UCLA

Coastal oceans are among the most dramatic, engaging, and dynamic locations the Earth has to offer. The Southern California Bight (SCB) is among those locations, full of iconic coastlines, economically important fisheries, marine protected areas, ports and shipping lanes, a national park, and a massive tourism industry. The SCB homes a diverse array of ecosystem types, ranging from rocky inner-tidal reef systems to giant kelp forests. The SCB also supports a coastal population of 23 million, making this a region of high human influence. Wastewater, rivers, and other sources of anthropogenic nutrients-enter this coastline in impressive quantities daily, heavily influencing the nutrient balance of coastal ecosystems. This dissertation provides a comprehensive analysis of anthropogenic nutrient influence in the context of micro and macro algae, first through a study of wastewater distribution, then through the impacts of kelp health through a nutrient stressed event. We also explore which regions would be most ideal to support kelp farming operations, amidst this anthropogenic influence.In Chapter 2, we present a mechanistic analysis of components of oceanic wastewater discharge in the SCB. Our goal was to understand productivity in the nearshore coastal area (0-15 km of coastline) and examine how it changes with and without chemical and physical components of the major wastewater plumes. We accomplish this by using five different scenarios of a wastewater model examining the mechanisms of buoyancy and inorganic nitrogen composition of outfall plumes. In this Chapter I demonstrate that the primary factors within treated wastewater that influence the productivity are the form of dissolved inorganic nitrogen and the buoyancy of the emitted plume. I show that the effects of increased buoyancy and nutrients on biomass are non-additive. Furthermore we identify a highly seasonal cycle in the influence of outfall scenarios on biomass in the surface ocean, with the largest impacts on NPP seen in the winter, when stratification in the water column is minimal. In Chapter 3, we illuminate the influence of anthropogenic nutrient inputs on the recovery and growth of giant kelp forests in the SCB. To do this we examine kelp forests before and amidst the 2014-2016 marine heat wave (MHW) an event which caused a large loss of kelp forest area. From this study we identify a significant positive relationship of anthropogenic nutrients and kelp forest area maintained through the 2014-2016 MHW. Additionally, we find that during this period there are large portions of the SCB that would be nutrient limited if not for anthropogenic inputs. In Chapter 4, we highlight the optimal locations in the SCB to cultivate giant kelp, and analyze the anthropogenic nutrient influence in these optimal locations. As demand for aquaculture, and in particular macroalgal cultivation, grows in the SCB, so has need for siting optimal locations. Our suitability analysis utilizes highly resolved biogeochemical models to find optimal nutrient (DIN), sunlight (PAR), and water temperature, as well as locational factors such as distance to port and depth in a rigorous spatial analysis framework, which builds upon others from this region. Our suitability results identifies highly suitable regions in the Santa Monica Bay and the Santa Barbara Channel. We find that of these two regions those located in Santa Monica Bay have the least potential interference with current kelp forest areas.