Episodic vertical nutrient fluxes and nearshore phytoplankton blooms in Southern California

Abstract

Three distinct phytoplankton blooms lasting 4-9 d were observed in approximately 15-m water depth near Huntington Beach, California, between June and October of 2006. Each bloom was preceded by a vertical NO 3 flux event 6-10 d earlier. NO 3 concentrations were estimated using a temperature proxy that was verified by comparison with the limited NO 3 observations. The lower-water-column vertical NO 3 flux from vertical advection was inferred from observed vertical isotherm displacement. Turbulent vertical eddy diffusivity was parameterized based on the observed background (, 0.3 cycles h 21 ) stratification and vertical shear in the horizontal currents. The first vertical nitrate flux event in June contained both advective and turbulent fluxes, whereas the later two events were primarily turbulent, driven by shear in the lower part of the water column. The correlation between the NO 3 flux and the observed chlorophyll a (Chl a) was maximum (r 2 5 0.40) with an 8-d lag. A simple nitrate-phytoplankton model using a linear uptake function and driven with the NO 3 flux captured the timing, magnitude, and duration of the three Chl a blooms (skill 5 0.61) using optimal net growth rate parameters that were within the expected range. Vertical and horizontal advection of Chl a past the measurement site were too small to explain the observed Chl a increases during the blooms. The vertical NO 3 flux was a primary control on the growth events, and estimation of both the advective (upwelled) and turbulent fluxes is necessary to best predict these episodic blooms.

Death from below: Investigation of inhibitory factors in bloom development during a wastewater effluent diversion

“…These rates are consistent with, and higher than, growth rates from further offshore (Landry et al 1995(Landry et al , 2009) and from the nearshore environment (Omand et al 2012). Growth rates were M A N U S C R I P T…”

The shape of the oceanic nitracline

“…Several previous studies have identified a linear nitratetemperature (NO 3 -T ) relationship beneath the nitratedepletion density in the California Current region (Strickland, 1970;Parnell et al, 2010;Omand et al, 2012). Profiles of NO 3 -σ t in the spatially averaged quarterly CalCOFI record appear relatively consistent over time (green segments, Fig.…”

“…Garside and Garside (1995) used a stepwise polynomial method to predict nitrate from temperature and salinity during regional phenomena, such as the North Atlantic spring bloom and El Niño/La Niña conditions in the central Pacific. Finally, firstorder linear regressions between nitrate and temperature have been used to predict nitrate in upwelling zones (Traganza et al, 1987;Dugdale et al, 1997;Olivieri and Chavez, 2000;Omand et al, 2012), although mixing and interleaving of water masses may confound this approach (Friederich and Codispoti, 1981). In coastal California, the relationship has been used to predict coastal nitrate concentration over the last century as an indicator of giant-kelp health (Parnell et al, 2010).…”

The surf zone heat budget: The effect of wave heating

“…Water temperature variations play a critical ecological role in the nearshore and are linked to variation in mussel and barnacle growth rates [Phillips, 2005], egg mass production rates of the coastal crab Cancer setosus [Fischer and Thatje, 2008], and barnacle recruitment rates [Broitman et al, 2005]. Temperature is also a tracer for nutrient delivery to coastal waters [e.g., Omand et al, 2012]. Pathogen ecology in swimming waters is affected by temperature, including Staphylococcus [Goodwin et al, 2012], Enterroccus [Halliday, 2012], and Campylobacter [Hokajarvi et al, 2013].…”