Nutrient criteria technical guidance manual : estuarine and coastal marine waters

Participants in the Tampa Bay Estuary Program have agreed to adopt nitrogen loading targets for Tampa Bay based on the water quality and related light requirements of the seagrass species Thalassia testudinum. Based on modeling results, it appears that light levels can be maintained at necessary levels by “holding the line” at existing nitrogen loadings. However, this goal may be difficult to achieve given the 20% increase in the watershed’s human population and associated 7% increase in nitrogen loading that are projected to occur over the next 10-20 years. To address the long-term management of nitrogen sources, a Nitrogen Management Consortium of local electric utilities, industries and agricultural interests, as well as local governments and regulatory agency representatives, has developed a Consortium Action Plan to address the target load reduction needed to “hold the line” at 1992-1994 levels. To date, implemented and planned projects collated in the Consortium Action Plan meet and exceed the agreed-upon nitrogen loading reduction goal. The Tampa Bay estuary is located on the eastern shore of the Gulf of Mexico in Florida, USA. At more than 1000 km, it is Florida’s largest open water estuary. More than 2 million people live in the 5700 km watershed, with a 20% increase in population projected by 2010. Land use in the watershed is mixed, with about 40% of the watershed undeveloped, 35% agricultural, 16% residential, and the remaining commercial and mining. Major habitats in the Tampa Bay estuary include mangroves, salt marshes and submerged aquatic vegetation. Each of these habitats has experienced significant areal reductions since the 1950s, due to physical disturbance (dredge and fill operations) and water quality degradation, particularly impacting the seagrasses due to loss of light availability. Five species of seagrass are commonly found in Tampa Bay, with Thalassia testudinum (turtlegrass) and Syringodium filiforme (manatee grass) dominating in the higher salinity areas and Halodule wrightii (shoalgrass) and Ruppia maritima (widgeon grass) most commonly found in lower salinities. The importance of seagrass as a critical habitat and nursery area for fish and invertebrates, and as a food resource for manatees, sea turtles and other estuarine organisms has been recognized by the Tampa Bay resource management community for several decades. In 1990, Tampa Bay was accepted into the U.S. Environmental Protection Agency’s (EPA) National Estuary Program. The Tampa Bay National Estuary Program (TBNEP), a partnership that includes three regulatory agencies and six local governments, has built on the resource-based approach initiated by earlier bay management efforts. Further, it has developed water quality models to quantify linkages between nitrogen loadings and bay water quality, and models that link water quality to seagrass goals. Recent recommendations from the National Academy of Science National Research Council (NRC) include those which regional watershed programs might consider in developing nutrient management strategies. The NRC recommendations are based on the process designed by the Tampa Bay Estuary Program partners to develop and implement a seagrass protection and restoration management program for Tampa Bay. Critical elements of the Tampa Bay process are to: