Hitting the sweet spot: why regular beach litter surveys matter

Hitting the sweet spot: why regular beach litter surveys matter

In 2023, citizen scientists put on their pink vests and surveyed the litter on 216 beaches around the country for our national litter database, Litter Intelligence. Every survey contributes meaningful data, but more frequent surveys give us superior insights into the litter problem as it presents on the local coastline.

Beaches vary in their physical characteristics, such as shape, substrate, and wind exposure, which means litter acts differently on different beaches. On some, it gets washed or blown away quickly, while on others, litter can end up in sheltered spots and stay there for a very long time.

Every survey, the beach is essentially ‘reset’ — the monitoring group removes all the litter, providing a clean slate for the litter to accumulate for the following survey. This is why the data from the very first survey at a given site isn’t representative of things to come: we don’t know how long the litter there took to accumulate. A beach with very little litter arriving may appear very ‘dirty’ because its characteristics mean it is good at retaining litter. Likewise, a beach that appears relatively clean may in fact receive a decent amount of litter, but the wind or tides take it away.

Citizen scientists conducting a litter survey at Tāmaki Makaurau Auckland’s Little Shoal Bay, July 2023.

Citizen scientists measure the litter problem in order to show how litter affects our coastlines long-term. We need this data to be able to observe variability and change over time according to seasons or weather patterns. 

Doing a survey every three months allows us to capture the ‘litter accumulation rate’ for the monitoring site. Each survey is a reflection of the long-term balance between arrival and departure of litter. This frequency also allows us to calculate litter ‘flux’, which is a measure of the rate of accumulation of litter over a set period of time, taking into account the period between surveys.

Citizen scientists auditing the litter. Little Shoal Bay, Tāmaki Makaurau Auckland, July 2023.

Citizen scientists who have been at it for a while will know it’s not always possible to do a survey at the three-month mark — some sites aren’t accessible all year round, the weather gets in the way, and sometimes people just aren’t available to do them. The good news is that less frequent surveys still provide useful data if we adjust it for the relevant time period.

However, three months is the sweet spot between solid data collection and manageability. This frequency aligns with the United Nations Environment Programme and Intergovernmental Oceanographic Commission guidelines on monitoring marine litter. More frequent surveys would obviously give us richer data, but we designed the Litter Intelligence methodology to be manageable by volunteers who are generously donating their time to tackle the litter problem.