All the streams flow into the sea

  • Contributor information: CNP

I’m a marine biologist. I know only too well that what we do on the land affects life in the sea. However, not everyone is aware of this, or if they are they don’t think it is of consequence to them. For years humans have used the sea as a rubbish dump. What goes in stays out of sight. Out of sight is out of mind. However, in more recent times we have come to realise that what goes into the sea does matter and it might actually affect us.

Marine plastics have been an eye opener for many. Our rubbish blown or dumped into streams and rivers can end up accumulating on the coast. This, combined with plastics and other debris washed in from around the world, is a very visual reminder that we humans have a wide area of influence. But the natural world is often impacted more by the things that we can’t see. Chemicals including pharmaceuticals, pesticides and detergents, and natural waste products like slurry from farmer’s fields and the very soil upon which our crops and cattle rely all end up washing off the land and end up in the sea. This is harmful, wasteful and preventable.

Seaweed mats resulting from nitrate run-off from agricultural land, Garron Pill, Pembrokeshire Coast - photo by Sue Burton

Image by Sue Burton showing thick green seaweed mats within an estuary resulting from nitrate run-off from agricultural land.

Too much of a good thing can be bad for us. The same is true of excessive nutrients in the form of phosphates and nitrates (from urban and rural land run-off and point sources) and their impacts upon aquatic and marine life. Every living being requires nutrients to thrive, but as with most things in life, moderation is the key. Too much nitrogen stimulates excessive plant growth. In the marine environment this primarily manifests as dense growth of opportunistic seaweed species in the form of thick green mats that cover the saltmarsh and mudflats, and also occasional phytoplankton blooms. These abnormal seaweed mats smother saltmarsh plants and seagrass beds, and can impede feeding birds. In addition, the eventual rotting of the mats consumes all the available oxygen in the water, suffocating wider marine species.

Impacts aren’t exclusive to the marine wildlife -– detached  rafts of seaweed also cause problems too with human users by entangling boat propellers and clogging nets, and the smell from decaying mats can impact local communities and tourists. In addition to nutrient pollution, soil run-off has a negative effect on the marine environment as the resulting increased sedimentation that results can smother and clog seabed species (and fish gills). Sediments can also carry ‘hitchhiking’ contaminants including pesticides, metals and bacteria. 

Nitrates survey results in MIlford Haven Waterway, as collected by SWEPT project

Image by the Pembrokeshire Coast NPA showing some of the results from the SWEPT project depicting widespread pollution within the Milford Haven Waterway in Pembrokeshire and highlighting the scale of the problem in just one catchment (a story that is repeated unfortunately in many areas of Wales and the UK). Nitrate levels are measured here in mg/l (nitrate samples above 1 mg/l are considered polluted).

SWEPT (Surveying the Waterway Environment for Pollution Threats) was a citizen science project that involved over 100 local people walking stretches of shoreline and recording freshwater inputs and any signs of pollution. The volunteers used easy portable colour-changing kits to test some of their freshwater sources for levels of phosphate and nitrate and were able to gain instant results that highlighted widespread pollution. Participants commented that taking part had increased their awareness of the issue of land run-off affecting the marine environment, and that was something that they had shared with their familiy and community.

You may have heard the often-used phrase that every second breath we take is as a result of the life in the sea (phytoplankton produce around half the oxygen in the Earth’s atmosphere). Nitrate from the land can result in over-production of phytoplankton, but this is short-lived as an overloaded system tips the natural balance and widespread degradation can result. If we don’t sort out what we negligently and deliberately dump into the sea then it could be us, as well as the fish, that are left gasping for breath.

Sue Burton is the officer for the Pembrokeshire Marine Special Area of Conservation. SWEPT won the Campaign for National Parks Park Protector Award in 2019.

Feel free to contact Sue via: 

Twitter: @PembsMarineLife  

Facebook: @PembrokeshireMarineWildlife