Skip Navigation LinksResearch Areas > Nutrients > Macroalgal Nutrient Dynamics in Upper Newport Bay

Project: Macroalgal Nutrient Dynamics in Upper Newport Bay

Background and Objective

Upper Newport Bay (UNB) represents a valuable ecological and recreational resource for southern California, but is increasingly subject to anthropogenic stressors including nutrient loads from the surrounding watershed. These can cause excessive growth of macroalgae and subsequent impairment of the Bay's beneficial uses. In order to address these issues, the Bay was added to the Clean Water Act 303(d) list and Total Maximum Daily Loads (TMDLs) were established in 1998 for nitrogen (N) and phosphorus (P). Previous studies in UNB showed that no strong linkage exists between water column N or P and macroalgal biomass. Therefore, there is a clear need for mechanistic studies investigating the processes in UNB that control macroalgal biomass. Increased understanding of the processes and mechanisms that regulate the growth and biomass of Enteromorpha and Ulva spp. is paramount to making informed management decisions for estuaries such as UNB.

The objectives of this study were to:

1) Investigate the contribution of nutrients from estuarine sediments to macroalgal growth and tissue nutrient content;
2) Determine if N or P is the nutrient most limiting to macroalgae;
3) Measure rates of N and P uptake by Enteromorpha intestinalis and Ulva expansa, the dominant, green, bloom-forming macroalgal species; and
4) Investigate the effects of variation in the frequency and concentration of nutrient pulses on macroalgal growth and tissue nutrient content.


This study was conducted from 2001-2002.


Four experiments were designed to evaluate the effects of nutrient dynamics on macroalgal growth. These experiments are summarized below

1) Contribution of sediment nutrients to macroalgal growth and tissue nutrient content:

Experimental units were constructed using water and sediments collected from three sites in UNB. Changes in water column and sediment nutrients were measured in three sets of experimental units for each site: (1) sediments + water; (2) sediments + water + E. intestinalis (algae); (3) inert sand (no nutrients) + water + algae. In units containing algae, growth and tissue nutrients (N and P) were also measured.

2) Identification of nutrients limiting macroalgal growth:

Enteromorpha intestinalis and water were collected from five sites in UNB. Portions of the water from each site were amended with nutrients to create four experimental solutions (control, nitrogen enrichment, phosphorus enrichment, and nitrogen and phosphorus enrichment). Algae were added to replicate experimental units, each filled with one of the experimental solutions. Water column nutrient concentrations, E. intestinalis biomass, and tissue N and P were measured.

3) N and P uptake rates:

Rates of N and P uptake by Enteromorpha intestinalis and Ulva expansa were investigated in 4 separate experiments. In each experiment, uptake of either N or P by either E. intestinalis or U. expansa was measured at various timepoints as a function of low, medium, and high water column nutrient concentrations and enriched or depleted algal tissue nutrients. Uptake rates of inorganic nitrogen and phosphorus were determined by measuring their disappearance from solution over time.

4) Effects of nutrient pulses on macroalgal growth and tissue nutrient concentration:

Over a 28-day period, Enteromorpha intestinalis and Ulva expansa were each given equal supplies of nitrogen and phosphate via pulses of different frequency (daily to monthly). Water column nutrient levels were monitored throughout the course of the experiment. Algal biomass and tissue N and P concentrations were measured at the end of the experiment.


Significant findings from this project were:

1) Sediments were an important source of nutrients to macroalgae when water column supplies were low. Growth and tissue nutrient concentrations (N and P) of Enteromorpha intestinalis were greater in the presence of estuarine sediments containing measurable nutrients, as compared to nutrient-free sediment controls. Moreover, macroalgal growth and tissue concentrations increased with an increase in initial sediment nutrient concentrations.
Enteromorpha intestinalis biomass (% change from initial) grown with either inert sand or estuarine sediment from 3 sites in Upper Newport Bay, demonstrating the importance of sediments in supporting macroalgal growth in estuaries.
2) N was the most limiting nutrient to macroalgal growth. P was secondarily limiting at some sites within UNB. Therefore, strategies to reduce macroalgal biomass in UNB should focus primarily on reductions in N loads to the Bay and secondarily on P loads.

3) Nitrogen uptake rates were a function of water column nutrient concentration and the recent exposure of algae to nutrients. Enteromorpha intestinalis and Ulva expansa were very efficient at consuming NO3 with uptake rates measured up to >200 mmoles g dry wt-1 h-1. Uptake rates increased with water column concentrations. In addition, nutrient-depleted algae had consistently higher rates of nutrient uptake than algae that were enriched with nitrate.

4) Algae efficiently stored large pulses of nutrients and used them for growth when the nutrient supply was low. Enteromorpha intestinalis and Ulva expansa grew most and had the greatest increases in tissue N and P content with daily, low concentration nutrient additions (cumulative dose of 28 mg N and 6 mg P over 28 days). As demonstrated earlier, however, these algae are also efficient scavengers of nutrients. As a result, significant algal growth was observed in all treatments, regardless of frequency of nutrient addition. Therefore, large infrequent nutrient loads should be considered in any macroalgae control plan, in addition to controlling chronic, low-grade nutrient inputs.


This project was conducted in collaboration with the Santa Ana Regional Water Quality Control Board (SARWQCB), Irvine Ranch Water District, Orange County Public Facilities and Resources Department, and Defend the Bay. It was partially funded by the SARWQCB.

For more information on Macroalgal Nutrient Dynamics in Upper Newport Bay, contact Martha Sutula at (714) 755-3222.
This page was last updated on: 6/30/2014