Offer it to local farmers, scoop it off pond surface, dry it in the sun and mix it with animal feed, hey presto. I don't have a large number of livestock or I might do it for you.
Duckweed is anything but a 'major issue' though. :dunce:
And your park ranger is wrong, the 'fertilising effect' of bird excrement would have absolutely no impact on the growth of duckweed in the pond.
Yes, very rich in protein (more so than Soya Beans) and it is eaten in some parts of South-East Asia, although most interest is in it's potential as a biofuel and animal-feed, given that it has the fastest doubling time of any flowering plant.
Other areas of interest include water remediation...