Sentence:  From the equilibrium sorption data which <WSD>are</WSD> available , it seems logical to expect that polyphosphate ions would be strongly sorbed on the surface of the dirt ( especially clay soils ) so as to give it a greatly increased negative charge . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)