Coastal residential canals harbor distinct water quality conditions and phytoplankton community composition

As urbanization increases, many regions around the globe are seeing an increase in the number of residential canal systems along their coastlines. These canals possess unique attributes that may facilitate water quality degradation, namely shallow depths, susceptibility to urban runoff, and limited flushing. Despite this, there has been little research on the water quality and phytoplankton dynamics of these systems. In this study, water quality and phytoplankton biomass/composition were quantified once per month in the fall and winter, and twice per month in the spring and summer, over a 1-year period at three sites along a mouth-interior gradient of a canal system on North Padre Island (Corpus Christi, Texas, USA). It was hypothesized that interior canal sites would exhibit symptoms of water quality degradation more regularly than a site at the mouth, and interior canal sites would also have higher chlorophyll a and distinct phytoplankton community composition compared to the mouth. Results showed that the mouth site exhibited lower inorganic nutrient concentrations and less pronounced variability in salinity and nutrients than the interior canal sites. Chlorophyll a was 2.5-3-fold higher in the canal sites than at the mouth on average, and diatoms dominated at the mouth while a more diverse assemblage dominated at the canal sites. Episodic to persistent hypoxia was observed at the canal sites, but not at the mouth. These findings show that artificial coastal residential canal systems have distinct and less desirous water quality conditions and phytoplankton communities, pointing to a need for additional research on the attributes of canals that foster these conditions to support effective ecosystem health management efforts.