Environmental impacts of coastal-plain activities on sandy beach systems: Hazards, perception and mitigation

Managed sandy beach environments along developed shores often appear safe and healthy because obvious hazards such as beach erosion and flooding are considered within the purview of various mitigation programs. A range of insidious and generally unseen hazards, mostly related to pollution, often pose greater threats to the wellbeing of beach systems than do the highly visible, well publicized shoreline retreat and inundation events. Some unseen hazards, such as submarine groundwater discharge (SGD) laden with nutrients from agro-urban activities on adjacent coastal plains, are pervasive processes of environmental degradation that occur so gradually that sequential impacts escape public attention. The contribution of SGDs to the coastal hydrologie regime is occasionally recognized in association with crescendo events associated with marine algal blooms that degrade water quality, bottom habitats, and coral reef ecology. Because the real dangers of SGD are probably unknown at this time, it is essential to initiate seepage meter studies of the already known high levels of nitrogen (N) and phosphorus (P) that are discharged to beach and nearshore environments. Locations of some of the larger submarine freshwater springs along the southeast Florida inner continental shelf are generally known, although volumes of flow have historically been reduced by reduction of head on the coastal, plain. Submarine groundwater provides, on a continual basis, the most direct nutrient linkage to nearshore environments. The insidious nature of the problem requires specialized detection techniques that incorporate site inspection of rock outcrop and reef morphology (for submarine springs and seeps), satellite and airborne remote sensing (coastal morphology, turbidity plumes), physical seepage measurement in situ, monitoring wells, and mini-piezometers to measure hydraulic flow.