Harmful Algal Blooms: Causes and Solutions

As promised, below is the paper I wrote for my Oceans class at Gtown on Harmful Algal Blooms.
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Abstract

Harmful Algal Blooms, known as HABs, have been increasing in intensity, frequency and duration in the last several decades in the coastal areas of the United States of America. While HABs occur naturally, studies suggest that they can also be anthropogenic. Due to the significant health and economic impact HABs can have, governmental organizations have worked to develop models to forecast future HABs, and researched anthropogenic causes of HABs as well as preventative measures. Through continuing to develop these models as well as limiting nutrient runoff into water bodies, much of the economic and health impact of HABs can be avoided.

 

Introduction

While all algal blooms can damage coastal ecosystems by preventing sunlight from reaching marine vegetation killing them and leading to hypoxia, harmful algal blooms are different as they consist of algae species that produce trace amounts of neurotoxins. While individual algae do not produce enough neurotoxins to harm wildlife or humans, large algal blooms which are composed of millions of individual alga, can produce enough to cause fish kills, contaminate seafood and render drinking water unsafe for human consumption (NOAA 2004). These blooms result in the loss of roughly $82 million each year in the United State alone (Hoagland and Scatasta 2006). This figure is a low estimate as many HABs go unreported, the environmental impact is unquantifiable, and the economic impact of an HAB is subtle in how it affects consumer decisions about seafood consumption or the value of waterfront property. Because HABs have such a large economic impact, governmental organizations such as the National Oceanic and Atmospheric Administration and the Northwest Fisheries Science Center, are working to monitor and forecast the blooms through programs such as Monitoring and Event Response for Harmful Algal Blooms (MERHAB) through NOAA and the Harmful Algal Blooms Program though the NFSC.

 

Body

Basics of HABs

Algae are single celled organisms, many species of which have chlorophyll and thus photosynthesize. Among other things, they require carbon dioxide, water, light, nitrogen, phosphorus and iron to survive. Individual algae are relatively benign but there are two types of algae that produce neurotoxins, diatoms and dinoflagelates (Dolah, 2000). Within these categories, different species are endemic to certain regions and produce unique neurotoxins. For example, there is the Karenia brevis which is found in the Gulf of Mexico and produces brevetoxins while the Alexandrium minutum is found off Western Australia and the Mediterranean and produces a neurotoxin that causes Paralytic Shellfish Poisoning (Barile, 2004). Large amounts of algae in an area, regardless of species can cause ecological damage through triggering hypoxia, but the distinction of a harmful algal bloom is limited to blooms of diatom or dinoflagelate species due to the dangerously high levels of neurotoxins they produce which can poison their ecosystem (Dolah, 2000).

These blooms occur when environmental conditions favor algae growth, often due to a large increase in the levels of nutrients such as iron, nitrogen and phosphorous. Nutrient levels in coastal environments fluctuate frequently through natural processes such as the changes of the seasons, wind currents, and upwellings causing HABs. However, increased human activity and pollution has augmented nutrient levels in coastal ecosystems resulting in higher frequency and intensity of HABs.

 

The Danger of HABs

While HABs occur naturally, increased iron, nitrogen, phosphorus and silicon levels in coastal regions which are caused by runoff from septic tanks, roads and farms have been linked to increased blooms, especially in the Gulf of Mexico. While most algae species require light and nutrients to bloom, only certain types of algae produce neurotoxins and the blooms of these species are thus deemed harmful by the scientific community. These blooms produce neurotoxins such as saxitoxins, ciguatoxin, and okadaic acid which can bioaccumulate in aquatic life causing fish kills and harm humans who eat seafood. Approximately 20% of food borne disease outbreaks are from seafood, half of which are caused by algal toxins (Dolah, 2000).

The different neurotoxins are byproduct of different algal species that are unique to various climates. Thus, there can be no standard monitoring device for the nation’s shores as they need to be calibrated to measure the different neurotoxins. But as waters warm due to Global Warming, it is possible that algal species that have been limited to warmer climates will migrate north (Action Plan, 2004). This lack of uniformity among HABs makes monitoring and predicting of the blooms complex, but all diatoms and dinoflagelates neurotoxins have similar effects and require the same micro and macro nutrients to bloom thus solutions do not have to be unique to the algal species.

 

Monitoring and Predicting

Advanced monitoring and prediction systems can help monitor water conditions and alert fishermen when HABs are eminent so they will stop fishing in order to avoid possible health issues. While there is no specific threshold of nutrient levels or nutrient ratios that cause HABs, the higher the nutrient levels and the more iron there is in an environment relative to other nutrients, the more likely a HAB will occur. Monitoring iron levels is key to the surveillance process because only trace amounts are required to encourage blooms as iron “exerts an important influence on the elemental composition of algal cells” (Weng, 2008). Also, algal growth is severely limited in environments that are macronutrient rich but iron deficient (Weng, 2008). Thus by monitoring nutrient levels with careful attention to iron levels, scientists can predict when conditions are favorable to HABs thereby determining the likelihood of a bloom.

Another way of monitoring the presence of harmful algae is through measuring the amount and type of toxins that have bioaccumulated in wildlife through capture and dissection. Through regularly sampling fish for biotoxins, negative human health effects caused by eating fish contaminated by HABs can be avoided. Both methods have their advantages and their disadvantages. By monitoring nutrient levels, scientists can predict when HABs are likely, however due to the complexity of these bloom events prediction is still relatively inaccurate. Measuring biotoxin levels in fish is very useful for avoiding human health effects of HABs, but as it does not predict future HABs, its utility is limited.

While monitoring and prediction is not an ideal solution to mitigate damages from HABs, the complex nature of HABs and the uncertainty of the exact conditions in which they form, as well as the political, economic and logistical difficulty of preventing them makes the monitoring and predicting of  HABs a vital measure in mitigating the damages they cause.  

 

Methods of Nutrient Reduction

The work of NOAA and similar organizations are also taking steps to reduce the frequency of HABs by trying to limit nutrient runoff into water bodies and cleaning up polluted water. Algal blooms, both harmful and non, are frequent where nutrient levels are high, also bloom intensity and duration are positively correlated with nutrient levels. Ergo, by reducing nutrient levels in a body of water, the risk of a HAB significantly decreases. The main methods of nutrient reduction are filtering nutrients from water runoff, limiting the amount of nutrient use in watersheds, and decreasing total water runoff.

Non-harmful algal blooms in a water body can be reduced through maintaining and replanting riparian forests around the body’s feeder streams as well as preserving wetlands along the streams and at their mouth. As riparian forest and wetland preservation and replanting can reduce the occurrence of non-harmful algal blooms, it is very likely that these efforts can reduce the occurrence of HABs. Forest and wetland development lower nutrient levels in water bodies by absorbing nutrients before they reach the open water ecosystem, by limiting the amount of nutrients that could flow into these water bodies, HAB frequency can be reduced.

Population growth has resulted in an increase in the amount of total waste generated. As a result, leaking and overflowing septic tanks have become a major source of excess nutrients. Through leaks and overflows, septic tank nutrients can leach into groundwater and flow into major water body drastically raising phosphorus and nitrogen levels (Barile, 2004). By renovating, replacing and repairing septic tanks by rivers and streams, nutrient levels can be limited in water bodies which in turn will also reduce HABs.

Although the link between iron and HABs is strong, it is the most difficult nutrient to limit. Iron levels are difficult to control as they are strongly influenced by wind currents bringing iron-rich dust from land (Weng, 2008). Another method of limiting nutrient levels in water would be to reduce the amount of fertilizers used by farmers. This would result in less nutrient-rich runoff limiting nutrient levels.

Through reducing the total amount of pavement and by using more water permeable paving materials, the total amount of runoff flowing into water bodies would decrease. Pavement does not quickly absorb water and highly paved areas suffer from higher rates of water runoff than non-paved areas. There are new technologies and methods of pavement that have increased permeability which can reduce the amount of storm water runoff and thus nutrient flow. Maintaining forests and wetlands can prevent urban sprawl and thus limit the use of pavement, preserving these natural areas with high water retention rates. Even if the nutrient level in runoff does not decrease, the reduction of the amount of rainwater runoff would result in water bodies receiving fewer nutrients.

 

Benefits of HABs

Algae photosynthesize and sequester carbon. Global Warming which is caused by increasing levels of carbon dioxide can have disastrous effects on the global ecosystem and human society. Because of the serious potential damage caused by uncontrolled Global Warming, reducing carbon dioxide levels is vital to maintaining a habitable world. There are many methods of reducing and sequestering carbon dioxide emissions, one of which is through biological storage. By encouraging large algal blooms, harmful or non, carbon dioxide will be sequestered thereby partially mitigating Global Warming. HABs are damaging to the local ecosystem while Global Warming is damaging to the global ecosystem. Thus by suffering a local problem, it is possible for a global issue to be solved.

Before the government commits to encouraging HABs to fight Global Warming the benefits and costs must be examined. HABs cause hypoxia, dead zones, and fish kills in a marine environment and it is difficult for an ecosystem to recover from these ecological disasters. Meanwhile, Global Warming is a problem on the scale of gigatons of carbon dioxide. HABs do not have enough biomass to mitigate the harmful effects of Global Warming in any significant capacity.  As the damage to the local ecosystem outweighs the benefit to the global ecosystem, HABs should be prevented to improve global environmental health.

 

Conclusion

Funding for HAB monitoring and forecasting programs must be increased in order to better forewarn against and avoid the damages of the bioaccumulation of neurotoxins in seafood. These efforts have been successful in the past and should be expanded upon. However, while monitoring the problem and reacting to outbreaks can avoid some of the financial cost of a HAB, it does not solve the issue. The only solution to anthropogenic HABs is limiting nutrient runoff. It would be nearly politically impossible to discourage farmers from using artificial fertilizer as that would result in lower crop yields and thus higher food prices. Limiting fertilizer use would also significantly hurt the agrichemical industry, thus making it an unlikely solution to HABs.

Maintaining and replanting riparian forests and wetlands would be a more feasible method of limiting nutrient runoff. These ecosystems absorb nutrients and restoring and maintaining them would be far less expensive and more politically possible than limiting fertilizer use, as there are fewer organizations with vested interest in developing these lands, they would provide habitat for wildlife and, in the case of wetlands, protect against hurricanes. While most nutrient runoff comes from farms, a sizeable portion does come from leaking and overflowing septic systems. As repairing these would be relatively inexpensive and it would provide immediate health benefits to the surrounding area, it is politically and economically possible to reduce the overall nutrient load through upgrading and repairing septic systems. Thus through creating models to predict and monitor HABs and by maintaining natural ecosystems as well as limiting nutrient flow into water bodies, the negative health and economic effects of HABs can be avoided.

 

 

Bibliography:

Action Plan for Harmful Algal Blooms and the Gulf of Mexico Coastal Ocean Observing System: Results from a Regional Workshop. USA. Department of Commerce. National Oceanic and Atmospheric Association. 2004.

Barile, Peter J. "Evidence of Anthropogenic Nitrogen Enrichment of the Littoral Waters of East Central Florida." Journal of Coastal Research 20 (2004): 1237-245.

 

“Marine Algal Toxins: Origins, Health Effects, and Their Increased Occurrence”, Frances M. Van Dolah.  Environmental Health Perspectives, Vol. 108, Supplement 1: Reviews in Environmental Health, 2000 (Mar., 2000), pp. 133-141

"Overview of Harmful Algal Bloom." NOAA.gov. 16 May 2007. Center for Sponsored Coastal Ocean Research. 26 Nov. 2008 <http://www.cop.noaa.gov/stressors/extremeevents/hab/overview.html>.

 

Weng, Huan-Xin, Xiang-Wei Sun, Jing-Ke Weng, Ya-Chao Qin, and Hailiang Dong. "Cruicial Roles of Iron in the Growth of Prorecentrum micans Ehrenberg (Dinophyceae)." Journal of Coastal Research 24 (2008): 176-83.