Harmful algal blooms and eutrophication: Examining linkages from selected coastal regions of the United States

Abstract

Coastal waters of the United States (U.S.) are subject to many of the major harmful algal bloom (HAB) poisoning syndromes and impacts. These include paralytic shellfish poisoning (PSP), neurotoxic shellfish poisoning (NSP), amnesic shellfish poisoning (ASP), ciguatera fish poisoning (CFP) and various other HAB phenomena such as fish kills, loss of submerged vegetation, shellfish mortalities, and widespread marine mammal mortalities. Here, the occurrences of selected HABs in a selected set of regions are described in terms of their relationship to eutrophication, illustrating a range of responses. Evidence suggestive of changes in the frequency, extent or magnitude of HABs in these areas is explored in the context of the nutrient sources underlying those blooms, both natural and anthropogenic. In some regions of the U.S., the linkages between HABs and eutrophication are clear and well documented, whereas in others, information is limited, thereby highlighting important areas for further research.

Figure 1

Nutrients in Gulf of Maine nearshore waters. Panel A: Concentrations of nitrate plus nitrite (NO₃₋ + NO₂₋) and silicate (Si(OH)₄) in the Kennebec and Androscoggin Rivers in Maine over the period January 1, 2001 to May 1, 2002 (data from Vorosmarty et al., http://www.gm-wics.sr.unh.edu/). Panel B: Concentrations of NO₃₋ + NO₂₋ and Si(OH)₄ collected in Casco Bay at the Southern Maine Community College dock, South Portland, Maine (from Townsend et al., http://grampus.umeoce.maine.edu/). Panel C: Mixing curves for NO₃₋ + NO₂₋ and Si(OH)₄ versus salinity for Gulf of Maine samples collected in a high- (April–May 2000), medium- (June 2000) and low-runoff period (July 2001) (Townsend et al., 2005). Assuming a northern Gulf of Maine coast-wide freshwater source concentration of nutrients similar to the Kennebec-Androscoggin (which was 32 µM Si(OH)₄ and 12 µM NO₃₋ + NO₂₋ in April 2000; n=49; http://www.gm-wics.sr.unh.edu/), and coastal seawater concentrations of ca. 8 µM of Si(OH)₄ and ca. 8 µM NO₃₋ + NO₂₋ and salinity of 32.5, Si(OH)₄ concentrations of 9.5 µM and NO₃₋ + NO₂₋ concentrations of 8 µM at salinity of 30 in April–May are expected (in agreement with those values observed in the mixing curve in Panel C).

Figure 2

A. Concentrations of DIN in western Great South Bay, NY (Suffolk County Department of Health Services station 250) from 1976 – 2000, before and after the onset of brown tides. B. Concentrations of DON in Great Peconic Bay, NY (Suffolk County Department of Health Services station 130) from 1996 – 2005, since the last occurrence of brown tide in this system.

Figure 3

Temporal changes in land uses, river flow, fertilizer use, and river N concentration in the Chesapeake Bay watershed. From Kemp et al. 2005 with permission of the publisher.

Figure 4

Available data for total and inorganic N and P concentrations for a 2 square km area at the Caloosahatchee River mouth and the extent of Everglades Agricultural Area (EAA) which is devoted to sugar cane fields for the time frame of 1949 through 2005. Nutrient data has been retrieved from the state of Florida STORET database; available data for the river from a variety of sources are listed on the figure. The change in the areal extent of the EAA has been modified from Brand (2002).