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%).