occurrence in soils from unimpacted catchments...
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Texas A&M University Water Management & Hydrological Science Program
IDENTIFYING SOURCES AND QUANTIFYING DIFFERENCES IN E. COLI OCCURRENCE IN SOILS FROM UNIMPACTED CATCHMENTS WITH VARYING LANDUSE
LUCAS GREGORY TERRY GENTRY, EMILY MARTIN, DAREN HARMEL & KEVIN WAGNER
Indicators of fecal pollution are the largest single cause of water body impairments in the U.S.
Fecal indicator bacteria such as E. coli are present in large intestine of all birds and mammals
FECAL POLLUTION
Impaired waters often have management plans developed to restore water quality
Goal of the plan is to reduce fecal bacteria loading Point sources: improve treatment Nonpoint sources: reduce loading from landscape
Must know the sources and their location prior
to managing
MANAGING FECAL POLLUTION
Source survey Physical observations and documentation of sources Costly approach, but useful…not perfectly effective
Computer modeling Can yield decent approximation Limited by input data and understanding of bacteria fate
and transport
Bacterial source tracking Shows sources impacting a waterbody Widely used, yet unknowns remain
METHODS FOR SOURCE DETERMINATION
DNA fingerprinting Enterobacterial repetitive intergenic
consensus sequence-polymerase chain reaction (ERIC-PCR) RiboPrinting® (RP)
Compared to DNA fingerprints housed in libraries
Texas E. coli BST Library (ver. 1-13) currently has 1,454 isolates from 1,291 known source samples Small mammals underrepresented
LIBRARY-DEPENDENT BST
Compared to library using 80% similarity for match 3-way split 100% ARCC
7-way split 92% ARCC
SAMPLE CLASSIFICATION
(1) Human (2) Livestock & Pets (3) Wildlife
Human (1) Pets (2)
Cattle (3) Avian livestock (4)
Wildlife, avian (5) Wildlife, non-avian (6)
Other non-Avian livestock (7)
Unknown isolates commonly found ‘Unimpacted’ areas
commonly have high bacterial levels Possibly wildlife Possibly naturalized E.
coli
QUESTIONS REMAIN
USDA-ARS Grassland Research Facility near Riesel, Texas
Intensive management and monitoring since 1937
Multiple land covers Native prairie Managed pastures Managed hay field Cropland
STUDY AREA
70+ yr. data record 13 monitoring stations and 15 rain gauges
HISTORIC WATER QUALITY
HYPOTHESES
H1: Sources of culturable E. coli in soil and
water from unimpacted catchments can be traced back to known sources of E. coli H2: Culturable E. coli counts in soils and water
under various land uses are different
PLANNED APPROACH
Monitor surface runoff E. coli loads from 3 intensively monitored catchments
Quantify E. coli levels in the upper 2.5 cm of soil in each plot
Screen soil and water E. coli DNA against existing Texas E. coli BST Library
Supplement library with known source samples targeting small mammals (rodents)
Compare differences in soil and water bacterial levels between land uses
Small mammal live trapping
Focus on building representation in Texas E. coli BST Library
Winter and summer sampling Winter complete with 16
deer mice sampled Not added to library yet
SOURCE ID
Used to help ID wildlife presence Aid in understanding
BST results Potential sources of
‘background’ E. coli
CAMERA TRAPPING
Primarily rely on Texas Library Supplement with
local small mammal samples ID sources of E. coli
in soils and surface runoff
LIBRARY DEPENDENT BST
12 samples from each plot Top 2.5 cm of soil
E. coli enumerated
with EPA Method 1603 (modified mTEC)
INITIAL RESULTS
INITIAL SOILS BST RESULTS
INITIAL SOILS BST RESULTS
Native prairie and cropland sites are not stocked by cattle
Managed hay pasture has been destocked for 4 years
Human influence very surprising
E. coli isolates from the same genotype are common within and between samples and sites Recent deposition from similar sources,
misidentifications due to transmission vectors?
UNEXPECTED RESULTS
Additional soil sampling Additional known source sampling
Continuous camera trapping for the next year
Pray for rain to get some runoff samples!
MOVING FORWARD
Reduced # of unidentified samples with addition of local known sources With runoff, will compare BST findings to
those in soil Should theoretically be the same
Will aid in determining loading and sources of
background E. coli in secondary environments
EXPECTED OUTCOMES
Funding support provided by the Texas State
Soil and Water Conservation Board through State Nonpoint Source Grant Program Funding.
FUNDING SUPPORT
