Vegetative stress and early indicators of peat collapse in mangrove forests with altered hydrology in Tampa Bay, Florida, USA

Abstract:

While mangroves are well adapted to periodic tidal inundation, the trees experience stress or mortality when hydrologic alteration causes accumulation of stagnant water. The resulting loss of belowground roots and increased peat decomposition can lead to a loss of surface elevation through peat collapse, furthering the degree of inundation. This study identified ten live mangrove forests across Tampa Bay (Florida, USA) with stagnant water and/or abundant adventitious root growth (a sign of stress) and compared vegetative, water, and soil characteristics of stressed and reference mangrove forests to identify early indicators of stress and peat collapse. Hydrologically stressed locations had stagnant pools of discolored water with low dissolved oxygen. Soil in the stressed sites had significantly lower dry bulk density than reference mangrove sites, as well as a higher percentage of soil organic matter and a higher proportion of root material. Belowground root growth rates and porewater dissolved organic carbon concentrations were highly variable across all site types. The low-density peat may be a result of in-situ decomposition and periodic export during high rain and inundation events. Altered hydrology due to anthropogenic alteration can often be improved; thus, proactive restoration is recommended to prevent mortality and peat collapse in affected mangrove forests.