New insights into impacts of anthropogenic nutrients on urban ecosystem processes on the Southern California coastal shelf: Introduction and synthesis

Abstract

Anthropogenic nutrient inputs are one of the most important factors contributing to eutrophication of coastal waters. Coastal upwelling regions are naturally highly variable, exhibiting faster flushing and lower retention times than estuarine systems. As such, these regions are considered more resilient to anthropogenic influences than other coastal waters. Recent studies have shown our perception of the sustainability of these systems may be flawed and that anthropogenic nutrients can have an impact at local and regional spatial scales within these larger upwelling ecosystems. Maintenance of an outfall pipe discharging wastewater effluent to the Southern California Bight (SCB) provided an opportunity to study effects of anthropogenic nutrient inputs on a near-shore coastal ecosystem. The diversion of wastewater effluent from a primary, offshore outfall to a secondary, near-shore outfall set up a large-scale, in situ experiment allowing researchers to track the fate of wastewater plumes as they were "turned off" in one area and "turned on" in another. In this introduction to a special issue, we synthesize results of one such wastewater diversion conducted by the Orange County Sanitation District (OCSD) during fall 2012. Anthropogenic nitrogen (N) from point-source discharges altered biogeochemical cycling and the community composition of bacteria and phytoplankton. Nitrification of ammonium to nitrate in wastewater effluent close to outfalls constituted a significant source of N utilized by the biological community that should be considered in quantifying "new" production. The microbial-loop component of the plankton community played a significant role, exemplified by a large response of heterotrophic bacteria to wastewater effluent that resulted in nutrient immobilization within the bacterial food web. This response, combined with the photosynthetic inhibition of phytoplankton due to disinfection byproducts, suppressed phytoplankton responses. Our findings have ramifications for future studies and 2 regulatory monitoring, emphasizing the need to consider chemical and biological responses to wastewater effluent in assessing effects of anthropogenic nutrient inputs on urbanized coastal ecosystems.

The Globalization of Cultural Eutrophication in the Coastal Ocean: Causes and Consequences

“…Upwelling is by far the largest source of nutrients to the SBC ecosystem as a whole, especially during the late spring and early summer (Warrick et al, 2005;Howard et al, 2017). N input via upwelling is estimated to be ∼ 0.21 × 10 9 kg yr −1 , a rate that is 2-3 orders-of-magnitude greater than the riverine inputs during wet, El Nino years (Warrick et al, 2005).…”

“…The trend has been briefly interrupted when dense oxygenated water flows into the basin during transitions from El Niño to La Niña conditions (Wang et al, 2017). Thus, anthropogenic nutrients can have an impact on local spatial scales within the larger upwelling ecosystem (Howard et al, 2017).…”

Disentangling Environmental Drivers of Phytoplankton Biomass off Western Iberia

“…However, the phytoplankton communities at a regional scale have complex variations, fluctuating from region to region and there is still much to unravel on community dynamics (e.g., Brotas et al, 2013;Brito et al, 2015). Additionally, these communities' responses are typically intertwined with local and regional coastal events and processes (Jones et al, 2013;Carstensen et al, 2015;Dorado et al, 2015;Howard et al, 2017). Determining how environmental changes in coastal ecosystems drive phytoplankton is essential toward understanding coastal ecosystems, particularly under the everpresent threat of anthropogenic climate change.…”

Oceanographic and Bathymetric Features as the Target for Pelagic MPA Design: A Case Study on the Cape of Gata

“…Thus, the origin of the less dense and nitrate-rich water observed at Stn 51 and Stn 52 might be the signal of the mixed desalination plant and thermal power station effluents, causing eutrophication of oligotrophic surface waters. The environmental effect of wastewater plumes, in terms of extension, duration, and effect on the pelagic community, is of increasing concern and requires multidisciplinary studies [94]. In order to confirm our observations and evaluate the potential impact of wastewater plumes in the area, remote-sensing detection of wastewater plumes [95] should be carried out in the area in the future.…”