What lies beneathWhat lies beneathAnd why you should careAnd why you should care

The Influence of Freshwater Inflow on The Influence of Freshwater Inflow on Macroinvertebrate Species Macroinvertebrate Species

Composition In Lavaca-Matagorda BayComposition In Lavaca-Matagorda Bay

Research AreaResearch Area

Lavaca BayLavaca Bay Four Sites, A-DFour Sites, A-D Sites follow gradient in Sites follow gradient in

salinitysalinity

LCRA - SAWS Water Agreement and ContractLCRA - SAWS Water Agreement and Contract

The Lower Colorado River Authority (LCRA) and The Lower Colorado River Authority (LCRA) and the San Antonio Water System (SAWS) have the San Antonio Water System (SAWS) have initiated a water diversion project initiated a water diversion project

Could transfer approximately 150,000 acre-feet of Could transfer approximately 150,000 acre-feet of water annually (49 billion gallons per year) from the water annually (49 billion gallons per year) from the lower Colorado River to the City of San Antoniolower Colorado River to the City of San Antonio

Water will be pumped approximately 170 miles up to Water will be pumped approximately 170 miles up to San AntonioSan Antonio

Freshwater InflowFreshwater Inflow

Inflows serve a variety of important functions Inflows serve a variety of important functions in ecosystems, including:in ecosystems, including:

creation and preservation of low-salinity creation and preservation of low-salinity nurseries nurseries

sediment and nutrient transport sediment and nutrient transport movement and timing of critical estuarine movement and timing of critical estuarine

species species

Benthic MacrofaunaBenthic Macrofauna (>0.5mm) (>0.5mm)

Important in trophic structureImportant in trophic structure Relatively long-lived and Relatively long-lived and

sessilesessile Some species sensitive to Some species sensitive to

changes in salinity and/or changes in salinity and/or pollutants, others tolerantpollutants, others tolerant

Excellent “indicator species” Excellent “indicator species” for water quality assessmentfor water quality assessment

Image courtesy of Microscopy UK

Dominant SpeciesDominant Species

Streblospio bendecti Streblospio bendecti is a pioneering is a pioneering species that can respond quickly to species that can respond quickly to disturbances in the environmentdisturbances in the environment

Mediomastus ambiseta Mediomastus ambiseta is an equilibrium is an equilibrium speciesspecies

Species ShiftSpecies Shift Mediomastus, an Mediomastus, an

equilibrium species, equilibrium species, had been dominate at had been dominate at most stations in the most stations in the previous sampling previous sampling period period

Low inflow of 33.2 Low inflow of 33.2 occurred previous occurred previous monthmonth

April’s true inflow was April’s true inflow was 1388 cfs1388 cfs

FW IndicatorsFW Indicators

Other FactorsOther Factors

Inflow and Salinity important, but so are:Inflow and Salinity important, but so are:

Sediment typeSediment type Nutrient loadingNutrient loading Mechanical/chemical disturbances, etc.Mechanical/chemical disturbances, etc.

These secondary factors not within the scope of These secondary factors not within the scope of this projectthis project

Importance of StudyImportance of Study

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