Factors Controlling Seasonal Phytoplankton Dynamics in the Delaware River Estuary: an Idealized Model Study

Abstract

Phytoplankton biomass in estuaries is controlled by complex biological and chemical processes that control growth and mortality, and physical processes that control transport and dilution. The effects of these processes on phytoplankton blooms were systematically analyzed, focusing on identifying the dominant controlling factors out of river-induced flushing, tidal dispersion, nutrient limitation, and light limitation. To capture the physical processes related to flow and sediment dynamics, we used the idealized width-averaged iFlow model. The model was extended with a nutrient-phytoplankton module to capture the essential biological-chemical processes. The model was applied to the Delaware River Estuary for the productive months of March to November. Model results were compared with field observations. It was found that phytoplankton blooms cannot form in the lower bay due to tidal dispersion, as water from the estuary and coastal ocean mix in early spring, and due to local effects of nitrogen limitation in summer. In the middle to upper bay, sediment-induced deterioration of the light climate limits the growth but allows for blooms in the mid bay, while no blooms can form in the turbidity maximum zone in the upper estuary. Further upstream in the tidal river, the effects of river-induced flushing dominate in early spring and prevent bloom formation. In the summer and fall, lower river discharges and higher growth rates at higher temperatures allow blooms to form and persist. Analysis of the connectivity between mid bay and tidal river blooms showed that coastal ocean phytoplankton may contribute to mid bay blooms, but do not penetrate beyond the turbidity maximum zone.

Phytoplankton alpha diversity indices response the trophic state variation in hydrologically connected aquatic habitats in the Harbin Section of the Songhua River

“…In spatial, the total phytoplankton abundance of wetland was strongly higher than that of river, coincid- www.nature.com/scientificreports/ ing with increaseing in the concentrations of TN. This indicates the most dynamic characteristics of phytoplankton community of the interconnected aquatic habits are closely linked to trophic state fluctuation, which agrees with observations by Hu et al 31 and Dijkstra et al 32 . In general, diatoms are considered as a vital component of phytoplankton communities in wetlands and rivers being typically the dominant taxonomic group in terms of species richness in such environments 33 .…”

Evolution of the long-term and estuary-scale phytoplankton patterns in the Scheldt estuary: the disappearance of net growth in the brackish region

“…The dissolved phosphorous concentrations range from 0.001 mmol L −1 at the seaside boundary to 0.007 mmol L −1 at the upstream boundary. These concentrations are at least one order of magnitude larger than the threshold values at which we expect nutrient depletion (Soetaert et al, 1994;Arndt et al, 2011;Dijkstra et al, 2019a).…”

“…The iFlow model has recently been extended by a phytoplankton model (Dijkstra et al, 2019a). The phytoplankton model is a dynamic model that describes the spatial and tidal evolution of phytoplankton concentration and the nutrients nitrogen and phosphorous.…”

“…We do not focus on the equation for the nutrient dynamics because the Scheldt estuary can be considered a nutrient-rich system, as mentioned above. However, we solve the nutrient dynamics in the model as done by Dijkstra et al (2019a) to guarantee that we do not falsely neglect nutrient depletion in the extreme limits in our sensitivity analysis. The model consists of a single-phytoplankton class and thus does not differentiate between diatoms and non-diatoms.…”

The Tagus Estuary as a Numerical Modeling Test Bed: A Review

“…Consequently, coupled hydro-biogeochemical model implementations in a 2-dimention setup become more usual in estuarine studies [44][45][46][47][48]. Throughout the years many models have been implemented to explore the influence of hydrodynamics in the transport patterns of salt, heat, nutrients and in the primary production of estuarine-coastal continuums.…”