Burton H. Jones

Water quality impacts of stormwater discharges to Santa Monica Bay

Urban stormwater runoff is a major source of contaminants to southern Californias coastal waters, yet little is known about the fate and effects of these discharges. A 3-year multidisciplinary project was conducted to investigate the dispersion of stormwater plumes in Santa Monica Bay and the resultant impacts on the water column and benthos. This paper describes the toxicity component of the study. Sea urchin fertilization toxicity tests were conducted on stormwater from the two largest discharges into the bay: Ballona Creek, which drains a highly urbanized watershed, and Malibu Creek, which receives runoff from a largely undeveloped watershed. Every sample of Ballona Creek stormwater tested was toxic (usually >5 toxic units), while Malibu Creek stormwater had a lower frequency and magnitude of toxicity (usually <4 toxic units). Surface water samples collected within the Ballona Creek stormwater discharge plume were always toxic whenever the concentration of stormwater in the plume exceeded 10%. The toxic portion of the Ballona Creek stormwater plume extended more than 4 km offshore on one occasion. Toxicity identification studies indicated that zinc was the primary cause of toxicity in both Ballona Creek stormwater and the discharge plume. No acute sediment toxicity (10-day amphipod survival) was present in the study area, although interstitial water toxicity was present at some stations located near the mouth of Ballona Creek. Differences in watershed characteristics likely were responsible for the greater toxicity of the Ballona Creek stormwater discharge plume. The Ballona Creek watershed contained a greater degree of urbanization (83% versus 12% for Malibu Creek) and the presence of a network of concrete flood control channels resulted in a stormwater plume containing elevated concentrations of toxins that received less initial dilution (compared to Malibu Creek) in the nearshore environment.

Northern Adriatic Response to a Wintertime Bora Wind Event

During winters, the northern Adriatic Sea experiences frequent, intense cold-air outbreaks that drive oceanic heat loss and imprint complex but predictable patterns in the underlying waters. This strong, reliable forcing makes this region an excellent laboratory for observational and numerical investigations of air-sea interaction, sediment and biological transport, and mesoscale wind-driven flow. Narrow sea surface wind jets, commonly known as “bora,” occur when cold, dry air spills through gaps in the Dinaric Alps (the mountain range situated along the Adriatics eastern shore). Horizontal variations in these winds drive a mosaic of oceanic cyclonic and anticyclonic cells that draw coastal waters far into the middle basin. The winds also drive intense cooling and overturning, producing a sharp front between dense, vertically homogenous waters (North Adriatic Dense Water, or NAdDW) in the north and the lighter (colder, fresher), stratified waters of the Po River plume. Once subducted at the front, the NAdDW flows southward in a narrow vein following the isobaths (contours of constant depth) of the Italian coast. In addition to governing the basins general circulation, these processes also influence sediment transport and modulate biological and optical variability

Evidence of subduction within cold filaments of the northern California Coastal Transition Zone

Profiles of 222Rn, chlorophyll, nutrients, oxygen, temperature, and salinity taken within a cold filament observed in satellite images of the northern California coastal transition zone provide evidence that there is strong vertical transport out of the surface layer by subduction processes occuring within these features. Layers of chlorophyll found below the euphotic zone have associated with them other characteristics of water that at one time had been in contact with the sea surface, including deficiencies of 222Rn with respect to 226Ra, elevated oxygen concentrations, and warm water on plots of temperature and salinity. The data indicate that the subsurface maxima in chlorophyll are derived from subducted surface layers and are not produced by in situ phytoplankton growth nor derived by particle settling. The presence of a 222Rn deficiency at depth further suggests that the subducted water had been in contact with the surface within the past week and indicates that the rate of vertical transport is approximately 25 m/d. This has important implications for the fate of the filaments and for the high primary productivity within them.

Monsoons boost biological productivity in Arabian Sea

Monsoons over the Arabian Sea—the oceanic basin that separates the Arabian peninsula from the Indian subcontinent—follow seasonal cycles, reversing directions twice a year, in summer and winter. Rather than spreading across the expanse of the sea, the southwest (summer) monsoon is often concentrated into a jet over the central Arabian Sea. Evidence suggests that variations in wind stress force substantial upwelling in the ocean to the west of the jet, and weaker upwelling or even downwelling to the east. This upwelling provides nutrients to the euphotic zone and enhances biological productivity.

Electronic properties of Mn-decorated silicene on hexagonal boron nitride

We study silicene on hexagonal boron nitride, using first-principles calculations. Since hexagonal boron nitride is semiconducting, the interaction with silicene is weaker than for metallic substrates. It therefore is possible to open a 50 meV band gap in the silicene. We further address the effect of Mn decoration by determining the onsite Hubbard interaction parameter, which turns out to differ significantly for decoration at the top and hollow sites. The induced magnetism in the system is analyzed in detail.

Buoyant plume dispersion in a coastal environment: evolving plume structure and dynamics

A field program has been devised to study the dispersion of a buoyant plume formed by the discharge of treated wastewater from the Whites Point outfall into the coastal ocean off the Palos Verdes peninsula off southern California. The program combines high resolution towed surveys of physical and bio-optical variables with continuous time series observations of current velocity. The observations show that after discharge the wastewater forms a submerged buoyant plume of relatively fresh, turbid effluent. Identification of the plume within the water column is complicated by the ambient thermohaline and particle fields which can exhibit natural variability comparable to that introduced by the plume. We present a simple method based on threshold criteria of three measured variables to identify effluent-containing waters under general conditions. The complexity of the effluent field is found to depend strongly on the temporal variability of currents over a period of several hours preceding the observation time and on the ambient density structure. Measurements of small-scale turbulent mixing activity show that high mixing rates occur over the diffusers due to buoyant convection in the rising plume. We use the distribution of turbulent activity to separate the actively mixing region in the rising plume from the passive effluent layer away from the diffusers. In background waters, turbulent patches are occasionally found with horizontal extents of about 1.5 km and vertical extents of about 5 m. Effective eddy diffusivities within these patches are of order Kz ∼ 10−4 m2 s−1.

Observations of a Persistent Upwelling Center off Point Conception, California

Centers of intensified upwelling occur throughout the world and are often associated with topographic irregularities along the coasts and continental shelves. Preliminary observations from a study near Point Conception, California, as well as previous observations from Peru, near 15°S, provide us with some generalizations about coastal upwelling centers. The mean structures of these centers appear to be well-defined regions of low temperature, high nutrient concentrations and low phytoplankton abundance, with characteristic gradients of each of these variables away from the center. The biological productivity of these centers results in the generation of organic particles. The impact of this near-surface productivity on the sediments will depend on the physical structure of the upwelling centers and the variability of this structure.

Spatial scales and evolution of stormwater plumes in Santa Monica Bay

Rainfall during winter storms produces extensive turbid, freshwater plumes in the coastal waters of the Southern California Bight. When the plumes result from urban runoff they contain toxic pollutants along with pathogenic bacteria and viruses, often resulting in closure of public beaches. We examined the spatial structure and evolution of stormwater plumes in Santa Monica Bay in 1996. The plumes resulted from freshwater discharge from the Ballona Creek and Malibu Creek watersheds which supply approximately 60% of the freshwater runoff to Santa Monica Bay. The spatial scales of the plumes were determined using shipboard measurements of water properties obtained from towyo transects and surface underway sampling. Salinity maps showed that the plumes typically extended 4-7 km offshore, consistent with scaling by the internal Rossby radius of deformation. Plumes extended along shore 10 km or more. Generally the plumes occupied the upper 10 m of the water column. The persistence time of a plume offshore of Ballona Creek was about three days based on a sequence of surveys in March 1996 following rainfall of about 21 mm. Limited comparison of plumes from Ballona Creek, which drains a developed watershed, and Malibu Creek, which drains a rural watershed, suggested that Malibu Creek required greater rainfall to produce an offshore plume. A stormwater plume offshore of Malibu Creek was observed on both sides of the creek mouth, possibly due to freshwater discharge from smaller surrounding watersheds or advection of freshwater discharges from the east and south. Plumes offshore of Ballona Creek mainly resulted from the creek itself and usually extended northward from the creek mouth, consistent with the wind forcing and the Coriolis acceleration.

Effects of a sewage plume on the biology, optical characteristics, and particle size distributions of coastal waters

The effect of a sewage plume on the biology, optical characteristics, and particle size distributions of coastal waters was evaluated around the Sand Island, Hawaii, outfall diffuser. In situ physical and biooptical data and Niskin bottle samples were collected during a 1-week cruise from September 25 to October 1, 1994. One or two layers affected by sewage could be distinguished in the water column: recently discharged (“new”) sewage plume waters and “old” plume waters. In conditions characterized by high Froude number the distribution of chlorophyll fluorescence in new plume waters was the same as for ambient waters, while for low Froude number, chlorophyll fluorescence increased within the plume, demonstrating the importance of physical forcing on effluent and phytoplankton interactions. New plume waters were associated with at least 2.7-fold increases in particle load, high concentrations of particles larger than 70 μm, increases in ammonium, phosphate, and silicate, and high levels of heterotrophic bacteria and Prochlorococcus compared to surrounding waters. Both new and old plume layers, but not phytoplankton layers, showed distinct increases in fluorescence for the excitation/emission (Ex/Em) wavelength pair Ex/Em=228/340 in nm, interpreted as particulate tryptophan-like fluorescence. Such fluorescence may be useful as a new in situ real-time indicator of waters affected by effluent discharges.

Hydrographic patterns and vertical mixing in the equatorial Pacific along 150°W

The WEC88 cruise sampled along a meridional transect from 15°N to 15°S along 150°W from February 17 to March 18, 1988, with a 6-day time series at the equator. The large-scale hydrographic patterns were typical for boreal spring. Equatorial maxima in dissipation of turbulent kinetic energy ∈, and of thermal variance χ, were found between 2°N and 2°S for the top 60 m. The equatorial time series coincided with a shift from southward to northward velocity, which returned the zonal current system to the equator. This led to a decrease in temperature, and increases in salinity, nutrient, and chlorophyll concentrations in the surface layer. Vertical diffusivity as well as ∈ and χ increased with the observed intensification of the Equatorial Undercurrent. Maximum values of ∈ and χ were observed at around 55 m, and the temporal trends occurred first at depth. Turbulent heat flux out of the mixed layer was the same order of magnitude as the penetrative irradiance at that depth. Maximum vertical heat flux occurred at depth in response to large diffusivity coefficients. The Richardson number was useful in predicting the regions of enhanced mixing in the meridional transect. However, for the equatorial time series, where the Ri was less than 0.45, intensity of dissipation was not proportional to Richardson number.