Well, eventually I managed to find an environmental angle to the wedding. It seems that the use of Welsh gold for the wedding rings might (just might!) pose a threat to trout and salmon spawning. As TIME notes:
Conservationists and environmental activists fear the April 29 nuptial will spark renewed interest in Welsh gold causing demand to spike—and sending gold prospectors into a frenzy. And that has consequences for the environment. Gold panners use shovels and hand-operated suction pumps to remove gravel and expose the bed rock of a river were the heavy metals are found. That disturbs gravel where salmon and trout have laid their eggs.
It seems that the issue emerged when a panhandler known locally as Irish Brian began digging holes that some officials said were deep enough to drop a car into. The Forestry Commission put up signs warning would-be prospectors they might well face unlimited fines and jail terms. It's not at all clear, however, that panning for gold is against the law. I particularly liked the comment from Vince Thurkettle, a full-time panner and former president of the World Gold Panning Association, who is reported as saying:
You get people poaching for fish but you don't ban all fishermen.