Nutrient Criteria Background - Wide array of opinions on how best to proceed from leading experts within a wide cross section of the Chesapeake Bay scientific community1, ranging from "...develop a salinity regime based set of nutrient criteria by working backwards from a set of established chlorophyll a criteria." to "Nutrient criteria are not scientifically defensible given there are so many factors/rates/processes that will influence the ambient concentrations at any time as well as their uptake by and influence on algal growth. Better to address the impacts themselves-chlorophyll a-versus focusing strictly on tidal water nutrient concentrations." to "Recommend viewing nutrient criteria not as a single criterion but as a package of conditions to be attained-TN:TP, silica availability, ambient nutrient conditions, light availability, total suspended solids, salinity-with full up front recognition that even full attain of these still to be established range of conditions favoring a certain, preferred phytoplankton assemblage may not result in that assemblage given the influences of other independent factors like flushing rates, temperature, etc." Points of Consensus Building - Bay specific ambient concentration based nutrient criteria should be based on conditions required to promote return of a more balanced, preferred phytoplankton community species composition. Such Bay nutrient criteria might contain the following components: Ambient concentrations of nitrogen, phosphorus—totals and species - Ratios of N:P Quantification of other conditions to be attained-silica availability, light penetration, salinity Existing state of the science will not support derivation of nutrient criteria directed the towards phytoplankton community species composition endpoint - Bay research should be directed towards filling in these gaps in our knowledge to set up for a time in the not too distant future when scientifically defensible nutrient criteria could be developed for the Chesapeake Bay Issues - We have not compiled a specific technical record of data supporting/not supporting development of Chesapeake Bay nutrient criteria - What will the states need during their Bay water quality standards adoption process to address this issue Next Steps - Draft up a recommendations paper and distribute to the Chlorophyll/Nutrient Criteria Team for review, comment, and concurrence 1 Extracted from Summaries of Meetings with Key Chesapeake Bay Scientists Regarding Bay Specific Dissolved Oxygen, Water Clarity, Chlorophyll a and Nutrient Criteria, June 2000. ------- |