Nutrient Loading through Submarine Groundwater Discharge and Phytoplankton Growth in Monterey Bay, CA

Abstract

ABSTRACT:We quantified groundwater discharge and associated nutrient fluxes to Monterey Bay, California, during the wet and dry seasons using excess 224 Ra as a tracer. Bioassay incubation experiments were conducted to document the response of bloom-forming phytoplankton to submarine groundwater discharge (SGD) input. Our data indicate that the high nutrient content (nitrate and silica) in groundwater can stimulate the growth of bloom-forming phytoplankton. The elevated concentrations of nitrate in groundwater around Monterey Bay are consistent with agriculture, landfill, and rural housing, which are the primary land-uses in the area surrounding the study site. These findings indicate that SGD acts as a continual source of nutrients that can feed bloom-forming phytoplankton at our study site, constituting a nonpoint source of anthropogenic nutrients to Monterey Bay.

Quantifying Processes Governing Nutrient Concentrations in a Coastal Aquifer via Principal Component Analysis

“…The source of silicate to the coastal aquifer was determined to be dissolution of aquifer substrate while the sources of nitrate and phosphate were undetermined [29]. SGD flux from the coastal aquifer was determined to be an important source of nutrients to the coastal waters throughout the year, but especially during the late summer/early fall (dry season) when other sources of nutrients to the bay, river discharge and upwelling, were limited [6,29]. SGD fluxes were similar year-round and modulated by tides and wave ramp-up [6,29].…”

“…Best estimates suggest that SGD water input to the ocean is equivalent to 60-400% of riverine water flux [1,4]. Nutrients transported to the ocean through SGD have been shown to affect marine biota, specifically the abundance and productivity of phytoplankton, macro-algae, and seagrasses, which have implications for organisms in higher trophic levels [5][6][7][8][9]. SGD is comprised of fresh groundwater, seawater that has circulated through the coastal aquifer, or a mixture of both water types [10][11][12].…”

“…Coastal aquifers often have high flow rates and nutrient concentrations can be heavily modulated by mixing with seawater [10][11][12]. Here, conservative mixing and other processes in the coastal aquifer of Monterey Bay, CA, an area where SGD was identified as an important nutrient source to the coastal ocean [6,29], are quantified. Data collected at four different locations along the coast of Monterey Bay were analyzed via PCA to provide an overall view of the relative importance of processes in the coastal aquifer that may affect the nutrient loads associated with SGD in the region.…”

Harmful Algal Blooms in Eastern Boundary Upwelling Systems: A GEOHAB Core Research Project

“…However, recent studies on the California coast show a significant input of nitrogen from wastewater effluent, riverine runoff, submarine groundwater discharge, and atmospheric deposition (Reifel et al, 2013;Howard et al, 2014;Lecher et al, 2015). Compared to the input from upwelling, these nutrient sources are smaller by at least an order of magnitude at system or regional scales.…”

Macronutrient status of UK groundwater: Nitrogen, phosphorus and organic carbon

“…Lecher et al, 2015;Rodellas et al, 2014), although very little work has been done on this topic to date in the UK. For marine receptors the ecological sensitivity is likely to be well below 1 mg/L.…”