What lies beneath And why you should care The Influence of Freshwater Inflow on Macroinvertebrate Species Composition In Lavaca-Matagorda Bay

Research Area  Lavaca Bay Four Sites, A-D Four Sites, A-D Sites follow gradient in salinity Sites follow gradient in salinity

 LCRA - SAWS Water Agreement and Contract The Lower Colorado River Authority (LCRA) and the San Antonio Water System (SAWS) have initiated a water diversion project Could transfer approximately 150,000 acre-feet of water annually (49 billion gallons per year) from the lower Colorado River to the City of San Antonio Could transfer approximately 150,000 acre-feet of water annually (49 billion gallons per year) from the lower Colorado River to the City of San Antonio Water will be pumped approximately 170 miles up to San Antonio Water will be pumped approximately 170 miles up to San Antonio

Freshwater Inflow Inflows serve a variety of important functions in ecosystems, including:  creation and preservation of low-salinity nurseries  sediment and nutrient transport  movement and timing of critical estuarine species

Benthic Macrofauna (>0.5mm)  Important in trophic structure  Relatively long-lived and sessile  Some species sensitive to changes in salinity and/or pollutants, others tolerant  Excellent “indicator species” for water quality assessment Image courtesy of Microscopy UK

Dominant Species  Streblospio bendecti is a pioneering species that can respond quickly to disturbances in the environment  Mediomastus ambiseta is an equilibrium species

Species Shift  Mediomastus, an equilibrium species, had been dominate at most stations in the previous sampling period  Low inflow of 33.2 occurred previous month  April’s true inflow was 1388 cfs

FW Indicators

Other Factors  Inflow and Salinity important, but so are: Sediment type Sediment type Nutrient loading Nutrient loading Mechanical/chemical disturbances, etc. Mechanical/chemical disturbances, etc. These secondary factors not within the scope of this project

Importance of Study Determination of minimum inflows is necessary to preserve the health of the estuarine and surrounding coastal ecosystems