Intertidal diatom communities reflect patchiness in groundwater discharge

We report on two discrete intertidal springs which discharge freshwater into Moreton Bay, Australia. Results from a seven month field survey which monitored chemical and hydraulic parameters, indicate fresh groundwater is continuously discharged from these features. Porewater measured from both groundwater springs (GWS) had consistently low salinity (0.07 ± 0.04 psu), pH (5) and high oxidation reduction potential (ORP; 194 mV) relative to the adjacent intertidal area (27.8 ± 16.7 psu; 6.8 pH; −92.3 ± 123.2 mV). Positive ORP, which suggests high dissolved oxygen, combined with lower concentrations of ammonium (N–NH4+) and higher concentrations of nitrate (N–NO3−) relative to the intertidal area, reveal that these sites transport and cycle nutrients differently than the surrounding beach. The C:N:P ratio from the GWS sites differs significantly (p