Coastal Lagoons Critical Habitats of Environmental Change
Coastal lagoons rank among the most productive ecosystems on Earth, and they provide a wide range of ecosystem services and resources. Anthropogenic impacts are escalating in many coastal lagoons worldwide because of increasing population growth and associated land-use alteration in adjoining coastal watersheds. The conversion of natural land covers to agricultural, urban, and industrial development has accelerated loading to streams and rivers that discharge into estuaries, leading to cascading water quality and biotic impacts, impairments, and diminishing recreational and commercial uses. Many coastal lagoons, notably those with restricted circulation, freshwater inflow, low flushing rates, and relatively long water residence times, are particularly susceptible to nutrient enrichment from surface runoff, groundwater, and atmospheric inputs. Natural stressors, such as hurricanes and other major storms, as well as impacts of climate change, including rising temperatures, more frequent and extreme floods and droughts can exacerbate these effects. The combined effects of these stressors include accelerated eutrophication, increased frequencies and geographic expansion of harmful algal blooms, and low oxygen bottom waters (hypoxia). Watershed management strategies aimed at controlling these unwanted effects are rightfully focused on reducing nutrient and other contaminant loading to these enclosed systems and include upgrading stormwater controls, adapting low-impact development and best management practices, advancing open space preservation, and encouraging natural treatment of nutrients by establishing riparian buffers and wetlands, and implementing government regulatory measures (e.g., total maximum daily loads [TMDLs] for nutrient limitation). More draconian strategies that have been used in some systems are dredging sediments, diverting rivers, creating inlets, and thereby increasing flushing.