Anthropogenic nitrogen is changing the East China and Yellow seas from being N deficient to being P deficient

Abstract

Addition of the increased anthropogenic nitrogen (NO x and NH y) emitted from northeast Asian countries to the Yellow and East China seas and coastal waters around Korea has resulted in an unparalleled increase in the nitrate (N) concentration relative to the phosphate (P) and silicate (Si) concentrations in the upper ocean. We found that for the Yellow Sea the increase in N over P was largely explained by increased atmospheric nitrogen deposition, whereas for the northern East China Sea, downstream of the Changjiang River plume, the trend in N increase relative to P was more associated with a change in the combined input of nutrients from atmospheric deposition and riverine discharges. In contrast, the dynamics of the N to P relationship in the southern East China Sea was largely controlled by a change in the intrusion intensity of the Kuroshio Current, which has a low N : P ratio. The disproportionate and persistent input of nutrients to the marine waters of this region over the past four decades has transformed extensive areas from being N deficient to being P deficient, and has concurrently decreased the concentration of Si relative to N. In coastal waters around Korea in particular, these shifts in the nutrient regime have been accompanied by a change from diatom-dominated to dinoflagellatedominated blooms. Given the complexity of coastal ecosystems, the associations between changes in nutrient regimes and biological changes need to be investigated in other coastal areas receiving increasing loads of anthropogenic nitrogen.

Interannual Variation in Phytoplankton Community Driven by Environmental Factors in the Northern East China Sea

“…In this study, we first observed that cryptophytes replaced diatoms in the NECS and were the dominant species in autumn and winter 2020. This recent pattern could be related to the overall nutrient transitions from N-deficient to P-deficient environmental conditions caused by anthropogenic nitrogen inputs in the NECS observed from 1980 to 2016 (Moon et al, 2021). Our result showed that the P-limitation indicated by ExN > 0 µM existed in all seasons from 2018 to 2020 (Table 3).…”

“…High DIN concentrations and DIP-limited environments in 2020 caused dinoflagellates and small phytoplankton groups such as cryptophytes, cyanobacteria, and prymnesiophytes to be more competitive than diatoms. In particular, cryptophytes were first observed as the dominant species in autumn/winter 2020 in the NECS, which could be related to increasing anthropogenic nitrogen inputs in the study area (Moon et al, 2021). Moreover, dinoflagellates, which predominated in spring 2020, tended to bloom at low phosphorus and high ExN conditions compared with diatoms.…”

“…Based on previous and this studies, we predict that spring blooms phytoplankton groups in the ECS would gradually change from diatoms to dinoflagellates both in coastal waters and the NECS. The main reasons for this prediction are based on (1) the overall nutrient transitions from N-deficient to P-deficient environmental conditions in the NECS in recent decades (Moon et al, 2021) and ( 2) increasing thermal stratification of marine waters as a consequence of global warming, which will inhibit nutrient inputs especially DIP inputs from waters below the mixed layer (Xiao et al, 2018). Such long-term environmental changes are more conducive to dinoflagellates than diatoms, which is consistent with model-based conservative forecasts for that diatoms will decrease by 60% and dinoflagellates will increase by 70% of the surface water in the ECS by the year 2100 (Xiao et al, 2018).…”

Controls on Organic Carbon Burial in the Eastern China Marginal Seas: A Regional Synthesis

“…Sedimentation rate, another well‐established control of OC burial in coastal systems (e.g., Bao et al., 2018; Blair & Aller, 2012; Cui, Bianchi, Jaeger, et al., 2016), has been altered by many changes in the Anthropocene such as land‐use, precipitation gradients, eutrophication, and damming. In fact, the Eastern China Marginal Seas (ECMS), which has historically been fed by some of the most sediment‐rich rivers in the world, has been disproportionality altered by such human activities (e.g., Moon et al., 2020; Wu et al., 2020) ‐ due to profound economic growth in the region (He et al., 2014). The ECMS provides prolific gradients of change for exploration, and thus offers a unique set of natural laboratories to investigate these questions.…”

Bioavailability of Organic Phosphorus Compounds to the Harmful Dinoflagellate Karenia mikimotoi

“…It should be noted that the increasing frequency of K. mikimotoi blooms aligns with the varying nutrient structure in the coastal waters of East Asia in recent years. Due to the rapid development of the human population and the concomitant increase in industrial and agricultural activities, the unbalanced input of nitrogen (N) and phosphorus (P) into coastal waters has caused an obvious increase in the N:P ratio in East Asia [ 21 , 22 ]. Phytoplankton normally suffer P deficiency in late spring and summer in this area [ 21 ].…”