Realizing ecosystem services: wetland hydrologic function along a gradient of ecosystem condition

Area of Science:

• Environmental Science
• Ecology
• Hydrology

Background:

• Wetlands provide critical ecosystem services, including habitat, pollutant removal, and microclimate regulation, often linked to their ecological condition.
• Regulatory assessments commonly use condition to evaluate wetland value, but the direct link between condition and all ecosystem functions, particularly hydrologic ones, is not always clear.
• Hydrologic function is crucial for many wetland services, influencing biogeochemical cycling, pollutant removal, floodwater retention, and microclimate regulation.

Purpose of the Study:

• To investigate the relationship between wetland ecological condition and hydrologic function.
• To test the hypothesis that ecological condition predicts hydrologic function, as assumed in regulatory wetland valuation.
• To assess how land use intensity influences wetland hydrologic functions and associated ecosystem services.

Main Methods:

• Assessed ecological condition using rapid and intensive methods, including Florida's official wetland assessment tool, across 11 isolated forested wetlands.
• Quantified hydrologic function by measuring hydrologic regime (water depth mean, variance, rates of change), groundwater exchange, and evapotranspiration (ET).
• Examined wetlands along a gradient of land use intensity, from minimally impacted to intensive agricultural and urban landscapes.

Main Results:

• No systematic variation in hydrologic regime (water depth dynamics) was observed across the condition gradient; reference sites exhibited a wide range of variation.
• Evapotranspiration (ET) rates were higher in intensive landscapes (urban, agriculture) due to increased leaf area, impacting microclimate regulation and carbon cycling.
• Groundwater exchange consistently reversed flow direction at all sites irrespective of condition, demonstrating a consistent buffering effect on regional aquifer levels.

Conclusions:

• Wetland ecological condition is not a reliable predictor of all hydrologic functions, challenging assumptions in current regulatory valuation methods.
• Evapotranspiration (ET) and its associated services (microclimate regulation, carbon cycling) are influenced by land use intensity, with benefits potentially amplified in developed areas.
• Isolated wetlands provide essential hydrologic services, such as aquifer buffering, regardless of their ecological condition, highlighting the value of "working wetlands" in diverse landscapes.