Oceanography at the land-sea interface [electronic resource] : linking physics to human health and ecosystems

This dissertation explores several physical processes and the associated scalar transport at the land-sea interface. In particular, it examines three issues with important implications on human health and ecosystems, namely, the surf zone entrainment of pollutants from coastal discharges, the flow and hydrodynamics over giant kelp forests, and the cross-shore transport by internal waves. Chapter 2 develops a novel, quantitative framework for estimating the surf zone entrainment of pollution at a wave-dominant open beach. Using physical arguments, a dimensionless parameter equal to the quotient of the surf zone width, and the cross flow length scale of the discharge. Numerical modeling of a non-buoyant discharge at an alongshore uniform beach with a constant slope is conducted using a wave-resolving hydrodynamic model. Based on 144 numerical experiments, an empirical relationship is established between the surf zone entrainment rate and the dimensionless parameter. The empirical relationship can reasonably explain seven measurements of surf zone entrainment at three coastal discharges. Chapter 3 characterizes the flow and subtidal momentum balance near a giant kelp forest in Santa Barbara, California, from a two-month field study. In the alongshore direction, the kelp forest diverts the predominantly tidal flow towards the outer edge and creates a net offshore flow from the interior. It also significantly changes the vertical profile of the alongshore flow. A simple model which accounts for the vertical distribution of kelp density is proposed, and can reasonably predict the velocity profiles within the kelp forest. The subtidal alongshore momentum balance at 7m isobath is mainly between the bottom pressure gradient force, surface wind stress, and drag imposed by the kelp forest. In the cross-shore direction, the flow is dominated by a vertically-sheared two-layer flow, which is damped by the forest. At the kelp-free region, the subtidal cross-shore momentum balance is mainly between the pressure gradient force, wave radiation stress gradient, and bottom stress. Across the kelp forest, the subtidal momentum balance cannot be resolved by the field data, potentially due to inaccurate measurements of the advection terms. A simplified numerical model of tidal flow over an idealized kelp forest, with no Coriolis, wave, and wind effects, suggests that the major subtidal momentum terms include the pressure gradient force, kelp-induced drag, and nonlinear advection terms. From the numerical model, the drag inside the kelp is estimated to be about 26 times that at the kelp free region. Chapter 4 evaluates the potential impact of the cross-shore internal wave transport on the surf zone water quality at Huntington Beach in southern California. The study presents physical measurements and a comprehensive set of surf zone water quality measurements collected during the summers of 2005 and 2006. Internal waves were found to be an important transport mechanism of nutrient-rich subthermocline waters to the very near shore in the Southern California Bight. Internal waves may also facilitate the transport of fecal indicator bacteria (FIB) into the surf zone, or enhance the persistence of land-derived FIB. Wavelet analysis of water temperature data reveals that internal waves are highly variable, with most of the energy concentrating around diurnal and semi-diurnal frequencies. The arrival of cold subthermocline water within 1km of the surf zone is characterized by strong baroclinic, onshore flow near the bottom of the water column. The bottom, cross-shore, baroclinic current is proposed as a new proxy to measure the shoreward transport potential by internal waves. This internal wave proxy is positively correlated with phosphate concentrations in both years, silicate concentrations in 2005, and fecal indicator bacteria measurements in 2006.

Advisor: Boehm Alexandria primary advisor. Thesis advisor
Fong Derek advisor. Thesis advisor
Fringer Oliver B. (Oliver Bartlett) advisor. Thesis advisor
Monismith Stephen Gene advisor. Thesis advisor