Geoscience Reference
In-Depth Information
non-growing seasons without the influence of
elevated discharge. These sites were selected to
represent the range of land cover and land
use within the basin. During both seasons,
measurements were made over a 3-day period of
stable weather and discharge. Field measurements
included specific conductance (YSI Model 30) and
turbidity (Hach Model 2100P). Three replicate grab
samples were filtered in the field (Whatman GF/F).
Because of the large number of samples, it was
necessary to freeze all samples prior to analysis,
which may have influenced some of the chemical
parameters. Three larger volume samples (1-4 L)
were also collected for particle analysis.
Thawed samples from each site were analysed for
dissolved organic carbon (DOC), total dissolved and
soluble reactive phosphorus (TDP, SRP), nitrate,
ammonium, dissolved organic nitrogen (DON),
total dissolved nitrogen (TDN), chloride, sulphate,
and the cations calcium, magnesium, potassium,
and sodium (methods given in Table 8.1). Total
suspended solids (TSS) were determined within
24 h of collection. Samples were filtered onto
preweighed glass fibre filters (Whatman GF/F),
dried, weighed (TSS), ashed (1 h, 550
◦
C), and
reweighed to determine the ash-free dry mass
(AFDM) of suspended particles.
Catchment land-cover was derived from 2001
and
Imagery. Land cover was classified by Jeff
Hepinstall and Hunter Allen (Warnell School
of Forestry and Natural Resources, University of
Georgia, Athens, GA 30602). Catchment land-use
was obtained from county parcel and tax records
and US Census data. Catchments were ranked
across three subjectively determined land-use
categories: scale, activity, and diversity. Scale
measures relate to the amount of land and land-
use activity available for socio-economic analysis
within each catchment. Activity measures relate
to recent changes and predicted future changes
in land use and ownership. Diversity measures
relate to variation in land use, building stock,
and household composition including population
age structure, racial composition, renters versus
owners, and the presence of children. Because
areas for census measurements are relatively large
and often do not follow catchment boundaries,
there is unavoidable error in assigning census data
to catchments and this error increases as catchment
size decreases. So census data were determined for
only a set of 15 larger catchments.
Data were analysed statistically in two steps.
Cluster analysis and principal components analysis
(Minitab, Minitab Inc., State College, PA) were
first used to reduce the number of both dependent
and independent variables. Correlation analysis
and simple linear and multiple linear regressions
2006
NASA
Landsat
Thematic
Mapper
Table 8.1
Methods used for laboratory analyses of dissolved chemicals.
Chemical measured
Method
Instrument
Dissolved organic carbon
Shimadzu TOC-VCPH TN analyzer
Total dissolved phosphorus
Persulphate in-line UV digestion,
ascorbic acid - molybdate
colorimetric method
Lachat QuickChem FIA
+
Soluble reactive phosphorus
Dionex 25A Ion Chromatograph using an AS18 column
Nitrate
Dionex 25A Ion Chromatograph using an AS18 column
Ammonium
Automated phenate method
Astoria 2 Autoanalyzer
Dissolved organic nitrogen
TN - (NH
4
-N
+
NO
3
-N)
Total dissolved nitrogen
Shimadzu TOC-VCPH TN analyzer
Chloride
Dionex 25A Ion Chromatograph using an AS18 column
Sulphate
Dionex 25A Ion Chromatograph using an AS18 column
Ca, Mg, K, Na
Perkin Elmer Analyst300 Atomic Absorption
Spectrometer
