DISSOLVED ORGANIC MATTER AND MICROBIAL REGULATION OF NUTRIENT RETENTION IN RESTORED FRESHWATER WETLAND ECOSYSTEMS

Restored freshwater wetlands are expected to intercept nutrients, support biodiversity, and recover biogeochemical functions impaired by drainage or land conversion. Yet apparent improvements in water quality can conceal contrasting processes of organic matter production, microbial transformation, temporary nutrient storage, and subsequent release. This review develops a process-based interpretation of dissolved organic matter (DOM) as both a substrate for microbial activity and an indicator of changing restoration conditions. Drawing on published studies of restored wetlands, microbial nitrogen pathways, phosphorus dynamics, and aquatic vegetation–DOM interactions, it distinguishes concentration changes from actual mass retention, and short-term transformation from durable sequestration. Particular attention is given to hydrological residence time, oxygen heterogeneity, sediment–water exchange, plant-derived carbon, and the mismatch between microbial genetic potential and realized process rates. Three comparative tables organize conceptual DOM fractions, microbial habitat controls, and monitoring strategies without presenting fabricated field observations. The synthesis argues that successful restoration cannot be judged by a single nutrient-removal percentage: interpretations should integrate molecular and optical DOM characteristics, coupled carbon–nitrogen–phosphorus transformations, seasonal export, and ecological recovery. A staged monitoring framework is proposed for identifying when recovered wetlands act as stable nutrient buffers, conditional processors, or episodic sources under fluctuating hydrological conditions.