If water-dependent and nonwater-dependent uses occupy separate portions of the same leased parcel of state-owned aquatic land, the rental rate for each use shall be that established for the use by this chapter, prorated in accordance with the proportion of the whole parcel that each use occupies. If water-dependent and nonwater-dependent uses occupy the same portion of a leased parcel of state-owned aquatic land, the rental rate for the parcel shall be subject to negotiation with the department taking into account the proportion of the improvements each use occupies.