UC San Diego

River plumes serve as major sources of terrestrial runoff into the coastal ocean, carrying land-based and estuary-modified particles, sediment, debris, and pollutants. Understanding river plume transport across temporal and spatial scales is important for assessing impacts on ecosystem and human health. This dissertation investigates variability in small river plume occurrence and transport from the low-inflow estuary (LIE) Los Peñasquitos Lagoon (LPL) in San Diego, California and has findings relevant to LIEs globally, which are common but under-studied.I show the occurrence of small river plumes in the far-field is influenced by climate patterns using 105 years of daily salinity measurements. Climate oscillations influence precipitation which impacts the tendency for small plumes to transport significantly into the far-field. This work illustrates that small, intermittent LIE plumes have a robust impact on coastal ocean freshening when there is enough rainfall. With higher resolution LPL plume observations collected during the Plumes in Nearshore Conditions (PiNC) experiment, we specify when small plumes occur depending on river, tidal, and wave forces using a reproducible parameter. We also show the variable nature of small plume far-field transport within one winter. The surf zone can change far-field plume behavior and control when and where plumes reach the inner-shelf. Once on the shelf, plumes following rain events are driven alongshore in the direction of the wind with a speed enhanced by buoyancy. To better resolve the processes around LPL and adjacent estuaries, a realistic coupled wave-ocean model is run. We find that the surf zone is a common pathway for plume coalescence, the interaction of two river's plumes, between LIEs. When one LIE's surf zone plume reaches an adjacent LIE, the incoming plume can continue in the surf zone with the local ebbing plume, or it can be forced offshore by the ebbing plume thus altering its fate. Alternatively, an incoming plume reaching an adjacent LIE during flood tide intrudes into the local estuary, impacting coastal dispersion and plume fate. Together, these chapters advance knowledge about the response of small plumes to varying conditions in the surf zone and inner-shelf, informing coastal transport of terrestrial materials including pollutants.