Dam-regulated nutrient inputs control the inter-annual variation of net primary production in the central Bohai Sea

Net primary production (NPP) is the foundation of marine food webs and the
biological carbon pump. River damming significantly impacts NPP in
marginal sea by changing nutrient concentrations and ratios in the coastal
zone. Clarifying the impacts of river damming on NPP in marginal seas can
help improve the management of living marine resources. We combined data
collection with field surveys to investigate the seasonal and inter-annual
variability of NPP in the central Bohai Sea, with a particular focus on
the effects of dam-regulated nutrient inputs (the Water Sediment
Regulation Scheme of Yellow River (WSRS)) on NPP. Our findings revealed
that the most significant factor influencing the seasonal variations in
NPP in the central Bohai Sea was SST, but NPP was nutrient-limited under
favorable SST conditions in summer. Large nutrient inputs resulting from
the implementation of WSRS significantly increased chlorophyll-a
concentration and NPP in the central Bohai Sea during summer. The coupling
of nutrient input and suitable temperature and light could maximize the
stimulation of NPP elevation. Furthermore, the substantial nutrient inputs
with high N/P ratio from the Yellow River led to a significant increase in
the DIN/PO4-P ratio, thus promoting the diatom/dinoflagellate ratios and
picoeukaryotes abundance. The growth of picoeukaryotes contributed to an
increase in chlorophyll-a, thereby exerting control over changes in NPP.
This study offers valuable insights into the effects of dam regulation on
offshore NPP, and help in our understanding of how marine ecosystems are
influenced by giant dam construction.