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Comments on Action Plan for Reducing, Mitigating, and Controlling Hypoxia in the Northern Gulf of mexico (GOM Action Plan)

Utilizing an Adaptive Management Approach certainly seems like a worthwhile strategy given the scientific complexity of this problem and need for a long term management approach for the Mississippi/Atchafalaya Basin in order to achieve measurable results in reducing the hypoxia zone in the northern GOM ("dead zone"). Even though the focus on nitrogen loading from the watershed as a way to reduce the extent/duration of the "dead zone" is understandable, the fact that the silicon/nitrogen, nitrogen/phosphorus, and silicon phosphorus ratios in the water column could result in changes in the phytoplankton composition (poised near Redfield Ratio for N:P:Si) should also be considered as a potential impact. A shift from diatoms to dinoflaggelates/nuissance algal species at the base of the food chain could have profound impacts in the living marine resources (LMRs) in the northern Gulf of Mexico (GOM). Thus the Action Plan should consider the nutrient loading rates for all three macronutrients and develop potential control strategies if silicon limitation replaces nitrogen limitation of the phytoplankton and poses a threat to alter the composition/abundance of the plankton community. Certainly at the present there is good evidence that dissolved nitrogen loading drives the accumulation of phytoplankton biomass, which upon its death/decay by bacteria causes the hypoxia in the bottom waters of the "dead zone".

Since the Mississippi River discharge rate and water column stratification vary from year-to-year, Coastal Goal 1A of a target nitrogen loading reduction goal of 350,000-650,000 metric tons by 2010 seems to be a more prudent strategy than 1B (reduction in extent of "dead zone" which varies with discharge rate and stratification) or 1C within basin/coastal goal (seems kind of vague). It is easier to relate monitoring results to program accomplishments if you have a target which is measurable, quantifiable, and has a cause/effect relationship to the problem of interest. I don't know whether the target in option 1A is achievable within 10 years and will leave that to other to comment upon.

In regards to environmental indicators it might be useful to develop some to indicate progress in the watershed sub-basins, besides just average phosphorus and nitrogen concentrations. Perhaps you could consider freshwater mussels or the abundance/distribution of gamefish as potential biotic indicators (need somebody with expertise in biotic integrity indices to think about this issue). Since the reduction of the size/duration of the "dead zone" is likely to take some time, it would be useful to have indicators of improved water quality within the watershed, so that citizens/municipalities can see some progress from their investments/volunteer efforts. Since the cause of this problem (mid-west agricultural belt) is spatially separated from those that will receive the benefits (coastal Lousiana), it would be useful to demonstrate some benefits upgradient within the watershed. Otherwise there will be a serious political problems in implementing this Action Plan.

Thanks for the opportunity to comment on the Action Plan.

Dr. David Dow
18 Treetop lane
East Falmouth, Ma. 02536-4814

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