3.3 Comparison of Connectivity Metrics
Both geochemical and microbial connectivity strength metrics performed
well in discriminating between sites that were connected as determined
by tracer injections compared to sites where we did not observe arrival
of injected tracer (Table 1, Figure 4). Across both injections, sites
with observed tracer arrival had higher connectivity strength values
(σg: =0.67 (mean) ± 0.02 (SE), σm: 0.77
± 0.03) than did sites with no observed tracer arrival
(σg: 0.33 ± 0.06, σm: 0.31 ± 0.03). At
sites with observed tracer arrival, σm was strongly
negatively correlated (R = -0.90, p-value< 0.01) with time to
peak (TTP) of the breakthrough curve, while σg was only
moderately negatively correlated with TTP (R = -0.59, p-value= 0.16)
suggesting σm may be more responsive to residence time
than σg. Because Pond-Con-01 had high leverage in the
correlation analysis, we also ran the analysis without Pond-Con-01 and
found that σm was still negatively correlated with TTP
(R = -0.74, p-value = 0.09), however there was no longer any correlation
between σg and TTP (R=-0.03, p-value=0.96).
In comparing the connectivity duration above 0.5 (Cdur)
for each site, σm and σg generated
similar results across sites (R = 0.96) but both generated substantially
different results than the Cdur as measured with
relative stage (σm: R = -0.13; σg: R =
-0.13) (Figure 5a & 5b). Both σm and σgmetrics identified stable connected conditions (100%
Cdur) at Main-Mid and Outflow and stable disconnected
conditions at Pond-Iso (0% Cdur, Figure 5c).
Conversely, the source-target stage relationship analysis identified
connectivity inflection points at Outflow, Pond-Iso, and Main-Mid with
Cdur ranging from low at Outflow (17%
Cdur) and moderate at Pond-Iso (55%
Cdur) and Main Mid (61% Cdur, see
Figure 5a & b). Even without these three sites, Cdur as
derived from source-target stage relationships was poorly correlated
with Cdur as assessed with σm (R = 0.21)
and σg (R = 0.24, see Figure 5). Despite strong
correlations between Cdur derived from
σm and σg, there were several sites with
substantively different Cdur between metrics including
Pond-Con-01 (σm = 46%, σg = 63%),
Main-Braid (σm = 80%, σg = 64%) and
Side-04 (σm = 30%, σg = 15%).