particulate nutrients in the

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NYS. For dissolved nutrients, a simple LOICA approach (Gordon et al., 1996) was applied. In the

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model, the mass balance of nutrients in the NYS included riverine input, atmospheric deposit, and

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the exchange with the BS and SYS. The mass balance of water (Q) and dissolved nutrients (M) in

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the NYS was as follows: 8

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QR+QP-QE+Qin-Qout+∆Q=0

(1)

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QR·CR(i) + QP·CP(i)+Qin·Cin(i) -Qout·Cout(i) +∆M (i)=0

(2)

Where Q represented the water flux for inputs (+) and outflows (-) over the NYS, ∆Q and ∆M

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were net budgets of water and dissolved nutrients in the NYS. C was the dissolved nutrient

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concentration in each water column. R, P, E, in and out respected rivers, atmospheric wet

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precipitation, evaporation, input from the BH and SYS to NYS, and output from the NYS to BH

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and SYS. “i” represented the forms of dissolved nutrients (DIN and DIP).

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For particulate nutrients, four major fluxes of particulate nutrients in the NYS were

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considered, namely the external input from rivers along the Liaodong peninsula coast (e.g., the

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Yalu River) and north coast of Shandong peninsula (e.g., the Jia River), the adjacent sea (i.e., the

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BS and SYS), marine source from phytoplankton production, and output flux through

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sedimentation of suspended matter. The mass balance of suspended particles (FS) and particulate

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nutrients (F) in the NYS was as follows:

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FSNYS=FSR+FSBS+FSSYS+FSPhy-FSSed+∆

(3)

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FNYS(i)=FR(i)+FBS(i)+FSYS(i)+Fphy(i)-FSed(i)+ ∆(i)

(4)

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Where FSNYS and FNYS were suspended particle and particulate nutrient fluxes in the NYS,

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respectively. NYS, R, BS, SYS, Phy and Sed denoted the fluxes of NYS, rivers, BS, SYS,

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phytoplankton and sedimentation, respectively. “i” represented the forms of particulate nutrients

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(TPP and TPN). ∆ and ∆(i) were the discrepancies in suspended particle and nutrient mass balance,

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probably resulting from the uncertainty of estimation or other fluxes not considered. FNYS(i) and

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FSed(i) were calculated as Eqs. (5) and (6), respectively.

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FNYS(i)=QNYS·CSNYS·CNYS(i)

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FSed(i)=FSSed·CSed(i)

(6)

Where QNYS, CSNYS, CNYS and CSed were the volume of study area, suspended particle

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concentration and nutrient concentration in suspended particles and surface sediments of the NYS,

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respectively.

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2.5. Drawing software and statistical analysis

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Surfer 11.0 was used to draw the isolines of horizontal and sectional distributions of physical

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parameters (i.e., temperature, salinity, SPM and Chl a) and ratios between dissolved inorganic N

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and P and total dissolved N and P, and between particulate inorganic N and P and total particulate

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N and P in the NYS. The interpolation method “Kriging” was selected in this study.

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Pearson correlation analysis performed by SPSS 13.0 was used to evaluate the relationships

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between dissolved and particulate N and P, and between them and environmental parameters (e.g.,

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salinity, SPM and Chl a). A value of p<0.05 (2-tailed) was considered to indicate a significant

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difference.

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3. Results

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3.1. Hydrographic features

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3.1.1. Horizontal distributions

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Temperature, salinity, SPM and Chl a in seawaters of the NYS were determined.

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Temperatures and salinity in surface seawaters varied from 20.32-22.88 oC and from 28.34-31.39,

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with a decreasing trend westward (Fig. 2). It was mainly influenced by the YSWC having high

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temperature, high salinity and low nutrients. SPM concentrations ranged from 9.50 to 33.40 mg/L

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with an average of 14.86 mg/L. Horizontal variation of SPM was small except a highest value at

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station B11-1. Chl a concentrations ranged from 0.10 to 8.27 µg/L, with an average of 0.81 µg/L. 10

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the nutrients discharged from rivers along the Liaodong Peninsula coast had an important effect on

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the enhancement of phytoplankton biomass in this area.

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Fig. 2. Horizontal distributions of temperature (oC), salinity, suspended particulate matter (mg/L) and chlorophyll a

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(µg/L) at surface seawaters of the north Yellow Sea.

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3.1.2. Vertical distributions

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Vertical distributions of hydrographic features in transects NYS1 and BX-5 are presented in

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Fig. 3. In both transects, temperature showed a decreasing trend with depth with an obvious

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stratification at 20 m depth. In contrary, salinity showed an increasing trend with depth with lower

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values at NYS1-2 near the coast due to the extending of high salinity from the middle NYS to the

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Bohai Strait. SPM showed an increasing trend with depth, reflecting the influence of sediment

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resuspension. Chl a did not display an obvious trend, with higher values at surface layer and 30 m

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layer. Higher Chl a concentration at 30 m layer coincided with a nutricline, suggesting that there

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still was sufficient light to ensure primary production.

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Fig. 3. Sectional distributions of temperature (oC), salinity, SPM (mg/L) and chlorophyll a (µg/L) along transects

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BX-5 and NYS1 of the north Yellow Sea.

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3.2. Dissolved N and P

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3.2.1. Horizontal distributions

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Dissolved inorganic and organic N and P concentrations are listed in Tables 1 and 2. TDP and

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TDN were main components, accounting for 79% and 87% of TP and TN, respectively. In the

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dissolved phases, DIN, DON, DIP and DOP concentrations ranged from 0.77-9.91, 0.02-26.36,

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0.01-0.67 and 0.01-4.67 µM, with averages of 4.50, 13.11, 0.19 and 1.03 µM, respectively. DIN 11

ACCEPTED MANUSCRIPT was mainly dominated by NO3-, followed by NH4+, and NO2- was lowest. In surface waters, DON

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and DOP concentrations were significantly higher than DIN and DIP concentrations and accounted

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for 83% and 74% of TDP and TDN at most of stations in the outer shelf waters. In contrast, DIN

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and DIP concentrations exceeded DON and DOP concentrations only at the northwest region and

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west region (Fig. 4 and Supplement Fig. 1). The similar phenomenon that DON and DOP as

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dominant forms of TN and TP also were observed in the adjacent seas (i.e., the BS and SYS).

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Briefly, DON and DOP concentrations accounted for 66% and 41% of TN and TP in the BS (Mi,

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2001), and while accounted for 51% and 50% of TN and TP in the SYS (Liu et al., 2003).

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Table 1 Concentrations of dissolved, particulate and total N in the north Yellow Sea.

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Table 2 Concentrations of dissolved, particulate and total P in the north Yellow Sea.

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Fig. 4. Horizontal distributions of DIN/TDN and DIP/TDP at surface seawaters of the north Yellow Sea.

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3.2.2. Vertical distributions

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Two cross sections were chosen to present the vertical distributions of dissolved N and P,

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which were transects BX-5 and NYS1. These two cross sections were typical to present the

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influence of YC and Bohai Sea input on the NYS. In both transects, DIN and DIP presented an

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increasing trend from surface to bottom layer (Supplement Figs. 2 and 3), which was accordance

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with thermocline. Similarly, DOP showed an increase from surface to bottom layer; however,

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DON did not display an obvious distribution trend with the maximum values at surface and

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subsurface layers, indicating biological production of DON in surface waters and bacterial

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degradation of organic debris at bottom waters.

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Vertical distributions of DIN/TDN and DIP/TDP in transects BX-5 and NYS1 are presented

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in Fig. 5. In both transects, DIN/TDN generally displayed an increasing trend with depth and 12

ACCEPTED MANUSCRIPT became the dominant species, representing more than 50% in bottom waters of stations NYS1-2

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and B7-5, indicating biological uptake of DIN in the upper water column. Conversely, DON/TDN

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displayed a decreasing trend with depth, indicating biological production of DON in surface

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waters. Besides, the decrease in DON at depth with a corresponding increase in DIN was the result

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of bacterial mineralization. Compared with N, DIP/TDP and DOP/TDP in both transects did not

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display an obvious distribution trend. In transect BX-5, DIP/TDP generally displayed an

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increasing trend with depth and DOP/TDP showed the opposite trend except station B3-5, which

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is located in the Zhangzi Island shellfish farm. Due to the discharge of fecal debris by shellfish,

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DOP/TDP at bottom water in station B3-5 displayed higher value. In transect NYS1, DIP/TDP

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remained fairly constant with depth except the higher value at surface water of station NYS1-6.

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Fig. 5. Sectional distributions of DIN/TDN and DIP/TDP along transects BX-5 and NYS1 of the north Yellow Sea.

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3.3. Particulate N and P

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3.3.1. Horizontal distributions

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Particulate inorganic and organic N and P concentrations are listed in Tables 1 and 2. TPN

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and TPP concentrations in the NYS ranged from 0.29-8.07 and 0.10-0.60 µM, with averages of

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2.46 and 0.23 µM, respectively. Different to the partitioning of inorganic and organic P in

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dissolved pool, PIP had a main contribution (65%) to TPP than POP. In contrary, PON was the

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predominant speciation of TPN (60%). In surface waters, all of PIN, PIP, PON and POP

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concentrations generally displayed an increasing trend from the center to the surrounding, which

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may be attributed to the terrigenous and phytoplankton inputs. However, the maximum values of

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PIN, PIP, PON and POP appeared at different region: PIN, PIP and PON at northwest region; POP

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at northeast region (Supplement Fig. 4). Horizontal distributions of PIN/TPN and PIP/TPP are

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ACCEPTED MANUSCRIPT shown in Fig. 6. In surface waters, PON and PIP concentrations were significantly higher than PIN

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and POP concentrations at most of stations. In contrast, PIN and POP concentrations exceeded

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PON and PIP concentrations only near the Zhangzi Island (Fig. 6). Particularly, PIP/TPP had

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higher values at the northern region, which may be attributed to the influence of terrigenous inputs;

5

whereas PIN/TPN had higher values near the Zhangzi Island, which was likely related to marine

6

inputs.

7

Fig. 6. Horizontal distribution of PIN/TPN and PIP/TPP at surface seawaters of the north Yellow Sea.

8

3.3.2. Vertical distributions

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Particulate N and P in transects BX-5 and NYS1 also were studied. PIN displayed different

10

vertical distributions in transects NYS1 and BX-5 (Supplement Figs. 5 and 6). There were two

11

distribution patterns for PIN in transect NYS1: the maximum value occurred at 20 m layer and

12

then decreased upward and downward for station NYS1-2, NYS1-4 and NYS1-6; the maximum

13

value occurred at bottom layer and then decreased upward for NYS1-8 and NYS1-9. PIN in

14

transect BX-5 generally presented an increasing trend downward. Differently, PIP, PON and POP

15

in both transects displayed the similar vertical distribution (Supplement Figs. 5 and 6). They had

16

the minimum values at 10-20 m layer and then increased upward and downward, which was

17

closely related to thermocline.

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Vertical distributions of PIN/TPN and PIP/TPP in transects BX-5 and NYS1 are presented in

19

Fig. 7. In both transects, these ratios did not displayed obvious variation trends. In detail,

20

PIN/TPN in both transects had higher values at 10-20 m layer, which exceeded 50% and was

21

closely related to thermocline; whereas higher PON/TPN appeared at surface and bottom layers,

22

where higher values at surface layer may be attributed to phytoplankton activities and higher 14

ACCEPTED MANUSCRIPT values at bottom layer were likely related to sediment resuspension and discharge of fecal debris

2

by scallop. Higher PIP/TPP values appeared at surface layer of station B13-5, which may be due

3

to the YSWC contribution. Besides, higher PIP/TPP also appeared at surface layer of station

4

NYS1-2 and middle layer of station NYS1-6 and NYS1-9, which were attributed to terrigenous

5

and Bohai Sea inputs. Higher POP/TPP appeared at bottom layer of station B3-5 and NYS1-2,

6

suggesting the contributions of discharge of fecal debris by scallop and terrigenous inputs,

7

respectively.

8

Fig. 7. Sectional distributions of PIN/TPN and PIP/TPP along transects BX-5 and NYS1 of the north Yellow Sea.

9

4. Discussions

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4.1. Influencing factors

11

4.1.1. Influencing factors on horizontal distributions

Dissolved and particulate inorganic N and P generally displayed a decreasing trend from the

13

northwest region to the middle region (Supplement Figs. 1 and 4). This distribution was mainly

14

influenced by riverine input along the Liaodong Peninsula coast. The Yalu River as main riverine

15

input of the NYS, delivers annually 25.1×109 m3 of freshwater and 113×104 t of particles into the

16

NYS (State Oceanic Administration, 1998). DIP, DIN, TPP and TPN concentrations in the Yalu

17

River were 0.87, 34.0, 2.32 and 5.74 µM (Li et al., 2012; Li et al., 2010; Wang et al., 2003; Wang

18

et al., 2004), which were far higher than average DIP, DIN, TPP and TPN concentrations (0.19,

19

4.5, 0.23 and 2.45 µM) in the NYS. Large amount of freshwaters and particles rich in dissolved

20

and particulate inorganic N and P from rivers entered into the NYS and then was transported to the

21

northwest region by westward LCC, causing higher dissolved and particulate inorganic N and P

22

concentrations in the northwest region. DIN, PIP and POP in surface waters had significant

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ACCEPTED MANUSCRIPT negative correlations with salinity with r=-0.718 (p<0.01), -0.721 (p<0.01) and -0.668 (p<0.01),

2

which indicating that DIN and particulate P were mainly supplied by the Yalu River. The influence

3

of riverine input on inorganic N and P distribution also was observed in other sea areas. It has been

4

reported that higher PIP concentrations in the inner shelf of East China Sea (ECS) was mainly

5

from the Changjiang River input, which was transported southward by the Zhejiang-Fujian

6

Coastal current (Yu et al., 2012). Yuan et al. (2009) found that higher PIP near shore of the

7

Jiaozhou Bay was obviously influenced by riverine input. Guo et al. (2004) and Ping et al. (2011)

8

reported that particulate P in the Arctic Ocean came from terrestrial inputs, including riverine

9

export and coastal erosion.

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DON and DOP had irregular patchy distributions (Supplement Fig. 1), which might be

11

related to biological activities, such as planktonic exudation, dissolution from detritus and

12

bacterial decomposition. Higher DON and DOP at the northwest region corresponded to higher

13

Chl a concentration, suggesting that the planktonic exudation was their main contributor. Higher

14

DON and DOP near the Zhangzi Island were mainly attributed to dissolution from fecal debris of

15

scallop. As one of the most important aquaculture bases, the Zhangzi Island was cultured by

16

sowing year-old seed freely on bottom layer. Its total production reached 12000 tons in 2005,

17

accounting for 46% of total bottom-cultured Patinopecten yessoensis production in coastal areas

18

of China (Zhang et al., 2008). Thus, the fecal debris of Patinopecten yessoensis played an

19

important role in higher DON and DOP near the Zhangzi Island. The influence of biological

20

activities on DOP distribution also was observed in other sea areas. Fang (2004) has reported that

21

DIP was the major form of TDP in inner and middle shelf waters in the ECS, but DOP

22

concentration surpassed DIP concentration in the outer shelf waters, suggesting that continental

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ACCEPTED MANUSCRIPT input was main source of DIP and high DOP was ascribed to high biological production. Rinker

2

and Powell (2006) found that the highest DOP concentration at coastal waters of the Eel River

3

Shelf occurred during summer with high primary productivity and surpassed DIP concentration.

4

There was no correlation among DON, DOP and Chl a in the NYS, suggesting that DON and DOP

5

may have other important sources (e.g., riverine input) to the NYS, which covered their marine

6

sources. DON and DOP concentrations of the Yalu River were 13 µM and 0.20 µM (Hu et al.,

7

2014; Hua et al., 1994), combined with runoff of the Yalu River (25.1×109 m3/yr), the riverine

8

inputs of DON and DOP from the Yalu River to the NYS were calculated to be ca. 4.6×103 and

9

156 t/yr, respectively. The Yalu River input as the dominant source of DON in the NYS also was

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found by Hu et al. (2014).

PON and POP showed higher values at northwest region and southern region, which were

12

dominantly affected by biological activities consisting of living and dead organisms and their

13

exudation and decomposition products and the Bohai Sea input. Since measurements of primary

14

productivity were not performed on this cruise, Chl a concentrations were used to infer

15

phytoplankton activities. The influence of phytoplankton activities on PON and POP was

16

supported by their relations with Chl a concentration, with correlative coefficients of 0.68 (p<0.01)

17

for POP and 0.54 (p<0.01) for PON when Chl a concentrations were <3.0 µg/L (Fig. 8). Higher

18

PON and POP values appeared at the northwest region, which were consistent with higher Chl a

19

concentrations. The influence of biological activities on particulate N and P distribution also was

20

observed in other sea areas. Yoshimura et al. (2007) found the significant correlations between

21

POP, PIP and Chl a in North Pacific surface waters, suggesting that P pools were associated with

22

phytoplankton activities.

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ACCEPTED MANUSCRIPT Besides, higher PON and POP concentrations also appeared at the southern region, which

2

might be related to the impact of neighboring regions (i.e., the BS and SYS inputs). The average

3

PIN, PON, PIP and POP concentrations were 1.11, 2.50, 0.59 and 0.35 µM in the BS (our

4

unpublished data) and 1.76, 5.36, 0.57 and 0.27 µM in the SYS (Yu et al., 2012), which were 2-4

5

times higher than those in the NYS (0.85 µM for PIN, 1.60 µM for PON, 0.15 µM for PIP and

6

0.08 µM for POP). The delivery of these particles rich in N and P by the eastward circulating

7

current of the BS and by the northward YSWC might contribute to the higher particulate N and P

8

concentrations in the southern region. The influence of coastal currents on dissolved and

9

particulate N and P distributions also was observed in other sea areas. Yu et al. (2012) studied the

10

impact of neighboring region (SYS) on particulate P concentrations in the ECS. They found that

11

higher PIP and POP concentrations in the northern ECS was attributed to the delivery of particles

12

rich in P of neighboring region (SYS) by the southward Jiangsu Coastal Current to the northern

13

ECS.

14

4.1.2. Influencing factors on vertical distributions

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Vertical distributions of dissolved N and P were influence by thermocline, YC and biological

16

activities. Thermocline was one of important factors influencing the vertical distributions of

17

nutrients. In spring, due to the delay of temperature increase in bottom layer, thermocline began to

18

form. Then in summer, thermocline became strongest and the temperature difference between

19

upper layers (i.e., surface and 10 m) and lower layers below 30 m reached maximum with the

20

differences of 7-10 oC. Due to the existence of thermocline, the water mixture between upper and

21

lower layers was prevented. Therefore, the lower layer with high nutrients could not be exchanged

22

to the upper layer, thereby causing the nutrient stratification.

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ACCEPTED MANUSCRIPT The YC was another important factor to affect vertical distributions of dissolved N and P. The

2

formation, development and decline of YC were synchronous with thermocline change. In spring,

3

cold water mass began to form at bottom layer of the NYS, and particulate N and P began to

4

accumulate in cold water mass (Yu et al., 2006). Then in summer, an obvious and stable cold water

5

mass having a large number of organic particles was entrenched in the middle region of the NYS.

6

Moreover, phytoplankton transformed a lot of dissolved inorganic N and P to particulate organic N

7

and P, and then these particulate organic N and P were accumulated in cold water mass. When

8

autumn came, particulate N and P at bottom waters were remineralised to dissolved inorganic N

9

and P, resulting in the higher dissolved inorganic N and P concentrations at bottom waters. The YC

10

as an important nutrient reservoir, contributed 46% and 64% of DIN and DIP to the NYS (Chen et

11

al., 2012). When water stratification weakened and disappeared in autumn, the YC would be a

12

great supplement of nutrients to seawaters of the NYS.

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Besides, the phytoplankton in euphotic layer needed to adsorb a large amount of nutrients to

14

maintain growth, which might lead to the lower inorganic N and P at the upper layer (Duan et al.,

15

2015). Moreover, the YSWC could carry seawaters with high temperature, high salinity and low

16

nutrients into surface layer of the NYS (Song, 2009), which diluted the nutrient concentrations at

17

surface seawaters to some extent. Consequently, above controlling factors together resulted in the

18

higher dissolved N and P concentrations at bottom waters than those at upper layers.

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Vertical distributions of particulate N and P were influenced by thermocline, phytoplankton

20

exudation and decomposition products, sediment resuspension and discharge of fecal debris by

21

Patinopecten yessoensis. Higher particulate N and P in upper layers were mainly from riverine

22

input and phytoplankton exudation and decomposition products. The contribution of riverine input 19

ACCEPTED MANUSCRIPT to upper layers has been discussed in the above section. Vertical distribution of POP in transect

2

BX-5 was coupled with Chl a (r=0.722, p<0.01), supporting the contribution of phytoplankton

3

exudation to upper layers. Higher particulate N and P in bottom layers were mainly from sediment

4

resuspension and the fecal debris of Patinopecten yessoensis and its dissolution. Vertical

5

distributions of PIP, POP and PON in transect NYS1 and PIP and PIN in transect BX-5 were

6

similar to SPM distribution (r=0.638, p<0.01; r=0.771, p<0.01; r=0.608, p<0.01; r=0.721, p<0.01;

7

r=0.625, p<0.01), suggesting the important influence of sediment resuspension. The existence of

8

thermocline led to the decrease of water mixture between upper and lower layers, resulting in that

9

the lower particulate N and P concentrations appeared at middle layer and then increased upward

10

and downward.

11

4.2. Interactions between different forms

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In the N and P cycles, there were transformations between dissolved and particulate pools

13

and between inorganic and organic forms through phytoplankton and heterotrophic bacteria

14

activities and adsorption/desorption processes (Bradley et al., 2010; Liu et al., 2016). The

15

traditional view of the cycling process between dissolved inorganic and organic N and P was that

16

phytoplankton used DIN and DIP while heterotrophic bacteria mineralized DON and DOP into the

17

inorganic forms supporting primary production (Bradley et al., 2010). In the NYS, DIN and DIP

18

concentrations were highly correlated (r=0.75, p<0.01; Fig. 8), indicating that their origins and

19

metabolic pathways were similar. Therefore, analysis of inorganic and organic N/P ratio could

20

lead to some interesting hypotheses about the importance of N and P for primary producers in the

21

NYS. Average DIN/DIP ratio and DON/DOP ratio in surface waters of the NYS were 28.9 and

22

17.6, suggesting the P limit to phytoplankton growth. This was consistent with previous study

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ACCEPTED MANUSCRIPT (Zhao et al., 2012). Compared with inorganic pool, N/P ratio in organic pool was closer to

2

Redfield value (16) and less than DIN/DIP ratio, suggesting that the assimilation processes of

3

inorganic P by heterotrophic producer community were more efficient or that the release and

4

production of inorganic N was more efficient.

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There was no significant correlation between DIN and DON concentrations in surface waters,

6

which was likely attributed to the DON uptake by phytoplankton. Higher DIN could be satisfied

7

with phytoplankton uptake; however, when DIN concentration was lower, phytoplankton needed

8

to use DON to meet cellular N demands, resulting in the N cycle being complex. The DON uptake

9

by autotrophs to satisfy their N requirement have been found in many researches (Berman and

10

Bronk, 2003; Bronk et al., 2007; Moschonas et al., 2015). Differently to N, DIP and DOP had a

11

positive relationship, with correlation coefficient of 0.57 (p<0.01, Fig. 8), suggesting that they has

12

same origins or that the assimilation rate of DIP by phytoplankton and the remineralization rate of

13

DOP by bacteria was equivalent. Besides, DOP was the dominant form of TDP and was 5.4 times

14

higher than DIP in the NYS. Lower DIP concentration was closely related to the phytoplankton

15

uptake, whereas higher DOP concentration was attributed to the riverine input, zooplankton

16

excretion, phytoplankton exudation, lysis or solubility of living and detrital POM. Although there

17

was a significant correlation between DOP and POP (r=0.72, p<0.01, Fig. 8), POP concentration

18

was far lower than DOP concentration, suggesting the contribution of solubility of detrital POM

19

was small leaving riverine input as the main source.

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Many factors can influence the interactions between particles and dissolved chemical

21

constituents (Fang et al., 2004). Interaction of DIN and DIP with inorganic suspended particles

22

was thought to occur via a reversible two-step sorption process, the first involving rapid 21

ACCEPTED MANUSCRIPT adsorption/desorption at particle surface, and the second involving slow solid-state diffusion of

2

adsorbed DIN and DIP from surface of particle to interior (Liu et al., 2016). In the NYS, TPN and

3

TPP accounted for 13% and 21% of TN and TP. PIN and PIP accounted for 40% and 65% of TPN

4

and TPP, indicating that PIN and PIP were important fractions and could contribute to DIN and

5

DIP level after desorption. In this study, there were significant correlations between PIN and DIN

6

and between PIP and DIP, with correlative coefficients of 0.52 (p<0.05, Fig. 8) and 0.60 (p<0.01,

7

Fig. 8), respectively. Interactions of DIN and DIP with organic suspended particles were thought

8

to occur via biological uptake and microbial remineralization. DIN and DIP were taken up by

9

phytoplankton and microbe and converted to PON and POP in phytoplankton and microbial

10

biomass. In turn when these phytoplankton and microbes died, PON and POP were remineralised

11

to DIN and DIP. Especially for PON, it could be decomposed by bacteria to NH4+ and ultimately

12

NH4+ would be oxidized to NO3- by nitrite oxidizing bacteria and nitrate bacteria. In this study,

13

there was a significant correlation between PON and DIN, with correlative coefficients of 0.77

14

(p<0.01, Fig. 8), suggesting that N uptake and remineralization occurred at equal rates. However,

15

there was no correlation between POP and DIP, suggesting that P uptake and remineralization

16

occurred at different rates. In the regression analyses, there were two or three stations out of the

17

regression line (Fig. 8, values in the ellipse). These stations are mainly located at the northwest

18

region of the study area, which were significantly influenced by terrigenous input and biological

19

activities, making the N and P cycling more complicated than other stations. That was, the

20

excluded stations in the regression line were attributed to the riverine input of inorganic N and P

21

and bacteria decomposition of organic N and P. Rivers had great contribution to inorganic N and P

22

there, resulting in the higher inorganic N and P values. Besides, it was reported that the bacteria

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ACCEPTED MANUSCRIPT abundance at this area was higher than others (Fan et al., 2015), thus, the organic N and P

2

remineralization rate at this area was higher, resulting in the more organic N and P decomposed to

3

dissolved inorganic N and P. Consequently, the proportions between different forms of N and P in

4

these two or three stations were different from other stations and thus their values were out of the

5

regression line.

6

Fig. 8. Relationships between dissolved and particulate pools and between inorganic and organic forms of N and P

7

in the north Yellow Sea. The values in the ellipse were excluded.

8

4.3. Sources of dissolved and particulate N and P

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Although horizontal and vertical distributions of dissolved and particulate N and P were

10

controlled by several factors, they were essentially attributed to their sources. Sources of dissolved

11

and particulate N and P to the NYS mainly included riverine input, the adjacent sea input and

12

biological input.

13

4.3.1. Riverine inputs

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Rivers that enter the NYS include two series: rivers along the Liaodong Peninsula coast and

15

rivers along the Shandong Peninsula coast. Rivers along the Liaodong Peninsula coast include the

16

Yalu River, Dayang River, Zhuang River, Biliu River and Dengsha River, with the total freshwater

17

and suspended sediment fluxes of 28.3×109 m3/yr and 250×104 t/yr, respectively (Cheng, 2000).

18

Among them, the Yalu River is the main river along the Liaodong Peninsula coast entering the

19

NYS with freshwater and suspended sediment fluxes of 25.1×109 m3/yr and 113×104 t/yr,

20

respectively (State Oceanic Administration, 1998). After entering the NYS, dissolved and

21

particulate N and P in these freshwater and suspended matter would be carried westward by the

22

LCC, resulting in the higher dissolved and particulate N and P at northwest region. Due to the

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ACCEPTED MANUSCRIPT absent data of N and P concentrations in other rivers (except the Yalu River) along the Liaodong

2

Peninsula coast, thus, the dissolved and particulate N and P concentrations in the Yalu River were

3

used to roughly estimate fluxes. DIN, DIP, TPN and TPP concentrations in the Yalu River were 34

4

and 0.87 µM (Wang et al., 2003; Wang et al., 2004), and 0.67 and 0.60 mg/g (Li et al., 2012; Li et

5

al., 2010), respectively. Thus, the riverine influxes of DIN, DIP, TPN and TPP by rivers along the

6

Liaodong Peninsula coast to the NYS were 9.62×108 and 0.25×108 mol/yr, and 1675 and 1500 t/yr,

7

respectively (Tables 3 and 4). Rivers along the Shandong Peninsula coast include the Jia River, Jie

8

River, Zhongcun River, Longkou River and other small rivers, with the total freshwater and

9

suspended sediment fluxes of 5.6×108 m3/yr and 140×104 t/yr, respectively (Cheng, 2000; Qin et

10

al., 1989). Among them, the Jia River is the main river along the Shandong Peninsula coast

11

entering the NYS with freshwater and suspended sediment fluxes of 3.03×108 m3/yr and 35.4×104

12

t/yr, respectively. Due to the absent data of N and P concentrations in other rivers (except the Jia

13

River) along the Shandong Peninsula coast, thus, the dissolved and particulate N and P

14

concentrations in the Jia River were used to roughly estimate fluxes. DIN, DIP, TPN and TPP

15

concentrations in the Jia River were 16 and 0.42 µM, and 0.42 and 0.66 mg/g, respectively (Liu et

16

al., 2009). Thus, the riverine influxes of DIN, DIP, TPN and TPP by rivers along the Shandong

17

Peninsula coast to the NYS were about 8.96×106 and 0.24×106 mol/yr, and 588 and 924 t/yr,

18

respectively (Tables 3 and 4).

19

4.3.2. Adjacent sea inputs

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The BS and SYS are adjacent to the west and south of NYS. Exchange between the BS and

21

NYS is through the Bohai strait, whereas exchange between the NYS and SYS is by the YSWC.

22

The Huang River is the main river discharging into the BS with the freshwater and suspended 24

ACCEPTED MANUSCRIPT sediment discharges of 486×109 m3/yr and 1.0×109 t/yr, respectively (Milliman and Syvitski,

2

1992). Although freshwater and suspended sediment discharges of the Huang River are large, only

3

~1% suspended sediment enters the NYS through the Bohai Strait (Martin et al., 1993). Thus,

4

suspended sediment exchange flux was ca. 800×104 t/yr from the BS into NYS (Cheng, 2000).

5

The input flux of seawater from the BS to NYS was 52.2×109 m3/yr (Hong, 2012). DIN, DIP, TPN

6

and TPP concentrations in the BH were 12 and 0.26 µM (Song, 2009), and 2.111 and 0.308 mg/g,

7

which were used to calculate influxes of dissolved and particulate N and P from the BS to NYS

8

with 6.26×108 and 0.13×108 mol/yr, and 1.69×104 and 0.25×104 t/yr for DIN, DIP, TPN and TPP,

9

respectively (Tables 3 and 4). Another major sea input to the NYS was SYS. The input flux of

10

seawater from the SYS to NYS was 290×109 m3/yr (Hong, 2012). DIN and DIP concentrations in

11

the SYS were 4.47 and 0.45 µM (Liu et al., 2003; Song, 2009), which were used to calculate

12

influxes of dissolved N and P from the SYS to NYS with 12.96×108 and 1.31×108 mol/yr for DIN

13

and DIP, respectively (Table 3). Particulate N and P from the SYS to NYS were mainly carried by

14

the YSWC. These suspended sediments mainly came from the Changjiang River. According to

15

report, about 100×104 t suspended sediment of the Changjiang River was carried to the NYS by

16

YSWC annually, accounting for 0.2% of total sediment flux of the Changjiang River (Cheng,

17

2000). TPN and TPP concentrations were 1.226 and 0.319 mg/g in the SYS (Yu et al., 2012),

18

which were used to calculate particulate N and P influxes from the SYS to NYS with 1226 and

19

319 t/yr, respectively (Table 4). In conclusion, the riverine inputs and adjacent sea inputs of

20

particulate N and P to the NYS essentially came from the Yalu River, the Huanghe River and the

21

Changjiang River, the order of which contributions was the Huanghe River > the Yalu River > the

22

Changjiang River.

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ACCEPTED MANUSCRIPT 1

4.3.3. Biological inputs Phytoplankton and bacteria were major sources of marine particulate organic matter (Aminot

3

and Kérouel, 2004; Noe et al., 2007). In the NYS, DOP, DON and PON were dominant

4

components in TDP, TDN and TPN, with average percentages of 83%, 74% and 60%, suggesting

5

the importance of organic N and P in the N and P pools of NYS. Moreover, biological activities

6

played an important role in the organic N and P concentrations and distribution. The details about

7

their influence on the organic N and P have been discussed in the section of “Influencing factors”.

8

It suggested that phytoplankton was the important organic N and P producer. The average primary

9

productivity in the NYS was 108.9 gC/m2/yr (Gao, 2009). Given that phytoplankton derived

10

particles in the NYS were dominated by particulate organic matter, the sediment flux of

11

phytoplankton particles was estimated according to phytoplankton organic matter, the

12

concentration of which was two folds of carbon content in phytoplankton (Meyers, 2006; Rios et

13

al., 1998). Estimation result yielded a phytoplankton detritus flux of 218 g/m2/yr. POP and PON

14

influxes produced by phytoplankton calculated based on the Redfield ratios (C:N:P=106:16:1)

15

were 2.65 and 19.17 g/m2/yr, respectively. Combined with area of 5680 km2, biological influxes of

16

particulate N and P were 10.8×104 and 1.5×104 t/yr, respectively (Table 4).

17

4.3.4. Budgets

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The mass balance of dissolved N and P in the NYS were calculated according to riverine

19

input, atmospheric deposition and exchanges with the BH and SYS (Table 3). Besides riverine

20

input discussed in the above section, atmospheric deposition also was an important input. The

21

rainfall flux in the NYS was 3.95×109 m3/yr. DIN and DIP concentrations in rainfall were 72.6 and

22

1.35 µM (Hong, 2012), which were used to calculate atmospheric fluxes of dissolved N and P with 26

ACCEPTED MANUSCRIPT 2.87×108 and 0.05×108 mol/yr, respectively (Table 3). In addition, water exchange flux between

2

the BH and NYS was 52.2×109 m3/yr, with a net water import of 2.2×109 m3/yr from the BH to

3

NYS. Water exchange flux between the SYS and NYS was 323×109 m3/yr, with a net water export

4

of 33×109 m3/yr from the NYS to SYS.

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Combined the dissolved nutrient concentrations in rivers, rainfall, BH, SYS and NYS with

6

water import and export fluxes, the dissolved nutrient budgets in the NYS were calculated. As

7

shown in Table 3, the net sink of DIN and DIP were 15.01×108 and 0.26×108 mol/yr, respectively,

8

indicating their removal from water column, including at the sediment-water interface, air-sea

9

exchange, sediment deposition and off-shelf particle export.

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Budgets of particulate N and P in the NYS were calculated according the import and export

11

of particle N and P fluxes (Table 4). The particulate N and P influxes had been discussed at the

12

above section. Results showed that the BS and rivers along the Liaodong Peninsula coast were the

13

major particle sources of the NYS, accounting for 57% and 18% of total sediment influxes.

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Particulate N was mainly from phytoplankton productivity and BS, contributing to 84% and

15

13% of TPN influx. Besides phytoplankton productivity (74%) and BS (12%), riverine input also

16

was an important contributor to particulate P in the NYS, accounting for 12% of total TPP influx.

17

In contrast, the TPN influx from rivers only accounted for 2% of total TPN influx.

AC C

18

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14

The export of particulate N and P was attributed to sedimentation. Sedimentation flux in the

19

middle NYS was reported as 0.22 g/cm2/yr (Qi et al., 2004), which was employed to calculate

20

annual sediment accumulation of the NYS. About 88% of particle input into the NYS was finally

21

deposited to the seabed. Combined with area (5680 km2) and N and P concentrations in surface

22

sediments, sedimentation fluxes of N and P in this study area were 6500 and 5200 t/yr, 27

ACCEPTED MANUSCRIPT 1

respectively. There existed huge negative missing fluxes of particulate N and P which were 11.3×104 t for

3

TPN and 1.31×104 t for TPP. These missing fluxes of TPN and TPP were primarily attributed to

4

the missing of PON and POP, which most likely resulted from the dissolution and mineralization

5

of particulate nutrients (especially particulate organic matter) in the euphotic zone, leading to less

6

phytoplankton debris left in the euphotic zone to reach the seafloor. It was reported that less than

7

30% of phytoplankton organic matter was finally buried in sediment (Davies and Payne, 1984;

8

Zhang et al., 2007). If the whole missing fluxes of particulate N and P were caused by dissolution

9

and mineralization, this output flux accounted for 88% of TPN and 65% of TPP influxes. It was

10

revealed that the fates of particulate nutrients and dissolved nutrients were obviously different,

11

with the former finally being recycled or buried and the latter being assimilated by phytoplankton

12

or removal from the water by denitrification (Zhang et al., 2007).

TE D

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SC

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2

Table 3 Dissolved N and P concentrations and budgets in the north Yellow Sea

14

Table 4 Particulate N and P concentrations and budgets in the north Yellow Sea

15

5. Conclusions

EP

13

The north Yellow Sea (NYS) is the typical coastal water, nutrients in which are influenced by

17

multiple factors, such as terrigenous input, adjacent sea exchange, biological activities and

18

hydrodynamics. At present, the research on dissolved and particulate N and P forms and their

19

behaviors in the NYS are scarcer. Therefore, this study will provide the data base for the future

20

research on N and P cycles in the NYS. Similarly to the most coastal waters, dissolved and

21

particulate inorganic N and P displayed a decreasing trend from coast to the middle area, which

22

was mainly influenced by terrigenous input; however, higher dissolved and particulate organic N

AC C

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28

ACCEPTED MANUSCRIPT and P were consistent with higher Chl a concentrations, suggesting the dominant effect of

2

biological activities. Differently, DIN and DIP concentrations presented an increasing trend from

3

surface to bottom layer, which was attributed to the Yellow Sea Cold Water Mass (YC). The YC

4

was unique to the Yellow Sea and as an important nutrient reservoir could contribute 46% and 64%

5

of DIN and DIP to the NYS. However, particulate N and P in the NYS were mainly from

6

phytoplankton productivity, contributing to 84% and 74% of TPN and TPP influx.

RI PT

1

There were transformations between dissolved and particulate N and P and between

8

inorganic and organic forms in the NYS. The interactions between dissolved inorganic N and P

9

and organic forms were through assimilation process of inorganic forms by phytoplankton and

10

remineralization process of organic forms by bacteria. The interactions between dissolved and

11

particulate inorganic N and P were through adsorption/desorption processes. These interaction

12

processes occurred simultaneously, resulting in the different distributions of N and P in dissolved

13

and particulate pools and in inorganic and organic pools.

14

Acknowledges

TE D

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7

This paper was supported by the National Natural Science Foundation of China-Shandong

16

Joint Fund (No. U1406403), the National Key Project for Basic Research of China (No.

17

2015CB452902, 2015CB452901), Youth Innovation Promotion Association CAS (No. 2016191)

18

and Program for AoShan Excellent Scholars of Qingdao National Laboratory for Marine Science

19

and Technology.

20

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AC C

EP

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29

ACCEPTED MANUSCRIPT 1

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ACCEPTED MANUSCRIPT Fig. 1. Study area and sampling locations of the north Yellow Sea. (a) sampling locations of transect NYS1; (b)

2

transect BX-5 and other sampling locations.

3

Fig. 2. Horizontal distributions of temperature (oC), salinity, suspended particulate matter (mg/L) and chlorophyll a

4

(µg/L) at surface seawaters of the north Yellow Sea.

5

Fig. 3. Sectional distributions of temperature (oC), salinity, SPM (mg/L) and chlorophyll a (µg/L) along transects

6

BX-5 and NYS1 of the north Yellow Sea.

7

Fig. 4. Horizontal distribution of DIN/TDN and DIP/TDP at surface seawaters of the north Yellow Sea.

8

Fig. 5. Sectional distributions of DIN/TDN and DIP/TDP along transects BX-5 and NYS1 of the north Yellow Sea.

9

Fig. 6. Horizontal distribution of PIN/TPN and PIP/TPP at surface seawaters of the north Yellow Sea.

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1

Fig. 7. Sectional distributions of PIN/TPN and PIP/TPP along transects BX-5 and NYS1 of the north Yellow Sea.

11

Fig. 8. Relationships between dissolved and particulate pools and between inorganic and organic forms of N and P

12

in the north Yellow Sea. The values in the ellipse were excluded.

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37

ACCEPTED MANUSCRIPT Table 1 Concentrations of dissolved, particulate and total N in the north Yellow Sea. NH4+

NO3-

NO2-

DIN

DON

PIN

PON

TN

DON/TDN

PON/TPN

TDN/TN

(µM)

(µM)

(µM)

(µM)

(µM)

(µM)

(µM)

(µM)

(%)

(%)

(%)

Min

0.69

0.04

0.05

0.93

4.44

0.05

0.13

12.34

47

15

56

Max

4.82

5.14

0.73

7.65

22.16

2.75

4.80

27.13

93

99

98

Average

2.00

0.62

0.27

2.89

12.00

0.60

1.81

17.29

80

70

86

Min

0.56

0.23

0.17

2.71

0.02

0.02

0.05

1.22

4

6

25

Max

5.10

6.82

2.10

9.91

26.36

3.49

5.15

39.44

85

99

97

Average

1.90

4.12

0.56

6.58

Min

0.40

0.04

0.05

0.77

Max

6.07

6.82

2.10

9.91

Average

1.95

2.12

0.42

4.50

SC

M AN U 1.05

1.80

23.57

66

59

85

0.02

0.02

0.04

1.22

4

2

25

26.36

3.49

5.29

39.44

95

99

99

13.11

0.85

1.60

20.07

74

60

87

D

14.14

TE

All

EP

Bottom

AC C

Surface

RI PT

Layer

ACCEPTED MANUSCRIPT Table 2 Concentrations of dissolved, particulate and total P in the north Yellow Sea. DIP

DOP

PIP

POP

TP

DOP/TDP

PIP/TPP

TDP/TP

(µM)

(µM)

(µM)

(µM)

(µM)

(%)

(%)

(%)

Min

0.01

0.01

0.07

0.03

0.26

64

48

15

Max

0.34

2.20

0.33

0.15

2.53

99

Average

0.10

0.68

0.15

0.08

1.01

85

Min

0.07

0.26

0.07

0.02

0.53

56

Max

0.67

3.94

0.30

0.36

4.59

Average

0.30

1.48

0.15

0.10

2.048

Min

0.01

0.01

0.07

0.02

Max

0.67

4.67

0.33

Average

0.19

1.03

0.15

66

72

40

62

93

90

93

82

61

86

0.26

56

40

15

0.36

5.02

100

90

96

0.08

1.44

83

65

79

AC C

EP

TE

D

All

92

SC

Bottom

84

M AN U

Surface

RI PT

Layer

ACCEPTED MANUSCRIPT Table 3 Dissolved N and P concentrations and budgets in the north Yellow Sea

CDIN

CDIP

Water fluxes

VDIN

VDIP

(μM)

(μM)

(×109 m3/yr)

(×108 mol/yr)

(×108 mol/yr)

9.62

0.25

0.09

0.002

2.87

0.05

RL

34 a

0.87 b

28.3c

input

RS

16d

0.42d

0.56e

72.6f

1.35f

3.95f

BH

12g

0.26g

52.2f

SYS

4.47h

Output from

BH

4.5

NYS

SYS

4.5

Atmospheric

Input to NYS

NYS

-

0.14

290f

12.96

1.31

0.4

50f

-2.25

-0.2

0.4

323f

-14.54

-1.29

-

1.9f

-

-

0.11

-15.01

-0.26

-

TE

Δ

-

6.26

0.45g

D

Evaporation

M AN U

deposition

SC

Riverine

RI PT

Budgets

RL: Rivers along the Liaodong Peninsula; RS: Rivers along the Shandong Peninsula. Data were from a Wang et al.,

AC C

al., 2003.

EP

2003; b Wang et al., 2004; c Cheng, 2000; d Liu et al., 2009; e Qin et al., 1989; f Hong, 2012; g Song, 2009; h Liu et

ACCEPTED MANUSCRIPT Table 4 Particulate N and P concentrations and budgets in the north Yellow Sea Fluxes (×104 t/yr)

Concentrations (mg/g) Budgets CPIN

CPON

CTPP

CPIP

CPOP

Fsed

FTPN

FPIN

FPON

FTPP

FPIP

FPOP

Bohai Sea

2.111a

0.132a

1.980a

0.308a

0.188a

0.120a

800b

1.69

0.11

1.58

0.25

0.15

0.10

RL

0.67c

-

-

0.60d

-

-

250b

0.17

-

-

0.15

-

-

RS

0.42e

-

-

0.66e

-

-

140b

0.06

-

-

0.09

-

-

YSWC

1.226f

0.303f

0.924f

0.319f

0.218f

0.102f

100b

0.13

0.03

0.09

0.03

0.02

0.01

Phytoplankton

-

-

-

-

-

-

123b

NYS

2.39

0.83

1.56

0.49

0.31

0.18

380

Sedimentation

0.52a

0.035a

0.485a

0.42a

0.34a

0.09a

Δ

-

-

-

-

-

-

SC

RI PT

CTPN

-

10.8

1.5

-

1.5

0.91

0.32

0.59

0.19

0.12

0.07

1242

0.65

0.04

0.60

0.52

0.42

0.11

209

-11.3

-

-

-1.31

-

-

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10.8

RL: Rivers along the Liaodong Peninsula; RS: Rivers along the Shandong Peninsula. Data were from a our other

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D

unpublished data; b Cheng, 2000; c Li et al., 2012; d Li et al., 2010; e Liu et al., 2009; f Yu et al., 2012.

SC

RI PT

ACCEPTED MANUSCRIPT

Fig. 1. Study area and sampling locations of the north Yellow Sea. (a) sampling locations of transect NYS1; (b)

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transect BX-5 and other sampling locations. Transects NYS1 and BX-5 are shown as red lines cross. YSCC: the

Yellow Sea Coastal Current; YSWC: the Yellow Sea Warm Current; KC: the West Korean Coastal Current, LCC:

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the Liaonan Coastal Current.

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Fig. 2. Horizontal distributions of temperature (oC), salinity, suspended particulate matter (mg/L) and chlorophyll a

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TE

D

(μg/L) at surface seawaters of the north Yellow Sea.

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SC

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Fig. 3. Sectional distributions of temperature (oC), salinity, SPM (mg/L) and chlorophyll a (μg/L) along transects

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TE

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BX-5 and NYS1 of the north Yellow Sea.

RI PT

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EP

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D

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SC

Fig. 4. Horizontal distribution of DIN/TDN and DIP/TDP at surface seawaters of the north Yellow Sea.

RI PT

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D

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Fig. 5. Sectional distributions of DIN/TDN and DIP/TDP along transects BX-5 and NYS1 of the north Yellow Sea.

RI PT

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SC

Fig. 6. Horizontal distribution of PIN/TPN and PIP/TPP at surface seawaters of the north Yellow Sea.

RI PT

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D

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Fig. 7. Sectional distributions of PIN/TPN and PIP/TPP along transects BX-5 and NYS1 of the north Yellow Sea.

ACCEPTED MANUSCRIPT 2.5 0.35

y = 0.0281x + 0.0218 (r=0.75, p<0.001)

0.30

2.0

0.25

y = 9.6227x - 0.1489 (r=0.57, p<0.01)

DOP (μM)

DIP (μM)

1.5 0.20 0.15

1.0

0.10

0.5 0.05

0

1

2

3

4

DIN (μM)

5

6

7

0.00

8

0.05

0.10

0.15

0.20

DIP (μM)

3.0

0.35 2.5

y = 0.087x + 0.1633 (r=0.52, p<0.05)

0.20

0.15 0.5

0.10 0.0

0.05 2

3

4

5

6

DIN (μM)

7

0.00

8

0.35

0.05

0.10

0.15

0.20

0.25

0.30

0.35

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1

0.30

SC

PIP (μM)

PIN (μM)

0.25

1.0

0

0.25

y = 0.375x + 0.107 (r=0.60, p<0.01)

0.30

2.0

1.5

RI PT

0.0

0.00

DIP (μM)

0.16

5

0.14

y = 0.8319x - 0.4333 (r=0.77, p<0.01)

3

2

0.12

POP (μM)

PON (μM)

4

0.10 0.08 0.06

1

y = 0.1106x + 0.014 (r=0.72, p<0.01)

0.04

0 0

1

2

5

6

7

0.0

8

Chl a (μg /L)

EP

AC C 0

1

2

3

PON (μM)

1.5

2.0

2.5

y = 14.015x - 0.2383 (r=0.68, p<0.01)

2

1

1

0

1.0

4

3

2

0.5

DOP (μM)

y = 0.2369x + 0.3582 (r=0.54, p<0.01)

3

Chl a (μg /L)

4

DIN (μM)

TE

4

3

D

0.02

4

5

0 0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

POP (μM)

Fig. 8. Relationships between dissolved and particulate pools and between inorganic and organic forms of N and P in the north Yellow Sea. The values in the ellipse were excluded.

ACCEPTED MANUSCRIPT 1. Dissolved organic N and P were predominant forms. 2. Spatial variation of nutrients was related to rivers and biological activities.

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3. The major source of particulate N and P was phytoplankton production.