Dissolved oxygen and pH as hydrological connectivity indicators for mangrove restoration site assessment: Evidence from a tidally attenuated Ramsar lagoon in Ghana

Mangroves provide significant ecological, economic, and cultural values while maintaining the biological diversity of neighbouring maritime ecosystems. However, the mangrove ecosystem of the Keta Lagoon Complex Ramsar Site (KLCRS) in Ghana is threatened by anthropogenic and natural factors that degrade water quality and undermine restoration efforts. This study assessed water quality parameters across four mangrove stand types to identify hydrological conditions suitable for restoration at the KLCRS. Four sites representing natural, degraded, replanted-and-doing-well, and replanted-and-not-doing-well stands were selected. Eleven sampling points per site yielded forty-four observations of dissolved oxygen (DO), pH, temperature, salinity, electrical conductivity (EC), and total dissolved solids (TDS), which were subjected to principal component analysis (PCA) and one-way ANOVA with Tukey HSD post-hoc testing. PCA identified DO and pH as the primary discriminators of restoration condition, collectively accounting for 72.5% of variance on the biological vitality axis. Mean DO and pH at the natural, degraded, and replanted-and-doing-well stands were statistically indistinguishable, while the replanted-and-not-doing-well stand recorded significantly lower values (DO: 1.1 mg/L; pH: 7.6), indicating compromised hydrological function. Although salinity did not emerge as a primary PCA discriminator, elevated and variable salinity at the failing site corresponded with reduced mangrove biomass. Critically, differences in DO and pH among stand types are interpreted as diagnostic indicators of differential hydrological connectivity within a seasonally closed lagoon system rather than as independent causes of restoration failure. Restoration of internal hydrological connectivity is identified as the primary intervention, as water quality improvement will follow naturally from restored tidal circulation