Improving Our Coastal Ocean

Maybe it was fishing with your grandfather…or exploring the rocky shores and tide pools…or simply watching your children build a sandcastle.

For some of us, it was that first dive under the waves, discovering an entire world beneath the ocean surface, and instilling a lifetime desire to help protect it. The coast is where many of us head for relaxation and recreation.

Almost half of the world’s population lives within 100 kilometers of the coast, which means that there is a heavy human footprint along many coastal areas that may extend far into the ocean.

All of these activities are happening in the same areas of some of the most ecologically important, diverse, and productive areas on the planet

A delicate balance must be maintained between our need for development and ensuring the integrity of the ecosystems along the coasts, otherwise environmental degradation will occur.

The Sustainable Development Goals, developed by the United Nations, are a blueprint for achieving this balance. They tackle many of the challenges our planet faces, from poverty to climate change, and clean water access to equality.

Of the 17 Goals and many sub-goals, Sustainable Development Goal 14.1 seeks, by 2025, to prevent and significantly reduce marine pollution of all kinds.

One of the greatest threats to the coasts where we can affect change comes from the pollution of excess nutrients from the land, mostly from agriculture and industry. When these nutrients enter the water, they change the natural equilibrium of ocean chemistry, fertilizing the growth of algae. This process is called eutrophication. Sometimes these algae are harmful, releasing toxins that can kill fish and impact human health. Other times, as seemingly harmless algal blooms naturally die and are decomposed by oxygen-consuming bacteria, the area may turn anoxic, whereby the marine life literally suffocate in the water.

The Sustainable Development Goals use objective measurements to quantify progress by each member country of the United Nations. But how can you consistently measure things like the amount of nitrogen or phosphorus around the coasts of every country all around the world? Unfortunately, we cannot at this time. But we can measure the amount of algae in the surface waters.

Satellites are equipped with sensors that can measure the amount of light reflected back into space. Marine phytoplankton (algae), use chlorophyll pigments in their cells to absorb light, especially red and blue colors, and undergo photosynthesis. Areas of the ocean with no algae reflect different proportions of the wavelengths of light than areas with high concentrations of algae. Mathematical equations can be used to convert the amount of light detected by the satellite to the concentration of chlorophyll in the water and correlate that to algal blooms.

We can map these observations of chlorophyll concentrations, and, over many years begin to understand the natural levels of phytoplankton in any part of the ocean to know when a bloom is occurring.

To achieve the goal of reducing and preventing eutrophication of the coastal ocean, and thereby unnatural blooms of algae, we need to answer two questions:

1. What are the annual trends for algal blooms in the coastal waters of each country?
2. How often are blooms occurring?

A team of scientists and engineers from the UN Environment Programme, GEO Blue Planet, and Esri have partnered to bring both the statistical expertise and technical know-how to develop a methodology that can be used to objectively and consistently answer those two questions. This methodology is now available in the official  UN Global Manual of Ocean Statistics .

Using tools in ArcGIS Pro, the methodology summarizes the satellite measurements of chlorophyll for each country's Exclusive Economic Zone (EEZ) using data merged across multiple satellite for many years by the Plymouth Marine Laboratory. From these large archives, we can spot trends where blooms may be increasing in frequency or intensity.

Next, near real-time measurements from NOAA are processed each day to characterize month-to-month fluctuations within the EEZs compared to their normal levels, and are reported back to the UN as being normal, moderately high, high, or extreme.

The information generated by the Index on Eutrophication is intended to provide insight for a given country over time - not to compare one country to another. Too many variable can skew results when making such comparisons, such as the number of river inputs, depth of the EEZ, major rain events per year, etc.

From the Level 1 annual reports we can see overall trends in chlorophyll impacts. In many cases, there are no trends from year to year, as blooms are very seasonal in nature. Level 2, providing monthly summaries, help to address that - providing more real-time information at finer spatial scales that can capture seasonal patterns and identify if they are more intense than expected.

Some countries are fortunate enough to have more advanced capabilities for monitoring coastal eutrophication and algal blooms: higher resolution satellite data, networks of buoys for measuring nutrients, sophisticated modeling resources. The methodology described above (Level 1) is scalable enough to be applied to other data sources at finer scales and more refined areas (Level 2).

For instance, the EEZ for the United States is 3.4 million square miles, so a single summary statistic isn't as meaningful as countries with much smaller or spatially complex EEZs. The U.S. may choose to re-run the analysis for state or regional coastal areas to improve their understanding how eutrophication varies across the world's largest EEZ. With GIS and the shared methodology in ArcGIS Pro, that is an easy undertaking.

The Sustainable Development Goals embrace open data, and there are multiple ways for anyone to access the original data or summarized results. The project's  Chlorophyll Hub  is a central point for accessing the many data types involved in the Level 1 analysis, along with resources for Level 2.

To simplify access and jumpstart your GIS projects, many of these resources are also available in  ArcGIS Living Atlas of the World , including EEZ summaries and analytical image services of global chlorophyll concentration.

This project is a critical first step in having a consistent way to improve coastal water quality worldwide. We will continue to enhance the methodology and incorporate other sources of data, as they become available, to improve estimates of nutrient loading and coastal eutrophication.