If you want you can use another method of selecting the layer by Ctrl clicking on it and then choosing a gradient. Swipe across on linear or reflected and the fill or gradient will only apply within the selection on that layer. I've chosen a noise gradient here.
Slight adjustments like these in the same color theme will add nice subtlety and extra depth to the overall design.
You can lower the fill to retain the layer effects but lower the actual color fill. Lowering the opacity will decrease both the layer itself (fill) AND any possible layer effects.
You could create a new layer and swipe across at a 45 degree angle like this. You could also choose a gradient fill layer and choose this from the dialog box. Then you would change the blending mode (to one of the light set or overlay set) in this case to let it seep on through.
I've chosen to mask the area that is directly above the two girls. This means that the gradient fill will no longer affect them from the fill layer above. Here is the gradient settings (foreground to transparent) followed by the masking job seen on the document and also in the layer mask icon in the layers palette.
You may have to read this 3 times: ...I could also Ctrl click on their layer and then click on the gradient layer and then Alt/Opt click on the new layer mask icon to get a perfect mask immediately (how cool is that!).
You could also add another gradient fill layer with black foreground to transparent like this if you want to. This comes in handy in plenty of situations to create a simple elegant effect (also using white esp. on lighter images..fading to white).
Or....Black with foreground color...(note the angle)
More Tutorials: 
