Changing Planet

Mississippi Mouth Identified as Hottest Hotspot of Human Impact on Coastal Areas

The first integrated analysis for all coastal areas of the world has ranked hotspots of human impact.

The hottest hotspot is at the mouth of the Mississippi River, says Benjamin S. Halpern, lead author of the study, with the other top 10 in Asia and the Mediterranean.

Nutrient runoff from farms draining into the Mississippi has caused a persistent “dead zone” in the Gulf of Mexico, where the river runs into the ocean. The dead zone is caused by an overgrowth of algae that feeds on the nutrients and takes up most of the oxygen in the water.


The hottest hotspot of land-based impact on marine ecosystems is the Mississippi River. The river plume is shown here as seen from space.

Image by NASA

The Mississippi mouth and the other hotspots are areas where conservation efforts will almost certainly fail if they don’t directly address what people are doing on land upstream from these locations, said Halpern, who is based at the National Center for Ecological Analysis and Synthesis (NCEAS) at the University of California in Santa Barbara (UCSB).

The study was published in the Journal of Conservation Letters.


Global hotspots where human activities on land are impacting coastal marine ecosystems. The numbers show the rank order of the hottest hotspots (red dots). The blue and green dots are land-based activities that are having an important effect on marine systems but not as much as those areas marked by the red dots.

Illustration courtesy B. Halpern and colleagues, NCEAS

“Resource management and conservation in coastal waters must address a litany of impacts from human activities, from the land, such as urban runoff and other types of pollution, and from the sea,” Halpern said.

“One of the great challenges is to decide where and how much to allocate limited resources to tackling these problems.”

“One of the great challenges is to decide where and how much to allocate limited resources to tackling these problems,” he said. “Our results identify where it is absolutely imperative that land-based threats are addressed–so-called hotspots of land-based impact–and where these land-based sources of impact are minimal or can be ignored.”

The study surveyed four key land-based drivers of ecological change:

  • nutrient input from agriculture in urban settings
  • organic pollutants derived from pesticides
  • inorganic pollutants from urban runoff
  • direct impact of human populations on coastal marine habitats.


Not All Coastal Waters Fully Impacted

A large portion of the world’s coastlines experience very little effect of what happens on land, nearly half of the coastline and more than 90 percent of all coastal waters, Halpern said.

“This is because a vast majority of the planet’s landscape drains into relatively few very large rivers, that in turn affect a small amount of coastal area.

“In these places with little impact from human activities on land, marine conservation can and needs to focus primarily on what is happening in the ocean. For example: fishing, climate change, invasive species, and commercial shipping.”

Coauthors from NCEAS are Colin M. Ebert, Carrie V. Kappel, Matthew Perry, Kimberly A. Selkoe, and Shaun Walbridge. Fiorenza Micheli of Stanford University’s Hopkins Marine Station and Elizabeth M. P. Madin of UCSB’s Department of Ecology, Evolution and Marine Biology are also co-authors. Selkoe is also affiliated with the University of Hawaii’s Hawaii Institute of Marine Biology.

NCEAS is funded by the National Science Foundation (NSF). The David and Lucile Packard Foundation, the National Marine Sanctuaries, and an NSF Graduate Research Fellowship provided additional support for this research.

Forty years in U.S., UK, and South African media gives David Braun global perspective and experience across multiple storytelling platforms. His coverage of science, nature, politics, and technology has been published/broadcast by the BBC, CNN, NPR, AP, UPI, National Geographic, TechWeb, De Telegraaf, Travel World, and Argus South African Newspapers. He has published two books and won several journalism awards. He has 120,000 followers on social media. David Braun edits the National Geographic Society blog, hosting a global discussion on issues resonating with the Society's mission and initiatives. He also directs the Society side of the Fulbright-National Geographic Digital Storytelling Fellowship, awarded to Americans seeking the opportunity to spend nine months abroad, engaging local communities and sharing stories from the field with a global audience. Follow David on Facebook  Twitter  LinkedIn
  • Roslyn Hogan

    Every year, legislators struggle with how to appropriate funding to the agencies supporting state government. This year has been no exception.

    House File 2458, as passed by the House on April 2 and the Senate on April 17, will very soon be considered again. Since the chambers disagreed, a Conference Committee will be assigned to make recommendations back to the members’ respective chambers unless the House concurs with the changes made in the Senate. There are two provisions included in the bill that Sierra Club Iowa Chapter opposes.

    Language included in the bill removed provisions that funds be spent on nutrient reduction. HF2458 appears to allow that funds be spent on any watershed project instead of on reducing nutrients. At minimum, the bill should require that funding be spent on reducing nutrients in priority watersheds that are included in 12-digit Hydrologic Unit Codes (HUC 12). See the HUC 12 watersheds.

    REAP logo
    Also, the bill changes the REAP formula so that a portion of the open spaces allocation will be used for state park maintenance and operations instead of appropriating it from the general fund as is current practice. Open spaces funding acquires and protects natural areas for all Iowans to enjoy. REAP is statutorily supposed to be allocated $20 million every year. This year’s appropriation bill allocates $16 million with part of the open spaces money allocated to provide maintenance and operations funding rather than its intended purpose.

    Iowa does not experience the same scarcity for water as some of its sister states. Why are we not ensuring its protection? Wouldn’t taxpayer money be better spent on requiring nutrient reduction?

    On the other hand, Iowa does not have the amount of open spaces that other states enjoy. Sierra Club Iowa Chapter does not argue that maintaining and operating Iowa’s state parks are not important. However, the Chapter believes that those funds should not penalize counties who rely on REAP funding to protect what few open spaces are available to them.

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