Effect of freshwater inflow on macrobenthos productivity and nitrogen losses in Texas estuaries : final report




Montagna, Paul A.

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"The primary goal of the current research program is to define quantitative relationships between marine resource populations and freshwater inflows to the State's bays and estuaries. However, we know that there is year-to-year variability in the population densities and successional events of estuarine communities. This year-to-year variability is apparently driven by long-term, and global-scale climatic events that affect the rates of freshwater inflow. Therefore, this report documents long-term changes in populations and communities that are influenced by freshwater inflow. The best indicator of productivity is the change in biomass of the community. A Secondary goal of the current research program is to quantify the loss of nitrogen in Texas estuaries. Nitrogen is the key element that limits productivity. A simple budget would account for nitrogen entering the bay via freshwater inflow, how it is captured and transformed into biomass, and finally how it is lost from the ecosystem. One aspect of nitrogen loss is very poorly understood: "How much nitrogen is buried and lost from the system?" We report here nitrogen content changes with respect to sediment depth. Presumably nitrogen is labile in the upper, biologically active, layers of sediment, and refractory at depth. Therefore, it is important to determine the sediment depth at which nitrogen content is at a low and constant value. ... The structure of this report is as follows. Chapter one is a manuscript which has been submitted for publication in the American Malacological Bulletin. This manuscript summarizes all biological data on mollusks taken to date and synthesizes current information on the biological effects of freshwater inflow on a key indicator taxanomic group. Chapter two is a compilation of biological and hydrographical data obtained during the last two years. Chapter three is a compilation of all the sediment data on nitrogen losses that has been collected to date. Chapter three also contains a brief narrative describing the data and drawing preliminary conclusions.
From University of Texas at Austin, Marine Science Institute ... to Texas Water Development Board
Interagency Cooperative contract TWDB contract no. 94-483-003
October 1994