Poster Presentation Abstracts

Connecting wetland salinity levels to freshwater inflows

Carla G. Guthrie, Junji Matsumoto, Dharhas Pothina, Texas Water Development Board, Bays and Estuaries

Following a state mandate to determine freshwater inflow needs of minor estuaries, the Texas Water Development Board is extending an open bay hydrodynamic and salinity transport model to include tidally influenced areas of coastal wetlands in the San Bernard/Cedar Lakes Estuary.  Wetlands serve as nursery habitat for estuarine species, as well as essential habitat for many other species.  While the overall goal is to determine a freshwater inflow regime which protects wetland plant diversity, growth, and production by maintaining acceptable salinity levels, this presentation focuses on two questions:  (1) How does freshwater inflow impact salinity in the open bay and therefore inundation salinity in the lower and middle marsh zone?  (2) How do inundation salinities influence soil salinities?  The study is being conducted in tidally influenced wetlands at San Bernard National Wildlife Refuge, Brazoria County, Texas, USA.  Low marsh areas are dominated by Spartina alterniflora.  However, the majority of area wetlands are mid-elevation marshes primarily composed of Spartina patens/Distichlis spicata nearest to tidal influence and Paspalum vaginatum/Schoenoplectus americanus farther upland.  A previous study in this wetland documented annual mean surface water salinities ranging 12 to 49ppt, while interstitial salinity ranged 15 to 68ppt (Miller et al. 2005).  Although our hydrodynamic models can simulate surface water salinity, they cannot simulate pore water salinity which is critical to plant production and survival.  In order to correlate surface and pore water salinity, we are collecting in situ salinity data in open water (seven sites) and in soil (four sites).  Field data show spatial variation in the correspondence between water level within paired soil and open water sites.  Soil salinities remain relatively stable despite salinity fluctuations occurring in open water sites.  To our knowledge, the relationship between interstitial salinity and surface water salinity is not well known.  This study provides a unique high resolution dataset which is being used to calibrate a hydrodynamic model and reveal patterns in the characteristics of salinity in coastal wetlands. 

Tolerance of Benthic Invertebrates to Reoccurring Hypersaline Conditions Resulting from Reduced Inflows in the Nueces River Delta, Texas, USA

Erin M. Hill, Brien A. Nicolau , Robert F. Duke, Aaron S. Baxter, and Paul V. Zimba, Texas A& M University- Corpus Christi, Center for Coastal Studies, Corpus Christi, Texas

Freshwater diversions and reservoir impoundments within the Nueces Basin have significantly reduced freshwater inflows into the Nueces Delta.  Salinities range from 0 to >60 PSU in the lower delta with hypersaline conditions being common.  Benthic invertebrates are important prey sources and changes in salinity affect the invertebrate food biomass available to resident and migratory bird and fish species.  Benthic data were collected monthly from the Nueces Delta, September 1997 to September 2008, and the top 90% contributing benthic invertebrate species were analyzed across six salinity zones to determine species salinity tolerance.  Multivariate Analysis (MANOVA) delineated two assemblages based on density within salinity zones.  Assemblage 1 consists of species with no significant differences (p>0.05) in density among zones, indicating salinity independence with species occurrence not notably influenced by salinity (Corophium louisianum, Chironomidae, Laeonereis culveri, Steninonereis martini, Capitella capitata, Oligochaeta, Nemertea, Heteromastus filiformis).  Assemblage 2 consists of species with significant differences (p<0.05) in density among zones, indicating this group is salinity dependent (Mulinia lateralis, Ampelisca abdita, Marphysa sanguinea, Streblospio benedicti, Scoloplos fragilis, Haploscoloplos foliosus, Glycinde solitaria, Mediomastus ambiseta, and Podarke obscura).  Filter feeders were only represented in Assemblage 2 indicating species with this mode of feeding are less tolerant to salinity shifts in the Nueces Delta. 

Minimum Inflow Analyses in Similar Adjacent Systems:   Why Not Use Similar Approaches?

Melody J. Hunt, South Florida Water Management District, West Palm Beach, FL, USA 

The importance of establishing minimum inflow criteria for coastal areas is becoming recognized world-wide. The majority of coastal inflow criteria that have been developed to date are for riverine systems. In south Florida, most criteria have been based on the presence of an oligohaline reach or freshwater floodplain, where a salinity sensitive species or community is established. Application of inflow criteria is very limited in non- riverine wetland- dominated systems such as Florida Bay and Biscayne Bay, with diffusely distributed inflow sources. In 2006 a minimum flow and level was established for northeastern Florida Bay. This inflow criteria applied a resource-based approach using the SAV indicator species Ruppia maritima (widgeon grass) located in ponds within the Everglades/Florida Bay transition zone, which remains a relatively natural area. Similar to previous efforts in riverine systems, impacts to this resource are defined in terms of a freshwater inflow regime and corresponding salinity levels required for survival of the freshwater habitat. During periods that illustrate impacts in the transition zone, resulting salinity conditions in northeastern Florida Bay were evaluated. The inferred effects on the seagrass community and its inhabitants are described under these low flow conditions to assess the impacts on the downstream Florida Bay ecosystem. Although adjacent and sharing common physical-biological attributes, the Biscayne Bay ecosystem differs from Florida Bay because the adjacent transition zone has been highly altered. The once wetland dominated watershed of Biscayne Bay now includes: the City of Miami and surrounding urban areas; agricultural areas; mining; a nuclear power facility; and other modified land uses. The overland flow component from natural wetlands, that once connected the natural tidal creeks to regional freshwater sources, no longer exists for Biscayne Bay due to development in the watershed. Although inflow criteria have been established in modified riverine systems in South Florida, and adjacent Florida Bay, this land–based difference makes it difficult to those approaches previously used and different approaches need to be considered for Biscayne Bay. 

Effects of Freshwater Inflow on Macrobenthos Productivity in Minor Bay and River-Dominated Estuaries

Terry A. Palmer, Paul A. Montagna and Jennifer Beseres Pollack, Harte Research Institute, Texas A&M University – Corpus Christi

This five-year study was implemented to determine the importance of freshwater inflow on benthic community composition in minor bays and river-dominated estuaries along the Texas coast.  Three river estuaries (Rio Grande, San Bernard River, and Brazos River) and four minor bays (Christmas Bay, Cedar Lakes, East Matagorda Bay and South Bay Coastal Preserve) were sampled for water quality, sediment quality and benthic macrofauna between September 2000 and July 2005. Nutrient versus salinity curves imply that coast-wide, Texas estuaries have conservative mixing of ammonium and silicate but are sinks for nitrite plus nitrate and phosphate.  In terms of benthic productivity as evidenced by abundance and biomass, the estuaries sampled were divided into three groups: San Bernard River and Brazos River had the lowest, the Rio Grande and Cedar Lakes were mid-range, and South Bay, Christmas Bay, and East Matagorda Bay had the highest.  Diversity was low in estuaries with salinities between 1 and 17, but increased with salinities of up to 30.  Diversity decreased again in hypersaline conditions however.  Macrofaunal community structure divided the estuaries into two groups.  The first group represented polyhaline communities and contained East Matagorda, Matagorda, Christmas and South Bays.  The second group represented oligo-mesohaline community characteristics and contained Lavaca Bay, San Bernard River, Brazos River, Cedar Lakes and the Rio Grande.  There appears to be a tipping point at about 17 - 22 where coastal systems change from oligo-mesohaline to polyhaline community characteristics.

Long-term trends and response of benthic macrofauna to climate variability in the Lavaca-Colorado Estuary, Texas

Jennifer B. Pollack, Paul A. Montagna, Terry A. Palmer, Harte Research Institute of Gulf of Mexico Studies, Texas A&M Univ.-Corpus Christi, TX 78412

The Lavaca-Colorado Estuary is the second largest estuary (1200 km²) on the Texas coast.  The volume of freshwater inflow that reaches the estuary is highly contentious because of the semi-arid climatic zone and high human demand for water in the estuary’s catchment.  The goals of this current study were to 1) examine long-term (>20 yr) trends and relationships between benthic macrofauna and hydrological conditions in the Lavaca-Colorado Estuary, Texas, and 2) consider the implications of these relationships as they pertain to observed climate variability and future climate predictions.  Temperature increased over the 20-yr study period however salinity and dissolved oxygen decreased.  Macrofaunal abundance, biomasss and N1 diversity also decreased over the same period.  Salinity was positively correlated with macrofauna abundance, biomass and N1 diversity.  Species abundance (P 0.017) was strongly negatively correlated with the Oceanic Niño Index (ONI), indicating that species abundance was affected by ONI, or perhaps by the resulting changes in river discharge rates and salinity levels. There was no correlation between biomass or N1 diversity and ONI.  Relationships between individual species and hydrological variables were also examined.

Estimating Freshwater Inflows Needed to Maintain the Ecological Integrity of Texas Bays and Estuaries

Angela Schrift, Texas Parks and Wildlife Department, Coastal Fisheries

The drought of record in Texas (1948-1956) had a significant impact on the economic resources of its estuaries.  For example, harvesting had to stop for bay oyster and white shrimp and many of the estuarine-dependent fish were unhealthy due to high salinity levels.  The need for freshwater inflows was recognized.   As a result, the Texas legislature passed the Texas Water Planning Act which gave consideration to the effect that upstream development had on bays, estuaries, and arms of the Gulf of Mexico.  In order to make decisions about the effects of upstream developments on our coastal areas, the Bays and Estuaries Program was developed to collect physical, chemical, and biological data necessary for state water planning.  In 1994, the Texas Water Development Board (TWDB) and Texas Parks and Wildlife Department (TPWD) published a report detailing the methodology that the state uses to estimate the needed freshwater inflow for Texas’s bays and estuaries.  An overview of the State Methodology is presented.

Development of an Ecosystem Model for Galveston Bay: Analyzing the Combined Effects of Fishing and Freshwater Inflows

Sutton, G. ⁽¹⁾, Guillen, G. ⁽²⁾

⁽¹Texas Parks and Wildlife Department,
1502 Pine Dr,  Dickinson, TX 77539; Glen.Sutton@tpwd.state.tx.us:
⁽²⁾University of Houston Clear Lake, Environmental Institute of Houston
2700 Bay Area Blvd, Box 540, Houston, TX 77058;Guillen@uhcl.edu

Management of estuarine fisheries has traditionally relied on single species population modelling, and management. Unfortunately, this approach neglects the complex interactions of various trophic levels and changes in environmental conditions.  A predictive management tool is needed that can incorporate these often non-linear interactions that are inherent in ecological processes and may materialize as a result of interaction with management actions. Ecopath with Ecosim (EwE) is one such ecosystem based stock assessment modelling tool that can incorporate complex interactions between fisheries and abiotic factors such as nutrient inputs, freshwater inflows and salinity fluctuations. We attempt to develop a predictive model of estuarine fish and invertebrate populations using an approach that can evaluate the relative impacts of fishing pressure and other environmental fluctuations.  The model predicts both short and long term responses to reduced freshwater inflow. Long term responses are an overall decline in productivity starting at the base of the food chain, while short term responses are less obvious and may even temporarily benefit top predators. Gulf Menhaden (Brevoortia patronus), Mullet (Mugil cephalus), and eastern oysters closely follow predicted primary productivity trends estimated using a freshwater inflow forcing function. Spotted seatrout (Cynoscion nebulosus) for example prefers a mid to high range salinity and will avoid fresher portions of the bay.  Better data fits for this group can be obtained by adjusting its vulnerability index using a salinity time series forcing function, in agreement with predictions made by foraging arena theory. That is, prey species taking refuge in low salinity regions become more available to predation as salinity increases.

Mangrove ecosystem vulnerability to climate chance effect in Yucatan Peninsula (carbonate settings), SE Mexico

Zaldivar-Jiménez, M. Arturo^1,2; Herrera-Silveira, Jorge A.^1,2; Teutli-Hernández, Claudia¹; Rivera-Monroy, Victor H.³; Coronado-Molina, Carlos ⁴; Hernández-Saavedra, Raquel ⁵, Caamal-Sosa, Juan P.; Perez-Ceballos, Rosela ¹

¹CINVESTAV-IPN, Unidad Merida, Km 6 Ant. Carr. a Progreso, Merida Yucatan, Mexico.

²United Nations Industrial Development Organization (UNIDO).

³Louisiana State University.

⁴South Florida Water Management District - Everglades Division.

⁵Estación de Investigación Oceanográfica de Progreso, Secretaria de Marina.

The coast of Yucatan Peninsula is characterized by semi-arid climate, hurricanes impacts, low tide, groundwater discharges and carbonate soil. This last condition limits the sediments source to mangrove forest and increases their vulnerability to the sea level rise. Permanent forest plot, SET bases and press level logger were installing in several sites in Yucatan Peninsula as part a long-term monitoring program. Our research is focused in the analysis of the potential effects of climate change on the Yucatan mangroves in relation with the environmental and hydrogeological characteristics of these region and the anthropic factors that impact these coastal ecosystems. Results showed in site with strong influence of groundwater discharges (springs), the mangrove forest had the highest structure value (complexity index =17) and litterfall production (16 t ha/yr). Vertical accretions show spatial pattern from 3.9 mm/yr to 1.0 mm/yr while the elevation varied from 5.3 mm/yr to -2.8 mm/yr according to wet or dry scenarios. The spatial differences are related with local forcing function as organic matter production, porewater storage and sediment type, as well as regional variables as erosion/deposition by storms and hurricanes.

Topic: Natural Sciences: Physical and Biological Dimensions of the Problem

Subtopic: Response of Coastal Environments to Sea-Level Rise