Patterns in measured GPP
Measured carbon uptake at the low marsh shows a negative correlation
with observed water level once seasonal patterns are removed (Fig. 2a,r = -0.40, 2018; Fig 2b, r = -0.30). For water levels
above the marsh surface (1 m NADV88), the detrended GPP rate tended to
be negative, indicating lower than average carbon uptake. Measured
salinity ranged from 20-40 ppt, with annual means of 28, 29.3, and 31.1
ppt for 2018, 2019, and 2020 respectively. Salinity fluctuations did not
have an obvious correlation with detrended GPP (r = 0.05, 0.02,
0.05 respectively for 2018, 2019, 2020). The literature is clear that
salinity decreases growth (Munns and Tester 2008, Vasquez et al. 2006,
Maricle and Lee, 2006), but the fluctuation in salinity at the low marsh
may not have been wide enough to drive observable variation in GPP
rates.