Thames21 has been cleaning up litter in the tidal Thames for 20 years with the help of local volunteers. Now that the big items are gone, we have turned our attention to the scourge of plastic pollution. Often single-use items, these enter the river at a rate faster than we can ever hope to remove them. Therefore, we want prevent them entering the river in the first place.
To better understand where to work, we are training volunteers to survey the litter. We want to answer:
- Which are the most common plastic items in the Thames?
- How are they getting into the river?
- Is the issue getting better or worse?
The plastic litter can be separated into two types: those that float (e.g. drink bottles, cotton bud sticks and food wrappers) and those that sink (e.g. wet wipes and sanitary towels). Conveniently, they deposit themselves at known hotspot sites, which is where we target our volunteer effort. In London there are about 20 floating hotspots and around 6 sinking hotspots.
We would like statistical expertise to help us answer our key questions. Particularly:
- Given that there are different sites of different sizes that have different litter items on them (i.e. floating vs sinking litter) what approach do we need implement to establish which are the most numerous items in the tidal Thames? This is an issue of stratification to combine data from different types of sites and establishing a monitoring regime to direct volunteers to particular sites at a given frequency.
- How can we tell whether the issue is getting better or worse over time? This might, for instance, require targeting a limited number of indicator species (such as drink bottles) for in-depth monitoring and establishing a monitoring regime that give us a degree a high degree of confidence of picking up a change in trend.
Helping us develop monitoring regimes to answer the questions above will greatly assist in answering a real-life question which will have practical consequences.