Eutrophication and Harmful Algal Blooms: A Scientific Consensus

Abstract

In January 2003, the US Environmental Protection Agency sponsored a "roundtable discussion" to develop a consensus on the relationship between eutrophication and harmful algal blooms (HABs), specifically targeting those relationships for which management actions may be appropriate. Academic, federal, and state agency representatives were in attendance. The following seven statements were unanimously adopted by attendees based on review and analysis of current as well as pertinent previous data: 1) Degraded water quality from increased nutrient pollution promotes the development and persistence of many HABs and is one of the reasons for their expansion in the U.S. and the world; 2) The composition - not just the total quantity - of the nutrient pool impacts HABs; 3) High biomass blooms must have exogenous nutrients to be sustained; 4) Both chronic and episodic nutrient delivery promote HAB development; 5) Recently developed tools and techniques are already improving the detection of some HABs, and emerging technologies are rapidly advancing toward operational status for the prediction of HABs and their toxins; 6) Experimental studies are critical to further the understanding of the role of nutrients in HAB expression, and will strengthen prediction and mitigation of HABs; and 7) Management of nutrient inputs to the watershed can lead to significant reduction in HABs. Supporting evidence and pertinent examples for each consensus statement is provided herein.

Figure 1

Average abundance (%) of the diatom Pseudo-nitzschia in the sedimentary record as a function of the nitrate loading in the northern Gulf of Mexico (redrawn from Turner and Rabalais 1991 and Parsons et al. 2002).

Figure 2

Relationship between the growth in human population (and presumably their nutrients) and HABs from Puget Sound, Washington State, where continuous monitoring of paralytic shellfish poisoning has been ongoing since the mid-1950’s. Plotted here is the relationship between human population in the region for the past 40 years (data were derived from the U.S. census) and the average decadal maximum recorded amount of paralytic shellfish toxins, PST (redrawn from Trainer et al. 2003).

Figure 3

Long term trends in the use of nitrogen based fertilizers and the number of occurrences of red tide blooms in Chinese coastal waters (modified and redrawn from Anderson et al. 2002 and Zhou et al. 2005).

Figure 4

Mean dissolved inorganic and organic N:P ratios for each of the major riverine systems of western Florida shelf sampled during the dry season of May 2004. Each bar represents the means of the stations sampled along an individual riverine transect. The insert box indicated the mean particulate N:P ratio. The general zones are indicated on the companion map of southern Florida (modified from Heil et al. 2007).

Figure 5

Long- term trends in brown tide in Peconic Estuary Long Island (open bars) and in Maryland Coastal Bays (closed bars; redrawn from Gobler et al. 2005 and Glibert et al. 2007).