Refinement and Validation of Habitat Quality Indices and Aquatic Life Use Indices for Application to Assessment and Monitoring of Texas Surface Waters

Kirk Winemiller, Ryan King (Baylor U.), Mark Fisher (TCEQ)

To support monitoring and setting standards for surface water quality, the Texas Commission on Environmental Quality (TCEQ) has adopted Aquatic Life Use Standards (ALUS) that rely on indices of biotic integrity (IBIs) and habitat quality indices (HQIs).  These essential tools allow natural resource managers and regulators to assess the status of ecological systems for evaluation of trends and compliance with established water quality standards.  Following several years of research by the Texas Parks and Wildlife Department (TPWD), the fish IBI used to assess Texas streams underwent major revision to reflect more accurately the major faunal differences among the state’s diverse geologic, climatic, and faunal regions (Linam, G.W., L.J. Kleinsasser, and K.B. Mayes. 2002. Regionalization of the Index of Biotic Integrity of Texas Streams. TPWD River Studies Report No. 17, TPWD, Austin, TX, 26 p).  The fish IBI has been researched more extensively than the HQI, therefore the latter index requires immediate study.  The issue of scale and resolution, both in terms of space (geography, watershed position, siting within stream reach) and time (seasons, hydroperiod, time elapsed since last major disturbance) must be examined quantitatively in order to evaluate the validity and reliability of these assessment tools.  This project examines treams with perennial surface water within the Brazos and Trinity river basins within the Texas-Central Oklahoma Plains, Texas Blackland Prairies, and East Central Texas Plains ecoregions.  Survey locations provide broad geographic coverage, a range of landscape features (including land use), and representation of a range of stream habitat conditions.  Annual surveys will describe and evaluate key metrics of stream habitat in relation to position within stream reach, watershed, and landscape (e.g., geology/soils, topography, land use) as well as fish assemblage structure.  Field surveys will be conducted between April 1 and Oct. 1 in 2006 and 2007.  The project will determine principal relationships between stream habitat features and sources of landscape variation, including indicators of watershed degradation.  The composition and structure of fish assemblages for use as biotic indicators of ecological status will be determined concurrent with stream habitat characterizations.  Statistical analysis of fish and habitat metrics will be conducted to determine their sensitivity to aquatic life uses (ALUs) as well as variation in temporal and spatial scales.  This project aims to determine the most useful (sensitive, reliable) metrics (individual elements, suites of elements, or aggregate variables derived from multiple elements) for creation of improved HQI and IBI for wadeable streams in the Subhumid Agricultural Plains (SAP) aggregate ecoregion.  

Demographic and life history responses of fishes to hydrology and disturbance in floodplain and channel habitats of the Brazos River, Texas

Steven C. Zeug and Kirk O. Winemiller

Several conceptual models predict fish population responses to environmental drivers such as hydrology however, few studies have explicitly tested hypotheses drawn from the predictions of these models (but see King et al. 2003).  The Flood Pulse Concept predicts that fish recruitment is enhanced by connectivity between floodplain and channel habitats provided that floods occur during periods of fish reproduction when water temperatures are warm.  The Low Flow Recruitment Hypothesis states that in systems with unpredictable flood dynamics, recruitment is optimized during periods of low flow when channel and floodplain habitats are isolated but flows are relatively stable and food resources are more abundant. Here we test the hypothesis that fish life history strategy determines the hydrologic regime under which recruitment is maximized, and that life history traits within species will respond to the hydrologic regime of each habitat.  Population demographics and a suite of life history attributes for seven species representing three divergent life history strategies are measured monthly in the Brazos River channel and two oxbow lakes with different connection frequencies to determine how these populations are influenced by environmental drivers (floods, drought).  The results produced by this study will provide a new model of fish recruitment in river-floodplain systems that incorporates spatial heterogeneity and flow variability, and is supported by empirical data.  In the context of instream flow allocation; these data can be used both to make predictions about which species may be affected by a proposed flow regime, and to design flow regimes that support the diversity of life history strategies that exist in these systems.

Association Between Brush Cover and Stream Fish Assemblages in the Pedernales River Basin, Texas

Jenny S. Birnbaum and Kirk O. Winemiller

One strategy for increasing the water supply in semi-arid rangelands is management of encroaching brush.  Removal of deep-rooted woody species, such as mesquite (Prosopis glandulosa) and juniper (Juniperus ashei), is believed to increase groundwater recharge of streams in areas where annual precipitation exceeds 450 mm.  In fact, the state of Texas is currently spending millions of dollars to subsidize brush management with the goal of increased water yields.  However, scientific examination of this claim is scarce, and studies have yielded conflicting results.  Effects of brush management on water yields are likely to be subtle and localized in accordance with geology, topography, and other landscape features.  This interdisciplinary study incorporates aspects of GIS, hydrogeology, herpetology, riparian vegetation ecology, and stream ecology to explore the issue of juniper management in headwater tributaries of the Pedernales River of central Texas.  We are surveying biota and abiotic characteristics, including fish, benthic macroinvertebrates, water depth, flow, pH, DO, substrate composition, and other physicochemical variables in order to understand how juniper management influences stream fish and benthic macroinvertebrate assemblages.  Additionally, we plan to address fish-macroinvertebrate relationships and macroinvertebrate-microhabitat relationships in on-going work.

Fish assemblages of the Casiquiare, zone of biotic interchange between Upper Orinoco and Rio Negro

Kirk O. Winemiller, Hernán López-Fernández, D. Albrey Arrington, Donald C. Taphorn (UNELLEZ), Leo G. Nico (USGS) & Aniello Barbarino Duque (INIA)

The Casiquiare River flows from the Upper Orinoco to the Upper Rio Negro which should permit biotic exhange between these two great river systems, yet several Amazonian faunal elements are absent from the Orinoco Basin (e.g., Osteoglossidae, <i>Symphysodon</i> spp.) and many allopatric sister taxa are divided between the basins (e.g., <i>Pygocentrus cariba, P. nattereri</i>).  The Casiquiare Basin contains diverse aquatic habitats, and water quality varies from clearwater to extreme blackwater conditions.  We examined fish assemblage structure relative to 11 habitat characteristics with dataset containing 215 samples and 454 species from surveys catalogued in the Museo de Ciencias Naturales in Guanare, Venezuela.  We performed canonical correspondence analysis based on species presence/absence using two dataset versions:  one that eliminated sites having <5 species, and species occurring at <5 sites; and another that eliminated sites having <10 species, and species occurring at <10 sites.  Results from both analyses were the same qualitatively.  The dominant environmental axis contrasted sites with blackwater versus clearwater conditions.  Longitudinal position on the mainstem Casiquiare was correlated (r²= 0.30) with CCA axis-1 scores, indicating blackwater conditions nearer the mouth and clearwater nearer the origin.  The second CCA axis was most strongly associated with habitat size and structural complexity.  Species were clustered using the centroid method and pairwise squared Euclidean distances calculated from species loadings on CCA axes 1-4.  Seven ecological groupings were identified:  (1) species normally associated with clearwater in large habitats, (2) species associated with structured habitats in blackwater, (3) species associated with a variety of mostly shallow habitats in blackwater, (4) species associated with channel shoreline areas mostly in clearwaters, and (5-7) three large, relatively ubiquitous species.  High fish species richness in the Casiquaire Basin appears to be a function of historical biogeography, high habitat diversity, and semi-permeable barriers to regional dispersal. 

Local, regional and historical determinants of stream fish assemblage structure: inferences based on taxonomic vs. functional groups

David J. Hoeinghaus, Kirk O. Winemiller and Jenny S. Birnbaum

This study examines the roles of local and regional environmental variables, biotic interactions and historic factors in determining the structure of local stream fish assemblages, and compares results derived from analyses based on taxonomic and functional groups.  Species abundance data were compiled for 157 stream fish assemblages in several river basins across Texas.  Species were condensed into functional groups based on trophic and life-history characteristics.  Local and regional environmental variables were either measured at each location or determined from scale maps and public access databases.  The original taxonomic and functional group datasets were analyzed using similarity indices, null-models of co-occurrence, and direct and indirect ordination techniques.  Results derived from taxonomic and functional group datasets are compared.  Inferences regarding the relative roles of local and larger scale factors in determining stream fish assemblage structure differ dramatically between analyses of taxonomic and functional groups.  Taxonomic analyses imply a prominent role of regional-scale environmental and historic factors, and local assemblages sorted according to a biogeographic pattern.  Functional group analyses suggest almost equal roles of factors representative of local and larger scales, and assemblages were distinguished by a habitat template irrespective of biogeographic province. The structure of local stream fish assemblages is ultimately determined by factors representing multiple scales, with the relative importance of each depending on the biological unit employed (species or functional groups).  We suggest that analyses using functional groups can more directly infer ecological responses to environmental variation, and therefore may provide a more fruitful avenue for developing and testing ecological theory of community organization across biogeographic scales. 

Habitat structural complexity and morphological diversity of fish assemblages in a Neotropical floodplain river

Stuart C. Willis, Kirk O. Winemiller and Hernán López-Fernández

High species diversity in structurally complex habitats has been hypothesized to be associated with niche partitioning.  To test this idea, relationships between habitat structural complexity in river littoral-zone habitats and ecomorphological diversity of tropical fishes were examined in the Cinaruco River, Venezuela.  Six habitat attributes were quantified in 45 sites spanning a range of structural complexity.  Fishes were collected during day and night to estimate species density and relative abundances at each site.  Twenty-two morphological variables were measured for each species.  Principal components analysis (PCA) of physical habitat data yielded two axes that modeled >80% of variation across sites.  The first two axes from PCA of fish morphological variables modeled >70% of variation.  Species density during both day and night was positively associated with high habitat complexity and low flow velocity.  Similarity of day and night samples from the same site was significantly greater for sites with high habitat complexity and low flow.  In general, mean local assemblage morphological PC scores were not significantly associated with habitat PC scores.  Thus, higher species density in more structurally complex habitats is associated with greater interspecific morphological variation and could indicate species packing via niche compression, expansion of total assemblage niche space, or both.  Average, maximum, and standard deviation of morphological Euclidean distances of local assemblages revealed positive associations with structural complexity and low flow.  These relationships held even when the positive relationship of species density was statistically removed from assemblage morphological data.  Findings suggest that both species niche compression and assemblage niche space increase when habitat complexity is greater and flow velocity is lower. 

Response of Oxbow Lake Biota to Hydrologic Exchanges with the Brazos River Channel

Kirk Winemiller, Tim Bonner (Texas State U.), Steve Zeug, Casey Williams (Texas State U.), Ray Mathews (Texas Water Devel. Bd.), Tim Osting (Texas Water Devel. Bd.) & Fran Gelwick

Fishes and aquatic habitat variables were sampled between June 2003 and September 2004 to obtain information on the ecological dynamics associated with river channel–oxbow lake connectivity in relation to instream flows.  The ecological study complemented a concurrent research effort undertaken by the Texas Water Development Board to document geomorphological and hydrological features that determine degrees of oxbow to channel connectivity.  The ecological study also examined fish population structure and dynamics at two river channel sites in the lower Brazos River upstream and downstream of the site selected for the Allen’s Creek reservoir.  Standardized fish samples were collected using seines and gillnets, with data analyzed separately as catch per unit effort.  Statistical ordination techniques revealed a strong gradient of fish assemblage structure that contrasted oxbow samples from river channel samples.  A secondary gradient was associated with seasonal variation in oxbow lakes.  In contrast to the river channel, oxbow lakes contained high densities of white crappie (Pomoxis annularis), sunfishes (Lepomis spp.), and shads (Dorossoma spp.).  A number of minnow species (e.g., Hybognathus nuchalis, Macrhybopsis hyostoma) appear to be fluvial specialists that always or almost always were collected from the river channel.  Several of these fluvial specialists were more abundant one to two months after periods of peak flow.  For species common in oxbow lakes, density tended to decline following periods of peak flow, which indicates a net export of individuals from oxbows to the river channel during floods that connect these habitats.  Consistent with this view were patterns of higher densities of these species in the river channel following periods of peak flow.  Fluvial specialists appeared in oxbow lakes in low to moderate numbers during periods of peak flow, but these sub-populations generally did not persist more than a month or two.  Densities of phytoplankton, zooplankton, and fish were much higher in oxbow lakes than in the river channel, and more so following prolonged periods of isolation.  Oxbow lakes that were formed more recently and that are located closer to the river channel had lower “control points” in the natural levee, and as a result flooded at lower discharge levels.  It is concluded that oxbow lakes of variable ages and geomorphological structures provide essential habitats that function to increase overall fish species diversity in the lower Brazos River.

Updated October 8, 2008