Less than 1% of Arizona's land is comprised of ______, but it's important to conserve what little is left because these patches of land can recycle and filter water.

The correct answer is wetlands. Wetlands are crucial ecosystems that play a significant role in water management. They have the unique ability to filter pollutants and recycle water, thus improving water quality. Despite their ecological importance, wetlands occupy less than 1% of Arizona's land area, making their conservation imperative.

Wetlands operate as natural sponges, absorbing excess water during periods of high rainfall and slowly releasing it during droughts, which helps to maintain water levels in surrounding areas. They provide habitat for diverse plant and animal species, contributing to biodiversity. Given their limited presence in Arizona, protecting these areas is vital for promoting ecological health and supporting the state's water resources.

The other options do not accurately fit the description provided in the question. Deserts comprise a large portion of Arizona's landscape; grasslands also cover significant areas, and riparian zones, while important, are typically associated with riverbanks and are not as limited in quantity as wetlands within the context of the question.