** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** PREDICTING FUTURE WEATHER PATTERNS AND WATER AVAILABILITY RELIES ON OUR ABILITY TO PROJECT EARTH'S CLIMATE THROUGHOUT THIS CENTURY. ECOSYSTEMS ON EARTH ARE BOTH INFLUENCED BY CLIMATE, AND IN TURN INFLUENCE CLIMATE ITSELF. ONE KEY FEATURE GOVERNING THE WAY ECOSYSTEMS AND CLIMATE INFLUENCE EACH OTHER IS A GIVEN ECOSYSTEM'S SOIL. THE WAY A SOIL IS STRUCTURED (E.G., THE EXTENT TO WHICH ITS PARTICLES CLUMP TOGETHER INTO AGGREGATES, THE SIZE OF ITS PARTICLES AND ANY AGGREGATES, THE AMOUNT OF ORGANIC MATTER SERVING AS BINDING AGENTS AMONG PARTICLES) DICTATES, FOR EXAMPLE, HOW MUCH PORE SPACE IS WITHIN A GIVEN SOIL, AT DIFFERENT DEPTHS. THAT, IN TURN, GOVERNS THE DEGREE TO WHICH PRECIPITATION CAN INFILTRATE THE SOIL AND BE STORED WITHIN A SOIL, VS. BECOME RUNOFF AND BE LOST TO WATERWAYS. THUS, UNDERSTANDING THE FEATURES THAT GOVERN HOW A SOIL IS STRUCTURED IS INTEGRAL TO PREDICTING HOW WATER WILL FLOW INTO AND ACROSS ECOSYSTEMS IN THE FUTURE, AND THUS HOW PRODUCTIVE ECOSYSTEMS CAN BE IN THE FUTURE.RESEARCH TO DATE HAS FOCUSED ON THE POTENTIAL FOR ORGANIC CARBON COMPOUNDS STORED IN SOIL TO BE INCREASINGLY TRANSFORMED INTO CO2 IN A WARMER WORLD, WHICH LIKELY WILL FURTHER EXACERBATE WARMING AS THE CO2 ESCAPES THE SOIL TO THE ATMOSPHERE. INSTEAD, WE FOCUS ON SOIL ORGANIC CARBON TRANSFORMATIONS AS THEY RESULT IN BOTH THE FORMATION AND COLLAPSE OF CLUMPS OF SOIL PARTICLES - SOIL AGGREGATES. WE QUANTIFY THE RATES AT WHICH AGGREGATES ARE FORMED AND COLLAPSE WITH VARYING CONCENTRATIONS OF AN ORGANIC COMPOUND THAT MIMICS ROOT AND MICROBIAL EXUDATES, AND WITH VARYING OVERBURDEN PRESSURES THAT MIMIC PRESSURES EXPERIENCED DEEP BELOWGROUND. WE ALSO WILL QUANTIFY THE AMOUNT OF THE ORGANIC COMPOUND THAT IS TRANSFORMED INTO CO2 AFTER ADDITION TO SOIL CORES. AT THE END OF THE EXPERIMENT, WE WILL QUANTIFY SOIL PORE SPACE, WATER INFILTRATION RATES, AND SOIL WATER HOLDING CAPACITY TO RELATE RATES OF AGGREGATE FORMATION AND COLLAPSE TO THESE IMPORTANT HYDROLOGICAL PROPERTIES. THIS INFORMATION WILL BE USED AS INPUTS TO MATHEMATICAL MODELS REPRESENTING INDIVIDUAL SOIL PITS, HILLSLOPES, WHOLE WATERSHEDS, AND THE CONTINENT TO INVESTIGATE THE DEGREE TO WHICH CHANGING SOIL PORE SPACE MAY INFLUENCE HYDROLOGIC FLUXES AT THESE DIFFERENT SPATIAL SCALES. ULTIMATELY, ACHIEVING THESE GOALS WILL HELP CLIMATE MODELS BECOME MORE ACCURATE IN THEIR PROJECTIONS OF ECOSYSTEM PRODUCTIVITY IN A CHANGING CLIMATE.