Dissolved oxygen, water clarity, and submerged aquatic vegetation (SAV) in the Chesapeake Bay have been degraded by an overabundance of nutrients and sediment. The Bay was listed as an "impaired water body" in 1999 under regulatory status related to the Clean Water Act. Improvements in water quality conditions of the Bay must be met by 2010 or a Total Maximum Daily Load (TMDL) for the Bay will have to be developed and enforced. The Chesapeake Bay Program (CBP) has finalized the water quality criteria and the subsequent nutrient and sediment “allocations” (amount of reduction) that are needed to meet these criteria. The jurisdictions in the Bay watershed recently developed tributary strategies to achieve the nutrient and sediment allocations. There may be some refinement to the allocations and tributary strategies as CBP conducts an evaluation of the progress in meeting the water quality criteria and load allocations.

The CBP Watershed Model and Water Quality Model are used to simulate different nutrient and sediment allocations and subsequent water quality and SAV response in the Bay. These models provide valuable insight into the amount of allocations needed to meet the water-quality criteria. However, there is a large degree of uncertainty about the “lag time” between implementing the nutrient and sediment allocations and detecting an actual improvement of water quality and SAV in the Bay. There are several components of “lag time” including:

1. The time between planning and implementation of a management practice;
2. The influence of watershed properties on movement of nutrients and sediment to the Bay; and
3. The time between a load reduction to the Bay and the actual improvement in water quality and SAV.

Additionally, the influence of climate variability (both short and long term cycles) affects the nutrient and sediment load delivery to the Bay and will have a large influence on water quality and SAV changes over time.

Better quantifying the factors that influence the “lag time” between changes in nutrient and sediment sources and improvement in the Bay’s water quality and SAV is critical to allow resource managers to implement nutrient and sediment reduction strategies and improve monitoring and modeling of the factors affecting “lag times” in the Bay ecosystem. The objective of this workshop is to provide the CBP with a better understanding of the factors affecting the “lag time” associated with improving water quality and SAV in the Bay and provide recommendations for improved monitoring and modeling of these factors. By holding this workshop in 2004, the information will be available for use to help improve development of monitoring and modeling approaches and implementation of tributary strategies.

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Understanding "Lag Times" Affecting the Improvement of Water Quality in the Chesapeake Bay Workshop Presentations

Scott Phillips, USGS Workshop Introduction and Objectives Session 1: Planning and Implementation of Management Practices     Cliff Randall, VA Tech Implementation of Point Source Nutrient Controls     Mike Bowman, VA DCR, and Gary Shenk, EPA CBPO Tributary Strategies and the Bay Watershed Model: Accounting for Management Practices     Mark Waggoner, NRCS From Planning to Implementation Session 2: Influence of Watershed Properties on Water Quality Response    Jeff Raffensperger, USGS Simulation of Sources and Transport of Nutrients in the Bay Watershed and Ideas for Improvement    Gary Shenk, EPA CBPO Water Quality Criteria Assessment Lag    Bruce Lindsey, USGS Residence Times and Nitrogen Concentrations in Ground Water Discharging to Streams in the Chesapeake Bay Watershed    Allen Gellis, USGS Source, Transport, and Storage of Sediment in the Bay Watershed    Donald Boesch, UMCES Chesapeake Futures: Implications of Land Use and Development on Nutrient Loads Session 3: Climate Variability, Load Reductions, and Improvement in Tidal Water Quality and SAV    Walter Boynton, UMCES Lag Times and Water Quality in Chesapeake Bay    Bill Dennison, UMCES Chesapeake Bay Submerged Aquatic Vegetation    Bruce Michael, MD DNR Water Quality and Habitat Response to Acute Events    Chuck Gallegos, SERC Some Observations on the Spring, 2000, Prorocentrum minimum, Bloom in Upper Chesapeake Bay Tributaries