Achill autumn day and the turnstones were there. I knew they would be; they always are at Otterspool. With their tweed plumage, bright red legs and rattling, confiding chatter, they delight me every time. With their clockwork skittering and scattering, they are best seen at high tide, when they take refuge on the steep sandstone steps from the promenade down to the River Mersey. There is a pecking order, with each one choosing a different step. I want to know how step status is agreed. Otterspool, in south Liverpool, was once just that – the Otter’s Pool. The otters, the pool and the apostrophe are long gone (we live in hope that the former will return), but today the area attracts much life, both human and non-human. Emerging from an place of 1950s municipal waste tips and spoil from the construction of the first Mersey tunnel, Otterspool is now a green place resurgent. Arrowheads of white poplar leaves point my way as though dispensed by a passing rose queen. Willows, sycamores and rowan, now largely bereft of leaves, shiver in the breeze. While runners run, cyclists cycle and children chatter, a flock of pink-footed geese fly downriver. I am drawn to the muddy exposure in the river where clay glints on a curlew’s bill and a piping oystercatcher’s call provides the melody of the day. The mud is punctuated by human detritus in all its glorious variety: shopping trolleys, one-wheeled bicycles, discarded pipes and much more, the Mersey seen as a waste repository. Yet sea beet grows at the edge of the promenade, brambles on Otterspool’s engineered topography provide nesting sites in spring, and wildflower beds are pollinator heaven. Occasionally, at high tide, harbour porpoises and seals can be sighted. None today, but this is no urban desert. Waste may soon to return to Liverpool, with the government’s plans to sequester carbon dioxide in rocks underlying Liverpool Bay. The sandstone awaits its pernicious guest, a function of our addiction to fossil fuels. Otterspool has known waste before, but how might the next phase of global heating change it? Might the turnstones be the first to tell? Under the Changing Skies: The Best of the Guardian’s Country Diary, 2018-2024 is published by Guardian Faber; order at guardianbookshop.com and get a 15% discount