Project Title: Modeling the effects of changes in turbidity on light available for submerged aquatic vegetation
Principal Investigator(s): Roger I. E. Newell, Raleigh R. Hood, Evamaria W. Koch, and Raymond E. Grizzle

Accomplishments
Scheduled Tasks:

1. Complete the development of our mathematical model in STELLA.
2. Publish manuscripts and refine the user interface of the model based on our preliminary demonstrations to resource managers.
3. Make verbal and hands-on presentations to Chesapeake Bay resource managers, at scientific meetings, and distribute the model via the internet.

Progress on Tasks

1. Continued Model Development:
   Our model simulates seston concentration, water clarity and seagrass density as a function of bivalve biomass and filtration, sedimentation and sediment resuspension. The details of the model can be found in our previous reports. This basic model formulation has not been altered since our last report. As we reported previously, we have recast the model so that wave fetch is explicitly considered, i.e., waves are propagated shore wards over a shoaling bottom with seagrasses present. The waves are progressively damped by friction against the bottom and the damping is accelerated due to increased friction where seagrasses are present. Thus, we now have a spatially explicit model coded in the STELLA computer language.

   Although STELLA has provided an excellent environment for the model development so far, it does not provide a convenient way to make spatially explicit calculations. Currently the only way we have to propagate waves toward shore is by making a series of model runs for different distances from shore. Then by taking the output from each successive run as input into the next run the influence of the wave can be propagated shoreward. During this reporting period we have put a considerable amount of effort into exploring ways in which we can overcome this problem without using other computer languages (e.g., Fortran) to code the model. Eventually we found a system, the spatial modeling environment (SME), developed by Thomas Maxwell (Maryland Institute for Ecological Economics), that will enable us to overcome this difficulty with STELLA. This SME environment transparently links icon-based modeling environments, such as STELLA, with advanced computing resources that will enable us to carry out spatially explicit simulations in a user-friendly graphical environment. A major advantage of doing this is that it will make it possible to carry out simulations where we can easily manipulate the location of the bivalves to determine the effects of position, as well as density and filtration rate, on water clarity and SAV bed density.

   We have just begun this final phase of our model development work, and we anticipate that it will be completed within the next several months We will then rerun the model for the scenarios described in our previous report and carry out model sensitivity studies to ascertain which model parameters have the most influence on the model-predicted interactions between bivalves and SAV. We will also carry out a series of simulations designed to explore the effects of oyster location on water clarity and SAV density.

   We have begun the process of developing a manuscript that describes the basic model. This paper will report the results from the model runs described above. We anticipate that this paper will be completed and submitted before the year is out. The major scientific focus of this paper will be to address the core questions of this project:

   • Is there a positive feedback effect of seagrass wave damping on seagrass growth, i.e., are seagrasses self-stabilizing with respect to waves.
   • What is the effect of bivalve filtration on seagrass distributions and density, and is there a significant difference between the filtration effects of clams versus oysters.

   As we discussed in our previous report our preliminary model runs have already provided preliminary answers to these questions:

   1. there is a positive feedback effect and seagrasses can be self-stabilizing due to their wave damping effects. However, this positive feedback effect happens only under relatively calm conditions and when plants occupy most of the water column (reproductive phase with long stems).
   2. with oysters present and actively filtering, seagrasses can grow further inshore whereas the effect of clam filtration is insignificant. The difference between the effects of clam vs. oyster filtration is due to the fact that the filtration rate of the oysters is more than an order of magnitude higher than that of the clams.
2. Disseminate Project Results We have made a strong effort to disseminate to the management and research community our insights into how bivalve suspension feeders can reduce turbidity and thereby benefit seagrasses. In addition to major presentations at the Fall 2001 ERF meeting (see last progress report) we have made the following presentations of this CICEET-funded research. The first two invited presentations are particularly noteworthy. The first was a workshop for Chesapeake Bay managers (Federal (NOAA/EPA) and Maryland and Virginia State officials) specifically organized to evaluate modeling approaches to assess the ecological function of suspension feeders, such a oysters and clams. The second was one of the monthly seminars for Maryland Department of Natural Resources managers.

   Newell, R.I.E., J.C. Cornwell, R.R. Hood and E. Koch. Beyond Water Clearance: Incorporating Other Aspects of Benthic Suspension-feeder Ecology into Estuarine Water Quality Models. Chesapeake Bay Program Scientific Technical and Advisory Committee Workshop:

   Newell, R.I.E., J.C. Cornwell, R.R. Hood and E. Koch. Beyond Water Clearance: Incorporating Other Aspects of Benthic Suspension-feeder Ecology into Estuarine Water Quality Models. Chesapeake Bay Program Scientific Technical and Advisory Committee Workshop: ÒSuspension feeders: A workshop to assess what we know, don't know, and need to know to determine their effects on water qualityÓ Chesapeake Bay Program Scientific and Technical Advisory Committee, Baltimore, March 2002.

   Newell, R.I.E. Role of Benthic Suspension-feeders in Maintaining Estuarine Water Quality. Maryland Department of Natural Resources Seminar series. March 2002.

   Newell, R.I.E., M. K. Wood, R. E. Grizzle, E. Koch and R.R. Hood. Modeling the Influence of Filtration by Bivalve Stocks on Turbidity and Seagrass Growth. National Shellfisheries Association annual meeting, Mystic CT, April 2002.

   Difficulties Encountered
   As discussed above the STELLA modeling environment does not allow us to conveniently make spatially explicit calculations. We are now in the process of porting our STELLA model over to SME which will allow us to make spatially explicit calculations.

   Anticipated Success in Meeting Project Objectives in Scheduled Project Period
   We have nearly met all the objectives we set out for this 24 month project. But as generally happens we still have several small aspects of the project that require completion. Based on our revised work plan we anticipate that we will have completed them all by November 2002.

   Tasks and activities for next reporting period
   
   Tasks for the next reporting period
   

   1. Port the model to SME, repeat previous simulations, carry out a full sensitivity analysis, run additional simulations for exploring the effect of oyster reef position on water clarity and SAV growth.
   2. Develop the user interface of the model in SME. Make any needed improvements and refine the user interface.
   3. Distribute the model via the internet.
   4. Write papers describing the model and the results of the field research in scientific journals.

   Work plan to accomplish tasks
   We have already initiated the work to port the existing mathematical model from STELLA to SME, which will finish the model development and implementation phases of the work.

   Concerns or difficulties
   Now that we have found a way to use SME to extend the capability of the STELLA system it means that we do not have to reformulate the model in Fortran we anticipate no major difficulties regarding the future progress of this project.

   Expenditures
   The grant is now closed.