Combine the water, wine, parsley, bay leaf and peppercorns in a large wide pot and bring to a boil. Reduce the heat and simmer for 10 minutes. Add the salmon and cook, partially covered, until the fish flakes easily when tested with a fork, about 5 minutes. Carefully remove the salmon from the cooking liquid and set it aside; discard the cooking liquid.
Place the potatoes in a saucepan, cover with water and add 1 teaspoon salt. Bring to a boil. Reduce the heat to moderate and cook until just tender, 5 to 8 minutes. Drain, transfer to a large bowl and let cool to room temperature.
When the potatoes have cooled, add the celery, eggs, scallions and chopped dill. Pat the salmon dry with paper towels and carefully break it along its natural separations into large flakes, discarding the skin and any bones. Add it to the potatoes and season with salt and pepper. Add 1/2 cup of the lemon dressing and gently fold all of the ingredients together with a rubber spatula.
To serve, toss the mesclun with the remaining 1/4 cup of lemon dressing. Arrange the mesclun on 4 dinner plates, mound the salmon and potato salad in the center, and garnish with fresh dill sprigs.