Associations of watershed and instream environmental factors with aquatic macrofauna in tributaries of the Pedernales River, Texas

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Title: Associations of watershed and instream environmental factors with aquatic macrofauna in tributaries of the Pedernales River, Texas
Author: Birnbaum, Jenny Sue
Abstract: Intermittent headwater streams serve important functions in semi -arid rangelands , both for humans and wildlife . However , few studies have assessed species -environment relationships for fish and benthic macroinvertebrate assemblages in these systems . Additionally , no published studies could be found that addressed the influence of juniper coverage in watersheds on assemblage structure of these taxa . Increased juniper coverage in recent decades is believed to be associated with decreased water yields in central Texas streams . During summer 2003 and spring 2004 , I examined potential effects of juniper cover on aquatic ecology . Fishes , benthic macroinvertebrates , and the physicochemical habitat were investigated in spring -fed headwater tributaries of the Pedernales River . My objectives were to : 1 ) describe the typical fish and benthic macroinvertebrate assemblages in headwater creeks of the Pedernales River basin ; 2 ) compare seasonal variability of fish and benthic macroinvertebrate assemblages ; 3 ) identify species -environment relationships in this river basin ; and 4 ) evaluate the influence of juniper coverage in the watershed , relative tolocal and landscape -level environmental factors , on the structure of fish and benthic macroinvertebrate assemblages . A total of 4 ,181 individual fish were collected in summer 2003 samples , 551 fish were collected in spring 2004 , 59 ,555 macroinvertebrates were captured in summer 2003 samples , and 51 ,500 macroinvertebrates were collected in spring 2004 . Assemblages were typical for the area and habitat conditions . Faunal richness was lower in spring than in summer , possibly due to a combination of sampling after a relatively dry period in the spring , and lack of winter refugia in the form of deep pools . Fish assemblages may structure based principally on abiotic factors in spring , the harsher season (less available water ) , whereas predation pressure may influence structure in summer . Another important environmental gradient for both fish and invertebrate assemblages contrasts pool and run mesohabitats . In general , juniper cover was weakly associated with fish and invertebrate assemblages , although it tended to be associated with relatively high quality habitat for sensitive taxa (flowing runs with coarse substrate ; deep , connected pools ) . In these intermittent streams , local -scale environmental factors probably are the dominant influences on fish and benthic macroinvertebrate assemblages . Implications for future studies are discussed .
URI: http : / /hdl .handle .net /1969 .1 /2411
Date: 2005-08-29

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Associations of watershed and instream environmental factors with aquatic macrofauna in tributaries of the Pedernales River, Texas. Available electronically from http : / /hdl .handle .net /1969 .1 /2411 .

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