Runoff and Eutrophication - The Consequences of Paving Paradise
This week I've been thinking about Joni Mitchell (singer-songwriter from 1964 to 2002). I'm sure that she wasn't thinking about algae when she wrote "Big Yellow Taxi," but when we paved paradise and put up a parking lot we drastically altered algal communities, which in turn affected many aquatic and marine ecosystems. Many people I've spoken to about this subject outside of the scientific community have asked me how parking lots on land damage aquatic habitats. While we haven't yet popularized aquatic cars requiring underwater parking lots, paved land indirectly affects aquatic environments by increasing nutrient input through runoff. Runoff is water that drains into a water system from a surface or area of land. It generally picks up nutrients and pollution on its way to the water. In a natural environment, much of the runoff is absorbed into the soil along with the excess nutrients and pollution. However, large areas of impervious surface area (like pavement) carry runoff without absorbing any of it, carrying all of those nutrients and pollutants into the water. These excess nutrients promote algal growth, which can block sunlight and limit oxygen. Under normal conditions, seasonal phytoplankton blooming is completely normal. However, when there is a consistent nutrient supply into the system, phytoplankton blooms can remain beyond their typical seasonal run. This process is known as eutrophication, which can result in seagrass bed reduction, coral bleaching, and many other damaging effects (see picture below). In the most extreme cases, eutrophication can result in harmful algal blooms (HABs). One of the more famous types of HABs is a "red tide" caused by Karenia brevis. It's famous for its red color and production of neurotoxins that cause mass deaths in marine life. HABs can also cause disease in humans when it accumulates in seafood. This is why states closely monitor HABs and their effect on marine life. NOAA also monitors them and issues forecasts when they occur in order to help people and fisheries make informed decisions about areas that may be temporarily affected by a HAB. Joni Mitchell was right: we don't know what we've got 'til it's gone. Therefore, we need to be doing what we can to limit runoff and stop the harmful effects of eutrophication before our amazing coastal ecosystems are damaged beyond repair.  |
| Eutrophication Effects Summary | Earp, H.S., Prinz, N., Cziesielski, M.J. and Andskog, M., CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons |
Suggested Reading:
Boynton WR, et. al. (2013) Multi-decade responses of tidal creek system to nutrient load reductions: Mattawoman Creek, Maryland USA. Estuaries Coasts 37: S111-S127
Cloern JE (2001) Our evolving conceptual model of the coastal eutrophication problem. Mar Ecol Prog Ser 210: 223-253
Gold AC, Thompson SP, Piehler MF (2019). The effects of urbanization and retention-based stormwater management on coastal plain stream nutrient export. Water Resour Res 55:7027-7046
Sanger D, et. al. (2012) Impacts of coastal development on the ecology of tidal creek ecosystems of the US Southeast including consequences to humans. Estuaries Coasts 38: 549-566
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