Ecological
Assessment of Seleniferous Agricultural Drainwater on Fish Inhabiting
the Grassland Water District and Adjacent Reaches of the San Joaquin River
The Problem
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View
of the San Luis Drain. |
Aquatic environments have been highly altered in Californias Central
Valley due to changes in hydrology caused by human development.
With implementation of the Grassland Bypass Channel Project in September
1996, agricultural drainwater contaminated with selenium was removed
from Salt Slough and from canals and ditches flowing through the
interior of the Grasslands. Instead, the agricultural drainwater
is now diverted into the Grassland Bypass Channel (formerly known
as the San Luis Drain), which then discharges into the lowermost
10.6 km of Mud Slough and, eventually, into the San Joaquin River.
Implementation of the Grassland Bypass Channel Project is believed
to have benefitted aquatic biota in canals and ditches, their associated
marsh ponds, Salt Slough, and the reach of Mud Slough lying upstream
from the terminus of the Grassland Bypass Channel because these
surface waters are no longer exposed to seleniferous tile drainage.
However, aquatic biota in Mud Slough downstream from the Grassland
Bypass Channel could be exposed to higher concentrations of selenium
because canals, ditches, and marsh ponds in the interior of the
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The
San Luis Drain (turbid water channel on the right) at its confluence
with North Mud Slough. |
Grasslands may have served as a biological filter for this trace element.
This subtask will compare the composition of fish species assemblages,
the body burdens of selenium in selected fish species, and selected
water quality variables from as many as 13 sites on the San Joaquin
River and tributaries traversing the Grasslands. In addition, this
subtask will determine if reproduction (a sensitive endpoint for selenium
toxicity) has been altered in selected fish species exposed to seleniferous
drainwater. This subtask is funded by USGS based dollars and a contract
with FWS (reimbursable agreement 1448-14420-97-N043).
Objectives
The purpose of this subtask is to better understand the extent to which the Grassland Bypass Project (GBP) in the Central Valley of California has altered environmental conditions for fishes in Salt and Mud sloughs and other surface waters within and downstream from the Grassland Water District (Grasslands), Merced County. Specifically, this subtask will attempt to determine if seleniferous discharge from the GBP has altered fish species assemblages and increased selenium body burdens in selected species. In addition, the subtask will attempt to determine if selenium-contaminated fish in the study area exhibit impaired reproductive success or other associated maladies. Results from this subtask are expected to help fine-tune the operation of the Grassland Bypass Channel so as to enhance the ecological value of the Grasslands and San Joaquin River for fish and wildlife resources.
Methodology
Fish Species Assemblages and Selenium Body Burdens:
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Barbara
Martin and Mike Saiki electrofishing on a slough in the Grassland
Water District. |
During September-October
1997, fish were sampled with bag seines, beach seines, variable-mesh gill
nets, and electrofishing from as many as 13 sites within the Grasslands
and adjoining reaches of the San Joaquin River. Captured fish were identified
and counted, then representative samples of green sunfish and bluegills
were retained for selenium determinations. All other fish were released
alive. In addition, water quality and other environmental variables were
measured to characterize habitat conditions at the various sites. Fish
samples were wrapped in plastic and frozen, then shipped to the BRD Columbia
Environmental Research Center (CERC) for selenium determinations. Cluster
analysis was used to determine if distinctive species assemblages were
present within the sampling sites. Multiple discriminant analysis was
used to identify the physicochemical variables that best explained the
species assemblages. Analysis of variance was used to determine if selenium
concentrations varied among the sample sites. Mosquitofish Reproductive
Success:
During May-July 2001, western mosquitofish were collected on
at least two occasions from the San Luis Drain at Gun Club Road (selenium-contaminated
site), North Mud Slough at Gun Club Road (reference site located upstream
from the mouth of the Drain; this site has not received seleniferous drainwater
since the Grassland Bypass Project became operational), North Mud Slough
at State Highway 140 (selenium-contaminated site located downstream from
the mouth of
the Drain), and the San Joaquin River at Lander Avenue (reference
site with no history of receiving seleniferous drainwater). About 20 pregnant
females (identified by prominent dark-colored spots
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An
adult female western mosquitofish in a test chamber (2-L glass
beaker). Note several newborn fry near the bottom of the test
chamber. |
on each side of the
abdomen) from each sampling site were held for as long as two weeks in
individual 2-L glass beakers to quantify live & dead births and make other
measurements. Within each beaker, the female was placed into a small-mesh
live-bearer enclosure to prevent cannibalism following birth of young.
Females were fed daily with Tetramin flaked food, and water in the beakers
was partially changed at 2-3 day intervals to prevent fouling. When females
gave birth, live and dead fry were counted, measured for total length
and weighed, and visually assessed for abnormalities (teratogenesis).
The fry were then preserved in a suitable fixative and stored for possible
histopathological workup (pending availability of funds) to further detect
and characterize teratogenesis and its severity. Immediately after completion
of the birthing process, female mosquitofish were sacrificed (wrapped
in plastic and frozen) for selenium determination by CERC.
Highlights and Key Findings
Fish Species Assemblages and Selenium Body Burdens:
During September-October 1997, a total of 9,795 fish representing 25
species was captured from 13 sampling sites in the Grassland Water District
(Grasslands) and adjoining reaches of the San Joaquin River in Merced
County, CA. Inland silverside (Menidia beryllina), green sunfish
(Lepomis cyanellus), fathead minnow (Pimephales promelas),
and western mosquitofish were most ubiquitous, found at all sampling sites.
In addition to these four species, bluegill (L. macrochirus),
redear sunfish (L. microlophus), largemouth bass (Micropterus
salmoides), threadfin shad (Signalosa petenensis), goldfish
(Carassisus auratus), red shiner (Cyprinella lutrensis),
common carp (Cyprinus carpio), Sacramento blackfish (Orthodon
microlepidotus), and black bullhead (Ictalurus melas) were
abundant or very abundant at one or more sites.
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Layout
of test chambers for adult female western mosquitofish awaiting
partition. |
Although several species exhibited restricted spatial distributions among sampling
sites, association analysis and cluster analysis failed to identify more
than one fish species assemblage within the study area. Comparisons with
historical (pre-project) data suggested that the taxonomic composition
of fishes within the Grasslands has not changed in response to the Grassland
Bypass Project. On the other hand, discharge of seleniferous agricultural
drainwater by the San Luis Drain is influencing body burdens of selenium
in fish inhabiting North Mud Slough and the San Joaquin River. Individual
green sunfish from the San Luis Drain contained as much as 23 ug Se/g (dry weight basis in whole fish), whereas composite samples of
bluegill from North Mud Slough contained as much as 18 ug Se/g (bluegill
were not captured in the San Luis Drain). Nevertheless, when compared
to historical data from selected sites, selenium concentrations in bluegill
have not generally varied over time in directions (upwards or downwards)
predicted for the Grassland Bypass Project. Results from multiple regression
analysis indicated that the concentration of waterborne selenium was the
single most-important predictor of selenium body burdens in green sunfish
and bluegill. Among bluegill, other environmental variables (stream channel
width, discharge, and specific conductance values) were also important
predictors of selenium body burdens.
Mosquitofish Reproductive Success:
In 2001, a new study was implemented to determine if western mosquitofish populations
inhabiting the San Luis Drain, North Mud Slough, and the San Joaquin
River suffered from impaired reproduction. This study was conducted
because fishes from seleniferous habitats contained body burdens
of selenium exceeding 4 ug/g dry weight, the proposed toxic threshold
for adverse reproductive effects. However, preliminary results from
field trials conducted during June-July 2001 did not detect evidence
of reproductive impairment. Pregnant female mosquitofish collected
from two seleniferous sites and two non-seleniferous sites produced
fry that exhibited >96% survival at birth. Cursory inspection of
the fry also did not suggest evidence of teratogenesis. Selenium
determinations in samples of adult females and their fry from the
reproductive trials verified that fish from seleniferous sites contained
more selenium than did fish from non-seleniferous sites. In addition,
newborn fry contained higher concentrations of selenium than did
postpartum adult females.
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Live
and dead (deformed) fry produced by an adult female western
mosquitofish inhabiting seleniferous agricultural drainwater
in the San Luis Drain during July 1985. |
Where Are We Headed In 2003
Field and laboratory work have been completed. During FY-03, statistical analysis and data interpretation will be conducted on data from the mosquitofish reproduction study. A final report will be prepared for FWS and BOR.
Project Contact
Michael Saiki
U.S. Geological Survey
Western Fisheries Research Center
Dixon Duty Station
6924 Tremont Road
Dixon, CA 95620-9648
Email: michael_saiki@usgs.gov
Phone: 707-678-0682 x617
Fax: 707-678-5039
Publications
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