- Water quantity
- Water quality
- Nature conservation
- Biodiversity loss
There are lessons to be learned from the Caribbean region for coastal management and land-sea interactions regarding water pollution issues. DeGeorges et al. (2010) emphasized the impacts of land-sourced pollution (especially sewage) in the coastal waters and on the marine environment, causing the eutrophication phenomenon & harmful algae blooms. Scientific literature highlights potential solutions for coastal water pollution, taking as an example the Caribbean region.
Large amounts of nutrient pollution in waters result from sewage (“brown water”), wash water (“grey water”) and agricultural runoff (fertilizer and natural components of soils) which affect coastal ecosystems. In the tropical waters, the inadequacy of secondary sewage treatment is seen as a major source of nutrient input, tourist resorts having often inadequate treatment systems; septic tanks in coastal areas with high groundwater tables often malfunction during heavy rain events, flushing huge quantities of untreated effluent into coastal waters. Even if they functioned properly, secondary treatment plants do not properly remove nutrients or viruses which can then be found in high concentrations in shallow coastal water creating risks for public health and the natural environment. As an alternative to expensive conventional water treatments, biological treatment using plants to absorb nutrients is highly effective in the tropics where plants grow year-round however this option is often ignored by sewage designers from temperate zones, where plants only grow part of the year.
Scientifics also point out the advantages of land disposal for secondarily treated sewage effluent and wastewater reuse options. As an alternative to coastal discharges, this area has extensive wetlands that could possibly be part of a secondary treatment/overland flow system, with the already nutrient-rich wetlands polishing the final effluent (nature-based solutions). Estuarine systems, such as the Greater St. Lucia wetlands in South Africa, act as nutrient purifying systems as nutrients from catchments are absorbed by vegetation, resulting in cleaner water entering the sea. Florida has recently ordered all the offshore sewage outfalls closed, and mandated that the water be treated and recycled, but will take 15 years to fully implement these steps. With land disposal, advanced (tertiary) waste treatment can be attained, and nutrients are recycled to land vegetation, which is usually nutrient-starved, taking carefully into account potential limitations due to the degree and type of pollution. Instead of being expensively treated and rejected in the system, wastewater could be reused, particularly by the agricultural sector which needs nutrient inputs, or by coastal golf courses which beg for nutrient-rich sewage effluent waters for irrigation, as costs of water (especially if produced by reverse osmosis) and fertilizers are high. For instance recycling of all effluents as irrigation is mandated in the dry Turks and Caicos Islands. Rezaei et al. (2018) show that although the reuse of wastewater increases the cost of implementation and maintenance of water systems, it increases the value of resource recovery and reduces eutrophication problems in the environment. A limiting factor will be the distance between the water reclamation facility and the end use which plays a significant role in economic and environmental (carbon footprint) indicators. Lack of existing regulations and guidelines for the implementation of a water reuse system, high water quality requirements, as well as challenges with social acceptance (particularly for urban uses), is at the moment, serious barriers to the implementation of such a system.
Wastewater reuse and land disposal require careful hydrological studies and can offer alternative solutions to water quality and quantity issues in many coastal-rural areas.
ADDITIONAL SOURCES OF INFORMATION
Many sources of information exist regarding best practices but are generally focused on one sector or one issue, we will only mention here the PERSEUS guide developed to achieve the good environmental status of the seas and coastal areas through communication actions, stakeholder involvement, and public awareness. The guide focuses on 3 key topics:
- tourism in coastal areas,
- marine litter
The guide gives key messages based on examples and best practices and proposes communication and awareness-raising actions. Many links and materials are available to promote and work in favour of the sustainable development of coastal areas which are intrinsically linked to their rural hinterlands.
This guide provides additional examples of practices that can be used to increase land-sea synergies and coastal-rural collaboration by tackling some of the issues faced by the COASTAL case study. More generally the PERSEUS project offers various tools and recommendations for scientists, policymakers, and the general public for the sustainable development of the Mediterranean and the Black Sea region.