Your still going to get the melt water when things start to thaw out Lisa , sadly that cannot be helped .
Our Polycarbonate roofing sheet covers allow photosythesis being double glazed, if we ever get any snow it is swept off as soon as it stops snowing .
So if your ponds edges are flat why not invest in a number of polycarbonate roofing sheets or invest in them and build a cover.
Which way you go would be down to you, some like ourselves just lay them atop the pond others build little greenhouse style structures instead and even build in an inspection hatch.
We use the same sort of polycarbonate sheeting on our filter housing but that is quadruple in its glazing .
I know about the insulating powers of snow from my military days but basically Lisa you a trade off between the snow insulting the ice and the growth of algae .
Once Meyer I would put have put algae down as a plant as you did as it produces oxygen in the same way as plants during daylight hours and C02 during the night time periods.
However it is now thought of as a unicellular or multicellular organism , that have chlorophyll and other pigments but lack true stems, roots, and leaves.
They occur in fresh or salt water or on moist ground, rocks etc.
Algae, which are now regarded as protoctists, include the seaweeds, diatoms, and spirogyra , did you know algae is acctually latin for seaweed ?
Dave